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Unread 01-09-2010, 12:01 PM   #1
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1984 CJ7 
Join Date: Oct 2009
Location: Oklahoma
Posts: 96
Motorcraft First Start Idle Help

ok i did the nutter bypass and motorcraft carb (manual choke) upgrade and my jeep runs amazing after it warms up having to hold my foot on the gas for about 5-8mins @ about 1500rpms, i was wondering isnt the fast idle suppose to do this for me, and if so how do i properly adjust the fast idle?

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Unread 01-09-2010, 01:29 PM   #2
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2000 XJ Cherokee 
Join Date: Apr 2002
Location: out in the garage - Minneapolis, Minnesota
Posts: 22,595
Is the choke hooked up ? Setting the choke partly or fully open should make the engine run faster until it is warmed up and then you set the choke to off.

When you pull the choke knob out, you cause a small "plate"to close over the opening of the carb. This has the effect of restricting the air entering the carb, which makes the air/fuel mixture richer (more fuel). A cold engine needs a richer air/fuel mixture to start and run. Also, when the choke plate is closed, a cam in the carburetor's throttle linkage acts to open the throttle plates slightly so the engine idle speed will be increased. So as the more choke is applied, the engine rpm will increase in unison.

1. Obviously, the colder the engine temperature, the more choke application and resulting richer air/fuel mixture will be needed (pull the knob farther out). A warm engine restart usually requires no choke at all. A cold engine on a warm day will likely need just a little choke, but not for very long.

2. Depending on how it's adjusted, pulling the choke knob out too far will likely prevent the engine from starting altogether, as this prevents the engine from getting enough air.

3. Once the engine has started, as it warms the engine rpm will continue to increase. The choke is pushed in in little increments to offset and reduce the idle rpm until it's no longer needed.

4. The usual goal is to get the choke all the way off as soon as practical to avoid wasting gas, creating excess pollution and causing possibly accelerated cylinder wall wear from the effect of the extra fuel washing the oil away. As soon as the engine is running smooth enough to idle normally, the chokes needs to be off. The choke is not a throttle lock and really shouldn't be use to increase the and hold the engine rpm once the engine doesn't need the richer air/fuel mixture.

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Unread 01-09-2010, 01:46 PM   #3
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1947 CJ2A 
Join Date: Apr 2008
Location: wv
Posts: 82
My son and I did the Nutter and Motorcraft carb swap and added a HCI dizzy. I fooled with the throttle and choke while he cranked. Once it started he held the revs up at the carb linkage while I twisted the distributor untill it would idle. Then we broke out the timing light and got it timed. I went with manual choke. Check to see if you have good vacuum at the distributor.
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