Date: Tue, 9 Jun 1998 13:01:44 +0100 (BST)
From: Peter Aslan
During the last two weekends I've spent some quality time in the garage trying to sort out some problems on a New bike. slowly I think I'm beginning to figure things out.
The bike was suffering from three major problems:
An annoying and possibly damaging backfire on overrun.
Incredibly poor fuel consumption, (20-25 Mpg).
An inability to pull beyond about 90 mph even in third gear.
The assumption was that the backfire was caused by a poorly fitting exhaust, a stainless item from Armours, and the poor fuel consumption and performance caused by repeated attempts by the DPO to cure a flat spot in acceleration several years ago.
So, the first weekend dawns, and I replaced the exhaust with one I've been keeping in the garage, its a sixteen year old 850 type with balance tube. I had the thing re-chromed about five years ago as it is a perfect fit, originally purchased from Andover Norton when they were in Andover. Both the stainless item and the Re-Chromed item are both 850 type with balance tube.
While I'm there I also drop the needle on both carbs by one notch, Now middle notch in No 3 Slides. This is to see if there's any difference in the flat out performance.
The first test run reveals the backfire is worse than before, and there is a possible slight improvement in top speed. I did notice however at the end of the run that the choke lever had moved back slightly, (therefore becoming slightly on). Definite evidence of some sort of misfire at high power RPM
My reasoning at this point is that the mixture is still screwy, and that the fit of the New (old) Exhaust may not be as good as I had thought.
Further thought on the subject and I conclude the problem with the backfire is probably due to either the over-rich mixture or an incredibly lean pilot mixture. The Pilot mixture had been set previously, by the DPO with a Colourtune, but this may have been performed on the bike with the engine cold, (ALL ADJUSTMENTS TO THE CARBS SHOULD BE PERFORMED WITH THE ENGINE HOT, AFTER ABOUT A 10 MILE RUN).
In the back of my mind is the knowledge that the problem with the backfire has only really been a problem on this bike since the carbs were changed by the DPO about 5 years ago. The New carbs were jetted exactly the same as the old, even down to the Sectioned Spray tubes, removed from the old carbs and installed in the new.
With the new exhaust on, the next course of action was to fully set up the Amals. To do this, I decided to return them to the same configuration as standard for the 850 Mk 2. In practice, this just meant changing the throttle slides for No 3 1/2, was 3.
The 3 1/2 Slides stuck in the carbs when I tried to fit them initially. So there was much cursing, and fine adjustment with some fine wet and dry, and Solvo Autosol polishing compound. With all the problems we usually get with these carbs wearing out, here I was actually removing material from the slides. Strangely enough there was no evidence of the carb bolts being over tight, thus causing distortion of the body. The old No 3 Slides were loose enough.
Once the Carb changes had been made, I attempted a 'rough' idle, on both cylinders. The Pilot mixture was set at 1.5 turns out, but while twiddling the slide stop screw I repeatedly found that the left (or near side) pot was missing now and then, this was making it near impossible to obtain any sort of idle. With the words, 'Carb problems are usually electrical in nature', ringing in my ears I looked up at the shelf at the back of the garage at the Boyer Electronic Ignition System.
I suppose I spent about half and hour trying to trace the missing sparks on the nearside pot. I checked all connections, cleaned the points, gapped the points, filled the pits out of the points, and re-gapped the points again. Still no change. The symptoms were entirely ignition system like, sudden loss of spark on one pot causing the idle to falter. When the plug cap was removed from the nearside pot, the offside pot idled entirely consistently, pop, pop, pop. Removing the other side and there was a Pop, Pop, silence, pop.
The thing about the Boyer is that it eliminates so much of the standard electrical stuff, not just the points but the mechanical advance/retard, the suppresser capacitors and ballast resistor as well. I suppose it took about two hours to install. I found that with the suppresser caps and resistor removed I could mount the Black Box between the coils on the bracket, using the two holes used to mount the capacitors with a tie wrap. This allows the cables be a lot shorter as well. I obtained bullet connectors and soldered every one of them.
The other good thing about the Boyer is that both Coils fire at the same time. It is, therefore, reasonable to assume that if you have a good even spark on one cylinder, then you should have one on the other as well. (the only difference being the Coil and Sparkler, which are easy enough to replace and therefore eliminate from inquiries).
