New advance springs, Same odd problem.

chef.tay

So I just replaced me old nasty advance unit springs with new ones from mikes and I still have this problem with the addition of a new one:

When I check the timing on my pamco and slowly rev the engine to 3000rpms the the timing mark just keeps on moving past the full advance mark. It's supposed to stop at that mark right?

The new problem that arose is that when i'm in forth of fifth gear and pull the throttle pretty hard it will suddenly act as if it's in neutral and just rev for a good solid second and then the power will kick in. Would this be due to the springs or am I completely missing it?

Thanks a lot everyone!

Taylor

xsleo

It sounds like your ATU is advancing to far, it should not go past the full advance mark.
Try adjusting the idle timing back toward the first f mark. If the ATU is working right you should be able to get the idle mark between the two f marks and have the total advance not go beyond the full advance mark.
The reving in 4th and 5th gear could be the clutch slipping under the hard acceleration. check your clutch adjustment.

pamcopete

chef.tay,

With a dual output coil, such as the one with the PAMCO, one of the wires from the coil will be positive and the other negative. The timing light works best with the negative wire and may produce erratic results with the positive wire, so try switching the timing light to the other spark plug wire.

Tomterrific

Hi Tay,

Let me guess, you did not time your bike at full advance. Rev the engine up to 3000 rpm or beyond to set the timing. It makes not a whit what the timing is at idle as long as the advance mechanism is functional.

Always time at full advance or risk over advance as the engine revs. Over advance leads to detonation which leads to holes in pistons. Use high octane at the pump in these old engines or risk detonation.

Tom Graham

pamcopete

Tomterrif,

To a certain extent you may be correct, but if there is excessive wear in the ATU then setting the timing at full advance will leave the idle timing in a retarded position and the timing from idle to 2,000 RPM will not be advanced properly.

If you cannot get the timing in both the "F" mark and the full advance mark, then it's time to install a new ATU.

chef.tay

It could be time for a new ATU like you said pete. The only thing is, I can't seem to get my current one out haha.

Tomterrif, I have tried setting it at full advance but then when I check it at idle it is retarded by a good centimeter.

I'm gonna try checking it from the other spark plug and then i'll get back to you guys.

Taylor

weekendrider

pamcopete, are you saying it won't advance at the correct rate(in my mind determined by spring resistance) or that it advances at a rate that is retarded from stock?

tomterrific can a worn atu plate be overcome by full advance timing or does the time come you just need to replace the plate and bobs?

It has been reported that trying to correct over advance by "tapping the stops" in results in broken tabs, over advancement and holed pistons.
Just a consideration if you're thinking about doing it.

weekendrider

Another note if you've replaced the springs and still get to full advance early you may need to clip the springs shorter. 1/2 a coil is what is recommended if I remember correctly.
aybe some who've done it will chime in.

Tomterrific

Think this way. If an engine is running at full advance rpm, which would be better? Running at the perfect factory timing or horribly over advanced? Over advance will blow an engine. Over retarded timing will have idle a little wonky. Pete is saying that if the advance mechanism is broke then it needs replaced. Probably obvious so I did not mention it but who knows who we are dealing with, right Pete?

Everyone agrees that timing at full advance is of utmost importance.

TG

XSiveAl

I just run points.. no pamco but, i had a similar problem.. got this off the net..

"Be sure to check your Yamaha’s advancer for correct timing at full advance. Some of these units have been known to over-advance the ignition. If yours does, have your dealer carefully bend the advancer’s flyweight stops until the fully advanced timing and retarded (idle) timing are correct." (from) BUILDING A BETTER TWIN by Joe Minton

and I've seen this info a few other places too, found a post with tech photos once when i was looking for it myself but, of course, I can't find it now. Never even occurred to me i could break it.. but that's normal Very Happy

I used the very sophisticated rubber handled screwdriver and hammer method... be very careful, you need a surprisingly little amount of force. You could use pliers too but you'd want to put rubber hose over them to avoid damaging the stops.

The mechanical advance is primitive but, engineered of a determined weight, balance and tension to properly align ignition timing with the needs of the engine through different rpm's.

somebody correct me if i'm wrong. The stops control the full advance point by limiting the travel of the flyweights and the tension of the springs controls the rate at which the weights "fly" out under centrifugal force to those stops. This increases the time it takes for the weights to reach the stops and helps to smoothly advance the spark. springs that would change the stop point could even be too stiff to work properly.

When i did it, i checked it with a continuity tester on the points and turned the motor over with a socket on the alternator nut.. you have to block the weights open, (at full advance) i used yamaha special tool #113657 "bent piece of plastic coated clotheshanger resembling a spring with arms".. that way i could watch very carefully to see where full advance was without running the motor. rotate ccw and maintain tension on cam chain. it works.

i gotta good question though,. is this a problem from the factory?.. had the ignition on these bikes always been this way?... that's possibly some thousands of over advanced miles on some of these motors.

XSiveAL

tacoswild

There are some other threads about this here, but if your atu is all put together correctly (disc can be on backwards, pins can be out of slots or worn in the slot) then the easy fix is to do something about where it stops. I've never heard from someone who broke the stop off, have heard from people that bent them okay. Doesn't mean it's 100% safe but the risk may be overblown. Personally I'd just put a dab of high temp epoxy on the inside of the stop. Use a little too much then file it back as needed to get the right timing at full advance.

xsleo

There is a predetermined amount of advance in tha ATU. Full is 38 - 40 , At idle is 13 - 15. So 25 degees is the advance.
As the pins and the weights wear, the stops can wear some to. The advance will grow.
How much is to much? If it grows to 30 degress in the ATU you can't get both the full advance and the idle advance.
Bending the stops may work on a fairly new ATU, but after 30 plus years of use they can break off. You can try bending them, I might try some epoxy first.
I would rather get a new one, they cost less than new pistons and a new ATU.

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