VW Air-cooled mis-fire/ poor running
Posted: Sun Apr 24, 22 5:21 pm
I'm not on any VW forums so hoping someone here can help. I know Dave999 knows a fair bit about VWs.
Here's the problem I'm having.
My wife's '61 bug running a 1641 twin port engine with twin Weber 34icts developed a severe misfire and would barely run.
On initial investigation I noticed the carbs were leaking fuel and there was also fuel in the sump. The car had only done about 30 miles since the previous oil change so I don't think any harm was done to the engine.
So I rebuilt and tuned the carbs using this guide https://www.wayoutwestie.com/aircooled- ... ed-engine/ and changed the oil. The misfire remained and after a road test the car would barely drive. I've changed the plugs, leads, cap and rotor arm and even bought a new distributor with vacuum advance. Timing is at 7.5° BTDC. Running points and set statically as my strobe light has packed up. I did change to Pertronix electronic ignition and flame thrower coil but changed back to points as the Pertronix was for a 009 dizzy that doesn't have vacuum advance. I left the new coil in place when I changed back to points and vac advanced dizzy.
The fuel pump is new and last time I checked the pushrod moved freely. I do have an electric fuel pump I might try but I don't think that is my problem though I may fit it just to rule it out.
Inlet manifold to cylinder head mating faces are nice and flat with new gaskets and sealant used so I'm 99.9% sure there is no air leak.
Today I went back over the basics and reset the valve clearances, points, timing and tuned the carbs again. The engine ticked over nicely and revved well after warming up on the drive for about 15 minutes with the occasional crackle through the exhaust. After a test drive of about 2 miles it started acting up again to the point it would barely run.
I'm starting to think l might have a cracked cylinder head as the twin ports are prone to cracking but I'm not sure that it would give these symptoms, I don't know what else to try though!
I believe the heads crack between the valves but I'm not sure it would cause the engine to run this bad.
I think I'll end up removing the heads to have a look as I feel I've tried everything else but before I do is there anything obvious I'm missing?
Thanks in advance.
Here's the problem I'm having.
My wife's '61 bug running a 1641 twin port engine with twin Weber 34icts developed a severe misfire and would barely run.
On initial investigation I noticed the carbs were leaking fuel and there was also fuel in the sump. The car had only done about 30 miles since the previous oil change so I don't think any harm was done to the engine.
So I rebuilt and tuned the carbs using this guide https://www.wayoutwestie.com/aircooled- ... ed-engine/ and changed the oil. The misfire remained and after a road test the car would barely drive. I've changed the plugs, leads, cap and rotor arm and even bought a new distributor with vacuum advance. Timing is at 7.5° BTDC. Running points and set statically as my strobe light has packed up. I did change to Pertronix electronic ignition and flame thrower coil but changed back to points as the Pertronix was for a 009 dizzy that doesn't have vacuum advance. I left the new coil in place when I changed back to points and vac advanced dizzy.
The fuel pump is new and last time I checked the pushrod moved freely. I do have an electric fuel pump I might try but I don't think that is my problem though I may fit it just to rule it out.
Inlet manifold to cylinder head mating faces are nice and flat with new gaskets and sealant used so I'm 99.9% sure there is no air leak.
Today I went back over the basics and reset the valve clearances, points, timing and tuned the carbs again. The engine ticked over nicely and revved well after warming up on the drive for about 15 minutes with the occasional crackle through the exhaust. After a test drive of about 2 miles it started acting up again to the point it would barely run.
I'm starting to think l might have a cracked cylinder head as the twin ports are prone to cracking but I'm not sure that it would give these symptoms, I don't know what else to try though!
I believe the heads crack between the valves but I'm not sure it would cause the engine to run this bad.
I think I'll end up removing the heads to have a look as I feel I've tried everything else but before I do is there anything obvious I'm missing?
Thanks in advance.