MEP-002 rough running

[justacitizen]

Hello guys, I know this is a very old thread, but I'm wondering your thoughts on a similar issue I'm seeing on an 002A I fired up for the first time last night.
I did all the filters, flushed it all out and put in fresh fuel with some seafoam and ATF.
Unit is very clean with only 8 hours on it since " Overhauled" in 1992.
It starts easily, runs very clean and takes a 4500 watt load with no problem. ( haven't tested any higher load yet ) While running I can hear an occasional dip in RPM ( also noticed on my kill-a watt as a 1-1.5 HZ droop for about a second or less ) where the motor stumbles for just a fraction of a second, then recovers.
Watching the governor arm, you see it lift up for a fraction of a second, then back down again.
This stumble probably occurs 1 or 2 times a minute, maybe less.
Exhaust is perfectly clear except for a tiny puff of black ( only visible under close inspection with a light ) right when the machine recovers.
I'm set up to test injectors and rebuild IP's myself, so looking for your thoughts as to the most likely culprit.
Also wondering if anyone has experienced a similar problem and if an air leak on the suction side of the fuel system could cause this. I noticed the suction line was loose at the tank when I went to prime the new filters and the fitting seems to have tightened up, but looks oddly crooked where the line meets the 90 degree fitting at the top of the tank.
Also noticed it seems loud inside the air cleaner with the end cap removed. ( possibly a sticky intake valve ) but sounds normal with cap on, and I have never run one with the cap off before....

Thanks.. Ray

there is a droop adjustment on the governor spring. this sounds like you need to adjust yours. it isn't difficult and the procedure is in the TM

 

[Ray70]

Correct, I know all about the droop adjustment and tried it, but this isn't a droop issue, its not lagging under load or hunting at all, its a split second mis-fire then quick recovery.

 

[justacitizen]

so it is an intermittent miss on one cylinder?

 

[Ray70]

That is what it appeared to be. hopefully I'm not saying this prematurely, but I think I may have solved it last night. The " oddly crooked looking " fitting where the suction line attaches to the fuel tank had a slight wet stain around it, so I gave it a little more "inward persuasion", then ran the machine again. It started right up, instantly ran clean, takes a 50% load with less than 1hz droop, no smoke at all under load and.... so far no mis-fires noticed.
I'm hoping that it was air bubbles in the fuel causing the mises, but only more load testing will tell! Fingers crossed!

 

[Chainbreaker]

Almost sounds as if the fuel line fitting to tank is/was cross threaded if it was on crooked. I would unfasten it completely and see if the threads are OK. Does the fuel line & fittings look like original mil-spec OEM or replaced with aftermarket lines? If aftermarket someone could have used wrong fitting. Fittings on all the braided fuel lines should be: AN-5 which is same as 5/16" JIC. Both are 37 degree fittings.

 

[Ray70]

Yes, definitely looks like it was cross threaded at some point, but seems to thread on easily and the tank fitting threads look fine. Maybe the Female threads in the hose end got mangled. Everything is original as far as lines and fittings and after further testing last night the problem seems resolved.
I've got a parts machine, so maybe I'll swap out the line and the RA fitting on the tank just for piece of mind. Otherwise a little more load testing and I think she will be ready to go on the market.

 

[Guyfang]

Ray, I always used Teflon tape on every fuel connection. If the machine was mine, I would remove and tape every connection on the set. That way you know it's done right.

 

[Ray70]

Good Idea, I never really thought of Teflon on flare fittings, but I think I'll give it a whirl, to be on the safe side.

 

[Demoh]

Wait what? Teflon on flare? Every bit of documentation and instructions say not to do that.

To my knowledge Teflon tape / pipe dope should only be used on tapered threads. Anywhere there are straight threads like flare, oring boss, banjo, etc... Teflon tape should not be used.

Granted, in a pinch ive used teflon tape on a straight pipe going into a NPT fitting because it HAD TO WORK.

In the air conditioning world if you get a flare that doesnt seal you use what they call a bonnet which is basically a special oring specifically for flare fittings.

 

[Guyfang]

Dont know what to tell you. Its SOP in the Army, and I have used it for 25+ years on Army equipment. As always, the trick is to not use too much. I do not use dope. Never liked it, wont use it. But tape? Always.