So, the bike now has a New Exhaust, Standard Carb settings and Boyer Electronic Ignition. I've also tightened up the Choke lever, so It wont drop down into the airflow.
So far, I've only been able to run the thing in the garage for a short time, Idle appears to be improved, but I'm still not sure about the offside pot, maybe I'll change the Spark plug before the next test ride.
Blipping the throttle reveals lots of backfires, but I haven't fiddled with the carbs yet.
PS: Both Coils were replaced several years ago with German 6v Type.
Stay tuned for the next gripping instalment.
Regards,
Peter Aslan (aka Captain Norton). Louden Quill Award.
Date: Wed, 10 Jun 1998 02:33:49 -0500
From: Gregory Nolan
While I don't profess to be any kind of whiz at tuning, how's your timing? Just a thought.
Greg Nolan
From: Peter Aslan
Date: Thu, 11 Jun 1998 08:34:32 +0100 (BST)
On Wed, 10 Jun 1998, Nolan, Gregory wrote:
> While I don't profess to be any kind of whiz at tuning, how's your
> timing? Just a thought.
31 Degrees at just over 5000RPM, as stated in the Boyer instruction manual, and set with a timing light.
The thing I haven't done though is check if the marker on the rotor is correct. If it keeps raining I'll get the dial gauge and timing disk out and check it.
Regards,
Peter Aslan (aka Captain Norton). Louden Quill Award.
Date: Tue, 9 Jun 1998 09:53:15 -0400
From: Peter l Gay
Very interesting, Pete. About loose pipes, a common problem in Matchlesses, where the pipe simply pushes into the head and is unsecured: brass shim stock in various thickness up to .010" is available in small quantities at the local hobby (model RR) store. I cut a piece so that its length = the circumference of the pipe, and about an inch wide. It's then folded in 1/2 lengthways and fitted over the head end of the pipe. The pipe is then installed with gentle persuasion from a rubber hammer. The brass (you could use copper, too) is soft enough so that it conforms to irregularities and makes a seal. Try difference thickness until you get a good snug fit.
About the carb flange face - it's not enough to guess that it's flat. Use a straight edge on the face with the carb held up to a good light. Your carbs probably have o-rings (not used on my '55-57 Monos) - make sure they are the right size and not age - hardened.
Pete the cheap.
Date: Wed, 10 Jun 1998 07:41:22 -0400
From: Gerard Harrison
Peter:
Maybe its a dumb question on my part but what type of exhaust port
gasket ring did you use when you mounted the pipes...there's two types...a
steel half-oval ring and a copper crush type ring....I found the copper
crush ones to form a better seal between the pipe and the exhaust outlet...I
had the same problem with backfires on the Norton engine and it was because
of air getting sucked in on the backoff...the crush type exhaust gasket(?)
resolved it.
Regards
Date: Thu, 11 Jun 1998 08:42:47 +0100
From: Peter Aslan
On Wed, 10 Jun 1998, Gerard Harrison wrote:
> Peter:
> Maybe its a dumb question on my part but what type of exhaust port
gasket
> ring did you use when you mounted the pipes...there's two types...a
steel
> half-oval ring and a copper crush type ring....I found the copper
crush
> ones to form a better seal between the pipe and the exhaust outlet...I
had
> the same problem with backfires on the Norton engine and it was because
of
> air getting sucked in on the backoff...the crush type exhaust gasket(?)
> resolved it.
I used a couple of gaskets from a Suzuki GS550, as suggested by Commando Dan several yeas ago. These are about a quarter of an inch thick, made of what looks like asbestos string with a thin metal outer. The whole thing crushes down very nicely. Its surprising how lose the lock rings get after the engines been run up a couple of times. The lock rings on my bike have been religiously tightened after every run and the seal looks good.
The thing that does still concern me, with the balanced type of exhaust, is the seal on the balance pipe. If all else fails, I might have a go at Shimming out the connections with an old beer can.
Regards,
Peter Aslan (aka Captain Norton). Louden Quill Award.
Date: Thu, 11 Jun 1998 21:35:08 -0700 (PDT)
From: Eric William Lamberts
On Thu, 11 Jun 1998, Peter Aslan wrote:
> Dan several yeas ago. These are about a quarter of an inch thick,
made of
> what looks like asbestos string with a thin metal outer. The whole
thing
> crushes down very nicely. Its surprising how lose the lock rings
get
> after the engines been run up a couple of times. The lock rings on
my bike
> have been religiously tightened after every run and the seal looks
good.
