Help with a low rpm miss on my 73 115 Evinrude?

[85Sunbird]

Yesterday I was trolling around moving away from the dock when all of a sudden the motor felt like it had hit bottom (I thought ) and as acting right. I went on ahead and gave it gas and ran it at full throttle for about 15 minutes or so and everything was fine. Just as soon as I pull it back to slow down I can fell the motor start quivering like it missing. Sitting there at idle it has a intermediate miss but if yiu take off with it it runs fine.

Can anybody tell me what could possible causing this? It seems like if it was a coil or power pack it would do it worse at high rpm's insread of low rpm's.

I have noticed that I have to turn the motor over alot more to get it cranked for the first time that day. After that it will fire right up as soon as you hit the key. I've already checked the choke and it is activating fully.

Any ideas?

Thanks.
Jason

 

[F_R]

Re: Help with a low rpm miss on my 73 115 Evinrude?

I have to mention this, although it probably isn't the cause. The '73s had a problem with the charge coils under the flywheel. Those are the two big coils that charge the ignition power pack. The bad ones were separate coils mounted on a common stator. The replacements were all potted together in epoxy. You can see them just by looking up underneath the flywheel. Since they gave so much trouble most were replaced long ago. Symptoms of bad charge coils were mainly hard starting, would run at speed ok if you ever did get it started.

I also suggest you check the spark plugs. Use Champion L77JC4 gapped at .040. Trash those surface gap plugs if you have them.

Thre are all sorts of "could-be's beyond that.

 

[ezeke]

Re: Help with a low rpm miss on my 73 115 Evinrude?

Check all of the hoses in the engine area. You may have an air leak.

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

Thanks......I'm not sure which one I have but mine seems to be all together and is coated in a green epoxy like substance. I've never replaced the charge coil on this thing though. I did try new plugs and it didn't go away. I've notoced it seems to do it worse when the motor is up to operating temp. We let it sit for 2 hours or more and cranked it on the hose and it was running fine. The hard starting seems to be a mystery to me. I mean it has to turn and turn before it ever hits the first time. once it cranks...it will crank fine the rest of the day.

Thanks,
Jason

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

Ok....have an update. I got out there last night and tried to crank the motor after it had been sitting for a few days. It hit just as soon as I hit the key for a split second and then quit. Then again I had to turn anf turn the motor over and it fianlly started but was missing intermediately and running ragged. Then I shut it off to go get my timing light to check to see if I could find out which cylinder was dropping out. When I went back to start it up......it cranked right up and was running fine. I let it run a few minutes and couldn't get it to start back missing. The last time it was doing when the motor got to running temp.

I'm stumped on this......what does it sound like to you?

Thanks,
Jason

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

anybody?

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

Here is an update.......I changed the charge coil and took the carbs apart to make sure they were clean and still no luck. The thing has to turn and turn before it will ever fire for the first time and ehren it does it is running ragged as all get out. I put a timing light on all the plug wires and they are loosing fire randomly. All 4 cylinders are doing the same thing. does this sound like a Power Pack problem?

Thanks,
Jason

 

[F_R]

Re: Help with a low rpm miss on my 73 115 Evinrude?

So what kind of spark plugs did you put in? The surface gap plugs are prone to do exactly what you are describing. That's why I said to change to L77JC4 gapped at .040. If that is what you have, then OK.

BTW, the green potted coils are the good ones.

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

I can't beleive that out of all these Evinrude and Johnson folks out there that nobody can tell me what could possibly be causing my problem. I don't think it's the plugs because I've ran surface gap plugs for years with no problems and plus I also tired another set and the same thing in happening.

Jason

 

[F_R]

Re: Help with a low rpm miss on my 73 115 Evinrude?

You said "possible". I gave you a "possible". It's your choice to follow or not follow. Besides, I could be wrong...I'm not in your boat at this moment. If you knew how much I fought those surface gap plugs with the same attitude you have........ Where do you think I got all this grey hair?

 

[ezeke]

Re: Help with a low rpm miss on my 73 115 Evinrude?

I think that at least one of the two low speed orifices in one of your carburetors may be clogged. Sounds as though you are running strong once the high speed jets open.

The low speed jets are behind the four brass cover screws on the sides of the barrels if you want to blow a little carb cleaner through them. They lead up to the floor of the throat by way of small holes. If you force the carb cleaner with the little pipe that comes with it, you can see if the liquid is going through by looking down the throats.

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

Problem solved.......replaced the power pack and it runs fine now.

Thanks again,
Jason

 

[wormboy]

Re: Help with a low rpm miss on my 73 115 Evinrude?

Jason,
Just a note-- I had a similar problem. For me replacing the powerpack alone wasn't sufficient to fix the random lack of firing at different cylinders; replacing the trigger alone didn't help either--- only replacing both seemed to solve it. i am clueless about why this would be the case, but think about the trigger if the problem reappears too soon.

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

Wormboy,
Fill me in......what is the trigger? Are you talking about the sensors on the timing base or something totally different?

Thanks,
Jason

 

[wormboy]

Re: Help with a low rpm miss on my 73 115 Evinrude?

I think it's also called a timer base or sensor ring-- on my engine I believe it is a ring that is inside the stator-- the repair was initially done by the one mechanic I found that bothered to really spend time trying to diagnose the problem, rather than just throw assorted parts to "see if that works" and charge parts and labor for the dang experiment.... this is why i enjoy this forum; I can do the same experiments and on the job training without the labor costs... and the advice is generally well considered!!

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

I got you now.....that what I thought you were talking about. To be honest we actually changed them also with no luck. The entire ignition system has been replaced peice by peice and tried after every peice was put on to see if that fixed it. Once we put the new power pack on...the motor cleared right up and ran fine. It's still a mystery how these things can run fine ine minute and go out the next.

Thanks,
Jason

 

[85Sunbird]

Re: Help with a low rpm miss on my 73 115 Evinrude?

I got you now.....that what I thought you were talking about. To be honest we actually changed them also with no luck. The entire ignition system has been replaced peice by peice and tried after every peice was put on to see if that fixed it. Once we put the new power pack on...the motor cleared right up and ran fine. It's still a mystery how these things can run fine ine minute and go out the next.

Thanks,
Jason

 

[wormboy]

Re: Help with a low rpm miss on my 73 115 Evinrude?

I hear that! the first guy i went to changed the stator-- which was probably ok-- and the powerpack, charged a mortgage payment and fixed absolutely nothing. the next guy charged little but also fixed little or nothing-- but I finally convinced him to keep at it, since at least he wasn't just throwing expensive parts at it. The stator the first guy put on was no good, as it turns out. that's when they figured it out-- or at least fixed the starting problem-- but they failed to notice fuel gushing out of one of the carbs, and hooked up two of the wires from the power pack incorrectly (reversed 3 and 5)--- which is when i gave up and tried to resurrect what little mechanical experience I've had. At least I KNOW the mechanic's questionable from the start-- and he knows that he don't know everything!So far so good-- thanks mostly to this forum!!