61 with autolite 4100 high idle for no apparent reason all settings are correct. | Ford Thunderbird forum club group 1955-2005 models

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61 with autolite 4100 high idle for no apparent reason all settings are correct.

paul4913

paul4913

Gold Member
Reaction score
6
Thunderbird Year
1961
Hi, I have a 1961 Thunderbird with an excessive high idle both cold and hot. All settings are correct, neither the fast idle or hot idle screws are engaged. The throttle is all the way closed, there are no apparent vacuum leaks. The vacuum gauge shows 19" steady when warm. It idleing so high that when you turn the key off, it diesels (keeps running briefly with the key off). Any ideas? thanks

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paul4913 said:
Hi, I have a 1961 Thunderbird with an excessive high idle both cold and hot. All settings are correct, neither the fast idle or hot idle screws are engaged. The throttle is all the way closed, there are no apparent vacuum leaks. The vacuum gauge shows 19" steady when warm. It idleing so high that when you turn the key off, it diesels (keeps running briefly with the key off). Any ideas? thanks
Click to expand...
What procedure did you use to adjust the timing? And does the vacuum advance work?
 
Thanks for you prompt reply. I disconnected the linkage and there was no change. I have not checked the timing or vacuum advance. I thought I should solve one problem at a time. The carburetor obviously needed to be rebuilt, so I thought that should be first. Just curious, how could timing and vacuum advance cause a high idle. I'm not a mechanic, so I don't know. Thanks for your help.
 
paul4913 said:
Hi, I have a 1961 Thunderbird with an excessive high idle both cold and hot. All settings are correct, neither the fast idle or hot idle screws are engaged. The throttle is all the way closed, there are no apparent vacuum leaks. The vacuum gauge shows 19" steady when warm. It idleing so high that when you turn the key off, it diesels (keeps running briefly with the key off). Any ideas? thanks
Click to expand...

paul4913 said:
Hi, I have a 1961 Thunderbird with an excessive high idle both cold and hot. All settings are correct, neither the fast idle or hot idle screws are engaged. The throttle is all the way closed, there are no apparent vacuum leaks. The vacuum gauge shows 19" steady when warm. It idleing so high that when you turn the key off, it diesels (keeps running briefly with the key off). Any ideas? thanks
Click to expand...
Hi,
Make sure that your secondary butterflies are completely closed. A quick way to check is when your engine is idling, stuff a rag in the secondaries. If the engine slows down or stalls, you have found the problem.
Good Luck,
 
I think what azfamily is trying to tell you above is that if your timing is too advanced the idle will be increased; possibly to the point that the carburetor adjustment screws are ineffective...

If you've ever twisted a distributor around you'll see the effect, you can retard the timing enough to stall the car and advance it enough to have a very fast idle; without changing anything else...
 
Go on YouTube/-Autolite 4100-How to adjust the choke (5/17/2017 by TechicalLee)
It shows a piston which can get gummed up. Use extreme care when cleaning the small parts may break. Watch the entire video, you may need to make all the adjustment he makes. Good luck
 
Heat said:
Go on YouTube/-Autolite 4100-How to adjust the choke (5/17/2017 by TechicalLee)
It shows a piston which can get gummed up. Use extreme care when cleaning the small parts may break. Watch the entire video, you may need to make all the adjustment he makes. Good luck
Click to expand...
Thanks for the reply. The carburetor version I have does not have the piston, it has a different type of choke. The choke is working correctly, closed when cold open when hot.
 
Douglemmo said:
Hi,
Make sure that your secondary butterflies are completely closed. A quick way to check is when your engine is idling, stuff a rag in the secondaries. If the engine slows down or stalls, you have found the problem.
Good Luck,
Click to expand...
I tried your suggestion and the engine stopped completely. I removed the carburetor and rechecked the secondary throttle plates. They were open very slightly because of the secondary throttle plate adjustment required by the shop manual. There is a very small set screw that when adjusted properly, opens the secondary plates just a tiny amount. I checked the adjustment, it was correct. For testing I removed the adjustment and the throttle plates are now completely closed.
 