[SNIP]
Do you tighten the exhaust nuts every time you ride? (!)
For sealing the exhaust, Honda makes a pretty good exhaust putty, as I recall....
Eric Lamberts
Date: Thu, 11 Jun 1998 09:58:35 -0400
From: Peter l Gay
Capt. Pete, please don't use old beer cans - if you fold them, they will split and not seal. Go to the model railroad store and look for the 4x6" packets of brass shim stock. It comes in thickness as low as .002". the thinner stuff may be cut with scissors. I cut a strip, the length of which = the circumference of the pipe, and about an inch wide. Fold in 1/2 the long way, and fit over the end of the inner pipe. If you get the assortment packet of shim stock, you can try different thickness until you get a seal. This stuff seals {M}'s gasketless exh. pipes in the worn-out alum. cyl. heads.
If I could find copper shim stuff, I'd try that, as it's softer and conforms better to irregularities. I just discovered an MSC outlet in Pawtucket, and will head up there today. Maybe they have it.
Pete the cheap.
Date: Tue, 9 Jun 1998 10:49:32 EDT
From: Stan Smith
Peter -
Not to state the painfully obvious, but have you checked your valves for proper adjustment?
Stan Smith
Rocky Point Cycle
Date: Wed, 10 Jun 1998 23:08:37 +1000 (EST)
From: Ian J Lock
<"Long familiar story - SNIP">
>Blipping the throttle reveals lots of backfires, but I haven't fiddled
>with the carbs yet.
Peter, If it were me I'd be checking to make sure valves are seated fully, & all operating freely.
Regards Ian
(From the Strzlecki Ranges, Australia).
Date: Tue, 09 Jun 1998 17:20:10 +0200
From: Espen Olsen
At 13:01 09.06.98 +0100, you wrote:
>So far, I've only been able to run the thing in the garage for a short
>time, Idle appears to be improved, but I'm still not sure about the
>offside pot, maybe I'll change the Spark plug before the test ride.
>
>Blipping the throttle reveals lots of backfires, but I haven't fiddled
>with the carbs yet.
I have had similar problems on my Combat. Installing new spark plugs one grade hotter cured the problem. I have to mention that the old plugs looked a bit sooted, but not as much as you'd expect judging from the misfiring.
Date: Tue, 09 Jun 1998 17:20:27 -0400
From: Gregg Kricorissian
At 01:01 PM 6/9/98 +0100, Peter Aslan wrote:
<<SNIP>>
>... I repeatedly found that the left (or
>near side) pot was missing now and then, this was making it near
>impossible to obtain any sort of idle.
<<SNIP>>
I've reported this a couple of times in the past, but Peter's problem is exactly like the frustration I went through with my MkIII a couple of years ago. I tried everything: carbs, coils, condensers, points, even replaced the spark plugs several times. Tired brand new Champion, and NGK. Even used ones. Two days down the drain!
Problem in the end turned out to be the spark plugs!
Solution: I fitted new Bosch Platinum plugs. Problem cleared instantly, with no other changes required. Just like waving a magic wand! These same plugs are still in the engine and going strong. One of the new Champions was bad right out of the box, the others had fouled in short order ... sometimes left side, sometimes the right. Until the plugs fouled, all the while I had a brilliant spark when I checked it.
Afterward, I found out the reason the Platinum's work so well: it's because their centre electrode is very small in diameter, and so it intensifies the spark. Apparently they were originally developed for the Porsche 911 engine, which till then had a real problem with plug fouling, even with high energy CDI ignition (and yes, I run Bosch Platinum's in my 911S as well!)
Here's hoping that Peter's solution is so simple!
.. Gregg.
Date: Tue, 09 Jun 1998 22:35:47 -0400
From: Mike Sarbacker
>Solution: I fitted new Bosch Platinum plugs. Problem cleared instantly,
>with no other changes required. Just like waving a magic wand!
I have experienced the same problem myself in the past and still continue
to resolve poor running, backfiring, and just wont start by replacing the
plugs
but I've continued to use the Champs.
Gregg, exactly what Bosch Platinum plug are you using, and do you use the recommended gap?
-Mike
Date: Tue, 09 Jun 1998 18:14:27 -0400
From: Jeff Bean
At 05:20 PM 6/9/98 -0400, you wrote:
>At 01:01 PM 6/9/98 +0100, Peter Aslan wrote:
>><SNIP>>
>>... I repeatedly found that the left (or
>>near side) pot was missing now and then, this was making it near
>>impossible to obtain any sort of idle.
