Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

adding pump to jett 90

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Old 09-04-2004, 04:41 PM
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BlackhawkCE
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Default adding pump to jett 90

Wondering if anybody's added a pump to a jett 90. I've got a GP F-14 with a jett 90 but i've never seemed to get it to run right. I keep having the problem of fuel flow to the engine. At idle I have air in the fuel line until i advance the throttle where it seems that there if finally enough muffler pressure to keep sustained fuel flow. I changed all my fuel lines this weekend and today fired it up to test but still the same problem. I can't set my needles because of this problem so my next thought is to maybe try a pump. Has anyone tried one on this engine or have some other suggestions?
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Old 09-04-2004, 04:51 PM
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Default RE: adding pump to jett 90

I doubt a pump is going to solve your problems.

Bubbles usually means vibration at some point. That or a leaky needle valve.
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Old 09-04-2004, 04:52 PM
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Default RE: adding pump to jett 90

Thats one nice looking F14. Any inflight/other pics?
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Old 09-04-2004, 05:10 PM
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BlackhawkCE
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Default RE: adding pump to jett 90

I've flown it only six or seven times. It is an absolute beauty to fly and the gear and door retraction is awesome. With the gear up it's definately fast but since I can't get the engine to run smooth I haven't been able to let her rip and see what it can do. I hadn't had it up enough to get any inflight pics yet and won't fly it until i fix the problem. I'll have to recheck everything till I get a solution.
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Old 09-04-2004, 07:08 PM
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Default RE: adding pump to jett 90

I have the .50 and .90 with no problems. Why don't you rig up a cheap test here and just disconnect the fuel line and muffler pressure line. Buy another fuel tank and strap it or secure it somehow using the plane as its own test stand and run it up again.

I have my .50 in an F20 and a .90 in an Ultra Sport. No problems. I doubt the pump will be a cure. Try the tank idea. Could eliminate some issues and narrow it down. You should keep them running as close to Jetts specs as you can like prop, fuel and such. Could be a bad plug too or the wrong kind. Ive had a plug like today. Wouild not start, took the plug out, was a bit dirty but lit up. I replaced it anyways and the engine (ST-G90) cranked right up. Wierd.

One other thing I bring up a lot which happened a few years ago. The fuel lines coming from the tank and through the fire wall were routed in such a way which looked fine but were actually crimping causing a fair ground run but lean out and got hot and quit in the air. There are manygremlins around.--Try the tank bit and see how it goes. Its a cheap test.

ORIGINAL: BlackhawkCE
Wondering if anybody's added a pump to a jett 90. I've got a GP F-14 with a jett 90 but i've never seemed to get it to run right. I keep having the problem of fuel flow to the engine. At idle I have air in the fuel line until i advance the throttle where it seems that there if finally enough muffler pressure to keep sustained fuel flow. I changed all my fuel lines this weekend and today fired it up to test but still the same problem. I can't set my needles because of this problem so my next thought is to maybe try a pump. Has anyone tried one on this engine or have some other suggestions?
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Old 09-04-2004, 07:19 PM
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daven
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Default RE: adding pump to jett 90

Got the first flight on my Corsair with Jett .90 today. Ran perfectly, no issues at all, but I am using a remote needle mounted to the firewall.
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Old 09-04-2004, 08:14 PM
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Default RE: adding pump to jett 90

Blackhalk:
If all else fails try a Cline regulator and a Dubro cinder bronze klunk.
They do wonders for tough tank problems.
Better reinforce the tank with nylon packing tape cause with a Jett 90
you may get 7+ lbs of tank pressure.

Syd
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Old 09-04-2004, 08:36 PM
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Default RE: adding pump to jett 90

Thanks guys for the suggestions. I found my problem though. I had a suspision of my canopy hatch pressing against my fuel tank causing a fluctuation in pressure so i took the hatch off and ran the engine up. The engine ran perfectly with smooth transition and no bubbles in the fuel lines. Problem solved. Just have to find a tank that'll fit better or shave some off my hatch. Thanks for the help though.
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Old 09-04-2004, 08:56 PM
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Default RE: adding pump to jett 90

You see, it's always something stupid isn't it?. We had a guy here a few weeks back. Takes up his GSP Corsair which he has flow countless times. For some reason the elevator is out of trim and cant keep consistent. Says the heck with it and lands.
Checks out fine on the ground. Blows it off and takes it apart to go home. We turned the tx on to check out the inside and the whole servo tray was loose thus causing all that movement.

That GP F14 is a nice plane.
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Old 09-07-2004, 11:29 AM
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Default RE: adding pump to jett 90

Blackhawk,

Glad to see you found the problem, and things are working out.

We have found over the years that 90% of 'engine' issues can be traced back to the fuel system. Most of the time its a kinked fuel line, or a cut in the clunk line or something similar to that. I had one issue last week very similar to yours where the hatch pressed on the top of the tank, and with the way he had his vent tube installed, the tank wall blocked off the tube! Plane ran fine with the hatch off, but would go lean quickly with the hatch installed (tank could not breath).

A great deal of the time the problem is vibration and fuel foam.

Air bubbles seen anywhere in the fuel system are frequently attribuited to fuel foam. Fuel foam can occur any time the fuel tank comes in hard contact with any fuselage structure. The energy (vibrations) from the engine will excite the fuel into a froth fairly easily. Easy fix...... isolate the tank with foam rubber so it does not touch anything, and be sure to balance the prop. It tends to work out that the remote needles 'highlight' fuel foam because of the pressure drop at the needle. The tiny fuel bubbles tend to become larger bubbles after they pass through the needle. With the conventional carb mounted needle, this still happened and caused the same issues....you just couldn't see what was happeneing.

The Jett needle valve will not leak, unless the packing nut is loose to the point you can easily spin the needle valve with one finger. Tightening that so the needle takes a little effort to move, it will not leak.

Btw.... somone mentioned the Cline regulator/pump. Some info on this.

Although I have done some testing with the Cline and Iron Bay regulators, I do not really recommend them for the Jett 90L. They both work well (i personally prefer the iron bay regulator), but unless the engine/muffler/fuel system is set up JUSSSSSSSSST right, the Jett will not run well with either.

Both require 'suction' at the carb to trigger the regulator to deliver fuel, and the big bore 90L carb does not suck hard enough in some cases. But I am still testing a bit

Bob
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