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  #1  
Old 04-12-2018, 07:50 AM
Mike Whipple Mike Whipple is offline
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Xs650

I'm getting the 650 tuned up and ready for sale (to raise money for the XS11 rebuild). I'm running into a carb tuning problem that I haven't seen before. It idles fine and runs great all through the RPM range, but doesn't want to come back down to idle... Seems like an air leak, but I sprayed carb cleaner all over the boots and nothing. The cable isn't sticking, and I can see and feel that the throttle is closed while this is happening. The only way to bring the RPM back down is to drag the rear brake and force it down until it almost stalls, then it idles beautifully. until I rev it up again, just wont come back down. Any Ideas?
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  #2  
Old 04-12-2018, 08:21 AM
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DiverRay DiverRay is offline
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Spray a little around the throttle shaft, or use an unlit propane torch to put the gas at the shaft. The other cause could be the sync. if they are out of sync, one will be pulling a lot more vacuum and it will cause a "runaway". Also make SURE there is nothing blocking the intake bell area if you have aftermarket air filters.
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  #3  
Old 04-12-2018, 12:10 PM
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donebysunday donebysunday is offline
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Clean those pilot jets

CLEAN THOSE PILOT JETS !
How long did it sit with the ethanol gas ?
I've done over 70 XS650s to put them back on the road, and this was the main reason for this problem.
You most likely had the carbs spotless, globules of ethanol and water cause the pilots to plug again, it almost like tiny bubbles of Vaseline in the fuel.
To compensate I turn up the idle speed screw so the engine is now running slightly on the main jets, this seems good at first but then once warm the engine heats the fuel and the tiny globes can now pass the pilot jets and your idle is set to high.
I suggest you flush the tank, petcocks, carbs and fuel lines, you need to look really close at those pilots, holding them up to the sun of other light source as the globs are transparent and the jets can look clear but are not.
DO NOT USE GUMOUT, I've found it to have little transparent globules in it. Gumout may use something like ethanol/alcohol that collects water if they don't bottle it up soon enough.
There are some other causes for this too, like plugged exhaust but I've only run into that twice.
To prove my point warm it up until the idle won't come down, adjust the idle speed screw back down to idle, does it run OK ? Maybe a bit of a stutter ?
When you let it cool down and start again, will it start ?
Please let me know !
This goes for XS11s too and all engines with carburetors .
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Old 04-12-2018, 11:22 PM
Mike Whipple Mike Whipple is offline
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OK cool, thanks for the tips guys. I'm gonna tear back into it this weekend.

I'll check the sync. didn't have an airflow gauge at the time but I got one now. And the intake is definitely after market. It's got pods. Witch brings me to my next point. The pilots are clean as ****! I guarantee there is no ethanol in the carbs. the carbs were in a box, dry as yer mom... lemme backup, this bike came in boxes. I bought new jets. the pilots are new. I saw the pods, googled the jets, it had stock, so I bought two sizes up (sorry I forget the numbers). more air more fuel right?

Here's some more history on the bike. I got it from a guy I used to work with. I picked it up cheap as a basket case. It came with the XS11. Neither one running. The 11 was complete, but had electrical problems that I quickly sorted out, and then found a dead cylinder, kinda low compression on the others. Aww ****, that's a whole new thread. So back to the 650. Basket Case! the engine was out. I put it in the frame and put the bolts in by hand so I could push it in my truck. But here's the thing...I don't know why he tore it apart! This guy was an aircraft mechanic. He knew his ****. It's super clean. No striped threads, No broken Bolts. All the hardware was labeled in ziplock bags. It's like a basket case wet dream! everything's here. It came back together in hours, and it's got compression. No idea why he took it apart. Here's the other thing. I can't ask him why he took it apart 'cause he's dead now. Turns out he was selling off his Yamaha projects real cheap because he was planning to hang himself in his basement a week later...well...I'm still trying to wrap my head around that one. All I know is that Randall didn't deserve to die, and that these bikes deserve to live.

