Question: What! Me Combat? MP Jet .061 Factory Race Special

Surfer_kris wrote:I would put it the other way around, to have the fuel flowing just like it would in a regular venturi with the needle on it...

The way you have it now you risk sucking air in around the needle into you fuel delivery. Put it the otherway around and a leaking needle would only mean that you might loose fuel out around the needle, if the pressure feed is strong enough.

The way he has it routed now, is the same routing that O.S. and Evolution engines with remote needle valves use so he should be fine. Plus if he routed the other way, it may not meter the fuel correctly.

See page 15 and zoom in to see the fuel line routing for a remote needle valve.
http://manuals.hobbico.com/osm/10-15-25-25la-manual.pdf

The fuel metering should be pretty much the same both ways, in fact the "OS way" makes the fuel flow backwards compared to when the same type of valve is sitting directly on the carb.

The only consideration, to me, is with the needle itself. The OS one (any many others) has an o-ring that seals around the needle, while the MP-Jet one is just a regular, split-collar, style which can leak around the threads. I have also put a piece of fuel line over the needle on some of my engines, not sure if it really changes anything though...

Surfer_kris wrote:
The only consideration, to me, is with the needle itself. The OS one (any many others) has an o-ring that seals around the needle, while the MP-Jet one is just a regular, split-collar, style which can leak around the threads. I have also put a piece of fuel line over the needle on some of my engines, not sure if it really changes anything though...

Without having an O-ring on the NV, routing the other way does make sense. Also, thanks for the explanation as I am seriously thinking of getting an MP Jet .061 for a future go fast turn left project.   

Shawn

One consideration to buying a new MP Jet is the glow plug availability. It's a strange fitting little drop-in. I'll take a picture of it next time I take the head off. Icarus has them for $6.95, but they might not be widely available. Otherwise I haven't really shopped or looked into it but you may want to check that before deciding.  
Rusty

AD: Yesterday I set up for a movie and flooded the little bugger with a spastic blast of prime from my syringe. I shot about 15 minutes of me flipping it, blowing into it, and discharging my glow lighter. I'll try again today. I'll put a Norvel starter spring on it to make flipping easier. Those are great universal springs that can be zip tied to a beam or whatever.

Ahh, sorry, gave up again after the first hundred mosquito bites. I did get some decent runs off of prime, and realized it wasn't drawing fuel. Primed the line and promptly flooded it again. The Norvel spring didn't work as hoped. Went back to the Skyray to finish that wingtip and control linkage. I'll try again when I have more patience.
Rusty

I am surprised to hear the Norvel starter spring didn't work. That is what I use on my MP Jets. I drill a hole in the mounting lug and do it all just like on a Norvel. If you are using the crank case pressure you have to have the needle adjusted pretty close for easy starting. It often takes a while to get that dialed in.

BTW, I am now a single man and will probably be bugging you guys a lot more again.