277 trouble

pamcopete

pamcopete

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This is a little unusual, but member mcgyver62 is having some issues with his recently completed 277 conversion and he or his mechanic thinks the problem is with the PAMCO 277 ignition. I don't think it is, and after some exchange of thoughts on the subject, I suggested that he return his PAMCO 277 system for a full refund and try a different system. Perhaps he will join us here and we can collectively try to fix his problem, but I would prefer to bow out at this time as the PAMCO should be replaced with a different system in order to satisfy him that it is or is not the ignition system.
 
motor was rephased by cycle improvements in waterloo Ontario. overbore to largest oversize all new bearings ,lectron carbs,pistons rings ,valves ,seats 3 valve job .etc.complete overhaul with all new parts,cam was done by webcam 277. motor was assembled by the owner and his top mechanic and cam chain crank etc were all degreed as per instructions,Pamco was installed as per instructions. motor would not fire.discovered that the mechanical advance had to be rotated 180 for the motor to fire.got it running carbs tuned and timing on left cylinder TDC bang on,right cylinder was running colder and firing retarded according to my buddy helping me at least 9 degrees.after 20 hrs of scouring over it I took it to my mechanic who did all the same checks ply he had all the fancy tools to do it.degreeing wheel ,piston stops strobe light etc he determined that my motor was in fact turning over at277 but that my ignition was out 10 degrees,i got another pamco from my distributer and it corrected my problem by 5 degrees.someone please for the love of all that is holy help me ride
 
277pic2.JPG


Kibbitzing here.

Has Mcgyver got 277 timing marks and the timing light is indicating the 5 degrees retarded. I will assume retarded but kinda wonder because 5 degrees isn't a lot? If the difference was split between the cylinders I doubt anyone but a racer would notice anything at 2 degrees off on an XS650 engine. 2 degrees is less than the variation inherent in a cam driven ignition? With all that said, looking at the board it appears straight forward to slot one pickup's and board mounting holes, and adjust the timing to spot on? Some crude math says 5 degrees is less than 1/10 of an inch at the pickup. or about the diameter of the the mounting screw threads.

Um I reread the specs and "Lectrons?" Those are kind of noted as crude WFO type carbs, I'd expect less than stellar "street performance" out of those. As an experiment perhaps swap carbs or needles and see which cylinder runs cold. The literature contains some hints that needle machining lacked consistency for at least some years of production.

Any time you are dealing with ignition, left right component swaps can be revealing, swap coils, wires, caps, plugs?
Again just some armchair thoughts, cause you asked and no one else has piped up.
 
Hey, Pete. Just thinkin' out loud here.

Thinkin' in terms of the gauss field being hemispherical, and timing changes from lateral inconsistencies:
Suppose magnet/trigger rotor had a slight swash/canted fit.
Suppose that a magnet (or more) had a weaker/stronger field flux.
Suppose that a magnet (or more) was seated at a different depth.
Suppose that the advance shaft has significant end play (maybe 0.020").

Suppose that the FET has a high, wide, or unstable gate hysteresis.
Suppose that the flyweights have uneven ear wear, and gravity pulls one down differently.
Acceleration/deceleration of the cam being non-symetrical, effects of worn advancer.

:shrug:
 
5 degrees is well within the cam chain slack cycling front to rear recheck chain tension? as an experiment run the adjuster in pretty tight and recheck timing? For testing only, do not run a cam chain so tight there's no plunger movement. I've always felt for best accuracy ignition should be triggered off the crank not the cam.
 
TwoMany,

Sure. All of the above except for the magnets strength as the same magnets are used to trigger both sensors. The IGBT is triggered by a square wave, so hysterisis is not a factor. The sensor zone of influence is conical. In any event, I think he has other issues that are not ignition related and if he were to describe those issues, we may make some progress.
 
the problem is that when the ignition fires TDC on the left cylinder it is retarded 5 degrees on the right cylinder.The pipe on the right is running 100 degrees colder and puffs of unburned gas are coming from the pipe.
 
gggGary said:
5 degrees is well within the cam chain slack cycling front to rear recheck chain tension? as an experiment run the adjuster in pretty tight and recheck timing? For testing only, do not run a cam chain so tight there's no plunger movement. I've always felt for best accuracy ignition should be triggered off the crank not the cam.
Click to expand...

The transistor is insulated from the plate by an insulating washer and two mica insulators, so it is not readily movable.

The cam doesn't just trigger the ignition, it also operates the valves and I am of the opinion that if there is erratic timing from the cam, then it may be beneficial to have the ignition cam based so whatever the error in timing may be, the ignition will follow the valve timing.
 
McGyver62 said:
the problem is that when the ignition fires TDC on the left cylinder it is retarded 5 degrees on the right cylinder.The pipe on the right is running 100 degrees colder and puffs of unburned gas are coming from the pipe.
Click to expand...

The ignition should fire at 15 degrees BTDC, not at TDC. The suggestion was made to split the difference so the right cylinder is not 5 degrees retarded. For test purposes, you could set the right cylinder to the correct timing mark and see if it then produces heat.

If you have been using TDC instead of BTDC, then that would put the right cylinder at 5 degrees ATDC and that could produce those symptoms.
 
gggGary we set the right cylinder at TDC and ran the 5 degrees advance on the left .right side ran beautiful.these lectronsare brand new and run fantastic and easy to adjust.you can eliminate them from the equation for sure . as for splitting the difference thats not really an acceptable solution to me .that means running one side advanced and the other retarded.I appreciate your input you getting the ball rolling on this thread :)
 
I am still of the opinion that making one pick up adjustable and dialing in the timing is trivial compared to the time and effort spent so far. It sounds like there is a "spare" board there now?
 
McGyver62 said:
gggGary we set the right cylinder at TDC and ran the 5 degrees advance on the left .right side ran beautiful.these lectronsare brand new and run fantastic and easy to adjust.you can eliminate them from the equation for sure . as for splitting the difference thats not really an acceptable solution to me .that means running one side advanced and the other retarded.I appreciate your input you getting the ball rolling on this thread :)
Click to expand...

Please clarify: Are you setting the timing at Top Dead Center (TDC) and not Before Top Dead Center (BTDC) ?
 
I walked away and chewed on this for a bit. After Pete's concern about gross timing is resolved it seems to me that for this engine the Pamco rotor needs to be degreed and marked then timing between the pamco rotor and the crank rotor compared. that would point the finger at the pamco timing OR the crank/cam relation as the issue. I do see the frustration level on both sides.
McGyver feels he's narrowed it down to a Pamco issue and Pete sees that the field of view may have prematurely narrowed to only his mounting plate timing accuracy. I don't know pete's manufacturing so can't comment to any tolerance that may or may not be between the two pickups. Looking at this it appears one rotor magnet triggers both pickups? So the plate relation between the pickups is the only likely "variable" on the Pamco setup?
 

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