1196 Big Bore Carburetors? or timing?

[Athedra]

Do I need to re-jet for the 1196 big bore?

I found the following, and don't know if it is my carbs or my motor.

For about 10km she goes perfect. Then she starts battling to run on high revs (6k and up). As long as I keep the throttle constant she goes ok. At pull away, I need to up my rev's to about 3k just to get away, else she just dies. She starts right up after she stalls, but still has no power. It happened twice to me today. Odd though is it only happens after moving for about 10km. At idle (Which she does without a problem), she has a backfire when turning and releasing the throttle. She picks up rev's no problem until I put load on the motor.

Any recommendations on where to start looking? Possibly timing?

Also noticed that suddenly all four carbs are pi$$ing fuel without the filter conversion. She used to just on 2nd carb which the filter conversion sorted out. These are the same carbs I had on the std 1100 motor.

Got me stumped. at the moment, and don't even know where to start looking.

[oseaghdha]

Maybe pickup coils, or fuel delivery.

[dbeardslee]

Did you ever check the vent lines on those carbs? Restrictions in the vent lines can make them overflow. If you've got filters on the end of the vent lines try taking them off. 'Course this assumes you've got '78/79 type carbs. JAT

[cywelchjr]

As I understand it, the big bore does change airflow so yes, you need to rejet. That said if it's leaking fuel you have needle valve/float problems, and that could be causing your problem as well. First things first, fix the leak, the carbs should not leak even if left on prime, and it CAN be fixed, but you may well need to replace the needle seats as it might be leaking around them (don't know if you have early or late carbs). If early carbs the seats might be leaking since it's metal on metal rather than metal on viton like the late carbs have.

[Athedra]

Yes, even went as far as removing the T-pieces joining the carbs. I got the impression that they where longer than what they should have been, so took them out completely. I left they holes open on the side of the carbs.

[Athedra]

As I understand it, the big bore does change airflow so yes, you need to rejet. That said if it's leaking fuel you have needle valve/float problems, and that could be causing your problem as well. First things first, fix the leak, the carbs should not leak even if left on prime, and it CAN be fixed, but you may well need to replace the needle seats as it might be leaking around them (don't know if you have early or late carbs). If early carbs the seats might be leaking since it's metal on metal rather than metal on viton like the late carbs have.

About a month ago (might be longer), I purchased a secondhand set of 79 carbs (if I read the threads correctly) because the original set's air/fuel jets was broken off in the bodies. I fitted new everything on them, but must admit I didn't change the diaphragms in the top of the carbs, merely sealed them with silicone. This resulted in Carb 2 continiously leaking after that. I suspected a bad needle and seat and as a test, swopped the needle and seat around with one of the other carbs, but my problem continued on Carb 2. I also did the credit card trick on the float settings (think I did that about three times)

On two or three occasions I thought I finally nicked the problem in the butt, but never really did.

On fuel delivery, I suspected a low float level, but then if I adjust them higher, then I would get a higher possibility of fuel leakage, and lower, would result in fuel starvation on high RPM's.

Just for interest........ If my diaphragms perished, would that give me problems just on higher RPM's when the motor is hot?. Read a while ago that these carbs work on three stages, where the high RPM's work directly on the needle. What problems would you run into on bad diaphragms?

[DiverRay]

Bad diaphragms will lead to running problems. As was stated before, you MUST fix the fuel leak BEFORE you can tackle the next "problem". Also, you did NOT state if you have put vacuum gauges on the carbs to sync them. If you have not, that is step #2, after fixing the fuel leak.
I would have left the "T" fittings on the carbs, and just put a short hose on it to keep most of the bugs out. With the big bore kit AND pod filters AND after market exhaust system, you should go up about three steps on the mains, and one step on pilot jets. This is JUST A GUESS, and should get you CLOSE to what you need for jetting.

