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1976 spark advancer ref #?

Posted: Fri Sep 22, 2017 7:18 am
by Hal
Hi guys,

I have a spark advancer unit here but I can't find the references for year.

It's has 371 stamped on it.

What year does that make it?

Re: 1976 spark advancer ref #?

Posted: Fri Sep 22, 2017 7:51 am
by ericheath
371 makes it a 75-77 advancer. IIRC, it has 32.5 degrees advance built into it. Combine that with the 5 degrees of advance at the flywheel that's 37.5 degrees advance.

The 78-79, 431 advance, has 27.5 degrees advance.

I didn't check the book on those numbers, but the 371 is the early number.

Re: 1976 spark advancer ref #?

Posted: Fri Sep 22, 2017 8:28 am
by Hal
Thanks Eric! That was very quick....what time is it where you are?

It was around 2pm when I posted from France....

I've just sold my fully rebuilt and tested '76 carbs, but the buyer has a 1979 GL1000 so I told him he needs the '76 cams and advancer to get best performance out of the carbs.

I said I'd give him the cams & advancer. I've found the advancer but the cams seem to have moved themselves from where they have been for 4 years minimum.

The Barn Gremlins again!

They will turn up, and I imagine his '79 will run with the '76 carbs, just not to full potential, am I right?

I'll send the advancer with the carbs and the cams when they show up....

Re: 1976 spark advancer ref #?

Posted: Fri Sep 22, 2017 9:06 am
by ericheath
Should run adequately. The intake runners from a 79 were 1mm less diameter. I'm not sure which would be best in the meantime.

Re: 1976 spark advancer ref #?

Posted: Fri Sep 22, 2017 12:36 pm
by Hal
I'd no idea the runners were 1mm less...amazing!

I'll tell him and he can play with them. Mine have the runners all polished up. ;)

Re: 1976 spark advancer ref #?

Posted: Sat Sep 23, 2017 7:51 am
by Whiskerfish
ericheath wrote:Should run adequately. The intake runners from a 79 were 1mm less diameter. I'm not sure which would be best in the meantime.
Is that for certain? I know the carbs are but I never even thought about the tubes.

Re: 1976 spark advancer ref #?

Posted: Sat Sep 23, 2017 10:47 pm
by ericheath
We all know I've been wrong before, but I bought a box of 37 intake runners to go with the dozen or do I had. None were marked. The 1200's were obvious, but the rest I had to measure and my findings were that they vary quite a bit. I assumed, but maybe incorrectly, that the 78-79's were the same as the 1100's. I can't say that for sure. I did have a set of 1100 carbs. I had a bunch that were pretty close to 1.4+- inches for the 1000 carbs which I assumed were early years. The others were nearer 1.3+- inches. I don't own, nor have I had, a set of 78-79 to compare. So I stand to be corrected. I think it's worthwhile to make sure all four are relatively close to the same. Real close to the same. I helped a guy who had a 77 with 78 carbs on it. In trying to get it run right we found three runners near 1.4" and one that was near 1.3"

Re: 1976 spark advancer ref #?

Posted: Sun Sep 24, 2017 8:19 am
by robin1731
Difference in sizes could just be production tolerances. Cast pieces like this aren't going to be very precise for a street ridden production motorcycle.

If there is a difference the one to use on a street ridden GL would be the smaller. Since these mostly stay at lower rpm. I've stated before, the intake ports and manifolds on these engines are too big from the factory. IMO Smaller would be better for all around riding on the street.

But what do I know about such things. lolol lolol ;) ;) shakehands shakehands

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