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**magman** · 08-09-2011, 20:45

Re: Engine cut-out on takeoff - suggestions

A friend had a somewhat similar problem with his Champ.

Only it did it EVERY time.

Replacing the Float Needle took care of it.

**Pearson** · 08-09-2011, 20:58

Re: Engine cut-out on takeoff - suggestions

It could be a vapor lock problem. But a list of all the possibilities would be very long. I have said it here before, and I will say it again; always look for the simplest solution. With that said, your remark about not being able to shut the mags off is of concern. The easy way to verify the switch is working is to select the off position shortly after you get it started. If the engine keeps running, obviously a bad switch.

Regarding a possible vapor lock problem, have you changed anything in the last few months? You mentioned the Hanlon Wilson mufflers, are they a recent add on? Have you tinkered with, replaced, or moved either of the mags lately, different fuel, recent carb adjustment, gascolator clean out? If you haven't "done" anything to the engine lately, I would put a laser thermometer on the cylinders immeadiately after another bogging episode to see if a valve isn't sticking at those high temps. Also check the carb heat flapper valve inside the airbox.

That is my 2 cents worth of ideas. I am sure you will get plenty more. Good luck!

**Dano"T"** · 08-10-2011, 01:22

Re: Engine cut-out on takeoff - suggestions

Originally posted by Pearson View Post

It could be a vapor lock problem. But a list of all the possibilities would be very long. I have said it here before, and I will say it again; always look for the simplest solution. With that said, your remark about not being able to shut the mags off is of concern. The easy way to verify the switch is working is to select the off position shortly after you get it started. If the engine keeps running, obviously a bad switch.

Regarding a possible vapor lock problem, have you changed anything in the last few months? You mentioned the Hanlon Wilson mufflers, are they a recent add on? Have you tinkered with, replaced, or moved either of the mags lately, different fuel, recent carb adjustment, gascolator clean out? If you haven't "done" anything to the engine lately, I would put a laser thermometer on the cylinders immeadiately after another bogging episode to see if a valve isn't sticking at those high temps. Also check the carb heat flapper valve inside the airbox.

That is my 2 cents worth of ideas. I am sure you will get plenty more. Good luck!

Thanks Richard....nothing has been changed....and it has only ever happened after it's quite hot. Sticking valve, I hadn't thought of that one, possibility I guess. It never quits.....just loses power really bad and always at the point where it's needed most, I pull back the throttle and it seems fine. I am replacing the ignition switch today since once before I had to cycle the switch back and forth to get it to shut off. I'm still wondering about unporting, since it always happens at high angle of attack while on one float and rotating back. I just don't know.....it runs perfect at all other times. The conditions are always exactly the same when it occurs. Keep the ideas coming, this is a phantom that I want solved before I'm in a situation that's critical. So far it's only happened while I've been on a large lake with lots of room (5 miles) in front of me.

**N96337** · 08-10-2011, 08:41

Re: Engine cut-out on takeoff - suggestions

Dan, do you have the nosebowl airflow going where it's supposed to? I also would think about a shield around the outside of the exhaust to maybe save a bit of heat to the carb to see if that helps? Bill Berle had a similar problem with an 85, didn't he? It's not running cargas is it?
John

**Pearson** · 08-10-2011, 09:53

Re: Engine cut-out on takeoff - suggestions

Ensuring that you have a full header tank would eliminate the unporting theory. Other than vapor lock, the only other area I would think the problem could be is the carb. Have you tried accelerating to a higher speed and using a more gentle rotation for takeoff? I know that wouldn't eliminate the problem, but it would let you know that it is something related to that angle, such as a carb float set too low. Or maybe the high angle is flooding the idle circuit with extra fuel causing it to flood out until the angle is decreased. I would try to check the cylinder temps immeadiately after it bogs to eliminate stuck valves as a cause before I took the carb apart. 220 degrees on the oil is getting pretty hot. I am sure others will chime in with other ideas soon.

**magman** · 08-10-2011, 10:27

Re: Engine cut-out on takeoff - suggestions

The BIGGER q to me is why it doesn't do it when "cold".

A chunk of loose muffler baffle would do it hot & cold - maybe.

RPM normally inceases @ lift-off & may be affected by valve springs.

Excessive Point Gap can cause "Point Bounce" ; again hot & cold.

Shorting P-lead-same story.

High Tem & High Power = Realm of Detonation?

