Need your advice!

[jweckley]

I am running a 1973 24 foot Aloha Toons. With a Mercury 700 Thunderbolt (70Hp) 1978 outboard. I have a 105/8 X 12 Prop only hitting 4000K RPM. I have a new Tach set at 6P per the instructions. Getting 18 MPH top speed 6 people with Gear. Is my prop the problem? Followed Seloc re sync procedure exactly. Rebuilt carbs. New gearcase oil/ No leaks. 50:1 on the top side. only runnign issue is right before it picks up the secondary's it stumbles still have to adjust. Based on the 200 RPM per pitch I need an 8 pitch? sound right? New fuel pump rebuild kit enroute and new plugs and wires. Any help is appreciated.

Thanks!

John

 

[lakegeorge]

Re: Need your advice!

I am running a 1973 24 foot Aloha Toons. With a Mercury 700 Thunderbolt (70Hp) 1978 outboard. I have a 105/8 X 12 Prop only hitting 4000K RPM. I have a new Tach set at 6P per the instructions. Getting 18 MPH top speed 6 people with Gear. Is my prop the problem? Followed Seloc re sync procedure exactly. Rebuilt carbs. New gearcase oil/ No leaks. 50:1 on the top side. only runnign issue is right before it picks up the secondary's it stumbles still have to adjust. Based on the 200 RPM per pitch I need an 8 pitch? sound right? New fuel pump rebuild kit enroute and new plugs and wires. Any help is appreciated.

I would think that a 14 x 11 prop would be about what you need, that being said, I don't see you getting any more speed than 18mph with 6 people. Actually 18 is pretty darn good.
Find out what rpm's the motor is rated for before doing anything.

 

[jweckley]

Re: Need your advice!

The engine is rated to 5500. I won't run over 5300. And maybe 5100 is a good number. I am not worried about speed. If 4 MPH is the right speed that's fine. Are there other variables keeping me from reaching 5000 RPM? It feel like it's lugging at 4000. I am hoping it's the prop a this point. The 10.5 number is about and inch and a half from the prop hitting the (sheild?) just above the prop on the engine(where the trim tab is bolted). So the biggest would be 11.5 inches diameter. MI prop Calc suggest an 8 inch prop? That seems fairley flat. Any suggestions will help. Thanks for your replies. You guys have it down.

 

[Bamaman1]

Re: Need your advice!

I cannot remember ever seeing an 8 pitch prop. You're methodically going through your boat, however your boat's pretty long and your engine's pretty small (by modern standards.) And who knows if your engine's in great shape due to usage and age.

Another issue may be small toons. Most older boats didn't have 25" toons which are easier to push.

Sometimes it's time to move up to something a little more modern--or be satisfied with marginal performance.

 

[jweckley]

Re: Need your advice!

The toons are 19". I wondered if it sitting low in the water would have that effect. I am only really worried about hurting the engine. Ive read that lugging the engine for long periods can be harmful. Should i try to re prop to gain the RPM. Not worth it?

 

[crb478]

Re: Need your advice!

I also have not seen an 8 pitch prop, and you should probably be looking for a 9 or an 11 pitch. If you are stuck at 4000 rpm and the motor is running right as well as the tach is accurate then you need a smaller prop, or your motor may be too low. Raising the motor can raise rpm's but only raise it to the point that it still pumps water well and you do not cavatate or blow out while running or turning. I would also try to get the motor set up to turn the full 5500rpm. You don't have to run it wide open, but that will keep you from lugging it which it sounds like you are doing now.

 

[jweckley]

Re: Need your advice!

Thanks for the responses. I have raised the motor and the first little wave i get it cavitates. The prop i have has no stampings of size just a part number which also indicates its a cupped prop. I am not sure if this makes a difference. I will talk to the local marina and see if they have a prop I can "rent"and try out.