carb overflow mystery

[chuck hahn]

Yes...clogged vent. Take the 2 screws out of the brown kidney bean looking part..being sure of how the BBs go back in. Then youll see a vent hole. Blow into it and see that air passes thru the vent. The vent channel igtself is a molded in tench in the grey base metal and is covered by the chrome cap cover. The outside air flows thru the channel and into the tank. Also , if you take off the black cover, youll see that there is an oring at the base of the lock cylinder that keeps gas from splashing up and out via the key hole..youll need to be sure the oring is good. While the cover is of, give the lock cylinder a good blowing out with some air and relubed the tumblers with a shot of penetrating oil.

[chuck hahn]

Or temporarily cap off the overflow nipples on the bottom of the bowls.

[barnbiketom]

TRUST ME
make sure the individual CARB VENT lines are not blocked or hooked wrong ( to each other)

if in doubt just reach in with needle nose pliers and pull them oof the carbs then retest

[Steve]

Wouldnt the circuits take up the same amount of fuel regardless of the gas level as long as their intake openings are submerged? Maybe at 25mm they are on the brink of no longer being submerged.

Oh, they will still be submerged. The problem is that fuel is drawn up through the jets by the air that is passing over the top. The air over the top is accelerated by the venturi, and the faster-moving air has less pressure. This lower-pressure air will suck the gas up the jets. Now, if the level of the gas is lower (due to setting the float height at 25mm vs 24mm), it will have to suck harder to raise the gas the extra mm. Since it doesn't suck any harder, it siimply draws up less gas, therefore, a leaner mixture.

I was looking for the reason you went with bigger jetting and saw that you have pods and cut-off drag pipes. Not sure that three main jet sizes will be enough for that combination, and a larger pilot might not have been necessary, but the part that confuses me is "plus one groove up on the needle". Did you move the clip down (toward the point) or up (toward the blunt end) of the needle? If you moved the clip UP one groove, like it sounds in your post, you actually LOWERED the needle, which will lean out your mid-range, you should have lowered the clip, which will raise the needle.

.

[wompin]

Ya what I meant was I raised the needle one groove, so theres more flow on midrange.

If three sizes up for the main isnt enough, do you have any suggestion for a proper jet size?

I had seen from a few sources that a good rule of thumb is 2 jet sizes up for pods and two for open pipes. Then one pilot size up for each 3 main jet size increase. I plan to baffle the drag pipes, and when I can afford it, put on a 4 into 1 with a nice turnout muffler. So I made a judgement call and went 3 sized up for main and one for pilot, plus the needle moved up one setting. I figure I can also back out the fuel screw more if needed.

[wompin]

TRUST ME
make sure the individual CARB VENT lines are not blocked or hooked wrong ( to each other)

if in doubt just reach in with needle nose pliers and pull them oof the carbs then retest

I just had the carb vents on #2 and #4 open with no tube on them. I figured vent through a hose or vent through a hose nipple is the same thing. Its still open to the atmosphere.

Obviously my #3 vent is providing vacuum to my petcock

[Steve]

I have seen that same suggestion list. I don't have a lot of experience jetting for mods like yours, so I can only repeat what I have heard from other sources.

What I have heard there (and seen many times here) is to add 2-4 sizes for a pipe (usually a 4-into1), depending on how free-flowing it is, and to add 3-5 sizes for pods. That would give you a range of 5-9 sizes, and you have only gone 3.

Also not sure how different it is jetting the VM carbs vs the BS carbs. We have two bikes that are non-stock. My #1 son has a 650L with pods and a pipe. I think the mains are 4 sizes larger than stock. #2 son has an 850G with a K&N insert in the stock airbox and a pipe. The mains are 2 sizes larger than stock. The needles have not been changed on either bike, nor have the pilot jets. The mixture screws have been adjusted for best mixture.

Hopefully someone with more VM jetting experience will speak up with some better suggestions.

.

[wompin]

Gas cap vent is functioning well and tumblers now freshly lubed. Thanks for the tip.

Ive got a hypothesis. I think since my petcock filter screen was missing and I had just put a faucet screen in its place, that some small particle must have made its way through the petcock, in between one of the float needles and its seat. During the test, it must have been cleaned out. When I cleaned out my gas tank there were a few rust flakes that may have been the culprit.

So, Ive ordered a nice in-line filter, and then I would bet that my overflow issue goes away.

Filter should be here either friday or monday. Ill let yall know how the next run goes.

[barnbiketom]

[QUOTE=wompin;1778117]I just had the carb vents on #2 and #4 open with no tube on them. I figured vent through a hose or vent through a hose nipple is the same thing. Its still open to the atmosphere.

Obviously my #3 vent is providing vacuum to my petcock[/QUOTE

again, make sure all the carb vents are open,

The HOSES MIGHT BE PLUGGED.

the #3 hose going to the petcock is NOT the bowl vent, it is a vacuum supply line.

the bowl vent for #3 is a different port. make sure they are all vented separately.

[wompin]

[/QUOTE]
again, make sure all the carb vents are open,

The HOSES MIGHT BE PLUGGED.

the #3 hose going to the petcock is NOT the bowl vent, it is a vacuum supply line.

the bowl vent for #3 is a different port. make sure they are all vented separately.[/QUOTE]

When you say carb vents/hoses, do you mean the overflow vents/hoses? Sorry for the confusion. Ill check all my hoses anyway. Thanks

[chuck hahn]

By VENT he means the ones on carb 2 and 4...the brass nipples up on the throat of the carbs. The nipple on carb 3 is the vac supply for the petcock. If the vents are plugged the air cant equalize bewteen the carbs and yes this will also cause an overflow of gas from the throats of the carbs.

[chuck hahn]

Put a piece of hose on them and blow to see if the air goes thru them.

[Big T]

Okay, just to clear up a misconception here, the pilot fuel screw should be at 1 turn as it only applies at idle

It does nothing above that.

If you went up 4 jet sizes, it's still lean. You should be at 122.5 or above

On the overflow issue, make sure the vents are clear and check the float bowl interior by taking off the float bowl, putting some gas in it and see is it leaks out the overflow

[mrbill5491]

You have a pic of your carbs?

[chuck hahn]

Well..actually Big T, it is also the primary circuit for up to about 1/8 throttle and its also functioning durrin g the transitional spots between accelerationg past the 1/8 throttle and then back to the idle position. And of all the things ive read here and from other very knowledgable men that were the dealership techs back then, the factory setting for the pilot screw was 3/4 out..just a teeny tiny bit lean but thats where it was to meet the EPA requirements for sales in the US. I have all my 1000s at 3/4 and all run great. They will run great at 1 out too, but then its actually high on the rich side.