Misfire Troubleshooting

Status
Not open for further replies.
oldmikew said:
Tornado,
There are two further carburettor possibilities... It is possible to get fuel starvation and flooding as a consequence of the isolastics , try changing clearances or tension . The other is you can have a more or less completely blocked carburettor filter and it will still flood on tickling but be erratic in fuel supply.
Do apologise for my seemingly elementary 'tips' but have personally have had weeks wasted on them . BTW to be sure you donot have a dropped needle you have to either sight through the carb intakes with mirror and torch or by feel if you have sensitive fingers
All the best with it
Click to expand...
Not disagreeing with systematically working through all possibilities, but the plug colors seem like a big clue. If you read the color as evidence of richness, ok could be carb related, if oil, would point in a different direction. I know it's simplistic, but if running a slightly hotter plug makes the misfire go away, I think that would indicate it's an oiling problem.
 
Tornado
A couple of possibilities.
i) When resleeved were the throttle slide clearances correct? According to John Healy's document on Amal tuning the correct clearance is .0035 to .004" for the slide in the bore of the carb body. I had a case of too tight a slide which was causing rich running. Some restorers are fitting slides to tolerances which are too tight.
ii) Are you certain that the throttle needle and clip are seated correctly under the throttle spring. I have had cases where the clip and needle have migrated up the spring causing rich and uneven running.
Andy
 
Could a case to cylinder gasket or sealer glob obstruct the oil drainage? I would make sure the wire you use goes past the cylinder to case joint .
 
I realize that this thread is already 6 pages and that I'm probably wrong, but I re-watched the video and it sounds like a mechanical noise to me. Might have a miss as well as a mechanical issue. I would use a screwdriver to listen to various parts of the engine and exhaust to see if I hear anything useful. Also, with the plugs removed, I would have someone kick it while I listened.
 
marshg246 said:
I realize that this thread is already 6 pages and that I'm probably wrong, but I re-watched the video and it sounds like a mechanical noise to me. Might have a miss as well as a mechanical issue. I would use a screwdriver to listen to various parts of the engine and exhaust to see if I hear anything useful. Also, with the plugs removed, I would have someone kick it while I listened.
Click to expand...
Just listened for first time (originally thought listening wasn't worthwhile - my bad) and agree with Marsh246
 
Single carb (RH) swapped back on to 2n1 mani. Quite a fiddle getting to this point, usual stuff like having the to carb off mani after just fitting after realizing the cable adjuster lock nut prevents my single carb cable from fully lowering slide...no other slack adjuster on it. So carb off, top off, spring/slide/needle out again. Cable removed, adjust nut removed from adjuster, all put back on again. now there's a little free play in the cable sitting in the adjuster and slide is all the way down.

(BTW, if anyone hasn't discovered yet, "screwing" the spring onto the cable is so, so, so much easier than trying to hold it compressed while fiddling the cable nipple into the slider hole; Just start the spring on the cable, already in the slide with needle fitted etc, and wind the spring while holding the cap steady, letting slide assembly rotate in the wind below as spring turns its way fully onto cable).

Can also report both carb needles were seated and on middle groove when removed.
Had a look within the intake ports to try and see valves....RH looks clean, was dry to a finger poke, LH was dark & shiny, had oil on finger after poking around. This is in line with the plug appearance from that side.

Last night after pulling tank, pulled off the coils, replaced them with the fresh lucas 6v pair that came with the Wassel EI. I'd used the new one in the past and seemed to be fine. Went back to the originals (for no apparent reason I can recall) early last year and they were also good. Fitted ring terminals at all the EI connection points instead of the spade connectors (Cliffa's rec.). Also confirmed I already have a direct ground line from battery, the DT headsteady, then on to the EI frame terminal ground point, with no intervening bullet connections. Confirmed with DMM volts at frame and head were same as those at +/- battery terminals (12.75v with ign off).

Cables need securing, Tank needs to go back on. Then should be ready to test.
 
Last edited:
Sounds like you found the oil leakage on the intake LH valve. I hope you poked that drain hole well enough. Your engine had a strong idle. It would be great if it was just that drain hole being clogged *finger's crossed*
 
o0norton0o said:
Sounds like you found the oil leakage on the intake LH valve. I hope you poked that drain hole well enough. Your engine had a strong idle. It would be great if it was just that drain hole being clogged *finger's crossed*
Click to expand...
Oil on upper surface of valve means it's coming from above/rocker side seal or guide, correct? Can't be from head gasket getting to upper side of valve?
 
