Slant Six Forum :: New carb, car sluggish, tops out at 20mph, black smoke.

Step up piston moves freely and returns smoothly under pressure from the spring. Full travel is around 1/2" from stop to stop.
Small circular gasket (rectangular cross section rather than circular o-ring) is present and seated at the bottom of the cylinder. It's a smooth sliding fit in the cylinder, and the spring goes down thru' the middle of it

I have to admit I'm not sure what it's purpose is or what it's sealing. Is it to stop fuel leaking past the piston and into the manifold when it's fully depressed/maximum vacuum?

Step up rod is a loose fit in the jet (I reckon the jet orifice is around 1.5 times the diameter of the rod)

The jet is screwed into the floor of the fuel bowl with a small gasket and seats without problem.

Author:	60 Plymouth [ Sat Sep 10, 2011 6:07 am ]
Post subject:	New carb, car sluggish, tops out at 20mph, black smoke.
Hi all, Just fitted a NOS 1963 Carter BBS (I rebuilt it a few months ago incase the seals were gone) from a reliable source and I'm having trouble getting the car to run. The engine is a 1960 and is bone stock. A904 Transmission. With the car hot (and choke wide open) she idles about 740 out of gear, a little high perhaps (not really much travel left on the screws) . At this idle, I get 15" vacuum, perhaps a little low? The distributor is an OCPNW electronic unit, I think 1967ish? Original curve. At idle I have about 7 degrees advance. The EI conversion was done a month or so ago. Increasing the base advance the car begins to run really rough. The car drives ok up to about 8mph. Whenever I try and accelerate, I get tons of black smoke and the car can't get past 20mph, acceleration is really sluggish up till then. The current Dizzy worked ok with the old, battered, knackered rebuilt '60 BBS. Any ideas? It appears to be very rich but I guess it could also be the curve in the dizzy (vacuum advance?). Anybody got a pretty good method for sorting all this out? I don't understand how a good carb can be so damn rich off idle. Thanks guys, I appreciate it.

Author:	SlantSixDan [ Sat Sep 10, 2011 6:52 am ]
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Something's wrong with the carb -- I would pay careful attention to the step-up piston/spring/gasket(!)/rod assembly to make sure it was assembled properly. My guess: step-up rod not properly inserted in floor jet and/or missing step-up piston gasket. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

Author:	60 Plymouth [ Sat Sep 10, 2011 8:52 am ]
Post subject:
Well, the problem seemed to just disappear. I went to get some fuel (car parked on a slight slope, need fuel to prevent it dying) and it just seemed to work. As if nothing had happened. I pulled the carb to find out if there was any dirt or somthing lodged in it but it all seemed fine, fuel bowl almost clinical. I guess somthing may have been fouling somthing and that's now been drawn through (and hopfully spat out of) the engine Oh well, all seems ok. I'm away for a week or so but when I get back I'll do some more vigorous testing and tuning, see if the problem rears its head again.

Author:	hantayo13 [ Sat Sep 10, 2011 12:24 pm ]
Post subject:
float/needle stuck open ?????

Author:	60 Plymouth [ Fri Oct 14, 2011 1:28 pm ]
Post subject:
Problem didn't disappear - Seems I can't exceed 35mph and acceleration is negligible. I've swapped my old carb back on and the car runs as it did. I'll pull the new carb apart again tomorrow and see what I can find, it looks in good order though so no idea what the problem is. The only other thing that gets swapped when I swap carbs is the PCV valve (old carb uses the road draught tube) so could that cause any issues?

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New carb, car sluggish, tops out at 20mph, black smoke. https://slantsix.org/forum/viewtopic.php?t=46272	Page 1 of 2

Author:	SlantSixDan [ Fri Oct 14, 2011 1:55 pm ]
Post subject:
Yes, it could -- how are you making provision for vacuum to the base of the new carburettor where it transmits to the PCV port? The '60 inlet manifold hasn't got this provision, do you have a later inlet manifold?

Author:	60 Plymouth [ Fri Oct 14, 2011 2:08 pm ]
Post subject:
Ah so the carb doesn't have internal porting to the PCV take off? The PCV is ported to a small (5/32 ish?) barb that's on the base of the carb. This appears to be the PCV takeoff when compared with BBS manuals. Not sure what manifold I have, images here: Excuse the messy engine bay, fuel line mod and more appropriate air cleaner now fitted (ah yes, I also change the air cleaner with the new carb - the new carb hasa proper slant 6 air cleaner and filter, the only difference is the tube has broken off. No provisions for EGR or anything else in the new air cleaner, only two holes in it, one for air and one for carb). I have a thick gasket that has a few 'nicks' taken out of the central hole that line up with ports on the base of the carb, I'll have to check tomorrow to see where they line up. These would allow the ports to see manifold vacuum.

Author:	SlantSixDan [ Fri Oct 14, 2011 2:23 pm ]
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Very important that the carb base gasket is installed with "TOP FRONT" at the top and front, otherwise the vacuum ports won't receive vacuum and the step-up rod will always be in the "up" (fully rich) position. Looks like you have a later manifold so no worries there -- should be easy to match up the carb gasket; the manifold has a 1/4" hole for PCV vacuum, so does the carb gasket. Line them up.

Author:	60 Plymouth [ Sat Oct 15, 2011 6:02 am ]
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Gasket was lined up correctly with all the ports in the carb aligned with ports in the gasket and manifold. Running out of ideas a bit with this - I've rebuilt the thing once and had it apart twice and I can't find a problem with it. Any checks I can do to the PCV to make sure it's functioning correctly? In the meantime I'm going to take it apart again, there has to be somthing not quite right.

