rejetting the carbs because of scratched cylinder

[digger658]

Got a '86 Evinrude 40hp that has always died when you put it in gear to troll. Idles ok and runs great WOT. Took it to local mechanic and he said he had to rejett the carbs due to lightly scratched cylinders around the ports to get it to idle. He said this was causing the pistol to not pull enough gas thru the cards to get it to idle in gear. He said this was the best he would be able to do with it.

Took it to the lake and it starts and idles OK. Put it in gear to troll and runs rough and shakes like it's hitting on one cylinder and dies. Ran great WOT. Took the cover off and noticed the idle screw was adjusted ALL the way in and I know that's not right.

Any suggestions?

 

[Daviet]

Re: rejetting the carbs because of scratched cylinder

I think if it were me, I would start with a compression test to see if I had a low cylinder causing a poor idle.
Then I would make sure the spark would jump a 7/16" air gap and was bright blue.
If the above was ok, I would move on to the carbs, they are not adjustable, so I would make sure all the passages were clean and the orifices were not plugged or restricted. Make sure to remove the core plug on top of the carbs and make sure the passages in there were clean.
Are you at a high altitude?

 

[multimech]

Re: rejetting the carbs because of scratched cylinder

I think what he was saying is that the cylinders lost compression. Either the compression is good or bad. To my knowledge changing jets in an engine with lost compression won't make a bit of difference. Besides that, your engine has an idle circuit which has an ADJUSTABLE needle, it is still at idle when you put it into gear. Another option if the compression is low (not much difference between cylinders and not 25 psi )is to run engine tuner through it and decarb it and then recheck the compression.

Find out the compression. If it is okay. Do a synch and link by the book and of course part of that check is initial timing. Then put the engine in a tank up to the water line it usually sits at. From your initial settings start to turn the needle until the idle is solid out of gear. Then put it in gear and make finer adjustments....adjust....turn up the rpms.....drop it to idle in gear again and let is sit there for awhile and make the adjustments accordingly. On some 40s and 50s this can be time consuming and difficult to get right.

Could be caused by a number of things. Are your carbs right? (cleaned thoroughly with no worn parts) No leakage into fuel system? etc.

 

[Daviet]

Re: rejetting the carbs because of scratched cylinder

What is your model number?

 

[digger658]

Re: rejetting the carbs because of scratched cylinder

Model number is E40ELCDE. Carbs have orifice, no idle adjusting screw. Compression is 130 psi on both cylinders. He said the leak down test was OK......not sure what that means. I live in the Ohio Valley basin so don't think altitude would factor in. Doing a spark jump test this week. I really don't think it's the carbs, I've tore them apart and soaked and cleaned them 3 times, mechanic did also.

Is there a online source for the synch and link?

 

[digger658]

Re: rejetting the carbs because of scratched cylinder

What is rejetting the carbs? Different orifices?

 

[Daviet]

Re: rejetting the carbs because of scratched cylinder

Yes.
You might check with a dealer, they have a chart, to see what orifice size you should have and compare it to what is in the carbs.

 

[metriccrescentwrench]

Re: rejetting the carbs because of scratched cylinder

.. Compression is 130 psi on both cylinders. He said the leak down test was OK......

That's strange, a cylinder which is supposedly scored enough to make the engine idle crappy but yet it has good compression and good leakdown numbers. A leakdown test is where compressed air is introduced into a cylinder through a specific sized orifice to measure how much air is escaping past the rings and valves (in the case of a 4 stroke).

If the idle timing were off it could make it act like it was before your "mechanic" messed with it (that would be covered in the link and synch procedure).

 

[Tim Frank]

Re: rejetting the carbs because of scratched cylinder

If the idle was good, and WOT as well, what is the RPM in neutral at idle just before shifting?
If idle SPEED is too low, it can stall when put in gear.

 

[digger658]

Re: rejetting the carbs because of scratched cylinder

Did a spark today. Motor will not throw a spark with a 7/16" gap, not until I screw the tested in to about 3/8" does it throw a good blue spark and that appears to be an erradic spark. It looks like the bottom cylinder throws a better sparks then the top. It when run briefly when I puul the top plug wire off the spark plug but will die instantly when I pull the bottom plug wire off the spark plug.

 

[Daviet]

Re: rejetting the carbs because of scratched cylinder

Go to the CDI electronics website and look up your engine. Use their trouble shooting guide to check out your ignition system.