I don't know anything about the Stromberg BXOV or Nicson intake, but carb icing is a temperature and humidity phenomenon.

Usually happens above freezing temp. along with high humidity. Ice can form when humid air is drawn through a venturi, while introducing gasoline and it sticks to the carb throttle blade first. It can build up considerably, even encasing the carb in extreme cases.

Heat is normally used to prevent icing, both from the cooling system and exhaust.

I'm guessing your intake has no heat, as well as the carbs.

Probably not your problem but possible, some carbs were very icing resistant, others not so much.

Spraying WD40 or similar, inside the carb air intake can prevent ice from sticking to the throttle blades temporarily.

Methyl hydrate is a good thing to add to your fuel if you suspect carb icing.

Thanks
Randy

From the factory the stock intake got heat from the heat riser valve on the exhaust manifold. The aftermarket L6 intakes generally don't have a provision for heat. The Offenhauser intake for my Chevy straight six has a provision for hot water heating to prevent the icing that you describe.

loosenut wrote:

---

Hi Randy. Thank you for your reply. I do have heat to the intake manifold via tubes from the exhaust headers and the base of the intake manifold. I will try the methal hydrate in the gasoline to see if that helps. I think I am running the fuel a little rich but can't keep it running long enough to set them up properly. Do you know if running rich would contribute to this problem? Again thank you for your help, John

---

 

John, running rich does not normally contribute to icing, as its the air that contains the most moisture. M/H doesn't really prevent icing as much as it prevents ice from sticking to things, such as the inside of the carb, similar to spraying WD40 inside the carb.

Carb icing is a pretty rare phenomenon, so I doubt you would experience it regularity over several days.

It's not easily repeatable, even if you were trying, not on the ground at least, a small airplane would be a different story.

Actually, although icing that becomes a problem on the ground is rare, ice often forms in a carb during normal operation, but evaporates soon after while on its way into the warm engine. It has to build up to be a problem, first on the throttle plate and venturi. I have seen carbs completely encased in ice, but that's very, very rare.

Chrysler 318 engines were problematic when their exhaust crossover passage in the intake manifold plugged up, causing the carb to take a long time to absorb engine heat. Thermac systems, with their exhaust manifold to air cleaner hoses helped considerably.

If you get a chance, post up some pictures of your setup, or better yet, a video if you have the skills. I don't say this sarcastically, as I certainly don't !!

 

Thanks

Randy

 

 

 

Happy to be of any help John!!

Strange you had trouble posting, it took me a few tries to post my message, as I kept getting a Shockwave ?? dropdown type message across the top of my screen, and it freezing, darn "computer ice"!!

Had to retype 3 times, very slow as I'm a one finger typer.

I don't even know what Schockwave is, and if it was related to my posting issue or not, but it seems O.K. now.

Thanks
Randy

Few more!!

Does the intake have provision for coolant system connections? Maybe not enough restriction in the exhaust system to allow hot gases to pressurise the intake and heat it fast enough. Maybe as a test a use an electric heat gun to warm up the intake setup then have a scond person keep the heat gun warming up the manifold while you run it. This will at least tell you if it is heating problems. 

Maybe the piping from the exhaust to manifold has blocked for som reason....

-- Edited by koolconvertible on Sunday 29th of November 2015 03:21:36 PM

Found this video while searching info on your carbs!!

Not all carbs run with the top removed, but this should help in diagnosing your issue.

Does your engine start with full bowls, then run dry, or over fill the bowls and flood the engine, or neither.

Or could you possibly have an ignition coil that overheats/fails after warming up. Check spark cold, then after it stops.

Step by step diagnosis. Looks like a nice setup!!

Thanks
Randy

Can you see the ice build up? Maybe try running with the airfilters on?

Thanks guys. Philip, I have not seen any ice buildup but base of carbs are very cold and sometimes when it shuts down the base of the back carb has "beads of sweat on the base. I have tried running it with filters on and off== no difference.
Don. Currently it will run for only a few mins then starts to stumble and vacuum drops off and then quits, Probably less the 2-3 mins.
It does seem reasonable that the short running time would indicate something other than icing.
Will try adding fuel to carb after it quits to see if it will restart.
Will check temperature before/after running.
I havn't noticed smell of fuel after shutdown but fuel pressure gauge indicated 4 PSi which i read is too high (2-2.5PSI according to an article on JJ). I have no regulator as yet and will add as soon as I get one. Maybe that is what is happening. I will pull the top off my carbs after my next start-up.
Got lots of homework for today so let you know later how I get along. Thanks, John

Thank you Cal for that. Cannot argue with anything you are saying, I believe my engine is running rich and I know it has a little more fuel pressure that it would like. so what you are saying makes sense.
Today I checked the temp of my carb base (47 F). Then I heated base of carb and the intake manifold with a heat gun. Then I started car. (had to adj distributor as was loose so was out of time?). Ran for several minutes (bit rough but it ran) Vacuum was about 17. Fuel pressure about 4. Tried to get it down to 900 RPM but stalled however it soon started. (I checked carb base and was over 100 F). Same thing again so I pulled top off carbs and all looked OK (to the untrained eye I might add). In a few minutes I had it running again and then it shut down. I took temp at carb base and still over 100F. I think I might have muttered something at this point!!. Anyway I pull the top off carbs and you guessed it "empty". Looked at filter bowl and it is half full. By now my battery is getting low so I quit for the day. I might add That I checked the spark after the engine warmed up and I think it was ok. SOO tomorrow is another day and we see what happens!!

Hi Philip: I was thinking... but only has less than I hour on it. Nowadays anything is possible. Would like to get it running for a while so I could check for vacuum leak and adj. the carbs a bit.

-- Edited by loosenut on Monday 30th of November 2015 07:55:43 PM

I have nothing to add to your problem diagnosis, but I just wanted to say that I love looking at your engine set-up.