Running Lean, Help?

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Liggett

Liggett
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So I think my bike is running lean, I just got it going after cleaning the carbs and put about 100 miles on it the past couple days. I checked the plugs and they are still white, and the pipes right off the manifold look yellow. How hard on it is it to keep running it lean and what can I do about this? It does have different pipes on it (looks like baffles are in there but who knows). Left side also heats up a lot faster than the right. Help? :shrug:
 
Running lean is the most damaging because the engine gets very hot. Running rich simply bungs things up with carbon deposits or raw unvaporized fuel.

Exhaust has a big effect on the flow of air through the engine.

Ideally you should jet. In the short term, however, you can try richening the idle mix with the screws and richening the mid range by raising the main jet needle (lowering e-clip). If your bike does not have notches on the main jet needle you can buy tiny washers to bump them up. Older bikes (70's) tend to have the notched needles, while the newer ones tend to lack them for emissions reasons.
 
I turned them out to 3 tonight they were at 1 1/4, think id be fine to drive it to work tomorrow with just turning them out and not messing with the needle yet?
 
One is just heating up faster than the other, but both eventually get hot? You're probably not synched in addition to being lean. Stick your hand in front of both mufflers when the bike is running; if the sync is way off you can feel a big difference in exhaust pressure.

The basic routine for this type of trouble shooting is to pull the carbs, clean everything, eyeball the butterfly valves to see if they look about equal, and then adjust your needle height and mixture screws. After all that you can follow up with a manometer synch.

If you have to ride the bike before you can tune it properly try and keep the rpms as low as you reasonably can.
 
If you don't already know, there are small o-rings at the bottom of the hole where the idle mix screws are located. These will deteriorate and allow air to leak around them, causing a lean issue. Replace them. You might also turn the idle mix screws out to 3.5 turns. As stated, your carbs are also probably out of sync. You detail any other specific issues with the way it runs - that would help us diagnose.
 
It also back fires out of the left pipe on decel, after it gets warmed up the idle speed rises at a stop, at higher rpms there's a stutter sometimes. I think that's it, im going to try the idle screws and see if i have time to raise the needles this morning before work. How hard is it to find the o-rings?
 
It looks like you've got a newer bike than me; the older ones don't have the o-rings. I hear about the deteriorating o-ring problem a lot, however. The only site I have seen that sells individuals parts like that is mikesxs, but I am not 100% on whether this is where people are getting them from.

Mikesxs sells parts for the 650, but some of the 650s use the same bs34 carbs. For example, I get all of my jets from there. Initial shipping is a bit high ($12+ minimum for me), so if you do order from there look around and stock up on all the other little bits you might need. The plus side is that they have amazing customer service; they seem like really nice guys.

So, ultimately there are several things that could be causing this lean condition and you're not going to know for certain what is causing the problem until you start taking things apart. Another thing to check is the air intake tract and the carb boots that sit against the engine; make sure everything is very snug. Your carb boots might also have blind plugs that can let in air if they are not sealing. Your exhaust has been altered too, and I am sure you would notice, but there could also be an exhaust leak. I found that when the engine is running lean it produced a fair amount of smoke that makes exhaust leaks obvious. Lastly, you could have something clogged in the passages of the carbs themselves.

Oh, and if you do order from mikesxs I would just grab some larger jets while you're at it because they are cheap. Post pictures too so I can provide better advice on jet size.
 
Yep, that condition can be caused by air leaking around the idle mix jet. Backfire is a sign of lean mix. If you also have a problem getting a proper 1200 rpm, stable idle, this can be caused by leaky o-rings. At any rate, since you have the bs34 carbs and don't know what has been done, order up a set. I got mine from Mikesxs. Came as 2 jet screws and 2 o-rings. You have to look down inside the hole very carefully to find the o-ring - if it is still there. I used a small hooked pointed probe to get mine out. Sometimes the tip(s) of the original idle mix screw is broken off. Replacement screws don't have quite as fine a tip and will be less likely to break off. If broken off, make certain the tip(s) isn't inside the carb. I also installed a set of choke rod seals and will do butterfly shaft seals sometime this year.

You can also get ignition wires from Mikesxs if yours are original. Same with the plug caps. Original plug caps often have no resistance value - burned open. Originally 10k from the factory. New NGK replacements will be 5K ohms and that is ok.

