Popping up the intake My type 4 engine with twin dellorto drla carbs runs well apart from a consistent pop up the intake at high torque in the lower end of revs . I’m at a loss to the reason . Is it the lockdown pumps possibly ?
A”pop” or “sneeze” out the top is lean running. My guess is a blocked idle jet. Not uncommon. You can pull your plugs and see which one is white or just clean all the jets.
Rebuilt both carbs this holiday . Both pumps weee full of rust . Test drive in a couple of days following a full engine service
not sure if its idle jet at low rev/high torque (i.e. pedal is pushed down) - but certainly could be lean, or indeed there is a problem with the timing or dissy... Could be the mechanical advance in the dissy is jammed up, but At light throttle the vac can on then dissy will come in and disguise this (if you use one with vac advance)... Could be the main jets are too lean. If it's run well before, the first thing I'd check is that the Dells are bolted down to the manifolds securely... mine were forever coming loose. Also check the fuel filter is on the correct way round, and no kinks in the pipe. ah bugger.... knew looking on here would get me procrastinating!
Yep as mentioned idle jets could be gummed up ,if they are ok yes do a leak test on the lower head to manifold with a spray of brakeclean or similar ,if the idle speed jumps you have a leak ,I have found that many manifold kits have big fat ass base gaskets ,they do seal but seat done after being fitted and will leak.....why are these supplied has got me stuffed if you suspect there is a leak check the torque on them . If your jets worked ok before you have outside issues ,keep checking and might pay to list your carb specs and what dizzy you have ,cheers.
It is probably worth listing jets and venturi size, as some combinations are not sucking air fast enough past the main jets at some speeds, leading to lean running on the transition between idle and the main jets. Playing with float level can change it, but some venturis are too big for a bus and the stock engine capacity, so they cant suck fuel through the main jets when needed as the vacuum is too weak. Maybe sized for a high revving fast accelerating Beetle application rather than a slower running bus, which sits at the awkward point for longer. Probably runs Ok on a wide open throttle based rolling road..
