Stupid Missfire driving me insane - FIXED!!!

[Moparnut72]

Well you've eliminated that. This is definitely a tough one.
kk

[kfz]

Well you've eliminated that. This is definitely a tough one.
kk

Starting to give up, or at least forget about for a bit. cant be easily resolved.

The fact it only does it while on the open road makes this very hard to pin down and fix.

Kev

[Tom H]

I think you have tried what I will mention, but this is what I would do from what I think you have tried.

Swap coils by removing coil 1's wires and attaching wires to coil 2 and 2's to 1's, plug wires and plugs from L to R.

Didn't follow...

If you have 2 fuel valves turn them both on. Probably won't help if the miss stayed on the same side, cheap enough to try.

Didn't fix...

Swap the points and condensers from 1 to 2.
Try cycling your kill switch as well as key switch. Could be vibration causing a loss of contact.

Didn't fix...

Well we have pretty much ruled out the electrical system unless there is a bad wire.

Valves adjusted correctly?

Fuel.... Make sure you have good flow. You may have filters on the petcocks in the tank. Also may have filters on the carb inlet.
Go through the carb on the bad side again. A bit of something may be partially clogging a jet. Check your hose to that side again.

After all that, if it still has a miss on the same side, you may need to try to bypass the ignition wires that are in the harness. For instance.... To power the coils run a wire from the battery to a temporary switch, then to the coils. Then the wires from the coils to the distributor.
I don't think this matters, but you might also make sure your coil mounts to the frame are not all corroded.

That's about all I got.

Good luck!
Tom

[bmc5733946]

I just found a duff brand new condenser on my Mille GT. Would start and sometimes idle, ran great well above idle, couldn't take off from a stop without lots of throttle and clutch slipping etc. etc.. Some of you may remember my story from my spring trip last year when I thought I had ignition problems that turned out to be a failed inlet needle in the carburetor. Well, this is a remnant of that experience, I had attempted to change condensers on the road and lost a screw which ended my trip. After returning home, I left the one condenser that had been changed because it is hardest to change. First mistake followed by countless others and little time devoted to correcting the issue, other bikes running, etc.. Today, after chasing it for the last several days interspersed with hours of contemplation and consultation with friends, I installed an unknown provenance, old Marelli condenser found in my stash and wahoo she runs!!!!! One lesson learned is that, although neither I nor anyone I have spoken with, have ever seen a condenser failure of this type, apparently they can fail without complete failure. The only condenser failure I have seen before this were shorted condensers that sent all input to ground, meaning no spark at all, not the intermittent spark I was getting. My timing light was instrumental in finding the problem.

Brian

[Moparnut72]

I had a condenser fail on an old /2 BMW that behaved much the same. Heat was the culprit but both cylinders would start missing, twin fire. I didn't bring it up because the /2's had magneto ignition.
kk

[pressureangle]

Here's a thought-

Your fuel crossover has a blockage going to the misfiring carburetor, lowering fuel level on high demand but idling fine. 

[Alfetta]

I had an old twin Honda that had very similar condition to yours. I discovered that the battery / charging system was week and the voltage would drop the longer the bike ran. this would cause one cylinder to start dropping out. have you inspected voltage at the coil ? and watched it over some time ?

I know this sounds silly, and that japs do things different than Italians, but it was the issue.  To this day i don't know why it was only one cylinder and all ways the same cylinder...

I hope you can get this resolved...

[kfz]

Here's a thought-

Your fuel crossover has a blockage going to the misfiring carburetor, lowering fuel level on high demand but idling fine. 

Ive checked this,  As it explains some of the symtoms.

The LH Carb has a double banjo so it feeds from the LH tap and from the crossover.  Both would have to be blocked/restricted.   There is fuel in the bowl.  The filters are clean as is the tank so there is no source or evidence of a blockage.  Plus when you crack the throttle is misses straight away, not like it take any sustained open settings. 

I dismissed it, but will check when i have the carbs off next.

