Stupid Missfire driving me insane - FIXED!!!

[kfz]

Only seem to come on these days when I have a problem , which is a shame.  True to form my Mille loves to come up with crazy issues,  this one is a missfire that is on the LH cylinder only.  The problem gets worse as the throttle is opened,  At idle and low throttle settings below 3K RPM its hardly noticeable but give her any gass and its horrible, as the LH cylinder cuts out maybe 50% of the time.  This is what ive tried.

• Cleaned both carbs
• Checked both Choke plungers are in good condition and fully closed
• Checked the needles havent climbed up the throttle springs
• Carbs kits recently applied (last 2 years)
• Fresh Gas
• Cleaned both fuel filters out
• Removed the points and checked for play in Disy
• Removed the points and retimed
• Swapped the coils,  points,  HT Caps, cut back the HT leads  (leads less than 2 years old)
• Compression test 190psi cold  210 psi warm
• Tappits checked

Really running out of the things to test.  any ideas????

Kev

[EldoEVert]

Only seem to come on these days when I have a problem , which is a shame.  True to form my Mille loves to come up with crazy issues,  this one is a missfire that is on the LH cylinder only.  The problem gets worse as the throttle is opened,  At idle and low throttle settings below 3K RPM its hardly noticeable but give her any gass and its horrible, as the LH cylinder cuts out maybe 50% of the time.  This is what ive tried.

• Cleaned both carbs
• Checked both Choke plungers are in good condition and fully closed
• Checked the needles havent climbed up the throttle springs
• Carbs kits recently applied (last 2 years)
• Fresh Gas
• Cleaned both fuel filters out
• Removed the points and checked for play in Disy
• Removed the points and retimed
• Swapped the coils,  points,  HT Caps, cut back the HT leads  (leads less than 2 years old)
• Compression test 190psi cold  210 psi warm
• Tappits checked

Really running out of the things to test.  any ideas????

Kev

Could be a condenser, our did you switch them out too?

[guzzisteve]

Get a Dyna3 and quit chasing issues, this is my fix, the REST is just a waste of time & aggravation.

BUT it would be the points & condenser all sourced cheap from China. I'm still running Magna Marelli points from my stash in the V7(the real V7). 
You need a few sets to get a good pair.

[kfz]

Get a Dyna3 and quit chasing issues, this is my fix, the REST is just a waste of time & aggravation.

I cant afford one,  they are quite expensive in the UK and funds cant stretch.  Plus the last one I fitted last 3 weeks before it died.  Back on the points.

[kfz]

Could be a condenser, our did you switch them out too?

Yes I did but I think at that time I tried it one the wrong cylinder.  So yes it will try that again!

Kev

[Huzo]

Can you put a timing light on the left cylinder and see if it’s electrical ?
If you bring the revs up gradually in neutral, will the engine climb to high revs.
5,000 rpm in neutral is only about 20% throttle, but in 5 th gear it’s closer to 70%. I want to know if the miss is a function of rpm or throttle setting.
Not possible you have a sticking or mal adjusted valve ?

[nc43bsa]

When you say you swapped the coils, etc., did you swap them from side to side or with other items?  If you swapped them side to side, did the problem stay on the LH cylinder?  If it did, have you tried swapping the carbs side to side?

That said, I agree with the faulty condenser theory.  In the past, I've had better luck with automotive condensers on bikes than I have with bike condensers from unknown sources.  Keep in mind that condensers are interchangeable as long as the value is the same, although the wire terminals and lengths may vary.

[Huzo]

When you say you swapped the coils, etc., did you swap them from side to side or with other items?  If you swapped them side to side, did the problem stay on the LH cylinder?  If it did, have you tried swapping the carbs side to side ?

Totally concur.

[kfz]

Can you put a timing light on the left cylinder and see if it’s electrical ?
If you bring the revs up gradually in neutral, will the engine climb to high revs.
5,000 rpm in neutral is only about 20% throttle, but in 5 th gear it’s closer to 70%. I want to know if the miss is a function of rpm or throttle setting.
Not possible you have a sticking or mal adjusted valve ?

