Slant Six Forum :: Help!

It will always start and idle smoothly
I can get through first most times but just into 2nd gear it starts choking. When i take my foot off the gas it smooths right out. once the "load" has been reduced I can give it gentle gas and it will go a bit more before choking out again.

The fuel pump has been replaced, i tried putting a filter in front of the pump and it only seemed to fill up about halfway while running.

I don't understand how putting a load on the engine effects the fuel delivery process.

Isn't the amount of fuel flowing to turn the engine at X rpm virtually the same no matter what the gears are doing?

so, when I'm testing it, I should watch my "Economy" gauge and see if the "choking out" occurs at the same vacuum level....

I've obviously been out of the loop in regards to quality parts vs cruddy parts. I did a lookup and the local Kragen Auto can get me the B&B carb as a rebuilt unit for $80 + core.

any recomendations on a good source?

I don't understand how putting a load on the engine effects the fuel delivery process. I don't get the functional difference between not in gear at 3000 RPM and in gear at 3000 RPM? Isn't the amount of fuel flowing to turn the engine at X virtually the same no matter what the gears are doing?
Steve

H'mm. Float level is certainly critical, but I don't suspect that's the problem here, for a few reasons. The car was running correctlY, and then it wasn't, with the float level not having changed. That suggests to me a clogging problem.

Also, the OP describes a choke-out condition, which doesn't sound to me like insufficient fuel level in the bowl.

My experience with too-low fuel level in the bowl of a BBS is that the engine acts as if it has a rev limiter on it at whatever speed and load sucks the bowl dry.

Ok, 1st - Thanks for the clarification, makes total sense now....

I start the engine with one press and release of the gas pedal, smooths out immediately, quiet little purr even.

I pull it down into 1st (3-on-the-tree), and ease the clutch out with a little gas.

engages smoothly and with some more gas she begins to accelerate.

80% of the time it makes it through 1st fine, lift it up into 2nd and re apply the gas, and between 5 and 15 seconds later it cuts out. If i continue to apply the gas it lurches like a horizontal pogostick, if i release the gas pedal it drops right to an idle, at which point i can then start to re-apply gas for the 5-15 seconds.

the 20% of the time it does the same thing in 1st.

I can "feather" the gas and limp it a bit but even then i occationally lurches.

see the original post for what we've tried so far....

oh so frustrating....

Author:	Josh [ Tue Oct 18, 2005 7:33 am ]
Post subject:
There are a lot of really great suggestions here. As for my experience: I had the EXACT same problem with my Dart about two months ago. It turned out to be that I had rebuilt the carb just one too many times, and the thing was shot. Replaced it with a different freshly rebuilt carb and it runs like a champ. Of course, it took about two weeks of trying everything else I could think of before I admitted to myself that it could be my shiny newly refurbished carb... -josh

Author:	440_Magnum [ Tue Oct 18, 2005 8:56 am ]
Post subject:	Re: Help!
Quote: It will always start and idle smoothly I can get through first most times but just into 2nd gear it starts choking. When i take my foot off the gas it smooths right out. once the "load" has been reduced I can give it gentle gas and it will go a bit more before choking out again. This symptom in particluar just screams "fuel delivery problem." Actually, it screams "fuel starvation getting into the carb's float bowl." At low power, the float bowl fills up and everything is fine. Then you put a load on it and the carburetor itself works fine and the car will "go a bit more" but when the fuel in the float bowl runs out, it flames out and stutters. Since the carb itself was rebuilt, I'd check the float system and needle valves. Make sure that not only is the float level correct, but that you're getting enough float DROP- in other words, make sure that the floats hang down far enough to let the needle valve open fully. If the float (sorry- just realized I've been speaking in the plural- I'm a V8 4-barrel guy by day ) doesn't hang free enough, the needle valve will restrict flow into the carb. Of course it could also be a fuel flow restriction EXTERNAL to the carb- bad fuel pump, clogged fuel pickup sock in the fuel tank, kinked/crushed fuel line, or clogged fuel filter. Good luck!

