Fox 15.....again.....

OK, gang, I'm out of ideas. I picked up a nice clean slant plug Fox 15 to go in my old fast pig Ringmaster Jr. On the test block, it pops and sometimes runs out the prime, but no more. Good compression, fresh plug(Fox short), fuel 10% nitro /28% castor, MAS 8-4 prop, checked back plate seal, NVA clean and passes fuel freely, NV settings over a wide range, metal uniflow tank level with the NVA, no muffler at this time, wet prime, dry, no luck. Any other thoughts?
Thanks,
Kelvin

LAST EDITED ON Jul-04-03 AT 02:41 PM (CDT)
 
If it will run out the prime but nothing else, sounds like you aren't getting enough fuel draw. Some nvas are very twitchy as to setting. I have had some needles you really had to crank open to get them to even run at all. One other thing you might look at is to make sure someone in the past hasn't taken it apart and put the cylinder liner in the wrong way around- I have had a couple used motors that were like this.

The hole in the spraybar might possibly be clogged, despite being able to blow fuel straight through. The backplate or cylinder base gasket could be leaking. Wait...this is a slant plug, so no cyl. base gasket. Or the cylinder could be in backwards, possibly the piston and head also reversed. Can you choke it and get fuel into the case enough to flood it? It could still be a leak, but I would tend to look first in the exhaust port and see if the bypass side is lower than the exhaust, and that the baffle is on the bypass side, etc. Anyway, those are my ideas. Steve

Steve, the spraybar hole is open. I took the needle out, held a finger over the end, and pressured fuel through the hole. It ran freely.

I checked the seal on the backplate, and even cleaned up a tiny casting flaw. I may put some silicone gasket material there, too. The fit doesn't look all that swift.

I had the head off to look inside, and I think the liner is in correctly, but I'll double check it.

I thought I had the needle valve nearly falling out, but I will look at that idea again.

Is there supposed to be a head gasket?

Thanks v. much!
K

Is there supposed to be a head gasket

Absolutely, a head gasket is required. AAnother thing is to make sure that your not using too large a fuel line. It will be loose at the fuel nipple, a good fit is necessary here.
I've had quite a few of these over the years some really were better then others.Some ran smooth, and some were real vibrators no matter what you did.
Incidentally the 15x that is on my small aeromaster is no slouch pulling it at an invigorating clip. This plane really would do well with an OS10LA
Dennis

> Is there supposed to be a head gasket
>
>Absolutely, a head gasket is required. AAnother thing is to
>make sure that your not using too large a fuel line. It will
>be loose at the fuel nipple, a good fit is necessary here.
> I've had quite a few of these over the years some really
>were better then others.Some ran smooth, and some were real
>vibrators no matter what you did.
>Incidentally the 15x that is on my small aeromaster is no
>slouch pulling it at an invigorating clip. This plane really
>would do well with an OS10LA
>Dennis

Yeah, it's supposed to have a head gasket- check the plug too. I had a .15X slant plug that was a one or two flip starter right out of the box. I had it on a Jr. Flite Streak (orange wings, all else black), that my late mother backed her '66 Ford Galaxie over when pulling out of the garage one time- really upset her. The Fox survived, but I lost track of it thru the years.

LAST EDITED ON Jul-04-03 AT 04:28 PM (CDT)
 
>OK, gang, I'm out of ideas. I picked up a nice clean slant
>plug Fox 15 to go in my old fast pig Ringmaster Jr. On the
>test block, it pops and sometimes runs out the prime, but no
>more. Good compression, fresh plug (Fox short), fuel 10%
>nitro /28% castor,

MORE Nitro, less oil! 15/20 as a test, at least.

>MAS 8-4 prop,

Get a lighter weight prop, wood or plastic, not composition.

>NVA clean and passes fuel freely, NV settings over a wide
>range, metal uniflow tank level with the NVA, no muffler at
>this time, wet prime, dry, no luck. Any other thoughts?

Swap plugs. It may not be as hot as the usual Fox item. Swap tanks, fuel line. There may be micro- pinholes allowing air in when it should be moving fuel. Verify where the spraybar fuel hole is pointing - it is a press-fit, but under pressure from a syringe, you should be able to infer, at least, where the fuel comes out. (I don't recall for certain, but it seems to me there should be a head gasket.)

P.S. I have not had one that wouldn't run properly, but there supposedly is some QA reputation attached to the 15X's, as if an abnormal (for Fox) percentage were duds from the get-go, or harder to deal with than they have seemed to me, anyway.

.
Kiwi

My slant plug 15 likes a 7x4 and 25% oil, like the rest of the fine Foxers. I have enlarged the head bolts to 440 now after repepeated loose head problems, similar to yours.MM

Kelvin,
Your setup should work. Have you checked to see that air is not leaking past the needle?

Good luck,
George

Send it to me!!! I'm running low on Fox .15's, and the World Famous "Meet & Meat Stunt Extravaganza / BBQ" is just around the corner. In case you have'nt heard, we hold the annual Fox .15 hurl at this contest every year. Anybody out there with a Fox .15 that they would like to donate to event, please let me know. Larry, NorCal Circle Jerks

Doesn't everyone have to throw the same Fox .15? If not, someone might get a lighter or heavier one...

Sacrilege! Sacrilege!

If its clean, but missing a head gasket, sounds like someone cleaned it up for ya. Are you sure the cylinder is in the right way? If it's backards it'd pop and not really run out the prime well.

I Take two to throw and I make a trophy with the nicest one that I have on hand. Each contestant gets three attempts for two officals. the longest hurl is scored. If anybody out there has a Fox .15 to donate or sell, please let me know. Larry, NorCal Circle Jerks.

How come you can't use the same engines to throw for several years in a row? What is there to hurt except the needle valve?

>How come you can't use the same engines to throw for several
>years in a row? What is there to hurt except the needle
>valve?
>
> Larry

Larry, do major league ball players use the same ball season after season? NNNNOOOOOOOOO. These here guys are pros!!!!
Kelvin

I guess it would depend on what the landing surface is..