Tips for Carbs in Cold Elevation - Don’t want EFI

[mpboxer]

Hey All, I have a stock 302 and Carter 4 barrel (basically Edelbrock 1405) and it’s awesome. Changed to off-road needles and seats and blocked the fuel passage to each bowl and it’s been great off camber, during climbs, and descents. When putting around about 8000 feet I turn my idle up a turn and back out my mixture screws 1/2 turn and there are no issues. Yes, it’s a little rich and there is lack of power but it doesn’t warrant me throwing in my next set of metering rods and springs. Maybe if I were tooling around at 12k feet I’d need to.

At home, Phoenix area, cold starts aren’t an issue whatsoever. Full manual choke two pumps of gas and she fires right up. On my last trip in the mountains it was extremely hard to start in the morning. Both mornings were about 25*F. I tried full choke combined with fuel which eventually flooded it. Tried no choke and pedal depressed to floor with no luck. I was cranking so much that I threw my jump pack on the battery just to make sure I was getting full cold cranking. Battery was fine. The second night I fired it right up before bed thinking maybe the block wouldn’t be so cold in the morning. Aside from waking up in the middle of the night to start it I’m out of ideas.

I’m just not ready to switch to EFI. There has to be tips or tricks to starting in these conditions. What do the members with more wisdom than me do? I was reading about pulling a vacuum line to allow more air in the engine when starting. Of course there is starter fluid, but don’t like that idea. Does anyone have some suggestions?

Thanks,
Mike

 

[67sport]

What weight of oil are you using? If you're remote, then block heater/oil heater aren't an option but thinner oil might be?
Does it crank quickly, or does it turn over slowly due to cold oil? In the very cold areas around here (north of here really) it was pretty normal to heat the pan with a torch to get things able to spin.

 

[mpboxer]

What weight of oil are you using? If you're remote, then block heater/oil heater aren't an option but thinner oil might be?
Does it crank quickly, or does it turn over slowly due to cold oil? In the very cold areas around here (north of here really) it was pretty normal to heat the pan with a torch to get things able to spin.

20w-50 VR1 (high zinc). It cranked normal.

 

[73azbronco]

remember full choke at altitude on a carb tuned for low altitude means lots of fuel, that's not vaporizing.

I was going to buy an identical offroad carb tuned for altitude , and swap it at the first stop, seemed like easiest way to make it work. I did not want to be playing with removing top of carb to swap needles out. Then I found the carb guy in Glendale who built me up a Qjet, that had an automatic altitude compensator, and turned it into a manual adjustment, 1/2 turn either way of a screw gets me set 2,000 or 6-7,000 ft up here in Payson.

Yours sounds more like a cold issue than altitude issue, or maybe both piling on. The fuel is not vaporizing. Simplest trick, try some starting fluid spray? Pull a plug when at altitude see how bad it looks. Might try hotter plugs buy one step hotter.

 

[cldonley]

As altitude increases, air density decreases, which means less fuel to achieve a healthy mixture. You might want to think about getting it leaner. If I remember correctly, backing out the mixture screws richens the mixture, so maybe go the other way a bit?

 

[mpboxer]

remember full choke at altitude on a carb tuned for low altitude means lots of fuel, that's not vaporizing.

I was going to buy an identical offroad carb tuned for altitude , and swap it at the first stop, seemed like easiest way to make it work. I did not want to be playing with removing top of carb to swap needles out. Then I found the carb guy in Glendale who built me up a Qjet, that had an automatic altitude compensator, and turned it into a manual adjustment, 1/2 turn either way of a screw gets me set 2,000 or 6-7,000 ft up here in Payson.

Yours sounds more like a cold issue than altitude issue, or maybe both piling on. The fuel is not vaporizing. Simplest trick, try some starting fluid spray? Pull a plug when at altitude see how bad it looks. Might try hotter plugs buy one step hotter.

I thought that too. The second morning I actually started off no choke (to allow more air) and it sparked instantly, but still resulted in a lot of cranking. That’s why I was thinking pulling a vacuum line may actually help.