So back to carb tuning...
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  #5  
Old 04-13-2018, 12:30 PM
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donebysunday donebysunday is offline
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Outcome

PLEASE LET US KNOW THE OUTCOME !!!!!
Ditch the pods for now can run on clean roads without air filters.
Stock jets, so you can start fresh.
Ethanol can dry up in the tank, looks clean, when fresh fuel is put in it slowly dissolves ruining your nice cleaning.
Were the carbs soaked ?
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Old 04-13-2018, 10:29 PM
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Did you buy the Mikuni jets? if not, yank then out NOW!!! As donebysunday said, go back to stock and start from there. I had a 650 with no mufflers, and ran it thousands of miles with stock jetting. So start with ALL STOCK PARTS, and once running change ONE thing, test, and then make another change if needed.
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  #7  
Old 04-14-2018, 12:33 AM
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+ DiverRay

I agree with DiverRay FOR SURE !
One more thing though, unless there have been modifications to the engine, (if so your are playing from scratch, again start from stock) the engine should run fine with no air filters or mufflers.
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Old 04-14-2018, 08:41 AM
Mike Whipple Mike Whipple is offline
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It was doing the same thing wit the stock jets. That's why I swapped 'em out. I dunno, I'm about to go tear into it now. I'll post again tonight and let you know what I find. Thanks again for all the advice.
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Old 04-15-2018, 01:24 PM
Mike Whipple Mike Whipple is offline
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Ok guys, so here's what happened yesterday.

Got back in there. The jets looked clean I blew 'em out real good anyway. The choke valves were super crusty...Like maybe I forgot about them on the first cleaning. It's possible, sometimes I can be a bit of a space cadet. So trying to think of anything else that I neglected, I realized I hadn't checked the float level. Measured and found them both to be a little low, so I raised 'em up a pinch in accordance with the maintenance manual. Got it all back together, fired it up, goosed the throttle...and...IT DID IT AGAIN! Damn it! I popped the choke open and closed real quick and it came back down to idle. goosed the throttle again...and... It came back down on it's own. Wait, what? it's working now. Huh. grabbed a helmet, and rode it down the street and topped it off with some fresh ethanol free, and rode around town for about 5 miles. No problemos, Runs great! It seems a little slow for the revs to fall back down to idle, but it always comes back down. Maybe I'm just nitpicking now and this is just how it runs. It's totally rideable. I'm thinking that's a sync thing because I left my airflow gauge at work (look out now, space cadet on wheels) so I just tuned 'em by ear.

Seems to be fixed now, but I still having trouble wrapping my head around what was happening and why it did it that one last time and never again. The low floats would make it lean, and from the looks of the plugs it's definitely been running lean. Gonna stick with the bigger pilots, and would consider raising the needles one notch, but I think I'll ride it for a while and be sure before I change anything else. Anyway a lean mix wouldn't cause idle runaway, Air leaks do that. how could the rpm stay up when the butterflies are closed. maybe the air leak was coming through the crusty chokes. that's the only thing on the downwind side of the butterflies. I dunno, sure felt good to ride it though.

Here's the new problem that came up. It's got a rattle coming from the cam chain. I tightened the tensioner about half a turn and the rattle went away but now there's not enough threads sticking out to get the cap back on.

I'd love to post some pictures but I'm not sure how.
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Old 04-15-2018, 03:43 PM
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out of sync can cause it to drop back to idle slowly. The low float will make it drop back slow as well, so it could be a combination. DO NOT DO ANYTHING ELSE TO THE CARBS until you have them SYNCED!!
After they are synced, you can then proceed to tune and adjust jets IF needed. I would start by adjusting the idle mixture of each carb, and re-sync the carbs. Then go for a ride with a plug socket, run it up in third gear to redline and pull in the clutch and kill the engine. Stop and pull plugs one at a time and check the color to see if you are lean or rich. You can change jets as needed from there. The pilot jet usually gets changed if you need to go up two or more sizes on the mains. Remember you will need to re-sync the carbs if you have to pull them to change the jets.
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  #11  
Old 04-16-2018, 07:20 PM
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Quote:
Originally Posted by Mike Whipple View Post
.

Here's the new problem that came up. It's got a rattle coming from the cam chain. I tightened the tensioner about half a turn and the rattle went away but now there's not enough threads sticking out to get the cap back on.

I'd love to post some pictures but I'm not sure how.
If you have a stock CCT still, you are adjusting it wrong.

