1991 Force 70hp surging above idle.

[Cannondale]

I've got a 1991 Force 70hp motor mounted on my 1990 Quantum 1600 X/B.

It starts easily and idles well, but when pushed above idle, it begins to surge....rpms swing withn a 200-400 range when held at a steady rpm.

What I've done to it so far......upgraded stator to the Mercury Red 16A using the upgrade kit (398-832075A5), new CDI voltage regulator (that will have to be returned and replaced...it allows voltage to shoot to 16V+ at rpm's above 1k.....won't hold the 14.4V like it should....drat!), new water pump kit/impeller, LU oil, spark plugs and cables.

Switch box tests good and all coils are good. Timing is spot on. All fuel lines leading up to the motor are new in the last six months and all fuel lines on the motor itself are new a month ago.


I'm thinking either the fuel pump is getting weak or the carb needs cleaning/rebuilding...which wouldn't surprise me one bit.

Any other thoughts other than the two fuel system components mentioned? Thanks!

 

[steveclv]

Re: 1991 Force 70hp surging above idle.

Certainly sounds like mild fuel starvation - about the 4th one this week

Carbs could be the problem if they are gummed up and the other area to check would be to see if there is a filter in the pickup tube in the fuel tank. Also the fuel pump diaphragm may have a pinhole leak that gives insufficient fuel flow at higher throttle settings.

I would doubt it was electrical - if it sparks, it sparks. But that overvoltage needs correcting in the interests of longevity.

 

[Cannondale]

Re: 1991 Force 70hp surging above idle.

Thx. Figured as much and really didn't think it was electrical. Wouldn't have gone the stator replacement route except the old black 9A one died an inglorious death and I figured it was worth the effort/expense of upgrading to the 16A red if I was going to spend the $$ on one anyway.