White gas-smelling smoke, right exhaust.

650cafexs

650cafexs

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Hiya folks, I'm new to the forums, and motorcycles in general (picked up my first bike, a 78 XS650 SE a week ago.) The bike ran fine without much problems getting it home from the seller, a little sluggish, but I figured it was from the bike sitting for a few years. I came out to the garage later the night I got it home, and found a puddle of fuel under the left hand side of the bike, my side cover paint blistered, and my frame paint running away - I'd shut the petcock on the left hand side off, but didn't realize there was one on the right-hand side for at least another day, after replacing shop towels in the air cleaner port to soak up the seemingly endless flow of gas. :banghead: .

Once I figured that business out, the bike ran decent for awhile, then seemed like the right cylinder was unhappy. Not really knowing anything about bikes and being pretty green when it comes to engine work (22 years old, first automotive project) I decided to tackle the cam chain / valve / timing to see if that would solve anything. I followed a guide for the cam chain, took a quick look at the pin, everything seemed normal. Adjusted the valves to where the guide said they should be (.004" on the intake end , .006" for the exhaust.) Followed the instructions, buttoned the valves back up, took a look at the timing, everything seemed to check out there, so I closed her back up and let her idle, everything seemed fine except for it was still idling around 2,500.

Aside from the idle, the bike seemed happier, no obscene noises or popping from the right hand side - I figured maybe I fixed it, or it just finally settled - took it for a couple 5 mile rides around the neighborhood, everything seemed better, aside from my neutral light mysteriously flickering and eventually dying (Didn't bother me, too much) - parked it, and got ambitious...

My girlfriend was with me and told me her brother adjusted the idle on their dirt bike all the time, and that she could show me how to lower mine - so I jumped on the idea without reading up on it after being careful and spending forever doing my first valve / cam chain maintenance dealie, and grabbed a screwdriver :( . We had a pretty good idea which screw it was, and she decided against what I now know to be the RIGHT screw - but I trusted her, and turned what looks like the idle mixture screw. The idle seemed to lurch for a second, and I was relieved, then it picked back up and that's when I knew we turned the wrong one. I tried to get the screw back to where I thought it was, then proceeded to turn the correct screw, and dropped the idle down to about 1,200 - 1,500.

After the bike idled for a few minutes, the right exhaust got noticably "poppier" and white, gassy smelling smoke starting coming out of the right exhaust - and now it does this whenever I start the bike and let it idle for a couple minutes. I'm just curious if it has something to do with me screwing the valves up? (Don't think so since it right nicely up until the carb incident) Or if turning the idle mixture screw on the left hand side of the carb could cause the white smoke from the right hand side. Sorry for the novella posting, just figured I'd try to be as thorough as possible :(
 
I think I had/have a similar problem. Irrespective of your petcocls being off/on, I don't think the bike should leak fuel like that. On my bike, the problem was the float height. I'd wait to hear from experts on the board, but it seems like float height is also your problem. It would also explain the white smoke (youre probably running rich).
 
I think the petcocks are different from stock - since there's no "Prime" option that people talk about when I read up, I just close them and gas stops coming out of my left carb (I think the right side was draining into the left carb while it was on the sidestand.)
 
Float height and new float valves. A quick "might work" is to open the drain plugs on the float bowls. You can carve up a quart oil bottle as a catch can. Run some fuel through and see what it looks like. look in your gas tank, rust? Sounds like someone may have already put mikesXS petcocks on your bike. Are the vacuum taps on the intake spigots capped off? If your bike has it's stock BS38s the the steel on brass float valves are touchy, doesn't take much for them to leak. Yes there is a fuel line between the carbs so they "can" feed from either side. Not sure if anyone ever had fuel flow problems at continuous high power settings using just one petcock. The later bikes only use one petcock and a tee.

650carbspecsreducedsizeey7.png

As always Trust NOTHING the PO said or did. The carbs need synching. Carefully check your oil for gas contamination. Keep the girlfriend away from the screwdriver. LOL
 
Look at the chart Gary posted. It lists the stock mix screw setting for your carb set. Reset them to that and you should be "in the ballpark". They should be fine tuned from there but I think that's still a bit beyond your capabilities, lol.
 
Thanks for the chart for the mix screws, I ordered a guide from mikesxs last week for the bike, but it's not supposed to show up til Wednesday-ish. I did what you guys said and re-set the screws to factory, but that didn't seem to do anything for the smoke problem. After letting it warm up today, I noticed that it seems like the right cylinder is "limping". The left one at the exhaust puts out a steady thump, but the right one kinda seems to fluctuate in volume and pulse, and the right handlebar vibrates a lot more than the left.

Judging by the smell on my clothes now, and it being daylight, it looks like the smoke definitely has a blue-ish hue to it. Is it possible that I misadjusted something when I was setting the valve gap, and it just took awhile for signs to show? Or are the blue smoke and unsteady exhaust a sign of something else / potentially more serious.

