70 h.p. force

Mwilson73

Recruit
Joined
Jul 29, 2022
Messages
1
I have a 1995 70h.p. force on a 20 foot sundancer pontoon,
it has a low rpm miss (around 17-1900 rpm)
And now at wot it will only reach about 3700 rpm and 14 m.ph. instead of it usual 4800rpm and 18 mph, it will surge up the rpm for a second or 2 and then back to 3700 rpm.
Things i have done.
Compression test, all cylinder within 5-10 p.s.i. of each other
removed and soaked carb and re installed
new fuel lines and filter from tank to carb, new primer ball
Rebuilt fuel pump
New plugs
Reset all carb and shifter linkages ( that was a pain)
Checked tank vent (its venting as it should)
It started this last year on our last outing, so when i opened it up for this years season i did all of the previous things i mentioned, took it out last night for the first time

it was running great for about 20 min. Then started back the way it was last year, lacking rpms and low rpm miss, at about 2100 the miss dissapears. But will not Rev above 3700 under a load. .
Fuel filter stays above 3/4 full at all times,
No fuel from the carb throat,
Pushing the choke while under way at wot, bogs it down even further.

Any help or advice would be appreciated before I give up and take it to the local shop.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,909
Can you post the actual compression readings on each cylinder? It seems you tried fixing the fuel related issues and also some synching items. Have you checked for broken reeds? Dismount the carb and check the reeds. Even better if you have one of those bore scopes (even cheap ones that connects to your smart phone) then you can do the inspection by opening wide (WOT position ENGINE NOT RUNNING) the carb throttle instead of dismounting the carb. The other thing that could also cause the misfire at certain speed is the trigger wires either grounding or shorting to ground at certain position.
 

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,739
Check for a consistent strong spark on all after she heats up and begins missing.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,818
Ruptured diaphragm in fuel pump ?-----Does spark jump a gap of 3/8" or more on each plug lead ?-----Sounds like it is running on 2 of 3 cylinders.
 
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