[dbeardslee]

On the fuel starvation issue - didn't you just have the gas tank sealed? They didn't by any chance gum up the vent in the filler door, did they? A plugged tank vent could cause the symptoms as it takes a little while before the vacuum builds in the tank and then at higher RPM's you get starvation. JAT (I know, I know - I've got vents on the brain today )

[Athedra]

Hmmmm. Now that could be. They did fit a new liner in the tank. My tank has that little pipe coming out the rear (seat side) of the tank. I will test it by opening the tank cap when it starts doing that and see what she does from there.

I will pick up a new carb kit and send the diaphragms in for repairs (If they are holy as suspected). The jetting, I will have to go shopping on the jets. Odd enough, last time I got prices, it would have been cheaper to fit suzuki carbs on the bike than redoing the carbs from top to bottom. I will look into it tomorrow. For some dumb reason bike shops over here are closed on sundays. Also the reason why I am home on sundays.

[DiverRay]

The pipe that ends up under the seat is to drain the water from around the cap, NOT to vent the tank. For jets, look into mikesxs.com . Just buy two pair of each, and DO NOT tell him it's for an XS1100. He will NOT want to send out a part for anything but XS650's. You need the large round style jets for the mains, #145 would be three sizes up, but I'd probably get the 142,5 and the 147,5 just to have them for tuning. for the pilot jet, get the #45, mikes part number 48-0510 style. This will be one size up from stock, and should work. You will have to reset ALL of the adjustments on the carbs, so plan on an afternoon.

[dbeardslee]

On the tank filler door - when you open it there's a metal piece with three small screws and a small hole in the middle. That's the vent hole. It's not to tough to disassemble and clean.

[DGXSER]

Doug, is the std vent the same as the specials that I did a write up on?

[dbeardslee]

Don - It's different, but similar. You could probably get at it by removing the lock as it's got the same kind of hinged strap. When I replaced the seal on mine I left the lock in place and removed the three screws surrounding the vent and took the whole thing apart. You can get at everything including the back side of the vent that way for a thorough cleaning.

[Athedra]

Had a look at the system today. I havn't done the carbs yet, but fitted temprary inline ball valves (Small chrome ball valves) into the system to save me some fuel until I can get to the root of the problem.

I changed the pipe system to adapt to the inline ball valves, and found the lefthand petcock trickling fuel no matter on what position. Drained the fuel, removed the petcocks, and found that my internal fuel filters has been removed, Assuming this happened when I sent the tank in to get lined. Opened teh petcocks and found ALOT of crap in there. Closed them up again, and now get even flow on both sides. I will get the filters from the guy or make some form of replacement for them.

WHile she stood idling, I popped of the cones (pods) and had a look at my carb piston lift. 4 doesn't lift, so the diaphragm on carb 4 is perished.

Thanks for the jet sizes, I will try and source them over here. Importing works out to expensive. Had a look at the vent, and was open. Thanks for the info on the water drain, didn't know that, and is help full info.

I will pop off the carbs tomorrow at work and get the mechanics to strip them for me. Then will try and source the jets and work my way from there. I will sync them once they are all together and leak bench tested.

The carbs seems to be my head ache, so am looking at alternatives. I read that GSXR400 throttle bodies are a perfect fit, so GSXR400 carbs should be the same thing. I have a GSXR400K7 standing in our workshop, so will test that theory tomorrow. From there it will be just jetting and then trial and error. Anyone tried a normal set of delorti sidedraughts on their bike yet? I can get hold of two delorti's at a good price, and with the stock airbox removed, there is enough space if they will work. They filter system should be fairly straight forward from there. Another possibility I thought of it rebuilding my old set from scratch. Then just run on the set I have now until the other set is complete..........

Too many things to think of at once......

[DiverRay]

The GSXR600 TBI works on the XS1100. I would thing the 400 would be too close together, and NOT flow the air required. mikesxs HAS a site in Europe, so they MAY have something that you can get the parts at a reasonable price. JAT