High Revving at Neutral Start. Changed Needles/Seats

[79xs1100s]

Bike ran fine until last week when I decided to give it a face lift and fix some finiky problems such as my leaking carbs. I got the seat from z1 enterprises the VX or XJ what ever Vitron ones. The 3 and 4 carbs which were originally the leakers still seem to be leaking and now when I go to start the bike in neutral the thing revs to the moon. Im sure this is stupid and ive heard it could be the float settings or something? Im a modern Auto Technician so i find Carbs aren't my strong suit, more computers. If someone could help. Ive checked the cable itself, no hangups, the throttle tube rolls fine and sets to "idle" if you will. I am 99% sure the vacuum line is attached etc. Could someone chime in and help? Thanks

'79 Xs1100 Special
No Octy
Uni Foam Filters
Kerker Exhaust
New Needles/Seats

[CatatonicBug]

First, did you sync the carbs? The RPMs "shooting through the moon" is normal when the choke is pulled out. Is the choke pushed in? Once the carbs are sync'd, you need to turn the RPMs down with the adjusting screw between carbs 2&3. Have you tried that yet?

[79xs1100s]

the carbs have to be sync'd after installing new needles?seats? thats all that was touched, the bike ran fine two days ago. Choke is not out, im thinking they leaked by or the floats are the problem and not the needle/seat as the bowls are probably overflowing with gas. And info as to whether they need to be synced after changing needles/seats would be appriciated

[DGXSER]

Think of it this way, how well an engine runs or each cylinder is firing is changing how much vacuum it is drawing at idle. Any shange in the mixture of fuel to air that cylinder sees, will change how strong of an explosion occurs in that cylinder, and how much vacuum it draws.

When you synchronize the carburetors, what your measuring and making even across the board is NOT the position of the throttle plates, but the amount of vacuum each cylinder is drawing at idle. So if you changed the needle valve and seat, you very well could have effected the synch of the carbs.

Now it does seem odd that it would have thrown it off enough to cause the issue your seeing, but it is not out of the question. IF the needle is leaking, then gas is either running out the air box or into the engine.

[CatatonicBug]

My rule is, any time ANYTHING changes in the carbs (including the amount of dirt in them), they need to be sync'd. The slightest change can throw them off just a bit. Granted, it may not be horrible, and you may not notice it, but they will likely not be sync'd.

[petejw]

did you just change the needles or
the floats as well, what have you got them set at?

[TopCatGr58]

Okay,

Signature says UNI Foam Filter(s), so I'm assuming you mean pod filters.

Where do you have the upper "T" fittings plumbed to, since you don't have or aren't using the OEM airbox? They can not be just connected to a vacuum line 2 way and then to each other. That will prevent them from venting, and these upper "T"s are the bowl vents, and need to plumbed to an open vent source. IF they are plugged, or the "T"s are gummed up and not venting, then the carbs WILL LEAK!!! Suggest you check that out, but it could also be the floats!?
T.C.

[79xs1100s]

the 2 vent lines are currently open to the air. I had the bike running on the stock air box with no filter for ever. Now its having an issue. It ran after I changed the needles and seats which is what gets me confused. The floats are the original the only this that was changed, touched or adjusted was the needles and seats. Im going to check my float heights today but I can Imagine thats the problem.

[79xs1100s]

How exactly do you measure the 25.5mm float height? And I and using the Virago Needles/Seats for clearification

[natemoen]

Well if you were running "forever without a filter" You could have sucked something into the carbs and have something clogged. The filter is there for a really good reason, and you need to have it there.

[79xs1100s]

by forever i mean a few months, and by it ran a few days ago it ran a few days ago, the carbs were cleaned with carb and choke cleaner im almost positive that has nothing to do with it.

[79xs1100s]

Im feeling like the vent lines coming from the carbs need to see vacuum if im not mistaken. They are open to atmospheric pressure and it revs to the moon, but when thet are plugged with a bolt, it wont even start. Can I just plumb them to the vacuum nipples on the carb boots? or will that not work?

[TopCatGr58]

Hey there 79,

We're trying to help, but it can be difficult on the net.

First, go back to the 2nd post in this thread, click on the LINK in Catatonic Bug's signature, and download the service manuals he has there...should be easy since your a modern computer kind of guy!

Secondly, the upper "T"s are strictly VENT tubes. NO VACUUM, especially non of the ports on the intake boots! They were originally connected to the OEM airbox, which would have just a slight lower pressure due to the intake air of the engine coming thru the box, but that was just so it could scavange any rare fuel fumes from those vents, the airbox nipples were really just static vent connections. With it revving with them open, sounds like the floats may be set too low, fuel level too high, so it's providing too much in the idle circuit and running too fast.

The manuals you will download will show images of where and how to measure the float heights....while the carbs are upside down, from the metal gasket surface to the top of the floats without depressing the spring in the float needle. The 25.7 is a +/- value of 1mm depending on performance and plug appearance.

Next, you say carb cleaner....but did you really fully disassemble the carbs, remove all of the jets, pilot and mains, and the main jet nozzle up thru the center of the carb body and out the opening that the vac. slide comes down thru?

The 3 screws on the front of the carbs at the throttle linkages are the synch screws. The ones on the TOP front are the pilot/idle jet screws, and there is of course the main large thumbscrew in between the 2-3 carbs at the back of the bank for setting the main idle.

After you cleaned the carbs, did you check the bench synch....verify that the butterfly valves were all at the same visible position of action when the throttle plate was closed/idle position?

Do you have INLINE fuel filters? Small particles of debris/rust, even old fuel line innards, etc, can come thru the lines and wedge between the floats and seats causing them to leak.

Also, the brass floats can develop pinholes in them and sink, again causing leaks.

Yep, lots to look at and check, good luck.
T.C.

[79xs1100s]

took the carbs back out and drained the bowls. My thought was as mentioned that the floats/needles/and or seats were somehow overfilling the bowl. I read that with the VX920 Virago needles and seats the float tabs were almost even but bent slightly, so i did such and checked any other obvious things. With the bowls empty, and petcock off i was able to then fill the bowls and get it to run fine as the carbs filled, The true test now will be to see if the carbs over fill again, if they do and i revs to the sky at idle, the problem is overfilling.

[natemoen]

I repeat TC's question. Did you COMPLETELY disassemble every piece of the carb and thoroughly clean and scrub it when you cleaned it?