Author:	60 Plymouth [ Sat Oct 15, 2011 7:19 am ]
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All check balls present and correct, all gaskets in the right place, nothing jammed, float level correct, the needle is seated in the jet (The needle is brass and appears to be straight, with no taper on the tip). Honestly have no idea what the problem is. Any suggestions? I'm wondering if the enrichment needle is too short or incorrect, which would mean that was faulty from the factory. Maybe my PCV is incorrect/faulty? p/n V195, made in the USA, manufacturer unknown/forgotten.

Author:	SlantSixDan [ Sat Oct 15, 2011 3:25 pm ]
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Quote: Any checks I can do to the PCV to make sure it's functioning correctly? Put thumb over end of PCV valve with engine idling; thumb should be firmly sucked up against end of valve. Quote: In the meantime I'm going to take it apart again, there has to be somthing not quite right. Did you already check if the step-up piston moves freely when you press it down, then springs back up immediately? And that there's a rubber O-ring at the bottom of its cylinder? And that the step-up rod is properly inserted into the floor jet? And that the floor jet has its gasket?

Author:	60 Plymouth [ Sat Oct 15, 2011 4:09 pm ]
Post subject:
Hi Dan, Been through it twice now and I'm not sure what to look for anymore: Step up piston moves freely and returns smoothly under pressure from the spring. Full travel is around 1/2" from stop to stop. Not sure about its sealing capability, I should try and do a test (press piston, thumb over port, release piston. I guess it should not return/return very slowly? Any other ports that communicate with it that would have to be plugged whilst doing the test?). Small circular gasket (rectangular cross section rather than circular o-ring) is present and seated at the bottom of the cylinder. It's a smooth sliding fit in the cylinder, and the spring goes down thru' the middle of it - I have to admit I'm not sure what it's purpose is or what it's sealing. Is it to stop fuel leaking past the piston and into the manifold when it's fully depressed/maximum vacuum? Step up rod is a loose fit in the jet (I reckon the jet orifice is around 1.5 times the diameter of the rod) and moves in and out freely with the piston. It travels the same 1/2" as the piston without binding anywhere. The jet is screwed into the floor of the fuel bowl with a small gasket and seats without problem. I'll check PCV tomorrow, see how that goes. Once again, thanks for your help, I appreciate it. I just must be missing somthing somewhere, no other explanation. All the best, 60 Ply

Author:	SlantSixDan [ Sat Oct 15, 2011 4:13 pm ]
Post subject:
Quote: Step up piston moves freely and returns smoothly under pressure from the spring. Full travel is around 1/2" from stop to stop. Small circular gasket (rectangular cross section rather than circular o-ring) is present and seated at the bottom of the cylinder. It's a smooth sliding fit in the cylinder, and the spring goes down thru' the middle of it All that checks out. No further seal test is necessary. Quote: I have to admit I'm not sure what it's purpose is or what it's sealing. Is it to stop fuel leaking past the piston and into the manifold when it's fully depressed/maximum vacuum? It's to make sure the piston remains down when it's meant to be down. Quote: Step up rod is a loose fit in the jet (I reckon the jet orifice is around 1.5 times the diameter of the rod) H'mm. If that's true, then something's amiss. The step-up rod's shank (the portion above the necked-down, smaller-diameter end) should not be a tight, frictional fit in the hole in the top of the floor jet, but neither should it be a loose fit. It should be a "just fit" with no discernible friction and no side slop. Take a look at your other carb for reference. Quote: The jet is screwed into the floor of the fuel bowl with a small gasket and seats without problem. This also checks out. Hey, something just occurred to me: are you quite sure the choke is opening fully even with the air cleaner fully installed, and that you've got the choke pushrod installed in the correct one of what might well be two holes in the choke lever?

Author:	60 Plymouth [ Sun Oct 16, 2011 5:10 am ]
Post subject:
Hi Dan, I allow the engine to heat up before I try doing anything to the carb, the choke opening fully was one of the first things I checked. I wired it open to see if there was any difference and there wasn't. FYI there's only a single hole for the choke push rod. When you refer to the step up rod and its stepped down shank - is this a noticeable step down (like a shoulder), or more like a gradual taper that you could only see with a mike? My metering rod appears to be a piece of brass rod, no discernible step on it. It's a straight shank its whole length as far as I can eyeball. I'll take apart the good carb and have a look. If the two appear to be different, is swapping metering rods and jets a viable method of getting the 'new' carb onto the engine? If these appear to be at fault, is there a source for known reputeable jets and step up rods?

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Author:	60 Plymouth [ Fri Oct 21, 2011 9:03 am ]
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SORTED! At leastI hope so . . . Air cleaner was fine resting on the carb, but when screwed down, fouled the choke lever. This was never a problem before because my original carb had a non standard air cleaner, the new one has a proper slant cleaner. Even though I wired it open, the fouling was enough to squeeze the push rod in such a way that it closed the choke up. I've not got the problem fixed yet - I'm converting to the electronic choke kit, so now have some new problems! In other news, a load of frothing in the radiator got me worried about head gasket failure. A compression test resolved the issue though: 141 150 150 148 148 148 There'd be a big difference in 1/2 cylinders for head gasket failure so I guess all'swell. Not bad!