Club 80-90 Forums

Have tried searching forums for advice but can't seem to find anything, maybe because this is normal for these vans. When accelerating hard there seems to be a flat spot mid range followed by a sudden burst of power (if there is such a thing with these engines!). Not consistent but noticable when engine both warm and cold. I have checked for vacuum leaks and all seems fine. HT leads distributor cap and rotor are all fairly new.

Was wondering whether this could be something to do with the vacuum activation on the second carb barrel? I know very little about these engines so any advice appreciated

Many Thanks

Could be the accelerator pump diaphram. From memory, VW used to advocate removing carb and catching fuel in a measured glass container, using so many strokes as an indication of fuel delivery. That said, timing only has to be off and that'll do it too.

yes there is a vacuum operated butterfly in the second venturi
It is not possible to test this though.

Item No. 1 here



you may well have a leak on the vacuum pipe or the diaphragm inside is holed.
very unusual to break these units.
I would be checking the mechanical advance bob weights and the vac advance.
It also should be timed

These symptoms also reflect the accelerator pump diaphragm failure or jet blockage (item 6)
check this by watching the fuel squirt into the venturi as a friend depresses the accelerator
all parts available

Well you can test it by slipping a longer pipe on and sucking to see if it holds - rather like the vacuum advance on dizzy but much easier to look at with carb off.

I think it's whether it opens at the right time could be the issue..

Yes, you're right Kev. Still, a few causes for this. Case of eliminating each in turn really. Definately worth checking action of accelerator pump and double-check timing.

Many thanks guys for the advice. It has helped by understand a logical approach to this.

1) Check mechanical and vacuum advance working OK
2) Check / replace fuel filter (needs doing anyway so why not)
3) Check for manifold / vacuum hose leaks
4) Check accelerator pump on carb
5) Buy and fit carb re-con kit

Cheers

Mark

OK, disconnected vacuum hose from distributor and plugged open end of hose. Went for a drive and flat spot / lack of power exactly same. Tried sucking on vacuum advance on distributor and could easily suck air through with little / no resistance. This makes me think vacuum advance has had its day?

Looks like I can get new vac advance from Brickwerks but there are also aftermarket distributors for not much more. Not Bosch and says ignition module has to be disconnected but do folks on here have any experience of them?

http://www.justkampers.com/shop/type_25 ... 03205.html

I think I should keep it Bosch as that has worked well for 20years and over 200K miles.

Will probable remove dizzy and rebuild whilst I'm at it but is it possible to just swap the vacuum advance unit with dizzy on engine?

Cheers

Noooooooooo. Never fit a 009 on a T25. They are not suited despite JK's claims. Its the anti-christ of distributors. Vaccum advance is needed for good performance. In fact your performance issues could well be resolved by fitting the right dizzy and until you do, diagnosing problems is going to be next to impossible.

Say no to 009 it is WRONG

fit the the right distributor and working vacuum advance

as i remember 009 is timed at 3500 revs, so you dont get optimum performance till it reaches that rmp...........(am i right with that or did i dream it??)

I have this exact same problem!

I have no mid-range, just a gentle take-off in low range, then a few seconds hesitation, ride the clutch a bit and then sudden power!!. High End is good once going. But the Flat-Spot is a pain.

I have fitted a new vac advance unit from brickwerks, new fuel pump, accelerator diaphragm looks okay, no visible holes in it, checked all vac hoses, but still this major flat-spot.

Anyone have any luck with solving this type of thing?

I am to go on holiday in two days, and this is the difference between taking my T25 or not.

Jason

I had this.. and had a blocked transfer jet
to check, this look down the venturi and get a friend to press the accelerator,from the jet , you should see a hearty squirt of petrol down the throat of the carb.

Hi, thanks for that, I can see a single line of petrol being squirted down, with some pressure, it hits the wall of the venturi just before the opening of the flap at the bottom.

How would I remove this jet, to check if it is blocked or to clean it?

If you can see a good squirt then it's OK
Your problem lies elswhere