Timing light is broken.

Yes, if you have both cylinders.  Pull the LH plug and the engine revs fine.  Pull the RH plug and misfire is apperaent and it grows worse more throttle is appiled.  Seems less effected by revs, so to me feels more fuel tan igintion.

Sticking Valve would effect the compression?  Compression is spot on.

[kfz]

Totally concur.

Swapped side to site,  So swapped the HT leads and points wires (red and Green) over so effectivly it was running the same points/condensor/HTleads but with the other coil and yes the fault stayed on the same cylinder indicating the coils ae good.

I'll try a condensor swap tomorrow. 

[PeteS]

You could just disconnect the condenser on the bad side. Its there to minimize arcing across the points. A few minutes out of the circuit won’t hurt anything.

Pete

[Huzo]

Timing light is broken.

Yes, if you have both cylinders.  Pull the LH plug and the engine revs fine.  Pull the RH plug and misfire is apperaent and it grows worse more throttle is appiled.  Seems less effected by revs, so to me feels more fuel tan igintion.

Sticking Valve would effect the compression?  Compression is spot on.

All good points…

[Sye]

Duff spark plug?

[kfz]

Duff spark plug?

Tried,  used a set i know out of the lemans that work.  No difference. 

Also doesnt explain why bike runs ok a low throttle or when cold.

[kfz]

You could just disconnect the condenser on the bad side. Its there to minimize arcing across the points. A few minutes out of the circuit won’t hurt anything.

Pete

disconnected the Condensor from rthe bad side and rigged up temp condensor with one ive tested and passed.  No difference.   

Acutally it may be a little bit better, but its hard to tell, the problem get worse as the engine gets hotter.   Just done 5=10 miles and its defiently still there.

[kfz]

Lets update the list , of stuff checked and tried.

Cleaned both carbs
Checked both Choke plungers are in good condition and fully closed
Checked the needles havent climbed up the throttle springs
Carbs kits recently applied (last 2 years)
Fresh Gas
Cleaned both fuel filters out
Removed the points and checked for play in Disy
Removed the points and retimed
Swapped the coils,  points,  HT Caps, cut back the HT leads  (leads less than 2 years old)
Compression test 190psi cold  210 psi warm
Tappits checked
Airbox cleaned
Breathers cleaned
K&N filter cleaned
Coils swapped side to side
HT caps changed
Plugs changed
Verified working condenser fitted


Any one have any ideas. getting desperate.    Im still suspecting the condensers. 
Kev

[Paul_Tim]

Inlet air leak?
Blocked exhaust?

[kfz]

Inlet air leak?
Blocked exhaust?

Ive refitted the airbox and its all in correct,  The bike ticks over no problem and runs well at low throttle,  I cant hear any leaks. Not only the elbow thats specifc to the LH cylinder.

Bike sounds the same,  not sure how I can check that.  Not displaying any symptoms such as overheating etc

[pressureangle]

Ohm your plug wires and verify their continuity. I developed a misfire on my pickup truck 7k miles after a new engine install, with of course all new ignition parts. I pulled my teeth out finding it until in despair I actually put the meter to the plug wires. One was so high as to be nearly an open circuit- that's the rub here, if you pull the plug or hold the wire to ground it will spark visibly in atmosphere but when you add the resistance of compression it will intermittently and increasingly fail to spark. The gap in my wire was nearly an inch long.

[kfz]

Ohm your plug wires and verify their continuity. I developed a misfire on my pickup truck 7k miles after a new engine install, with of course all new ignition parts. I pulled my teeth out finding it until in despair I actually put the meter to the plug wires. One was so high as to be nearly an open circuit- that's the rub here, if you pull the plug or hold the wire to ground it will spark visibly in atmosphere but when you add the resistance of compression it will intermittently and increasingly fail to spark. The gap in my wire was nearly an inch long.

The leads a recent about 2 years old.  Im going to make a new lead up now...  Doesnt really explain the symptoms though.

