[MrLundt]

I have started a new thread in hopes of attracting some fresh ideas about a stale problem. This has baffled me since early August, but with a lot of advice from this forum, I’ve been able to eliminate a lot of possibilities; however, the solution is still a mystery. For more background info, read the thread titled “1988 Mercury 100 hp w/ acceleration problems”.

The motor: This is a 100 h.p. motor w/ a 2+2 system. The top two carbs get fuel at idle and the bottom two get enough to keep the pistons lubed but not enough to fire. At increased throttle, all 4 carbs contribute.

The problem: When the boat is on the water and I am at WOT, my motor is functioning at about 50%. It will not even get on plane. The situation improves when I squeeze the primer ball. I can squeeze until my hand cramps up and I get about 90% out of the motor but when I stop squeezing, the motor returns to a dog.

Suggested solutions: In a moment of defeat I took the motor to a mechanic who looked at it and said I needed a new stator. (I’m not sure he actually did any tests). Because the performance of the motor improved when I squeeze the primer ball, I’m reluctant to believe that I have an electrical problem.

With guidance from this forum, I have ruled out many fuel supply problems. Results of various fuel pressure and vacuum tests are w/in the specs listed in my shop manual leading me to believe my fuel lines and fuel pump are OK. The carb bowls are getting fuel, I’m just not sure if fuel is getting into the cylinder.

I replaced the accelerator pump that is supposed to give the 3rd and 4th cyls a “squirt” of fuel when the throttle lever depresses the accel pump. This did not resolve the problem. I just removed and dipped the carbs in cleaning solution but have not had a chance to see if that helped. Sounds good in the driveway w/ muffs but no way to tell if bottom two carbs are contributing until I get it on the lake.

What’s next: Is there anything specific to this 2+2 system that I should look for. Besides contributing the “squirt”, does anyone know how the accelerator pump contributes to the motor output at high throttle? A fuel line branches off the main line between the 2nd and 3rd carb and leads to the accell pump. Another line leaves the accell pump and goes to the back of the motor. Looks like it is using bleeder lines? Could I have a problem there?

Thanks to all who have contributed to the other thread and thanks in advance to new contributors who may have fresh ideas to this stale problem.

[bhile]

Did you ever rebuild your fuel pump? Including the check valves?

[MrLundt]

Rebuilt fuel pump about 4 years ago. Would be glad to do it again if I thought it would help. It's cheap enough. Fuel pressure test on the lake gave reading of 6 psi at wot. My Clymer shop manual says specs should be 2-3 psi at idle and 4-6 psi at wot. Called Mercury this morning to confirm specs. They report 4-5 psi at wot. More pressure seems to help but is likely compensating for another problem further down stream. Squeezing primer ball may not be forcing fuel through pump. There is a "T" fitting in the fuel line just before the pump where a bleeder hose connects. I wonder if squeezing the primer ball is forcing fuel through bleeder hose into bottom cyls?

[MrLundt]

I guess after several failed attempts to resolve my problem it would be expected that I might be a little pessimistic about my latest attempt but I shouldn’t have been. A $20 bucket of Chem-dip was all I needed. I soaked all 4 carbs in chem-dip on Sunday. There was no way to tell if I had made any progress w/ mufs in the driveway but running it on the lake today provided all the answers I needed. I was pleasantly surprised when my boat climbed up on plane w/ no hesitation from the motor. I don’t have a tachometer on it but it sounded and performed like it should. I guess my carbs were not as clean as I thought they were when I first looked at them in August. The moral of this story is: when someone that doesn’t know what their doing tells you their carbs are clean, better ask them what that means to them. To me it meant there was no gunk or varnish in the bowl. I did not take the top cover off to look at the jets or other holes. Something must have been clogged because after the dip and the air compressor, the motor works like it should! Thanks to all who posted. It was the suggestion to get the pressure/vacuum gauge and instructions on how to use it that helped me rule out a lot of the problems and lead me to focus again on the carbs. I couldn’t have done it without you. THANK YOU!!!!