Cold Carburetor??

[JOHN COOKSON]

Mike

You can always take the back flame arrestor off and try choking by holding your hand over the carb throat while you use a remote starter switch or someone else in the cockpit starts the engine. This should help narrow down whether you have a choke issue or not.

How do you have the choke adjusted? The movable arm needs to swing through its entire range and not hit the fixed arm or anything else such as the outer cover in the hold down bracket.

Also, is the poppet valve on the choke plate somehow not right?

TRUE GRIT

[lat 64]

Pretty much every car with a carb has a pre heater hose that goes to the air filter to introduce warm air. Usually it gets the warm air from the exhaust heat.

Many cars have iced up and broke down because this hose was not in place.

Yes, that was always my understanding. It could be mine was missing. There was no evidence of it on my car though. Not a trace. Often those things got dysfunctional long before the engine wore out. I restored quite a few to meet emissions inspections on the old junk I drove.
The two-stage Weber it had was really quite reliable and had a well-designed automatic choke.

As I wrote, I have the habit of warming up the engine on the boat and then turning it off to let everything warm up. This is because It typically shuts down and dies during the first few minutes while I am puttering about. I am wondering now if I am responding to something like carb ice.
I think the possibility is real. We have a cool harbor. It's can be 45 deg. in the morning some days. It never gets really warm down there until afternoon on a midsummer day. Also dampness is an issue too. I take many steps to ventilate to avoid a moldy boat.

You got me thinkin'

R.

[joe_db]

Take the flame arrestor off and look. 45 degrees and 60% humidity is about the worst possible combo for carb ice.
I know a damp 45 degree day caused so much carb ice in a Cessna 150 I had to taxi with it on* to make it to the runway without icing up

* carb heat bypasses the filter, so we normally do not use it on the ground.

[lat 64]

Take the flame arrestor off and look. 45 degrees and 60% humidity is about the worst possible combo for carb ice.
I know a damp 45 degree day caused so much carb ice in a Cessna 150 I had to taxi with it on* to make it to the runway without icing up

* carb heat bypasses the filter, so we normally do not use it on the ground.

I'm a couple of months out before I can do this check, but I can easily find carb-ice conditions this spring. I looked again at your chart in post# 5. It looks like I'm very often the blue zone at least. I am understanding that "glide" power settings is low manifold pressure? That is, a greater pressure drop across the venturi? That would be just like when I am running the engine at a high idle with no load at the slip.

I'm now excited to look into this. It fits the problem of shutdown I have been dealing with since I owned the boat.

I'll have to get my camera ready and try to make this happen so I can see if it's real or just my over-thinking it.

Good thread,

Russ

[joe_db]

Glide = low power. The bigger the pressure drop - i.e. less power and the throttle plate mostly closed - the bigger the temperature drop.
Your manifold pressure gauge would have a "high" reading if it is the Isspro or similar because it reads inches of vacuum and high number = low pressure
Airplane gauges are backwards and read absolute manifold pressure.

I'm a couple of months out before I can do this check, but I can easily find carb-ice conditions this spring. I looked again at your chart in post# 5. It looks like I'm very often the blue zone at least. I am understanding that "glide" power settings is low manifold pressure? That is, a greater pressure drop across the venturi? That would be just like when I am running the engine at a high idle with no load at the slip.

I'm now excited to look into this. It fits the problem of shutdown I have been dealing with since I owned the boat.

I'll have to get my camera ready and try to make this happen so I can see if it's real or just my over-thinking it.

Good thread,

Russ

[lat 64]

Glide = low power. The bigger the pressure drop - i.e. less power and the throttle plate mostly closed - the bigger the temperature drop.
Your manifold pressure gauge would have a "high" reading if it is the Isspro or similar because it reads inches of vacuum and high number = low pressure
Airplane gauges are backwards and read absolute manifold pressure.

Thanks, I think I have it right then.
Just the other day I was explaining Bernoulli's principle to a teenage girl. Finally made sense to her when I used the perfume atomizer example. Just find a person's point of reference and you'll get the ideas across.

You pilot's owe a lot to Bernoulli I think.

R.

[mike7a10]

Update

OK...let me start by saying I'm not a mechanic. Having said that I have been pretty successful in keeping my old A4 alive and kicking including a total rebuild a few years ago with a lot of help from this website.

That being said...my hard start problem kept coming back to the choke as I had previously said. I dropped the carb as promised and everything seemed fine. I was about to reinstall it and I decided to pull out a few A4 manuals I have in the boat.

I looked, and looked (you get the picture) and suddenly it dawned on me that the choke butterfly valve looked wrong. I had installed the choke valve upside down with the top of the valve oriented "forward" (the poppet valve was at the "bottom").

After reinstalling it right-side-up (poppet valve "up") and oriented with the top of the valve oriented towards the back of the carb, the motor started right up.

Installing the choke valve backwards had caused the spring to pull the choke shut. Now the spring pulls the choke to open.

I tested it several times after the "fix" and it is running great.

I was overjoyed and feeling pretty dumb at the same time. I seem to be getting used to this feeling as an A4 owner... duh! So thank you again to everyone. Your collective advice helped me to figure it out.

Mike
S/V Plan Sea

[hanleyclifford]

Been there, done that

You got a lot of company - the older I get the more often it happens. Sign in shop: "DOLTO" (Don't overlook the obvious).

[lat 64]

I choke on humble pie often

Nice work,

I voted a green thumb 'zup on your last post. This is not an obvious repair. I can see myself doing the same thing. (I know, that's not saying much)

Russ