650 - A Couple Of Questions

[G0FHM]

Just been out to the shed, armed with an AVO.

Resistance across the primaries of both coils is just shy of 5 ohms (manual says 3-5R).

Sounds OK Good!

Secondary on new coil 17.4K and existing coil 15.8K. Just for fun, I stuck the meter across the secondary on the coil with the duff leads and came up with 11.3K.

The manual says (although that figure is not supposed to be gospel) 30-35K for the secondaries, if the windings are in sound condition.

OK so they are both down Should that be a major problem seeing as they are not that far apart?

DC voltage at the + of the coils is the same as at the battery with the ignition on. Good Good Oh!

What next to look at?

I did see a video on youtube of some American chap from the deep south having a dead pot on his 750. But once I decoded the constant profanities and filtered them out, it was basically him pointing under the seat and blaming a connector under there! Surely though, if it's wasted spark, then that would affect No. 1 too?

Would there be any mileage in scrapping the connectors between the ignitor, pickup and wiring loom for nice new bullets with heatshrink? Might be worth putting in a temporary bypass to the loom Will have a bash at that tomorrow

Also, the advance/retard on the pickup seems a bit heavy (compared to the distributor on a car). Again, would it be in order to take the pickup backplate off and give the mechanism a bit of lubrication? I did notice that when I turned the shaft by hand it didn't immediately spring back, but was rather slow.... I wonder if this is the cause of the revs being slow to drop? DefinitelyRighto, will try a squirt of WD40 first!

And finally, by taking the pickup backplate off to access the advance/retard mechanism, is there any scope for me to inadvertantly alter the ignition timing? or is it fixed? 100% certainty (I'm leaving well alone then.. Don't want to cause any more problems!



Hope that is of use

Extremely useful!

Sorry the blue does not show up very well on the black but as I'm using the Android Slab I can't change it easily

No problem, Windows phone showed it up well!

Looking like you have a mix of probs.

Tell me about it!

Although if you have a fault the does shift with the ht lead swap, then it is pointing to the carb on #4

No - Misfire stays on No.4 no matter how I swap the coils/leads about! I'm not sure what the problem could be with the carb. Needle valve appears to be good, as I can fill the float bowls, then blow down the feed pipe, and air does not go through, it's solid. Diaphragm seems to be ok - Push the piston up, and put a thumb over the hole, and it stays there. Spraying WD40 into the back end of the carb made no difference to the engine note. Misfires even on full choke, so not a starvation problem. Had the needle jet out and all good, and the pin is in the groove at the end. Jets are standard, as listed in the manual

Try swapping the coils over and see if it migrates to 2&3

Already done that - About as much use as mammaries on a fish!

Auto advance needs to nice and free to return, try a splash of WD40 first before taking it to bits.

Thats the first option!

I'm at a total loss as to what the problem could be - Unless the carb is flooding the cylinder to the point that the fuel is not even burning? I'd expect at least a bit of pinking where the fuel is exploding in an uncontrolled manner.....

Bloody thing!

[G0FHM]

Ok guys.... Make sense of this:

I've popped out the intake air stub between the backside of the carb and the 4 way collector before the airbox.

Firing it up and revving gives 3 cylinders. If I put the end of my finger on the end of the piston, I can feel it pulsing up and down by a small amount, in time with the needle flick on the vac dial. So that appears to be working ok.

Here's the funny bit!

If I place my hand over the opening on the backside of the carb (not enough to completely seal it and prevent air from getting in), the engine will suddenly jump up to 4000rpm, and run cleanly. This is proved by a hot downpipe, and a hot sparkplug.

Also, I can feel the odd pop and splutter as the airflow going in is being momentarily interrupted.

Does that help give any answers?

Any ideas?

PS, Krytie, I did the WD40 thing on the advance mechanism, no need to risk naffing up the timing

[G0FHM]

Well, whatever the problem was, it's now fixed!

I took the carbs off again, and removed the inlet stub.

The only conceivable thing I can think of, is that when I put the new O rings on the stubs it must have jumped out of the groove - However it showed no signs of being pinched.

I stuck it into the groove with some silicone, and put it all back together.

Will have to put it down to an air leak, but only a minor one, just enough to cause a problem as I sure as hell couldn't detect it by the usual means!

Thanks for all your help guys!

J

[callyboy]

Glad you sorted it.

When I took the carb rubbers of the project pop engine the poor old seals were flat as a pancake,rock hard and cracked in loads of places.

Its the sort of thing that people never really look at but can effect the running of the engine quite badly.

Cheers

There is an interesting article somewhere I will try and dig out about them.

Pete

[G0FHM]

Pete,

The existing O rings were green, and like you stated flat as a pancake and very brittle (in fact I think I snapped one in half!).

The only thing I can think of is as the new ones were smaller than the groove, it must have popped out as I offered it up.

Oh well, I've got the dunce hat on, and the missus did a victory lap of the garden waving her hands in the air, to chants of "I bloody told you so"

Right - On to the next major headache

J