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IO-360 M1B Intake Tube Seals - Backfiring

mfleming

mfleming

Well Known Member
Patron
Two things.

First question. Does anyone have advice or a written procedure for replacing the intake tube seals on the sump end of the tube? Photos below.

I have gotten some great advice from a respected member of VAF about trouble shooting my problem but just casting a wider net.

Second question. Can an intake leak on the intake tube cause a massive backfire? The backfires during hot starts have blown out the air filter several times. Always on a hot start. It happens whether I start on the left impulse Slick, right P-Mag or both. It happens when the mixture is being used in as it's trying to start.

I've had experienced mechanics and pilots watch me hot start and find nothing wrong with my technique (I've tried every technique I can think of.

intake-tube1.jpg intake-tube2.jpg intake-tube3.jpg
 
Not sure why you thing intake seals are the root issue.

As far as backfire, before doing anything else I’d check ignition timing. Remember for this engine the:
- Mag is 25 degrees BTDC
- pMag is also 25 degrees, but to set this timing you move the crank to TDC, then blown into the pMag manifold pressure tube to tell the pMag to set the timing. Do not make the common mistake of setting the pMag timing when the crank is at 25 degree BTDC. If you forget to do this, the pMag will actually be at 50 degrees BTDC.

Carl
 
To install. It's Just a big orange silicon O-ring . Be careful not to cut the o-ring on the sharp edge of the tube o-ring keeper. Any intake leak lowers the demand of fuel from a mass flow sensor. Meaning less fuel to the engine at all times.
 
Carl Froehlich said:
Not sure why you thing intake seals are the root issue.

As far as backfire, before doing anything else I’d check ignition timing. Remember for this engine the:
- Mag is 25 degrees BTDC
- pMag is also 25 degrees, but to set this timing you move the crank to TDC, then blown into the pMag manifold pressure tube to tell the pMag to set the timing. Do not make the common mistake of setting the pMag timing when the crank is at 25 degree BTDC. If you forget to do this, the pMag will actually be at 50 degrees BTDC.

Carl
Click to expand...
I don't know what the root cause is. This intake leak is the only thing I've found out of order so far.
Timing - Been there, done that. Any other suggestions? This darn engine has 160 hrs on it and it's been backfiring on start up since new.
As stated in the OP, the backfire can happen with any combination of ignition being on or off.
 
mfleming said:
I don't know what the root cause is. This intake leak is the only thing I've found out of order so far.
Timing - Been there, done that. Any other suggestions? This darn engine has 160 hrs on it and it's been backfiring on start up since new.
As stated in the OP, the backfire can happen with any combination of ignition being on or off.
Click to expand...
I do not see how an intake leak can cause this problem. For that matter how do you know you have an intake leak?

Not trying to piss you off, but after many hot starts I finally gave into following the guidance on how to do hot starts. Even so I can advance the mixture too soon and end up with an engine with fuel/air too rich to run. The cure is always to open the thottle, mixture at cut out, and crank. In a few blades the engine purges the excess fuel and runs. At that point an easy advance of the mixture and we are off.

Carl
 
Carl Froehlich said:
I do not see how an intake leak can cause this problem. For that matter how do you know you have an intake leak?

Not trying to piss you off, but after many hot starts I finally gave into following the guidance on how to do hot starts. Even so I can advance the mixture too soon and end up with an engine with fuel/air too rich to run. The cure is always to open the thottle, mixture at cut out, and crank. In a few blades the engine purges the excess fuel and runs. At that point an easy advance of the mixture and we are off.

Carl
Click to expand...
No worries...I'm all ears for fixes...either mechanical or how to operate. Everyone who's been around this engine thinks there's something wrong with how it starts...just trying to get good input.

EDIT: I do like the idea of allowing a few blades to rotate before easing the mixture in. I tend to start pushing the mixture in as soon as the engine starts turning over.
Leak - There is oil dripping from two of the intake tubes at the sump with slight blue stain.
 
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(Small) Induction leaks can easily cause loud popping in the exhaust as a result of combustion instability(s); typically a very lean local condition. It is not a "backfire" or after-fire but the terms are often mistakingly interchanged. Harder to detect than to fix. Keep us informed.
 
mfleming said:
There is oil dripping from two of the intake tubes at the sump with slight blue stain.
Click to expand...
Just for data point, I also have the same M1B at about 72 hours but I don't have the leak like you have. I have some very minor oil leaks but not around the intake tubes
 
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