low rpm at WOT

[btruong]

hello, i have a 94 suzuki dt40 that hasnt been run in like 6 years. well i recently started gettin the boat up again and i have ran into a problem. initially, the throttle wouldnt even open fully (remote control linkage problem) and i resolved that with a few throttle cable adjustments. so now it opens fully (the carb) but the engine still wont push as hard (boat wont go as fast) as it used to. it was rebuilt 6 years ago (the outboard). and i dont have a tach, so i cant get exact rpm readings. but by the sound i can tell its lower. also, i just had a new prop installed that is 1 pitch higher than stock. what can be restricting my wot rpm? thank you!

 

[btruong]

Re: low rpm at WOT

can somebody please help me? sorry if im being pushy but im really confused and stuck right now. i believe its the fuel pump, but i would like some expert opinions before shelling out the cash for one. again, thank you, i have recieved a lot of help from this forum.

 

[99yam40]

Re: low rpm at WOT

6 years is a long time, rust can do bad things to the inside of a motor (bearings, rings,cylinder walls)A motor that sat up that long could have issues if it was not stored properly.
Start from scratch and test compression and spark on all cylinders.
make sure timing is doing what it is suppose to at idle and WOT.
Check fuel supply system pressure and vacuum, and clean the carbs.
You really need a tach to make sure it is turning the proper RPM.

 

[btruong]

Re: low rpm at WOT

:/ shoot, rust in the block?
compression test came back with 100 on the top and 120 on the bottom. service manual recommends 94. (psi)
spark plugs are good with appropriate gaps, and im sure they fire.
the carb was just cleaned.
my only concern happens to be the timing or the fuel supply. any suggestions on how to diagnose it?

ps, the engine idles properly (a little shaky due to unbalanced compression) but it doesnt pick up with the throttle.

 

[btruong]

Re: low rpm at WOT

2 quick questions.
i recently took off the fuel pump and disassembled it. according to the parts diagram, theres supposed to be a spring. no spring on mine though. could this be the cause?

also, i recently replaced my propeller. it used to be 14p but i went up to 15p, because the boat's for fishing so the hole shot isnt really a concern of mine. the boat is a 16 ft center console Cobia with about 2 adults average on it. could the pitch be too high?

 

[Red Snappa]

Re: low rpm at WOT

2 quick questions.
i recently took off the fuel pump and disassembled it. according to the parts diagram, theres supposed to be a spring. no spring on mine though. could this be the cause?

also, i recently replaced my propeller. it used to be 14p but i went up to 15p, because the boat's for fishing so the hole shot isnt really a concern of mine. the boat is a 16 ft center console Cobia with about 2 adults average on it. could the pitch be too high?

Yes- props make a huge difference.

 

[btruong]

Re: low rpm at WOT

so my pitch is holding my engine back? if i had to buy a new one, what would be the recommended pitch?

 

[deejaycee_2000]

Re: low rpm at WOT

Your recommended pitch is between 13p and 16p so your prop is fine .... get a fuel pump rebuild kit ....