Running a 20hp LT on a 1436. Max RPM seems to be 2900 in the water(3030 out) with an 8x4. Don't have an exact speed but seems just as fast as my 13hp was. Cav plate does seem to be running about 6" under water. My questions are:
Shouldn't I be getting more RPMs?
What could be causing this?
How can I correct it?
Thanks

I've never had a tach on a long tail, but I would imagine you need to be running higher RPM's. check your throttle cable. Make sure it hasn't slipped where the clamp holds it in place on the motor. Bend your cab plate down a little more to let it ride higher in the water. I bet it's bent upwards some. Take some of the bend out of it

Should be about 4000 oow and at least 3400 in water.


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I'd run a 9" prop on a20 horse long tail . I run a 9x4on my 16hp

Get a 9x5 for that 20hp
You'll be happy with it

Backwaterinc.com

should definitely be spinning 3500 to 3800 in water rpms. I would think a 9x5 would be close to correct

Ran it again today, 3250 rpms and 13 on GPS.... Still seem off

Plate is right below the surface. 2 people on boat no gear. Prop is 8.5x? Upon further measuring.

Sounds like a worn prop. Get a new prop the size suggested in the above posts.

Will do hopefully put an order in next week. While most people /companies suggest 9x5 is there anyway I could get away turning a 9x6 effectively? I run a light boat and the 9x6 is recomended for a 20 by go devil. I'd be happy running the same speed with fewer rpms. And have bore bite in mud. Just a thought though.

I would try and figure out the rpm problem first. You would think if the prop was worn it would turn higher rpm's than waht it would do with a new prop. Ya'll correct me if im wrong but once he is turning good rpm's with the current worn 9x5 he could maybe try going to a 9x6 considering he has such a light boat?

First, I would make sure I had good tach readings.
Second, I would suspect the engine governor (linkage settings etc) .
Third, take physical measurements of the prop to check for wear at the tips, then suspect maybe it could be the prop "pitch".

---- How many RPMs you getting Wide Open Throttle with one man and no gear (straight line, smooth water)? Are you getting up on plane?
Can you reach back and push the governor linkage when driving (in the water) to see what max WOT rpm you can get from that existing motor/prop combo?

I will assume the tach is accurate
How do you adjust the governor? just bend the tabs? what is a good WOT in the water?
Prop was measured in anoter thread title "what prop is this"

Boat will plane with 4people on it.
will try to reach back next time I go out an push the linkage


Can i Just get a large pitch prop and connct my throttle right to the carb since I dont have to worry abou over-revving?

Your 14X36 "boat will plane with 4people on it" and a 20hp longtail?
That not too bad ... well it's miraculous !

Depending on your tach -=-- depends if it's direct driven or impulse, etc. They can be quirky if impulse (ie has a wire that wraps around the spark plug and has a digital readout). Some little impulse tachs can have a built in delayed response that can mess-you-up depending on how you read it. Some kinda have to be stared at a long while until they 'even out', or they will stutter 300-500 rpms.

Governors (and rev limiters) are a huge mystery that should be studied per the individual motor.
Never mess with "adjusting" a governor unless you know exactly how YOURS works.
They can adjust by as simple a means as a stop screw, OR switching holes for the springs on their "arms", BUT be sure to find out how yours exactly works FIRST.
They vary a lot from engine to engine , and often have a touchy super-sensitive relationship with the carb throttle.
All that is why they can be the first source of rpm problems.

"Can i Just get a large pitch prop and connct my throttle right to the carb since I dont have to worry abou over-revving?" .....
If your tail hits an object and hops out of the water how you gonna keep the revs down?
Those final rpms and gps speeds will always be limited by the fact that engine needs to keep from thrashing its' flywheel, or floating its valves, or breaking its connecting rods or.....

Ran it again today with just me in the boat, at 3250 I was getting 17-18mph. By pushing the governor arm/bypassing it I was able to get a around 3600.
Prop was originally a 8.75x5 but worn down closer to 8.5. Would moving to an 9x5 or 9x6 give me any gains? Would be happy to go up in pitch and get WOT to be around 3100 if there woul be any performance gains

see my above post ^^

Yes a 9x5 would work better. 8x5 (yes being worn down 1/2" matters) you're losing minor speed and pitch.

Get a new prop - use the one you have as a spare.