Frankie the Fink said:
I think what azfamily is trying to tell you above is that if your timing is too advanced the idle will be increased; possibly to the point that the carburetor adjustment screws are ineffective...

If you've ever twisted a distributor around you'll see the effect, you can retard the timing enough to stall the car and advance it enough to have a very fast idle; without changing anything else...
Click to expand...
Thanks for your reply. After making sure the secondary throttle plates we completely closed I bought a digital timing light with a rpm reading. With the fast and hot idle screws still backed out, the rpm was 1780 in park. At idle when at normal temperature in drive the idle was 1200 it is supposed to be 450. I disconnected and capped off the vacuum advance and checked the timing. It was 22 book says 6. I adjusted the timing to 6 and the rpm dropped to 780, much better but still too high. The shop manual says the the rpm has to be below 500 to eliminate the mechanical advance. The book says the minimum timing adjustment is 2. I tried it and the engine started running rough and the rpm only dropped to 740. The choke is working correctly. Any other ideas
 
paul4913 said:
Thanks for your reply. After making sure the secondary throttle plates we completely closed I bought a digital timing light with a rpm reading. With the fast and hot idle screws still backed out, the rpm was 1780 in park. At idle when at normal temperature in drive the idle was 1200 it is supposed to be 450. I disconnected and capped off the vacuum advance and checked the timing. It was 22 book says 6. I adjusted the timing to 6 and the rpm dropped to 780, much better but still too high. The shop manual says the the rpm has to be below 500 to eliminate the mechanical advance. The book says the minimum timing adjustment is 2. I tried it and the engine started running rough and the rpm only dropped to 740. The choke is working correctly. Any other ideas
Click to expand...

Today I reconnected the vacuum advance line. The rpm in park jumped to 1850 and the timing went to 14. I set the timing to 2 in hopes the idle would be low enough to not diesel. I even put it in reverse to further lower the rpm, no luck it dieseled anyway. Looks like more than one problem. Since the car has 85000 miles and has engine and trans leaks in areas I can't fix, I think a rebuild is in order. There is a restoration garage locally that has an excellent reputation called Fantom works, I'll up save some money and take it there. Thanks for all the replies
 
FantomWorks is run by Dan Short, I visited it several times and graduated from Old Dominion University down the street. Dan's rep is good or bad depending on who you talk to.. If you set the static timing to spec (vacuum advance plugged) and can't get the idle down then something is amiss. I will say that sometimes 60 year old engines don't work exactly as the factory spec'ed them. My 63 Corvette is supposed to idle at 500 RPM but it's "happy place" is 650....
 
paul4913 said:
I tried your suggestion and the engine stopped completely. I removed the carburetor and rechecked the secondary throttle plates. They were open very slightly because of the secondary throttle plate adjustment required by the shop manual. There is a very small set screw that when adjusted properly, opens the secondary plates just a tiny amount. I checked the adjustment, it was correct. For testing I removed the adjustment and the throttle plates are now completely closed.
Click to expand...
The fact that your engine stopped completely when you plugged up the secondary butterflies tells me that gas is getting into your engine thus causing the high RPM. Have you had the carb rebuilt by an experienced Autolite rebuilder. I still believe you have a carb problem. Maybe you shold have adjusted the set screw for the secondaries below the factory setting. It can be done with the carb on the engine.
 
Would this not be a vaccum leak sucking air in causing the high rpm? Could be one of the many vacuum lines / brake booster etc - have you isolated all those to see if the engine slows?
 
I figured out what the problem was. There is a check ball and weight in the idle and main fuel passageway to limit fuel during idle. The check ball in the rebuild kit was the wrong size and allowing too much fuel for idle. I put the original check ball back in and it is now idling just as it should. Thanks for all the help.
 
I have always wondered what exactly that check ball did. Thanks for the update. It had to be extra gas getting into that carburetor somehow. Sporting on billionaire
 
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