Sputtering to a Stall

[Esteban]

Congratulations on solving the fuel/carb problems.

... I wonder if it might have something to do with the amount of shims between the master and the firewall? I seem to remember having to add or remove those shims for a similar problem...

Marshall, as a temporary or troubleshooting measure, backup the two nuts that secure the master cylinder, and see if that reliefs the pressure. As RiverPatrol mentioned, some shims might be missing. Did you install the piston from the Corvette master cylinder rebuild kit? If so, there could be the reason.

As Ron mentioned in your other thread: The piston in the corvette kit is an exact match other than the hole where the rod goes is not drilled as deep as the Patrol piston. I would only use the Vette piston if the Patrol piston was damaged. All you would need to do is shorten the original rod, this would be a last case scenario. You still need to free up that rod in the original piston though

[Marshall]

Thanks!! I did use the piston from the Corvette build. I've taken it apart and put in the original piston and swapped on the new rubbers. I also found a metal shim in my box of stuff from the previous owner, it's a half of the footprint of the mc where it bolts to firewall. I'll use this as well on the top of the mc to make the rod and the brake pedal more of a 90 degree junction.

I think doing both these suggestions it'll be fixed! Then I can actually use my brake adjusters and not just have them fully backed out.

[Marshall]

Update:

Brakes: Put in new master cylinder rebuild.... BUT, the cylinder plunger seal had a little knick out of it, and right on the edge. I put it in HOPING the little knick out of the rubber seal wasn't large enough to leak and relate pressure. But, unfortunately it did leak, and didn't hold pressure. SO, I was back to needing another full rebuild just to get a new rubber gasket. No one wanted to break up their rebuild kits and just sell me the seal. (I tried calling all Corvette shops I could find in the US). I was frustrated and didn't want to pay the full price for another rebuild kit, and didn't want to wait for shipping. So, I did a Google similar image search on the rebuild kit. I found many other kits that 'looked' the same, but something was off. After many dead ends, I finally found out that from 1951-1966, (I think), that about 20 GM cars had the same master cylinder dimensions. AWESOME! So I called a few shops to check on the list of cars I found it to be compatible with. I ran down the list and landed on a 1963 Chevy 1/2 Ton Pickup. This was all the same dimensions, and the rebuild kit seemed the same. So I picked it up from my local O'Reilly's for only $12. Installed it and it works! But, like the Corvette rebuild the cylinder needed to drilled out several mm for the pushrod to sit accurately.

Here's all of the other cars I found that I think all have the same master cylinder, (or at least the same rebuild kit):

1955-57 Chevy Bel Air, 150, 210, Nomad
1962-66 Bonneville, Catalina
1951-63 Chevy 1/2 Ton (what I used, and can vouch that it fits and works) BRAKEWEAR Part# 22961 NAPA Part# UP253
1965-66 Chevelle

So, now my brakes are set. (for now)

Back to fuel issues. After putting everything back in with new inline filter and a clean carb - it would run for about 30 seconds, then stop. I took apart the carb again, ran some diagnostic bench tests. The float needle was getting stuck, therefore preventing fuel through. So I saw the brass fitting was a bit snug, the needle brass casing is square, and fitting into circular space. I lightly sanded down the corners of the square - seemed better, and was't sticking. Reinstalled, same result. Would run for 20/30seconds, then stall. I took the carb back off. The rubber tip of the float needle was still sticking. So, a buddy of mine swapped in an aluminum tipped needle for me. Reinstalled - it would run, and then stall. This time ran for longer. I checked the carb and it was smoking white smoke. Looked up possible causes: now it seems the float needle isn't sealing properly, therefore letting in too much fuel and flooding. First not enough fuel, now too much.

So... My plan is to get another float needle, (one that has a little hook on the top), and drill a hole in the float arm and attached that sucker to it. The needle tip will be rubber, like original one, but with it connected to float arm, it'll prevent it from getting stuck closed. Is this the best solution? Any ideas out there? Thanks!

[RiverPatrol]

Rob is the carb meister, he should be able to tell you if you're headed in the right direction.

Great post about the master cylinder compatibility.

[moore_rb]

Marshall, it sounds to me like your float level and float drop may be set incorrectly. If the float level is set too high, then the volume of fuel allowed into the bowl can force the floats to jam the rubber tip of the needle up into the seat. It can also cause the flooding you are seeing.

I would have to look up the float level and drop specs for your Rochester carb- I have them around here somewhere, but that is my guess- to become jammed up into the seat, that needle is fighting both the force of the fuel pressure, as well as the force of gravity... It seems really odd to me that it could become stuck that easily...

[Marshall]

Thanks Rob. I installed the new needle with a pull clip to link to float. Now not sticking, but definitely way to much fuel. I've adjusted it down several times, and I think I'm getting close. I pulled the Rochester Manual and opening it back up to try to get as close as I can to their specs.

Screen Shot 2015-11-21 at 8.36.14 AM.png

[moore_rb]

PERFECT- That is the exact procedure I was referring too.

For a Rochester B Carb, Here are the specs I use for each measurement (these specs vary by source, but I've found these numbers to work the best for me) :

Total Float Drop (minimum float level) - measured from the bottom edge of the carburetor top's gasket, to the lowest point on the float, with the float hanging down fully: 1.75" (+/- 1/16") - You adjust this measurement by bending the little tang on the back of the float arm (the one that rests against the fuel inlet fitting)

float drop.jpg

Max Float level- measured with the carburetor top INVERTED, and taken from the edge of the gasket, to the bottom edge of the float (which will be on top since the carb lid is inverted): 1.25" (+/- 1/32") - You adjust this measurement by actually bending the armature attached to the float

float level.jpg

[moore_rb]

Oh! - One more thing I forgot- The shape of the floats vary on Rochester B carb's - The early ones have round floats, and the later ones have rectangle floats (similar to the pictures I posted above)

Going by memory- I think yours is a later carb, and the numbers above should be correct... But if yours has the round floats, then let me know- I have a set of alternate measurements that are specific for the round ones (that are buried in some other notebook, somewhere else, but I could find them if I had too)...

[Marshall]

Thanks Rob. I do have an earlier one, the floats are round.

Also, what main jet do you use? I think mine is a 56, I'll double check when I open it back up today.

I also found this, mine is 7009254.

CarbSpecs.jpg

[moore_rb]

Cool- Another excellent resource- I'll have to keep a copy of this one


The 56 Jet should be fine fine for you in LA -