Carb adjustment after changes

[Jim Booth]

I rebuilt the carb and put an adjustable main jet in. Also added the quick connect throttle cable fitting. I think I got the cable length adjusted back to where it was so the control is about where it was before. Now comes getting the main and idle jets right. I started with the main opened 1 1/2 turns I thought it would idle as before since I didn't touch the idle screw but it dies. I'm still out of the water. What's the method to get these set up before I launch ?

[Dave Neptune]

How did you "rebuild the carb" without disassembling? You could of easily blown something through the main jet and it could of lodged in the idle passages which are much smaller.
Is the throttle arm against the "stop" IER the idle speed set screw?

Dave Neptune

[capnward]

1 and 1/2 turns out from the seat on the main jet is correct for an initial setting. Turn the idle screw in until it seats, then 1 turn out. Turning the main jet out makes it richer, turning the idle screw out makes it leaner. I would guess that if it dies, it is too lean. I may be wrong. It may be dying for other reasons. When you had the carb apart, did you run a thin wire around in the idle jet, and the idle ports?

[Jim Booth]

I had the carb apart to flatten the halves because it was leaking gas last season. I sanded both sides with 600 grit on a sheet of plate glass and lots of lube. Along the way, I blasted carb cleaner through all the passages, so it wasn't a complete rebuild. But the engine ran and idled fine last season.

So I guess I should leave the main adjustment at 1 1/2 turns out, then work on the idle mixture screw as I reduce rpm.

When the throttle control is all the way back, the throttle arm is on the stop.

[Dave Neptune]

Jim, the sanding dust could easily plug up an idle passage or an idle jet. If you do not get any response from the idle air adjusting screw, get the idle passages blown clear for sure. The idle jet is around .018", very small. You could of blown other KRUD into them by not removing them.

Dave Neptune

[sastanley]

Dave, is there any danger in removing the idle mixture adjustment screw completely for cleaning and blowing out that area? I guess the only issue is to mind the spring, as you unscrew it, but that is why I am asking?

[Dave Neptune]

Shawn, it's no problem. By the time your unscrewed there is no contact with the spring so no "sproing" resulting in verbal abuse practice while searching.
You can blow into it and have no issues unless you go nuts with the air. The screws passage is upstream of the jet and E-well that feeds it so it is possible to blow out the Idle Jet but not the idle ports as the Idle Jet restricts the flow in that direction.

Dave Neptune

[campbdon]

Hi, I hope it is correct form to piggyback off this thread for a related question.
My symptom is dry sooty plugs (all 4). The engine idles reliably at min throttle at 800RPM (approx) without stalling, and accelerates "explosively" when throttled up sharply. From other threads I gather I should look at cruising at higher RPM than is customary for me (ie: 2000 rather than 1500 RPM), and/or the mix is too rich so should lean out a bit on the main jet (It's at 1.5 turns backed off I believe). I don't have the adjustable but can do that manually. Any other advice please and thanks?
DonC

[Dave Neptune]

More info

Don, on the stock late model carb there is only an "idle AIR adjustment needle" that adjusts the air flow to the jet for mixing. And unless you or someone has added the "adjustable main jet" there is no real adjustment available or necessary other than idle.
If your plugs are dry and sooty you are way to rich somewhere. Since you have good response when revving we can set the exhaust aside for now.

First be sure the choke is all the way backed off VIDSUALLY and remove the flame arrestor. Now start and look into the carb throat while running and see if you see any fuel puddling in the throat of the carb. If so it is probably something to do with the floats.

Did you do any carb work? If so what did you do? Is fuel leaking anywhere?

And yes it is usually better to start a new thread to avoid confusion on your part and for those trying to diagnose the problem at hand.

Dave Neptune

[roadnsky]

So I guess I should leave the main adjustment at 1 1/2 turns out, then work on the idle mixture screw as I reduce rpm.

Jim-
Attached are the instructions that come with the Adj jet.
I assume you followed them?

Note in the instructions the caution about the internal washer. (2nd paragraph)
Could that be your issue?

[JOHN COOKSON]

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ex TRUE GRIT