Misfire Troubleshooting

Have you checked your valve clearances?

It's difficult to tell, but it look like a black puff from the left @ around 5 seconds in?

Another source of air leaks ( although I don't think that's the problem here) is a split or not tight balance pipe.

I removed the Lucar blade terminals from my standard coils and put hoop connectors on instead, as I found they were loose on the blades. ( you can just crimp them a bit with pliers though ).

Did you swap the HT leads / caps?

Put a piece of tape by the throttle and mark the throttle positions, quarter, half, three quarter. Go for a ride and see at which position the misfire is the worst. Misfire at same throttle position in different gears likely carb. Misfire at same rpm in different gear likely ignition.

Tornado said:

EI ignition so should not explain why only LH side issue.

Click to expand...

I had a dodgy engine earth, well I can't be certain but an intermittent spark on one side was cured by fitting an earth wire directly from the head to the battery with a link to the Boyer box. The clue was when I accidentally left the HT off the good side plug the bad side came to life and as a single cylinder fired perfectly. I knew then the coils and wiring were good and the Boyer (had already swapped boxes, coils, HT leads etc etc) so it had to be down stream of the plugs and only the earthing could be at fault.

Many whiles ago I dealt with same side mis-fire ,tried all of above , think in the end it was running a dedicated ground from head to battery and starting with pristine brand new plugs , no doubt getting all the little things done as mentioned above played a part as well , I threw all the used but cleaned plugs in garbage and keep close eye on plug condition to this day , I also run a mix of 70% high test 91 oct and 30% 116 oct race gas to keep things working even better ... with patience and perseverance you will get your smile back !

norton bob said:

I would also wonder about the inlet valve seal which may be worn or just popped off on the oily cylinder. As a side issue looking at the good plug I wonder if the timing is far enough advanced in the main area of use( mid range running). Might be that although the timing is set correctly at full revs you are getting a too slow advance. Not something you can normally adjust out. A feature of some systems.

Click to expand...

I did have failed inlet seal on LH side last year. Replaced both (they just crumbled away while removing) with KibbleWhite Viton's....done with head still on bike using Ludwig's magic spring compressor gizmo. But the smoke I was having from that was only on throttle roll-OFF, momentary while blipping from idle. The new smoke is more constant when rolling ON.

Supercat said:

Have you checked your valve clearances?

Click to expand...

Yes, right after checking head bolt torques...all were fine.

cliffa said:

It's difficult to tell, but it look like a black puff from the left @ around 5 seconds in?

Another source of air leaks ( although I don't think that's the problem here) is a split or not tight balance pipe.

I removed the Lucar blade terminals from my standard coils and put hoop connectors on instead, as I found they were loose on the blades. ( you can just crimp them a bit with pliers though ).

Did you swap the HT leads / caps?

Click to expand...

Yes the video didn't capture much of the smoke...need to find a darker background and a bright sunny day to try recording again. But, if you watch very carefully, you can see smoke on LH pipe a couple of times.

No balance pipe on the bike....my original balanced headers failed at weld branch. Replaced with non-balanced pair in good condition.

I like the idea of rings on the coils....will work on that.

htown16 said:

Put a piece of tape by the throttle and mark the throttle positions, quarter, half, three quarter. Go for a ride and see at which position the misfire is the worst. Misfire at same throttle position in different gears likely carb. Misfire at same rpm in different gear likely ignition.

Click to expand...

Will work on that....

Tornado said:

Silencers are muted...
I do have some opened silencers have not fitted yet, can try those.

Click to expand...

I would try that.
Could be an obstruction in the exhaust ( long shot..)

