Air cooled vanagon engine miss

Please help! I have an engine misfire that comes and goes, usually
happens after a 30 mins at highway speeds then slow to 60kph. Misfires
at all revs and throttle settings. Won't idle at under 3,000rpm. If
left to cool down starts fine and goes for 30k's or so on highway then
misfires again. It backfired once during acceleration in first.
Sometimes you can drive through the misfire and then runs fine again
for a while. Seems the hotter the day the worse it plays up, but
always goes fine after letting it cool for 30 mins. Mechanic had
fitted new after market electronic ignition and coil. He reckons he
has checked them out, cleaned carby's and it only fixed the problem
when he backed off the tappets to have 6" & 8" clearance. The engine
has a CU prefex (South African) and he couldn't find it listed so
thought it must not have had hydraulic tappets. I told him it
sometimes has a noisey tapped cold, and then disappears when hot. This
means it has hydraulic tappets.

Anyway he reckons the valves must have been riding. The were adjusted
30,000k's ago to hydraulic specs, ie screw adjuster in until just no
clearance, then screw 2 full turns in.

I don't see how the valves could be riding, or how they could cause a
jerking misfire. If they were riding wouldn't it misfire everytime it
got hot?
Have checked for vacuum leaks, timing, replaced high tension
leads/caps/spark plugs. I havn't been able to test on a hot day, but
now I have bloody noisey tappets.

Any advice would be greatfully received!

Neil

Check out this link http://www.bostonengine.com/articles/hydraulicll.htm
seems to describe the problems you are having.
Hope this helps

Tim


"Batterstyle" > wrote in message
om...
> Please help! I have an engine misfire that comes and goes, usually
> happens after a 30 mins at highway speeds then slow to 60kph. Misfires
> at all revs and throttle settings. Won't idle at under 3,000rpm. If
> left to cool down starts fine and goes for 30k's or so on highway then
> misfires again. It backfired once during acceleration in first.
> Sometimes you can drive through the misfire and then runs fine again
> for a while. Seems the hotter the day the worse it plays up, but
> always goes fine after letting it cool for 30 mins. Mechanic had
> fitted new after market electronic ignition and coil. He reckons he
> has checked them out, cleaned carby's and it only fixed the problem
> when he backed off the tappets to have 6" & 8" clearance. The engine
> has a CU prefex (South African) and he couldn't find it listed so
> thought it must not have had hydraulic tappets. I told him it
> sometimes has a noisey tapped cold, and then disappears when hot. This
> means it has hydraulic tappets.
>
> Anyway he reckons the valves must have been riding. The were adjusted
> 30,000k's ago to hydraulic specs, ie screw adjuster in until just no
> clearance, then screw 2 full turns in.
>
> I don't see how the valves could be riding, or how they could cause a
> jerking misfire. If they were riding wouldn't it misfire everytime it
> got hot?
> Have checked for vacuum leaks, timing, replaced high tension
> leads/caps/spark plugs. I havn't been able to test on a hot day, but
> now I have bloody noisey tappets.
>
> Any advice would be greatfully received!
>
> Neil

The air-cooled Vanagons (1980-82) have a number of common features with
the late model Bus, vintage 1978-79. Does your Vanagon have a
temperature sensor that attaches at the #3 cylinder? My '79 Bus had a
problem similar to yours which first showed itself as a subtle
high-speed miss before getting dramatically worse. When the temperature
sensor was replaced, the problem was solved.

Robert Winters wrote:

> The air-cooled Vanagons (1980-82) have a number of common features with
> the late model Bus, vintage 1978-79. Does your Vanagon have a
> temperature sensor that attaches at the #3 cylinder? My '79 Bus had a
> problem similar to yours which first showed itself as a subtle
> high-speed miss before getting dramatically worse. When the temperature
> sensor was replaced, the problem was solved.
>

He's got carbs; does not apply...

Speedy Jim
http://www.nls.net/mp/volks/

> at all revs and throttle settings. Won't idle at under 3,000rpm. If
> left to cool down starts fine and goes for 30k's or so on highway then
> misfires again. It backfired once during acceleration in first.

Do you have simple olddays ignition with a capisitor on the distributor? Try
to change it with a new /other one...
Greetings from Denmark....
Michael


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.809 / Virus Database: 551 - Release Date: 09-12-2004