Author:	SlantSixDan [ Tue Oct 18, 2005 9:07 am ]
Post subject:
H'mm. Float level is certainly critical, but I don't suspect that's the problem here, for a few reasons. The car was running correctlY, and then it wasn't, with the float level not having changed. That suggests to me a clogging problem. Also, the OP describes a choke-out condition, which doesn't sound to me like insufficient fuel level in the bowl. My experience with too-low fuel level in the bowl of a BBS is that the engine acts as if it has a rev limiter on it at whatever speed and load sucks the bowl dry. You get a rhythmic 'VROOMuhhhhVROOOMuhhhhVROOOMuhhhVROOOMuhhhh" effect as the fuel bowl fills and empties, fills and empties, fills and empties, and the car won't go any faster. That doesn't sound like what's going on here.

Author:	66bcuda [ Tue Oct 18, 2005 9:44 am ]
Post subject:	back to school...
This is great! lots of good ideas and avenues to check on... I really appreciate the help! The fuel pump has been replaced, i tried putting a filter in front of the pump and it only seemed to fill up about halfway while running. The hose between that filter and the pump seemed to be a bit "kinked" because of the small space between the steel line and the pump. It was dark and I was looking to eliminate variables so i removed it. The filter in front of the carburator (after the pump) is definately full. I don't understand how putting a load on the engine effects the fuel delivery process. I don't get the functional difference between not in gear at 3000 RPM and in gear at 3000 RPM? Isn't the amount of fuel flowing to turn the engine at X virtually the same no matter what the gears are doing? Sorry if i seem dense, but i think it will help me troubleshoot if i understand conceptually what's happening. If it's too much to type here, then I'll just file the question till the next /6 get together and ask face to face. Steve

Author:	SlantSixDan [ Tue Oct 18, 2005 9:52 am ]
Post subject:	Re: back to school...
Quote: The fuel pump has been replaced, i tried putting a filter in front of the pump and it only seemed to fill up about halfway while running. Putting a filter before the pump isn't adviseable. Quote: I don't understand how putting a load on the engine effects the fuel delivery process. Increased load = decreased manifold vacuum, which causes the carburetor's power valve to open and admit more fuel. Quote: Isn't the amount of fuel flowing to turn the engine at X rpm virtually the same no matter what the gears are doing? No.

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Author:	66bcuda [ Tue Oct 18, 2005 10:53 am ]
Post subject:
so, when I'm testing it, I should watch my "Economy" gauge and see if the "choking out" occurs at the same vacuum level.... I've obviously been out of the loop in regards to quality parts vs cruddy parts. I did a lookup and the local Kragen Auto can get me the B&B carb as a rebuilt unit for $80 + core. Any known issues with these? (other than Kragens general stupidity....) if so, any recomendations on a good source? Thanks again for all of the time and thought everybody has put into this for us. Steve and Heather

Author:	SlantSixDan [ Tue Oct 18, 2005 11:58 am ]
Post subject:
Quote: so, when I'm testing it, I should watch my "Economy" gauge and see if the "choking out" occurs at the same vacuum level.... Good plan. That "economy" (vacuum) gauge can really help diagnose a lot of driveability faults. Quote: I've obviously been out of the loop in regards to quality parts vs cruddy parts. I did a lookup and the local Kragen Auto can get me the B&B carb as a rebuilt unit for $80 + core. No, they don't supply rebuilts, they supply "remanufactured" carburetors of very low quality. Junk. Don't; you'll be sorry you did. In the event you do wind up getting a replacement carburetor of whatever type, keep your original unit for later build-up instead of turning it in for a core (to be abused and destroyed by the "remanufacturers"). This goes for all parts stores, not just Kragen. Quote: any recomendations on a good source? Depends what you're after. I have a brand-new (not "remanufactured") carburetor to fit your application, send me a private message if you want more info.

Author:	440_Magnum [ Tue Oct 18, 2005 3:36 pm ]
Post subject:	Re: back to school...
Quote: I don't understand how putting a load on the engine effects the fuel delivery process. I don't get the functional difference between not in gear at 3000 RPM and in gear at 3000 RPM? Isn't the amount of fuel flowing to turn the engine at X virtually the same no matter what the gears are doing? Steve Throttle position is different. In neutral, you can maintain 3000 RPM with the throttle very nearly closed, very minimal air/fuel flow through the carb, and high manifold vacuum. In gear and moving the car, the throttle has to be cracked much wider open to sustain 3000 rpm, so the fuel flow is consequently higher and manifold vacuum is consequently lower. In this condition, fuel may be being drawn out of the carb bowl faster than it can be refilled, which may be why you get a good "surge" of power at first, and then it falls on its face when the bowl empties. It took me a long time to get my brain around the difference between engine speed and actual air/fuel flow rates, which depend on both engine RPM AND manifold pressure/vacuum. You're not dense in fact just the opposite at high RPM/ light load! (OK, that was a really, really bad pun...) One more question- Dan pointed out that you described the engine as "choking." Was that just descriptive, or does it REALLY go rich (with the consequent cloud of black smoke out the pipe) because if that's the case, my whole analysis goes "phut" and you have a different problem than fuel starvation.

