1979 25 hp Engine running issues

[spacemonkey77]

Hey guys. You all helped me a few weeks ago with some seal replacement work and what I thought was a knocking noise! I got everything back together and it ran great at first but has now developed this running issue. See the video. I’m not sure if it’s a fuel issue, or an electrical issue. Perhaps timing and linkage issues?

any ideas where I should start?

Compression is good. 120 both cylinders! I checked all my grounds and they are good. Fuel pump test showed no leaks out the hole! Power pack and coil packs are about 2 yrs old! I used a timing light on the plug wires and both cylinders seem to be firing fine! Plugs are a little wet. I rebuilt the carb probably six months ago and have used the boat regularly. Only ethanol free at 50:1

 

[spacemonkey77]

Here is a second video that shows it’s doing it at a higher idle as well

 

[racerone]

The low speed mixture is too lean. -----Or throttle plate is opening too early.-------Post a picture of the adjustable stop on the throttle rod that goes to the carburetor.----Post a picture or video of that little brass barrel stop.

 

[spacemonkey77]

Ok awesome. Unfortunately I won’t be able to get back to it until Thursday. If I get a chance tonight after the kiddos are in bed I’ll try

 

[F_R]

racer aced it. No doubt about it, that motor is lean sneezing

 

[oldboat1]

While warmed up and running, turn mixture needle 1/8 to 1/4 counterclockwise (richer). Repeat as needed, or lean it out slightly if it stumbles.

To my ear, the motor is idling a little fast (throttle stop/throttle control rod adjustment). In gear, should idle around 650 rpm or so, higher idle in neutral. You should be able to shift into gear without any jerking if it's tuned correctly.

 

[spacemonkey77]

Awesome, thank you for the info. I will richen it up. As for the idle, yes it was running high. I had it throttled up a little in the video. I have a tachometer on it and it idles around 800 in neutral and a bit lower in gear. Any lower and it stumbles and dies!

it is already running richer than I’ve ever had to run it. Since I just replaced the top and bottom seals would that cause it to need to be richer?

is it common to have to change the low speed idle depending on temperature? It seems to run fine or better when it’s warm out and then run poorly when it’s cold out!

 

[F_R]

Heck, I notice a difference in needle settings between winter and summer on my own motor. And I live in FLORIDA.

 

[oldboat1]

Bad seals would cause lean running (if running) -- might involve attempts to correct by enriching the mix. So rather than running richer after the seal replacement, I think you would be adjusting leaner (?) There may be other issues -- idle circuit on top of carb might not be fully cleaned, or the point of an old needle might be broken off in the orifice. Hard to say from here.

A little similar to what F_R says, I have a motor that needs to be set a little richer for cold starting, then adjust back to the original setting.

 

[spacemonkey77]

OK I finally made a video yesterday of the linkages on my throttle.

 

[flyingscott]

Look.at the screw on the side of the motor by the tiller linkage. That is your idle speed screw it might be set to high.

 

[oldboat1]

Roller on cam follower might be worn down, needing replacement (might be referred to a a cam sleeve).

(edit. Also looks like the retaining ring at the top of the sleeve might be missing -- not sure.)

 

[racerone]

Usually at idle there is a gap between the follower and the cam.----If throttle plate is slightly open at idle then the motor is going to SNEEZE like it is doing in your video !!

 

[Newyota]

I had an issue on my 20hp like this and ran the gammett on things.One thing I found air was being sucked in the fuel pump to block gasket even though it felt tight .I gave the two screws a slight turn and that stopped that air leak.My pistons were more of a Tan color on top instead of black and plugs were white also and then pistons and plugs got blacken after the gasket was tightened.Also then had the lead shot on top of carb. pop out and it was sucking air badley and lean sneezing terribly.Got that plugged up and it fixed that issue.Sounds like for sure air being sucked in somewhere.