engine stopping

[luv-brd]

Am having trouble with my 7CCM, 85 shutting down in cold weather. Had the carb rebuilt by aircraft company in Oklahoma last summer for annual. No problem until first freeze last November here in South Central Texas. Had carb heat on and upon landing engine shut down. Since it is electric start, I FINALLY got it started and taxied to terminal. No problems again until last weekend when we had 30 degree weather. Started and ran great while flying about 35 miles to another field. No problem on landing or re-starting about 45 minutes later. While starting my run up, it again died and I finally got it started by using the primer. Ran great until landing about 45 minutes later where it died on runway, and started using primer again. Shut down for about 20 minutes, it started, did ok thru the run up and no problems while landing at my field.

Don't know what to look for. I double strain the fuel, check for contamination in both tanks before each flight. Use carb heat each run up and landing, and am using 100 LL.

Has anyone had this type of problem, or does anyone have any suggestions?

Any help would be appreciated.

Thanks,

Lance

[Ron Babos]

The only things that I would look for is make sure the carb heat is actually working. An rpm drop does not always mean it is sucking hot air. The first thing to crap out from carb ice is the idle circuit , at which point a primer is the only way to start it again. If it starts it may not idle again. However , if some time has elapsed before the restart , some of the heat in the cowl will melt the ice at which point it will idle again . If the engine will run at midrange and full throttle ok , and the problem only shows up in icing conditions, that would be my first area to check. Obviously it works at higher rpms because you got to your destination? What type of carb is it , Stromberg or Marvel? Ron

[John]

This is very similar to a problem my brother was having on his 85hp Reed Clipped Wing Cub. Engine ran fine but was prone to stopping on the runway after landing or would be difficult if not downright impossible to start within an hour or so of shutting it down. He had the carb rebuilt but it didn't help. Turned out the problem was quite simple and we couldn't believe it had slipped by all this time. The part where the carb bolts to the intake spider was the part for a 65hp Continental instead of an 85hp. It bolts up exactly the same and it works but it has a significantly smaller inner diameter and therefore gives a corespondingly lower flow. Replaced it with the correct part and the problem went away. I would have expected reduced performance from the 65hp intake but the main thing experienced with it was the engine stopping on or after landing and being difficult to restart. Needless to say there was a significant performance increase after changing it out. We realized that the plane had not performed all that great prior to this but no red flags had gone up.....after all is was Cub! Ha!
John

[Jody Wittmeyer]

Friend of mine just had similar problem with his C-85 (7BCM) We thought it was an intake leak, but could never find it. Turns out, one of the gaskets that go between the cylinder and intake elbow was missing. He replaced it and solved the problem of engine stoppage at idle power.

[LOWELL]

If you have a Stromberg carb, it could be a high fuel level. A high level
will cause lots of carb ice even in the summer, plus spark plugs will be black
with soot. Had a friend with simular problem. There is a big difference
in weight of 100oct and auto gas. If it set up for 100oct (13/32") and you use auto (heaver), could be the problem. Check the spc. gravity of the
fuel you are using and compair it to the chart in the OH manual.
Best of luck

[Ron Babos]

Lowell: If the float level is set for 100ll and you use auto fuel, if in fact it is more dense, would that not raise the float sooner and you would have slightly less gas in the bowl? I burn a mix of auto and 100ll and sometimes straight 100ll. What measurement would you go with on the fuel level in this case when setting up the new delrin needle that I'm about to install? Ron

[Dennis]

Ron, I think you are correct. Check this out: The distance a given float (mass/volumn is constant) "sinks" into various liquids is inversely related to the density of that liquid. Therefore, if a float is placed in a more dense liquid (heavier), the float will set higher than in a less dense liquid. In a float bowl, the results of changing to a more dense, or heavier, fuel will be a higher setting float which in turn shut off the inflow of fuel sooner and thereby produces a lower fuel level in the bowl. Clear as mud.

However, is this really important? My sources indicate that the specific gravity of different grades of gasoline ranges from about .68 to .74 or a difference of only .06. I am not sure if 100LL is included in this range. However, for the ranges indicated, the change in the distance of the bottom of the float below the surface of the gas will change by only .06. So if a given float sets .5 inches into a bowl of gasoline, a change in specific gravity of .06 will result in a change in fuel level of .003 inches. A quarter inch depth and a change in SG of .06, will yield a difference in fuel level of only .0015 inches. Hummmmm

I would be interested in knowing the specific gravity of 100LL if someone has that information.

Dennis

[Ron Babos]

Dennis: With people flying with the wrong spiders, and missing intake gaskets, the differences in fuel densities it seems won't make a rat's petunias bit of difference. Now if we get into air density acting on the suction effect of the carb in relation to engne vacuum, at a specific fluid level Na let's not go there! Ron

[Nathan K. Hammond]

I'll just assume that the engine idle is set correct?

nkh

[markl]

Seems pretty clear that your engine quits because it is too LEAN at idle. Look for an induction leak. I had problems like this from three different (at different times) causes. To find an induction leak safely, consider attaching any source of compressed air to your carb heat air intake on the carb. Make attachment with hose, duct tape etc. I used my HVLP turbine. Put carb heat in On position and throttle open. Spray soapy water on all intake parts. I had a cracked airbox and wrong intake gaskets.
Another time I had little hairs??? collected in the idle jet inside the carb?? Try adjusting the carb idle mixture as it could have been set too lean and worked OK in the summer. Have you done an idle mixture check? When engine is warm after checking mags and carb heat - go to idle rpm and put carb heat on an see what the effect is.
For more ideas try putting this question on www.aeronca.westmont.edu as there are there are Aeronca folks there who are not on this list.

[LOWELL]

I checked the spc. grav. of Shell reg. and compaired it with 100LL. In
the O.H. manual on the Stromberg carb, both weights of fuel falls in the
13/32" float level.....see float level conv. chart. I used the FBO's gauge
for checking the numbers. We get our 100LL from Louisville, KY. It comes
up the river on a barge from where ever. If the float level is set at 13/32"
with the fuel I use it will make no difference. The level has to be set very
accurate...a 1/32" makes a big difference, and with the accurate head
pressure. The pilot did not state what Mags he was running. You can have
problems with the Coil, breaking down, mostly when HOT (heat soaked) or
even when Cold. Also the cond. playes a big part, they can also play havic. I ran into a problem with the late model Case Mags....bad coils on
both mags. And bad cond. on a Bendix Mag S-20 series. I spent the best
part of an hour proping a 450 Stearman before it started. The pilot THEN
told me the coils were WEAK when hot....I could have KILLED the SOB!