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11-22-2019, 11:55 AM | #1 |
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1940 stock flathead idle "dip" when stopping at a traffic light
I have a stock '40 that runs well but tends to have a rather large temporary RPM "dip" when returning to idle to the point it feels like it's going to stall out.
After a second or so it returns to a normal speed but I tend to pull the throttle knob to get it past this point for fear of having to restart in front of traffic. Does anyone have any ideas as to what this could be? The float bowl screws, baseplate nuts, etc. all seem tight. Any advice is appreciated-thanks. |
11-22-2019, 12:04 PM | #2 |
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Re: 1940 stock flathead idle "dip" when stopping at a traffic light
It may be running slightly lean, or the float level might be a little low. As you stop, the fuel surges forward in the float bowl, away from the metering area. This sudden leaning out gives you the dip you are describing.
That's my guess. Mart. |
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11-22-2019, 01:12 PM | #3 |
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Re: 1940 stock flathead idle "dip" when stopping at a traffic light
Your engine idle speed may be too low. Increase it and see if it helps. Also be sure your clutch pedal free play is correct so the clutch disc is completely released. As the clutch ages, the free play decreases, and any drag can affect the engine idle.
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11-24-2019, 05:49 PM | #4 |
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Re: 1940 stock flathead idle "dip" when stopping at a traffic light
Check the throttle return spring. It may be on the bellcrank.
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04-15-2020, 02:09 PM | #5 |
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Re: 1940 stock flathead idle "dip" when stopping at a traffic light
Thanks for the great tips, to close this thread I simply turned the curb idle screw up about a 1/4 turn. Believe it or not, 1/2 turn was too much and resulted in a high idle. Now that the weather has warmed up to the 70s it's back to it's old tricks again with the idle dip, almost to the extent that it seems to droop way low and/or shudder a bit so not sure what that means; maybe the float level is a bit low.
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04-15-2020, 10:37 PM | #6 |
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Re: 1940 stock flathead idle "dip" when stopping at a traffic light
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Owner/Operator of 'Jailbar Ranch' on the side of Mt. Pickett. Current stable consists of 1946 1/2 ton pickup turned woodie wagon with FH V8, 1947 Tonner Pickup (red) mostly stock with exception of a cummins 6at turbo diesel, 1946 Tonner Pickup (green) with 226 cu in 6 cyl flathead, 1979 Toyota landcruiser wagon, completely encased in 1947 Ford Jailbar sheet metal. Ok, cornbinder rear fenders..... 'Rusty ol' floorboards, hot on their feet' (Alan Jackson) |
04-16-2020, 12:43 AM | #7 |
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Re: 1940 stock flathead idle "dip" when stopping at a traffic light
Just a wild guess... Distributor advance plate sticking, unable to normalize immediately on idle down.
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04-16-2020, 12:58 AM | #8 |
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Re: 1940 stock flathead idle "dip" when stopping at a traffic light
I'm in the same boat of increasing the cold idle speed. If you have good compression. Lowering the idle speed to get that lump sound is interesting and sounds great.
Pulling the choke usually means a lean condition. Throttle rod might be linkage. . Last edited by Tinker; 04-16-2020 at 01:10 AM. |
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