Fuel System: CARB Adjustment

[aftontrix]

I have my 1957 289 running great but it idles rough at 700 RPM. I have replaced points, condenser, distributor and rotary caps, spark plugs and wires, fuel pump and had the Stromberg WW rebuilt by TBOW.

I bought a dwell meter and set the dwell. I guess the next thing is to adjust the carb. I have read that I should turn the needles in until they affect the idle and then back off one turn. Is this correct? I assume the two needles shown in the attached photo of my carb are the ones referred to. Is this correct? Thanks

[E. Davis]

If you replaced the points it would be a good idea to recheck the timing. A vacuum guage is handy when fine tuning the carb. I always try to keep the needle on the guage at the steadiest and highest reading. Good luck.

[Ron Dame]

Yes those are the two screws. It could be that you need to turn them out as well, but before you go there and besides what you have done and what E. Davis suggested, have you adjusted the valve clearance? I agree, a vacuum gauge is a wonderful diagnostic tool, and it's fairly cheap, although maybe not easy to find. Check this site for how to read the gauge http://www.secondchancegarage.com/public/186.cfm

I have my 1957 289 running great but it idles rough at 700 RPM. I have replaced points, condenser, distributor and rotary caps, spark plugs and wires, fuel pump and had the Stromberg WW rebuilt by TBOW.

I bought a dwell meter and set the dwell. I guess the next thing is to adjust the carb. I have read that I should turn the needles in until they affect the idle and then back off one turn. Is this correct? I assume the two needles shown in the attached photo of my carb are the ones referred to. Is this correct? Thanks

[StudeRich]

It may very well have a Vacuum leak, spray some starting fluid, WD40 etc. around the Intake Ports of the Intake Manifold and see if the Engine speed picks up.

Also check the vacuum Advance Tube, Carb. Base and Mounting Gasket for leaks.

[Tom Bredehoft]

My experience when setting timing (for what it's worth) with a vacuum gage.
I got the engine warm, disconnected the vacuum line to the distributor and plugged the line. I connected the vacuum gage to the port on the base, (could be for a PCV line) My carb is a CWFB, not a Stromberg, and the distributor vacuum line is ported, ie., when the throttle is closed, so is the vacuum line.
I loosened the screw holding the distributor and with the engine at low idle adjusted the timing until I got the highest vacuum reading, about 16 inches.
At this point I put the timing light on and found that it was timed about 15 degrees advanced. I backed it down to about 6 or 7 deg advanced and the vacuum stayed up there.
The engine runs smoothly, the only problem I have is when it drops out of low, at 45 MPH or so, (under heavy throttle) it goes straight to drive and wants to bog down under full throttle.

[E. Davis]

Tom: I too timed my 289 with a vacuum guage. I started by setting it at the factory recommended mark with the timing light. I then hooked up the vacuum guage and ajusted the distributor until I reached the highest reading on the guage and retarded and advanced the distributor slightly until I heard and felt the "sweet spot". At that point I checked the timing marks with the light and it was at 10 degrees advanced. It starts on about two cranks and runs great through the entire acceleration cycle from idle to wide open without any gliches. I might also mention it has a mopar electronic ignition which may require a different timing setting than the old factory points system.

[Flashback]

I think everyone has answered everything except your question. What works well for me is turning the adjustment all the way in( DON'T FORCE) till they stop, Turn out two and one half turns. Then start engine. (It should be already at operating temp.) Turn in, one at a time till engine gets noticibly rough, then turn out till the engine smooths out (purrs like a kitten) . Do other the same.

[StudeRich]

/Cut/

That could be because not many of us expect those idle richness screws to do much. It is not likely they will change anything, it is more likely that there are other issues.

[Mike Van Veghten]

IF...the carburetor is in good condition...the Mixture screws WILL.......have an effect on the way the engine runs.
Now of there's a lot of slop in the throttle shafts, the butterflys don't fit correctly, etc., then yea...the mixture screws might not do much.

As for things to check -
1. The carb. is adjusted correctly.
2. The points are in good shape and adjusted correctly. The condensor is working correctly. The timing is somewhere close.
3. When was the last time the valves were adjusted...? Lightly misadjusted valve WILL make an engine run rough at idle.
4. Vacuum leak somewhere.

Mike

[52hawk]

Double check that no plug wires are crossed-especially #5&7. I say 5&7 because I've seen a few engines sound OK,except at idle,with those wires crossed.[because of the firing order].Also,wires 5&7 should always be kept seperated from each other.

[tbirdtbird]

some good suggestions here.
wonder about a compression test...? possible weak cyl? It is an easy test to do

[DEEPNHOCK]

(1) Dwell first.
(Set to low dwell number. Rubbing block wears faster than point surface, so the dwell will 'rise' through the acceptable range as the rubbing block wears)
(Dwell increases as gap decreases...)
(2) Then timing.
(3) Then carb adj.

Dwell affects the timing.
Timing affects the idle.

Always do that in that sequence.
HTIH
Jeff

[woodysrods]

I have never been good with carbs. but it is so nice to be able to read this information on the forum.
If you follow all of these tips I am sure you will be a ble to make her "purrr like a kitten".
Good Roads
Brian