XS650 Ignition timing revisited - Are we too advanced?

[Bumblebee]

Sorry! Of course that might help!
I'm using a Boyer ignition. The title says it's a 1982 Heritage special but it has BS38 carbs from, I believe, 75-76 with the odd ball pilot jets. (That was frustrating to figure out!)
Attached is a pic from 3 weeks ago. I have since rebuilt and set the timing to factory settings. It takes forever to warm up but runs great once it has.
The advance shows just to the left of the bottom groove in the side cover at elevated rpm. Which is actually a little too advanced.
When I try to retard further, idle becomes unstable and rpm returns to idle slowly

 

[5twins]

When you rebuilt it, did you replace the timing chain? Sounds like the old one was stretched out. That's one of the reasons for the amount of advance growing over time. Other is a worn advance unit, but you don't have one of those.

 

[Bumblebee]

It's got pod filters and aftermarket exhaust.
Running:
45 pilot jet
145 main jet
And needle is one groove below center. (So needle is slightly raised)

 

[Bumblebee]

No, timing chain not replaced.
Maybe that's where I went wrong. It seemed to be tight (in side play) and in good condition otherwise.

 

[5twins]

You appear to have '75 or older BS38 carbs? Ones that are not linked and each have their own throttle cable? Your jetting doesn't seem too far off for the early sets, maybe a bit rich on the mains. Your needle setting is stock for those carbs. Usually installing larger mains requires leaning the needles a step, so that would be slot #3 (from the top). I think I'd play with the jetting a bit more. Lean the needles a step (to slot #3), increase the pilots one size to a 47.5, and reduce the mains maybe a couple sizes. Your pleated style pods are also no good for these CV carbs and can cause tuning issues. UNI straight foam pods are the best pod choice. For your BS38s, you would want the UNI UP4200 .....

The links are so small on the cam chain, it's difficult to judge wear just by wiggling it around and looking for "play". Normally, if the motor you're rebuilding has anywhere near 20K miles (or above) on it, you just replace the chain. It's not that they can't or won't last that long or longer, it's just that they need proper maintenance to do so (keep them adjusted properly). Most of these bikes never got that so the chains are often toast by about 20K miles.

 

[Bumblebee]

Correct about the carbs. Not linked, 2 throttle cables and upside down pilot jets.
I'll try your jetting recommendations. I was mistaken about the pilot jets. They are 47.5 currently. I went a little rich on the mains because I wanted to be extra cautious about burning pistons. What a pain to repair! I'm just working in my garage and don't have a lift, so moving that lump in and out is tuff!!
As far as the cam chain, I bought this bike from a guy near Fort Worth quite a few years ago. It never ran quite right, which I attribute partially to the carbs. Wrong pilot jets.
I have no clue how many miles might be on the engine as, in retrospect, I think he cobbled this bike together from multiple donors.
I retired last year and finally have the time to get serious about making it into what I've wanted ever since I saw a Mule motorcycle by Richard pollock.
Even with the issues I'm having, it runs better now than it ever has. I just don't want to burn another piston!!
I really appreciate you taking time to share your knowledge!

 

[gggGary]

Can take a bit of effort, fiddling to get those two cable carbs perfectly synched. and a pinched or moved cable will change it so you can do it again.
unlike the linked carbs it's a two step process get the cable/slides matched then get the idle stop screws matched.
"throttle shaft seals, intake leaks".

 

[5twins]

You can get an idea of how much cam chain wear or stretch there is by placing the crank on the TDC mark and checking to see where the cam is. With a good, unstretched chain, the slot mark on the side of the cam sprocket should face up (or down depending on which cylinder's compression stroke TDC you're at). Now obviously, you can't see the slot mark on the cam sprocket with the motor assembled, but it just so happens that it aligns with the locating pin hole for the advance assembly on the right end of the cam, and you can see that .....

 

[Bumblebee]

I replaced the butterfly shaft seals and intake boots. I've sprayed all around the carbs with carb cleaner while it's running and found no leaks.
When I did the top end rebuild, the cam was badly worn so I replaced it and the rocker arms. OEM cam from ebay and new rockers from mikesXS.
With the pistons at TDC the hole in the cam is very slightly off from vertical. In fact the alternator timing mark is a little past the mark.

 

[gggGary]

Since you seem to have a bitsa assume nothing? make sure pilot type matches float bowls.

 

[5twins]

Your chain doesn't appear to be too stretched out. I think it should still run OK like that. I'd concentrate on tuning your carbs better, especially their low speed circuits. Try to get the mix screws dialed in correctly. The given factory spec or setting is really just a starting point. They should be fine tuned from there to find their best setting. It should be close to that factory recommendation but may not be exactly at it.

 

[Bumblebee]

Yes, they are BS30/96. I fought that for a long time before I stumbled across a reference, probably by one of you two, that there are 2 different float bowls.

 

[Bumblebee]

I have played with the mixture screws.
Honestly, it doesn't seem like they make much difference. Paraphrasing the old Indian from The Outlaw Josie Wales...
"I will endeavor to persevere"

 

[Bumblebee]

Thank you both for your help!

 

[gggGary]

Clutching at straws a bit, but confirm your timing mark agrees with piston TDC?
An old saw? If your idle screws don't change how it runs, your pilot jet needs changing.
Float levels checked visually...
PS it seems like this isn't your first dance and you have a very good handle on the process.

 

[gggGary]

PPPS LOL All BS 38's 70 to 79 have the pilots and mains in the float bowl, only the later 80-83 BS34's have them up in the carb.

 

[Bumblebee]

I'm a retired aircraft mechanic and spent some time back when this bike was brand new, working at a Yamaha shop. I've been lurking here for a long time and have read many, many threads and gotten wisdom from the 2 of you, lol.
The pics I posted were taken at the same time. Pistons at TDC confirmed but timing mask a little off. I think the cam chain stretch might explain that.
Floats have been checked frequently during the 100's of times I've removed and reinstalled the carbs.
I suppose the best I can do is continue tweeking until I land on the magic formula. I was hoping there might be something obvious to you, that I overlooked.
Scared to get on the freeway again because I really, really don't want to do another rebuild!! It needs to be RIGHT this time, lol.

 

[Bumblebee]

Clutching at straws a bit, but confirm your timing mark agrees with piston TDC?
An old saw? If your idle screws don't change how it runs, your pilot jet needs changing.
Float levels checked visually...
PS it seems like this isn't your first dance and you have a very good handle on the process.

When you say idle screws, do you mean mixture screws or the idle adjustment screws?
The idle adjustment screws make a difference but the mix screws don't do much.

 

[Jim]

When you say idle screws, do you mean mixture screws or the idle adjustment screws?
The idle adjustment screws make a difference but the mix screws don't do much.

Yes, if the mix screws don't do anything, it could be (probably) the pilots are too big
What kind of airplanes did you work on? Retired A&P here too.

 

[Bumblebee]

Yes, if the mix screws don't do anything, it could be (probably) the pilots are too big
What kind of airplanes did you work on? Retired A&P here too.

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