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Carb adjustment with Air Conditioning
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Turborail
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Joined: June 12, 2005
Posts: 5
Location: West Valley City Utah USA
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PostPosted: Sat Oct 04, 2008 7:10 am    Post subject: Carb adjustment with Air Conditioning Reply with quote

A friend of mine in Singapore is having an issue with this car stalling while the A/C is on. Any help would be greatly appreciated:

I've been playing hell with the carb settings since day 0. I can set up timing and everything right (32deg BTDC @ 3500 RPM on my 009) and adjust the idle and fuel mixture settings properly, but once I turn on the A/C, the idle RPMs will dip to below 800RPM, causing the engine to stall. Now if I bump the RPM up using the bypass screw (I have a H30/31 carb). I can get the engine to idle at approx 850RPMs. This is ok, until I go for a long drive, everything heats up to proper temps and the A/C is running. If I let the accelerator off suddenly at a stop light for instance, the RPMs will drop below 800RPMs before picking up again, sometimes resulting in a stall. If I turn the A/C off, the whole thing works properly. I'm guessing during the short time when the throttle is suddenly closed. The fuel/air mixture suddenly becomes too rich because of my long intake manifold. The bypass screw is pretty much at it's limit, if I try to increase the idle RPM with the A/C running, the O ring will run out of carb to seat in and cause air in-leakage. I'm gonna try bumping my advance up a little (I'm running 92 octane which is like the lowest octane I can find locally) and see if it helps.
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li_gangyi
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Joined: August 15, 2008
Posts: 455
Location: Singapore
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PostPosted: Sat Oct 04, 2008 7:45 am    Post subject: Reply with quote

That'd be me... Embarassed

I was thinking of putting a little microcontroller hooked up to the low side of the ignition coil so the clutch will only kick in at say above 1000 RPMs. Don't know if that'll result in a notceable stumble though...

I've "spoken" to keifernet over PM about it. He's working on a throttle positioner thingy modified with a little solenoid that'll move the throttle slightly when the clutch kicks in. I haven't got the throttle arm on my H30/31 so that's a little hard to implement (I could possibly get like a parts carburetor and take the throttle arm off that I suppose...). He also suggested I could try adjusting the fast idle screw a little to bump the idle up with the throttle plate.

I've also seen some hack jobs where the spring perch in the distributor is bent so the advance range is reduced. At idle the advance was sitting at 16deg BTDC and it goes to 35deg BTDC at 3500RPMs. I suppose that'll make the engine run a tad warmer.
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