18 hp tohatsu runnig bad at speeds

[elitl]

my engine runs great in idle.at high rpm it misses,took to dealer cleaned the carb same thing. changed the plugs same thing,starts on first pullevery time.the top plug was black when i changed them ,bottom plug was clean.can anyone help?

 

[John_S]

Re: 18 hp tohatsu runnig bad at speeds

Get a service manual. Worth every penny.

How does the spark look on that top plug? compared to bottom plug? If bad, do you have two coils? Swap and see if problem moves? If it did, found bad coil. Otherwise continue tracing further back.

 

[TOHATSU GURU]

Re: 18 hp tohatsu runnig bad at speeds

Check compression and spark. If Okay clean the carb again....Make sure that when the carb is cleaned it is allowed to soak for at least 5 hours in the cleaning solution.

 

[elitl]

Re: 18 hp tohatsu runnig bad at speeds

iwas told by dealer it has good compession.also the dealer cleaned carb ,50 bucks. :'( do you think it could be a coil?if the coil was bad wouldn't it be hard to start

 

[TOHATSU GURU]

Re: 18 hp tohatsu runnig bad at speeds

Ignition system parts can be all the way bad or sometimes bad. Nineteen times out of twenty it's still a clogged carburetor....And $50.00 was 1/2 what most dealers would charge which kind of leads me to believe that it wasn't cleaned with a lot of love.

 

[elitl]

Re: 18 hp tohatsu runnig bad at speeds

checked fire weak fire on top plug .only has on coil ::|where can i buy a coil online?it is a m18c2 engine

 

[John_S]

Re: 18 hp tohatsu runnig bad at speeds

While Elvin will respond "Any Nissan or Tohatsu Dealer", do not be afraid to give him a call. d

But, before shotgunning the coil, it is probably rather expensive and non-returnable, swap plugs and retest. If it moves with plug, its not the coil. Next, check the primary and secondary coil windings with an ohm meter. The manual has the acceptable ranges for each. But, assuming you have two coils in one module, you should be able to compare the primary to primary, and secondary to secondary, without the manual. The differances might be enough for you to pull the trigger on that shotgun.

Did I mention geting a manual? d

 

[John_S]

Re: 18 hp tohatsu runnig bad at speeds

I looked at my Nissan 18E when I got home. The coil looks to have one primary and two secondary coils.

From my manual, which should be the same for your engine:
- at 68 degrees F
- Primary Coil Resistance 0.25-0.37 ohms (need a good meter to get accurate readings below 1 ohm)
- Secondary Coil Resistance 3075-7625 ohms (measured from sparkplug lead wire element to black coil lead)