I bought a new 1945 for my slant, and I've got it running what I can call decent. Some days, it runs GREAT... but when it's humid or it's rainy outside, the thing runs horrible. I searched, and the only way to tune this carb apart from idle mixture is by changing jets.

I was thinking about this, and I thought an easy way to keep this thing tuned would be to just get an adjustable fuel pressure regulator and make a few turns of an adjuster screw when the weather changes instead of taking the carb apart and re-jetting.

The plan so far (since my stock gas tank and sender are gone) is to cut out my rusted out spare tire well and throw my plastic fuel cell/sender in there, and get an electric pump, regulator, and plumb a new fuel system. I have a narrowband o2 sensor bung in my exhaust, and a gauge up front, and that's how I can tell it's air fuel ratio changes that are causing my inconsitancy. I've messed with fuel pressure in EFI cars, so I have an idea of how to tune fuel pressure, but the few things I'm not sure about:

-is the idle mixture circuit dependent on fuel pressure? like if I have my idle mixture tuned perfect, and I change the fuel pressure.. will it affect the idle mixture?

-is there any kind of adjustment to where you can adjust the regulator from inside the cab? I am going to get an electronic fp gauge to stick in the cab ( I am a gauge whore), and it would be nice to mount a knob somewhere and be able to tune while I drivee.

Is it new, or remanufactured... what's the part number on the float bowl?



Carbs are not like EFI, in the respect that 'turning up' the pressure would be great if you were running a pair of big thirsty 4 barrels on a pure drag motor... with the 1 barrel you have to watch it, if the pressure overcomes the needle and seat assembly it will flood the carb and engine...

idle mix is dependent on the thottle position screw and the idle mix screw at the base of the carb... main metering (above 1800-2000 rpm-ish) is dependent on the main jet at the bottom of the carb bowl assembly...


you may also want to check for manifold leaks, that can cause some idling and drivability issues...

-D.Idiot

Carbs aren't like EFI at all. The fuel pressure in the float bowl is the same as atmospheric pressure, and you basically set your fuel pressure so that you have enough pressure to deliver the fuel at the top end but not so much that it overwhelms the needle valve and floods the float bowl.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Humid rainy weather, running rough?

Makes me think of things other than carb trouble.

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

The others are correct; putting in an adjustable fuel pressure regulator will not help solve this problem, and will contribute new problems to the mix. If you do any mod to the fuel line, make it this one. DusterIdiot's question about whether the carb is really brand new or is in fact "remanufactured" is a good one. The bad-running-when-humid-or-rainy suggests you've got trouble with your secondary-side ignition components (rotor, cap, plug wires, coil).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I agree with Dan, in that it sounds like an ignition issue. Years ago, I had a Dodge Dart Swinger that behaved this way when it rained. I changed the plug wires and the problem went away.

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"Ja, Ich fahre ein altes auto."
'78 Volare 225
'67 Charger 318

ahh, thanks.. that makes sense about the fuel bowls.

The carb is a NOS holley (it's a little different than the stock one visually, but linkages and everything else works), and the car has a NOS chrysler distributor, new extended tip rotor and cap, new accel wires, and a new msd blaster coil. The only thing I have left to do on the ignition side is upgrade to HEI.

could base timing that's off cause problems like that? I've thrown everything at this car, and done everything possible (adjust lash over and over... still ticks, new intake/exhaust gaskets along with milling the surface of both manifolds flat, no cracks in the heat riser part of manifold, no vacuum leaks) and it still chugs out the tailpipe at idle sometimes. The car drives great, it's just the idle kills me (especially with worn out motor mounts). The timing pointer on my balancer isn't visibile, so I just timed the car by ear.

