Tohatsu M90 Top End RPM LOW

[cmarinello]

I cant seem to get anymore than 4000rpm indicated when running. <br /><br />Things i have done,<br />1. Removed the carbs and cleaned all parts. <br />2. Adjusted timing.<br />3. Cleaned fuel filter<br />4. Replaced plugs.<br />5. Cleaned the fuel filter<br />6. Cleaned the fuel pump. <br />7. Adjusted all linkages per mfg recommendation<br /><br />I am at my wits end. <br />It does seem to make a jump to about 4100 when i press in the keyswitch and activate the choke for about a sec. Not quite sure what this means. <br /><br />Thanks in advance for any help

 

[dobers]

Re: Tohatsu M90 Top End RPM LOW

are you sure your running the right prop??

 

[TOHATSU GURU]

Re: Tohatsu M90 Top End RPM LOW

Starving for fuel at high end. Carbs, reeds, fuel pump/lines probably. Could also be a compression problem.

 

[cmarinello]

Re: Tohatsu M90 Top End RPM LOW

I will replace the fuel lines.<br />I have checked the reeds and they are within spec. <br />The carbs have been cleaned and adjusted to mfg specifications. <br /><br />Another interesting note is that when i start the engine and manually move the carb linkage the engine will go to 5000 rpm. <br /><br />The prop is ok. This problem has persisted since the start of the season. It was much worse, not even reaching 3000 until i cleaned the carbs. <br /><br />Not quite sure what the fuel lines have to do with this. <br /><br />also when i removed the carbs to clean them and looked at the floats i noticed the were not adjustable as they are made out of plastic, meaning the tab is plastic and not adjustable. <br />The float height did seem a little high.

 

[TOHATSU GURU]

Re: Tohatsu M90 Top End RPM LOW

Any leak in a fuel line our fuel fitting will allow air into th system causing the engine to starve for fuel. You might want to clean the carbs again.

 

[cmarinello]

Re: Tohatsu M90 Top End RPM LOW

Thanks Elvin.<br />I will make sure that all the fuel line connections are tight when replacing. <br />What would be a good way to check that there is enough fuel going to the carbs. <br />Is there a way to check the pump as far as output. <br />Do you think i should replace the mixing valve? where the oil and gas mix before going into the carbs. <br />I didnt do anything with this when i cleaned the carbs last time.<br />Thanks in advance

 

[TOHATSU GURU]

Re: Tohatsu M90 Top End RPM LOW

If the prime bulb goes soft while you are under a load then the problem is a fuelpump back to the tank issue. I've never seen a bad value there so that's probably not the problem. I would redo the carbs and check compression.

 

[cmarinello]

Re: Tohatsu M90 Top End RPM LOW

Elvin,<br />So i should depress the bulb while its running to see if its soft?<br />checked the compressions and they are ok.