Poor idle

Pluto

Cadet
Joined
Oct 5, 2003
Messages
7
My 150 1981 Johnson has a very poor idle but runs good above 2800 RPM. Have set the trottle links, rebuilt carb, set timing, change plugs, change spark wires, decarb pistons, check stator timing base power packs coils for resistance and seems ok.<br /><br />How can I check the peak voltage from the stator and from the CDI? Is there a special toll/meter?
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: Poor idle

There are special meters that will reveal those measurements but it's unlikely you'll need those expensive pieces of equipment.<br /><br />With the spark plugs removed (all of them), rig up a spark tester whereas you can set a 7/16" gap. If a strong blue lightning like spark jumps that gap on all cylinders, all of the ignition components are in good condition.<br /><br />If the spark appears weak on only a few cylinders, the usual cause is a weak coil or poor continuity in the spark plug wire, or no contunity between the primary and secondary wire within the coil itself. This can be checked with a simple ohm meter.<br /><br />If the spark is existent on both banks and is perfect on one bank, but not on the other bank, that would indicate a stator problem which is usually visible in the form of a cracked and/or leaking stator... easy to spot.<br /><br />If the spark is perfect, or you have corrected it to be perfect and still have a idle problem, and assuming that you have not made any mistakes in the linkages, overlooked anything pertaining to the carburetors, the following may be your problem. But first... just in case the idle air bleed jets in the top portion of the carburetor may have been mixed up with other jets similar in appearance, those jets should be .032 jets which are marked 32 on the jet themselves (OMC #320016).<br /><br />The fuel recirculating valves in the intake manifold should be checked to make sure that fuel/air flows only in one direction... from the inner portion towards the hose connection.<br /><br />Now, various V/6 engines in that year and hp range were known to have either slightly warped intake manifolds and/or block (crankcase) surfaces. This allowed a conflict/crossover of crankcase pressure between cylinders. The simple cure was/is to use a double gasket on the intake to crankcase surface area.
 

Pluto

Cadet
Joined
Oct 5, 2003
Messages
7
Re: Poor idle

Joe: thanks for the quick response, as you can read this idle problem is driving me crazy. Yesterday I got hold of Stevens Co. and ordered a device that goes with the Fluke Meter (already have) that can read the peak voltage in order to test the stator and power pack peak volts at starting rpms, I will be posting results of this test. For the time been, what you wrote looks very interesting, the recirculation valves were already tested and changed one, no <br />improvements. The idle air jet, I do not know the size of the jet but with the engine on at iddle I cover the jets with my fingers and I did not noticed any change at all!!!!!!!!!! Was I supose to notice a change????<br /><br />On the doble gaskets for the crossflow improvement, were you talking about the gasket between the carb. and the intake manifold???? Can I go ahead and add the other gasket just to scratch off one posible troble point???<br /><br />Thanks once again
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Re: Poor idle

To quote myself...."The simple cure was/is to use a double gasket on the intake to crankcase surface area."<br /><br />That is..... between the intake manifold and the block. The large gasket.<br /><br />Covering the idle air bleed with ones finger should make that particular cylinder run rich, increasing the flow of fuel to that cylinder.
 
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