KEv

[kfz]

I had an old twin Honda that had very similar condition to yours. I discovered that the battery / charging system was week and the voltage would drop the longer the bike ran. this would cause one cylinder to start dropping out. have you inspected voltage at the coil ? and watched it over some time ?

I know this sounds silly, and that japs do things different than Italians, but it was the issue.  To this day i don't know why it was only one cylinder and all ways the same cylinder...

I hope you can get this resolved...

Ive had this before as well.  Ive got a voltmeter on the bike and there is no voltage drop.  Also I jumped the coils directly off the battery to test the power feed and it did nothing.

Kev

[kfz]

for those that havent seen the Utube video of the bike running in the garage on 2 and then 1 cylinder here it is.   You can see how well the bike runs.  Once she is out on the road she turns into a bucking misfiring mess as the bad cylinder chips in and out around 50% of the time.

https://youtu.be/scKplrYKWvg


Except for a another complete condenser change  and maybe a coil change (thou im loathed to start messing with good bikes)  ive no further electrics to check.    I might swap the carbs left to right.

Kev

[Stretch]

Also doesn't explain why bike runs ok a low throttle or when cold.

Runs okay when cold, eh?

Coil(s) going bad? I had one going bad on my SR500 that only acted up when hot.

Maybe your coils are on the way out, and there's an additional component that's
not quite up to snuff on the RH side, and the combination is conspiring to cause a miss
on that side only. Coils AND/OR condensers past their best?

Only a theory - but what else haven't you tried?
Plug caps?

You've got my sympathy - there is nothing - NOTHING - more frustrating or harder to
troubleshoot than an intermittent electrical issue.

Maybe also check the carb tops/linkages to make sure something isn't moving/leaking when you roll on the throttle,
which is causing a lean condition?

                                                                               Stretch

[John A]

It’s driving me crazy now too. Try a heat gun on the coils since it’s heat related. You’ve had your hands on the the problem, what ever it is. Besides heat and throttle setting is there anything else that changes it?

[MattP]

hears a way to check under load on road I got a bike years ago with a dumb sparkplug cap that was supposed to and did light up every time the engine fired to look cool, how ever dam good test tool If you can,t find one I will try to find mine and send to you on loan, It was on a motoguzzi v50 not that matters in the least. 

[kfz]

Massive thanks to BMC,  you where spot on mate!!  The problem was


CONDENSER

Found an old condenser in the spares box and jury rigged it on.  Hey presto fixed!!!.  Now I did this at least 2 times previously and it didnt work why?  Because first time i had the wrong cylinder and the second time I strapped it to the engine and it cooked it.  Didnt matter what i did after that it was ruined.  An confusingly it was ruined in a way that replicated the original problem.

Lessons learnt here is why I went wrong.

1.  On the problem I did what most people do and pulled he plugs, the LH (Bad cyl) was spot on and the RH (prefectly fine) was a bit rich.  This immediately had me chasing a fuel problem on the wrong cylinder.
2  The standard cause of the this would be choke plungers or the needle winding up the spring. This wasted loads of times screwing with the plungers.
3  Stripping the points plate and checking the disy bearings was a honest check.  but wrong and time consuming
4. Dont assume new or even checked condensors are good and dont boil them to death.
5. Some problems need load on the engine.

Where i went right.

1.  Pulling the plug leads off a running bike on the open road under load is a good way to tell actually which cylinder is bad. 

[Huzo]

So the primary function of the condenser is to stop acrcing across the points.
How did the faulty unit cause the breakdown of spark in use ?

[Tom H]

 

Tom

[pressureangle]

So the primary function of the condenser is to stop acrcing across the points.
How did the faulty unit cause the breakdown of spark in use ?

Condenser goes to ground. If it fails 'short' it basically grounds the points.

[Huzo]

Condenser goes to ground. If it fails 'short' it basically grounds the points.

Thanks PA.

[Stretch]

WOO-HOO!!!! 

