Carb riser on stromberg 81 carb

[coatings03]

Happy 4th to all barners,
I have a question about the downdraft carbs using the carb risers 4”;6” and 8”. What significant benefit does this have installing a 2-carb set up on a model a engine.

Thank you,
Jim m

[emf]

Check out this site. it seems they won't help a bit under 5000 RPM...

Spacer

Frank

[coatings03]

Frank,
Very good article explains the process and answers that question!��

Thank you,
Jim m

[MrBruce]

Originally Posted by coatings03

Happy 4th to all barners,
I have a question about the downdraft carbs using the carb risers 4”;6” and 8”. What significant benefit does this have installing a 2-carb set up on a model a engine.

Thank you,
Jim m

I'm fighting the problem (never run a downdraft before) with a Stromberg 97 on a Model A which is inserted with a Lions head. Runs good except for start up. It is flooded without any choke...has to burn off gas...bothers me as I don't want to wash the rings out. Only time it doesn't blubber is when I have just driven it? I'm wondering if the fuel pump pressure is too high? I've got a "Burns" setup with two Stromberg 81's but feel I don't need two carbs so am not going to use it. Any help on the fuel at start up...?

[1931 flamingo]

Try swapping one of the 81's for the 97 or have "Uncle Max" on the EV* forum rebuild the 97.
Paul in CT

[MrBruce]

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Originally Posted by 1931 flamingo

Try swapping one of the 81's for the 97 or have "Uncle Max" on the EV* forum rebuild the 97.
Paul in CT

The 97 is new. I don't want to break the set of two 81's from the Burns manifold as I am going to get rid of that set up. I'm wondering about taking the block out from under the carb and then hooking it up as gravity feed instead of the electric fuel pump? I picked up a gauge to see what pressure the pump is putting out and see if it could be two high? I heard that it shouldn't be more 2.5 lbs pressure from the pump? Just trying to get the fittings correct to hook up the gauge

[Jim Brierley]

Mr. Bruce, I would shut your fuel pump off 30 seconds, or more, before turning off the engine. This eliminates any pressure in the system. Residual line pressure will push fuel into the bowl as the engine sits there, and cause your starting problem. I shut mine off as I enter my driveway. You might also check the fuel level in the bowls to be sure they aren't too high. A pair of 81's isn't too much in most cases but I recommend one 97 for a mild touring engine. I run three 81's on my speedster, it runs great and gets good fuel mileage.

[Jim Brierley]

emf, Not sure that I agree with the article on spacers. I believe longer 'runners' give more velocity, so run better on the street. Try them on your A and see how they work.

[MrBruce]

Originally Posted by Jim Brierley

Mr. Bruce, I would shut your fuel pump off 30 seconds, or more, before turning off the engine. This eliminates any pressure in the system. Residual line pressure will push fuel into the bowl as the engine sits there, and cause your starting problem. I shut mine off as I enter my driveway. You might also check the fuel level in the bowls to be sure they aren't too high. A pair of 81's isn't too much in most cases but I recommend one 97 for a mild touring engine. I run three 81's on my speedster, it runs great and gets good fuel mileage.

Jim
That's the info I was looking for, I was shutting my tank off coming down the road but I don't think the shut off is that good so I had bought a switch and was going to do what you said. So, you confirmed what I was thinking...thank you...not used to these down draft carbs. Love the looks of them.

[emf]

Jim, I was just pointing to an article that talked about risers. My pair of 81's on a Burns manifold run just fine for me without risers.

Frank

[1929]

I have a 97 on mine, I just disconnected the fuel pump and regulator, I was getting similar problems. I do prefer to run gravity feed because its 2 less items I need to worry about. The only problem is, I cant go over 60mph on gravity.

[coatings03]

I’m going to first try running gravity feed, see how that works out. Keeping the 81’s as low as possible without any phenolic spacers. Spoke to Charlie Price(Vintage Speed-Florida) he mentions keeping the carbs low and use 2nd carb with just a slight crack opening!

Jim m

[Jim Brierley]

emf, I don't run risers either, and have good luck with them. I do some racing, and have seen a lot of articles on this, so just repeating what I have seen, and believe.

[George Miller]

Originally Posted by MrBruce

Jim
That's the info I was looking for, I was shutting my tank off coming down the road but I don't think the shut off is that good so I had bought a switch and was going to do what you said. So, you confirmed what I was thinking...thank you...not used to these down draft carbs. Love the looks of them.

That is what I do with my 94 and electric pump. shut it off before I get to the garage. It does away with the gas perking when you stop.