J75TRCIM 1981 Fast idle

Just started motor after rebuilding all 3 carbs and replacing fuel lines. Hard starting and ran very fast at idle. I checked all linkages. I don't see idle speed adjustment. I retarded the timing by bulking backwards on the timer base and the engine slowed to normal. When I let it go back the engine revs way up.

what should I check or adjust.

you need to perform a link and sync.
at the same time, you can set initial and advanced timing using Mr. Reeves' method.

The idle screw is right by where you are moving the timing linkage to slow it down. Look for 2 screws one on top of the other the bottom one is your idle screw. But first make sure you have the throttle cable tightened up enough to pull the linkage snug to it. Otherwise your idle will be high because the throttle cable is controlling it.

Thanks, just one question - right now the idle screw has no effect at all. The butterflies are completely closed as they should be. This is supposed to be the "idle position" correct? If the timing is slowed at idle will it also affect the WOT advance?

cant find reeves method, where should I look for search.

Here ya go then:

joereeves
Gold Level Contributor


Join DateFeb 2001LocationCentral West FloridaPosts13,428

[h=2] Re: timing 115 hp johnson[/h] (Timing At Cranking Speed 4°)
(J. Reeves)
The full spark advance can be adjusted at cranking speed,"without" have the engine running as follows.

To set the timing on that engine, have the s/plugs out, and have the throttle at full, set that timer base under the flywheel tight against the rubber stop on the end of the full spark timer advance stop screw (wire it against that stop if necessary).

Rig up a spark tester on the #1 cylinder plug wire. Hook up the timing light to the #1 plug wire. Crank the engine over and set the spark advance to 4° less than what the engine calls for.

It's a good idea to ground the other plug wires to avoid sparks that could ignite fuel that may shoot out of the plug holes. I've personally never grounded them out and have never encountered a problem (fire) but it could happen.

I don't know the full spark advance setting your engine calls for, but to pick a figure, say your engine calls for 28°, set the timing at 24°. The reasoning for the 4° difference is that when the engine is actually running, due to the nature of the solid state ignition componets, the engine gains the extra 4°.

If you set the engine to its true setting at cranking speed, when running it will advance beyond its limit by 4° which will set up pre-ignition causing guaranteed piston damage! You don't want that to take place.

No need to be concerned about the idle timing as that will take care of itself. The main concern is the full advance setting.

Be sure to use your own engines spark advance settings, not the one I picked out of the air here in my notes.
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Thanks Joe

You say that idle speed takes care of itself. Is there as an idle speed timing setting. I would think that rebuilt carbs, new hoses and new carb lines would help the idle not screw it up. Its frustrating after doing all that work to have worse condition. I never changed the linkages. What causes the high speed idle, it revved to about 1800. I cant imagine a problem with carbs. I also see that others have the same condition sometimes, I am trying to understand why this happens. I got 140 psi all 3 and brand new fuel system with no leak.

re-read it. Idle TIMING takes care of itself, there is a separate idle speed adjustment that you will likely change between driveway and ramp.