need help from a carb guru...

[chopitdropit]

1982 xs650, BS34's

From the beginning...

Bought bike with carbs that were supposed to have been rebuilt at yamaha shop, but set for a year and laquered up. Cleaned them and checked everything out (twice), reassembled and bike fired up but with high idle.

Discovered air leak at right carb boot where it bolts to cylinder. After no success stopping (there was no rubber coating left where they meet the cylinder and gaskets and sealer didn't help), I ordered new boots and diaphrams from JBM (also had a questionable diaphram).

After installing new parts, I discovered that I now had an air leak at the left boot BUT other than high idle and a little miss at mid throttle (which seemed to improve if I ran at half choke) the bike ran like a bat outta hell...so tired of messing with it, I hit the open road for a day of riding with no probs other than the irratating high idle (which I am still trying to seal...).

OK..now for the new problem. I went out to work on it today and on top of the high idle, it is backfiring a bit and running rough at all ranges and the left cylinder is putting out a lot more forceful exhaust than the right cylinder.

This has to be something else besides the high idle from the air leak, because I rode all day yesterday with no other problems????

Any ideas?

I might mention I am running pods, straight exhaust (homemade) and have no idea what jets, but this doesn't seam to be an issue when I'm riding.

Also I noticed that the Orings on my air mix screws are not really O's but kinda flat on one side...but they are both the same..is this normal? (they are out 2 1/4 BTW which is where they were when I got the bike). I have nothing to gauge by...this is all new to me...just learning as I go.

Oh...valves are adjusted. Also have freshly red koted tank cured properly, clean filter, new petcock (non vacuum and ordered the boots with no vacuum fittings, and am running clear gas line so I can see my gas flow)

Stumped...

Just noticed I posted a pic from when the carbs were off...haha

Additional info...just pulled the plugs, right side good, left side black sooty although that is the side sucking extra air? But from what I have read on the forum, many have bikes that run good and one plug is black sooty.

 

[xjwmx]

I wouldn't claim to be a carb guru, but I am a decent debugger. First, before you do anything else, fix the known air leak(s) at the boot. Then you can adjust mixture (since you've had the mixture screws out), and carb balance. At that point ask for help if something has you baffled. Test the new diaphragm seal by blowing in the oval at the top of the bell and the piston should go up and stay as long as you blow, then float down medium speed.

As for the mixture o-ring, I had one out and took it to an experienced mc mechanic to get a replacement. He said it was ok, though it looked squished and flat and shrunk and otherwise terrible to me. It ended up working fine. He said the threads do the real air sealing.

 

[gggGary]

+1 on XJWMX's advice. See my recent post and pics of a piston/cylinder that was most likely run lean with an air leak. Don't do it.

 

[xjwmx]

P.S. The oem diaphragm is keyed at the top and that in turn orients the umm Slide Vacuum Port (little hole) a certain way. If you did not pay attention to this when you replaced the diaphragms it might not be important, or it might be. As much as I've had these apart, I don't remember if the piston itself is keyed. Probably not otherwise it would then be keyed twice in effect..

 

[gggGary]

That IS a biggy but the JBM instructions cover it pretty well.
The pistons are not keyed and alignment is critical as the wedge at the bottom must face correctly.

 

[scott s]

By "boot" do you mean manifold? You said you got new boots/manifolds; there's a known issue with some new aftermarket manifolds. The ethanol in todays fuel decomposes (for lack of a better word) the rubber.

Maybe try finding some good used manifolds. Are you running a gasket between the manifold and head?

 

[xjwmx]

The pistons are not keyed and alignment is critical as the wedge at the bottom must face correctly.

I have the opposite of photographic memory.

By "boot" do you mean manifold?

Yeah but it's only analogous to a manifold because manifold means joining of two or more things, like a car intake manifold carries mixture out to multiple cylinders. These ones stay two all the way down though.

 

[gggGary]

I have not heard of any failures of the JBM boots and purchasers have given good reviews. A possibility is a leaky vacuum diaphragm in the petcock.

 

[chopitdropit]

Hey xjwmx and all...the mix screws haven't been out since I went through the carbs and are set back up just like they were...I have ridden since...

I have the http://jbmindustries.com/HOLDERS.html boots and diaphrams...top of the line. Diaphrams operating perfect and slides in correct. Hole/wedge towards engine as per instructions. (The new diaphrams are not keyed..just gotta be careful).

Boot...yes...manifold. JBM's are tops, no fuel breakdown, highly recommended by many on forum and I've only had them two days. Strange thing is, when the left one was showing a leak by spraying carb cleaner, I took it off and applied a layer of black magic gasket maker and lightly tightened, then after it set up I torqued it down. then I let it cure. Fired it up and sprayed again, engine died...hence still has air leak, right? So I just pulled carbs and went to remove the boot/intake...tomato/ tamoto...lol, and it is glued/sealed on there solid, can't even get it off, so how the hell is it showing a leak?

