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| Stalling out mid-throttle https://www.slantsix.org/forum/viewtopic.php?t=45016 |
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| Author: | skurdnin [ Wed May 18, 2011 10:33 am ] |
| Post subject: | Stalling out mid-throttle |
Well, I thought had my car running good, but a new issue has come up recently. When you put the peddle about halfway down, the engine will sputter, and if I'm going slow enough it will just die. I've been playing with the carb for days and can't figure it out. If I ease into the throttle, it won't happen, but if I go from idle to mid-peddle it will happen almost every time. I turned the idle mixture screw all the way in, and the car didn't die, which can't be a good sign. It ran rough, but didn't die at all. I have a Holley 6145. I was thinking of just finding a different one barrel to put on there, but if it's not carb related, than that would be a waste. |
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| Author: | wjajr [ Wed May 18, 2011 11:36 am ] |
| Post subject: | |
You may have several things causing stumbling. Items to evaluate are: The accelerator pump providing a good shot of fuel when throttle is opened. Stumbling during small or mid sized throttle opening may indicate that your accelerator pump is failing by not providing a full shot. A quick way to determine it function is with engine off, choke open, look into carburetor while opening throttle. One should see a nice strong squirt gas being expelled while opening. If it dribbles, or comes on late in throttle opeing it needs a rebuild. Second condition to consider is a vacuum leak, this would cause idle problems. Thirdly; idle speed adjustment maybe too high causing a problem transitioning from idle to running on main jets. When this adjustment is too great, the idle circuit won’t respond to idle mixture screw adjustment. |
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| Author: | BUCKET 636 [ Wed May 18, 2011 5:12 pm ] |
| Post subject: | |
I had this exact same problem with a NOS Holley 2280. I put a new accelerator pump stem rubber and gaskets in it and wallah,no more bog. |
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| Author: | skurdnin [ Wed May 18, 2011 9:25 pm ] |
| Post subject: | |
Thanks for the replies. It looks like the accelerator pump is working correctly, although I'm not sure exactly how much fuel is supposed to be dispensed. There is a decent shot. I rebuilt the carb when I first got the car, and I replaced all the inner gaskets, but I don't believe I replaced the pump. There are no apparent vacuum leaks, and the car idles fine. I will have to play with the idle settings some more, though. I don't have a tach, so I've been setting the idle by feel. I didn't realize that it could render the mixture screw useless. |
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| Author: | SlantSixDan [ Wed May 18, 2011 9:51 pm ] |
| Post subject: | |
If you're getting a good solid shot of fuel from the accelerator pump, it's probably fine. Check for a blown vacuum advance pod or cracked/damaged/disconnected vacuum advance hose. The hose should go directly from the correct port on the carburetor (called "Spark advance" or "OSAC" in the annotated carb diagram you can find via link below) to the distributor with no stops in between. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. |
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| Author: | skurdnin [ Thu May 19, 2011 9:40 am ] |
| Post subject: | |
The distributor is hooked up to the OSAC valve, and I replaced the vacuum line a few weeks. The timing is set at about 13 BTDC (factory was 12 according to the sticker under the hood.) I had the timing up to 16 BTDC just to see if it would help, but it didn't make a difference. The plugs are good, the plug wires are good. I replaced the fuel filter, and the fuel lines under the hood. I'm almost certain it's an air/fuel issue, I'm just not sure what else to look at. I was looking at the choke today, and it was open when the car was off and not warmed up (it hadn't been turned on since yesterday.) It was pretty warm outside today, however. Would the ambient air temperature be the reason the choke wasn't closed when the car was off? |
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| Author: | wjajr [ Thu May 19, 2011 11:52 am ] |
| Post subject: | |
Choke will stay open after engine cools as long as gas peddle is not depressed or throttle opened. Once throttle is cracked open before a cold start, that choke plate will than snap shut, and won’t crack open or pull off required ¼†+/- until engine develops vacuum. One engine starts, choke opening is governed by heat from manifold, or electric bi-metal thermal spring. [quote]It was pretty warm outside today, however. Would the ambient air temperature be the reason the choke wasn't closed when the car was off[/quote] Choke will stay open after engine cools as long as gas peddle is not depressed or throttle opened. Once throttle is cracked open before a cold start, that choke plate will than snap shut, and won’t crack open or pull off required ¼†+/- until engine develops vacuum. One engine starts, choke opening is governed by heat from manifold, or electric bi-metal thermal spring. This is why when starting a cold carbureted engine one must first depress accelerator peddle to set choke to a closed position, release accelerator and depress it a second time about ¼ of its travel just before cranking engine over. By starting a cold engine each time in this way, the choke and high idle cam will always be free and respond each time as designed, and the proper shot of fuel from accelerator pump will be administered. If you don’t start the engine as described the choke will become lazy and or sticky, not enough raw gas will be dispensed from accelerator pump, and after a period of time choke will fail to fully close making cold starting much harder. |
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| Author: | SlantSixDan [ Thu May 19, 2011 7:16 pm ] |
| Post subject: | |
Quote: The distributor is hooked up to the OSAC valve
No, run the hose directly from the distributor to the carburetor, skipping the OSAC valve.Quote: and I replaced the vacuum line a few weeks.
And the vacuum advance pod itself is…known good? Unknown?Quote: choke today, and it was open when the car was off and not warmed up
Before or after you opened the throttle? Even once the engine has cooled down, the choke will not close until you open the throttle.
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| Author: | skurdnin [ Fri May 20, 2011 3:42 pm ] |
| Post subject: | |
Whoops, meant to say the distributor is hooked up directly to OSAC port on carb, bypassing the valve on the air cleaner. I believe the vacuum pod is in working order, and after doing some more research I'm going to pull the carb off and take a look at the accelerator pump. Do you have any particular retailer you prefer for a pump? |
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| Author: | SlantSixDan [ Fri May 20, 2011 3:43 pm ] |
| Post subject: | |
If you're getting a solid "shot" of fuel when you operate the throttle lever, it's difficult to imagine the accel pump being the problem. I like the carburetor kits from www.daytonaparts.com . |
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| Author: | LUCKY13 [ Sat May 21, 2011 3:26 pm ] |
| Post subject: | |
Sounds like it needs jetted up a bit. A pump shot can only cover up so much of a lean spot and if you make it squirt extra then it gets a rich spot that gets lazy until it cleans out the extra fuel. Jet it up 2 to 4 sizes and I bet your problem goes away. Jess |
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| Author: | skurdnin [ Sun May 22, 2011 7:37 am ] |
| Post subject: | |
When I looked to see the shot of fuel before I was just moving the throttle on the carb itself, and it appeared to be working fine. Today I had someone press the pedal while I watched the carb, and fuel comes out right at the beginning of the throttle, and when the pedal is to the floor, but not in between, unless you feather the throttle the entire way down. I'm going to take the carb apart and see if I can resolve that. |
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| Author: | skurdnin [ Sun May 22, 2011 10:46 am ] |
| Post subject: | |
Well I got the pump out of the carb, and I definitely didn't replace last time I rebuilt the carb. The springs feel like they have good action, but when I press the throttle linkage down to compress the pump, the pump only shoots back up into place about half the time. Would that be the issue right there? |
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| Author: | wjajr [ Sun May 22, 2011 2:47 pm ] |
| Post subject: | |
I would say you located the problem, a worn out accelerator pump. |
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| Author: | skurdnin [ Mon May 23, 2011 2:33 pm ] |
| Post subject: | |
After closer inspection, I realized that I am missing the ball check valve and weight. That's definitely an issue. I'll be tracking down a ball and weight tomorrow. |
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