9.9 low speed miss

outboardnut · Jan 24, 2007

Hi all.
I'm getting punished by a little 9.9 HP Evinrude. It's a 1974 model.
It has a low speed miss and is being a real booger. I'll have to admit I'm feeling a bit hummilated and embarrassed.

Ignition system.
I installed new points and condensers, and replaced one coil. Point gap was set at .020 when the rub block was at the "set" mark on the crankshaft. It has good HOT spark, jumps about 1/2 gap. I can't detect a miss with my adjustable spark gap tester. It also has the correct brand new NGK spark plugs installed.

Fuel system:
It seems to be missing from running lean. I cleaned the carb twice. Tried a fuel pump and carb from another engine (1976 15 HP) and it still does it.
When it coughs, I can catch it with the choke to get it back up to speed.
I'm about to pull all my hair out because of this low speed miss. Does anyone have any ideas on what I'm missing? I have a video of it running posted here:
http://www.youtube.com/watch?v=_qAJOgQCVmE

outboardnut · Jan 24, 2007

Re: 9.9 low speed miss

well youtube gobbled up the video a little. My hands don't move that fast!
The sounds on the movie sound off too.... I wouldn't hit the choke till after it stalls.

F_R · Jan 24, 2007

Re: 9.9 low speed miss

WAG: Lower crank seal?

outboardnut · Jan 24, 2007

Re: 9.9 low speed miss

What do you mean, WAG?
Motor is devoloping good compression, 120 pounds and even on both cylinders.

OBJ · Jan 24, 2007

Re: 9.9 low speed miss

obn.....try a couple things....

First, check the cam roller pick up. Make sure that when the reference mark on the cam is centered on the cam roller, the throttle plate just starts to open.

Turn the low speed needle in untill it GENTLY seats and then back it out 1 1/2 turns.

When you cleaned the carb, did you soak it out and blow it out? Was a carb kit installed?

On your carb, there is a low speed needle bearing that goes back into the hole that the needle rides in....little plastic deal that can crumble after a lot of use. Did you replace it if you had the OEM kit?

I think your problem is in the carb...either the set up (as I posted above) is off or there is still some junk laying in the idle passage. Apparently it goes OK with the throttle opened up?

outboardnut · Jan 24, 2007

Re: 9.9 low speed miss

I tried a carb from a different engine that I know works... and it still has the same problem.
It acts like it's running lean to me....it coughs and misses but when I give her a choke it comes back and smooths out.
The cam roller pickup mark on this one is like a triangle. I believe it's supposed to pick up on the starboard side of the roller. I checked it once, will look again.
Do I not wanna know what WAG is? lol
Thanks

chrish · Jan 25, 2007

Re: 9.9 low speed miss

is the motor running in nutural? or do you have the prop off?

F_R · Jan 25, 2007

Re: 9.9 low speed miss

WAG = Wild A-- Guess

If the seal is bad, it will suck/blow air past the lower main crankshaft bearing which is a ball bearing. That will show up as a lean condition on the lower cylinder, but the upper will be ok. It won't affect the compression, which is taking place above the pistons.

Trouble is, it is a lot of work (pull powerhead) to find out if it is a good or bad guess.

OBJ · Jan 25, 2007

Re: 9.9 low speed miss

I usually go for the SWAG theory......Scientific Wild A$$ Guess..........d

I noticed in the video that adjusting the low speed needle. Still acts like a dirty carb. Have you noticed, is there any oil laying around under the flywheel?

cobra 3.0 · Jan 25, 2007

Re: 9.9 low speed miss

I have a 15 Evinrude of the same year, basically the same motor, which has been acting like that for the last 2 to 4 years(well maybe not that badly). It starts up well and runs smooth, but coughs a little at times when trolling and will quit here and there. This engine is used every weekend as soon as ice is out. My mechanic neighbor mentionned to me a while back that it was probably a worn lower crankshaft seal...just like FR mentionned.

My bets are on the seal.

marinemech1 · Jan 25, 2007

Re: 9.9 low speed miss

change plugs to champion ul81c
make sure motor is warming up (thermostat)
is exhaust plugged?

perkdp · Jan 26, 2007

Re: 9.9 low speed miss

You've swapped out the carbs. So, how about the gaskets behind the carb and between the intake and block?

You may be able to squirt some oil around the carb base and intake/block to find a leak. If the oil is thick it will seal the leak temporarily and you can hear the rpm change.

But in the video, it sounds more like a spark miss to me.
Is it possible there is wobble in the armeture plate causing the points to open irratically ?

ezeke · Jan 28, 2007

Re: 9.9 low speed miss

Another possible problem that could be relevant was that the 1974 and 1975 9.9 and 15 models had a high point on the cam only 10 degrees wide. You need to be more careful with those models when setting the timing.

outboardnut · Mar 2, 2007

Re: 9.9 low speed miss

Well the motor is fixed

I believe it was because the point gap was not set precisely enough. These models are VERY picky!
Thanks for all the help, Jeff

9.9 low speed miss

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