If you have an ACCT, there is no adjustment needed.

So what type of tensioner do you have ?
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Old 04-17-2018, 07:43 AM
Mike Whipple Mike Whipple is offline
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Well...I'm assuming it's the stock one because everything on this bike is stock and it needs adjustment. But whenever I make assumptions it it makes an ass out of me and umptions...or something like that. If it's the automatic kind, It's broken. So how do I identify?
If it is the stock CCT. The book said to adjust it until the thingy in the middle was flush. I found that a little vague. If I tighten it there will be no more threads for the cap to go on. It was only on there about a quarter turn anyway. does this mean I should back it off? that's a little counter intuitive.
obviously I'm doing it wrong, or something's wrong. Sooo... You wanna throw me a bone here. the book didn't help much and I'm not about to start turning adjusters to extremes and see what happens.
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Old 04-17-2018, 11:20 AM
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Quote:
Originally Posted by Mike Whipple View Post
Well...I'm assuming it's the stock one because everything on this bike is stock and it needs adjustment. But whenever I make assumptions it it makes an ass out of me and umptions...or something like that. If it's the automatic kind, It's broken. So how do I identify?
If it is the stock CCT. The book said to adjust it until the thingy in the middle was flush. I found that a little vague. If I tighten it there will be no more threads for the cap to go on. It was only on there about a quarter turn anyway. does this mean I should back it off? that's a little counter intuitive.
obviously I'm doing it wrong, or something's wrong. Sooo... You wanna throw me a bone here. the book didn't help much and I'm not about to start turning adjusters to extremes and see what happens.
When you go by the book it does not mention final setting or final adjustment, what the book gives you is as if the engine had not been run yet as like just after a rebuild. So follow the book for your first setting, then start and warm the engine, loosen the adjustment until you hear a little noise then tighten just until you don't hear cam chain slap, NO MORE THAN THAT then lock it with the nut. I always put a folded cloth/shop towel under the cam chain adjuster, there will be a little leakage of oil there, not much.

I've been accused of not having enough play in the valves because my XS650s run and idle so quiet. I then ask the accuser to start their XS650, sounds like tin can full of change being shaken.
Oh yeah that's what they are supposed to sound like ? ? ?
Years ago I did a little experiment (nearly burning my fingers, hurting anyway) of what happens to the valve adjustment as the engine warms up.
Most people think the valve clearance becomes tighter when the engine is hot, *NOT TRUE* the valve clearance becomes greater as the engine heats up. When I adjust the XS650s valves I adjust to the lesser of the manuals suggestion, gets a tiny gain in performance and sounds better.
The aluminum head expands more than the steel rocker arms, pivot shaft, and the valves/seats increasing clearances on the valve train but lessening/tightening clearance on the cam chain.
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  #14  
Old 04-17-2018, 03:59 PM
motoman motoman is offline
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Cam chain adjustment is done with engine warmed up first. Engine HAS to be not running for this adjustment and timing pointer on TDC.
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Old 04-17-2018, 04:42 PM
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Quote:
Originally Posted by Mike Whipple View Post
Well...I'm assuming it's the stock one because everything on this bike is stock and it needs adjustment. But whenever I make assumptions it it makes an ass out of me and umptions...or something like that. If it's the automatic kind, It's broken. So how do I identify?
If it is the stock CCT. The book said to adjust it until the thingy in the middle was flush. I found that a little vague. If I tighten it there will be no more threads for the cap to go on. It was only on there about a quarter turn anyway. does this mean I should back it off? that's a little counter intuitive.
obviously I'm doing it wrong, or something's wrong. Sooo... You wanna throw me a bone here. the book didn't help much and I'm not about to start turning adjusters to extremes and see what happens.
I owe you an apology Mike, sorry to confuse you. I forgot you were working on an XS 650. I haven't dug into mine yet so I can't be of any assistance but it looks like your in good hands with donebysunday.

I'll be watching and learning for now
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1979 XS1100SF (stock-euro mods planned)
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1983 XJ750MK Midnight Maxim (semi-restored DD)
1977 XS650D ( patiently awaiting resto)

Sometimes it takes a whole tank of gas before you can think straight.
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