[bmc5733946]

KFZ I am so glad that my difficulties have had a beneficial affect for you! Sometimes when our difficulties come to an end we must feel some amusement  and at least chuckle knowing that at some point we simply missed "it". I am smiling with you and having a private chuckle at my own difficulties hope you are too!!!

[Huzo]

I am also very pleased for you, I know how you felt and now feel.
As an aside, can you give some insight as to why the bike would rev relatively freely in neutral but not under load ?
I guess the conventional wisdom is that the spark was weakened enough so as not to be able to fire the mixture under the higher cylinder pressures of increased throttle settings ?

[John A]

I am also very pleased for you, I know how you felt and now feel.
As an aside, can you give some insight as to why the bike would rev relatively freely in neutral but not under load ?
I guess the conventional wisdom is that the spark was weakened enough so as not to be able to fire the mixture under the higher cylinder pressures of increased throttle settings ?

An aviation plug tester has a chamber that is pressurized. The plug is inserted and the pressure dialed up to around 80+ as the plug is steadily energized. The spark goes away on a bad plug. I was always going to fool with regular plugs in one but never made an adapter. A lean mixture is harder to ignite and I think that’s why some engines get jetted on the rich side.

[Huzo]

An aviation plug tester has a chamber that is pressurized. The plug is inserted and the pressure dialed up to around 80+ as the plug is steadily energized. The spark goes away on a bad plug. I was always going to fool with regular plugs in one but never made an adapter. A lean mixture is harder to ignite and I think that’s why some engines get jetted on the rich side.

Ok John.

[John A]

Ok John.

I can’t even tune a gasoline engine so it’s just the ravings of a lunatic 

[john fish]

Massive thanks to BMC,  you where spot on mate!!  The problem was


CONDENSER

Found an old condenser in the spares box and jury rigged it on.  Hey presto fixed!!!.  Now I did this at least 2 times previously and it didnt work why?  Because first time i had the wrong cylinder and the second time I strapped it to the engine and it cooked it.  Didnt matter what i did after that it was ruined.  An confusingly it was ruined in a way that replicated the original problem.

Outstanding.  Glad you found the problem.  One of the great things about WG is the input from some genuinely smart people.  Brian is one of those guys who it pays to listen to. 

[wirespokes]

I've been told that a failed condenser can mimic just about any running problem you'll run into. They don't just fail open or closed.

Very well done finding the issue!

[Scout63]

Nice work sorting this one out off. Threads like this are so valuable and interesting.  Reminds me once again that all fuel problems are electrical and vice versa. Points systems are my Achilles heel so I always install EI early on (not intending to hijack the thread with THAT discussion).

[Stevex]

I fitted the Gammatronix ignition amps to my LM2. You ditch the condensers, which is a bonus. Not to be confused with electronic ignition, this is a step up for the points ignition.
https://gammatronixltd.com/epages/bae94c71-c5b6-4572-89a1-e89006e78fbe.sf/en_GB/?ObjectPath=/Shops/bae94c71-c5b6-4572-89a1-e89006e78fbe/Products/NewTwinC-12VNEG

[kfz]

I fitted the Gammatronix ignition amps to my LM2. You ditch the condensers, which is a bonus. Not to be confused with electronic ignition, this is a step up for the points ignition.
https://gammatronixltd.com/epages/bae94c71-c5b6-4572-89a1-e89006e78fbe.sf/en_GB/?ObjectPath=/Shops/bae94c71-c5b6-4572-89a1-e89006e78fbe/Products/NewTwinC-12VNEG

Considored fitting an amplifier system.  Makes sense really. 46 quid is quite a saving over EI.

[Bulldog9]

Great news, and glad you have it sorted out.

My Convert is the first motorvehicle I've had with points since probably 1980. I haven't messed with them, and am afraid to. The bike runs well, and I am hoping it will continue to do so till I am back on the East coast and take it to Charlie 

Like many, I have learned much from this thread, and super happy you got it sorted out.