Upgrade ignition?

Wingedwheel

Wingedwheel

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After a long and exhausting battle with my runaway advance on the ‘76 I am almost ready to order an electronic iggy and be done with the problem once and for all. I’m leaning toward a BB for reliability and cost reasons. The stumper is I cannot get the carb idled down enough to keep revving between 3-4k from happening. I’ve shortened both springs one loop, weights snap back no issues yet I still get the runaway revving in the range mentioned. Blip the throttle up to 4k and she falls right off. Seems like the iggy would solve any issues.
 
Wingedwheel said:
After a long and exhausting battle with my runaway advance on the ‘76 I am almost ready to order an electronic iggy and be done with the problem once and for all. I’m leaning toward a BB for reliability and cost reasons. The stumper is I cannot get the carb idled down enough to keep revving between 3-4k from happening. I’ve shortened both springs one loop, weights snap back no issues yet I still get the runaway revving in the range mentioned. Blip the throttle up to 4k and she falls right off. Seems like the iggy would solve any issues.
Click to expand...

WW: I wonder if a carb slide may be sticking....?
 
Wingedwheel said:
After a long and exhausting battle with my runaway advance on the ‘76 I am almost ready to order an electronic iggy and be done with the problem once and for all. I’m leaning toward a BB for reliability and cost reasons. The stumper is I cannot get the carb idled down enough to keep revving between 3-4k from happening. I’ve shortened both springs one loop, weights snap back no issues yet I still get the runaway revving in the range mentioned. Blip the throttle up to 4k and she falls right off. Seems like the iggy would solve any issues.
Click to expand...
I`m still half asleep but what is a "BB"? I also agree with MaxPete, it sounds like it may be a carb issue.:shrug:
 
halfmile said:
I`m still half asleep but what is a "BB"? I also agree with MaxPete, it sounds like it may be a carb issue.:shrug:
Click to expand...
I think, Boyer Bransden electronic ignition. It's not perfect but it's a decent choice. I would buy one again.

IMO, the other ignition system worth a look is the Trispark.
 
No Pete it’s the advance. Revving takes over at 3k and will drop off above 4k a carb slide would affect all ranges I would think and I’ve been in those carbs many times with everything working fine. It all started with the advance throwing a spring. Yes BB, Boyer Bransden
 
Ladies and Gentlemen I always keep on about the electric problems Like a demented parrot
But not this time I believe it is carburetor related
I know that if the idle is high it can run up in rev I would back that one out.
I had worn advance unit but never the effect rushing the engine .It could advance early and stall not retarding.

Perhaps tie up the weights with a string or so see if it helps

I know very little about carburetors and the one you have if stock nothing. Air leak ?
But I don't believe this problem is an advance unit problem right now
 
If someone could explain to me why it only does it between 3-4K which is the midrange and AFAIK that’s the range the advance unit is doing its thing. I can idle the carb down to just below 1K and it’s almost a non issue, almost but then the idle is too low and the bike dies. The advance unit had thrown a spring when the issue first appeared and I replaced both with OEM and have been fiddling with it since last spring and I can’t move on to other waiting projects until this issue is resolved and riding season is pretty much wrapping up. Right now it’s not too bad but soon enough working in the cold garage is not gonna help my motivation.
Jan_P said:
Ladies and Gentlemen I always keep on about the electric problems Like a demented parrot
But not this time I believe it is carburetor related
I know that if the idle is high it can run up in rev I would back that one out.
I had worn advance unit but never the effect rushing the engine .It could advance early and stall not retarding.

Perhaps tie up the weights with a string or so see if it helps

I know very little about carburetors and the one you have if stock nothing. Air leak ?
But I don't believe this problem is an advance unit problem right now
Click to expand...
Jan I may be able to test that theory. I have another set of carbs I can throw on there before I do anything else.
 
I would be 99.9% certain that the issues will be with the 3 very small holes in the roof of the venturi - these draw fuel directly from the float bowl through the pilot jet via the fuel screws and into the venturi in front of the closed throttle butterflies
 
i am pretty certain that the issue you are having ahs to do with carburation/air intake.

On the topic of ignition. Sasche does look interesting, but I am not sure about the very low advance numbers at idle. Sasche rep told me that they find old bike work better at that low of an advance with modern fuels. Not mine, but I have a modified engine.
Trispark seems to be sold out of units for XS650, but smedspeed has some on hand. He also tells me that that he is close to getting an ignitech pick-up/setup configuration recommendation for a street XS650. He does stock ignitech as well.
 
Wingedwheel said:
Jan I may be able to test that theory. I have another set of carbs I can throw on there before I do anything else.
Click to expand...
Think I mentioned it before? :umm:

Would take less than 5 min to safety wire the advance weights in the retard position and run the bike. Should be pretty convincing proof, once and for all on carbs vs advance.

Seems a bit quicker and easier than swapping carbs. :shrug:
 
Your saying your advance weights are advancing the timing and not coming back down? Pull the cover off the right side where the advance weights are and then put hook up a timing light then point it at the weights.

I've had carb sliders sticking on another carb bike before causing bike not to return to idle, I've also had a sticky throttle cable (XJ650), really hard to see but you push on the throtle down at the idle set screw for an XS to make sure its all the way down.
 
Jim said:
Think I mentioned it before? :umm:

Would take less than 5 min to safety wire the advance weights in the retard position and run the bike. Should be pretty convincing proof, once and for all on carbs vs advance.

Seems a bit quicker and easier than swapping carbs. :shrug:
Click to expand...
You did Jim and shame on me for not trying it yet. I have a million excuses right now as to why I’m not getting to it. It’s amazing how much needs to be done around the house and the yard going into fall and I have two new additions to the family but again, just excuses. IMG_8571.jpeg
 
I sent a message to tri spark, here is the reply:

Q: Hi, can you share the advance curve vs rpm for the Yamaha XS650 system (not rephased)?

Also, do you offer a Firebox equivalent for XS650?

A:
Thanks for your inquiry.

Our Compass system for the Yamaha XS650 (not rephased) follows the same advance range as the original factory system, but with more subtle transitions. The advance begins at approximately 1400 RPM and reaches full advance by 3500 RPM, with most of the advance occurring before 3000 RPM. Half advance is achieved at 2000 RPM. This design provides excellent low-end throttle response, a stable idle, and reduced risk of pinging or knocking.

While I don't have a specific drawing to share, I hope this description gives you a clear idea of the advance curve.

Unfortunately, we do not offer a Firebox equivalent system for the Yamaha XS650.
 

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