Motor Question

[kendizzle]

First post here. Looks like a great sight!

I have a late 70's Johnson 100 hp engine. It starts, idles, and tops out at about 15 mph. It will not get past 15, yet runs great until then. This is my first boat, so I'm not too familiar with 2 stroke engines. Any idea what could be causing this? I will take it to a motor mechanic if needed, but dont want to spend more than its worth. Thanks.

[Makitcnt4u]

Welcome to the site. How much did you pay for the engine? How old is it? Does it sound funny like it's overrevving?

[kendizzle]

I paid $900 for the boat and motor. The guy had it checked by a motor shop and said that it was either a stretched cable or gas line blockage. Knowing my luck, it cant be just that easy. It runs perfectly fine, it just wont get faster than 15 mph.

[jeffman]

JOSH,
Â* Â* Check the fuel filter, it may be clogged with rust or debris. At any rate, it probably needs to be replaced.
Â* Â* Put a set of water muffs on the motor, pull the cowl and check to see if the spark plug wires are sparking across. You can put your hand on them to see if you feel a little buzz from the spark if you care to. Pull the magneto and check the points to see if they are burned. While you have the mag off, check the half moon key to see if it is partially sheared (This would retard your timing)
Â* Â* Take the gas line loose from where it comes thru the splash well and put the end in a gallon of gas (or gas/oil mix if your motor is not oil injected) if it runs good on fresh fuel, you need to drain all the fuel out of your tank(s), it has soured because somebody did not put stabilizer in the tank before they stored it. If the boat has set for quite a while, this is probably your problem. While you have the cowl off, push the trottle as far foreward as it will go, then grab the throttle linkage under the cowl and see if it will move any farther open. I doubt very much if the cable is stretched, as 15 mph is about 1/4 throttle. If it is the cable causing the problem, it may just need adjustment, not replacement. You may also pull the cowl and have someone else drive the boat while you lay on the back deck and work the throttle linkage on the motor by hand to see if you get any more speed out of it. If it was a stretched throttle cable, I don't think you could get enough power or speed to get the boat up on plane.
Â* Â* If none of the above ideas fix the problem, you should probably take it to a boat mechanic as it may need the fuel pump diaphram replaced or the carbs cleaned.
Â* Â* Have you pulled the plugs and checked the gap, or replaced them?

JackL

[kendizzle]

This is what confuses me. It has new plugs which are gapped, the carb has been cleaned, the powerpack is good, and i drained and replaced the fuel. I'll give the other suggestions a shot. Thanks.

[Makitcnt4u]

I would of also thought that it was a fuel system problem. Check the fuel pump to see if it's going bad or has a blockage. Also check the fuel filter for something blocking it.

The throttle cable could have corroded or siezed up where the speeds from 15 & up are controlled.

I would check the fuel system first though

[kendizzle]

THanks for the tips guys. I'll let you know if this solves it or not.