><<SNIP>>
>
>I've reported this a couple of times in the past, but Peter's problem
is
>exactly like the frustration I went through with my MkIII a couple
of years
>ago. I tried everything: carbs, coils, condensers, points, even replaced
>the spark plugs several times. Tired brand new Champion, and NGK.
Even
>used ones. Two days down the drain!
>
>Problem in the end turned out to be the spark plugs!
>
>Solution: I fitted new Bosch Platinum plugs. Problem cleared instantly,
>with no other changes required. Just like waving a magic wand!
[SNIP]
Please give me the "exact" # of these plugs....and please don't tell me they're the same as your 911 i.e. W5PO (nickel electrode/platinum tip)..I know they're $28.00 per/each.
best
bucbean
Date: Wed, 10 Jun 1998 11:29:39 -0400
From: Gregg Kricorissian
At 10:35 PM 6/9/98 -0400, Mike wrote:
>Gregg, exactly what Bosch Platinum plug are you using, and do you
use the
>recommended gap?
I've had a few questions along this line, so here's the answer:
Plug type: Bosch no. WR6DP
Gap: standard from Bosch (0.028" as I recall)
Hope this is of help: it certainly eliminated my problems with fouled plugs.
Cheers,
.. Gregg
Date: Wed, 10 Jun 1998 16:46:22 -0400
From: Gregg Kricorissian
At 09:38 AM 6/10/98 -0700, Harry Nangle wrote:
>IS THIS PLUG FOR 850 COMMANDO OR WOULD IT MATTER .
Harry,
The WR6DP is a direct cross to the Champion N7-Y, according to Bosch's list. It should work in both 750 and 850 engines, since I believe they all use the same plugs, except for Combat engines under extreme conditions.
.. Gregg
Date: Wed, 10 Jun 1998 14:09:44 -0400
From: John S. Morris
>Solution: I fitted new Bosch Platinum plugs. Problem cleared instantly,
>with no other changes required.
I've noted your solution for this problem but am left with a niggling thought -- since other bikes run quite nicely on standard plugs, do you suppose there's the possibility that the plug change is actually masking another problem?
Curious,
John
Date: Thu, 11 Jun 1998 09:30:40 -0400
From: Gregg Kricorissian
At 08:12 AM 6/11/98 +0100, you wrote:
>[Total Snip]
>What Number Bosh plugs go in your Commando then..
>
>Regards,
>
> Peter Aslan (aka Captain Norton). Louden Quill Award.
Peter,
Just in case you missed my posting on the NOC list, the WR6DP is a direct cross to the Champion N7-Y, according to Bosch.
By the way, I had a routine look at the ones on my MkIII yesterday after a ride, and they look perfect.
Hope all's well with you...
.. Gregg
Date: Thu, 11 Jun 1998 09:45:45 -0400
From: Gregg Kricorissian
At 02:09 PM 6/10/98 -0400, you wrote:
>I've noted your solution for this problem but am left with a niggling
>thought -- since other bikes run quite nicely on standard plugs, do
you
>suppose there's the possibility that the plug change is actually masking
>another problem?
After a lot of thought on the topic, I don't think so (I have a personal obsession with ensuring I find root causes :=) ). The plug change was the very last thing I did, after days of ensuring *everything* else was spot on.
This is significant, because up to that point, I had a real bias against the Platinum's: a friend had them in his Volvo a few years back, and one failed on him ... the centre electrode (which is quite slender) fell out one day, and he found himself driving home on 3 cylinders. As a result, I went to the Platinum's as a last resort, after trying my favourite NGK's and Champions.
(I say "favourite NGK's", since they were the only manufacturers for years that could make a plug which could stand up to the rigors of high performance 2-stroke engines ... a hard-learned lesson during the 1960's when I worked summers in a bike shop).
.. Gregg
Date: Thu, 11 Jun 1998 17:21:54 +0100
From: Edridge Martin
>At 02:09 PM 6/10/98 -0400, Greg Kricorissian wrote:
>>I've noted your solution for this problem but am left with a niggling
>>thought -- since other bikes run quite nicely on standard plugs,
do you
>>suppose there's the possibility that the plug change is actually
masking
>>another problem?
