View Full Version : High Idle Speed
07-22-2006, 12:08 PM
I have a 1993 351 engine with the 4160 Carb.
Problem: I posted this problem last year and thought I had the problem resolved since I had the carb. rebuilt due to poor performance. Well it runs great now except it will idle high (1200 rpms) after a hard run (WOT) and the only way to fix the problem is to cut off the engine and then restart. This fixes it every time.
Is it possible that I have an ignition problem or do I still have a carb. problem?
07-22-2006, 12:42 PM
disconnect your throttle cable while it's happening to see if it's cable induced.
does your igniton timming come back to it's idle spec ?
any other symptoms like rough running or smoke, hard starting etc..?
If it ends up idling fine without the cable attached, you'll probably need to replace it and after 13 years, you're about due if it gets a lot of use. Tape a wire or strong cord to the old one when you remove it and you'll have an easy way to pull the new one into the bilge for reinstallation.
east tx skier
07-22-2006, 02:15 PM
I bet that your throttle cable is binding at the gap (just to the port side of the carb). Do you have perfect pass? If so, when you turn your key off, then back on, the servo winds tight, which undoes the bind in the cable, thereby giving you normal idle again.
Look at your throttle cable. It should be nearly level. If not, see if the brackets can be adjusted or replaced to make it level, or mount your PP servo facing down a little more so that the cable is as close to level as possible.
I had this exact problem last year and that was the problem. It happened after I installed a taller intake manifold. There is a mounting plate for the throttle cable on the intake and it raised it up enough to cause the bind.
07-23-2006, 12:55 AM
I do not have perfect pass on my boat and I tried the throttle cable removal when the problem occurred but no effect.
Still have to shut engine down and then restart for the idle to return to normal.
Check the pivot for the throttle plate- if they wear badly enough, the holes the ends are in may become oval and the plate will bind or the pins on the ends may wear in a way that they cause this. I saw it once on an older Tristar and it drove me nuts.
Ihad a similar problem once. After I went at higher speeds then tried to idle down my idle would't come all the way down.
It was the spring not being tight enough. The throttle cable pushes forward then back but there is a spring under the throttle cable that pulls the arm the rest of the way back. You've probably checked that already but I thought it might be worth a try.
Just re-read your questioin. I bet that is your problem. That's exactley what mine did. I also had mine rebuilt and when I got it back I didn't put the the spring in the correct hole, therefore wasn't getting enough "spring" from the spring. Next time your out give it a try. My bet is it's been doing this since you hooked up your rebuilt carb. Or tighten up your throttle cable.
07-23-2006, 11:17 PM
This problem occurred both before and after I had the carb. rebuilt.
It seems that the key to the problem is in the fact that I have to shut off the engine and then restart and it works fine.
If the throttle cable or spring was an issue wouldn't the problem still occur when I cut the engine off and then restart?
Yesterday when the problem occurred I removed the cable connection while the boat was running with the high idle problem and it made no difference thus eliminating the cable as the culprit.
A mechanic once told me when you think it is a carburetor problem it is probably an ignition issue and when you think you have an ignition problem look at the carburetor.
"A mechanic once told me when you think it is a carburetor problem it is probably an ignition issue and when you think you have an ignition problem look at the carburetor."
Yikes! I wonder how fast he was at finding problems. Intermittent problems are a PITA, whether they're mechanical or electrical but I don't think it makes sense to look at a carb when there's no spark or at the ignition circuits when there's no gas getting to the intake, though.
07-24-2006, 02:02 PM
Just a thought, do you have an electronic or manual advance distributor? One of the club members had a Nautique that was doing that and it was the timing advance weights in the distributor sticking. Shutting off the engine would allow the weights to pop back to full rest postion. That you have to shut the engine off is the key me thinks.
08-01-2006, 01:00 PM
I have been on vacation for the last week so I am just now reviewing my post.
I have a manual advance distributor. If the sticking waits is the problem how do you fix it?
The cap, rotor, coil wire and bottom plate inside the distributor need to come off and they'll be visible. It's common for the springs to rust and this not only can make them stick, it can keep them from stretching at all or they can break. They're available from most car parts stores.