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weber 38/38 idle issue

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tuning these things is a pretty beaten topic, but i can't find an answer to my issue. carb has always been an issue and running rich since i bough the car, bought a gasket kit for the carb and did that, new solenoid, and new main jets. but i can't get it to run off the idle jets alone(idle set screw is too far in, roughly 3 turns, and it runs obscenely rich, about 10.5 afr). when it is running, you can turn the idle mixture screws all you want, and nothing changes.

given the previous state of tune the car was in when i bought it and pulled it apart, i don't think it ever ran off the idle jets. the previous solenoid wasn't even wired into the car. and when it was connected, didn't function.

ive tried setting the idle mixture screws at 1/2 turn out, and going all the way out to 3 turns (in 1/2 turn increments) and no luck. i cant back the idle set screw out without it stalling.

idle jet: 60

air: 185

main: 135

thoughts??

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i'm running a .050 idle jet, mine idles fine.

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i'm running a .050 idle jet, mine idles fine.

i think thats my problem. i tinkered some more, and its now running well with the mixture screws only a 1/4 turn out. ill have to get some smaller idle jets and start again.

that leads to a second question though now that it will run. im running what i think is a bmw sport 300 cam (although not for sure). is that duration long enough to make my air/fuel ratio go wonky when i stomp on it? the gauge goes very rich when i stomp on it (and stays there until i let go, so it should be the accelerator pump, as that is only a temporary condition), but a 135 shouldn't be to big?

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Guest Anonymous

webber carb is very sensitive to float level, check and tinker here before wasting money on jets

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webber carb is very sensitive to float level, check and tinker here before wasting money on jets

checked it when i did the gaskets, it did need a slight adjustment with the new needle valve, but not much.

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Patrick of Midnight Motorsports did a wide band tune on my 38/38. Stock, healthy engine with strong compression; tii distributor and electronic ignition; and tii exhaust manifold with stock exhaust. Here's the final settings, and the car runs perfectly:

idles: 60

mains: 140

air correctors: 175

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I thought i'd add my current settings to the conversation.

Emulsion tube: F-50

air corrector jet: 185

main jet: 142

accelerator pump jet: 70

idle jet: 45

i've gone from a 60 idle jet to my current 45. i'm still running rich.

I rebuilt the carb and tried to set the float level per the instructions, as close as possible.

i've got 175 psi across all four cylinders

292 Schrick cam

rebuilt vac-advance distributor set to 10 BTDC at around 1000RPM

my idle speed is around 950-1000 RPM

my air mixture screws are out about 1/2-3/4 turn IIRC

i notice that after freeway driving when i slow down to city driving the idle is more rough in 1st and 2nd gear. this is more noticeable after the engine is thoroughly warmed up.

i do try to set the carb when the engine is warmed up, too.

there is no dead spot when going from 2500 to 3000RPM

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Jerry/guys,

My prior '74 2002 had the motor rebuilt with a 292 cam and 9.5:1, my brother Marty and myself put on a 38/38 and all we fumbled with were the idle jets, kept everything else (jets, etc.. ) as sent from the box; changed idle jets from what the 38/38 came with, 42's, went to 50; had a pair of 60's as well from a jet kit and tried those but went back to 50; had a bit of a lopey idle but I was content with it, 900 rpm's

Tim

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Correction, stock idle jets for the 38/38 are 45's, went to 55's with the '74 2002 I had with the 292 cam and 9.5:1

Tim

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