wot rpm

This topic has 9 replies, 3 voices, and was last updated 14 years, 9 months ago by pointman821.

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September 15, 2011 at 3:57 am #423935

pointman821
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since i have had my boat (94PII 150 Johnson fast strike) my wot rpms have been fairly consistent at a smidge below 5500 rpms. havent changed props or anything (4 blade 25p ) was running my boat the other day and at wot, i was reading 5800, today i ran it and it was topping out at 6000, and probably had a little more left before i noticed it and backed off the throttle some to keep from blowing my power head. now granted, i was running a light load today with empty live wells and only 1/4 tank of fuel, but i dont get the sudden RPM increase. the only thing i have really adjusted is my jack plate settings, but im running it lower than i did when i was running around 5500. any ideas?

September 15, 2011 at 11:57 am #423936

Bass Cat Boats
Keymaster

Have your engine compression checked again soon, before you run it. If the compression is spot on, or if it is off either then have a bore scope run to verify walls condition. It is either a ring, port, sleeve or something. It could be an electronic glitch also causing erratic readings.

September 15, 2011 at 2:53 pm #423937

Bass Cat Boats
Keymaster

im pretty sure its not the hub slipping and the motor runs nice and smooth, hole shot is what has always been,but i didnt think about it possibly being an internal engine problem but i will check that. thanks for the advice.

September 15, 2011 at 4:43 pm #423938

Bass Cat Boats
Keymaster

Hence the old saying, “they run best just before they blow”.

September 15, 2011 at 4:58 pm #423940

gchagler
Participant

Were you getting any more topend mph than usual at those higher rpms?

September 15, 2011 at 11:23 pm #423942

pointman821
Participant

it seemed as though i was getting a little more top end speed, of course it was turning 6000 rpms and the pad was breaking water less than a foot from the transom. the motor definitely doesnt lack for power. itll still put you back in your seat if you gun it from mid throttle.Last edited by pointman821 on September 15th, 2011, 11:27 pm, edited 1 time in total.

September 15, 2011 at 11:26 pm #423944

pointman821
Participant

Bass Cat Boats wrote: Hence the old saying, “they run best just before they blow”.i sure hope not. im gonna pull the compression test on it this weekend and see if its any different than when i first got the boat back in april.

September 18, 2011 at 7:08 pm #423946

Bass Cat Boats
Keymaster

ok, results from compression test are as follows left side of engine(looking from behind the motor) top to bottom….120,121,120 psi.right side of engine top to bottom…..135,119,122 psi. im pretty familiar with the problem if you have one cylinder thats got a significant lower reading than the rest, but one thats 15 psi above all the rest? im in unfamiliar territory here. any advice or tips would be much appreciated.

September 18, 2011 at 8:02 pm #423947

Bass Cat Boats
Keymaster

We dont think you have an issue with those numbers, though we hardly ever see one so high.

September 18, 2011 at 8:20 pm #423949

pointman821
Participant

i was thinking the same thing. ive done a little research and have found out that carbon deposits could actually cause the rings to exert more pressure on the cylinder walls. i havent fogged the engine since ive had it. i think ill try that and see if the pressures equalize a little. even if thats not the problem, a fogging is cheap insurance and certainly couldnt hurt.thanks for the reply bcb.
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