[kfz]

Whats really pissing me off about it, is my daughter is leanring to ride, So I need the bike to go out doing practice/training rides.  I can Take the FZ750 but its bit of a waste bimbling round at 45-50 mph,  doing town work and figure of eights.

Video of how well the bike runs with no load.  Soon as it gets out she turns into a stuttering mess.

https://youtu.be/scKplrYKWvg

[Bob Wegman]

Many years ago my brother had a Yamaha DT250 which would run fine until it would just quit, leaving you wondering what was wrong .  It would start again maybe with one kick, maybe fifty.  I changed plug, condenser, points, retimed it.  No good. Finally found the point wire was broken inside the insulation five or six inches back in the harness.  It would just make contact then separate which caused the engine to quit.

[Huzo]

  Soon as it gets out she turns into a stuttering mess.
https://youtu.be/scKplrYKWvg

You are referring to the bike I trust….

[Huzo]

Ok, can you take the airbox off and when the cylinder fails, spray some fuel into the Venturi.
Simply to see if it fires and then you can definitively rule out electrical.

[nc43bsa]

Many years ago my brother had a Yamaha DT250 which would run fine until it would just quit, leaving you wondering what was wrong .  It would start again maybe with one kick, maybe fifty.  I changed plug, condenser, points, retimed it.  No good. Finally found the point wire was broken inside the insulation five or six inches back in the harness.  It would just make contact then separate which caused the engine to quit.

I had a single cylinder race bike that would run perfectly for 1/2 to 3/4 of a lap.  The week before it had run like a scalded dog all weekend, but it broke a tooth off a transmission gear and I had to replace the gear.

As it turns out, in repairing the transmission I had disturbed the points wires just enough to fracture the last few strands so the broken ends were touching just enough to run until the engine got to full temperature.

[Moparnut72]

I'll throw this out. In our outboard racing group we had 3 boats that could be rented to race. The purpose was to entice new people into the sport. At one point we had one boat that ran fine on the beach but when it went out on the course it would lose power and even die. I fiddled with it for quite a while but could find nothing wrong. I finally replaced the fuel line and all was good. Even though it flowed fine on the beach under full power it failed.  I think what was happening was that ethanol in the fuel had broken down the internal part of the hose and it was being blocked with internal deterioration. Might be something to look at.
kk

[John A]

I once bought a non running T that had been given up on. I found a small bare spot on the coil wire to the points that was rubbing on the frame. It had chrome bores so I wasn’t going to run it anyway  so I was taking it apart when I found that. I found a half plugged idle jet on the other side. No wonder they gave up on it

[kfz]

Many years ago my brother had a Yamaha DT250 which would run fine until it would just quit, leaving you wondering what was wrong .  It would start again maybe with one kick, maybe fifty.  I changed plug, condenser, points, retimed it.  No good. Finally found the point wire was broken inside the insulation five or six inches back in the harness.  It would just make contact then separate which caused the engine to quit.

I think the issue must be something like that.  Probably load related.

[kfz]

I once bought a non running T that had been given up on. I found a small bare spot on the coil wire to the points that was rubbing on the frame. It had chrome bores so I wasn’t going to run it anyway  so I was taking it apart when I found that. I found a half plugged idle jet on the other side. No wonder they gave up on it

Jets are clear,  idle is spot on. Never a problem.  Only a problem while revving out on the open road.

[kfz]

I'll throw this out. In our outboard racing group we had 3 boats that could be rented to race. The purpose was to entice new people into the sport. At one point we had one boat that ran fine on the beach but when it went out on the course it would lose power and even die. I fiddled with it for quite a while but could find nothing wrong. I finally replaced the fuel line and all was good. Even though it flowed fine on the beach under full power it failed.  I think what was happening was that ethanol in the fuel had broken down the internal part of the hose and it was being blocked with internal deterioration. Might be something to look at.
kk

Fuel lines are recent, ive already had my fuel lines disintegrate (we went to E10 last year).   The bike is running double banjos with a crossover line, so it go a lot of fuel line capacity and the lines are shared.  Unlikely to causee a problem on one cylinder.