Absolutely puzzled...engine problem 750

Scout63

VIP MEMBER
Joined
Nov 24, 2016
Messages
481
Country flag
Throttle cables out of adjustment? Maybe the takeup on the problem side is looser that the good side?
 

texasSlick

VIP MEMBER
Joined
Jan 2, 2013
Messages
2,947
Country flag
Pretty sure more than 2 carbs off perfectly running bikes have been tried on problem side with same results .... doubt he changed out cables during his carb testing
I am inclined to agree with you, in that the problem resides in carburetion.

Wasted spark ignition rules out mismatched timing.
There is still the possibility of weak spark due to a ground fault. The spark tester should clear up that possibility.
We should wait for the report of the spark tester before speculating further.

Only thing left is carburetion, despite a switch out x2. I can remember at least one other member of this Forum claiming a carb switchout did not change anything, but ultimately it was carb related.

Slick
 
Joined
May 11, 2010
Messages
2,408
Country flag
I am inclined to agree with you, in that the problem resides in carburetion.

Wasted spark ignition rules out mismatched timing.
There is still the possibility of weak spark due to a ground fault. The spark tester should clear up that possibility.
We should wait for the report of the spark tester before speculating further.

Only thing left is carburetion, despite a switch out x2. I can remember at least one other member of this Forum claiming a carb switchout did not change anything, but ultimately it was carb related.

Slick
I too await the sparklers...and rest assured the cables, sync, all adjustments were carried out with meticulous attention.
 

cliffa

VIP MEMBER
Joined
May 26, 2013
Messages
1,492
Country flag
A few suggestions Onder,

If you are running standard style coils check the link wire between them. ( if you still have the Lucar blade connectors I would swap them for hoop style, but that's an aside).
Reverse the wiring to the coils and see if the cool running changes side.
Run run two wires straight from the battery to the Pazon to eliminate the ignition and kill switches, and earthing issues.
Swap silencers.

Cheers,

cliffa
 
Joined
Jan 31, 2010
Messages
2,160
Country flag
Frankly, the symptoms don't indicate an ignition system issue. If the bike runs properly at higher RPM/load, then the Ign system is fine. Ignition systems can work properly at low speed/no load but NOT work under load but the opposite is ...well, I suppose it's stupid to say that anything is 'impossible'...so I'll say, 'extremely unlikely.'

The symptoms point to fueling related issues - carb settings/defects, vac leak, etc. Try the engine running/turn petcock off test I mentioned in post #26.
 
Joined
May 11, 2010
Messages
2,408
Country flag
A few suggestions Onder,

If you are running standard style coils check the link wire between them. ( if you still have the Lucar blade connectors I would swap them for hoop style, but that's an aside).
Reverse the wiring to the coils and see if the cool running changes side.
Run run two wires straight from the battery to the Pazon to eliminate the ignition and kill switches, and earthing issues.
Swap silencers.

Cheers,

cliffa
Running single coil dual HT leads, tested out fine, replaced with new identical, tested, makes no difference. No diff is ignition key is jumped either. No kill switch in system. Coil earth direct to battery. Spark with plugs out against head impressive spark.
 
Joined
May 11, 2010
Messages
2,408
Country flag
Frankly, the symptoms don't indicate an ignition system issue. If the bike runs properly at higher RPM/load, then the Ign system is fine. Ignition systems can work properly at low speed/no load but NOT work under load but the opposite is ...well, I suppose it's stupid to say that anything is 'impossible'...so I'll say, 'extremely unlikely.'

The symptoms point to fueling related issues - carb settings/defects, vac leak, etc. Try the engine running/turn petcock off test I mentioned in post #26.
Since it clearly is getting fuel and it is clearly rich Ill try lowering the float. New amals seem to set the float higher than the old ones I notice.
 
Joined
Jan 18, 2020
Messages
180
Country flag
One thing you've not mentioned. How about the exhaust system? Any leaks or restrictions?
Easy to check if I'm barking up the wrong tree.
 

cliffa

VIP MEMBER
Joined
May 26, 2013
Messages
1,492
Country flag
Since it clearly is getting fuel and it is clearly rich Ill try lowering the float. New amals seem to set the float higher than the old ones I notice.
The reason I mentioned swapping the silencers is I wonder if you may have an issue with the left one not allowing exhaust gasses to escape properly. That would probably give the appearance of a rich mixture in the combustion chamber. Pehaps a baffle is out of place for example?
 
Joined
Apr 20, 2011
Messages
4,794
Country flag
The reason I mentioned swapping the silencers is I wonder if you may have an issue with the left one not allowing exhaust gasses to escape properly. That would probably give the appearance of a rich mixture in the combustion chamber. Pehaps a baffle is out of place for example?
Or, someone accidentally pushed a potato up ones muffer o_O
 

Lineslinger

VIP MEMBER
Joined
Feb 26, 2017
Messages
562
Country flag
My 2yr. old grandson put a couple of his little toy cars down the left exhaust...his sister ratted him out.

Point being I never would have known the exhaust was blocked.

This is really a stumper, did you spray down the suspect area while running with cleaner or starter fluid to see if there was any change? All around the suspect side of the head and exhaust rosettes?
I am thinking bad seal or unseen crack.
 
Last edited:
Joined
Jan 31, 2010
Messages
2,160
Country flag
Since it clearly is getting fuel and it is clearly rich Ill try lowering the float. New amals seem to set the float higher than the old ones I notice.
Do the petcock off check and you are automatically checking to see if the float level is the issue without actually having to do anything. If the bad cylinder suddenly improves as the fuel level in the bowls drop, then it is telling you that the float level is too high in that cylinder, essentially causing flooding at idle/low speed. Easier to make the test rather than adjust the levels if they don't need it.
 
Joined
Nov 10, 2006
Messages
1,305
Country flag
Onder, I've probably missed this one, there's a lot to read through.
Years ago I had similar a similar fault and thought it was the Boyer, the dual coil tested out okay. I sent the whole lot to Boyer including the coil as instructed. Boyer phoned me telling me it was the coil and they were right. Swap the coil.
Trying times, you'll find it and it'll be something bloody daft.
Dave
 
Joined
Feb 19, 2020
Messages
4
Country flag
Have you checked your choke cables. Are they both fully opening and closing and both in sync. worth checking.
 
Top