1978 evinrude 25hp engine problems

[Scheidjr]

Just trying to get some help on my older outboard. It’s a 1978 evinrude 25hp, I bought it about a year ago and rebuilt the carb and got it running with some muffs pretty easy. Now I have finally got the chance to put the boat into water. It seemed to run at idile pretty well but when I throttled it up it was obviously only running at about 1/3 power. I could barely get a 16 foot aluminum boat on plane. If anyone could give me some ideas of what the issue might be please help me out.

 

[flyingscott]

Compression and spark test need to be done.

 

[jimmbo]

Timing advance and sync to carbs needs checking if spark and compression are good. Fuel delivery. When you say you rebuilt the carb, to what extent did you disassemble the carb? Correct and all gaskets replaced?

 

[Scheidjr]

The carb got rebuilt with all new gaskets.

 

[fireman57]

Check for spark too. You might have a dropped cylinder due to bad coil. Do compression test first as mentioned and make sure it is worth going any further. These engines will idle on one cylinder but not run very fast one just one.

 

[Scheidjr]

Thanks

 

[Scheidjr]

So checked the spark in both cylinders and got a good spark in both. Just checked the compression and it’s sitting right at 60 for both as well, without doing to much research those numbers seem pretty low. Just trying to figure out the best way to move forward. Do you think it is something worth digging into and ultimately repairing?

 

[racerone]

Test with another gauge.----Check tightness / torque on head bolts.---The compression if correct is a sign of bad things.---But it could just be the head gasket blown / leaking between the 2 cylinders.

 

[fireman57]

Definitely on the low side. Did you actually remove the high speed jet and clean it? Also,make sure your timing advance mechanism is moving as the throttle increases. You can do this without the engine running.

 

[fireman57]

You can also have someone pump the primer bulb as you are running to rule out a weak fuel pump. If it picks up just replace the pump.

 

[flyingscott]

Don't do anything until you get the compression figured out!!! 60 psi is about 1/2 of where you should be hopefully just your gauge.

 

[thatone123]

Along with how hard these ol' buggers are to start with the manual starter, the next thing is that many times it is hard to get carb clean first time out. Rebuild is kind of a misnomer on carbs as many will go to they totally wear out if they are cleaned. It is really cleaning that does the improvement unless there are distinct bad gaskets. I've hardly ever seen one with worn parts that need a "rebuild". I'm sure some here will disagree. Sometimes the tip of the needle valve will be worn. You would have to have a really old carb to be worn enough to have worn parts. I know there are some, but from inspecting dozens of carbs have never come across one, so it has to be rare.