Overflowing Carburetors

[sixtynine]

Hi all.
I am having difficulty with my 78XS1100E that I bought some 3 mth. ago. The problem is carb. continues to overflow into air
intake even after all the following work has been done:
. carb. completely disassembled and thoroughly cleaned
. floats checked for bouyancy and all floats (with hinges) 80% submerged.
. float height set to 26mm with gauge
. float valve needle and seat polished...still overflows
. new needles and seats installed
. gas level checked using Ken Talbot's method. Level in #1,2,3 the same, level in #4 1 mm lower, i.e. within tolerance. Float valves worked as required. Gas level approx. 10 mm below underside of carb. throat.
. Carb. reinstalled and prime switched on. No leakage.
. Engine started after several cranks. Running rough and LEAKING AGAIN through air intake drain.

Any and all suggestions will be greatly appreciated.
Roald, Madoc, Ontario

[Ken Talbot]

Now it's time to rebuilde the petcocks. Really - the floats shold do the job but you might chase around a long time getting them right. The fact it is leaking says the petcocks are also not working properly so you might as well dive into them. If you get the petcocks working, you won't have to worry any more about the floats.

[ratbyk]

Carb Flooding

Some suggestions,
1. Lower float level to 24mm.
2. When carbs are off this time examine the needle and seats with a magnifying glass looking for dirt.
3. Install an in-line fuel filter to prevent crap from the tank getting into the carbs.
4. Side car Kev had this same problem and was pulling his hair out. He ordered 4 new plastic floats from Mikes XS. Problem was solved. The floats were for an XS650 using Mikuni 34 mm carbs. Price was right also, only $10.00 each.
I have one carb that has been giving me a rich run problem. I have ordered one of these floats to try and correct. It has not arrived yet but has been shipped.
5. Remove a fuel line at the petcock and make sure there is no fuel flow past the petcock if there is no vacuum present.
Ken/Sooke
78E Ratbyk
82 FT500 "lilRat"

[sixtynine]

Overflowing Carburetors

Hi again
Petcocks have had replacement kits installed and are working OK. No leakage when engine shut down. Petcocks for 78E have fuel filters in the tank and is part of the petcock assembly.
Roald

[sidecarKev]

Did you check your floats in hot water? Floats might not appear to leak when you dip them in some water to test them for leaks. If you take a room temp float and plunge it in hot water the air inside the float will expand slightly and send a stream of bubbles out if there is a leak. Or you could take your floats out right now and give them a shake to see if you hear any gas in them. This will work as long as they had been sitting in gas for at least a couple hours.

Long story short, if you tested the floats by putting them in room temp water for a few seconds, I would think about testing them again.

[Ken Talbot]

Say what - it is leaking into the airbox when the engine is running? And, the petcocks are working properly to shut off the fuel flow when the engine is not running? Is there any chance that you have plumbed the fuel line to the upper Ts between the carbs rather than the lower Ts?

[rover]

On each pair of carbs, there are two tees. The upper one should connect by a hose to the front upper part of the airbox. This is a float bowl vent. The lower tee connects to the fuel line. If the upper is connected to the fuel line, the fuel will flow into the carbs ABOVE the float valve. This will cause flooding when the engine is running, and all the time if the petcock is on prime. The overflowing fuel will run into the airbox, and also to the engine, and get into your oil. If the upper tees are capped off, the float bowls will not be vented. Either hook them up, or connect them to a length of hose with a filter on the end. They work far better connected to the airbox. Hope this will help. If not, take a break to rest your mind. Then go back over all the steps again with PATIENCE. The end result will be well worth your efforts; these are awesome bikes to ride when working properly. Good luck

[ratbyk]

Flooding

Good guess rover. I think you have found the problem. I know I was scratching my head on this one until Ken T suggested the plumbing problem. Your suggestion makes the most sense.
Ken/Sooke

[sixtynine]