>
>After a lot of thought on the topic, I don't think so (I have a personal
>obsession with ensuring I find root causes :=) ). The plug change
was the
>very last thing I did, after days of ensuring *everything* else was
spot on.
>
>This is significant, because up to that point, I had a real bias against
>the Platinum's: a friend had them in his Volvo a few years back, and
one
>failed on him ... the centre electrode (which is quite slender) fell
out
>one day, and he found himself driving home on 3 cylinders. As a result,
I
>went to the Platinum's as a last resort, after trying my favourite
NGK's and
>Champions.
>
>(I say "favourite NGK's", since they were the only manufacturers for
years
>that could make a plug which could stand up to the rigors of high
>performance 2-stroke engines ... a hard-learned lesson during the
1960's
>when I worked summers in a bike shop).
>
>.. Gregg
I was under the impression that it was common knowledge that Commandos
had weak ignition, or at least poor coils. Decent ignition cures a lot
of problems, and whizzo plugs etc. are simply a crutch to help a deficient
system. Did you not see my last mail re- ignition as part of this thread?
Cheers,
Martin
Date: Tue, 09 Jun 1998 15:27:34 -0400
From: Jeff Bean
At 01:01 PM 6/9/98 +0100, you wrote:
>During the last two weekends I've spent some quality time in the garage
>trying to sort out some problems on a New bike. slowly I think I'm
>beginning to figure things out.
[Snip]
Peter....I went through this same mess many moons ago. I fashion myself a pretty good mechanic, and was in fact buffaloed for about six months. Here's what I found. The "German" coils have a "weird" nipple which is to say that unlike those we normally see with a metal "cup" that accepts the "crimped" on spark plug wire contact, they are meant to "accept" a "bare" wire. There is actually a threaded "impaling" pin that requires the "bare " wire to be "twisted" into the nipple so that the pin "impales" the centre of the wire. If you try to push in a "crimped" "contacted" plug wire it will not fit in deep enough and create an "arcing" situation that will "raise hell" with the ignition process.. in a weird intermittent fashion.. Just a thought.. get a flashlight and look at/in that nipple.
bucbean
Date: Wed, 10 Jun 1998 20:45:00 +0100
From: Edridge Martin
>From: John S. Morris
>>Solution: I fitted new Bosch Platinum plugs. Problem cleared instantly,
>>with no other changes required.
>
>I've noted your solution for this problem but am left with a niggling
>thought -- since other bikes run quite nicely on standard plugs, do
you
>suppose there's the possibility that the plug change is actually masking
>another problem?
Back in the seventies the American M/C magazine 'Cycle' (I think) ran
an article
comparing various motorcycle ignitions after doubt had been cast on
their ability to do their job. Depressingly, Norton was only saved from
being the weakest of all the tested bikes by the presence of a Ducati.
Even more depressing was the fact that the best M/C ignition at the time
(Z1 Kawasaki) was feeble when compared to a stock car type Delco coil.
Without going too in depth the verdict was that M/C ignitions as a whole were not up to snuff. I don't think electronic ignition really helps much in the output department. That's down to coils and much has already been said/written on that subject. So to answer your question, yes I think the plug's ability to produce a spark with a low output system simply masks the fact that the coils are weak. Just my opinion.
Date: Thu, 11 Jun 98 09:24:55 PDT
From: Jordan
Easy enough to put in a bigger auto coil to improve sparks. The newer
"transformer" type coils are nice in that they're smaller due to the armature
extending outside and forming a closed loop for the magnetic path. Hang
on, isn't that how Honda did it since aeons ago?
Jordan
Date: Thu, 11 Jun 1998 05:48:02 -0700
From: Marty MacLean
Jordan wrote:
> Easy enough to put in a bigger auto coil to improve sparks.
I did the 'Cycle' magazine conversion on my Z-1 20+ years ago - with 4 $6 Delco colds and a pair of Chevy points. Simply put, it worked completely. The points lasted; plugs fired just fine at red-line. The only problem was stuffing the coils up under the tank. I think it was a great idea - and incredibly cheap.
Marty
Date: Fri, 12 Jun 1998 01:56:14 EDT
From: Michael Taglieri
>> Easy enough to put in a bigger auto coil to improve sparks.
>
>I did the 'Cycle' magazine conversion on my Z-1 20+ years ago - with
4
>$6 Delco colds and a pair of Chevy points. Simply put, it worked
>completely. The points lasted; plugs fired just fine at red-line.
