7RT Carby Running Rich
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5th Wheeling
Joined: Oct 2021
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7RT Carby Running Rich
Folks,
Our '51 C1BA Flathead in our M47 pickup seems to be running too rich with a very black sooty tail pipe as evidence. It has a 7RT carby. Where should I first look to find the problem? The ignition timing has been reset with the distributor vacuum line disconnected. Engine starts well when cold or hot with 17 -19 of vacuum at the wiper vacuum connection when hot. It has a slightly rough idle and all the tweeking of the idle screws wont smooth it out to my liking.
Thanks for any replies.
Our '51 C1BA Flathead in our M47 pickup seems to be running too rich with a very black sooty tail pipe as evidence. It has a 7RT carby. Where should I first look to find the problem? The ignition timing has been reset with the distributor vacuum line disconnected. Engine starts well when cold or hot with 17 -19 of vacuum at the wiper vacuum connection when hot. It has a slightly rough idle and all the tweeking of the idle screws wont smooth it out to my liking.
Thanks for any replies.
Parts Nerd Extraordinaire
Joined: Sep 2010
Posts: 4,367
Likes: 1,785
From: Western NY
Leaking power valve is a common issue. Be sure to get the proper style power valve and nylon gasket as discussed here:
https://www.ford-trucks.com/forums/1...l#post19202480
https://www.ford-trucks.com/forums/1...l#post19202480
Fleet Mechanic
Joined: Jun 2020
Posts: 1,907
Likes: 763
From: Hillsborough NJ
I’m pretty new to these engines, only 2 years since I bought mine, but I’ve noticed a common thread with flattys I’ve seen at shows, black sooty tailpipe and slightly rough idle.
Mine is pretty much the same. It starts, runs, cruises, just fine. New carb, points, condenser, plug wires, plugs. Adjusted timing, dwell, spark advance operates to spec, idle mixture, good compression in all 8, vacuum 18-20”. Guess what, slightly rough idle, sooty tailpipe.
I think (in my very novice opinion) that plug condition tells you more than tailpipe. Remember these vehicles don’t have any pollution control at all.
Then again, I could be all wrong.
Mine is pretty much the same. It starts, runs, cruises, just fine. New carb, points, condenser, plug wires, plugs. Adjusted timing, dwell, spark advance operates to spec, idle mixture, good compression in all 8, vacuum 18-20”. Guess what, slightly rough idle, sooty tailpipe.
I think (in my very novice opinion) that plug condition tells you more than tailpipe. Remember these vehicles don’t have any pollution control at all.
Then again, I could be all wrong.
Thread Starter
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5th Wheeling
Joined: Oct 2021
Posts: 26
Likes: 0
I’m pretty new to these engines, only 2 years since I bought mine, but I’ve noticed a common thread with flattys I’ve seen at shows, black sooty tailpipe and slightly rough idle.
Mine is pretty much the same. It starts, runs, cruises, just fine. New carb, points, condenser, plug wires, plugs. Adjusted timing, dwell, spark advance operates to spec, idle mixture, good compression in all 8, vacuum 18-20”. Guess what, slightly rough idle, sooty tailpipe.
I think (in my very novice opinion) that plug condition tells you more than tailpipe. Remember these vehicles don’t have any pollution control at all.
Then again, I could be all wrong.
Mine is pretty much the same. It starts, runs, cruises, just fine. New carb, points, condenser, plug wires, plugs. Adjusted timing, dwell, spark advance operates to spec, idle mixture, good compression in all 8, vacuum 18-20”. Guess what, slightly rough idle, sooty tailpipe.
I think (in my very novice opinion) that plug condition tells you more than tailpipe. Remember these vehicles don’t have any pollution control at all.
Then again, I could be all wrong.
Thread Starter
|
5th Wheeling
Joined: Oct 2021
Posts: 26
Likes: 0
Leaking power valve is a common issue. Be sure to get the proper style power valve and nylon gasket as discussed here:
https://www.ford-trucks.com/forums/1...l#post19202480
https://www.ford-trucks.com/forums/1...l#post19202480
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Cargo Master
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That horse hair element type needs to be cleaned in solvent periodically.
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5th Wheeling
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BTW should there be idle sensitivity with the idle screws too far out like there is when idle screws are too far in?
Fleet Owner
Joined: Jul 2004
Posts: 27,294
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From: NM
Usually if the screws are too far out, it will begin to "roll", cycling up and down. I'd try them as far in as you can go and still get a reasonable idle. It may require resetting the throttle a little.
Fleet Mechanic
Joined: Jun 2020
Posts: 1,907
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From: Hillsborough NJ
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5th Wheeling
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Tuned
Joined: Aug 2011
Posts: 261
Likes: 28
You might want to check your float height if it’s to high the gas will percolate up and out of the venturis causing an uneven, rough idle. Had same issue with my 94 carb, lowered the float and problem went away. I believe the final setting on my float was about 1.5” - 1.15/32 “.
Fleet Mechanic
Joined: Jun 2020
Posts: 1,907
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From: Hillsborough NJ
I am beginning to think that my carburation is not healthy because if I wind both screws out to the last thread I can't get what you describe a "roll", it just stays the same. But winding them too far in from 1-1/2 turns to 0 definitely has a huge influence on engine idle to the point where it will stop.
If you’re still not satisfied, either send it out to cowboy John, Charlie NY, or buy a repop from Chuck’s Trucks. I’m running the repop with the rebuild from Charlie NY in my toolbox as a spare.
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