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Hi All,
I have been lucking for some time and I must say I have found most answers to all my questions! Saying that here is my problem..... I purchased a 1966 442 convertible with tri-power, TH400 and a MSD EFI ignition over the summer, drover it all summer with relatively no problems. at the end of the summer I started having idle problems....in park up to temp the idle is roughly 800 rpm but when I am driving and coming to a stop the idle/rpm starts going up so much that when i come to a complete stop it wants to spin the tires, if I put it in neutral it drops back down to roughly 800RPM.....another scenario... if I am backing into my garage and I need to pull forward and backwards, its fine in revers but when I put in drive to pull forward it wants to take of like a rocket.
So thinking it could be a carburetor issue and that the carbs looked like they needed a good overhaul anyway I had then rebuilt. I got them installed and setup by a rebuttable local shop and the results where amazing, much more responsive and no hesitation. BUT still have this high idle problem when in drive and at a very low speed to a stop. The mechanic thought maybe it could be the vacuum advance so he disconnected it and checked the timing and vacuum with everything where it is suppose to be (according to him). Has anyone experienced this type of thing? could it be a transmission issue? linkage issue?
Check your motor mounts. Since you have a hard linkage to the carb, if the driver side mount is broken the engine will torque upwards and pull on the throttle.
I'd check the main rod on your throttle linkage. Yours looks to have been welded together & it might be too tight & when you put it in drive the "torque" in the drive train might be causing the center carb to be held open more. Are your motor mounts OK??? Can you have someone stand beside the car(so they don't get run over) & watch what the center carb does when you put it in drive???
I'd check the main rod on your throttle linkage. Yours looks to have been welded together & it might be too tight & when you put it in drive the "torque" in the drive train might be causing the center carb to be held open more. Are your motor mounts OK??? Can you have someone stand beside the car(so they don't get run over) & watch what the center carb does when you put it in drive???
Thanks Rob.. We did that yesterday and didnt see anything change in the linkage when I put it in drive. I am going to check the motor mounts tonight to see if that could be the culprit. its really strange..if I am in park and put it in drive the RPM doesnt change that much its when i am moving and come to a stop, thats when RPMs jump up.
2 things I'd check, (1) springs in the distributor may be too light and are not returning weights at idle, (2) disconnect the outer carb linkage and run on the center carb only to isolate problem. Detail items, center carb fwd. stud is too short, vacuum line to brake booster needs clamp, why is spiral insulation melted on fwd. carb and does linkage contact it when fully open?
The center carb has a hot air idle compensator valve. The valve is located in the fuel bowl center section. It sits @ the rear of the venturi between the two bores and is held it with two screws. It's a bi metal spring looking part and it's function is to open when the temperature gets high enough to let a direct vacuum into the veturi and raise the RPM. When I build these carbs I always block the passage off by tapping the hole and plugging it with a 1/16 pipe plug. I've seen them blocked with lead and other types of metal but I tap them to make sure it doesn't come out and go through the engine. You also have the wrong firewall mechanism to use with tri carbs. You have the automatic mechanism where as the tri carb uses a different mechanism that has a different longer bellcrank that allows the carbs to open correctly. Your mechanism can be converted with the correct parts needed for proper operation. If you're using the switch for the 400 kickdown,then you can't convert it. Tri carbs were not available on automatics,thus the problem.
Last edited by 66-3X2 442; March 15th, 2021 at 08:37 AM.
I don't know if this is possible, but warm it up, put it on the driveway, and disconnect the linkage (and make sure the carb internal springs are working.) Then start it back up and idle it around at bit, and it shouldn't do the behavior if the engine is tugging on the throttle linkage. If it still does, it's a different issue.
Have to agree the linkage from firewall to carb is not straight (weld) and could be hanging up.
The throttle rod on a tri carb is not straight,it has a angle bend in it. The 4V throttle rod is somewhat straight but has a dog leg off set in it. The throttle rod on his setup is way wrong.
The throttle rod on a tri carb is not straight,it has a angle bend in it. The 4V throttle rod is somewhat straight but has a dog leg off set in it. The throttle rod on his setup is way wrong.
66-3X2 442 totally agree that this throttle rod is a mess...I have searched high and low and cant find a replacement...any suggestions?
66-3X2 442 totally agree that this throttle rod is a mess...I have searched high and low and cant find a replacement...any suggestions?
I might could probably come up with a rod but unless you do something about the wrong firewall mechanism,it would be difficult to make work. Send me an email @ pchopesq@aol.com and I'll try to help you.
I might could probably come up with a rod but unless you do something about the wrong firewall mechanism,it would be difficult to make work. Send me an email @ pchopesq@aol.com and I'll try to help you.
well I wanted to update you all on my idle problem. First thank you all for all the input! Especially a BIG thanks to 66-3X2 442 for your tips!
After checking and ruling out different items I found that the accelerator rod from the firewall to the center carb was 1/2” to short and bent at the wrong angle.
I am back to normal thanks to you all👍
March 15th, 2021, 05:00 AM
