Loop frame electrical gremlins

[Don-Spada]

I have just read the thread on the distributor, that sounds quite informative and may help you out.

V7 ignition problems

Continuing the discussion from Loop frame electrical gremlins: Re the comment about swoping the coils out there is only one coil on the loops, try checking the distributor as the rotor arm can be out of alignment with the cap, when on full advance on no 1 make a mark on the rotor where the cap lines up, turn the engine over to number two and check that cap lines up with the rotor. I have discover that if you are one tooth out onto distributor it runs lovely on no 1, but number 2 completely mis…

[banquo]

@Odradek

Yes I have vacuum gauges. Carbtune with the steel rods.
Trouble is I get no real reading at all from the right cylinder.
It barely gets the rod to move.

Surely this is the root of the problem, and all the ignition issues are not related at all? Even with the HT lead disconnected on the offending cylinder, there should still be a vacuum drawn. If there’s no vacuum, either the inlet valve isn’t opening when it should, or there’s a gaping hole somewhere that’s preventing the cylinder from drawing a vacuum: e.g. exhaust valve stuck or burnt, holed piston, etc. For an easy check, you should be able to check for vacuum by sticking your hand over the carb mouth, and spinning the starter with throttle wide open. My guess is there’s no vacuum to draw fuel/air in, and it’s the cause of that you need to diagnose?

[Odradek]

Thanks.
New distributor cap and rotor arrived yesterday, so I popped them on.
Idling on both cylinders now, a bit rough so far, but a huge improvement.
I still have trouble trying to balance the carbs, so yes, I’m thinking there’s an air leak somewhere.

Compression in both cylinders is good, so I’ve ordered two new manifold gaskets.
That’s the next step.

Will check for vacuum

[banquo]

This is a daft suggestion, but you’ve been through so many options maybe even these are worth looking at… Is it possible to reverse the pushrods on a Loop? I know it’s possible on the singles… The outcome would give symptoms similar to what you describe: good compression but no vacuum, because it would be sucking from the exhaust… Only if it’s always been like this since you got it of course…

[Odradek]

Don’t think it’s likely. The bike does run. And there’s plenty of air pressure coming from the exhausts.
Yesterday with the new cap and rotor it was going quite well.
I rolled it out to the street and rode it up my driveway and into the garage.
Not insured for the road so far, and I haven’t bought myself a helmet yet, so that’s my limit at the moment.

Started it this evening and it actually seemed to be acting up again, but on the opposite cylinder !

Right cylinder which had been giving trouble now warmed up very quickly while the exhaust on the left cylinder was still cold. Can’t do too much of that in the evenings at the moment as the people next door have a baby that goes to bed quite early.

Hopefully I get to try the new gaskets on the intake manifolds this weekend.

[banquo]

Good luck then: the answer will no doubt appear at some point!

[Odradek]

Replaced the inlet manifold gaskets this afternoon.
Strangely whoever had done it last had installed two gaskets on each one.

Could this have resulted in an air leak, between the gaskets ?
Didn’t have much time after that, but started bike up.
Still seems to be idling on left cylinder only, and some backfiring now.

Checked carb floats while I had them off the bike.Seem fine.

I’ll investigate more tomorrow.
Will double check the ignition timing again.

[Odradek]

I think I may, just may, have located the culprit for all my woes.

One of the springs in the distributor, on the advance mechanism, seems to have lost it’s springiness.
In fact it might not even be the correct spring at all.
There is no tension on the advance weights, and a lot of free play in there.

Looks slightly different to the springs pictured on Gregory Bender’s site.
https://www.thisoldtractor.com/moto_guzzi_loopframe_distributor_rebuild.html

My glee is short-lived though.
Looking on Stein Dinse, the replacement spring looks just like mine.
Maybe that’s not the problem.

From Gregory Bender’s site, explaining the pics he has …

Please note that this distributor was set up to use two of the shorter, eight coil advance springs. Mark Etheridge of Moto Guzzi Classics likes this modification. From the factory, one shorter eight coil spring and one longer nine coil spring were used.

[ranton_rambler]

I think 2 gaskets is normal - to reduce heat transfer to the carb.

[Speedy23]

I dont know this - but is it possible to fit the springs the wrong way round?

[Odradek]

Fingers crossed, but I might have finally sorted this out. .
Replaced the advance springs. Taking it apart it was obvious that nobody had done this in 50 years.
It was filthy in there.
Put in new springs, which was like doing keyhole surgery, and lubricated the weights a bit. I think that it had been stuck on full advance. Idling okay at the moment. Touch wood.
Thanks to everyone for all the help and suggestions.

[350lcjohnny]

Many bob-weight advance retards have one tight spring and one loose one. This is because as the weights move out they encounter more centrifugal force so they tend to move out quicker increasing the advance in a non-linear way. At that point the 2nd spring comes into play and slows the rate of advance.

[Eldo74]

I have a 73 Eldo as well. 2 inlet gaskets per carb is standard for heat protection.

[Odradek]

Thanks.
I just have one each side at the moment, but will order two more.