IMCub

My Feedback: (1)

OK, under the premise that there are not stupid questions (but the world is full of inquisitive idiots) ....

I'm trying to breaking my first 4 stroke, Magnum 30 4-stroke ... I hooked it up to the fuel tank as on all my 2 strokes ... the exhaust port to pressurize the tank ... the line with the clunk feeding the inlet for the engine.

So things seem ok for the 1st couple of tanks ... but as I continue to lean it out ... the engine won't get about 8500 RPM. Suddenly the pressure line falls off and the engine comes up to full speed ... Oops.... When I reconnect the pressure line ... the engine stumbles again....

Any thoughts? Is there something special about the 4 stroke plumbing that I'm not aware of?

Any help would be greatly appreciated.

Dave

ChuckAuger

My Feedback: (12)

You sure you're not just real rich?? and when the pressure line comes off it goes "lean" and come on up?? then put the pressure back on and go rich again?? Just a thought.

Have you ever got it leaned out at all ( I realize you are breaking it in)?

Basil Yousif

My Feedback: (3)

Could your fuel line be leaking air in. Sometimes the fue line end gets enlarged and doesn't seal against the metal fitting very good. Try to replace the fuel line with a little smaller diameter size to get a better seal if the existing line fit's loosly.

William Robison

My Feedback: (3)

IMC:

I go with ChuckAuger. You aren't getting air in, you're gettng too much fuel.

But if it runs fine with the pressure line disconnected from the muffler, and some do, leave it disconnected.

Check high and low speed needles, do the nose held high test for 15 or 20 seconds, if everything goes fine, fly the plane and don't worry about it.

Bill.

IMCub

My Feedback: (1)

too rich ... could be ... I started at the recommended 2 1/2 turns and moved it in progressively 1/4 turn each 5 minute run. I'll put the wing on it and take it to the field where I'm sure one of the old hands will be able to get it set up. I just hate wasting good flying weather breaking in a motor ...

Thanks for the suggestions.

Cheers!

Dave

Sprink

Incidentally, which prop you using?

A long shot I know, and I doubt it would cause your symptoms, but a club mate was having all sorts of problems with a 90 size 4 stroke. His engine would run far better when not attached to the pressure nipple.

In the end, he tracked the problem down to the pressure nipple not being drilled out properly, ie it was closed. His tank was therefore slowly depressurising as fuel was sucked out.

When he drilled out the nipple, his engine ran fine after that.

Something to try anyway.

David Smith

My Feedback: (1)

I've run four strokes for about 20 years and not one pf them has ever used muffler pressure. I've flown them in sports aerobatic aircraft and never had any engine problems no matter how violent my manoeuvers.

91zulu

My Feedback: (2)

Thats the same thing that happen to me with my TT91 on a P-51. Couldn`t get the engine to stay runing with pressure. Took it off and problem solve, and this engine has a big carb.

yard-dart

My Feedback: (35)

Cub,

I don't think that the 2 1/2 turns out from the very start is enough, causing the engine to be deprived of the extra oil that is needed during the critical break-in process. I would run the engine a little more rich for several tanks, regardless of how well it is running, to insure that it is getting sufficient oil during this very critical time.

John