That’s pretty slick on the altitude adjustment.

I think you are correct and the fuel is not vaporizing. It’s a pain to remove the factory air cleaner, can starter fluid be sprayed in a full vacuum port on the carb (ie where my brake booster hose would go)?

 

[Broncobowsher]

Back off on the choke.

I remember pilots learning to start there small aircraft. What works great in Phoenix doesn't work that great in Showlow. Black polywags puffing out the exhaust. Back off the choke to better match the lack of air. Now it starts.

 

[mpboxer]

As altitude increases, air density decreases, which means less fuel to achieve a healthy mixture. You might want to think about getting it leaner. If I remember correctly, backing out the mixture screws richens the mixture, so maybe go the other way a bit?

If I back out the mixture screws on the front and allow more air in wouldn’t that help compensate for the richer fuel environment?

 

[Broncobowsher]

The fuel in the bowl may be boiling off sooner as well. Boiling point drops as altitude increases. Are you sure the long crank wasn't a lack of fuel in the carb?

 

[mpboxer]

Back off on the choke.

I remember pilots learning to start there small aircraft. What works great in Phoenix doesn't work that great in Showlow. Black polywags puffing out the exhaust. Back off the choke to better match the lack of air. Now it starts.

I tried that the second morning from the start and I had instant spark, so I think you are dead on. It still resulted in a lot of cranking but the results were better from the start.

 

[mpboxer]

The fuel in the bowl may be boiling off sooner as well. Boiling point drops as altitude increases. Are you sure the long crank wasn't a lack of fuel in the carb?

Plenty of fuel. I could smell it it was that bad. Definitely flooded with choke closed.

 

[EPB72]

If I back out the mixture screws on the front and allow more air in wouldn’t that help compensate for the richer fuel environment?

Backing out mixture screws make it richer on carter AFB and eldelbrocks as well,,

 

[gr8scott]

If I back out the mixture screws on the front and allow more air in wouldn’t that help compensate for the richer fuel environment?

Those screws on the front are idle mixture screws. They only adjust idle mixture.

 

[mpboxer]

Those screws on the front are idle mixture screws. They only adjust idle mixture.

Thanks, I understand that. At 8000ft I only have to adjust my idle speed and mixture. It still runs rich but doesn’t warrant me changing metering rods/springs.

 

[mpboxer]

Backing out mixture screws make it richer on carter AFB and eldelbrocks as well,,

Ok so backing out my idle mixture screws on the front, which allows more air in, makes it richer?

 

[Oldtimer]

The idle mixture screws controll the amount of gas that the gets sucked into the air stream. As you back them out you get more gas, causing a richer mixture.

 

[Broncobowsher]

Ok so backing out my idle mixture screws on the front, which allows more air in, makes it richer?

Screws don't adjust air, they adjust fuel.

The idle speed screw that is the idle stop screw, the one that adjusts the minimum flow through the butterflies, that is the only one that adjusts airflow.

Do you have a lot of motorcycle background? Those are the only carbs I know of that have an adjustable air bleed screw for idle mix.

 

[mpboxer]

The idle mixture screws controll the amount of gas that the gets sucked into the air stream. As you back them out you get more gas, causing a richer mixture.

Well shoot I’m probably making it worse and compounding the issue. I won’t adjust those or maybe I should be turning them in a bit when up in elevation.

 

[mpboxer]

Screws don't adjust air, they adjust fuel.

The idle speed screw that is the idle stop screw, the one that adjusts the minimum flow through the butterflies, that is the only one that adjusts airflow.

Do you have a lot of motorcycle background? Those are the only carbs I know of that have an adjustable air bleed screw for idle mix.

Thank you!

None at all.

 

[mpboxer]

Just giving an update. Cold weather camped this weekend. Placed my Mr. Buddy heater under the oil pan for about 15 minutes to heat up the oil a little. Turned off heater. A little starter fluid and she fired up first time. Elevation was only 5,600ft and around 28 degrees.