Logo
FULL SITE MENU

1976 70hp problems

N

nailbag

New member
My 76 70hp evenrude will start, idle and run on the muffs and in the tank but will not accellerate when you get to the lake. My mechanic has attached/adjusted the control cables (on an 84 15ft Cajun bass boat), replaced the carb gasket, cleaned/adjusted carbs (twice), rebuilt the fuel pump, checked coils and replaced one, compression is 100+ on each cylinder, checked flywheel key, checked fuel, changed prop and every time he takes it the lake, the same result, no accelleration after you put ii in gear. He is still working on it but may be running out of ideas. Would appreciate any ideas from then forum.
 
Last edited:
Re: 76 70hp problems

With the spark plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame..... a real SNAP. If this hasn't been checked, do so.

Assuming that you do have the above spark, that problem would be due to failure to manually clean the high speed jets that are located in the bottom center of the carburetor float chambers..... OR..... the throttle butterflies are opening too soon in relation to the timing (Throttle roller making contact with the cam before being centered with the scribe mark).

Also..... although it is unlikely that those carburetors haven't been modified as required in the past 34 years, many of the 1976 70hp Evinrude & Johnsons were equipped with flawed carburetors that required special modifications to correct the exact problem you mention. If you would like to have the specifications (bulletin) on this modification process, click on my name to the left and email me.
 
Re: 76 70hp problems

Sorry Joe I been reading so much info I got it mixed up. I'll relay it to the mechanic.
Thanks for the bulletin.
 
Re: 76 70hp problems

The mechanic had already checked the jets and throttle butterflys. He then did a leak down check and found a drop to 60% on one cylinder and some drop on the others. He pulled the head and found no scoring on the walls. He advised a ring job and is putting together an estimate. What is the price range of a ring job? Any other ideas? Thanks Joe.
 
Re: 76 70hp problems

Joe, was that Johnson service bulletin 1429 dated sept 1976? I've done this mod years ago and yes it does work. Thanks for jogging my memory.
 
Re: 76 70hp problems

One more thing, maybe a can or two of BRP engine tuner would also help the problem. That is of course going buy directions on the can. I just can't get into cyl leak down tests on 2 strokes. For 4 strokes they are great.
 
Re: 76 70hp problems

I have no idea why some people go into that so called "Leak Down" test on a two stroke outboard. Franky I feel that it is the most worthless wasted portion of time existing. What one's interest should be in that area is compression.
 
Re: 76 70hp problems

Thanks Joe and Boobie,
As you can tell, I'm new to this. I will get the mod letter to the mechanic so we can see if it has been done. Also will try the BRP engine tuner. Right before the leak down check, he did another compression check and all cylinders were still at 100+. Is there other things to try before tearing the engine apart? Thanks again for all the help.
 
Re: 76 70hp problems

AND, also crankcase piston vacuum. ie, top ring free and bottom ring or rings stuck. Good compression but no suck. No suck, no proper fuel mix.
 
Re: 76 70hp problems

Joe, that was a Johnson service bulletin. If you remember right Johnson and Evinrude were seperate back in those days. The bulletin numbers were some times different. No big deal if it helps the guy out. Hope his mechanic has all the right drill bits.
 
Re: 76 70hp problems

Joe, I have a complete 75 70hp Johnson (has bad piston). Will the carbs interchange with the Evinrude? If so, is this a possible solution if the Evinrude carbs have been modified. I'm going to recheck to see if he manually cleaned the high speed jets. In your opinion, is a ring job a possible fix for this problem? Thanks.
 
Re: 76 70hp problems

What is the actual compression of each cylinder of your engine?

If the compression is what it should be, performing a rebuild (ring job) is a waste of time as it isn't going to improve anything.

The 1975 70hp carburetors? Look them over. If they're identical is all aspects (appearance, linkage, whatever), give them a try BUT you'll need to make sure that they aren't fouled in any way.

No offense intended but it sounds like your mechanic is searching for straws. Have you checked with anyone else?
 
Re: 76 70hp problems

I don't know what the exact compression is, he told me each cylinder was 100+. I will check on this. What is the recommended compression on this motor? I have not compared the carbs but will as soon as I can. No offense taken. I know he is searching for straws. That is why I have brought my problem to the forum. I will be telling him again about the mod sheets and the BRP engine tuner. At this point, I'm willing to try anything. I haven't taken it to anyone else yet but that is an option. I.m open to any and all ideas. Thanks Joe.
 
Re: 76 70hp problems

Hi Joe--- My mechanic has cleaned the hi-speed jets, the timing checked, checked the spark, checked all fuel lines, replaced the prop, rebuilt the fuel pump, rebuilt the carbs. I talked to him yesterday and he said he would go through the other set of carbs and try them. He said he would check all tank vents and pickup tube in tank and check the engine performance using a portable tank. He has worked on many older johnson/evinrude motors and has been succesul. This one has him baffled but he hasn't given up hope and is willing to try anything that might work. Thanks
 
Re: 76 70hp problems

You state " He has worked on many older johnson/evinrude motors and has been succesul."

Good, glad to hear that.

See if you can find out what the actual compression reading were.
 
Re: 76 70hp problems

Hi Joe---Good news. The mechanic used the mod sheet on the carbs and that fixed the problem. I took it out yesterday and it started, idled, and when I put it in gear and advanced the throttle it took off. Kind of slow getting on plane but it got there and ran great. The compression was 105 on each cylinder. He also found a bad coil after he redid the carbs. The mechanic really appreciated the advice from the forum and you Joe. He feels the mod on the carbs did the trick. I'm going to the lake this weekend. Thanks again.
 
Re: 76 70hp problems

Very glad to hear that your mechanic is willing to acknowledge that he can learn something from others that have been there...... a good sign. Hopefully your problems are behind you, at least for awhile anyway. Good luck and happy boating.
 
Whoever is needing that carburetor modification bulletin.... click on my name to the left and send me a PM with your email address. Also remind me what you're emailing me for. With your email address, I'll attach the bulletin for you. (Joe)
 
Re: 76 70hp problems

nailbag said:
Thanks Joe and Boobie,
As you can tell, I'm new to this. I will get the mod letter to the mechanic so we can see if it has been done. Also will try the BRP engine tuner. Right before the leak down check, he did another compression check and all cylinders were still at 100+. Is there other things to try before tearing the engine apart? Thanks again for all the help.
Click to expand...


Boobie...what does BRP engine tuner do, remove carbon deposits?
 
It removes carbon deposits but the best thing it does is free up stuck rings. When I was still working I used it all the time. Good product.
 
Back
Top