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Hi. I'm new to this forum. I have a 58 Chev. Stepside P.U. with a 235 ci. I rebuilt it app. 10 years ago and updated the electrical system to a 12 volt system. Recently, I have been having problems with shorts etc. and decided to replace the wiring harness. I purchased a new one from Jim Carters (12 volt alternator system) and put it in with no problem. However, when I started it up, the engine now idles at approx. 1200 rpm. It used to idle at approx. 700 rpm. No adjustments whatsoever were made to the carb (Holley 390). I've since tried to adjust the carb and can't get it to idle below 1200 rpms. The throttle screw is out all the way, the mixture screws have been adjusted, and I checked the secondary adjustment. Since everything remained the same except the new harness, I can't understand why the engine is idling almost twice as fast. Common sense would tell me it is getting too much gas. Can anyone help me out with this problem? Thanks in advance. I forgot to mention that I have a Stovebolt mini HEI distributor and a 1 wire alternator installed.

Hi-

The first thing I would check it to remove the throttle linkage from the carburetor to make sure the throttle linkage isn't binding and not allowing the throttle blades to close completely. If they do close completely and the idle is still high, I would suspect a vacuum leak either at the carburetor or a vacuum line. Try plugging any other vacuum lines going off the carburetor and see if the problem goes away. With the engine running you can either use some WD-40 or similar lubricant spray directed at the base of the carburetor while the engine is running to fine the leak. The spray covers the leak and the idle will fall for a split second. You can also use a hose attached to a propane canister with the hose directed around the base of the carburetor..a change in idle speed will tell you if their is a leak. Are you sure you just don't have the timing too far advanced on the distibutor? If you disconnect the vacuum hose to the vacuum advance on the distibutor will the idle drop? That would tell me the throttle blades are open too far and to inspect the carburtor further.

Joe

Thanks Chevy1. I will try your suggestions when I get off work today. I'll let you know how it goes.

Chevy1 is on the right track. I put a new throttle cable on my truck and was having the exact same problem -- sure was frustrating!!! I couldn't figure out WHAT was up!! Turned out, I installed the cable-housing too snug -- there needs to be some play in it -- so I reinstalled, left some slack, and my idle was back to normal.

You might also check to make sure your vacuum advance isn't bound up. Is the wire between the coil and distributor slack enough?

Chevy1,
I got a chance to work on the truck on Sunday. This is what I found out. I checked the throttle linkage and made sure there was enough free play and verified it was not binding. Next, I checked for vacuum leaks using the WD 40. I didn't find any and the idle remained the same when I sprayed the carb. vac. ports etc. I only have one vacuum line running off the carb which goes to the vacuum advance. The others have been capped off and are not leaking. I do have a power brake vacuum line coming from the manifold which showed no leakage either. When I pulled the vac. advance line, idle increased. However, when I put my finger over the vac. advance line, idle speed dropped significantly. Much more than when the vac. advance line is hooked up to the can. This may be normal, I don't know. With the vac. advance dissconnected, I checked the timing. Keeping in mind that I can't get it to idle lower than 1200rpms, the timing was 25 deg. advanced. I was able to back it down to app. 12 deg. before the engine started to stumble. At 12 deg., the idle speed went down to app. 950rpms. Using Horvath's suggestion, I also verified that the wire between the coil and distributor is not binding. I also checked the plugs. They were burning clean (no soot) I still don't understand why the idle increased so much just because I put a new harness on. Maybe I hooked up the first harness wrong and had been driving with it that way all these years. At this point, I lost. Any other advice would be greatly appriciated.

Lets see here:

Regarding the vacuum line to the power brake booster. You shouldn't have any higher RPM with the line connected to the booster then when the line is removed and plugged with your finger. That tells me you have a vacuum leak on the booster or around the grommet on the booster that the check valve plugs into. Disconnect and plug the vacuum advance line going to the distributor...that will lower the idle more. I'm thinking when you dropped the new distributor in, it's advanced a tooth or two too much.

Try plugging the vacuum line going from the carburetor to the booster as well as the line going to the vacuum advance canister. The idle speed should be lower. When the idle lowers adjust your mixture screw to gain the highest rpm and then back off the idle screw more to lower the RPM'S. Let me know what happens and then will work from there.

Joe

Thanks Chevy1. I will try the suggestions as soon as I can. Between the job and the kids, I probably can't get to the truck until this weekend, so I'll let you know what I found out. I don't know if it makes a difference, but when I backed the timing off to 12 deg., the vac. adv. can is now pointing towards the right headlight instead of towards the front of the truck. (went from app. 6 O'clock to app. 7:30).

12 degrees is pretty far advanced for a 235, you may find that to be your problem. Go for 5 btdc with the advance disconnected. Did you, by any chance, change your points and condensor with the wiring job? Timing is affected by point gap.

All very excellent points to check.
I agree with chevy1 that there is some leakage at the vacuum brake booster. (should be the same idle speed with it connected to the booster or with your finger plugging the end of the hose.
As per 4onthefloor, setting point dwell(point gap) is a must before setting the timing, hoever, I do not think the mini HEI has points :p

4onthefloor,
I put in an after market GM HEI distributor from Stovebolt Eng. Co. about 4 years ago so I didn't have to worry about worn points, etc. anymore. Stovebolt's installation instructions suggested setting the timing between 12 and 18 degrees advanced. It appeared to be running fine at that setting until I changed the harness. The instructions also said do not use an ignition resistor with the HEI unit. I'll try to back it off further and see what happens. Thanks.

Chevy1,
I got a chance to work on the truck this weekend. I was able to determine that there were no vacuum leaks in either the brake booster or in/around the carb. I called Tom Langdon from Stovebolt in ref. to the HEI dist. He felt that my throttle plates were not closing fully to allow the throttle to drop. He suggested I take the carb. off and look at it from the bottom and verify the plates were closing. I did so and found they were not. The choke adjustment screw was in too far and not allowing them to close. After backing it out, I could see the plates closing further. Also, I found I had hooked the vac. ad. to the vacuum port below the throttle plates and the vac. advance can was fully advanced from idle. I switched to the port above the plates where there is no vac. until the plates are opened. When I put it back together and fired it up, I was able to get the idle down to 500-700rpms and set it from there. Thanks for the help. I learned a lot on what to look for when trouble shooting engine problems.