prop question

[natedawg]

my 1972 125 needs to get a few more rpms (about 300 to 500rpms) and it has on it a 13 3/4 x 15 should i go to a smaller dia. or less of a pitch?

 

[vano6990]

Re: prop question

Less pitch = Higher RPM <br />High pitch = Lower<br />I read somewhere 1% change in pitch (plus or minus) should equil about 200 change in RPM.

 

[ob]

Re: prop question

Tell us what length,hull style, and approx weight boat you're pushing with the 125,so we can tell whether the 13 3/4 X 15 should rap out more.You may have another issue.What rpms are you getting now at wide open throttle?Did it ever turn higher rpms as propped?

 

[natedawg]

Re: prop question

well the boats glastron 1981 weight is about 1000 lbs ita a vhull the boats is new to me so i dont know what the history it has about 115psi on all 4 cylinders and the timming is good the throttle is open all the way at wot but the plugs are old and they look like avation plugs are these ok to use in this? <br /><br />oh i i do have trim tilt on it so i tryed to trim it out but no help b4 the boat slowed down

 

[natedawg]

Re: prop question

ok i may have found my problem the plugs that are in it are autolight 2852 and they are not the correct ones. they are for the more high power systems ive been told. they look like avation plugs to me. <br /><br />Any sugestions?

 

[ob]

Re: prop question

The correct plugs for the 1972 125 John/Rude is Champion QL77JC4.The optional Champion plug for sustained high speed operation use is,L76V surface gap.

 

[natedawg]

Re: prop question

thanks i also nottice that there are two diffrent sizes of threads on one head... same plug but diffrent sizes in threads.... do you think this could be my rpm problem?

 

[natedawg]

Re: prop question

not having the right plugs?

 

[ob]

Re: prop question

Not having the right plugs is most definately "A" problem.Correct it and we'll see if you still have more issues.The different size threads may indicate that one head has been oversized due to stripped holes or a previous owner experiment.You'll need to make sure that the seating surfaces for the correct plugs are original depth and the proper heli-coils ,if needed,are able to be installed.Hard call on my end without seeing it.