Misfire Troubleshooting

Status
Not open for further replies.
You going to try the LH carb now to see if the issue still repllicates, so you can eventually gi back to two carbs?
 
gortnipper said:
You going to try the LH carb now to see if the issue still repllicates, so you can eventually gi back to two carbs?
Click to expand...
Well I will likely leave the RH on for a little bit. Honestly got a bit overjoyed at how well it went out on the road. The new silencers sound wonderful and there's more power on tap than I recall from previous single setup days with balance pipe and muted silencers. Honestly could not feel any diff at full accel, WOT than with duals (but that was back with muted silencers of course).

There's much to consider. Can't understand why LHis giving problems as there's nothing noticeable blocked. Maybe its got a unseen crack giving air leak or maybe the jets are shot.

I am liking the single simplicity. But im also still curious to know what a well running dual can be like.
 
Great progress!

I seriously hope you test the LH carb too... we’re all dying to know!

Don‘t shoot that carb just yet, remember you changed the coils too (post 107) and fitted new terminals.

Also... manifolds... I recall someone on here chasing there tail for ages before disovering a hairline crack in one of their manifolds.

Yer gotta keep goin‘... can’t leave us all hangin’ ...!
 
It's up to you of course if you want to check those bolts!
I bought an 850 mk2a
One of bolts fell out, it took out the the alternator/inner chain case and bent the gearbox output shaft
All scrap
The previous owner had not fitted the tab washers
 
baz said:
It's up to you of course if you want to check those bolts!
I bought an 850 mk2a
One of bolts fell out, it took out the the alternator/inner chain case and bent the gearbox output shaft
All scrap
The previous owner had not fitted the tab washers
Click to expand...

Considering that,.... the oiling of the cylinder stopped, the primary/crankcase rubber gasket was displaced, there was a small puddle under the bike, and the engine oil level was down below the dipstick, the first thing is to see if the missing oil has been blown out the crankcase into the primary. (and displaced the crank oil seal) A simple pulling of the primary level drain plug could show a high level of oil in the primary...

If there is a sizable amount of engine oil in the primary, then the primary has to be opened up, those bolts have to be checked/renewed, a new crankcase oil seal has to be fitted, BUT of equal importance is the discovery of why that seal and the gasket blew out, which points to a breather blockage IMO.

... or you can just change the carburetor again... :rolleyes:
 
Got to sort out before you go far .... would be interested in amount of oil you dumped in before riding home .... think I have most of a twin VM 32 setup you could try down the road .... not for me but you may like .... also make sure to use new dog bone washers or whatever proper name is of tab washers on 3 inner cover bolts .....
 
Certainly will get into primary, likely today. The gasket that fractured and slipped out was not the rubber outer to inner seal but the paper inner to crank case gasket. Was renewed when I had cover off for gearbox rebuild two Januarys ago. Did fit fresh tabbed washers on those these screws. Whats a better hold of fast option, red or blue loctite, considering temps on the casing?
Crank oil seal was new from three seasons ago after orig blew out from wet sump pressures. When that happened, oil filled primary to lead to loads being tossed out the felt "seal" opening, coating everything rearward. I'd wager oil seal is still there, a screw loosened or fully feel out and the gasket broke up.

I put in 1 L 50W syn Lucas oil from nearby auto shop. That brought level to mid dip.
Ill add that two days before, I'd drained sump and cleaned gauze to check for gold or detritus, all good. Didnt add oil afterwards, so might have already been bit lower that I usually have after it restocked sump.
 
Fast Eddie said:
Great progress!

I seriously hope you test the LH carb too... we’re all dying to know!

Don‘t shoot that carb just yet, remember you changed the coils too (post 107) and fitted new terminals.

Also... manifolds... I recall someone on here chasing there tail for ages before disovering a hairline crack in one of their manifolds.

Yer gotta keep goin‘... can’t leave us all hangin’ ...!
Click to expand...
Crack in one mani is a possiblity. Though carb spray didnt detect, not always a definitive test. The mani's were never swapped during the testing so far. Is the balance pipe a place for such cracks to develop?
Will have yet another go on the LH carbie. Even though fluid can flow from the fuel passage to jet, there may be some restriction in there still. Is there a chemical soak known to disrupt that crud?
 
