Hi All: Need your help on this. I have a chev 261 set up on a stand. It has been freshened up and I am running 2 Stromberg BXOV on an Nicson intake. Also have Fenton split exhaust with heat tubes to the intake.It has stock distributor and coil as well as fuel pump. Has new H2O pump with rad with antifreeze. I set the timing using a vacuum gauge (runs best about 16 "). When running it shows about 4 psi fuel pressure I have read these carbs run best with approx 2.5 psi. When I first started the engine it ran well and probably ran 15-20 mins at one time. However on subsequent startups it will only run a few moments until it slows down and eventually stops. (I have not been able to properly set the carbs as I can't keep it running long enough! Both carb's are ice cold. It will not start again for several hours and then same thing. Another thing that is happening is the exhaust becomes very hot. I have rubber exhaust tubes coming off a muffler and by the time it shuts down it is extremely hot. Question: Is what happening apt to be carb. icing. If so would/could the higher fuel pressure be a cause?I have no experience with this phenom. and at a loss to know what is happening. This is a new challenge for me and probably in over my head but sure having fun. Any help would be appreciated.
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.
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
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.
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In garage, 296 cid inline six & TH350...
Cam, Toronto.
I don't judge a man by how far he's fallen, but by how far back he bounces - Patton
Hi Cameron: Thank you for the reply. I do in fact have heat to the intake from the exhaust however it has not seemed to make any difference. Last couple of times I tried to run it it shut down in just a few mins. (3-5 mins I would say) Seems awfully fast for icing to happen but then I do not know what I am looking for either. I know the carbs get awful cold fast and then it slowly dies. Maybe I am solving a problem that is not occurring. Start fresh on Monday. Thanks again, John
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 !!
Thank you Randy. That is the best explanation of icing I have read. Very helpful and makes me think more going on than simple icing. I have never done a video but can post some pics. Thanks again for your help, John PS Currently having a bit of trouble with this site- very slow??? I will try to put on pics later today.
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.
Sorry I got a couple of duplicate. Accidentally added them before I figured out what I was doing. Still hav'nt figured how to selectively delete. Old age is a wonderful thing:)
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
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cutting a roof off a four door is NOT a convertible.....
65 Parisienne convertible.one of 49 built for RHD export market,402BBC, T400, 2500 stally, posi rear, upgraded brakes with front discs, FUEL FAST efi custom built by me.
Thank you guys: I will check out each item you have mentioned. I am really wondering if for some reason I am running out of gasoline--- but those carbs get sooo cold.
Can you see the ice build up? Maybe try running with the airfilters on?
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cutting a roof off a four door is NOT a convertible.....
65 Parisienne convertible.one of 49 built for RHD export market,402BBC, T400, 2500 stally, posi rear, upgraded brakes with front discs, FUEL FAST efi custom built by me.
On a start up, does it run OK for a minute of so, then quit?
Could be a vacuum leak? As was said, a bad coil? No fuel? Those would be my 3 guesses, my first thought is vacuum leak, which may be the hardest to find for sure.
Doesn't seem logical that you would be getting icing that fast. Use an infrared heat gun to check temperatures of the carbs (and fuel?) before you start the motor and while "cold" like you say it is.
After it quits, dump a bit of fuel into the carbs and see if it runs. Too much fuel pressure will usually overpower the needle and seat and cause flooding. Are you smelling excess gas after it quits?
If nothing works, can you remove one carb, block off that carb, and try running it on one carb? On tri power V8's, these carbs are unique in that they are made to run on the center carb and the 2 end carbs act like the secondaries of a 4 barrel, they only kick in on demand. In your setup, are the carbs the same and they both run all the time? Multiple carb setups frequently have issues with vacuum leaks.
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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. 1963- Pontiac top selling car in Canada
Mahone Bay, NS Still not old enough to need an automatic
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
There is a lot of good advice in the above replies. I have recently experienced the same kind of symptoms with the Rochester Quadrajet on my old 71 GMC truck. I'm going to go out on a limb with the suggestion of excess fuel/rich mixture/flooding....then carb icing.
Back in the day when I was flying piston driven helicopters carb icing was a BIG deal. The only time we operated without carb heat was when it was extremely cold...-30 or thereabouts and prior to landing when the checklist called for 'mixture rich & carb heat cold'.
If I remember correctly, (+ 40 years ago) carb icing is a phenomena that can occur any time there is moisture in the air (except for extreme cold when moisture is suspended as frozen particles). Strangely, carb icing was most prevalent during the summer with high humidity. The Franklin's & Lycoming's would let you know when they required some heat when there was a drop in RPM and the engine started to run roughly. An application of carb heat cleared up the situation almost immediately....
Good luck...please let us know what you find out.
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1949 Pro Street Meteor Coupe, 468 BBC, 4L80E, Narrowed 9" 3.50 posi
1966 Biscayne post, 427 L72, M21, 4.11's 16600 original miles
1966 Hemi Satellite 4 gear 59K original miles 1968 Z28 302MO, M21, 3.73's, cowl plenum induction
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!!
Sounds like your getting there! Maybe fuel pump issue?
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cutting a roof off a four door is NOT a convertible.....
65 Parisienne convertible.one of 49 built for RHD export market,402BBC, T400, 2500 stally, posi rear, upgraded brakes with front discs, FUEL FAST efi custom built by me.
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
New fuel pumps have certainly been known to be crap. Glad to see you are making progress.
Don
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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. 1963- Pontiac top selling car in Canada
Mahone Bay, NS Still not old enough to need an automatic
I have nothing to add to your problem diagnosis, but I just wanted to say that I love looking at your engine set-up.
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Prince Edward Island
'64 Parisienne CS "barn find" - last on the road in '86 ... Owner Protection Plan booklet, original paint, original near-mint aqua interior, original aqua GM floor mats, original 283, factory posi, and original rust.
Thank you Don and Darryle: I have had a lot of fun putting this thing together. I have no idea what I will do with it when done (may will be determined if I get it running or not):)
