1979 80hp

[BP1969]

So I spent a bunch of time restoring this old boat to a fishing machine. When it came to the motor it has good compression in all 4 cylinders so I went to work on it thinking hopefully it's a good motor. Put a new impeller in it to get the telltale going. Found out the wrong jets were in for altitude. Fixed that. Replaced all fuel lines and filters. New plugs an primer bulb as well. Had the motor running perfect on muffs several times and the throttle response was perfect. So I dropped it in the water today and I never left the boat ramp. It would start but I would need to choke it or it would just die on me. Primer bulb was fine but just acted like the Jets were completely clogged. Disappointed I came home put it on the muffs and it ran perfectly. Crisp throttle response on the muffs and never died on me on the muffs. I guess my question is is there some kind of pressure thing going on. With the lower unit on land and in muffs it run prefect but today putting the lower unit in the water it didn't run. Any help would be great. Thank you in advance.

 

[Chris1956]

Yes, back pressure from being underwater. That motor needs to have the idle mixture adjustment made in the water, in gear at idle speed, with the motor warm.

Set the idle mixture screws to 1-1/2 turns open, and adjust from there. Yo will likely need to richen each carb a bit to have any acceleration. So trial and error...try to accelerate. If it dies or hesitates, open idle mixture screw on top carb 1/8 turn. Try to accelerate again. If it dies, open mixture screw on bottom carb 1/8 turn. Retest acceleration in that pattern until you get reasonable idle and good acceleration.

 

[BP1969]

Thank you so much. I will give that a go tomorrow afternoon and report back with hopefully good news.

 

[BP1969]

That definitely worked and got me of the dock and on the lake. With the limited time I had I got it going but still a little sluggish and not as crisp as I would like. Got it to 27mph at wot (gps) at just under 4000 rpm. I am hoping with better turning I can get the rpm's up to 5500 where I think max rpm is. But if I get it tuned correctly and still just under 4000 then I think my prop is not right. Definitely a newby to the prop stuff. Mine is a 3 blade and says 21p. Any advice for the proper pitch prop if needed. Thanks again.

 

[Chris1956]

Check the spark plugs for color. If they are all the same color, they are all firing. 4000 RPM seems low for an engine working properly. Is Tach accurate? I would have expected you to have a planing issue if max RPM is only 4000.

A 21 Pitch prop is usually a bit too high for that motor, however, it really depends on boat size, hull type, weight etc.

 

[BP1969]

I did take the plugs out to just make sure I had good compression . I had 105 even in all cylinders. I did put in a new tech. It seems accurate from what I am hearing from the motor. All plugs looked the same just a little wet with fuel. They are the gapless type. Yes planning was a little slow. Just a note I do have the correct jets in but I am at an altitude of 9310' of elevation. The boat is 16' feet and very light. Any tips on correctly checking spark and cylinders fireing? Thanks. This forum is the best.

 

[Chris1956]

If all cylinders are the same color, you are not getting water in the cylinders. A timing light on each spark plug wire will verify all are firing.

Your tachometer should be set on 6P or 12C, which ever you have.

Do you have the correct main jets for your elevation? Std jets are only recommended for up to 5000 feet.

You probably need a 17 or 19 pitch prop. Not sure which would be best, however, if tach proves to be accurate, a 17P prop will get you about 4800 RPM plus a bit more, due to getting back into powerband of motor..

 

[BP1969]

Yes I did get the correct main/jet for my altitude. My tach is set for 6p. I will get a timing light and make sure I have spark and the cylinders are all firing. Thanks

 

[BP1969]

Bought a spark gap tester. I hope that was sufficient enough.definitly have spark in all cylinders. Got a nice jolt from all cylinders multiple times.

 

[Chris1956]

Nice jolts are good.....

 

[BP1969]

Ok took it out yesterday. Went from a 21prop to a 17 prop. Rpm went from just under 4000 to just over 4000. Thought I would see rpm improvement.it was strong to plane and felt crisp. But trolling every once in a while the rpm would just slow until it stalled out. Also once in a while at mid throttle punching it to wot it would stall out and other times it would be perfect. The only thing I can think now is the fuel pump not working perfectly. Ordered a rebuilt kit. Any thoughts on this. Thanks

 

[emoney]

Make sure you're getting full throttle out of the controls too. Have you checked throttle advance with the hood off, to make sure it's extending all the way? Some of those controls have an adjustment/different holes. If the throttle isn't advancing all the way, you can usually move the cable, at the control box, down to the lower one.

 

[Chris1956]

I would have expected a larger change in RPM when you installed the 17P prop. Your sure your tach is working correctly?

Your rectifier is good, as well, as the tach is driven by the same AC signal that powers the charging system.

 

[BP1969]

It really does seem that my tach is working properly from the rpm's that I can here but I'll learn how to check if the rectifier is working properly. All the throttle cable looks like it is working properly. I did notice that the throttle stop screw could be turned counterclockwise out about a 1/4 "

 

[Chris1956]

Carb throttle plates should be nearly wide open at full throttle. Then throttle stop should be set to keep them from pushing hard against stop on carb body.

So you would loosen throttle stop, open throttle all the way lightly touching carb throttle plate stops and then tighten throttle stop to keep throttle from bending carb linkage.

 

[BP1969]

Then it looks like everything is set on. Those plates are wide open, maybe they could go a 1/16 more. My rpm situation is puzzling. The way it just lost rpm while trolling and stalled out or at middle throttle to full throttle once in a while would stall out I think is my fuel pump not working properly. Unless I am missing something really simple.

 

[BP1969]

I guess if the fuel pump kit doesn't do it I just might be running at a high elevation.9310'
and maybe just to prop down again to maybe a 14pitch prop. But then I'll go 10mph. Doesn't make sense.