My first thought is a intermittent loose or bad electrical connection . Possibly when engine moves letting out clutch it cuts out . You could try hooking direct from battery to coil and see if it helps. Do not run long if you have a resistor feeding coil. John
I would start with a compression test just to make sure the motor is sound. Then a vacuum test. Remember 85% of carb problems are ignition. You have the ability to figure it out, good hunting.
Check your engine earth, maybe it was left off when you replaced the clutch . In which case it could be earthing ( grounding) through the clutch linkage and disturbing that earth path when you use the clutch. Just put a jumper lead from the block to the frame or direct to the battery earth post and see if it cures the problem. A really obscure issue might be too much crank end float, if the crank is moving forward when you push the clutch in it will change the timing as the crank gear mesh with cam timing gear changes.
I could give you two dozen things to check, but without a compression test you're wasting your time. Are all cylinders even and have full compression?
Given that it runs well except under the circumstance mentioned, it certainly sounds like there is an electrical issue. As mentioned, check engine ground. I'd also be tugging on wiring while the engine is idling to see if there is an intermittent connection somewhere. Does it act the same whether you Gingerly let the clutch out, or Mary Ann it?
Mine was breaking down the same way and every now and then at speed over a bump or dip in the road, Turned out the coil + wire had a break on a downward bend just off the terminal and while accelerating or hitting the right bump it would break connection for a split second causing a miss. Tried all sorts til I found it, just my 2cents
That will help diagnose that one cylinder that is low. If the reading goes up with some oil in the cylinder then it's probably a problem with the rings. If it stays the same you've got a sticky or bent valve.
Give the 80 lb # 2 cylinder a squirt of oil also. All should be within 10% of each other. Like others have said if they come up it's rings. If not, it could be sticky lifter, spring, burnt valve, bent valve, bad cam, head gasket.
Technically that's # 6 at 35lbs. Are you losing water? Does it steam out of the tail pipe? Does it steam out of the drivers tail pipe,if you have duals? By steaming I mean water vapor long after it has had time to warm up. Quick checks..... With the car not running and the engine cold take off the radiator cap.. Take a big sniff, yes use your nose at the radiator inlet. You should smell coolant only. If it smells of exhaust or gasoline. That's a clue. Still with the cap off crank the engine....let it warm up. Stay away from the open radiator! Rev the engine. If coolant erupts out like a volcano......this is a sign of a blown head gasket or cracked block. The gasoline in the coolant..... Blowing coolant out the open radiator means exhaust gasses are pressurizing the coolant system. Sometimes a blown head gasket or cracked block will present this way.......most of the time it's a cracked block or cylinder wall that pressurizes like this. My personal experience shows a blown head gasket presenting with either oil in the coolant or water in the oil. My 8BA with the cracked cylinder would blow water out the radiator like a volcano..... That same engine would idle cool all day long. Rev it....it would blow all the coolant out.
Can you take the oil pan off or is there something in the way? Has this motor been rebuilt? If so how many miles ago? Looks like #2 and #6 have issues. If it has a lot of miles on it, I would pull it and go through the whole thing.
I would send the carb and the dizzy out to reliable builders also. You don't want to be chasing problems with a freshened up motor. Good luck.
Pull the head off the offending cylinder by loosening all the bolts. Do not remove them. Crank engine over until you see movement at the head. Compression will help you here. After draining the oil pan and removing the bolts. If you don’t have enough room to squeeze out the pan you may have to remove the two front engine mounts at the pumps. Remove stabilizer supports in the side near the bell housing if you have them and raise the front of the engine. After removal you should be able to disassemble the push rod from the crank and push the piston down to remove it. Watch for broken rings.
If you cannot tell a difference between the 2 accelerator pump settings, it is definitely the carb. Hard to know what for sure, could be overall too rich or too lean. Or it could be a problem with the accelerator pump.
Has fuel tank ever been cleaned? Are there any cracked rubber couplings in the fuel line possibly sucking air? Has the fuel pump been replaced recently with a quality manufactured specimen? Jeez. My parts bin has several old fuel pumps that look good but are not. Beats me why I save all this junk.
If you hadn't had the engine running already I would suggest trying a little oil down the weak cylinder to see if it is dry. But with the engine running already it should not be dry. My guess is you either need a valve grind or you got bad rings or stuck rings. You will need to get into the engine to find your problem. Damned shame and I hate to say it but that is where I would be at in your situation.
I hate to be critical of someone trying to be helpful. People really need to read the whole thread before posting. Not that I have been guilty in the past for the same thing myself.
When you say a lot of wear, do you mean it has a deep ridge? Remember to use a ridge reamer on that cylinder before you pull the piston up. Then check the cylinder for taper. Maybe time to bore. Check for broken or stuck rings. Also broken ring lands in the piston. The guy that mentioned fuel pump problems is absolutely right, they can sap the power, and also fuel line cracks, and hose leaks.
Pig tail between points and condenser , also vacuum advance blown or arm loose on breaker plate . Compression maybe , but if it is I don’t it’s goin to run good in other gears Sent from my iPhone using The H.A.M.B. mobile app
Deep ridge if you are not going to reuse the pistons why worry about piston damage on removal. They are just scrap. He checked the fuel pump rod for length but did he check the amount of travel?
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