If the timing mark isn't visible, something's wrong. Slipped crank pulley outer ring, base timing way off, or something similar. Could be the timing is OK enough for the engine to run, but close enough to "wrong" that all it takes is moisture in the air for the spark to start jumping to the wrong terminals.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I guess I'll break out the piston stop and mark TDC on the balancer myself then. Each time I drive the car, I have to change something on the carb. Last night the car was running great and not misfiring, at operating temp the car was idling around 1000-1100 in park and about 700-800 stopped in drive. I get in it for work this morning, and after warming it up, it's idling at about 800 and missing/chugging out the tailpipe once or twice every few seconds, and about 600 stopped in drive with a little bit of miss still there (not as bad). After work, I get in and as soon as I start it up it's idling real smoothly at about 600 rpm, and stopped in drive it was a little less than 500 rpm and the motor is running so slow (smoothly with no misses, though) that the whole car is shaking. I had to turn the idle speed screw clockwise 3 times to get the idle back up to about 800/600 today, but if I would have done that yesterday it would be idling at about 1500/1200. With the idle issues aside, the car drives like a DREAM at rpm.. cruising down the street or going down the hiway, the engine runs like butter.. and the miss goes away as soon as you hit the gas. I actually managed to do about a 20 foot long burnout as I was pulling out of the carwash last night!

Maybe old carbureted cars just end up being inconsistent like this? This is my first carbureted car, I'm used to having an EFI car where it idles/runs the same whether it's 20 degrees and snowing or a dry 110 outside. I wonder if it could be a misadjusted choke? I was thinking about buying one of those electric choke conversion kits to see if it would help out.

No, there is something the matter with yours.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

defrag010,

Something is wrong with your carb. I had a 1945 and it too was fine at cruise but it also developed a vacuum leak that was somewhere above the base plate where the carb body joins the base. My carb would get very frosty on occasion during the winter months. I am thinking that it may have developed a hair line crack. I set that carb aside and tried another 1945 which ran fine but only got 18 to 20 mpg after many rebuilds and never changed. The floats would occasionally rub and stick and throw the idle off or the fuel would boil and vapor lock after shut off.

I eventually swapped it out for a 1920 Holley per Doc's suggestion which is much easier to rebuild and tune. A very consistent performer and has the potential to get much better mileage with very little effort. Mine runs like this, pump the gas once in the morning weight 20 seconds, put it in gear and go. It will idle in gear a 600 rpm for hours during rush hour traffic, stop and go on the freeway, day after day, and still take off like a scared jack rabbit. Out of gear the idle is set for 750 rpm, which never changes through out the seasons. It is about as close as you can get to EFI.

I would try another carb. SL6 Dan has some good ones available. Do the fuel line mod so your not boiling the fuel and run a good quality metal gas filter and run the extra thick stock carb spacer. As far as fuel regulators go I run the Mr. Gasket unit set at 4 lbs.

Hope this helps!

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

1. Why? No pressure regulator is needed.

2. You are a braver man than I. See this thread and try a few google searches on the subject; here's one of many applicable results.

(Yes, I do have new carburetors in stock.)

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan,

To clarify, I don't use Mr. Gasket fuel filters, only the fuel regulator that looks like what they sell. I bought mine 15 years ago before they were Mr.Gasket brand. Doc suggested I might try it for mileage improvements. So I though I would give it a try.

The fuel filter is the stainless steel unit Summit Racing sells and I am also using a Perma-Cool fuel water separator since we have been getting allot of water in the gas in our area. I am not sure if it is from bad practices for oil storage, for fuel price gouging or if the ethanol attracts the water. I don't like beads of water running around in the the bottom of the carb's float bowl or any other debris for that matter....

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I don't know what I did, but I got the car running alot better. I got a MSD blaster coil, accel wires, and did an HEI conversion and the car runs real smooth now. The only thing I have left to do is set the lash again because it's a little noisy.

There is one problem, though, that I can't fix no matter how much I play with the carb. When the engine is cold, it idles at about 800 out of gear and about 700 stopped in gear. Once the engine warms up and I do alot of driving, the idle will go up to about 1000-1100 out of gear and a strong 700 stopped in gear.

This is a long shot but it sounds like the fast idle cam (bellcrank or rod) may be hanging up giving you a higher idle now and then.
On my 1945, I ran an extra strong throttle return spring. I never trusted the one on the shaft because as you have said the idle may change from time to time.
Give that a try and maybe the idle will settle down.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG