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5 hp tohatsu low RPM amp propeller pitch

mhunton

New member
"I have a 5 hp tohatsu and I a

"I have a 5 hp tohatsu and I am having trouble running at trolling speeds. The engine is new and I have had a mechanic adjust the carb but I just can't go slow enough. My boat is a 14 ft Lowe sea-Nymph (140lbs). I weigh 190 lbs, so even with my gear I'm not pushing much.

When running at low speed, the engine misses and then dies. I don't have a tach but the RPMs sound quite low so like I said I don't think it is the carb but who knows. If I adjust the idle screw so it stops missing it doen't die but then I go too fast.

My thought was to change the propeller from the standard 8 (7.9 X 7.9) to the 7 (7.9 X 7.0). I'm sure the change in pitch from 7.9 to 7 will slow me down, but then I worry about high RPM at max throttle. Like I said I'm not pushing much.

So then I look at the engine specs and it says maximum RPM 5500. Like I said I don't have a tack. I have an old model for a car. Can I use that tach on 4 cyl. and then multiply by 4?

Finally, I know that the only difference between the 5 hp and the 6 hp is carburetion. The 6 hp max RPM is 6000. How would a change in carburation change the max RPM from 5500 to 6000?

I generally don't run the engine at maximum throttle but I understand the safety principle behind not exceeding the max rating. But what gives on the max rating difference between the 5 hp and 6 hp?"
 
"I understand that better carb

"I understand that better carburation can increase the horse power and therefore the RPM, but if I change to a lower pitch prop the RPM will also go up due to less load. How high can I let it go. 5500, or 6000 RPM. They warn you when changing props to not let the RPM exceed maximum ratings. The maximum rating for the 5 hp is 5500. For the 6 hp it's 6000. Would it be safe to change the pitch of my 5 hp until I reaches the 6000 RPM level?"
 
With the carburation I have on

With the carburation I have on the 5 hp do you think I even need to worry about hitting the max RPM with the 7 pitch prop? What If I went down to the 6 pitch prop? These props cost about $70 a piece. Kind of an expensive experiment if it runs the RPM too high.
 
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