GL1000 `78-`79 Advance timing unit

[Panrider1300]

Hello Everybody, I`am from the Netherlands and I have a GL1000 KZ from 1979.

It is a full restauration object and now I am busy with the ignition.
I have found a different advance timing unit then according Randakks site and the parts manual must be in there.
I can not ask the former owner.
Behind the point there is a 371 unit. I first thougt, is this a different engine? I checked all the numbers, but this one of the latest GL1000 engine. I have post the pictures.
According the parts list there must be a 431 unit in there. Because the engines from the year 78 and 79 are different.

Is this even possible with this advance unit, to have a smooth turning engine?
What are the symptoms with this unit?

Even on Ebay there are 371 units for sale with the text that they are for a 78-79 model.

I checked the Flywheel. The text on it matching the 78-79 engine. I found a article on Randakks site about this.
viewtopic.php?p=811755#p811755

Can someone explain this? Thanks.

[gltriker]

If a previous owner had installed the pair of camshafts from a 1975-1977 GL1000 engine onto your 1978-1979 GL1000 engine, per Randakk's tech article, the #371 ignition advancer assembly may have simply accompanied the transplanted left side camshaft.

https://www.randakksblog.com/performanc ... #more-4653

another scenario;
Both cylinder head assemblies, perhaps the left hand cylinder head assembly only, may have been installed in place of the original factory installed cylinder head assemblies?



interesting carburetors' details from Randakk
https://www.randakksblog.com/early-vs-l ... b-specs-2/

[Panrider1300]

Thanks for your reply.
What are the symptoms with a wrong advance timing unit?

[Fred Camper]

Nothing affecting performance, my 1977 has the same unit and runs great. If it has the earlier (hotter) camshafts like mine does, it is then a matched set. The 1978 and 1979 camshafts had a bit more low end torque but gave up power above 4000 rpm.

[redglbx]

Pan,, it basically boils down to matching the advancer to the cams used,,,, I went through all this with my 80 CBX where they went with a 2 step advancer in the 80’s and all the experts said there was a big difference in using the previous 79 advancer so I found & installed one.. I really couldn’t feel much if any difference, maybe a little softer down low.. running it on my friends dyno confirmed the earlier single stage was indeed a little softer in the low end but the difference was pretty small..

Later when I installed 79 cams later it picked up a little power (2hp) which was supposed to be a huge improvement but actually advancing the intake cam +6deg picked up another 3hp but really flattened the torque curve out, not as peaky.. But truefully the oe 80 cams with the 2 step advancer should’ve kicked the snot out of the 79cam/advancer setup because it made a lot better & flatter power curve…

So I guess my long winded response to all this is just run what you have, but I would say it is preferable if you have the proper cams matched to it..

[Panrider1300]

Thanks for the help everybody.

I have open up the left side and i found the answer. It is really a 431 camshaft.
See the picture.

So my search for the right unit will go on.

[redglbx]

Yepper, 78-79 cam,, but I’ll add that I wouldn’t make myself crazy over finding the correct advancer… does your bike spark knock ?

[Panrider1300]

Sorry, I have still questions.

Does anybody know the exact difference between the 371 and 431 unit? I have read the numbers from Randakk tech blog.
But what is the mechanical difference?
If i see the pictures online it looks like they are exactly the same, Even the rotor is the same.
The only thing i can see are different springs.

Is the rotor the same?
Is it exact on the same point?
Are the bumps on the rotor the same?

I think that the 431 unit, because of the weaker springs, rotates earlyer than the 371 unit.
What do you think?

[gltriker]

edit:

[Panrider1300]

Thanks, but that is not my question. I have seen this page too.

[Fred Camper]

Since they increase base advance from 5 in 1975-1977 then up to 10 in 1978 and beyond, the 431 then limits the total advance to 27 instead of 32 (to get the same total advance on both). So if your bike has the base timing at 10 and runs the 371, your total timing is now 42 instead of the intended 37 BTDC. So 5 degrees of more advance on your bike if the base advance is 10 degrees as marked on the crank. But the same if your base advance is 5 BTDC.

[Panrider1300]

Thanks for this explanation.

Problem for me is to find a 431 unit.
What are the symptoms to use the 371 unit?

Ignition timings i find it difficult.

[Fred Camper]

Lose of top advance horsepower. The mixture get ignited while the piston is a long way before top dead center and power is lost with 42 degrees of total advance. I am not a tuner but that is my best idea.

[redglbx]

Fred, great explanation ! But I’ll add that it’s all a maybe thing ,, I have seen several of the same engines where some want more total timing and some want less, it all depends on a number of things, your explanation I would consider mostly spot on but again it depends on the exact engine.

It may make more power with the 371 advancer but it may not which is why I said I wouldn’t get to excited about it,,, frankly I would be more worried about spark knock with the 371 (faster) advancer because the 78/79 cams have less cam advance to make more midrange/low end, less cam overlap..same effect you get by changing the valve lash from .004in to .006in,, but that’s why I would be worried about preignition/spark knock..my .02 for what it’s worth.. Either way great explanation Fred..

By the way Pan if you can find a 431 (slower) advancer I would really pay attention to your fuel mileage with both advancers , one will probably do better than the other and that’s the one I would personally use if it doesn’t spark knock. By the way the faster vs slower thing is purely opinion at this point w/o hooking it up to something to measure it like a Sun Disgnostic Machine.

[Panrider1300]

Very happy today. I found a 431 unit. Very Lucky that i found one Just 40 km away from my house.
I taken it apart and cleaned the unit.
The weight is exact the same with the 371 unit.
The bumps on the rotor are slightly different.
Different springs. And the arms are moving closer.
I have made pictures.
Thanks everybody for the support.