prop issues?

[hump99gt]

So I'm pretty new to the whole boating world. As far as the hull I don't have alot of info on that or that I can find. Its a Tornado Tahti year I would have to guess is 70's even the registration dosn't list it. But its very close looking as the Glastron in "Live and Let Die," It has a 72 85 horse Johnson on it. The prop on it now is a Quick Silver 13x19 alum. I gps at 36mph Wot at 4,000 with a ave load. From looking on here and reading a bunch of post that just dosn't sound right at all. Any thoughts?

 

[180shabah]

Re: prop issues?

Speed sounds good, start by verifying the tach. Also, it would be helpful to know the gear ratio in your motor.

 

[hump99gt]

Re: prop issues?

Oh I forgot to mention the boat is 15' long. I'm pretty sure the tach is hooked up correct at idle its at around 1000 or there about. I'm just woundering if the prop is too much because it has been fouling out 1 plug when I ran it at a no wake speed for maybe 3 min. I have no idea what the gear ratio is. How would one find that out?

 

[180shabah]

Re: prop issues?

Hooked up properly, doesn't mean it is accurate. For 4000 rpm to be good would mean a gear ratio of about 1.75:1, I would expect the ratio to be 2:1 or lower, which would put your true rpms at 4600+

Gear ratio should be listed in your motors manual, or somebody else here may know it.

 

[hump99gt]

Re: prop issues?

Yah sorry I don't have any manuals to the motor.

 

[steelespike]

Re: prop issues?

You can figure the ratio.Pull the plugs rotate the flywheel till prop turns once. and count the rotations.On some motors one plug will foul if the diaphram in the fuel pump is split. Can't speak for the V4s.Spark could be weak on that cylinder
You can test it with a spark tester from the auto store.
Depending on the weight and type of bottom the 19 is close to what you need.
You may want to check compression and be sure the carb is opening all the way.

 

[hump99gt]

Re: prop issues?

Okay I just checked it took 2 full turns of the fly wheel to get the prop to make one full turn. I had the boat in no long ago and the guy working on it said I had good blue spark on all 4. The compression was 100 on the one side and 90 on the other.