MacGregorSailors.com

Hi guys, have been delving deeper mechanically into my motor, a 1995 Tohatsu 50D. Has always been reliable.

One of the carb gaskets was leaking a bit of gas so I rebuilt all 3 carbs.

Now when I am driving, the motor won't go above 2100 rpm. If I leave it in neutral and use the throttle paddle, can get the RPMs as high as I want. It idles fine, no excessive smoke. A bit perplexed why in gear behavior is different from neutral.

Did I mess something up in putting carbs back together? Float level or main jet nozzle or something?

In gear vs neutral rpm doesn't tell you much. If it was running fine before you "fixed" it, then my guess is you have one carb goofed up. If it truly idles fine (hard to tell on a two stroke), then possibly only the high speed jet in one carb.

Pulling the plug wires off one at a time at speed would be one way to find which cylinder is the problem, but you'd need some non-conducting tools to prevent a really horrible experience. I wouldn't suggest this method unless you've done it before many times.

I might try leaving the air box off and running it, putting your hand over each carb intake to see if that changed anything. The bad carb will either show no change or an improvement as you richen the mix by blocking air flow. Good carbs should bog down when you cover the intake.

When you rebuilt them, did you run a thin wire through all of the jets and air passages before reassembly? Something the size of a ground pepper flake could do it.

Finally, did you get it all back together correctly? Any hoses not connected? Did you check for wiring plugs that you might have missed? Plug wires tight on plugs? Tank venting ok?

If you have an inductive timing light, or other spark testing device, you might check for plug firing- just in case.

Good luck!

Jimmy, you are brilliant. Finally got out there. You were right on how to diagnose. Found the lower carb didn't fade when covering air intake.

Dismantled, cleaned out again with carb cleaner and solved the problem. While I was in there, cleaned other two as well for good measure.

Now having some irregular idle, even after adjusting the idle screws on carbs. So more to fiddle with!

Thanks again

hschumac wrote: ↑Mon Jul 27, 2020 11:02 pm Jimmy, you are brilliant. Finally got out there. You were right on how to diagnose. Found the lower carb didn't fade when covering air intake.

Dismantled, cleaned out again with carb cleaner and solved the problem. While I was in there, cleaned other two as well for good measure.

Now having some irregular idle, even after adjusting the idle screws on carbs. So more to fiddle with!

Thanks again

Glad you got the big issue solved! Good job!

I was lucky to grow up around some really smart people. My dad was a railroad mechanic, mechanical engineer and civil engineer (dual licensed), who could fix anything. My uncle was a marine engineer/naval architect and machinist. Both grew up during the depression, so "buying a new one" was not in their vocabulary. They taught me everything they could, but it was like pouring water on a stone.

A 3-cylinder two stroke is not going to idle smooth enough to balance a nickel on edge on the cowl. If it's runnng on all three and will idle without stalling, that's good. An occasional glitch is pretty normal. If you've seen it idle better in the past, keep fiddling, but make sure you're not fixing something that ain't broke (what I do all the time).

Good luck, and glad it's running better.

I don't have any specific experience with this engine, but every multi-carb motorcycle or outboard engine I've ever owned had to have the carbs balanced to run properly. If the manifold vacuum was off even a little they ran terribly.

Be Free wrote: ↑Tue Jul 28, 2020 7:24 amI don't have any specific experience with this engine, but every multi-carb motorcycle or outboard engine I've ever owned had to have the carbs balanced to run properly. If the manifold vacuum was off even a little they ran terribly.

Presumably, you can make your own manometer using small vinyl tube and water. All three tubes filled to the same level, with enough room to move without sucking the fluid out of the tubes when throttling down from speed. Old-school motorcycle carb balancers were just a bunch of tubes, so why not make your own?