Paulekins

Hi all i am building a nitro air boat and i have noticed that a lot of the builds have the fuel tank level / in line with the carb
but on the life size boats the fuel tanks are lower down

what i would like to know is are there any low voltage nitro fuel pumps out there that i could use
as i don't have enough back pressure on the manifold to get the pressure that i need
i am using a tiger 40 engine which is 4" above the fuel tank
help please

1QwkSport2.5r

Perry/Conley Precision makes the Perry VP-30 fuel pump that operates on crankcase pressure to power the pump. The problem with these pumps is they often require a Perry pump carb that can better handle the higher pressure the pump provides. Most stock Carburetors do not do well with pressure due to not being designed for pump use. That said, I've tried using a pump on a TT .46 with poor results. My installation had the tank 3" below and 2" behind the engine. The engine would run good without the pump with the fuel tank so far away from the engine, but it wouldn't idle for beans. You could possibly use a carburetor with a smaller throat - this will help with fuel draw; but it will limit power from the engine. I have also tried using a header tank or hopper tank as the Heli guys call them - I didn't have any better luck with this. If you insist on putting the tank below the engine, you will have to find a compromise with needle settings and just run the idle speed higher. Typically I shoot for 2,600-2,900rpm with a typical tank setup but with a non-typical tank setup, expect 3,500-4,000rpm to still be reliable since fuel draw gets better as rpm goes up.

At the end of it, I would suggest moving the fuel tank behind the engine. This is the most reliable method and is what I do on all of my boats now.

Paulekins

thanks for your help i don't want to put the fuel tank that high as it will make the air boat top heavy and some what unstable and liable to topple over
so i might go down the route of the pump with a slightly high tick over

1QwkSport2.5r

If you use a pump, you will need a pump carb too. The "package" is over $100 and is difficult to setup. Anyone that's used one has taken it back off.

I'd like to see a picture of your boat. For a .40 engine, I'd use a 6-8oz tank which would not make a boat that top heavy. I have a 20cc 4-stroke on a boat designed around a 10cc 2-stroke and it won't flip over on itself just because of the much heavier engine.

If I were you, I'd NOT use the pump at all, save yourself the money, and try to run a fast idle with the stock engine/carb setup and low fuel tank. I really would hate to see you spend a pile of money on something that may not work. Those pump systems are not easy to dial in. Trust me, I've been there.

1QwkSport2.5r

If you still insist on using a pump and pump carb, here are the links you'll need to order the parts.
Pump - VP30 regulating pump -$42. http://www.perrypumps.com/prod02.htm
Carb - Perry pump carb - depending on which "Tiger" engine you have, it could be one of several. See link. $58. http://www.perrypumps.com/prod01.htm

Paulekins

thanks for the info
i have taken the plunge and moved the tank up
so that the carb is about 1" from the top of the fuel tank and 2 1/2" from the bottom of the tank
i looked at the various pumps and the thought of drilling and tapping the end of the engine to put in a nipple was just too risky (for my luck)
i am just waiting for some epoxy to go off on the new mount then i will be able to do an engine test
i will be posting some pictures of the build in the next couple of days

crispyspa

I ran a Perry pump on a .60 thunder tiger. I literally had 12" of fuel line to the engine as I had the tank buried in the hull. No special carb. It ran fine. The pump I had had an adjustable pressure regulator.

1QwkSport2.5r

A .60 uses a lot more fuel than a .40 does and has a bigger carb. It might be circumstantial that it worked. The regulator is adjustable to a point - but in some cases, to adjust it down far enough would have the regulator screw falling out. I did it on a TT .46 and couldn't throttle it below full open otherwise it would flood itself out. I had the regulator backed off so the screw was literally held in by a single thread. I put tape on it to keep it from falling out.

I know a guy using a Fox .74 that he couldn't get to run right. Added a Perry pump and pump carb and it runs worse than it did with the stock carb... Again, maybe circumstantial.. Either way, I would recommend a check valve and cline/iron bay regulator before using a pump. Glow engines with smallish carbs draw fuel good from a distance; sometimes the needle valve needs to be opened more to get it to draw good.

Hydro Junkie

What do you mean "manifold"? Are you talking a stock expansion chamber exhaust or are you talking a header between the engine and a tuned pipe?

Paulekins

what i meant to say was the exhaust as in a standard exhaust
and i decided to do away with a pump and i moved the tank as i said in a previous comment
but on the rebuild i am thinking of doing i will be using a HP 61 gold cap RC glow Engine which i picked up cheap i was going to fit a 90 but my pockets arnt that deep lol
and i would like to use a pump so i can lower the fuel tank but that all depends on if i can tap a hole in the back of the crank case
but that is a future build

the finished air boat is at
http://www.rcuniverse.com/forum/rc-a...l#post12223142