Jett Q500 throttleablity  
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Jett Q500 throttleablity - 2/24/2008 9:14:08 PM   
ChrisAttebery



Posts: 373
Joined: 9/15/2004
From: Gilroy, CA, USA
Status: offline 		Hey Guys,

I just bought a Jett SS40 CAPS motor. From what I have gathered it's somewhere between a Sport Jett and a Q500 motor. It's got a carb with no low end needle and a milder timed sleeve compared to the Q500. It's designed to meet a requirement for the motor to idle for a certain time to be legal for racing use. Sounds like a good motor for speed sport flying and I can't wait to get it in the air.

There's been a few Q500 motors listed on the auction site and I'm wondering if I should just go ahead and get one. The question is can you throttle back the Q500 motors? Does the carb have the metering groove cut it in like the SS40 motor does? If not, how do they run with a Jett Red carb? I'm not looking to idle out and back to the pits, but I would like to be able to throttle down to say 1/3-1/2 in between speed runs. Our field is a bit short to be running a Q500 wide open, especially since I'm not used to flying at that pace all the time.

Thanks in advance for your input,


Chris

_____________________________

WM T-34 - OS 46AX - Club racers
Rusty Miss Ashley - Nelson Q40
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RE: Jett Q500 throttleablity - 2/25/2008 3:26:39 AM   
Bill Vargas



Posts: 1554
Joined: 1/6/2002
From: Team Coldies, CA, USA
Status: offline 		You may just want to find or get a sport jett carb that will enable you to throttle back and idle. Todays Q500 engines are meant to haul butt for a couple of mins then throttle back to "kill" the engine and glide back to earth all the while bleeding off the speed for that perfect grease on dead stick landing. So in short a Q500 engine is either on or off.


BV

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If it ain't leaking oil, then something's wrong,,, USMC, RETIRED!

(in reply to ChrisAttebery)
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RE: Jett Q500 throttleablity - 2/25/2008 4:44:25 AM   
fizzwater2


 

Posts: 797
Joined: 8/16/2004
From: Paola, KS, USA
Status: offline 		My Jett Q500 engine does NOT have the small groove in the barrel like the CAPS version does. It's pretty much on or off..



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no matter where you go, there you are..

(in reply to Bill Vargas)
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RE: Jett Q500 throttleablity - 2/25/2008 5:27:53 PM   
ChrisAttebery



Posts: 373
Joined: 9/15/2004
From: Gilroy, CA, USA
Status: offline 		Guys,

Thanks for the replies. One more quick question. Does the Q500 carb cut the fuel off when you pull back or does it just shut the air off?

When I raced boats the last few motors I had had a straight spray bar in the carb, not even a needle valve. We all used BVM type third channel mixture controls. They worked well enough that you could pull back to say 25% of your top speed. Those motors would throttle down to a raspy high idle, maybe 5000 rpm, kind of like a top fuel dragster. That's all I'm really looking for.

If I can get hold of a motor for a decent price I'll talk to Dub about carb options and see what he has to say.

Thanks,


Chris

_____________________________

WM T-34 - OS 46AX - Club racers
Rusty Miss Ashley - Nelson Q40

(in reply to fizzwater2)
       Post #: 4

RE: Jett Q500 throttleablity - 2/25/2008 5:30:30 PM   
daven



Posts: 6894
Joined: 12/7/2001
From: Andover, MN, USA
Status: online 		The quickie motor cuts the air off, and I have seen them run for extended periods of time at a reduced carb setting. Nothing reliable, but they will sputter along at times.

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Dave Norman

klasskote.com
supertrc.com

(in reply to ChrisAttebery)
       Post #: 5

RE: Jett Q500 throttleablity - 2/25/2008 5:44:22 PM   
DonStegall


 

Posts: 624
Joined: 8/8/2005
From: Monroe, NC, USA
Status: online
quote:

ORIGINAL: ChrisAttebery

...

If not, how do they run with a Jett Red carb? I'm not looking to idle out and back to the pits, but I would like to be able to throttle down to say 1/3-1/2 in between speed runs. Our field is a bit short to be running a Q500 wide open, especially since I'm not used to flying at that pace all the time.

Thanks in advance for your input,

Chris


Chris,

I have a Quickie JETT with the RED JETT carb. I used to use it for test flying Quickies. But it has found on new home on World's Fastest Sky Raider Mach II? . It will idle down to 3000 rpm's reliably. The only issue is getting the settings right so that it doesn't quit when it comes on the pipe. You have to have the idle set just right, and you can't be too rich.

The RED JETT carb is not the same as the SS40 carb. It is a dual valve carb.

There are certain throttle positions that don't work real well. You either want to be at a low to fast idle, or full throttle. In other words, the mid-range is touchy, both on settings and in flight. But it is an awesome engine for being able to go fast and still be able to land under power.

It is loud though. If your club has noise issues, it is a lot louder than a sport .40/.46 ... Which is one of the reasons I'm flying at Lowe's Motor Speedway more often now. No noise issues like some other area clubs.


_____________________________

Don Stegall
RCPRO - http://www.rcpro.org - http://www.rcpylon.com

(in reply to ChrisAttebery)
       Post #: 6

RE: Jett Q500 throttleablity - 2/25/2008 6:27:34 PM   
ChrisAttebery



Posts: 373
Joined: 9/15/2004
From: Gilroy, CA, USA
Status: offline 		Don/Dave,

Thanks for filling in a few more of the details.

I don't think the noise should be a problem. Our field is in an isolated area near a freeway. As far as I know there aren't any noise restrictions.



Chris

_____________________________

WM T-34 - OS 46AX - Club racers
Rusty Miss Ashley - Nelson Q40

(in reply to DonStegall)
       Post #: 7

RE: Jett Q500 throttleablity - 2/27/2008 9:56:31 PM   
ChrisAttebery



Posts: 373
Joined: 9/15/2004
From: Gilroy, CA, USA
Status: offline 		Well, I got to run the SS40 today. It fired right up and pulled a APC 9.5x7N at 17500 on the bench. Th throttle is funny. It was turning 10K+ at 1/8th throttle. Pull it all the way back to about .010" opening and it "idled" down to about 4500. I ran it up and down for a couple minutes and it throttles fine, it's just between 10K and 17.5K. I had to plug the muffler to shut it down.

When I tried to restart it I think it was flooded and my Radio South Pro driver hasn't been charged in a while, so I couldn't get it to restart.

Now I need to get a couple of the recommended 8.5x7.5 props so it will pop over 20K.

Chris

_____________________________

WM T-34 - OS 46AX - Club racers
Rusty Miss Ashley - Nelson Q40

(in reply to ChrisAttebery)
       Post #: 8

RE: Jett Q500 throttleablity - 2/27/2008 10:01:30 PM   
ChrisAttebery



Posts: 373
Joined: 9/15/2004
From: Gilroy, CA, USA
Status: offline 		Last night I rememebered that one of the guys I raced boats with had a Nelson QM40 motor mounted on an outboard. It used a carb and it woul idle to some extent (~10k). The more I think about it the problem Don described is probably due to the "mini" pipe coming in and out of tune. On the boats we used full pipes and depending on the peakyness of the pipe some would do what you described.


Chris

_____________________________

WM T-34 - OS 46AX - Club racers
Rusty Miss Ashley - Nelson Q40

(in reply to ChrisAttebery)
       Post #: 9

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