stalling

henryshake · Posted: September 12, 2007, 12:29 am Post subject: stalling

advice please.

'76 xs. Bike would run fine, but then started to stall when idling, or slowing down while not in gear. Also hesitated from 1/8 to 1/2 throttle. Rebuilt the carbs, which I had already been intending to do. Started out ok, but noticed much more hestitation at 1/2 throttle. Then more stalling. Bike starts out idling fine, but after a minute or two idle falters to around 1000rpm, then drops off and stalls. Will start again and will stay running if I give it gas, and may idle briefly before stalling. Engine rides rough.

Needle is at 2nd notch from the top (the flat end). I just moved them from the 3rd position and now bike is worse.
Floats at 24mm.
ixture screws at 2 1/2 turns out.
Plugs are black and sooty.

At first I thought it was too lean, now is it too rich? I can't even tell....

Admittedly have yet to check the ignition timing. Will do that next. Then start over putting all the carb settings to spec and see what happens.

Any suggestions?

INXS650 · 650Rider Supporter Joined: Mar 22, 2007 Posts: 645

If plugs are black, running rich. May be flooding out at idle. Recheck float height, and put your needle back in the middle. This is probably where your hesitation got worse. Lowering the needle leans it out, but will/can make it hesitate.

xsjohn · Posted: September 12, 2007, 9:19 am Post subject: Re: stalling

Sounds like the mixture screws are too far out....I would put the needle back in the original position and turn the mixture screws in some for a start....like maybe 1 1/2 turns and test......

Working on some custom needles to resolve the hot side syndrome.....

John

henryshake · Posted: September 13, 2007, 11:33 pm Post subject: Re: stalling

Thanks for the replies.

I went in and put the needles in the middle position and put the floats at just over 25mm. It runs better now, sounds louder and meaner, but is pretty gutless on acceleration. And the right cylinder seems to be pretty hot – The exhaust from the muffler is very warm. I dialed the mixtures screws out – 2 on the left and three on the right. This gave a bit more acceleration but it's still overall very weak feeling and the right side is still hot. I want to go and lower the right side float to about 24mm.

Anything else to remedy the lack of jump?

INXS650 · 650Rider Supporter Joined: Mar 22, 2007 Posts: 645

Get a bigger bike. To me, these bikes aren't about acceleration, they are about nostalga. May try raising the needle down one (raise the needle) and see if this helps with the hotter right. Do you still have the factory jetting? See Johns posts, he can steer you in the right direction with the factory stuff.

xsjohn · Posted: September 14, 2007, 7:51 am Post subject: Re: stalling

The problem with the hot side is in the main needle

John

henryshake · Posted: September 14, 2007, 9:33 am Post subject: Re: stalling

Is it ok to have one carb needle in a different position than the other carb or does that throw balance off too much? Though I guess balance is already off....

INXS650, I only want as much acceleration as I already had with the bike before I started all this messing about. I know it's not a speed demon.

xsjohn · Posted: September 14, 2007, 9:43 am Post subject: Re: stalling

It can.....

John

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

The first thing I'd do is determine if your jetting and carbs are correct for your year. These bikes are so old, there's no telling what a P.O. has done to them. Here's a chart with stock specs .....

img163.imageshack.us/i...cs1qb3.png

You said you rebuilt the carbs. If you used rebuild kits, many times the jets and, in particular, the needles are the wrong sizes.

From your photo, it appears you have the alloy topped BS38s. If they have a linkage and one throttle cable, they could be the correct '76-'77 set but they may also be a '78-'79 set. The 2 sets look much the same on the outside but are jetted completely different. You must base your jetting on what was stock for your year carb set, not the year of the bike.

henryshake · Posted: September 16, 2007, 2:42 am Post subject: Re: stalling

Thanks for that chart of the carb parts. You are right, the pilot jet was 27.5 instead of 25, so I put the old jets back (pretty sure these are the stock carbs). Also checked the points and timing. Needle clips are at mid position, floats at 25mm. Mixture screws 2.5 turns out. Still sluggish with reduced torque, though still sounds louder than before. And no more hesitation. Just throttle sluggish and unresponsive.

Haven't changed needle height; didn't want to changed too much at once. So right side is still hotter.

To clarify, the higher the main needles, the richer the mix? So if I put the clip from the third position to the fourth from the top (flat head of needle), it would be richer and help cool the cylinder?

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

Yes, lower the needle and it sticks into the needle jet more at any given throttle opening, blocking more fuel flow. This is a leaner setting. Raise the needle (lower the clip) and it obstructs the needle jet less, allowing more fuel to flow. This is a richer setting.

Your 2.5 turns out on the mix screws is too much for your carbs if they are the originals. It would probably be fine if you had '78-'79 carbs as their spec is 2 1/4 turns out. That could be the cause of your black plugs. The plugs are probably burning clean at higher speeds but as soon as you come to a stop and allow the bike to idle for a bit, that rich mix screw setting is blackening your plugs.

henryshake · Posted: September 18, 2007, 2:02 am Post subject: Re: stalling

Put new plugs in and the bike is running much better. Running cooler. When I started it up after the new plugs went in, lots of smoke blew out of the left side, though a short ride cleared it. Don't know what's up with that. Plugs are still black, so will put mix screws further in. Still slight hesitation at 1/8 throttle which can easily be pushed through. Mix screws might fix that too.

henryshake · Posted: September 18, 2007, 11:02 pm Post subject: Re: stalling

Thanks INXS650, xsjohn and 5twins. You've been very helpful.

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