Bike idles choppy, and pops

[1980 xs650special]

Alright, so I'm pretty new to the world of xs twins but i've been learning alot. My bike has been running decent but has recently started acting up...to my knowledge the bike is mostly stock. I synced the carbs as best I could with the old glass bottle method. It will idle fairly well at the standard 1200 rpm but it will then start to stutter and eventually die. If I turn the idle screw up it then starts to pop out of one side. Also because it is the bs34 "lean machine" carb setup, the idle is very slow to fall...wondering if I could do with a bigger pilot jet. I already removed the plugs and turn the mixture screw out...and that helped...but i'm still not where I wanna be. Any suggestions?

 

[angus67]

pilot could be plugged in the carb that pops, runs on. take apart and clean it , insuring that when u spray in one hole, carb cleaner comes out some where else. take your air jets, (one per carb) and main jets(one per carb) and emulsion tubes, ( the brass holey thing your needle slide down in, one per carb), let them soak in carb cleaner while cleaning the carb passages.
make sure your floats are still sealed, and measure and adjust the floats as nessessarry.
do you have a good filter ? other that the screens in the tank? if not,get a new on installed before you run gas thru your freshly cleaned carbs. its not hard, hardest part is getting the damn carbs off of a stock bike, wich I gather yours is untouched?
While your at it, take note of your main jet sizes, but consider leaving them alone untill you try just cleaning the carbs out first, then you will know what jets to start increasing by. It ran before with those adjustments, just see if a thourough cleaning does enuf.
dont forget rebiuld kits for your carbs
http://www.mikesxs.net/products-36.html#products

 

[Pandorasglocks]

Sound like your running lean to me. Have you thoroughly cleaned the carbs?

Do you mean when you start to rev it off of idle it dies? My 38s did that once and I found a piece of sand in one of my pilot jets

You should also check for air leaks if you haven't already. Spray small amounts of carb cleaner around your intakes/carb bodies and see if the idle jumps up.

 

[gggGary]

The BS34s can run fine and will return to idle with no popping or delays. I had 2 and have 1 now after complete carb work they both run great. About 3 turns out on idle screws both mine are stone stock intake and exhaust. One has xs John needle jets on the other one I added a washer to raise the stock needles a bit. +3 on pilot jet woes.

 

[1980 xs650special]

Well, I took the carbs apart and cleaned them right after I got the bike...put in new air filters(that helped alot)and stuck everything back together. I ran it for about a month with the pop on the right side till I just got sick of it. I had it idling at about 1500 but the popping went away when I turned it down to 1200. Except now it will idle down and then it will momentarily stutter and fight to run, then if I don't rev it will die. That is why I tried the carb sync... its better but not completely. Also it does not pull cleanly from take off through first gear...kind of stutters...clogged pilot?

 

[Pandorasglocks]

Heh, probably not a good idea to ride around with a backfire, your problems may spread further then the fuel system. Did you check for air leaks?

 

[angus67]

clogged pilot, .....or popping carb's float valve is randomly sticking, causing random leaning of that carb, and when that happens, the engine stutters. gotta figure it out before you 'hole' a piston. I'm betting sticky float.
I meant fuel filters, by the way.

 

[1980 xs650special]

Well it doesn't really pop much anymore...except sometimes when I let off the gas on decelleration. Today I just noticed when I slow down from a stop it will stutter and want to die but if I caught it and gave a little rev it would come back up to normal and idle seemingly fine...

 

[bloodthirstysystem]

popping on decel is a lean pilot circut. did you set the idle mix screw? try turning it out a 1/4 turn (richer) and see if that helps

 

[1980 xs650special]

Right after I got the bike I turned the mix screw out to about 3 turns. I'm thinking maybe I have an air leak somewhere...might try new carb boots and gaskets along with a new vacuum line. They have some cracks. Also another cleaning...I have heard that you should discard the little screen in the float chamber...any thoughts? Also any ideas on how to sync the carbs aside from buyin vacuum gauges?(on a tight budget) I tried the glass bottles...they worked ok, but when I put the hoses on it would slowly idle down and eventually die.

 

[Pandorasglocks]

When I synced my carbs I first just eyeballed em off the bike, got the idle screw really low and looked through the carb towards a light. I then slowly opened the idle screw until one side started to let light in and adjusted that way, real ghetto lol. I then used the clear tube method attached to the vacuum barbs of the carb holders to dial them in. Did you check for airleaks yet? no use in spending money if nothing is leaking.

 

[bloodthirstysystem]

i sync mine with a piece of paper (carbs off) and close them until both have the same grab on the paper, like using a feeler gauge. works great

if your vacuum hoses are leaking - get a box of assorted caps from the auto parts store. remove vacuum hose from both carb holders, set petcocks to prime and start it. see if that works.

 

[xjwmx]

Also because it is the bs34 "lean machine" carb setup, the idle is very slow to fall....Any suggestions?

My stock bs34s with capped mixture screw has as good a throttle response as you could want. If you start making internet guru modifications on something that isn't running right, it'll take you the rest of the summer before you have something to ride (if ever).

 

[xjwmx]

popping on decel is a lean pilot circut. did you set the idle mix screw? try turning it out a 1/4 turn (richer) and see if that helps

Popping on decel is a lot of things. Turn the SYNC screw 1/8 turn increments for 1/2 turn both ways from nominally balanced and the decel popping may stop. But you need to go through the whole bike. We could list the things to check, but it would amount to going through the whole bike

 

[msmary]

check for intake and exhaust leaks. can of carb clean, spray on intake and exhaust manifolds while bike is running. if the idle bobs you need to replace the manifolds. also soak the carbs for a day or so in a good carb cleaner and make sure you run a small piece of wire through all the jet holes. *note once you clean again make sure you resynch the carbs. try k&l supply company they have a carb synch gauge set for about $70 which is still cheaper than paying a shop

 

[XSLeo]

As far as syncing the carbs get 15 foot of 1/4 inch clear hose. About $5 most anywhere.
Find the center, mount the hose to a piece of wood, a yard stick works good. With the center at the bottom and the hose running up both sides.
I used clear packing tape to hold the hose.
Hang this device up so the loop hangs down. Put some colored fluid, I used tranny fluid. Into the hose so it comes up about a foot on both sides of the loop.
Now hook one end of the hose to each vaccum barb on each carb, start engine. If synced the fulid will be at the same level in the hose. If not adjust the sync till the levels match.

 

[1980 xs650special]

Well, thanks for all the help, I have her running pretty well now...I installed one size larger pilot jets, new float bowl gaskets, new intake gaskets, and new carb holders(the old ones were pretty cracked) I synced it as best I could without the gauges. It no longer pops at all, either at idle or on decel...also has way better throttle response! Comes down from a rev much quick than it did before! I thought I was all set to ride and then my clutch cable snapped a block from home yesterday So I am otta commission for a few days till a put a new one in...oh well, such are the joys of owning a classic! Thanks guys!