Tweaked my SUs according to previous suggestion and they work well. Thanks all!!

Fall check is good. Butterflies centered up nicely and close freely. Idle screw is turned in sightly over 1 full turn. Each jet is adjusted about 11 flats.

New issue now. After running the car for 10 of 15 minutes and shutting in off for 20 to 30 minutes, I find that on restart. It starts right up but races for a few moments. If I switched the ignition off and back on 3 of 4 times the engine rolls back to a normal idle. Sort of like there is some fuel pooling in the intake manifold after shutdown that gets burnt on startup.

If I let the car sit for an hour of more, no racing willl occur.

Float level is correct and I am using GrossJets. I use Marvel Mystery Oil in the dashpots.

Is it possible that the oil is too thin and providing insufficient damping?

Or:

Is it possible for fuel to be admitted through the carb after shutdown due to engine heat?

Your thoughts?

Mine does the same thing, but only on the hottest days of summer, and cenrtaily not in spring or now, and I know the car is not running rich -- nice light tan plugs. I'll just live with it till I can't stand it any longer.
Bob S.

This is not uncommon to a set of SU's running a little rich. Once the carbs, and not jus the engine warms up the fuel level rises a bit and runs a tad too rich. you reall need to do the tune when the engine is and carbs are warm but not hot.
First question, which needles are you using?
Is the engine/airflow modified?
does the carbs have lift pins?

My first assumption is that the carb jets are set a little too low (rich). 11 flats is too low even for a modified engine, depending on which needles you're using.

The way to do this is to lift the pistons, one at a time. and have the idle rise just about 50 rpm while idling at ~650-700 rpm. The rpm rise should last for 2-3 sec then settle back to the set idle. If the rise is greater or longer, the carb is running too rich. If the rise is not noticable, or drops, the carb is too lean. Back off the 11 flat position until you have no change when lifting the piston of the oppposite carb. Do this in small changes for each carb until both have the same small rpm rise and fall.
This is somewhere around 8-9 flats, not 11 flats. When youre done, raise the idle to 900 rpm and turn each jet nut 1/2 flat lower (back off).
--
'89 245 Sportwagon, '04 V70 2.5T Sportwagon

Needles are SMs.

Engine is a stock B18 and I do have lift pins.

Idle is about 900 and right now I do get the right rpm increase. So I guess I need to run the tuning drill again.

No everyone agrees, but my take is that racing/high idle can only be caused by unwanted air, not fuel (with some mild exceptions if the motor is basically mistuned).

Got a PCV valve that might be hanging open, or something like that?

Phil;

I totally agree with you about false air, but need to correct you on your statement about the PCV valve...

The PCV valve is ALWAYS open allowing Positive Crankcase Ventilation, hence the name, but its flow is fairly limited so it doesn't add up to much of a "vacuum leak" ...the ONLY time it closes is if there is positive pressure in the intake manifold (backfire)...it would be waaaay bad to allow the flamefront (and much moreso the pressure) into the crankcase.

Cheers

Ron,

We're both right.

The PCV valve is always open a little bit except when closed by positive pressure in the intake (backfire, as you said). But it's not an on-off affair -- at high vacuum (idle / off throttle), it's very restricted, allowing just a slight bit of crankcase air through (blow-by is minimal under these conditions, so there's not much need to vent the crankcase aggressively). This should have almost no affect on idle mixture or speed.

Under low vacuum (full throttle / maximum blow-by) it opens wide, but there's still very little flow through it simply because the vacuum is low, so again there's negligible impact on tuning.

So, I don't know that this is a common failure mode, but if the valve were to somehow stick in the wide-open position under high vacuum conditions, you'd have significant false air through the crankcase.

Yeah.... I found out about that when I forgot to reconnect the PCV after setting the valve lash. Scared hell outta me. PCV is at least 18 years old and could be gummy for sure. Will check that.


thanks