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Discussion Starter #1
I have a '64 122s with a 1974 B20F motor.

The motor has Weber DCOE 45's, has been bored (years ago) and has an aftermarket cam 'kit'.

I am hoping you can help me diagnose a problem with the motor as it 'misses/pops (not backfires - but pops)' consistently - and fouls the plug in #2 cylinder (counting from the front).

There is also 'spitting' out of front carburetor #2 venturi.

I've recently installed new spark plugs, cap, rotor, and plug wires

I've also adjusted the valves carefully -on more than one occasion.

The distributor is Serial 003 aluminum - and already has an 'electronic' module in it. The car also has an MSD ignition module (mounted under the dash) and MSD coil.

The distributor shows signs of medium/high wear (significant shaft play in housing).

The compression appears to be within tolerances:

1 = 136
2 = 152
3 = 160
4 = 145

The car ran very strong until one day the missing ensued.

Please advise thoughts and thanks in advance.
 

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My first thought is a wiped out cam lobe. Pull the valve cover, turn the engine and see if the exhaust valve on #2 cylinder is moving as much as the other valves.
 

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Welcome to Swedespeed, Mario.

"...The car ran very strong until one day the missing ensued..."

Are you saying that the "popping" did not exist one day but did exist the next?

George Dill
 

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Discussion Starter #4
Thanks George (and Phil).

It's hard to tell what the catalyst was for the 'change' in performance. The car has essentially been a garage queen for 10+ years - but is driven around the neighborhood at least monthly. It was during one of these excursions where the car appeared to lose power.

The 'spitting' out of venturi #2 of the front carb has been there for quite some time. The 'popping' out of the tailpipe is a newer symptom.

The carbs have also been recently rebuilt by a 'professional' - but the car essentially ran the same before and after the rebuild. The carb rebuild was done because it was time - as opposed to being done to cure the symptoms mentioned.

I've changed the plugs a number of times - with the #2 plug coming out black (but dry) and the others tan.

Hence, the issue(s) appears to be centered around the #2 cylinder (which has 'good' compression).

Thanks in advance.
 

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If the problem suddenly appeared, it is most likely a carburetor problem.

Checking for cam lobe wear is very easy to do though, so try that first so that you rule it out. Also, check timing. If the engine runs, rev it up and down and make sure the centrifugal advance work well.

If all that checks out, then most likely something is clogged at the carb. I have no idea what type of carb that webber deal is, but there are a few things that apply generally to carbs. You either have a stuck float valve which makes it too reach, or you have something clogged which makes it too lean.

Here is a few easy tricks you can try. Remove the fuel supply to the carb, and pick up the fuel by an oil can (or plug the hose with your finger). Let the engine run until it consumes all the fuel in the bowl(s). That will make the float valve(s) open completely, and if something is clogging it, it will be released. Also, if the engine was running rich, you may see a temporary relief as the float level is dropping. Then, re-connect the fuel line and see what happens.

If this fails, and your engine runs bad even in neutral when you rev up, you can try something else. Disconnect fuel again and run until dry. Then use starter fluid instead of gasoline, and see if you can rev the engine up and down without hesitations. If you see an improvement, then there is certainly something wrong in your carb(s).
 

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The float bowl is common for both barrels on a DCOE, so any problem with that would show up in both cylinders.

There three different circuits on each barrel -- idle, progression (or low-speed), and high-speed. If the popping goes away above 3000 RPM, it's possible there's some blockage in the idle and/or progression circuits, which do share a common jet. If it happens both above and below 3000 RPM, it's very unlikely that the carb is at fault.

Ignition advance problems would show up on all cylinders, not just #2. Timing would not cause popping unless it was severely retarded to the point the engine would barely run.

Check the lift on the #2 exhaust valve...
 

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While you are checking valve lift, might as well check them all. They should all lift at least 3/8". Cam failure can happen suddenly.
 
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