So one point I'm unclear on, I think oOnortonOo eluded to, can the oil contamination fully explain the misfiring? Maybe the LH carbie is acutually fine and the blocked oil drain was the entire cause of the problem....
 
It's tough to be the sole person insisting on a certain diagnosis, when 10 other members are saying, "carburetor!" Given the fact that we're all just reading your impressions on a website and watching the videos you made, it's never as definitive as doing diagnosis with the bike right in front of you... The blue/white smoke is oil smoke. How other people could conclude carburetor is beyond me to understand. Read one of my first posts where I mention that the type of smoke splits the diagnosis path into 2. Personally, I thought your engine sounded good, with just enough oil entering the head to make it miss occasionally. You had good compression too.

WTBS, I would still insist your carb was fine all along, and the miss was from drowning the intake valves seals in oil. Vacuum pressure sucked the oil right past the seal. (and later both cylinders showed oil burning, but the side where the drain hole was,... showed less oil burning, because the left side was sucking oil off the top of the puddle, and the oil drain hole was working just enough to keep the RH puddle low enough to only occasionally give a puff...

In a certain way, you went crazy making many changes at once, so even though you have a good result now, you can't point to a single change you made and say which change cured the problem.... and so the "carburetor" people will still insist the problem was the carb, and I would never agree.

If you think I was right, then read my last post where I outline the things to check to finish up your repair... Check the primary seal, check the primary/crankcase bolts, check the breather if the primary seal is blown out... The bike sounds strong in the last video. Good persistance on your part.
 
Last edited:
Would try the other carb since you set up for that now , didn’t see enough oil missing or burning to cause miss ( my opinion only) , I’m no expert like some of the folks on here .... part of using knowledge that resides here on this forum is being able to sort out who knows what and how they know .... much easier to sort with one change at time as mentioned above and previously .... good luck !
 
Primary off. Top inner cover bolt sitting in bottom of outer. Mangle washer. Also what upon closer examination, two halves of what appears to be chain roller. Found one link on chain with about 1/3 of roller missing. Must be at least one other somewhere on chain.
Cogs looking fine at this point.
New chain to be ordered & fitted.
 
Tornado said:
Primary off. Top inner cover bolt sitting in bottom of outer. Mangle washer. Also what upon closer examination, two halves of what appears to be chain roller. Found one link on chain with about 1/3 of roller missing. Must be at least one other somewhere on chain.
Cogs looking fine at this point.
New chain to be ordered & fitted.
Click to expand...
Looks like you got lucky
Maybe buy a lottery ticket today
!! Cheers
 
Hopefully there's no other damage
I'd check the alternator rotor and stator very carefully
Also the gearbox output shaft for straightness
But check everything
Cheers
 
o0norton0o said:
It's tough to be the sole person insisting on a certain diagnosis, when 10 other members are saying, "carburetor!" Given the fact that we're all just reading your impressions on a website and watching the videos you made, it's never as definitive as doing diagnosis with the bike right in front of you... The blue/white smoke is oil smoke. How other people could conclude carburetor is beyond me to understand. Read one of my first posts where I mention that the type of smoke splits the diagnosis path into 2. Personally, I thought your engine sounded good, with just enough oil entering the head to make it miss occasionally. You had good compression too.

WTBS, I would still insist your carb was fine all along, and the miss was from drowning the intake valves seals in oil. Vacuum pressure sucked the oil right past the seal. (and later both cylinders showed oil burning, but the side where the drain hole was,... showed less oil burning, because the left side was sucking oil off the top of the puddle, and the oil drain hole was working just enough to keep the RH puddle low enough to only occasionally give a puff...

In a certain way, you went crazy making many changes at once, so even though you have a good result now, you can't point to a single change you made and say which change cured the problem.... and so the "carburetor" people will still insist the problem was the carb, and I would never agree.

If you think I was right, then read my last post where I outline the things to check to finish up your repair... Check the primary seal, check the primary/crankcase bolts, check the breather if the primary seal is blown out... The bike sounds strong in the last video. Good persistance on your part.
Click to expand...
I'm interested in what you say about the oil causing a misfire
Have you had this happen in the past?
I only ask as I've had some bikes that smoke worse than a 2stroke in the past (sorry Greta but I had to get to work!) but never had a misfire from too much oil whether it be worn/loose valve guides or piston blow by etc
So I would never think of excess oil being burnt as the cause of a misfire unless it was really bad
This is just experience of course, hence the question?
Cheers
 
Tornado said:
Primary off. Top inner cover bolt sitting in bottom of outer. Mangle washer. Also what upon closer examination, two halves of what appears to be chain roller. Found one link on chain with about 1/3 of roller missing. Must be at least one other somewhere on chain.
Cogs looking fine at this point.
New chain to be ordered & fitted.
Click to expand...