Carb overflowing

Thank you all for your replies.
However, I am no further ahead after rechecking hoses, floats, etc. New needles and seats and resetting floats to 24 mm did not help. I can set up the carbs on the bench, connect the gas tank petcock to lower hose on a set of carbs, connect a clear hose to bowl drain, switch to prime and bingo it all works..., fuel shuts off and fuel level is as shown on Ken Talbots photo. Same for other set of carbs.
Now I put the carbs back on the bike and I am ready to go places. Switch to prime to fill bowls and gas pours out of the carbs at the airbox. I have done this umpteen times with same results. A biker friend with considerable mechanical knowledge is also running out of hair.
I had come to the conclusion that the floats were too small with insufficient bouyancy to shut off the flow of fuel so I stopped in at the local bike shop to ask about new floats. The mechanic told me to keep my brass floats and not to get plastic ones. He told me to reset the float height with the spring in the needle fully compressed instead of just touching the tab. This was done but with same results.
I am getting discouraged to say the least.
Roald

[sixtynine]

overflowing carbs

P.S.
Just to reply to Ken's questions.
Yes, carbs continue to overflow into airbox with engine running. No flow from petcocks with tank sitting on floor.
Roald

[rover]

One more thought. If your carbs have the pressed in float valves, held in place by a small screw and clip, there are o-rings on the outer part of the valve body. These are very easy to damage when removing and installing. Also the body where the needles enter is very easy to distort. With the floats removed, check EACH o-ring, and also check each of the brass tubes on the outer housing. I used non-business end of a drill bit (don't remember what size) to check and see if one or more of the tubes had been crimped from removing them. If one or more of these are out of round, the valve will not seat every time, causing a fuel leak past the float valve. Get new o-rings that are gas-proof, but be careful to use the proper size, or they could get torn from installing them into the holes they fit into. It may help to chamfer these holes slightly to keep from damaging the o-rings. And do not let frustration cloud your judgement. Look everything over with a good light and a magnifying glass, and take nothing for granted. A tip for removing these valve bodies; put a snug-fitting drill bit or metal rod inside of these tubes to keep from crimping them, and you can remove them with a pliers.

[TopCatGr58]

Hey there 69,

You state you hook the carbs up to a tank on the bench, but is it the same tank from the bike? Also, you said you rebuilt the petcocks, have you tested the petcocks since with it not hooked up to the carbs, putting it in PRIME as well as On and RSV to see if they leak, like into the vacuum port instead of just thru the supply port of the petcock? They should only flow on PRIME, and then only out of the fuel port, not the vacuum port.

You have a 78E, which has just 1 fuel supply nipple from the petcocks, the other nipple goes to a vacuum source, usually the port on the #2 carb intake boot, so if the petcock vacuum valve is messed up, could be getting fuel thru that route into carbs, and then back flowing into box? Exactly how are ALL the hoses routed from the petcocks and the carbs, both fuel supply and vacuum lines and vents? Just trying to help?

PS, I wouldn't rely on just the filter screens in the tanks, I've seen lots of fine rust particles get past these and down into the carbs!!
T.C.

[strom]

I had that same problem.... when I first assbemled the engine.

Guess what was it hehe....
Intake cam out of sync.... instead of pulling air in, it pulled some in and blew some out. I didn't know what it was till I put on some cone air filters I borrowed from a friend. My pants were soaked in gas, the bike didn't wanna run properly.....

Take off the valvecover and check cam timing. Dots on the cams should allign with arrows on the centermost bearing thingies, when #1 and #4 pistons are at TDC. The crank should be on the T mark, if you take off left side engine cover.

LP

[sixtynine]

Overflowing Carburetors

Hello All
PROBLEM SOLVED......I asked myself the question again and again. "why does it work on the bench and not on the bike, what is different in the setup????
The difference : Bowl vent hoses are not connected when on the bench. When on the bike they are connected to the airbox nipples. So I remove the airbox and and check these nipples. It turns out that they are brass tubes about 2 inches long with a small dia. bore AND THE ARE CLOGGED SOLID WITH DIRT.
This meant that when gas was filling the bowls WHEN ON THE BIKE, there was nowhere for the air to go and therefore pressure would build up in the bowls, preventing the floats from seating the needles.
So I ream out the brass tubes with a wire, reinstall it all, switch to prime... NO LEAKAGE. Engine starts and purrrrs. I put 100 km on the bike yesterday with no problems. Must go and get a licence now.
Thank you all again
Roald