Quote:

ORIGINAL: 1QwkSport2.5r

The JettStream muffler's pressure fitting has a much smaller hole than most of my other engines, but it does provide plenty of pressure to the tank.

The hole in the pressure fitting only transfers pressure to the fuel.
When en engine of this size is running at full-throttle, it only needs to throughput less than 0.4 cc of gas per second, to replace the same volume of fuel drawn into the engine through the carburettor.
So its orifice size is virtually inconsequential to tank pressurization.

Its throughput needs to increase temporarily, during transition; to increase/decrease the tank pressure.
The volume difference is greater, as the tank becomes emptier.


But I have yet to see an engine 'drown' from excessive fuel pressure, after a quick closing of the throttle to idle.

Alright gentlemen... 1 bought a perry vp-30 fuel pump from my LHS to put on my TT .46. The nipple they provided in the package was missing a gasket so I made one. Without the gasket, the nipple wouldnt seat all the way. If I seated it all the way, I worry that the threads might be damaged since the metal is so thin and there is barely 2 threads there as it is. I figured it would come loose and fall out. Will this cause any interference when the engine warms up? I test fit it cold and it didnt hit the conrod, so I'm assuming its okay but wanted to make sure before I put it all back together.
Here's a picture. Gasket in place, nipple lightly seated. I was going to use blue locktite on the threads and maybe a teeny dab of RTV silicone on the gasket.

H!
Just screw it all in and file off the treads protruding!

The threads don't go all the way up the base of the fitting. Where the threads stop is where the fitting stops when screwing it in. Seriously there is not even 2 full threads for the fitting to grab into as it is.

It should be OK...you obviously know to be very careful of not over-tightening...

Those Alum. fittings sure seem fragile don't they?

Maybe get a heavy duty Brass one instead, for added peace of mind? (less chance of it breaking off later on from vibration? )

Mac's sells 'em...and I think Fox does too...

Oddly, I'm not concerned about the fitting itself. I'm more concerned with the backplate. The metal is very thin on the inner wall of the backplate. Maybe 1/16" thick at best. I have some brass fittings, but they must be 4-40 threads. The fitting that came with the pump is 6-32 and thats what I tapped it to not knowing the fitting wouldn't seat all the way.

I put it in with locktite on the threads, and RTV on both sides of the gasket and snugged it up as tight as I was comfortable with. If it falls out, it won't get lost because of how the radial mount is attached so worst case scenario if it falls out I have to retrieve it manually.

I'm going to plug the pressure fitting hole in the muffler, too since its not needed anymore. (of course this is the wrong thread too)

Hi!
Seriuosly! Why use a Perry pump at all???

I have done this with some success.  Simply find a strip of aluminum sheet.  Cut a good size piece that will cover much of the back plate.  Then epoxy it to te back plate, then drill and tap.

Jaka - The reason is this: The idle needle must be opened too far to compensate for having to pull the fuel so far. On the test stand, the tank was directly below the engine. On the boat, the engine is (carb specifically) is 2" farther forward from the tank. The last time I ran the boat, I got the mixture dialed in to where I wanted it, but it would not stay running without glow attached. I had to make an adjustment on the angle of the engine which lifted the carb a bit higher than originally also. When its all said and done, the centerline of tank is 6.5" below the carb and 2" behind. Considering the engine must pull fuel from the back of the tank (which is another 2 1/2 inches away), I think realistically this is the best way to eliminate fuel delivery problems from the equation. The engine ran fine on the stand, but we all know once the engine goes into a plane (or in my case a boat) there are other variables effecting the performance (or lack of) of the engine.

I used a tach to set the needles. If I kept it WOT, it would stay running fine but back down to idle or mid-throttle it would up and quit. Glow plug soaked with fuel. I cleared the crankcase and cylinder several times. I tried leaning the idle needle down more, but that created a lean transition and very high idle. I'm trying to go with the lesser of two evils by using the pump.

Thanks for the tip. I might try that.

Hi!
But why not just mount the tank behind the engine?

Because I don't want to. I'm looking for speed, and I dont want a chance of the fuel tank coming off or loose while moving at 40+mph. Not to mention, the fuel tank isnt exactly aerodynamic. Here's a picture of my boat, motor mount, and if you look under the engine you'll see the fuel tank in its compartment.

The pump wont look as appealing mounted next to the engine as the engine itself would, but at this point I dont really care. I do know I dont want the tank behind the engine.

That's some nice lookin' craftsmanship Tim...[8D]

Thanks, Tom... It took me almost 6 months to build it. Here's a better picture of it. (the motor mount changed since this pic was taken but its the whole boat..)

Here's my Kamikaze flat bottom boat thread:
http://www.rcuniverse.com/forum/m_10...mpage_2/tm.htm

Makes me want one.  But I would need a small boat to retrive it. Oh well.

If the engine is running like it should, you shouldnt need to retrieve it much. I use a fishing pole to get mine back if I flip it or the engine quits. I also have a small inflatable raft I got at walmart that would probably work good too.

Hi!
Get a Tettra "Bubbleless tank" and you will not need a pump!

Everyone else tells me that a bladder tank is not going to fix fuel draw problems. It's obvious that fuel draw is a problem with a tank installation such as this, the pump is a logical choice. I already have the pump and plan to use it. I just don't see a bladder tank doing doing any good besides not having bubbles.

Hi!
Well! try it and you will see!

Jan,


[link=http://www.darrolcady.com/Tettra_Tanks/tettra_tanks.html]Tettra tanks[/link] are only offered (at least by Darrol Cady) in small volumes; and the choice is very limited.

Those offered by [link=http://jettengineering.com/accy/tank.html]Jett Engineering[/link] are more numerous and a bit cheaper.

1QwkSport2.5r, I'm afraid you will need to mount this type of tank, just aft of the engine.

Your boat may indeed have problems drawing air and foam when bouncing over waves, but IMO that is not your current problem.

This is getting a bit... frustrating. I seem to be getting a lot of conflicting information. Bubbles are not a problem. Fuel draw is. I have to have the idle needle out so far to draw fuel, it drowns the plug and the engine quits. The last time I ran the engine, I dialed in the needles and had it singing really nicely but on that particular day I had to leave a glow driver on it because it would quit otherwise. I tried 5 different brand plugs with the same result. (The TT will not even run on the fox hot idle bar plug I have) Since the needle is open so far. The pump advocates say you can put the tank anywhere using a pump. So I bought a pump. The VP30 has a regulator built in. If the pump advocates are wrong and I can't , I think the plug is getting drowned by the extra fuel. That day I had to pull the plug 3 or 4 different times to clear the flooded cylinder. I have never needed to prime the engine since fuel will not stay up to the carb anyway. Cranking the engine brought fuel up to the carb rather quickly. The "drag the tank behind the airplane" kind of statement that I've seen some people use in reference to using a pump is what convinced me to use a pump. Several people have said a bubbleless tank will not promote fuel delivery; merely provide bubble-free fuel whereas others have said a bubbleless tank is the miracle from beyond the cosmos that will cure the need for a pump. The last time I checked, an 6oz tettra tank from Darryl Cady is about $22. That is the biggest tank he has listed. 6oz would probably be okay, but thats over half the cost of a pump and it means less run-time. Jett has more sizes and are a little bit cheaper, but I dont see how this is going to make a difference with providing proper fuel draw without using a pump. The engine ran fine on the test stand, but not on the boat because the tank is farther away than on the stand. (not much, but enough to make a difference.)



Maybe I need to go electric with it and say the heck with it. The boat will probably end up being lighter and probably plane out..

(edited for content)