Tohatsu D motor will not run

[daveracerdsh]

I honestly hate having to make this post...but I have a Tohatsu D stock motor that has issues that nobody, including some people way smarter then me, can figure out. Here is whats going on: Motor is the first Tohatsu D stock motor made. it has great compression.....135 to 140 on all three cylinders. Motor has been on a slow decline for 2 years. 2 years ago, I could pull my best prop at a race site in Oregon and see close to 84 mph...last year, saw 82 with it, this year, barely 75. Same boat. Same fuel. Same oil. Same driver. Etc Etc Etc. Now, motor is only running on top cylinder, yet is has strong spark. Went thru carbs, they are pretty simple. Have replaced electronics with three seperate units....no change. Motor starts....you get it warm, put your hand over carb one and it kills motor. Put your hand over carb 2 or 3 and nothing happens. You take the number one plug wire off plug one, motor dies. Take wires off 2 or three? No change. All seals are good, bottom, top, exhaust, head gasket, oil drive, you name it. All seals were new when rebuilt this last March. Checked flywheel....has not sheared key or anything like that. There are about 6 very intelligent people that are totally stumped by this. Oh yea....reeds are fine....brand new. Also, I have run motor with the kill switch wires unhooked.......What on earth are we all missing here? Any help would sure be appreciated. Dave

[65R]

I've never looked at a Tohatsu, but if you haven't yet I would look at fuel system. Simple problems I've seen are bad fuel line, fuel pump, fuel bulb, fuel filter. Just a thought. We all like puzzles, keep us posted

[65R]

I've also seen bad grounds cause issues, (use star washers) just throwing ideas out

[Black Sheep]

Do you use a squeeze bulb?

[daveracerdsh]

star washers on all grounds, no sqeeze bulb

[brian]

Does your fuel line fill top down, bottom up or middle fill? Spark, fuel, air sounds like fuel. Could be way out of time with a broken crank. Wise man said change one thing if not that put original part back on. My guess. Weak fuel pump. Are spark plugs 2 and 3 hot use laser temp gun. Are all three bowls full of fuel when you run it hard and stop? These are my 12:30 am questions and thoughts.

One other fun test...put a sqeeze bulb on and do the same tests while adding pressure to the fuel line. If it runs better fuel pump or line issue.

[chuck w]

Puzzles are fun.
Sounds like cyl. 2 and 3 are doing something at higher speeds if you are doing 75. I am assuming it uses a diaphram fuel pump that uses crankcase pressure. Remove the crankcase pulse line from fuel pump squeeze primer bulb and see If fuel is leaking out causing bottom cylinders to flood through crankcase. Could be pin hole in diaphram. If that doesn't work I would switch carbs around and see what your findings are.
Good luck

[benf27]

Have tried new spark plugs? They do go bad sometimes.

[kampenracing]

The first Tohatsu that we purchased new never ran good. No matter what we did we couldn't figure it out. Finally figured out the crank was broken new from the factory.

[Fast Freddie]

Are #2 and #3 coils wired opposite?

[ricochet112]

Start the motor with your spark tester connected to 2 & 3 and see if there's spark while it's running. If you have spark, pull an intake and or exhaust cover and look at the pistons and rings.

Double check the trigger/sensor wires from trigger to pack, and pack to coil to make sure they're not crossed

[Black Sheep]

We should hook it to my Power Absorption / Adjustable Friction Device...

[3 Point Drifter]

Check the vacuum pulse lines from the crank to the carbs, making sure they aren't cracked or ill fitting at the carbs. Any loss of the pulse will not allow the fuel pump diaphragm to send fuel to those carbs. Check #2 and #3 plugs for signs of a lean burn. When the engine is at higher rpm's it's probably making just enough pulse to pump fuel to the bottom 2 cylinders.

[daveracerdsh]

Thanx for all the ideas. Got off work today and did not have a chance to check HR. A few more things I have done/checked. I replaced all the fuel line, from the tank to the fuel pump and the lines in between the carbs. I took carbs off and again made sure the float levels were correct...I purchased all new needles as well as floats today and installed them. I put a brand new out of the box fuel pump on, replaced all bleed lines and check valves, put on a new head gasket, new gasket behind the oil pump drive cover, new base gasket, replaced the two exhaust gaskets, checked that all ground wires are good and made sure they had star washers, new kill switch, checked all wiring for the 5th time to make sure it is wired correctly....and I used different gas, oil, and a new fuel tank just to take everything out of the equation. Checked the compression one more time, also bought a second set of new spark plugs. Motor fired up in test tank.....got it warm, held it at 2 k rpm.....and put a small piece of cardboard in front of carb one. Motor died. Re started motor, did the same with carbs 2 and three....nothing. In chatting withEd Runne today, his advice is that I am losing base compression someplace. Bad pistons, something internal. I do want to thank Tim Fihn for sending me another powerhead this afternoon. dave

[Yellowjacket]

First, look at the plugs you've taken out of cylinders 2 & 3... The plugs will tell the story.

Are they wet or are they dry?

Since you have an oil pump you may have oil on the plugs if they aren't firing, but look for fuel. If you don't have fuel on them it's the carbs or induction.

You can do a shot of fuel into one of the two not working carbs and see if the motor kicks. If it kicks then do the other carb on the non-working cylinder and see if it kicks.

If they're damp you may not be getting enough fuel and if they're dripping wet you may have too much.fuel but the plugs will tell you the story.

You said the engine has cylinder compression. If you're losing base compression it has to be overboard or between the cylinders. If it's overboard you'll see the spooge leaking out. If it isn't then it isn't overboard.

To check for internal leakage put cylinder #2 at bottom dead center and take the plug out. Make sure cylinder 3 is high enough for the ports to be closed. Restrain the flywheel so it won't turn. Put the output of your shop vac to blow into carb # 3. If you get air leaking out of # 2 plug hole and the exhaust then it's leaking between # 2 and 3.

This isn't rocket science.