The
>only problem was stuffing the coils up under the tank. I think it
was
>a great idea - and incredibly cheap.
I did this years ago with a Honda 350, using two K-mart coils. The mail problem I had was that the points (original) tended to pit tremendously, so the condenser was clearly not right, but I didn't know what to do about it then (or now, for that matter). Would it be expected that the condenser would need to be changed with different coils, and how would you get it right? Would the one recommended for use with that coil in a car be a good starting point?
------------------------------------------------
'Mine goes up to 11'
------------------------------------------------
Date: Fri, 12 Jun 1998 08:44:16 -0700
From: Marty Maclean
Michael Taglieri wrote:
> >> Easy enough to put in a bigger auto coil to improve sparks.
> >I did the 'Cycle' magazine conversion ...
> I did this years ago with a Honda 350, using two K-mart coils. The
mail
> problem I had was that the points (original) tended to pit tremendously,
> so the condenser was clearly not right, but I didn't know what to
do
> about it then (or now, for that matter). Would it be expected that
the
> condenser would need to be changed with different coils, and how
would
> you get it right? Would the one recommended for use with that coil
in a
> car be a good starting point?
I used the stock condensers (re-mounted out in the breeze) - but put variable resistors in line to each set of points. Once I figured out where to adjust the resistor (in a very short time), I was able to retain the good performance and keep decent point contact life.
Marty
Date: Fri, 12 Jun 1998 17:40:57 -0700 (PDT)
From: Eric William Lamberts
On Fri, 12 Jun 1998, Michael Taglieri wrote:
> >> Easy enough to put in a bigger auto coil to improve sparks.
> >I did the 'Cycle' magazine conversion on my Z-1 20+ years ago -
with 4
> >$6 Delco colds and a pair of Chevy points. Simply put, it worked
> >completely. The points lasted; plugs fired just fine at red-line.
The
> >only problem was stuffing the coils up under the tank. I think it
was
> >a great idea - and incredibly cheap.
>
> I did this years ago with a Honda 350, using two K-mart coils. The
mail
> problem I had was that the points (original) tended to pit tremendously,
> so the condenser was clearly not right, but I didn't know what to
do
> about it then (or now, for that matter). Would it be expected that
the
> condenser would need to be changed with different coils, and how
would
> you get it right? Would the one recommended for use with that coil
in a
> car be a good starting point?
> Mike Taglieri
I think the capacitor used with the coil in a car would be a good starting point. If there is a lot of sparking you need a higher capacity condenser. If there is pitting on the negative point of the points you need a higher capacity condenser. If there is pitting on the positive point of the points a lower capacity condenser is needed.
For the whole discussion, go to the library and check out an old auto mechanics textbook. They used to go on and on about this, although I suspect no one much cared after about 1955..
Date: Thu, 11 Jun 1998 21:17:29 -0400
From: Gregg Kricorissian
At 10:40 AM 6/11/98 -0400, John asked:
>I'm curious, how did you measure the output of the coils?
Two ways:
A friend has a neat coil tester made during the 1950's. It is powered
from the 110 volt mains, and feeds the coil primary with a continuous pulse
train (from an old auto-radio "vibrator" by the sound of it), and "measures"
the output on a variable spark gap. Always thought it would be a good thing
to build one day, but it's never gotten to the top of the priority queue!
.. Gregg
Date: Fri, 12 Jun 1998 15:13:47 +1000
From: Geoff Haines
On 13 June 1998 5:16 Jordan Wrote:
>Points life is a consideration when changing coils. I've heard of
cases
>where it hasn't been good, so you're lucky.
>Arcing is controlled by the condensers.
>Does anyone know if there's some formula to ascertain correct
>capacitance of the condensers, given some coil data?
>Jordan
Hi Jordan,
The condensers and coils form a resonant tuned LC circuit with lots of electrical 'ringing'. This causes multiple sparks on the HT side and reduces points arcing on the LT side. If you know at what frequency the circuit wants to fire, the formula would be C =3D 1/(L(2*pi*f)^2) [where ^2 means "squared"] but you need to know things like the self-resonating frequency and inductance of the coils. Trial and error on the test bench is probably the easiest way to work out the best capacitance to produce the highest energy spark. Using a Morse key (or similar) in conjunction with a coil, several condensers and a spark plug should work OK.
