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timf

stalling in turns

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My '57 Pontiac Starchief with a 347 cu in engine unexpectedly stalls while rolling through either a right or left turn, and occassionaly, while coming to a stop. If I start the turn from a stop, it does OK. I've gone through the entire fuel system chasing this problem, and I'm looking for advice in its repair. I rebuilt the Rochester 4GC to factory specs and installed a new fuel pump. The new fuel pump puts out @4psi and its volume exceeds one quart in one minute. The fuel line from the tank to the pump is undamaged and clear. It supports a minimum of 10 inches vacuum. I removed, cleaned, and inspected the fuel tank and its sending/pick-up unit. The power valve and its corresponding vacuum actuating rod seems seems to funtion properly. Idle speed, choke, and mixture adjustments have no effect on this problem. However, the frequency and severity seemed to be reduced after I raised the primary float setting from 1 3/8 inches to 1 1/4 inches--the float drop was kept at 1 13/16 inch. I upgraded the ignition with an MSD 6A amplifier, and inspected the distributor's vacuum and centrifugal advance. The engine starts-up and comes off the choke step good. It idles smooth and pulls a minimum 15 inches vacuum. On the road, it has adequate power with no missing, and has normal operating temperature. The problem appears after driving awhile and becomes more frequent the longer you drive it. Please let me know if anyone has an idea of what demon I need to slay next to solve this problem. Thanks

TimF

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...It sounds just like those last batches of Dodge Diplomat police cars (1988). That last batch that Chrysler made came with the two barrel carb instead of the four barrel and everytime you turned around quick to chase someone, they'd stall.

....Do you remember those Wayne?? grin.gifgrin.gif

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The factory spec for the float setting is 1 3/8 inch. The float drop is 1 13/16 inch. I suspected the float level as well, and raised it to 1 1/4 inch. This helped but did not solve the problem. I'm afraid I'm simply masking the real problem. Its those twin floats on those long arms that really make the early Rochesters a challenge.

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An old-time carburetor guy told me a few years ago that a 4GC would have to have the fuel level raised above factory specs anytime an aftermarket carb kit with rubber-tipped needle was used- sometimes up to 3/8" higher depending on engine. Most kits available now also do not have different primary and secondary needle/seats as the OEM Rochester kits do.

I have one on a 64 Olds that drove me up the tree with the same symptoms, and I have yet to tweak all of the stalling out of it. I found that using a Rochester kit gave me better results than even a HyGrade or Echlin could deliver, and I think those are generally the best aftermarket.

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You all seem to be chasing this as a fuel problem, but here is a "fuel" problem I had a few years back. Pretty much the same symptoms, corners and rough roads it would cut out and stop. Tried everything I could think of. Then one day while I was working on the engine while it was running I stumbled on the problem. I had an after market tachometer connect to the distributor and wound the wire around some fender supports to get it up to the fire wall. After years of slight rubbing from body flex on corners the insulation had rubbed through. Now when the body flexed it shorted out the ignition but it felt like fuel loss.

Now you probably don't have a tach but you may have a strange route for the coil/distributor wire.

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I had exactly the same problem with a Ford 6 once. It turned out that the carburetor's attachment bolts had loosened, and the weight/momentum of the air cleaner was causing the carb to lean to one side or the other. The instant vacuum leak that caused my car to stall would likely be slightly mitigated by raising the float level, just as you describe. Check your attachment bolts/studs/etc. as well as any bolts/screws/studs that hold the body of the carb together. If you find some loose ones it'll probably be your problem.

If so, you'll likely need to replace the gasket in that area rather than just tightening the hardware to fix the problem. After rocking back and forth like that a few times the gasket is probably cut or stretched.

Good luck! smile.gif

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Thanks, I'll double check those items. I've had the carb off and disassembled numerous times and so far managed to locate a new base gasket for the reinstallation. The gist of what you saying is that there may be a vacuum leak I have not considered. I wonder if the top lid of the carb itself could be warped enough, or the overused top-lid gasket could be giving a false signal to the power circuit. That's food for thought I will look into. Thanks for giving me a new angle of attack.

TimF

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Thanks for the info. I'll try to locate a rochester rebuild kit. I only raised the primary side 1/8 inch and left the secondary side at stock settings. Do you think I should have raised both primary and secondary floats? This is good food-for-thought. Thanks

TimF

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tighten the screws that hold the top of the carb to the carb bowl body. If they are not loose then it might be the carb top to bowl body gasket is bad allowing gas to slosh over from the bowl into the carb and down the manifold.

