Runs better on prime

[gsx1100]

Here the story been having problems lately with my number 3 cylinder not firing when its cold and sometimes wont fire when its hot. So upon tinkering I plug the vacuum line and turned to prime, and instantly the bike fired on all four. I already rebuilt the petcock, and no gas comes out of the fuel line when not running. I suspect not enough vacuum pull to the petcock or the rebuild kit didn't do its job, any suggestions.
Thx in advance

[Suzuki mad]

Fit a pingle tap.

[Bribird]

or it could be some gunk or dirt/rust in the on position tube. How did it do when it was on reserve?

Just a thought, what is the condition of you intake O rings and intake boots? If you have a vacuum leak on the #3 cylinder(the one with the vacuum to petcock port), that could be your problem.

[gsx1100]

Boots are in good shape. My vacuum line to the petcock is hooked between 2 and 3 is that right. I completely stripped down so i may have gotten one of the lines messed up.

[BassCliff]

Hi Mr. gsx1100,

Check out this page:

Where Do These Hoses Go?

The (larger) fuel line goes from the petcock to the nipple between #2 and #3 carbs. The (smaller) vacuum line goes to the nipple on the front of the #2 carb. We're talking CV carbs, right?


Thank you for your indulgence,

BassCliff

[Bribird]

exactly what kind of bike are we talking about?

[gsx1100]

Its an 83 gs 1100 e with constant velocity carbs. Its hard to imagine it not having to do with the petcock because it runs very well with it on the prime setting.

[Steve]

If you have CV carbs, the hose that fits between 2&3 is the fuel inlet line.

There are also hoses between 1&2 and 3&4, those are vent lines and just go back over the airbox.

There is a vacuum fitting on #2 that should go to the petcock.

Also need to make sure that you are numbering your carbs/cylinders correctly. #1 is under your clutch hand, #4 is under your throttle hand.

You can test your petcock to see if it's working properly. Connect some hose to the fuel tap, place the other end in an appropriate container. Connect some vacuum tubing to the vacuum port. Suck on the vacuum line to see if fuel flows. When you stop, the fuel shoud stop. Now turn the petcock to PRIME and compare flow rates. That will tell you if your petcock is OK.

.

[gsx1100]

All the lines are hooked up right, ill try the petcock test but i don't know if im getting a strong enough vacuum to open the plunger to allow the full amount of fuel in. What would cause a week vacuum from the carbs.

[Steve]

It doesn't take much vacuum. If the engine is running at all, there will be enough vacuum to open the petcock. However, you might need to check to make sure there is not a leak in the o-rings on the intake boots and also check carb sync.

.

[gsx1100]

A little update, tried to start the bike cold with it on prime and the bike ran on three cylinders. I blew into 1 of the 2 breather lines and it started running on four. For some reason it doesn't like to start cold.