Wait... what?? Broken primary chain?? They don't break unless something gets jammed in them. Not good.

baz said:
Hopefully there's no other damage
I'd check the alternator rotor and stator very carefully
Also the gearbox output shaft for straightness
But check everything
Cheers
Click to expand...

Roger that.. if that inner primary bolt got jammed between the chain and sprocket, the gearbox mainshaft MUST be checked. DAMHIK
 
baz said:
I'm interested in what you say about the oil causing a misfire
Have you had this happen in the past?
I only ask as I've had some bikes that smoke worse than a 2stroke in the past (sorry Greta but I had to get to work!) but never had a misfire from too much oil whether it be worn/loose valve guides or piston blow by etc
So I would never think of excess oil being burnt as the cause of a misfire unless it was really bad
This is just experience of course, hence the question?
Cheers
Click to expand...

As I said previously, had tornado made changes 1 at a time, we could know for sure what caused the misfire. No doubt in my mind that the OIL smoke stopped because he poked the drain hole. Feel free to argue that his video shows his bike smoking from a rich fuel condition. Do you think his video shows that? I don't, and as soon as I saw his video that's what I said. Coincidentally enough the side that had the misfire was also the side that was smoking significantly. When the oil infiltration issue was cured, the misfire was cured too.

Granted, he made numerous changes at the same time so it's not definitive. Maybe he'll put the carbs back to the original configuration and we'll see if the misfire returns.

On all the different engines I've rebuilt in my lifetime, I've had a lot of different surprises. If you want me to say there's a possibility that oil getting sucked into the intake could cause a random misfire, I would say it could. If you want me to say it always does, I would say of course not. Many of us have probably pulled a spark plug out of an engine that ran and been surprised that the spark plug was caked in oil... but that engine still did run.
 
o0norton0o said:
On all the different engines I've rebuilt in my lifetime, I've had a lot of different surprises.
Click to expand...

There are always surprises and "a'ha" moments. I had been struggling with a weak pulses from one pot and an erratic mixture for a few weeks now, and was beginning to think the worst.

Long story short, during my constant in-and-out of the carbs changing needle positions, slides etc. the upper cable nipples on the Madass gantry were progressively being thrown out of alignment. This was affecting the static slide position. I hadn't caught it until a few days ago because I routinely check the operative synchronization of the slides before putting the air filter back on, and nothing here had changed.I happened to take a look through the back of the carbs with the slides seated and thought "that doesn't look right", sure enough the problematic pot was a good 1/8" lower, so I got out the small bore guages and reset then. BOOM, problem solved

Seems the OP has sorted out the problem, and I'm sure buried somewhere in the pages of tips was just such a check
 
o0norton0o said:
As I said previously, had tornado made changes 1 at a time, we could know for sure what caused the misfire. No doubt in my mind that the OIL smoke stopped because he poked the drain hole. Feel free to argue that his video shows his bike smoking from a rich fuel condition. Do you think his video shows that? I don't, and as soon as I saw his video that's what I said. Coincidentally enough the side that had the misfire was also the side that was smoking significantly. When the oil infiltration issue was cured, the misfire was cured too.

Granted, he made numerous changes at the same time so it's not definitive. Maybe he'll put the carbs back to the original configuration and we'll see if the misfire returns.

On all the different engines I've rebuilt in my lifetime, I've had a lot of different surprises. If you want me to say there's a possibility that oil getting sucked into the intake could cause a random misfire, I would say it could. If you want me to say it always does, I would say of course not. Many of us have probably pulled a spark plug out of an engine that ran and been surprised that the spark plug was caked in oil... but that engine still did run.
Click to expand...
Yes I see what you are saying
The smoke in the video looks like oil to me not richness
No doubt that the drain hole being blocked can cause this
It's only the issue of the oil causing a misfire is what I'm asking about, I'm keen to know because it's something I have never come across
I'm not doubting anything, just interested
 
Status
Not open for further replies.
Back
Top