Author:	440_Magnum [ Tue Oct 18, 2005 3:42 pm ]
Post subject:
Quote: H'mm. Float level is certainly critical, but I don't suspect that's the problem here, for a few reasons. The car was running correctlY, and then it wasn't, with the float level not having changed. That suggests to me a clogging problem. Hmm indeed. But, floats do sink. Grit does get into needle valves to make them bind. Grit also gets into carb passages in weird ways that might only block them under high fuel flow. Quote: Also, the OP describes a choke-out condition, which doesn't sound to me like insufficient fuel level in the bowl. I asked a follow-up. I assumed that "choke" was descriptive of the engine falling flat, not a literal equivalent of applying the choke and getting a rich mixture. Quote: My experience with too-low fuel level in the bowl of a BBS is that the engine acts as if it has a rev limiter on it at whatever speed and load sucks the bowl dry. I guess one or both of us is reading ourselves into his words, because it sounds to me like you're EXACTLY describing his situation with the exception of a surge of power when you first get on it after backing off- which by the way is part of my experience of a restricted fuel delivery to the carb.

Author:	66bcuda [ Tue Oct 18, 2005 3:48 pm ]
Post subject:	imagine this...
Ok, 1st - Thanks for the clarification, makes total sense now.... I start the engine with one press and release of the gas pedal, smooths out immediately, quiet little purr even. I pull it down into 1st (3-on-the-tree), and ease the clutch out with a little gas. engages smoothly and with some more gas she begins to accelerate. 80% of the time it makes it through 1st fine, lift it up into 2nd and re apply the gas, and between 5 and 15 seconds later it cuts out. If i continue to apply the gas it lurches like a horizontal pogostick, if i release the gas pedal it drops right to an idle, at which point i can then start to re-apply gas for the 5-15 seconds. the 20% of the time it does the same thing in 1st. I can "feather" the gas and limp it a bit but even then i occationally lurches. see the original post for what we've tried so far.... oh so frustrating....

Author:	argentina-slantsixer [ Tue Oct 18, 2005 6:55 pm ]
Post subject:
did you use a vitton/nylon tip or other synt material needle/seat assy? sometimes (and with modern fuel formulation being more "cruel" to plastics and derivatives) it will make your needle crazy, your float is dropped but the needle allows little or no gas into the carb. I also think as 440 magnum that your fuel bowl is starvating. Maybe your main fuel jet is way too small for the metering circuits.

Author:	Charrlie_S [ Wed Oct 19, 2005 6:47 am ]
Post subject:
I would try another new fuel filter, and see if it makes a differance. Could also be the "sock" in the tank plugged up. Sure sounds like fuel starvation to me.

Author:	Rust collector [ Wed Oct 19, 2005 6:56 am ]
Post subject:
Me too

Author:	gonescootin [ Wed Oct 19, 2005 7:53 am ]
Post subject:
what about the sock on the pick up tube in the gas tank?

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Author:	440_Magnum [ Wed Oct 19, 2005 10:10 am ]
Post subject:	Re: imagine this...
OK, that still sounds like fuel starvation to me. Since some work was done on the carb recently, I'd give that a look just in case it is something mechanically binding in the float system. Then I'd check all the other fuel-related things folks have mentioned. Quote: Ok, 1st - Thanks for the clarification, makes total sense now.... I start the engine with one press and release of the gas pedal, smooths out immediately, quiet little purr even. I pull it down into 1st (3-on-the-tree), and ease the clutch out with a little gas. engages smoothly and with some more gas she begins to accelerate. 80% of the time it makes it through 1st fine, lift it up into 2nd and re apply the gas, and between 5 and 15 seconds later it cuts out. If i continue to apply the gas it lurches like a horizontal pogostick, if i release the gas pedal it drops right to an idle, at which point i can then start to re-apply gas for the 5-15 seconds. the 20% of the time it does the same thing in 1st. I can "feather" the gas and limp it a bit but even then i occationally lurches. see the original post for what we've tried so far.... oh so frustrating....