Rough Starting Franklin

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Jungle Jim
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Rough Starting Franklin

Post by Jungle Jim »

I have a 108-3 with a 165 hp Franklin engine that runs real rough at start up. It won't idle below 1300 rpm unless I pump the throttle or give it a shot of primer. I have pulled the engine through and all the cylinders have good compression. The mags and intake seals and gaskets are new. If I run it at 1500 rpm for a minute or two it will idle real smooth and not have any symtoms of a problem.

Any advice would be appreciated.
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N2
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Post by N2 »

Jim, have you tried mogas in that engine? I have heard from people that Franklins really don't like the 100LL and I'm wondering if you’re just running into fowling problems. Below a certain RPM range the cylinders don't get hot enough for the Bromide to scavenge the lead out of the cylinder thus giving you this rough running. Don’t forget that engine was designed to run a lot less lead that what is contained in 100LL. Just a thought.

My O320 purrs on Mogas compared to that blue crap loaded with lead. I run MMO in the fuel as well to keep everything nice and lubricated up top.
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Last edited by N2 on Tue Jun 15, 2004 6:00 am, edited 1 time in total.
Putting money into aviation is like wiping before you poop....it just don't make sense!
Jungle Jim
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Rough Starting Franklin

Post by Jungle Jim »

I have been running Mogas exclusively. I have found that in the past it would foul the plugs real quick. I went out yesterday and changed the plugs and it might be a bit better, but it is hard to tell. I still have to pump the throttle to keep it running. the only difference is that it might be down to less than a minute now. Also none of the plugs were oil fouled as some of the airport hobos speculated. Once it's running smooth it stays that way throughout the flight at all engine speeds. Sure has me stumped.
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624
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Post by 624 »

:)
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Last edited by 624 on Wed Jun 16, 2004 1:57 pm, edited 1 time in total.
N2
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Post by N2 »

Jim are you saying the mogas is fouling the plugs or when you ran 100LL? I would try some MMO in the fuel 4 oz to every 10 gal.

Copied from an article by Ben Visser of Shell Oil in the Southern Aviator,


"Answer

The American Society for Testing and Materials (ASTM) is the controlling agency for both the auto gas and avgas specifications. The ASTM D- 910 specification for aviation gasoline lists about 30 different limits or tests, which must be met prior to releasing each and every batch. Most blends of auto gas would meet many of these specifications, or the difference is totally insignificant. For example, avgas is dyed blue while auto gas is normally clear. So other than for identification purposes, there will be no difference in performance. "
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Putting money into aviation is like wiping before you poop....it just don't make sense!
Jungle Jim
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Posts: 436
Joined: Wed May 26, 2004 6:29 pm

Rough Starting Franklin

Post by Jungle Jim »

The engine did foul plugs wuth 100LL, but since the change to Mogas this problem has disapeared. I also use MMO religiously.
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