'79 XS1100F Carb Issues; Poor Performance on the Main Jet.

[bikerphil]

The bike will never run right with Y265 needles, I have tried them and they are not even the right ones for our series carbs. It's a shame that K&L doesn't know this and they don't even care. Smaller diameter needle = excessive fuel.

Ordering from XJ4EVER is easy, just shoot them an email telling them what you want and you should get a quick response back.

[banzaibob]

The bike will never run right with Y265 needles, I have tried them and they are not even the right ones for our series carbs. It's a shame that K&L doesn't know this and they don't even care. Smaller diameter needle = excessive fuel.

Ordering from XJ4EVER is easy, just shoot them an email telling them what you want and you should get a quick response back.

Is he on vacation or something? I've been trying to get in touch with him via e-mail and a conversation on the xj forum since yesterday?

[bikerphil]

Is he on vacation or something? I've been trying to get in touch with him via e-mail and a conversation on the xj forum since yesterday?

I don't know, he usually responds within a day.

[banzaibob]

He got back with me....nice guy. This is what he said:

"Hi Bob, thanks for writing.

Th HCP23265 needles that we offer are the "Y265" needles which are the aftermarket versions of the multi-position 5GZ6 needles.....in other words, you can et the needle "height" within the vac piston at various levels, so as to allow you to "tune" the fuel flow thru the main jet. In your situation, where the engine is running very rich, the needle would need to be clipped in the highest slot, thus lowering the needle within the fuel jet/emulsion tube, and thus resulting in a leaner mixture for most of the travel of the needle thru the jet.

The 1978-79 XS1100 carbs are mess, mainly due to a variety of design modifications that were occuring with the BS34 carbs in those years. For instance, early versions of the BS34 carbs supplied the pilot fuel jets (which are unique to each "versions of these carbs) thru the main fuel jet (and thus require much larger main jets.....so that enough fuel can be used to supply both the main fuel circuit [i[and[/i] the pilot fuel circuits. There was also a block-off screw (or, on later models, a rubber plug) that prevents fuel entry into the pilot fuel jet port from the bottom; the fuel for the pilot circuit has to come thru a drilled passage from the main fuel circuit bore. The lack of the bloock-off screw (or rubber plug) will create an overly-rich fuel condition thru the pilot fuel circuit (which may only manifest itself once the throttle is opened past the 1/3-point----as in your case----when all of a sudden an "overly rich" pilot circuit is now supplemented by the main fuel circuit becoming active.

Let me know if this helps!


Len"

I tried writing him back and thanking him but the forum website won't allow responses for some strange reason. Glitchy.....

So.....he gave me a lot of insight. In many ways it's back to square one. I re-read the original post that I made last winter about this bike....at one time it would rev but only with no air filter. It was still rich however and the plugs would foul.

If anybody regularly corresponds with this Len guy, PLEASE convey my thanks to him.

[bikerphil]

Here is the genuine 5GZ6 on the left and the aftermarket Y265 on the right. There is a subtle difference and like I said, my bike ran poorly with the latter...

It is amazing how little a difference has such a big effect.

[banzaibob]

Got a partial update:

Dropped the needles all the way down. Genuine Mikuni jets came in the mail today. Installed everything. Took it down the road WITHOUT air box. Success! (kind of) It revs to red line under load without loading up. Took it back home and put it on the lift, synced the carbs, adjusted the fuel screws...idled perfectly. Installed the stock air box and stock air filter. Took it back down the road....STILL revs to redline under load. HOWEVER......it now acts like it has a vacuum leak. It coasts and hangs up on idle for about 5-7 seconds and then dies. Tomorrow I'm going to remove the air box and look for problems.

[DiverRay]

Look at the plugs on the carb boots. If they are hard and old looking, buy new ones. The other usual suspect are the throttle shaft seals.
For testing, you can use a propane lighter or torch. Don't light it, just allow the propane to exit at a LOW rate, and put it near the suspect leaks. Engine will rev if you have a vacuum leak.

[cajun31]

Those early carbs were very tunable with all the right components still there. Aftermarket not so much. Just a headache. I prefer the later carbs. Are the carb boots original? As far as you know have they ever been removed or replaced? The reason I ask is because there were originally gaskets between the carb boot and the engine. If those gaskets are still there it would be better to just remove them and put a light coat of Yamabond or something similar. Makes for a better seal. When I rebuild carbs I always completely disassemble the carbs and replace all the throttle shaft seals. As Ray pointed out they are a source of leaks too. Sounds like you are very close though.

[banzaibob]

Update to the update:

I might have been a bit premature about revving to redline. Yes, it can be coaxed smoothly to redline with about 1/2 to 2/3 throttle but pinning the throttle produces the same problem ALBEIT not nearly as bad. In fact, before, running at full throttle in the higher gears it would simply run rough and misfire but it wouldn't rev above 4500-5000rpm or so. Now it will continue to climb but misfiring the entire time. Backing off the throttle will smooth it out. Looking at the spark plugs? Black and sooty. On one run I had the air filter in place. On the next, I removed the air filter and bottom half of the air box. I definitely ran better without the air filter and the bottom half of the air box BUT it still had the underlying problem.

As far as the "vacuum leak" type problem; it is not a vacuum leak. I tend to think that it may just be a intermittent float problem on one of the carbs. When I removed the bottom of the air box, it was a little wet from gas. It should not be ANY wet from gas. Float level is my first guess. Bottom line, something is not metering gas correctly

So the next step would be smaller main jets. With a fairly loud, non restrictive exhaust that appears non-intuitive to me. But reality is reality. I have dropped the needles down all the way....it definitely improved things. But there is nowhere left to go without what would be weeks more of experimentation and guessing with leaner needles.

Seriously....I am considering buying a used set of carbs from an '80-'83. I'd rather ride this g*ddam thing than turn it into a science project.

[DEEBS11]

You could also have cracked high tension wires. You could wrap them with black electrical tape to see if it makes a difference.

[DiverRay]

Float levels will do it! Also, a sticking float due to gasket or the needle/seat not being correct. I would do the floats BEFORE changing the main jet. Look and see how close to the gasket the floats are. Gasket can be trimmed with a sharp knife if your not sure.

[oldyam80sg]

I would be very leery about buying used carbs on the internet as mentioned. Could be issues not mentioned in the ads. Float pins the posts could be broken, stripped threads etc.