Detonation can lead to Pre-ignition & Power would drop off.

Hot deposits lead to no shout-off.

You may want to verify Ignition Switch operation with an Ohmeter or Timing Light BEFORE changing it.

**Guest** · 08-10-2011, 15:04

Re: Engine cut-out on takeoff - suggestions

my bc12d used to cut out when nose was too high and the nose fuel level was too low

**mikeg** · 08-10-2011, 16:29

Re: Engine cut-out on takeoff - suggestions

Found the finger strainer missing in the tank of a T one time and the elbow had a small chunck of rubber hose stuck in it.

Change fuel hose over to #6 (3/8" I.D.)

Found a mud daubber's nest in the fuel feed hose in a 7AC one time as well. Check fuel flow out of supply hose at the carb. Should be a solid steady flow of fuel the diameter of the hose I.D.
Later,
Mikeg

**jim cooper** · 08-10-2011, 17:43

Re: Engine cut-out on takeoff - suggestions

First thing I would do if I were a good carb. person would be to rebuild it, checking float carefully and where its supposed to be. Somewhere in the past I remember something like this. It WAS the carb. JC

**flyguy** · 08-10-2011, 19:10

Re: Engine cut-out on takeoff - suggestions

The first and easiest thing I would do is to check out the magneto switch and connections or replace the switch. If you had to cycle it to get a good ground on the mags, even once--you may have a dangerous problem. I doubt the switch has anything to do with the loss of power thing, but then you might get a surprise there too.

I just deleted an additional comment concerning the mufflers. Looked that kind up and since they have shrouds (right?), probably not the problem. Do you have good air flow coming in under the crankcase? I have only been running 160 to 180 max oil temperature on my C-85.

DC

This could go on forever. Just remembered: I just sold my hot rod camaro, and it would run on after shutting off the ignition, so you may have experienced that. Main reason with it was the over lean idle mixture (not adjustable) and high under hood temperatures. Your ignition switch may be OK.

**Dano"T"** · 08-10-2011, 20:48

Re: Engine cut-out on takeoff - suggestions

The cowl is a tight fit...seems there is not a good outlet at the back/bottom of the cowl. My 85 runs similar temps. The common thread is it always does it when it's hot...I always takeoff from the left float and it never misses a beat unless it very hot/humid and I have been giving rides over and over. I had a 50/50 avgas mogas mixture in this time.....earlier times had mogas....thinking vaporlock? HMMM. I really need to address the cooling anyway, I just wish I could pinpoint the problem. I do have the 3/8" fuel lines as I mentioned before.

**Ron Coleman** · 08-10-2011, 23:41

Re: Engine cut-out on takeoff - suggestions

First, I would change the switch. Then I would make sure that the control yoke shaft is lubricated. Then I would make sure that the throttle control cable is firmly anchored near the carb (grab the cable while the engine is hot and try to pull it back and forth). I had a problem when I leveled off on takeoff, the engine went to low rpm. The rubber grommet holding the cable got soft when it got hot and the cable would slack off and drape in such a way that when I moved the yoke back it pulled the throttle , but not would not move it when I pushed the yoke forward.
If you change the switch, I wouldn't fuss, otherwise, I would lube the primer, the carbheat cable, and the throttle cable. A badly corroded switch may react to any pressure on the panel, usually preventing the switch from shorting the mags and killing the engine.
When the engine looses power does it run rough or is it still smooth, just slow down? Get a laser thermometer (harbor freight) and check the cylinder heat temps next time you have this problem.
RonC

**magman** · 08-11-2011, 07:18

Re: Engine cut-out on takeoff - suggestions

When running the Mag Switch opens the circuit to ground.

It might be an idea to disconnect the P-leads & make a completely new Temporary Test System.

Many aircraft use SPST switches in place of a "Mag Switch".

With a "5 mile Runway" that could help find a cause.

**jim cooper** · 08-12-2011, 18:32

Re: Engine cut-out on takeoff - suggestions

An excellent article in this months "Vintage" magazine from EAA. A carb. expert explains that MANY strombergs left the factory with improper machining, causing the float to be misaligned. In order to rectify this the carb. must be retooled. Otherwise you get lower horse power due to engine running too lean, which is, also not good for the engine. While some say this is old news, it may not be to some. 3 of the 6 he checked were produced incorrectly at the factory. Sloppy tolerances!JC

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Engine cut-out on takeoff - suggestions

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