I have a beetle with a quite worn 1641 and standard carb. It has a 009 with Compufire, I made the mistake of giving it some love, such as filling it with BP ultimate, adjusting the valves and replacing the plugs and ever since it is misfiring under load. Starts ok but when revved or under load pops and farts.

To date I have changed the plugs again and new copper ignition leads. This fixed it for a day then it went back to worse popping and farting.

I have now put in a new rotor and dissie cap, new fuel filter and removed the carb and cleaned it and blew out the jets and orifices with compressed air.

It now goes a bit better but still popping and farting under load. Any suggestions to fix it would be really welcome
Cheers.......Wayne

Wayne
I would re-do the valves. Sounds like they might be too tight when it gets hot. Give it a go, nothing to loose.
Good luck.
Tony

start from the beginning
Do a full tune up - valves, points, timing

I have had Compufires go before, and this is one of the ways they go. You could try putting points & a condenser in it and see if that helps - they are a lot cheaper than trying another Comufire (unless you have another one or can borrow one).

Get rid of the high octane too. Unless the 1641 is a high comp motor you wont need more than 91. Steer clear of ethanol though. Would explain why the problem went away after new plugs.. Fouling up due to the fuel.

Yea, dilute the 'good stuff' fuel with normal 91 and see if it gets better.
The old dak dak is low compression and higher octanes have been known to cause running issues cos high octane needs higher compression to burn properly.

As per above start with the basics

Tappets, Timing, Plug gap etc

then look at filter and lines make sure you have flow

Thanks guys. Doubt it is the fuel octane as I have been using Ultimate for some time. I have rechecked the valves and found the exhaust valve on #2 was tight again (same as last time). I re did all the valves but it made only a slight improvement. Too much other stuff happening right now so I will get back to it after Valla and let you guys know when I find the problem. Cheers and thanks again

If a valve clearance keeps going tight then it could mean the valve seat is sinking. Or as the exhaust valve the stem could be stretching and getting ready to break.

I can't think of any other reason for that to be happening.

Hi,
Have You checked the Hi riser heater pipe underneath the inlet manifold.
I have had a couple of them rust out which lets the manifold get very COLD if the outside temp is coolish.. it also allows the exhaust to leak...

Air Cooled VW engines don't like any leaks in the exhaust or inlet manifolds etc...
it looks like it maybe a cracked head...

I presume You have used a timing light on it...
I don't like 009's especially if they aren't genuine..
I don't believe using 98 octane should cause problems, E91 or E95 I wouldn't use.. [ethanol]
Did You use anti-seize or similar on the spark plugs??
I do on ALL alloy heads...
I did have a bad spark plug a couple of years ago... it tested Ok initially and it did go a few hundred KLMs before it started to play up.. the engine idled and drove Ok except on the highway/expressways etc over 90KMH.. it was like half spark on & off... but the engine didn't misfire etc..

Best of Luck

LEE