1975 9.9Hp Evinrude Misses at mid-range

[OptsyEagle]

My motor seems to miss when I run it in gear at about mid-throttle. It idles not too bad and moves forward slowly ,OK. As I add throttle is seems to cough and miss but if I keep adding throttle it seems OK again. I don`t seem to have any problems at WOT. When the miss occurs, I tried squeezing the primer bulb to no avail and I enriched the carb mixture to no avail. The carb`s idle adjust is set well.

I tuned it up this winter by changing the condensers and points and I set the point gap to 0.020 inches. I adjusted my flywheel key to align with the cam. I would think that if I had a problem with my flywheel key, the motor would have problems at all ranges.

Any ideas.

 

[Daviet]

Re: 1975 9.9Hp Evinrude Misses at mid-range

When was the carb overhauled last? Check the fuel pump diaphram, remove the pump and see if there is gas in the passage that goes to the block.

 

[Monte1961]

Re: 1975 9.9Hp Evinrude Misses at mid-range

I would concur with Daviet! Just so you have a better understanding, Theres also and intermediate fuel/air circuit also that's between low idle and wot. That would also explain your mid throttle miss. Post back and let us what happens.

 

[OptsyEagle]

Re: 1975 9.9Hp Evinrude Misses at mid-range

The carb was cleaned last year. This intermediate circuit; are we talking inside the carb? I will check the fuel pump.

If my points were somehow not gapped right (I may re-check this) could it throw out the timing so that the motor seems to run OK at idle and WOT but cough at mid-range?

 

[Monte1961]

Re: 1975 9.9Hp Evinrude Misses at mid-range

yes its inside the carb. When you say the carb was cleaned, do you mean overhauled with new carb kit or just sprayed with carb cleaner and reassembled?

 

[OptsyEagle]

Re: 1975 9.9Hp Evinrude Misses at mid-range

yes its inside the carb. When you say the carb was cleaned, do you mean overhauled with new carb kit or just sprayed with carb cleaner and reassembled?

Overhauled with new carb kit, new welch plug, new slow speed bearing and seal, etc. I use fuel stabilizer over the winter as well. This intermediate fuel circuit? Is it observable on this particular carb. I have seen the high speed and slow speed and doused them well with carb cleaner and blew them out with compressed air as well as every other cavity I could see.

Anyway, I checked the fuel pump by removing it from the block and squeezing the primer bulb till it was hard. No fuel leaked out.

I then took the flywheel off again and re-checked my points. One was at around 0.014" and the other around 0.018". They are new points and I know I set them between 0.020" and 0.022" and tightened the screw hard. I rotated the cam by hand a few times and checked them again. I am thinking that since they are the cheaper Sierra points perhaps they have worn down upon first operation or something. Anyway, they are set again to the 0.020" spec and I will try the motor again later this week.

Do you think points at 0.014" and the other at 0.018" would create an intermediate range miss or cough?

 

[Monte1961]

Re: 1975 9.9Hp Evinrude Misses at mid-range

To try and answer your question, the intermediate is between low idle and cruse. and yes your points being out of adjustment could be a possibility. You said you readjusted them. Did it help? Seeing that you say it runs good at low and wot, I cant really see anything else but fuel related. Post back and tell us what you find. Good luck.

 

[OptsyEagle]

Re: 1975 9.9Hp Evinrude Misses at mid-range

OK, here is an update for anyone interested. I mentioned how I changed my points this spring, adjusted them to 0.020" gap and then had a problem of a miss at medium throttle. So I removed the flywheel and one of the points was now 0.014" and the other about 0.018". I re-adjusted them back to 0.020" and tried it again. Same problem. Starts not bad, idles Ok. I can pull either spark plug at idle and motor continues to run. WOT seems fine although without a tach, I cannot say if I am getting full power, but at mid range it misses and coughs and sputters.

So I removed the flywheel again (I keep looking there because the motor worked fine until I did my tune up this spring) and that point that was at 0.014" that I increased to 0.020" was now about 0.016". The other was about where it was originally at around 0.020". The screw was tight on the lower gapped point.

So I disconnected the wires and put a multimeter on that point. As I rotated the cam I got continuity when the gap closed and open circuit when it opened, but ... around half of the revolution of the cam, the continuity would open then close again, way before it should. This was very quick but would happen everytime. The other point seemed to work fine with only one open circuit per revolution, timed at the perfect spot.

I am not really sure why that point would slightly open (maybe by 0.001" ) and then quickly close again when the cam was not supposed to be touching the rub bar of the point. When I removed it I did notice that the material on the rub bar was fraying off slightly. I guess I have to chock this problem up to using cheap Sierra points (that's what I get for trying to save a buck) although I have used their points on my '76 15HP with no apparent problems.

Anyway, I cleaned up the old ones, adjusted the gap and set them with the multimeter. I am finally getting only one open circuit, per point, per revolution, so I think I may have solved this one. It was raining yesterday when I was working on it and couldn't fire it up. I'll be at the cottage next week and give you the final result.

Anyone seen this problem before? Still kind of questioning why it seemed to only show a problem at around medium throttle.

 

[Rick.]

Re: 1975 9.9Hp Evinrude Misses at mid-range

Sounds strange. I don't see why one would do that and not the other. Even if they were inferior it's the cam that tells them what to do and when. Rick.

 

[AlTn]

Re: 1975 9.9Hp Evinrude Misses at mid-range

possibly a weak return spring is allowing the rub block to lift off the cam?...just throwing this out

 

[OptsyEagle]

Re: 1975 9.9Hp Evinrude Misses at mid-range

Yeah, something like that.

The fraying material on the rub block could have been bundled up a little, at the bottom of the block where it was difficult to see when it was on the motor and somehow touched the cam just a little at some point as it turned. The other point didn't really have a fraying problem.

Or as AITn says perhaps it had a weak spring.

Pretty wierd all the same. Whatever it was the electrical operation of that point was certainly not working to the design parameters, so I am glad I changed it. Let's hope the motor runs well and I will be glad to add this problem to the mystery of the mind category.