rough running on climb-out

[Stumpy]

So...installed my "new" yokes yesterday and we thought a trip up was in order. Running normally until about 100 agl and not enough room to set back down. Pulled the power back to 1900 or so and she smoothed out. Gingerly got a little altitude and tried again--20 second of power and then automatic rough. Got turned around and back down.

Thought I'd fiddle a bit tonight. Warmed her up a bit, ran her up to 2300 (A-75, sensenich 70/40 wood) for 60 seconds three separate times, no problem. Blipped the mags several times at power, and had drops of 25 +/-. She didn't cut out either.

Almost wish she had...can't fix it if she won't do it again. Makes me nervous though and I have places I need to go darn it. Had about 7.5 gallons of mogas/100ll mix in the tank, so she certainly didn't come un-ported. Unfortunately I didn't apply the primer while having the post-take-off problem yesterday.

My first thought was fuel...as in the needle valve (original neoprene) in the Stromberg had stuck, or the float/fuel level isn't right and at full power after awhile there just isn't enough there. I actually don't get a puddle under the cowl if the gas is on (used to). Last night it was left on for 20 minutes or so while I was pulling the lower cowl and no unsightly Stromberg gas puddles developed.

Any ideas? Seems like the electrics aren't the culprit. Mebbe a blockage that's now cleared? I have little faith in aeroplanes (even Taylorcrafts) that miraculously heal themselves... ;-)

[mike lutz]

Re: rough running on climb-out

Stumpy,a friend of mine had the same exact problem with his luscomb with a A-65 couple years ago.He always run a mix of fuel from bulk storage at his facility.Long story short,he was delivered auto fuel with methonal in it,and his needle swelled up also.He run 100 oct. in it till he got a different needle for his carb.

[cvavon]

Re: rough running on climb-out

Stumpy start with the easy things like the screen in the gascolater then the screen at the carb inlet also when you have the line off the carb in let check fuel flow out of the line then it's time to take the carb apart.Also what type of hoses are in your fuel system as some are not good for auto fuel with methonal also the age of them could be brakeing down inside them and restrick the flow.

[M Towsley]

Re: rough running on climb-out

Stumpy, If you are running mogas you need to change to the stainless, or nylon, needle and corresponding seat. Especially if you don't test every batch of mogas you purchase due to ethanol swelling the neoprene needle. The old, old neoprene wasn't really susceptible, but the not so old is.

[Stumpy]

Re: rough running on climb-out

Fellas,

Checking flow this afternoon. My mogas source is always the same...and I test it regularly....this winter I even put three separate "original" (part number handscribed on them) neoprene needles in jars of mogas for a week or so and checked them for swelling, etc. Everything looked and measured fine. I flushed my main tank several times a couple of months ago too, just for the heck of it.
I previously had a SS needle and the correct seat installed in another carb, and had the usual fuel puddle when the gas was on. I will probably make an effort to lap it in better with mayonnaise and go back to that. Still, she ran up just fine for over a minute three times yesterday...doggone if I could get her to repeat what she did on takeoff Wednesday, and I hadn't made any changes. That seems to rule out the electrics...mebbe. Gascolator is a new one installed this winter (in the correct direction too). I have the new style fuel lines encased in braided steel from the main to the gascolator and gascolator to carb.
Oh well...will continue the quest...

[cvavon]

Re: rough running on climb-out

Stumpy in my stromberg manual there is a 1/4 28 plug on the side of the carb it is the feed to the main jet to the main discharge nozzle pull it and turn on the gas valve and flush out this passage as this is for high speed running also could blow it out with air.

[M Towsley]

Re: rough running on climb-out

Stumpy,

I thought the mogas STC's required you to use a stainless steel needle, perhaps I am getting mixed up on that. I got rid of the neoprene and went to the S/S needle and correct seat. A little lapping and mine doesn't leak.

[cvavon]

Re: rough running on climb-out

Marty I just got my EAA auto fuel stc and read it. It does not say any thing about the float needle that was the only time i have looked at it. In my carb i have a stainless needle that was lapped and it does not leek.I think the rubber needle is his problem.

[M Towsley]

Re: rough running on climb-out

Thanks, Chuck. I thought one of my old STC's required the S/S needle, maybe not.

The only problem I had with my engine was when I was running mogas exclusively. Since 100LL and MM no problems whatsoever, (knock on wood).

[Stumpy]

Re: rough running on climb-out

Well, I just rigged a tube to the carb bowl plug and timed my fuel flow there for starters. Tail on the ground, 7 gallons in the tank. 18 minutes 8 seconds per gal. with the cap on, 18 minutes 5 seconds cap off...works out to 3.33 gals per hour...hmmmm...not quite enough eh? Obviously venting isn't the issue...gonna check flow out of the gascolator first but reckon the carb is coming off. I held the clear tube I was using alongside the carb body with the gas on and the fuel level was about right on tail up or down. Reckon she just isn't getting enough. Mr. needle is obviously suspect. Thanks guys, will keep apprised.

[cvavon]

Re: rough running on climb-out

when you get done you will know your fuel system very well.

[Stumpy]

Re: rough running on climb-out

Certainly will...was already way too familiar with it though, ha. Flow to the carb through the gascolator is 31.58 gph (1 min 54 sec/gallon)....no vent, finger screen, fuel line or gascolator issues I reckon. Tried it through the carb with the carb screen out for the heckuvit and it took close to 19 minutes a gallon....so it appears pretty doggone obvious wherein the trouble lies eh? Off comes the Mr. carb.....anyone gotta spare MS 10-4233 laying around homeless? ha ha. If strombergs were gold I'd be a wealthy man...

[woodmw]

Re: rough running on climb-out

thanks, chuck. I thought one of my old stc's required the s/s needle, maybe not.

The only problem i had with my engine was when i was running mogas exclusively. Since 100ll and mm no problems whatsoever, (knock on wood).

ouch!!!

[Mark Julicher]

Re: rough running on climb-out

My limited experience is that a stuck needle kills the engine dead, but an incorrect float drop will cause a sputter and then allow running at a reduced power setting.
Perhaps the float is hanging up on something or got partially waterlogged.

[astjp2]

Re: rough running on climb-out

I would also ohm out your plugs, 5k ohms or less, high resistance will cause weird crap to happen at RPM...even if you find that your carb needle is the problem, I check my plugs every year. Tim