It could be the valve stem or around the valve guide, but like some have mentioned, if that drain hole is clogged and the valve seal is under "water" in the oil pool, it's going to infiltrate past the seal because of vacuum pressure... As I said, if you poked that drain hole good, I'm hoping you fire it up and there's no miss. It probably will burn some of the oil in the exhaust for a while, so if you ride with buddies, maybe hang back for a few miles until the smoking clears... ;)
 
So you have the dedicated ground attached to the ST head steady , would prefer to hear you had it attached under one of 3 bolts holding head steady to head , thought that was correct way when suggested I try it several years ago , I know nothing , so if you positive that is perfect ground point , it is your bike ....
 
Craig said:
So you have the dedicated ground attached to the ST head steady , would prefer to hear you had it attached under one of 3 bolts holding head steady to head , thought that was correct way when suggested I try it several years ago , I know nothing , so if you positive that is perfect ground point , it is your bike ....
Click to expand...
It's attached to the DT plate bolted to the head. There are two smaller threaded holes on the forward edge (for hooking up the suspensory spring thingie which I do not have (yet??). So in good solid contact with alloy plate and thus the alloy head. Testing volts at plate or elsewhere on the head gives same voltage as directly on +/- terminals of batt.
 
Hi Tornado,

"Had a look within the intake ports to try and see valves....RH looks clean, was dry to a finger poke, LH was dark & shiny, had oil on finger after poking around." doesn't sound good.

While you have the tank off maybe it will be easier to check that you can see the stem seal is in place ?

Do you know if it's an RH4 head ? (it should be stamped just above the right hand exhaust tappet cover ).

Cheers,

cliffa.
 
  • Like
Reactions: baz
Oil on top of the valve usually means valve stem seal has gone
Or the guide is worn out
The guide is loose in the head
Or the head is cracked in the guide hole
Block the oil feed to the head to confirm
Then pull the head and repair it, I hope it's not cracked
 
Ok, just did a 30 mile highway run. Not a single misfire, loads of response very smooth. Smoke seems tobe lingering a bit some puffs at idle and roll on, on LH. Very small amt on RH. Im stopped up at a coffee place. After getting brew, I see a small oil patch under bike. Drips off sump drain plugs but they are snug. Checking oil, im below dip stick, about half way down tank. Having another rider fetch me some oil before trotting home. Looking around under bike I see no oil on rear tire or mudguard. Engine above casing looks ok. I found 1/4 of the inner primary to crankcase gasket slid out by itself. Very odd. Maybe one of the three bolts has let go and flooding primary.
 
Tornado said:
Ok, just did a 30 mile highway run. Not a single misfire, loads of response very smooth. Smoke seems tobe lingering a bit some puffs at idle and roll on, on LH. Very small amt on RH. Im stopped up at a coffee place. After getting brew, I see a small oil patch under bike. Drips off sump drain plugs but they are snug. Checking oil, im below dip stick, about half way down tank. Having another rider fetch me some oil before trotting home. Looking around under bike I see no oil on rear tire or mudguard. Engine above casing looks ok. I found 1/4 of the inner primary to crankcase gasket slid out by itself. Very odd. Maybe one of the three bolts has let go and flooding primary.
Click to expand...
If those bolts have come loose do not ride the bike or start the engine until sorted
 
Well made it home. Sorry Baz! Hopefully no harm done.

Before departing, tried a bit of fine adjusting on mixture and idle screws. Seemed better, but then started popping a fair amount on throttle roll offs/when shifting. Also found reving up slightly on roll off. Couldn't dial that out again.

Anyway, generally a successful test. No misfires and oil smoke pretty much gone after riding back. Will pull the fresh plugs to see what they look like.
 
So basically great news , other than the other niggles ..... sometimes it best to go slow when sorting these type of things ..... not always the worst case , eh .... I see a Mik in your future , you going to love it !
 
So,... I would say that you cleared a blockage in the rear drain hole which solved the intake valve being underwater, the misfire it caused, and oil entering the cylinder from the head. The oil that has disappeared from your crankcase has probably been pumped into your primary case now, since there was no oil really on the ground. The small amount of oil on the ground probably came from the joint between your crankcase and primary case, because the gasket was displaced due to the crankcase pressure which has blown out the primary side oil seal. That also means you probably have some sort of breather blockage, so the air pressure from the piston downstroke is what displaces the crankcase seal. That means you'll be taking off the rotor and stator to renew that seal, and check those screws that Baz was telling you about...

At least that's my armchair diagnosis. I'd say you did well, and got lucky it wasn't something bad...
 
Last edited:
Status
Not open for further replies.
Back
Top