Carb issues

[sbig]

I am helping out a cousin, trying to get his 1980 XS1100 going. As far as I can tell this is an SGB model. He bought this bike after it had sat for several years. The carbs were very gummed up, I have had them off twice cleaning them out. Floats seem to be operating fine. Fuel petcocks have been rebuilt. I have clear fuel hose and external filters installed so I can see fuel entering the carbs.

The engine starts up fine using the choke system, but seems to take quite a long time to warm up, even in warm Florida weather. After a few minutes the engine starts racing, so I push the choke into the mid and then the off position, engine stays running most of the time, but advancing the throttle past idle results in backfiring through the carbs and stalling. I can rev the engine if the choke is on, and it sounds very good with just very minor missing/backfiring. This is with the airbox removed, carbs open to atmosphere.

So I have not removed every single component of the carbs, have not done anything with the choke circuit since it seems to be working, have not removed the diaphragms but they do move up and down and make a nice sucking sound when moved.

I am looking for ideas on what would be wrong in the carbs. Idle circuit seems good, main jet circuit seems good, so what controls the midrange where the problem seems to be?

[rpgoerlich]

If it's been sitting for any length of time you'll want to remove the main jet & washer, pull the emulsion tube and clean it. Turn in the pilot adjust screws lightly and count how many turn out they are(so you know where to put them back as a starting point), remove them to clean out the idle circuit(dont lose the washer, oring and spring). Make sure the tips aren't broke off. Pulling the slides, cleaning them and polishing the slide bores do wonders for a snappy throttle. Make sure the float levels are correct. Then, try putting the airbox back on it and syncing the carbs if you've already checked valve clearances.

[sbig]

If it's been sitting for any length of time you'll want to remove the main jet & washer, pull the emulsion tube and clean it. Turn in the pilot adjust screws lightly and count how many turn out they are(so you know where to put them back as a starting point), remove them to clean out the idle circuit(dont lose the washer, oring and spring). Make sure the tips aren't broke off. Pulling the slides, cleaning them and polishing the slide bores do wonders for a snappy throttle. Make sure the float levels are correct. Then, try putting the airbox back on it and syncing the carbs if you've already checked valve clearances.

Thanks. I will try those ideas. I did have the main jets out but did not remove the tubes. What should I use to polish the slides? Is a scotchbrite pad acceptable?

[natemoen]

Yup. Do a thorough good cleaning of every orifice and piece otherwise it will never be right. Here is a thread to help.

http://www.xs11.com/forum/showthread...b+cleaning+101

[cywelchjr]

And make a note of the fact that the carbs that have the o-rings like the 1980 models use, MUST have good o-rings to really run right. Also it sounds like as others have said that the carbs are NOT fully clean.

Also, for the mixture screws, on the 80 carbs they will look a bit like the tip has broken off, but it didn't. Mikuni changed the screws and gave them a blunt tip that won't get stuck in the hole and break off like the earlier carbs can. That doesn't mean you can crank down on them, but just be aware that blunt tip does NOT mean they are broken.

[bikerphil]

Don't know if it's been mentioned, but it isn't necessary to seperate the bank of carbs for a good cleaning.

[sbig]

And make a note of the fact that the carbs that have the o-rings like the 1980 models use, MUST have good o-rings to really run right. Also it sounds like as others have said that the carbs are NOT fully clean.
....

Meaning the o-rings on the idle mixture screws?

[natemoen]

Yup, that's the o-rings he is talking about.

[Larrym]

A Cousin to Keep on the X-mas List???

Do be gentle with the float pin posts or they'll snap/break:



(Just a pic of someone else's FUGLY repairs on a couple posts...)

And if you find yourself having been in/out of those carbs more than 3 times and the engine STILL misbehaves:

Remember there are two other "systems" which need to work properly.

(Electrical and Mechanical)

[sbig]

Well I have the carbs completely taken apart with the exception of the mixture enrichment rods and throttle linkage. The idle mixture o-rings are toast, they are flat, not o-ring-ish at all. Are these still available from Yamaha?

Also I found more gunk around the emulsion tubes and stains on the slides where it looks like they sat during the long period of not being used. So, I'll be looking for o-rings and cleaning the parts up tomorrow.

When assembling the idle mixture screws and o-rings, do you try to seat the o-ring first, or place the washer and o-ring on the screw first and install as an assembly?

The needle seat holder o-rings may need to be replaced also, as those holders came out very easy.

Thanks for all the great tips.

[bikerphil]

Put the spring, washer, then O-ring on the needle, then tilt the carb body sideways and install the assembly. MikesXs has those O-rings new. I've re-used the old ones before successfully.

[Ken Talbot]

Well I have the carbs completely taken apart with the exception of the mixture enrichment rods ....

So, you're getting closer, but still not there. The "choke" rod needs to come out so you can get the enricher plungers all out or you'll never get the last of the orifices clean. Also, be sure to clean out the orifice located at the bottom of the float bowl. I believe this will bring you pretty close to the legendary "triple clean".

Once everything is squeaky clean, the carbs will need to be sync'd and 'colortuned'. Then, and only then, you can start working on checking out the jetting situation to see if it is running rich, lean, or just right.

[sbig]

So, you're getting closer, but still not there. The "choke" rod needs to come out so you can get the enricher plungers all out or you'll never get the last of the orifices clean. Also, be sure to clean out the orifice located at the bottom of the float bowl. I believe this will bring you pretty close to the legendary "triple clean".

Once everything is squeaky clean, the carbs will need to be sync'd and 'colortuned'. Then, and only then, you can start working on checking out the jetting situation to see if it is running rich, lean, or just right.

OK, I took this advice and now have all those parts out and the carbs all separated. The bracket screws that hold the carbs all together were a real bear. I had to carefully arrange some wood blocks for support, apply heat and use an impact driver. No damage with the exception of one screw, so all is well so far. On to the cleaning steps, if I can find a good carb cleaner. This junk they sell now as spray carb cleaner seems no more potent than crappy E-10 gasoline.

That orifice at the bottom of the float bowl... anyone know exactly what is does? The last time I had the carb bowls off, one of those was really plugged bad. I finally found a welding tip cleaner of the right size to get it unplugged.

[natemoen]

You van let them soak in pinsol and used compressed air to clean all the little passages and orifices. Also there are paint gun cleaning brushes that work well for cleaning, harbor freight sells some for like a buck or two.

Also might be time to start changing out the screws on the carbs with stainless allen bolts.

[Larrym]

Name that Hole???

That orifice at the bottom of the float bowl... anyone know exactly what is does? The last time I had the carb bowls off, one of those was really plugged bad. I finally found a welding tip cleaner of the right size to get it unplugged.

It's the metering orifice for the "enrichment" system (Choke...). Fuel is drawn into that teensy-weensy hole and then up through the pipe into the carb body/enrichment system.

See this post from bikerphil:

http://www.xs11.com/forum/showpost.p...12&postcount=2

Or NOT as in the case when it's plugged up.

Good attention to details ya got going on.