1975 70hp johnson no WOT

Hello I have a 1975 70hp johnson model number 70esl75b that has me beating my head against the wall . A year ago when I bought the engine I had no power at WOT and I found the bottom carb high speed jet was plugged and it has worked great till two weeks ago . It started doing the same thing so I rebuilt all three carbs , new plugs , it will spark across a 7/16 gap , all new fuel lines , good compression and still won't Rev out I'm running out of things I know to do . Any help at all would be greatly appreciated .

Are throttles plates inside of carbs opening up all the way. Try pumping primer bulb while running,have asst. do this.If it gets wot, fuel restriction, or weak pump.

Ya everything opens up all the way , the choke plates aren't closing like I've seen some people have trouble with also and no change when pumping primer bulb . This one really has me shaking my head because nothing I do changes anything at all .

timing advance?

I thought about that but not real sure how to test that . When you put the engine in gear the timing advance lever starts moving forward before anymore throttle is given . Other than that I don't really know how to test it

Test compression.---------Inspect reed valves.

Compression is good , 115-120 in all 3 cylinders . I'm not sure what a reed valve is

Did you actually carefully clean the high speed jets again (all of them) with a piece of single strand steel wire as you did once before? If not, do so. It sounds like you're going down that same road.

There are two main causes (of course many others too) that occur to many engines that result in what you describe, and that is a sticking timer base and clogged high speed jets. You know how to clean the jets.

The timer base should move freely and smoothly from its retarded (idle) position all the way up to the full spark advance position where the timer base would be right up against the rubber cap attached to the head of the full spark advance screw.

(TEST)
Engine NOT running, spin the prop and put the engine into forward gear. Now, have someone slowly advance the throttle to full throttle while you observe the timer base to see if it indeed advances to the full spark advance stop as it should.... smoothly with no sticking.

Let us know what you find.

I have made sure that the timing advance moves all the way to the stop smoothly and it seems to . I'm getting ready to go dunk it again now and see if anything has changed after going through the carbs again . . Jets are very clean can see right through them perfectly .

Well we have new life . I launched it and it took off like a bat out of hell all the way across the lake . Buuuut lol after idling for problems 30 minutes fishing I went to take off again and it did the same thing so I held my hand over each carb and the only one that about didn't make it die was the top so I pulled the plug wire and no spark . So I'm gonna order a new coil and hopefully it solves everything . I guess it was showing good spark until it gets hot .

Happy motoring!!