T25 - Loss of engine power after long drive

[philos]

I have recently purchased a T25 sheldon hightop 2.0 Aircooled 1981 Webber carburettor conversion fitted, On a recent trip to the Gower i experienced a increase in engine noise(miss firing) and a loss of power. After Pulling onto the hard shoulder for 5 mins and restarting the problem disappears. The RAC inspected the engine and suggested that the valve springs may have perished thus causing the the engine to miss-fire(turning off the engine resetting the valves?). Not knowing much about engines , I was wondering if this seems a plausable reason for the missfiring. I've tried putting redex through the tank and this seems to settle the problem for a while.
The van works fine on short journeys and on idle the engine sounds fine.
I have not heard any tapping noises from the engine at any stage.

Grateful for any suggestions

[LeeCarey]

Hi philos,
I had a similiar problem on my 1984 Aircooled. It would conk out on a long journey and then if left for a short while would be back to normal. The problem turned out to be a vacuum building up in the petrol tank (probably because the tank breather tubes are blocked). A quick check is when the problem occurs stop and undo the petrol cap, if you hear a hiss then this is your problem. A temporary fix that I have done is to cut a small slot across the rubber gasket of the petrol cap which allows the air in via the petrol filler cap. Since this has been done there have been no further problems.

Good luck

Lee

[philos]

i will give this a try, thanks Lee

[VWCamperfan]

Overheating can cause these symptoms also, check timing isnt too far advanced and mixture isnt running too lean.

[jason k]

check every bit of tinware is present and that the engine seal is intact. mixture and timimng are very important too.
how hard were you driving it before the probs occured??
is the petrol filter clean ??
sometimes the rubber filler neck seal perishes and allows water in to the tank which can cause running problems.
where are you situated as someone can reccomend a good garage. most local ones wont have a clue what to do with these things

just to make you feel a bit better the rac mans diagnosis sounds like utter bollox to me!!

[philos]

thanks everyone ,

The problem normally occurs when the van is underload on a slope. It Could well be a overheating problem as suggested. I will try adjusting the throttle + fuel mix on the weekend.
The Fuel filter has been changed in 1991 so it probably could do with a new one. I try to keep to speed to no greater than 55-60 on the motorway/duel. The problem has exclusively occured at these speeds.
I am lucky enough to have a VW van specialist at the top of the road , Roath Cardiff. So i can take it there if the problem persists.

[Rozzo]

just to make you feel a bit better the rac mans diagnosis sounds like utter bollox to me!!

here here. since the valve springs are metal it would be difficult for em to "perish"
why do they set these tossers on
good luck with it, there are some good suggestions above

[jason k]

you mean cardiff classic vws do you.
good lads there , know their onions too.

but a new fuel filter is £1 from any car shop and fitted easily in two mins.
the filter is located on the drivers side just under the sill by the front wheel.

if its not been changed since 91 its the first thing i would look at!!

[oldiguana]

perished valve springs had got to be one of the best ive ever heard!!

[colinMSC]

is it one of those with 4 long pipes to each cylinder, as they are not verry good at all
if it is one like i described there wont be much you can do to cure it.
I had one fitted acouple of years ago and could not stop the fuel from freezing in the inlet manifold, in summer she ran well . but soon as winter hit she was almost undrivable.
it poped and banged and lost all power on hills but run ok as long as you did not rev it .
luckly i did keep the original carbs so we re fited them
which cured everything.

[Laurie]

The clue is that after a few minutes it runs OK again. Carb icing. Them thar bloody Weber progressives are supplied without any modification to go from a ford manifold onto flange that is miles away from a heat source.
They're not jetted properly, either.

Hopefully, behind the manifold (in front near the bell housing) is a cup with a rubber washer on it. That's where the old carbs picked up heat from, even though they were close to the heads! You may be able to fabricate a box to go over the air cleaner and run a paper hose to it with warm air from the air pick up. We used to do this with Nikki carbs.

[ghost123uk]

With the symptoms you describe in your first post I agree with Laurie

Likely carb icing on that setup.

Jees, how come the RAC bloke couldn't come up with that, as the symptoms are just so "carb icing" ones. Perished valve springs indeed !!