All these little things can mess up the way the engine runs and will help to restore your bike to peak running condition. Once sorted out, these engines start easily and run well and reliably. BTW, you probably already know your year engine has solid state ignition - no points to mess with. A "Capacitive Discharge" ignition unit is used to fire the plugs.
 
Thanks for all the input guys! Here's what I got as of more info for you lol...This morning I pulled the diaphragms and put 2 small washers on the jets to raise them u, then turned the idle screws out to 3 turns.

Side note, only the right carb has a working choke plunger, the left is sealed but the little tip that connects to the choke rod is broke so when I pull the choke only the right one works. The replacement is on the way, the ebay dude said it would of been here by last friday or this monday....it better hurry up!!

I got it running this morning and had to pull the choke and screw the idle up a little, it was idling fine, I turned the choke off and gave it some gas and it wanted to fall on its face, with the choke pulled back out i could give it gas. I was able to ride it down the street, came to a stop and it died. I couldn't get it running again and had to push it back home then take the car to work :banghead:. Just got home from work and I pulled both plugs and the right one was black and the left was still white. They were both white on wednesday before I tried any of this. I also noticed on the left carb where the butterfly shaft is, is damp with fuel. I'm thinking that o-ring is shot and giving me a big ol air leak? I did put new carb boots and gaskets on and air filters. I haven't noticed any exhaust leaks but I am going to check next time i get it running. All this seems to go with the whole left side heating up much faster than the right, because its running lean. I think. I have a laser temp gun for work I brought home, anyone know the operating temp of these things? I don't want to run it too lean and fry it. So here's where I'm at now, I am going to order the air screws, butterfly shaft o rings, and just cuz choke rod seals right now. I appreciate all this and hopefully soon I can contribute!
 

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Buy at least 1 step larger pilot.

In my experience raising the main jet needle to richen the mid range simply caused flooding at low rpms. I suggested it as a temporary fix, but this may be causing your excessive richness on one side. Currently I actually dropped my needle 1 notch below stock (leaner) and my idle, very low rpms, and starting are reliable. I have pods in addition to exhaust and with 3 steps up on the main jet I am still way too lean in the mid and high range.

In my experience the carbs on these bikes do not respond well to tuning with the main jet needle. I, and another user, have had to lower the main jet needles and step way up on mains to compensate for this leaning action.

Check out this thread for my attempt at an explanation for this phenomenon:

http://www.xs400.com/forum/showthread.php?t=5338

I just ordered every main jet size from 147.5 to 160, but they won't come in until next week.

If your main jet needles are allowing fuel to flood into the venturi the idle mix will be impossible to determine; you'll get false rich readings from the plugs and might lean your idle air mix when in fact it is too lean. At one point I exhaustively started the bike, only let it idle for two minutes (no revving at all), and then pulled the plugs, adjusted, and repeated until the plugs look yellowish, but before they begin to be carbon fouled.

Be extra super careful removing the plugs a lot. I already had to sleeve one side of my engine. Also if you're removing the plugs a lot take off the points cover. This reduces the risk of cross threading on the left side. Only finger tighten the plugs to start.
 
Don't do any tuning...none, until you get the butterfly shaft seals and the enrichener (choke) fixed. Who knows. With everything fixed, it may run very well.
 
I ordered all the stuff from mikesxs last night and it will be here tuesday, I am going to start by replacing all the seals, cleaning again, and then trying it out. Then i'll go into the fun of tuning it. I'm trying to decide if i should go get some pods since i ordered bigger jets and needles.

Bcware, do you recommend using antisieze on the plug threads since the heads are aluminum?

I hope I can have it running good by next wednesday! Might need to take a day off work just to play with the damn thing all day!
 
I have heard of people using anti sieze on the plugs, but it probably isn't useful for me. My bike is garaged and I pull the plugs regularly. I would definitely recommend it for something stored outside or a bike that doesn't get tinkered with often.

It is not a bad idea to just replace the seals before tuning to see if everything works. Hold off on ordering pods until you determine whether or not the jets you have are sufficient should it come to that. Who knows, your exhaust may be close enough to stock to avoid jetting.
 

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