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are you sure you don't have anything floating in the tank? That gasket sealer blows up to the size of a hot dog when floating in gasoline for a few months. If your problem is intermintent.

Also, I have a '50 buick and it turn out to be a lose needle valve seat. The brass fitting was not tight, and the needle value would bind.

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<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> I can put my lips together and blow at 4 psi! Shouldn't it be more like 10-12 psi for a 50's era fuel system? </div></div>

According to my 1961 <span style="font-style: italic">Motor Auto Repair Manual</span>, the fuel pump pressure spec. for a 1957 Pontiac is 4-5 psi. In fact the upper limit of the highest spec. they list is 7 psi. The 4 psi reading on your fuel pump is within factory spec.

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I owned a 62 buick with a 4GC.

It had a dashpot on the throttle which when letting off the gas would allow the throttle to slowly return to idle. I know that when this was broken the car would stall when letting off the gas and braking.

During high speed turns, the car would stall and I think due to fuel sloshing around in the fuel bowl uncovering the jets.

These carbs also can have float adjustment troubles. Sometimes if they flood and you cant understand why, the problem is the back of the float hitting the inside wall of the float chamber when it rises. Take off the float and hold the swivel pin area of the float all the way against the back wall of the float chamber, the rear of each side float should just barely touch the back inside wall of the float chamber. Also check float alignment with the gasket off and air horn upside down with no needle valves. Float should be well centered and exhibit only slight side to side rocking. Each float ought to touch the air horn at the same time so the flotation pressure of both floats will be equal

The best level is 1 3/8 on the primary and 1 5/8 on the secondary. The carb also has an internal fuel connection between the primary and secondary sides to equalize the fuel levels in each bowl.

I currently have 2 4GC's in a boat and when the boat rocks side to side the engines do slightly cut out. I suppose again due to fuel sloshing around in the bowls. I personally dont think these are very well designed carbs. 4MV is better, if it would fit which is unlikely.

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After much head scratching, I once traced stalling on corners to a bad column-mounted ignition switch

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Can you specify a little bit:

"unexpectedly stalls while rolling through either a right or left turn"

Is it in all turns?

Is it hapening only in a turn?

What speed ?

What kind of curve - wide?

Reason why im asking is that there may be a nice idea from your answears.

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Hello All! I've had my 62 Buick Skylark Alum V8, Rochester 4GC since Dec 2004. Has had a problem stalling in slow left turns only, not if I put in Low, or give it a little throttle. I figured it was a float adjustment issue so finally pulled the crab which was 'rebuilt' before I bought the car from an AACA member. Inside I found the 4 bowls pretty clean (minor 'dust') and the accelerator pump seal in very good condition. I read these two threads, and also viewed Mike's Carburetor video rebuild info.

I adjusted the floats to be level, one of each of the 4 was about 1/32" off even/level, and I increased the float height (about an 1/8" to start with ), based on info here.

in my case know it's NOT an ignition issue as I replaced the points/condensor last spring and the related wiring.

Cold this evening in the 40's, so took a while to 'warm up'. Results- a little better, but so many comments and so many variables. Did have to decrease, then increase the idle screw during my test runs around the hilly neighborhood. Overall, doesn't stall so quick.

One comment was made about the 'dashpot mechanism'- mine seems to work, but the comment made me wonder if it's 'as effective' as it should be (slowing the butterfly closure smoothly') So just sharing my experience. You all have it down- all the variables, all the mechanical and mental chalenges in our 'strive for perfection of the classics'.

I have rebuilt many Rochester marine & Carter AFB's ( Chrysler 413 & 440's) and on both my 63 Imperial 413 Interceptor upgraded to Edelbrocks (650 & 750 cfm) which HAVE NEVER given me any issues at all, cold or hot, even with the modern ethanol gas. I'm also in the process of rebuilding some early Stromberg CD's on my TR4 and a Holly 1920 for the Dodge A100 slant 6 project. So its been carb November.

Will see how the Skylark does after a good run and re-entering 'city' traffic'. Has to be next week, will be away till next weekend.

Edited by Sherman D Taffel (see edit history)

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There was a specification to adjust those dashpots but I don't know where to look it up. You could try extending it further to see if it helps. Keep track of how many turns you make so you can return it to it's original position if it doesn't work.

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I had a similar issue after a tune-up on my 1956 Cadillac. The idle was so low that it shut off making a turn....or so I thought. I did need to goose it up just a touch but I was having a vapor-lock issue. The timing was actually off and the engine was getting very hot, so the fuel evaporated in the fuel line. Once I was on the timing marks I adjusted the idle up a hair and it seems to be okay now. Just another area to check. You would know it if your engine was running that hot though.

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