Not running full speed consistently

[alwayzfishin]

I have a 1981 Starcraft CC with a 91 Evinrude 88 SPL for power. The problem is this: it does not always reach full speed after getting on plane. Usually after being on plane for 15-20 seconds she settles down and takes off like a shot. Just had a new prop and hub kit installed to match the original. All 4 cylinders test ok for spark and compression. No water in the bottom of the boat, and no excess of equipment on board. Only other thing I can think of is a stretched throttle cable. New fuel filter in-line and also use Star-Tron. Boat does not have trim tabs and adjusting manual engine tilt only changes the hole shot speed. Is there anything else simple I might be missing? I have a good mechanic, but don't want to pull the boat if I don't have to, for obvious reasons! I have a tach on order to check the RPM's but I'm hoping someone has an item on their checklist that I don't. Thank you in advance!

 

[mikesea]

Re: Not running full speed consistently

maybe a bad plug or coil kicking in after the load settles.Is the boat new to you,?did the problem receintly occur ?have you ever had it operate as you believe it should?Did you have the problem before the new prop.If after,I say the prop would be the problem.Props are sometimes machined and the marking not changed,so an original prop could have had diameter and or pitch machined and the markings not reflect that actual machined prop

 

[alwayzfishin]

Re: Not running full speed consistently

It actually started with the old prop. Bought the boat in Sept. Not knowing the actual age of the prop I figured new was the way to go. I was convinced it was a spun hub, but the mechanic that helped me install it said no, the splines looked fine. The only condition that I found that would make a difference was water in the bilge (no float valve-that's next!) I've had 5 people on this boat flying around with no problem. Last week I got it settled down and took off with no problem. This week- no luck. Does the engine need to be at normal operating temp before it will perform? Also, how does double-clamping affect the fuel line? We pulled all the plugs and they looked fine, along with good spark and compression in all 4 cylinders. With an 88HP motor, I have the potential for a rocket which would help in going further to fish as opposed to locally. Granted, I can go 200 yards from the ramp and catch fish all day so distance is not really in issue until the Stripers start running in the fall. Like I said, I have great mechanics at the Marine shop, but I'm hoping I just missed something dumb. Not really comfortable with checking the cable adjustment without someone on hand to show me how to do it right.