1977 70hp Johson, wont take beyond about 1/4 throttle, always stalls beyond that

[78Thundercraft]

Ok guys, have one kicking my butt.:facepalm: I'm a newbie on here (posting wise)
Give me some alternatives to check, I've got tunnel vision. Here's the problem child:

1977 Johnson 70hp. 120lbs compression on all three cyls. Factory reeds looked good. Boiled out carbs and rebuilt, including the linc & sinc. Throttle pickup timing at 0, max timing at 17 deg as specified. Replaced power pack as # 3 was not firing. Input to the pack is 200 plus on all cyls, well above the 170 spec (using CD 77 tester). New plugs at .030 gap. New water pump and fresh gear lube. New fuel pump (rebuilt the original and installed new just in case) Also, I also tried the tank, fuel, and line from my 78Thundercraft that runs 35+ w/ the 85hp no problem, so that's out.

70 starts easily, shifts into gear fine, but in gear in the water she will not take past about 1/4 throttle and she starts to stall (always!). If you pull back she will continue to run, if not, she stalls out.

I'm at wits end :facepalm: and need a fresh set of eyes, or brains, on this thing. Anyone run into this before or have some ideas??????? The iggi coils are still OEM, so that was one thought but the timing light does show steady spark.

ASE auto technician here so feel free to get technical. But, experience counts on these things and that's where you guys come in. Ok, lets see what you've got for me to try next. Fire away.

Thanks,
Raymond

 

[BonairII]

Re: 1977 70hp Johson, wont take beyond about 1/4 throttle, always stalls beyond that

Did you check the QUALITY of spark? Or did u check for the PRESENCE of spark?

 

[cdn-pk]

Re: 1977 70hp Johson, wont take beyond about 1/4 throttle, always stalls beyond that

Sounds like a fuel delivery issue... but....

yes agree check for good strong blue spark. should jump 7/16 of an inch.

Also is your timing advancing after your carb butterfly have started opening? and are the butterfly's opening all the way open at wot? If the butterfly's open without the timing advancing she'll stall out.

 

[78Thundercraft]

Re: 1977 70hp Johson, wont take beyond about 1/4 throttle, always stalls beyond that

Good one on the timing advance. I've read that elsewhere now too.
Have adjusted the roller away from the cam to get substantially more timing (10-15 BTDC) before the throttle blades begin to open. She has WOT and choke is working correctly. I have come to the conclusion that the 0 degree to 5 ATDC given by the manual is just flat wrong. My v4 has over 10BTDC @ throttle pickup that runs like a top. Adjusted for about the same advance on the 70.

NOTES: She did have hot blue spark over 7/16 the other day in testing. Also forgot to mention, hitting the primer bulb was no go. Will try the new linkage adjustment tonight in the water and see how she does (fingers crossed) and let you know what happens.

May also try shortening the throttle rod as currently I can't reach the short mark at all with the roller. Also, from the former gaskets it looks like she's had a carb rebuild in her recent past. Possible the last guy got totally lost on the linc adjustments and I/we are having to sort alll back out (good case for why shops charge more when other work on it 1st. lmao!)
Thanks guys,
Raymond