OK, I'll summarize what's been done to reduce the repetitive suggestions:

1. Amal carbs: Resleeved over winter; jets (260 main, 105 needle) and needles new 2k miles ago; Needles on mid-groove...ran like that past two seasons reasonable well. All air/fuel circuits fully cleaned and flowing well, verified several times now; Slides balanced with dowels and for WOT position; No chokes on the carbs; Checked/greased idle & mixture screw o-rings.
2. Wassel EI: Recently confirmed timing correct at 30 BTDC at 4-5K rpm. Connections all firmly seated. No wiggle-induced misfiring at stator wires. Bike starts up really well, one kick or two. No kick-backs.
3. Coils: Swapped left for right (by migrating plug ends left/right)...no change in issue, stayed LH side. This eliminates coils as the issue.
4. Plugs: LH dark, possibly oily but not fuzzy/sooty. RH light brown. Have changed NGK to Champion yesterday and same colouration developed within 30 minutes (previous photo was the NGK's that came off).
4. Valve clearances and head bolt torques good.
5. Exhaust roses re-snugged up yesterday...no changes to issue.
6. Timing chain replaced and tensioned (using the intermediate gear holding bracket from OldBrits) as per manual, done over this winter.
7. DT Headsteady fitted this winter. Ground engine at the head baseplate (alloy).
8. Tested for leaks on all manifold surfaces, balance connector tube, flanges, headgasket joint using both WD40 and carb cleaner. Could not identify any area affecting rpm (with hot engine, both at idle and 2500 rpm).
9. No header balance pipe; muted silencers (originals). Have an unmuted set to be fit soon.
10. Intake valve seals renewed (Viton KW's) last year when puffs from RH side detected at throttle roll-OFF at blips from idle. Done without removing head. Solved puffs. New smoking is quite different as it's on throttle roll on and continues for longer periods while rpm's rise.
11. Compression tested yesterday on hot engine. Both sides come in at around 150 PSI...similar to what I found 6 months ago. No ability to perform leak down test in my humble parkade working area :-(


I'll add more to this list as I recall other items or do new things....

I had to improve the fit of the throttle cables in the carb tops, to get rid of a hesitation in throttle response.

I’ve also had to poke a wire through a pilot jet.

Tornado said:

Yes the video didn't capture much of the smoke...need to find a darker background and a bright sunny day to try recording again. But, if you watch very carefully, you can see smoke on LH pipe a couple of times.

No balance pipe on the bike....my original balanced headers failed at weld branch. Replaced with non-balanced pair in good condition.

I like the idea of rings on the coils....will work on that.

Click to expand...

Hi Tornado, actually I meant the balance pipe on the inlet manifolds. (presuming you are running twin Amals).

Cheers,

cliffa.

I noticed you are running a 105 needle jet, I thought the standard was 106. I don't think that's your problem. It seems you've covered all the logical causes. Could be something daft like the slide facing the wrong way?

Solved a similar problem yesterday on my 74 Roadster... is your spring support for the warning light assimilator touching one of your coil terminals?
Mine would idle fine but off idle it would miss, thought it was carb related but it was the assimilator vibrating and contacting the positive coil terminal.

Torry, have you taken your bike out of town and given it a good old fashioned work out this season ....not talking stop and go around city , good back road run ....

cliffa said:

Hi Tornado, actually I meant the balance pipe on the inlet manifolds. (presuming you are running twin Amals).

Cheers,

cliffa.

Click to expand...

Inlet manifold connection tube is fresh 1/4" fuel line rubber hose....good tight fit, no cracks in hose nor anywhere in manifolds/balance pipes (at least as far as heavy carb cleaner spray while running could detect).

cash said:

I noticed you are running a 105 needle jet, I thought the standard was 106. I don't think that's your problem. It seems you've covered all the logical causes. Could be something daft like the slide facing the wrong way?

Click to expand...

I'm sure I used the standard jets/needles in the 32mm carb for 850 MKII setup...when I set these up last year. So if that's 260/106 then that's what I used.

Craig said:

Torry, have you taken your bike out of town and given it a good old fashioned work out this season ....not talking stop and go around city , good back road run ....

Click to expand...

Yes, did a few highway runs, one over 40 min. Made no difference. misfires not so noticeable at highway speeds, but not completely gone.

MarcoNC850 said:

Solved a similar problem yesterday on my 74 Roadster... is your spring support for the warning light assimilator touching one of your coil terminals?
Mine would idle fine but off idle it would miss, thought it was carb related but it was the assimilator vibrating and contacting the positive coil terminal.

Click to expand...

Interesting, but alas no assimilator on bike since fitting SparkBright voltage indicator LED. Also wrapped my coils with insulator UHMW tape where the clamps wrap around coil casings...in case there's some internal shorting going on.