Topic: What would cause gas to seep from air screw?

[hapsh]

First, the bike runs great.  However, I noticed that my #1 carb has a little gas/varnish seeping from the air-screw. The spark plugs look very good except my #1 plug looks darker than the other 3.  My first thought would be that I have a small blockage in the idle circuit causing the idle mixture to come out somewhat from the airscrew instead of from the carb throat.  But the bike idles and runs great so it must be pretty minor.  Is this just normal from hot riding?  Anyone see this before?

[scondon]

Any help in letting us know what bike you're talking about is appreciated. Don't know whether you have fuel or air screws but they generally have an o-ring in the passage. If you're weeping out of an air screw I would also check float height.

[Hush]

Always hard to guess if these bikes are idling well or not as the fact they have 4 cylinders masks bad idling.
Mine was running abit ruff this week in the shed and I did the "ouch" test on the pipes, number 3 was stone cold and I remembered that my partner had done a wee repair job on that plug lead the other day, pulled it apart and sure enough lead was not making contact with plug cap, quick fix and all 4 passed the "ouch" test.

[martino1972]

did you check if maybe the airscrew was ready to fall out(like in unscrewed it self)??

[hapsh]

Sorry, I put the bike info in the secondary subject field and it didn't show up.  Its a 71 CB550 with a 76 engine and carbs.  The carbs have airscrews (filter side of carb).  Also they don't have orings because they are airscrews.  And no, the airscrew is not falling out, I noticed the seeping when I was making an idle mixture adjustment for the hotter weather and all the airscrews were still at 1.5 turns out.

Always hard to guess if these bikes are idling well or not as the fact they have 4 cylinders masks bad idling.
Mine was running abit ruff this week in the shed and I did the "ouch" test on the pipes, number 3 was stone cold and I remembered that my partner had done a wee repair job on that plug lead the other day, pulled it apart and sure enough lead was not making contact with plug cap, quick fix and all 4 passed the "ouch" test.

I've done vacuum syncs and checked the exhaust temps and all seems good.  I have been able to balance the vacuum very well between the cylinders and have not found any cold exhaust pipes.

[scondon]

 Check the fuel level/float height in #1. Too high and it will richen things up(sooty plug) and when you put bike on side stand level will rise on the airscrew side of #1/2 carbs(away from #3/4 airscrews). Also, if gas is weeping from anywhere else it can pool in the airscrew recess giving the appearance that screw is the source of leak. Those are my guesses

[hapsh]

Cool.  I will have to drain the floats into a cup and see if they are all the same, if they are maybe #1 is just sticking or leaking by.  The level is not high enough to come out the overflow tube however, or maybe that is clogged too.  Thanks.

[scondon]

 If your carbs are the type that drain from the stem when you turn the drain screw then there is a very good way to check levels. Attach a clear hose to the stem and bend it upwards against the carb body then open the drain screw. You can then see the levels as they are inside the bowl. Battery drain tubes are good for this purpose but you will need to cut about an inch from the ends as they have a small vent hole pierced in the tube. A small hose clamp will be needed as well since the tube is a bigger diameter than the bowl stem.

   Levels should be even across all four carbs and be at, or a smidge below, the float bowl gasket line(similar 750 carbs, guess it's the same for your 550). Centerstand the bike to get carbs as level as possible when measuring.

[TwoTired]

What setting are your air screws at?  If they are open more than stock setting, maybe you need to stretch the spring to hold the screw tighter in position?   Maybe the spring's gotten weak with age?  Stretch them a little longer.

You might also put some thick grease on the threads to help seal them.


Be wary about the drain-the-carb-bowl measurement technique.  The first one you drain will also have the contents of the fuel delivery hoses.  Kinda have to do it twice, and start with a different carb for the first drain, which ought to measure higher than the rest.


Cheers,

[hapsh]

What setting are your air screws at?  If they are open more than stock setting, maybe you need to stretch the spring to hold the screw tighter in position?   Maybe the spring's gotten weak with age?  Stretch them a little longer.

You might also put some thick grease on the threads to help seal them.


Be wary about the drain-the-carb-bowl measurement technique.  The first one you drain will also have the contents of the fuel delivery hoses.  Kinda have to do it twice, and start with a different carb for the first drain, which ought to measure higher than the rest.


Cheers,

The screws are at 1.5 turns out and have not moved since I last adjusted them.  They seem pretty snug.

[tonycb650]

Seems like you could just fill the float bowls, turn off the petcock, remove the fuel line to the carbs, then drain float bowls into a cup.

[scondon]

Seems like you could just fill the float bowls, turn off the petcock, remove the fuel line to the carbs, then drain float bowls into a cup.

    Don't forget to remove the hard fuel lines between the carbs I know, I know, probably not enough fuel in these to make a difference for this method of measure   Still don't like this method as it only tells volume disparity, and then only loosely. OK for pointing to, or ruling out, extreme problems.

[tonycb650]

Ya, I thought about the hard lines , only after I posted. I think TTs way of doing it by filling the float bowls after measuring each one would be better. (TTs right! BIG SUPRISE!)