Need some help with carbs and motor issues.

rustynail99

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ok guys my name is Rusty and i recently started working on a 79 stock xs650. PROBLEMS:
1. Butterfly flaps on the bs38 carbs have gap even with the idle screw all the way out (couldnt find if this could be adjusted any more then what i have done.
2. Idles at about 3,000 to 3,500 RPM even with the idle screw all the way out.
3. Right side cylinder is running much hotter then the left, and is smoking where the left is not.

any suggestions for how to fix any or all of these problems would be great. thanks.
it was not running when i bought it and it seemed like it was a carb problem so we took them apart and cleaned them well. After we Put them back together the butterfly flaps seemed like they may have too much gap in them even when the idle screw is all the way out. i did adjust both sides so they now have an even amount of gap, but we stuck them on to see if we could at least hear it fire up. it did, but is idleing at about 3,000 to 3,500 rpm, which is obviously way to high. the right side cylinder is also running considerably hotter then the left and the right side also smokes. i am pretty new to working on these types of bikes, and i am on a college student budget so i am seeing if anyone might have any answers or suggestions as to the problem. thanks.

Rusty
 
- blue-white smoke or black smoke...
-blue-white is oil..cold motor then stops is valve stem seals..keeps smoking on a warm motor are oil rings or head gasket​
-black is petrol..running rich..carb adjustment​

- try loosening the screws on the butterflies, then closing them in the carb-this will centre them..do them up before releasing...will have to take them off the bike

- read the carb thread xs650.com t=43

- is normal for the rhs to run a little hotter
 
Also, there is the syncronizer screw between the two carb's. If that's out, I mean not adjusted correctly' the idle won't come down. That would also cause your heat & smoke problem's. Do read the post from INXS, It will help to solve some of the issue's/ mysterie's on the carb's. And how to syncronize them properly. BTW, it is normal for the right side to run a little warmer. And like inxs said try the butterfly screws after you check the sync screw.
 
the smoke was blue-white, and seemed to continue while it was warm. as far as the temp difference im glad to hear that the right side usually runs a little hotter but im talkin after 3-5 minutes of running you can hold your hand on the left side and can only barely touch the right. the right is also the side the smoke is coming out of and there is no smoke on the left. also do you think it seems like i might just need to do a top end rebuild. i was trying to avoid taking the motor apart but if it must be done, then it must be done. with the carbs i did adjust the synchronization screw to make sure there was an even gap so there wasnt more gas and air going into one cylinder. i will definitly try the trick with the screws. if that doesnt work, would you have any other suggestions or is it time to go carb shopping? also by your reactions im thinking i was correct that there is definitly not supposed to be any gap and that is probably causing my idle problem. if i am mistaken, feel free to call me dumb and set me straight. i am all for constructive critisim! :D jsut a rookie trying to learn from the more experiences. thanks for all of your help! :)
 
- spend some time on these carbs and theyre fine, at this stage you could probably do better spending money on other things...even if you do later eventually upgrade your carbs these will provide a good learning curve

- oil rings often give problems, if piston bore clearances are good they can be retensioned come stretched.. xs650.com post 2880 i check and sometimes do this with new ones too
 
as far as the temp difference im glad to hear that the right side usually runs a little hotter but im talkin after 3-5 minutes of running you can hold your hand on the left side and can only barely touch the right.

Are you talking about touching the headpipes? If you can touch the left headpipe like that after even a min, it's not firing on that left cylinder. When they say the right hand cylinder is usually hotter than the left I think they are only talking about less than 20 degrees difference and that's using a temp probe on different parts of the head and cylinders. Where and how are you checking the heat coming off each side? If you are using your hand on the exhaust and the left is that cold, it's not firing at all. Check for a good spark then check the carbs and carb holders again.... Something is definitely not right.
 
i pulled the exhaust pipes off and there seems to be a pretty good amount of carbon buildup on the inside of the cylinders, just from what i can see through the exhaust port. so im assuming it has been running too rich. is there a way to clear the carbon, could this be contributing to my problems, should i just not worry about it for now, and is this bringing me ever closer to a top-end job?
 
hey travis, i was only using my hand on the cylinder, and the left was warming up. it seemed like it was definitely firing, but i could be wrong. seems like there is definitely an issue with one of the cylinders, im just not sure if the right is running way to hot, or if the left is running cold or with my luck they are both all messed up. i will see if i can put the pipes back on and try the butterfly flap trick with the screws and give it another go. anything paticular i should look for? im a harley guy and have only worked on them a fairly minimal amount. but im not sure how long this motor usually takes to get warm to the touch etc. thanks again for all the help guys. i would be a lost puppy if it were not for these forums and the knowledgeable people that frequent them.

Rusty
 
I'd say it's just the left not firing.. Start it and remove the left side spark plug cap and see if changes the way it runs. If not, then you know you it's not firing on that side. The engines get pretty damn hot especially if it's idling at 3-3.5k, so the right might be just fine... Don't run it too long though unless you have a big fan in front of the motor.
 
travis. ok i will definitely give that a go and see what happens. i know i should have spark on that side because we pulled the plugs and checked the spark before we put the carbs back together. so hopefully it is running or i think i might have a serious problem. just out of curiousity, do you know what might cause the left side not to fire if there is spark and the carbs are clean and working properly? ill keep you posted on my results, and thanks.
 
Yeah.... the carbs aren't clean and working properly when you think they are (no fuel)... or could just be way out of sync. Or no compression.
 
ok guys i finally was able to get back out there and do some motor testing.the left cylinder is definitely not firing. i am yet to do a compression test because i have not been able to get the right adapter yet. however i did check the pressure coming out of the rear of the pipes with my hands and there was actually a lot more pressure coming out of the left (the non firing side). i also cut off the cocktail shakers on both sides and the blue/white smoke that was coming out of the right side seems to have stopped. do you think the cocktail shakers could have been the cause of the smoke? also tried to adjust my butterfly flaps and there is still enough of a gap to see light through them when you hold them to the light, but not alot. so it is still idling at around 3-3500 rpm. any help would be great. thanks guys.

Rusty
 
G'day Rusty, sorry but your story is a little vague. Here's what I'd do:
Check & adjust cam chain
Check & adjust valves
Remove advance rod, clean, lube & re install
Check points gap (maybe new points & condensers) & staticly time with a light (important to do the correct points first)
Pull the carbs once more, make sure all the passages are 100% clear
Reassemble carbs, make sure inlet manifolds (unifolds???) are secure & no possibility of vacuum leaks. Also make sure there are no other vacuum leaks on the carbs.
Sync carbs with a piece of paper or such
2 brand new plugs
Most of this should be covered in the tech section
If it still doesn't go, well you tried, pack the whole damned thing up, whack it in a box & send it to yamaman Australia :cheers:
 
Ok, I just checked the tech section, most of those are yet to be covered.
Still, that's your list, so I'm sure between all the good folk here, we can talk you through that list!
 
- odd that, im about half way through writing that all up - started last weekend then got side tracked, will try to finish it tonight if no one else wants to do it...got lost trying to locate my photo file
 
Please do INXS, your how to's are easily read & understood. :thumbsup:
Plus we can all go over it with a fine tooth comb once your done & set you straight if we need to :D
We'll all owe you a :smoke: & a :cheers:
 
especially me! thanks guys. im going to compression test it next week to, so that might give me a better picture of what its up to. :D i really dont know what im doing, but im armed with a clymer manual, awesome forum people, and a little sense (very little) :banghead: so hopefully i can get this beast burnin down the road. :bike:
 
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