Backfiring through Carburetor Rajo Overhead Sprint Car

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Model T Ford Forum: Forum 2012: Backfiring through Carburetor Rajo Overhead Sprint Car
Top of pagePrevious messageNext messageBottom of page Link to this message  By Joe Andulics on Friday, August 03, 2012 - 09:29 pm:

Got the sprint car running, almost. It starts right up but it feels like I'm chasing my tail getting the Winfield carburetor tuned right. It's a model T engine with a Rajo B overhead. The carburetor is a single BB Model S. First problem is the fuel pressure. I'm using a hand pump to pressurize the tank to a maximum of 2 P.S.I.. Even then the carburetor wants to leak between the float bowl cover and the strainer bowl and the float bowl cover and the float bowl. New gaskets without sealant and the surfaces are flat and without cracks. Should I expect some leakage? The engine was stumbling so I lowered the float. The level was at the bottom of the inspection hole. I lowered the level approx 1/32” and that seemed to take care of the stumbling and coincidentally the carburetor doesn't leak as bad. At higher RPM the engine backfires through the carburetor so I assumed it was leaning out. I've got the idle set at 20 clicks, the intermediate at 36 and the high speed at 42. The needles are the earlier blunt style so the greater the number of clicks. It still wants to backfire through the carburetor when I push it hard. Is the float level now too low?

Or do I have an ignition issue or vacuum leak?

I'm running a Bosch DU4 magneto with the gap set at 0.012. Plugs are Autolite 3923 gaped at 0.018

I'm hoping someone has had or has a similar setup and share some “secrets”. The last AARA race is in September and I'm hoping to make it, but I'd rather have the car running well now, rather than tune it at the track. Thanks

http://www.youtube.com/watch?feature=player_embedded&v=5vgjgQQmHds


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Saturday, August 04, 2012 - 12:28 am:

Look for a vacuum leak. Did you use rings and glands?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan McEachern on Saturday, August 04, 2012 - 01:37 am:

Winfields can't tolerate much more than 1 1/2 psi fuel pressure. The float level should be right at the bottom of the hole.

I would suggest leaning the intermediate until it pops just off idle then fatten that up until it stops. Then tackle the hi speed the same way-
one or two clicks makes a huge difference-If it pops going from mid to WOT, a few more clicks on the intermediate may help. Make small changes and drive it- its a pain, but the only way.
I don't have a carb in front of me- make sure you are turning the screws the correct direction- several are air bleeds so they adjust opposite a jet. The float bowl should not be leaking- sounds like your fuel pressure may be a lot of the problem- put one of those adjustable fuel pressure regulators in line somewhere.
Dan


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Eubanks, Powell, TN on Saturday, August 04, 2012 - 08:24 am:

How about a tight valve?


Top of pagePrevious messageNext messageBottom of page Link to this message  By tim moore on Saturday, August 04, 2012 - 08:53 am:

Try this site to set up the Winfield:

http://www.nwvs.org/Technical/2104WinfieldHV.pdf

Tim Moore


Top of pagePrevious messageNext messageBottom of page Link to this message  By Joe Andulics on Saturday, August 04, 2012 - 10:05 am:

I think I created my own problem when I lowered the float level. I did so hoping that would take care of the leaking. I've found an adjustable 1-4lb. regulator that I'm going to try and then reset the float so the gas level is to the bottom of the inspection hole. As far as making adjustments following the same article that Tim directed me to, since it's an S carburetor there is no accelerating pump adjustment. I turn the needles in until they lightly stop and count as I turned them back out.
The carburetor was rebuilt years ago by Les Bowman, who was somewhat of a Winfield guru. I don't have any reason to believe that I'm not causing my own problems. I've got no local help, and I'm trying to avoid as much trail and error as I can (I get jittery tightening screws down in a pot metal carburetor). Thanks and keep the suggestions coming. I'm real close now!


Top of pagePrevious messageNext messageBottom of page Link to this message  By joe bell on Saturday, August 04, 2012 - 06:40 pm:

Joe, I was into the hot rod cars before the T's, is there enough spring pressure for closing the valve at higher RPM's? I had one that would act up at the higher rpm's till I installed a heavier valve spring pressure. Make sure there is still enough clearance in the spring on high lift so you do not bend push rods or wear the cam lobes off.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Andrew Webb on Saturday, August 04, 2012 - 07:07 pm:

Hi Joe
I have the same set up, why do you need a pump is the fuel tank sitting low?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Joe Andulics on Saturday, August 04, 2012 - 09:21 pm:

Want to work the carburetor settings first, then look at ignition/valve.

Yes my tank sits lower than the carburetor.

Thanks, I have a Holley 12-804 regulator on order from Jegs. It's adjustable from 1-4 lbs. The gage on my dash is worthless. It's an old original and I have to tap the glass to get it back to 0. Hope to have the fuel pressure regulator and the float level reset by Friday. We'll let you all know how it works. Thanks


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