Geoff
Date: Fri, 12 Jun 1998 19:06:30 +1000
From: Jordan
Written By Geoff Haines:
>The condensers and coils form a resonant tuned LC circuit with lots
of
>electrical 'ringing'. This causes multiple sparks on the HT side and
>reduces points arcing on the LT side. If you know at what frequency
the
>circuit wants to fire, the formula would be C = 1/(L(2*pi*f)^2) [where
^2
>means "squared"] but you need to know things like the self-resonating
>frequency and inductance of the coils. Trial and error on the test
bench is
>probably the easiest way to work out the best capacitance to produce
the
>highest energy spark. Using a Morse key (or similar) in conjunction
with a
>coil, several condensers and a spark plug should work OK.
>Geoff
That's great. To be clear, what should one be looking for? The longest gap that produces a consistent fat blue spark, with little points arcing? Can you substitute say, a "greencap" for the normal condenser?
Jordan
Date: Mon, 22 Jun 1998 13:26:03 +0100 (BST)
From: Peter Aslan
Well, out in the garage there have been some developments.
The coil HT connections were checked and remade, I'm using new HT leads that were made for me by the local auto store.
New Plugs were installed.
The Tappets were all checked and adjusted, Valve actions looks fine.
BTW, the new gaskets for the tappet covers needed to be cut down with a knife after installation, look much bigger than the originals.
Before I finished, I decided to strip and clean out the carbs. Everything stripped out ok, and I even managed to pull the Petrol Idle plug out with a wood screw. By blowing down each part of the idle circuit, and comparing it between both carbs I established that there was nothing blocked up in the Idle side of things.
Two things I did notice however:
Firstly one of the carb o-rings was apparently larger than the other and had been caught between the flange of the manifold and the carb body. Hard to believe there was much of an air leak here though.
Secondly, I decided to use two new float needles, and found that the float height changed.
The New Needles made the float higher.
Holding the float bowl the right way up and level, and by depressing the float tang and needle with my index finger, the other end of the float, (the side away from the pin), is now about 1/16th above the side of the bowl. Previously it was below.
I've only managed to run the bike up in the garage for about 10 Minutes so far, but the idle is a lot faster than it was before and the bike sounds a lot better. Consistent on both sides.
More to follow when I get to grips tuning the carbs.
Regards,
Peter Aslan (aka Captain Norton). Louden Quill Award.
Date: Thu, 2 Jul 1998 09:06:04 +0100
From: Peter Aslan
It's hard to express the satisfaction I felt last night when it finally dawned on me that I had resolved the infamous Backfire Bomber problem.
The Cause: The Float Needles.
The Ones supplied with the New Carbs were too long, causing the float height to be too low, causing the fuel to be too low in the carbs, causing the mixture to be seriously out of kilter.
The strange this is, one of the symptoms of this problem was v poor fuel consumption, I assume the was due to the mixture being so far out that it was taking excessive fuel to achieve the same level of performance.
No more backfire. No more misfire at max throttle,
It was a true joy to take the bike out for a ride last night. The most fun you can have with your cloths on.
It was like I'd just got an extra 10BHP, just like the old Point and Squirt performance I remember the ol Commando was capable of.
Which leaves me wondering were this leaves all the carbs who's float height was adjusted by moving the brass seat in the float bowl.
Regards,
Peter Aslan (aka Captain Norton). Louden Quill Award.
Date: Thu, 2 Jul 1998 22:18:38 -0700
From: Russ Williams
> The strange thing is, one of the symptoms of this problem was v poor
fuel
> consumption, I assume the was due to the mixture being so far out
that
> it was taking excessive fuel to achieve the same level of performance.
Hi Peter,
I have the same strange problem with my '81 Bonneville. It runs very
lean and hot, but only gets about 18 mpg which is pitiful.
Russ Williams
'54 Series "C" Vincent Black Shadow
'81 Triumph T140ES Bonneville
'63 Triumph T20SS Tiger Cub plus 2 Basket Cubs
Date: Fri, 03 Jul 1998 17:42:44 -0300
From: Pete combat
Peter Aslan wrote:
> It's hard to express the satisfaction I felt last night when it finally
> dawned on me that I had resolved the infamous Backfire Bomber problem.
> The Cause: The Float Needles.
[SNIP]
The brass may be better made , but I have had the bike starve quite a few years back and threw out those so called float needles and have never looked back since.
For once plastic rules
Pete combat