Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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Grease Monkey
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Grease Monkey
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Hello. Im new to this forum. i have a 1951 Chevrolet 3100 Panelvan with a original 216. The car had been sitting for 30 years when i got it.
Long story short, got the car running but runs like crap. I have rebuilt the carb, and distributor cap, plug wires and plugs are new. Also adjusted the valves.

The car starts and idles without a problem. Idles very good. But as soon as i try to revv it. It just pops and shoots trough the carb. It doesnt only pop one time. If i keep my foot on the pedal and try to revv it, it just keeps popping and shooting and eventually dies. It isnt possible to drive it like this. If i pull out the choke it gets a little better. So i got to drive it 3-400 meters last week with choke.

I can see a squirt of fuel when i pull the throttle. so it seems like the acc pump is working.

Any ideas?

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Oil Can Mechanic
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Repetitive backfiring through the carburetor when revved is the classic symptom of a flat camshaft lobe. Some newer Chevrolets had a bunch of trouble with that. Over the years I don't think I have ever heard of it happening to a 216, but other people in here will know more about that than I do.

If it were my car, I would take all the plugs out so it cranks easy, take the valve cover off, crank it, and just watch the valves moving. If the cam is the trouble, less motion on one valve should stick out like a sore thumb while you watch..

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You have a sticking intake valve. Pour some ATF through thr carb. air horn with the engine running at a fast idle and let it soak over night.

Last edited by Chev Nut; 06/23/21 08:06 PM.

Gene Schneider
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devilsix, welcome to Chatter.
The information you provided I am inclined to agree with previous answers.
Tony


1938 1/2 ton Hope to drive it before I retire
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This is something that could blow your muffler apart.


My 1951 1 Ton is now on the road! My 38 Master 4 Door is also now on the road .
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Grease Monkey
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Grease Monkey
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Hello again. And thank you for all your help. Took the valve cover of today and started it up. Unfortunaly it seems that the cam is not round. All valves moves the same.

Could it be a bad valve that doesnt Seal?

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You have an intake valve hanging up at higher engine RPM,s The 216 never wore off a cam lobe


Gene Schneider
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Also possible broken valve spring


Gene Schneider
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I had one a long time ago that the main spring on the points broke. The thinner copper coated electrical contact would let it idle great but when revved up had symptoms just as described. The points just floated over the lobes and it ran like crap. Started on a list of possible causes and one by one eliminated them. I did not have a dwell meter when I was 17, I think it would have showed up at higher speeds. Have you checked the dwell at anything other than an idle? It would probably also show up as a weak point spring if flexed.

Art

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Backyard Mechanic
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are you sure all the plug wires are on the right plugs

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Grease Monkey
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All the wires are in correct order. Have checked that many times. But why does it rev good with choke? When i pull out the choke it idles very High But revs much better then without choke. Sounds to me like its a carb problem?

If i take a compression test or leakdown test i can find out if a valve is hanging open?

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A compression test will indicate any cylinders that are weak where as a leak down test will indicate if valves or rings are leaking.
Tony


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Going back to the beginning of your thread, I'm wondering whether the fuel mixture is too lean -- a classic cause of popping back through the carburetor. I would remove the carburetor again and recheck the float level setting, the metering rod setting and that there is no obstruction in the high-speed circuit. A vehicle which sat for 30 years is quite likely to have dried-up gasoline residue in the passages, orifices and jets. If the idle circuit is clear, but the high-speed circuit is partially blocked, it could explain the problem.

I'm sure some of our carburetor experts will weigh in with their thoughts on this.

All the Best. Chip


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I tend to agree with Chip. If it backfires with no choke but revs with no backfire with choke, it's lean. If the motor was not lean, revving it with the choke would make it stumble, cough, and smoke.

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Shade Tree Mechanic
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I need help with almost the same problem. 1949, 216. Starts and idles great. give it a bit of throttle, and it starts to sputter and backfire. New points, plugs and wires, condenser and router. Rebuilt the carburetor and the problem is still there. I don't want to put to much time or $ into the 216.{I want to drop in a 235 ( '56 with low miles) BUT room to do it and a helper.} I will check over everything again but I did all the "little checks" many times and can not find the problem. I am open for any more ideas.

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If it is back firing through the carburetor advance the timing another 6 to 8 degrees using the octane selector and making sure the heat riser is working correctly.
If you have a Carter W-1 is the metering rod properly adjusted? This is important and a special tool is used.
It is normal for it to back fire until fully warmed up.

When does it pop back, when throttle is suddenly opened or at a steady speed?

Last edited by Chev Nut; 03/20/22 10:21 AM.

Gene Schneider
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Rochester carburetor. Also tried advancing timing a bit and doesn't change. Looks Like I will be replacing the engine sooner than later.

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Grease Monkey
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I realize this is old but I thought I would throw my 2 cents in. We run a carburetor shop and most of the time a customer rebuild carburetor needs to be rebuilt. Theres alot more to rebuilding a 1 or 2 or 4bl carb than meets the eye. So my suggestion is to have the carb rebuit profesonaly or try another 1. A lean carb will back fire through the top. Incorrect Timing is usualy backfires out of the exhaust. But anything is possible.
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