Also, when I pulled the carbs, I tilted them to get them out and fuel poured out of right carb and hardly nothing from left, so float or needle may have been sticking...guess I'll find out soon enough..pulled bowls and floats/needles operating ok now, but could have freed up from all the movement. These carbs are really clean...like new.

Like you said...gotta figure out this leak first...seams so simple..and it's kicking my ass.

The new boot solved the right side leak..no gaskets, not required...check out the website link.

 

[chopitdropit]

Hey gggGary...not using vacuum petcocks...harley peanut tank regular petcock, ordered intake boots without stems. All that is done away with.

 

[gggGary]

easy to check gas level on those. Put a piece of clear plastic tubing on the drain. Run it UP alongside the carb. Engine not running turn the petcock to prime, open drain screw fairly quickly a full turn or so. fuel should be near or just slightly below the float bowl carb seam. IIRC a battery vent tube will work fine for this.

 

[chopitdropit]

easy to check gas level on those. Put a piece of clear plastic tubing on the drain. Run it UP alongside the carb. Engine not running turn the petcock to prime, open drain screw fairly quickly a full turn or so. fuel should be near or just slightly below the float bowl carb seam. IIRC a battery vent tube will work fine for this.

Cool...never thought of that. Thanks for the tip!

Knocked off for the night...This thing is obnoxious loud...gotta pacify the neighbors a little after the last two nights...lol, but, damn, gotta work during the day.

 

[chopitdropit]

One more question.....which way do the mix screws go leaner (more air) in or out,bs34s
1982 I think

 

[gggGary]

Rich is out on the mixture screws. Your 2 1/4 sounds reasonable 3 1/2 is about max.
Agreed on the washers, as long as they are there and not split they are probably fine. An 82 is set up pretty lean from the factory after you get basic running handled you might want to do some plug chops and she how they look. You haven't mentioned charging or voltage, the stock TCI ignition while usually reliable is not fault proof. And low system voltage can do funny things. Are your alternator brushes good?

 

[chopitdropit]

Thanks for the reply Gary. I pulled and checked the washers again and they are good. Figured out they are new and the reason they are flat on one side is there is also a little washer I forgot was there. I'll do some chops when she's back together. New battery, haven't checked brushes, but runs just as good with lights on as off...will check tho.

 

[chopitdropit]

These carbs are kikkin my ass.

AND..I just read the whole carb guide, so now I can't think straight.

No questions...just a comment...figure ya'll have been there.



I'm gonna go get drunk.

 

[XSLeo]

Just to clarify, the mix screws don't effect the amount of air in the mix, they adjust the amount of fuel.
Turning the screws clock wise closes the opening, thus decreasing the fuel, making the mix leaner.
Turning the screws counterclockwise opens the opening, increasing the amount of fuel, thus richening the mix.

 

[5twins]

To expand on Leo's post, yes, these are true mixture or fuel regulating screws, not "air" screws as so many mistakenly like to call them, even the factory in some of it's publications. But they do not regulate straight fuel, they meter the already made fuel/air mix coming from the pilot jet, and only about 25% of it. The rest of the mix flows unmetered out the 3 holes clustered by the butterfly plate .....

This is why the mix screws only have a limited effect and are used for fine tuning. To make larger adjustments in idle mixture strength you need to change the pilot jet size.

 

[chopitdropit]

Ok, so they are just, more or less, a fine tuning.

Question...I have resolved my other problems...air leak etc. Now the right carb is great and the left is way rich fouling plugs. I have the mix screws at 2 turns out (factory on this 1982 says 3 1/2).

I replaced the o rings in the float needle seats and inspected the needles. Neither looks worn but I am going to order new ones because they look different from each other. The rubber tip looks longer on the right one even though they both have a nice cone shape. I also took the choke circuit apart and cleaned it again.

I've had these carbs apart and recleaned/blew out about five times now in 5 days.

So my question is, would it be unusual to have to set the mix screws differently on each carb since they are more of a fine tune? Thought about turning the left in more and leaving the right alone.

Even though I haven't personally synced the carbs (still trying to find time to absorb how to do it) they were synced before and I haven't messed with the setting and until it fouls the plug the bike runs pretty choppy at lite throttle but smooths out and runs like a bat outta hell when you're in it.

At least I am getting there.

 

[nj1639]

Haven't done it but I like the idea of the 'popsickle stick method' of synching the carbs. Chopsticks would prolly work just as well.
Take the air box or air filters off and set a couple of same diameter sticks in the carb inlet throat. As you turn the throttle, both sticks should move the same- at the same angle. If not, adjust untill they do.
Seems pretty simple.
Side note....xsjohn would set the mix screws as each carb required, judging by a warn up run, shutdown while moving and then a plug inspection.