Checking the pilot circuit question

[Coyote]

I am taking the carbs off again tonite. Tomorrow I will remove the bowls, floats and pilot jets. With the carbs inverted, the plan is to fill each pilot hole with fluid and see that it runs through all at the same speed. I hope I find that one is partially blocked. That would nail down the culprit.
My question is where should the air screws be to perform this test? All the way in? Removed or set at the book 1 1/2 turns out??
If all proves good in the fluid test, I will remove the floats and make sure none are leaking. Then I will triple check the float height. If all this prooves good, I'm gonna install the 3 over pilots and see what happens. It's about to drive me nuts.

[Wayne Meuir]

I have never heard of anyone testing a carb this way. Looks to me that it would be easier to just clean all of the circuits and be sure that none of them are plugged up.
I always soak the carbs in carb cleaner, blow them out with compressed air, spray them with aerosol carb cleaner making sure the spray makes it through all the orifcies, followed by more compressed air, then re-assemble.

That has always worked for me.

Wayne

[Coyote]

Wayne, I wish I could make everyone believe how clean these carbs are.
When I first rebuilt them, each one spent 24 hrs. in Chem-Dip including the floats that were held submerged by wiring on a large nut. Then all were rinsed in super hot water. Then they got a Lime-Away treatment to remove any white residue left and to brighten the metal. I blew 100 psi into every orifice and EVERYTHING was clear. Then I ran the whole mess through the dish washer and blew it all out again to be sure.
Then I assembled them, whetted them down with WD-40, wrapped them in a heavy plastic bag and put them on the shelf till I was ready to install. These carbs are super clean outside and inside.
I am 99.99% sure I won't find anything wrong inside.
So why the slow return to idle? Everything points to an air leak. Well I have eliminated that as well. Intake pipes are brand new and sealed with grease when installed. The only other place air could leak in is where the vacuum ports are for using a carb rack for tuning. There are 3 of these and none leak. I have tested all 3 with WD-40 applied with a brush. No bubbles or disappearing WD and no change in engine RPM.
Like I said. It's about to drive me nuts.
Anyway, I thought filling the pilot holes with alcohol and watching them drain through gravity might reveal something.

[Suzukidave]

A bad cylinder base gasket can also provide a vacum leak .

[tz375]

Chris,

We believe that the carbs are really clean. All we are saying is that the symptoms sound like a lean mixture and if it isn't an air leak, then it's most likely a partial blockage.

What I do is to blow carb cleaner through each drilling and repeat on teh other carbs for comparison. That way I check each part of the circuit and compare the outflow.

I pay special attention to drillings in float bowls and the by pass orifices for the slow jets.

Two other possible leaks are in the fuel tap/vacuum hose- check that with a Mityvac and see if it holds the vacuum.

On the 550, isn't the vacuum hose a convoluted affair that goes through the linkage plate. Are you 110% sure there are no leaks in there?

The other place to check is the base gaskets as Dave suggested. It's unlikely that you managed to force the keystone rings inupside down, but that would hurt running at any speed.

If I were closer, I'd come over and give you a hand.

[H2RICK]

If I were closer, I'd come over and give you a hand.

Me, too.....
We'd have that sucker fixed in no time flat with 3 brains like ours on the job.
Of course, talk is cheap....for me.....especially at a distance.....

[ja-moo]

Have you done a pressure/vacuum test? A crank seal could be expanding when hot letting in air. Is there oil behind the points plate? You might even run some propane into the crankcase with the motor running to see if it changes the idle. (be careful!)