78 70hp evinrude idles way too fast

[optimizer]

My motor idles at 2200 rpm with the throttle plates completely closed. I just finished rebuilding the carbs because they were gummed up so badly the motor barely ran. Now I have the opposite problem and I can't get it to slow down. The only way I can bring the rpms down is by closing the choke plates and resrticting the air, or severely retarding the timing to 15 deg BTDC. Any suggestions are greatly appreciated.

 

[optimizer]

Re: 78 70hp evinrude idles way too fast

I meant to say 15deg ATDC.

 

[thirdm]

Re: 78 70hp evinrude idles way too fast

hey optimizer-<br /><br />did you reset all of the adjustment screws in the carb??? i don't know the specs of your engine, but i always use 1 1/2 turns out from completely closed as a guide. if not, try this and see if it helps....<br /><br />mason

 

[optimizer]

Re: 78 70hp evinrude idles way too fast

There are no adjustments to be made on this carb type. It has a high and low speed orifice that cannot be adjusted. The only adjustment that can be made is setting the float level correctly. I did that according to the manual description.

 

[JB]

Re: 78 70hp evinrude idles way too fast

Ahoy, Optimizer. You have an air leak. The most likely spot is around the edges of an off-centered throttle plate. Other suspects are gasket surfaces, fuel pump mounting surface, reedplate mounting surfaces. Look for any place that air can get into the crankcase, but focus on your carbs.<br /><br />Good luck.<br />Red sky at night. . . <br />JB

 

[thirdm]

Re: 78 70hp evinrude idles way too fast

optimizer,<br /><br />do you know how to do the wd-40 test? i thought about an air leak earlier, but i try not to get out of my realm when it comes to boat engines. anyway, get her running and then get a can of wd-40 (with the little red straw if possible) and start going around all of the places that could possibly be sucking air and spray WD-40 on them - if your idle goes down - that is the spot of your leak.<br /><br />mason

 

[optimizer]

Re: 78 70hp evinrude idles way too fast

Thanks guys, i'll try and find a leak and let you know how i make out.

 

[optimizer]

Re: 78 70hp evinrude idles way too fast

Well, I tried the wd40 leak test everywhere suggestd by JB to no avail. Is there an alternative to wd40 that works better? It seems to barely affect the idle rpm, even if I spray it directly into the carb. <br />I checked the edges of each throttle plate as suggested by JB but could not see any noticeable gap.I also disconnected the linkage between the three plates and closed them individually to make sure that one wasn't staying open,when they move in unison.<br />I tried closing one choke at a time and the rpm went down each time. It seems I definitely have a leak, I just can't pinpoint it.

 

[Vin P]

Re: 78 70hp evinrude idles way too fast

Try spraying carb cleaner instead and look for the speed to increase when you find the vacuum leak.

 

[adrian bick]

Re: 78 70hp evinrude idles way too fast

YOu may have to adjust the throttle stop screw and the throttle cable. Good luck

 

[optimizer]

Re: 78 70hp evinrude idles way too fast

I already backed them off so the cam no longer touches the roller on the throttle plate linkage. The throttle plates are completely closed and it is still idling too high.

 

[optimizer]

Re: 78 70hp evinrude idles way too fast

I tried to find an air leak without succeeding. I practically sprayed down the whole engine with carb cleaner without observing any change in the revs. Any other ideas out there why I can't get my revs down?

 

[Bear]

Re: 78 70hp evinrude idles way too fast

When cleaning the carbs, did you find the idle jets? How did you clean them? Maybe new jets will get your rpms back to normal. I don't know how your carbs works but i think there is an other circuit for idle rpms.<br />Maybe I'm all wrong.<br />/Bear

 

[optimizer]

Re: 78 70hp evinrude idles way too fast

I cleaned the carbs by soaking them in "Gunk Hydro Seal II", a fluid for cleaning engine components, including carborateurs. Then I used compressed air to blow out all orifices and passages. They were sqeaky clean after that. I would think that if there was any obstruction, the fuel flow would be reduced and the revs would be lower, not higher. I am still baffled. I am thinking of taking it in to a evinrude dealer, as I have exhausted my troubleshooting skills.

 

[kev_79]

Re: 78 70hp evinrude idles way too fast

Optimizer, check that timing spec again. I may be totally wrong, but 15 ATDC. That sounds really high for idle. I thing it should be closer to 5 degrees or so, but I may be wrong. Good luck, and tell me what you come up with

 

[optimizer]

Re: 78 70hp evinrude idles way too fast

Kev, that's the problem - with the timing set to specs the engine idles way too fast. It will only slow down if I severely retard the timing.

 

[kev_79]

Re: 78 70hp evinrude idles way too fast

What is the spec? I thought that you meant spec was 15 ATDC.

 

[Chum Slick]

Re: 78 70hp evinrude idles way too fast

I have a 1975 70hp Johnson and I believe the timing is 17 degrees BTDC. Timing on your motor should be close to the same. My manual covers your motor, I'll check what timing on your motor should be and get back.<br /><br />Keep the bait in the slick...

 

[kev_79]

Re: 78 70hp evinrude idles way too fast

My wrench said at idle, timing should be 2-4 degrees ATDC and around 19 ATCD@WOT. Good Luck

 

[kev_79]

Re: 78 70hp evinrude idles way too fast

sorry I meant btdc. I keep getting this s**t mixed up. Is your timing indicator movable? Just wondering, on my merc it is, and that could be out if so. I also had a bad light/connection once when I was setting timing, and caused it to misread. Hope you figure it out. Good Luck