1993 70hp Evinrude runs great except at idle in gear

[bds1078]

Hi guys,

Bought a "rebuilt" '93 70hp for $1200 last week. Mechanic says top cylinder was redone (piston, rod,bearings,rings, carbs rebuilt and impeller), but balanced and properly torqued with the other two cylinders. I hope I haven't been duped. I made the rookie mistake of not checking compression beforehand. Cranked great on the hose, shifted good, idled good.

Mounted and took to lake today. Cranked easily but did not want to idle in gear. Once going however, she blasts out of the hole and cruises nicely the way it should with no hesitation whatsoever. Ease off the throttle a bit back down to idle and she just does not want to stay there. A bit of a challenge while docking or trailering.

Has a bit of a tiny jitter at idle much like my old Merc used to. Got back home and surprise! The exact same compression as old Merc. 135-115-135. Seems a little suspect for a recent rebuild? However 1984 60hp Mercury ran well for many years at that compression, still is. I have read the middle cylinder can be troublesome on these blocks.

My questions are - Could the loaded idle problem relate to the off compression, or should I double check his carb work? (low speed jet). Idle revs seems good, but should I turn up a bit? (unfortunately no tach yet) Could it be something more insidious like a reed valve, but then again wouldn't that have surfaced at mid-high range which was awesome? Your knowledge appreciated,

Brad

 

[patrick4266]

Re: 1993 70hp Evinrude runs great except at idle in gear

If it was me I would try turning it up a bit.

 

[bds1078]

Re: 1993 70hp Evinrude runs great except at idle in gear

Will do, Patrick. Thanks!

Any thoughts on the reeds upgrade? I have heard of folks lauding the Boyesens for smooth idle, but I wonder if that's 'putting perfume on a broodsow' if she's already 20lbs low middle cylinder? I really hope that compression reading is a fluke caused by something else, if not I'm ticked. The motor was advertised to me as 'balanced'. That ain't balanced. Of concern is he put the double oil break-in hours on the rebuild on a hose, not in a tank or at the lake. I've heard those motors can overheat easily. Perhaps he did the damage himself?

 

[patrick4266]

Re: 1993 70hp Evinrude runs great except at idle in gear

I have a 91-70 hp rude. If I was you I would check the compression again. I would also double oil it for a while just to be sure. As far as over heating your right about that. What you need to do is relocate the "pee hole" to the top. Thers a service bulletion about that. I don't think you have a problem with the reeds. Just try to idle it up a little.

 

[bds1078]

Re: 1993 70hp Evinrude runs great except at idle in gear

It appears someone already relocated the peehole at top, and she pees good. I haven't been double oiling, but have put in a dab heavier than the usual 50:1. Will tinker today and see what happens.

 

[bds1078]

Re: 1993 70hp Evinrude runs great except at idle in gear

Oh yeah - checked compression cold this morning. Still 135-115-135. You can tell how clean the new top piston is, lower one looks normal, middle one is black. Would decarbing be worth the effort?

 

[abwehrly42]

Re: 1993 70hp Evinrude runs great except at idle in gear

I have a 1992 Johnson 60hp. I swapped on a set of 70hp carbs. The roller on the middle carb is lined up with the mark on the cam, all the butterflies move at the same time, and I adjusted the throttle stop so the butterflies are perfectly flat at WOT. Unfortunately, it idles at 1900rpm on the muffs. The carbs are tight on the intake, the base gaskets are in good condition, and no fuel leaks. Is the idle adjustment the other large screw adjacent to the throttle stop screw (two flat head screws threading up below the cam)? If not, where can I find the idle adjustment? Should I attempt to change the idle, or could there be a problem with my installation? The air box is off; I put a vacuum cap over the nipple where the hose coming from the air box connects to the motor.

This motor ran great and idled around 850rpm with the 60hp carbs. The only thing that changed is the carburetors. I have a factory service manual on the way, but would like to sort out the idle ASAP.

Thanks for any help.

 

[abwehrly42]

Re: 1993 70hp Evinrude runs great except at idle in gear

Disregard my question, I just checked and the middle cylinder compression is 0. No damage to the head, luckily.

 

[RZR2007]

Re: 1993 70hp Evinrude runs great except at idle in gear

Disregard my question, I just checked and the middle cylinder compression is 0. No damage to the head, luckily.

What happened?? I think I would be heading to the mechanic you bought this from!

 

[abwehrly42]

Re: 1993 70hp Evinrude runs great except at idle in gear

I laid the motor on its side while I was working on the boat. The needle stuck in the middle carb. There was a loose connection on the key switch which I assumed was the culprit when the motor slowed down and died going down the lake. I kept running it for a few months, and found the melted piston when I was swapping the carburetors last weekend. I am suprised how well it ran on two cylinders. It wouldn't idle as smoothly, nor rev quite as high, but other than that no major indicators that my motor had a major failure.