45" Dumas scarab, a classic.

what sort of temps should i be seeing on the engine? water is flowing through the head and manifold. the cooling jacket seems pretty hot when i get done running it.

It's got a prather 275 on it now. My uncle did some work to it, I'm unsure if it was helpful or harmful.

Roxyflash said:

What prop you running ?

Click to expand...

Justin BeaVe BeVier said:

It's got a prather 275 on it now. My uncle did some work to it, I'm unsure if it was helpful or harmful.

Click to expand...

A 275 Prather running surface drive should push that hull with some pretty good speed… I run the same prop on my F- mono (.90)

I’m betting the strut is either too high or at the incorrect angle.. that’s why it’s throwing the rooster tail straight up and not back…

That motor may not have enough power to pull the prop at the proper position, that’s a lot of hull to push thru the water… may need to prop down and lower the strut.

Post up a few pictures of the transom and hardware at different views,,, we might be able to give a few more suggestions once we see them..

The header as well as the motor probably being low timed is what is keeping it from turning the rpm it needs to really get that prop going. But as Frank mentioned a pic of the side looking through the strut and back would help figure it out for you .

I've played with the strut height a little, I can find a happy medium where it revs and goes, but it feels like a n/a RX7, it's great at turning gasoline into noise.


I did notice the starboard trim tab wasn't mounted flush with the bottom of the hull, I'm fixing that and I was told to sand the bottom of the hull with 320, so I repainted it tonight and I'll sand it down tomorrow.

Maybe it just needs more power.

The nipple coming out the side of the pipe, does that need to be hooked to the fuel tank vent like a nitro? Or is it for water cooling the pipe?

Also, how hot should this be running?

If the nipple is coming out of the big part of the pipe then that would be for nitro now if its where the header connects to the pipe then that would need water to not melt the orings.

It has a little up in it which maybe it needs because I see the trim tabs are all the way up as well. being surface drive which i am betting the boat was made to have the shaft coming out the bottom and the prop being lower you might have to get more rpm to make it really set up on top of the water and go. It looks like he detounged that prop which is ok. But as someone else said that prop is throwing water up and not back so it needs some cup in the edges to direct it backwards.

If it was me I would get a new header from zippkits if you want the pipe to come out the middle back of the boat either a 100 degree or 105 degree header. then shorten it to 13.5 inches to the largest part of the pipe. that means using solder or a string measure from the end of the engine to the middle of the largest part of the pipe and make sure you measure trying to go in the middle of the tubing as you wrap your string/solder around to find your length.

I would also get a 7016 propeller from him and try that. you might need to look up how to balance a propeller . you can use a block of foam stand 2 razor blades on their ends sharp side up as level as you can and use a rod or something that fits in the propeller to set on the blades and watch which blade falls low then sand /file the back of the blade only to balance it. try to get it where no matter where you put it it stays still resting on the razor blades.

That motor might not have a pipe timed cylinder so if you really love that boat you might think about getting that 138 dollar 26cc engine off ebay I mentioned.

Boats are a big learning curve and it is hard to explain it all but if you just tinker and have fun with it you will enjoy it.

If it seems like just too much hassle then try to get another boat such as a seaducer gas boat that is already setup by someone and save your frustration. that boat is old technology but could be made to work but it will take some effort and money thrown at it.

you can get the chinese engines here for $134 shipped from the USA. coupon code tit-racing.

https://www.tit-racing.com/collecti...cy-engines-fits-hpi-baja-5b-5t-5sc-ss-rovan-1

boat will be nice once you get the right prop and header. I personally dont think a new engine is called for. $50 and some setup effort and she will be going mid 50's.

that prop looks to be de tonged.. it needs to go..

Start with a new prop
Move that water pickup as far up as you can and still get water to the motor

I agree, I think that boat would work better with the drive tube coming out of the bottom and sub surface drive..
use a strut sucked up tight against the transom and a simple sleeve bearing on the cable shaft. Switching to a dual pick up rudder blade will clean up the hardware nicely too.. you will need to prop down when switching to sub surface, as the prop will no longer be free wheeling and doing more work.

Never have liked those tiny ride plates…
4” L shaped stainless steel ride plates set 1/8 inch above the bottom of the hull will give you more surface area to make adjustments with..,
Simple and easy, bolt them on, adjust them with a set of hand tongs.. set and forget.

Doing just these small things will make that boat more enjoyable and easier to maintain..

Mid 50s would be absolutely wild. I feel like right now we're probably in the mid 20s,

Wasted wages said:

Doing just these small things will make that boat more enjoyable and easier to maintain..

Click to expand...

Honestly, I just love tinkering with it trying to make it faster.

Grimracer said:

that prop looks to be de tonged.. it needs to go..

Start with a new prop
Move that water pickup as far up as you can and still get water to the motor

Click to expand...

Ordering new prop, header, pipe, and prop balancer tomorrow.

Joe at zippkits said I only need one water pickup, so the extra one is going. I think I'm going to try the 7016/3

that boat with the full length strakes doesnt need any lift in the prop. if it spins a 275 like that, an octura 470,472,670 would be great. i think joe has similar to all those on his site . if ur doing this as a side/fun thing on a budget ,zippkits has all you need ,just get what u want when u want it . for a 23cc all the stuff would benefit, the exhaust system he has will work nice.
o yea water pickup on the right only ,,even can swap that out for a zipp rudder at some point.
also gizmomotors is good esp if u catch a sale

I would take a straight edge on the bottom of hull run trim tabs flat then strut try 3/8 up from bottom flat also get a stock 275 prop balance and sharpen it try it the motor is turning good rpm’s so the new pipe might help but there’s other problems the strut water pickup needs to go it a anchor causes big drag

Something makes me feel like the engine is way too far back.

ACTION JACKSON said:

Looks like a 55 inch scarbe

Click to expand...

i've thought it was a 45" this whole time, you're the only one that said its a 55", thats stuck in the back of my head for the past few weeks, yesterday i broke out the tape measure, sure enough, its a 55"

kind of a bummer, the extra 10" is going to require more motor than i have to get it into the 50s.

Justin BeaVe BeVier said:

Something makes me feel like the engine is way too far back.

Click to expand...

It does look far back. I guess it would depend where it balances. It is a long boat. it should balance I would think about 1/3rd of the way up from the back. That pipe looks nice. That extra 10 inches will make that thing be able to run in rougher water. I think even if it doesn't do 50s it will still be a blast once you get it running right on the water.

Davidkrienke said:

It does look far back. I guess it would depend where it balances. It is a long boat. it should balance I would think about 1/3rd of the way up from the back. That pipe looks nice. That extra 10 inches will make that thing be able to run in rougher water. I think even if it doesn't do 50s it will still be a blast once you get it running right on the water.

Click to expand...

It should get along pretty good, I'm honestly having a great time tinkering with it and working on it. Tinkering with this has got me wanting to do a scratch build, I may attempt a 1/10 electric crackerbox.

I've also got a little abs 20” deep v that warehouse hobbies sold 20 years ago, my uncle lined it with wood and epoxy and had an airplane engine in it, it was on the water once then was torn apart.

I may update that, I've got an OS LA .40 hanging around.

I got a 30+ QJ mod Im working on Id be willing to sell for a reasonable price.

Dave Gilles said:

I got a 30+ QJ mod Im working on Id be willing to sell for a reasonable price.

Click to expand...

I might pickup a stock one and port it myself.
Thanks though.