Also, looking in the tank, it looks there's either some rust, or another type of rust-like build up I'm not aware of in the tank about inside about where the fuel level would be after a fill-up. I'll try the float-bowl drain later today, I've gotta head out to band practice though (in my car =(. )

Edit: Also, after the bike warmed up a bit and I backed the choke all the way off, I gave the bike a few slight rolls on the throttle to around 2,500 and the right exhaust back fired and popped a bit as the rpms dropped back to idle, went away after a few minutes. Sorry I forgot to mention that =/.
 
So I'm still having a High RPM idle issue, could my floats maybe out of wack after being so old? both are still brass lol. It idles fine, I hit the throttle it climbs and stays there a for a minute and then goes to normal. This was before I changed my oil and both filters yesterday, which was black and only about 1.7 qts came out...…..some how.....before I changed everything I noticed I was getting a white gasy smelling smoke out of the right side. I have no air leaks around my intake, I did that test with carb cleaner. I'm running 87 unleaded no alchy, with the stock oem settings for the carbs.
 
gggGary said:
Well most likely is a float valve not stopping flow.
Click to expand...
ugh..but they're new :banghead: if my floaters were off a little on the left side just ever so slightly. could that cause too much fuel to go in if it's not the valve? I'm just starting to wonder if some how the area on the floaters that the pin goes through to keep it level got bent some how and maybe it's miss measuring the fuel in the bowls.
 
Last edited:
Grimmith said:
...If I buy the new floats in the thread you just posted do I have to do any changes to the carbs or valves? or does it just do it's job like the OEM float but looks different?
Click to expand...

If they're the cruzinimage floats, they'll need some serious twisting to get the float heights equal, will likely scrape the sides of the float bowls, then have to set float heights using the "clear tube method"...
 
have you tried simply adding an extra spring to the throttle shaft ?
If your carbs have the original springs they are probably a little tired after 40 years .
Find a nice strong spring and add it to the throttle shaft and see if that brings the idle speed down more quickly.
Naturally this assumes that your carbs are in sync with the correct idle mixture settings and your idle speed is below 1200rpm and your floats are correctly set and you haven't got an inlet air leak etc etc;)

Something like this would be easy enough to rig up for a test
s-l1600 (1).jpg
 
Grimmith said:
the float valve parts all came with the OEM carb rebuild kit, gaskets, jets, etc. The floats are the stock OEM ones. If I buy the new floats in the thread you just posted do I have to do any changes to the carbs or valves? or does it just do it's job like the OEM float but looks different?


These ones? https://www.mikesxs.net/yamaha-xs65...79-bs38-cv-oem-256-14985-00-127-14186-00.html
Click to expand...

Those floats have been known to have slop in the pin area.......This can make them stick when the bike is on the sidestand
 
peanut said:
have you tried simply adding an extra spring to the throttle shaft ?
If your carbs have the original springs they are probably a little tired after 40 years .
Find a nice strong spring and add it to the throttle shaft and see if that brings the idle speed down more quickly.
Naturally this assumes that your carbs are in sync with the correct idle mixture settings and your idle speed is below 1200rpm and your floats are correctly set and you haven't got an inlet air leak etc etc;)

Something like this would be easy enough to rig up for a test
View attachment 146782
Click to expand...


So are you saying when I hit the throttle and it stays idle that it could be because of the intake kinda holding the carbs open from the pressure due to the weak springs?? cuz that makes sense like fuck lol, never would have crossed my mind. Even though I turn the throttle and it clips back like normal it can still be too weak?
 
TwoManyXS1Bs said:
If they're the cruzinimage floats, they'll need some serious twisting to get the float heights equal, will likely scrape the sides of the float bowls, then have to set float heights using the "clear tube method"...
Click to expand...
TwoManyXS1Bs said:
If they're the cruzinimage floats, they'll need some serious twisting to get the float heights equal, will likely scrape the sides of the float bowls, then have to set float heights using the "clear tube method"...
Click to expand...
…..so what floats do I get? lol
 
Best deal on genuine Mikuni floats seems to be from 650Central, less than $20 each. Gary has used quite a few of them and hasn't been disappointed yet. For the best float needle and seat assemblies, bite the bullet and buy them directly from Yamaha.
 
5twins said:
Best deal on genuine Mikuni floats seems to be from 650Central, less than $20 each. Gary has used quite a few of them and hasn't been disappointed yet. For the best float needle and seat assemblies, bite the bullet and buy them directly from Yamaha.
Click to expand...
yupper I keep a few sets on hand cuz nothing else comes close.
 
gggGary said:
What floats did you buy? I will only use genuine Mikuni for a variety of reasons. 2many attempted to fix some aftermarket floats to work correctly. He gave up in frustration. And if twomany gave up what chance does a mere mortal have?
http://www.xs650.com/threads/cruzinimage-bs38-carburetor-floats-review.51657/
Click to expand...
I was convinced those floats would have worked out of the box. They didn't look straight but I don't think they were dragging on anything. But yes, I'd get genuine floats too. Hopefully it's a one time thing.
 
Yes, it should be, considering that many of the originals are still holding up fine. What I've seen destroy them is a badly gummed up carb that sat that way a long time. That gas varnish actually eats into the brass. That means it destroys the jets too.
 

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