Occasional drop in power on hard acceleration

[MrBeard]

Hi all

I am really impressed with this forum and the quick and useful comments I have received so far.
One more thread that I need a little help with please.
Not being massively technical I have searched but did not fully understand if the thread answered my question.

When driving the T25 drives really well, but when you put your foot down hard on the accelerator to suddenly try to increase revs there I often a drop in power for about a second then it respond nicely.

I mentioned this brefly in a previous thread and kevtherev commented

transfer jet.... but that's a new thread

Thanks kevtherev, but what does that mean?

cheers
MrBeard

[kevtherev]

Two reasons that I can think of...
Air leak, from a vacuum hose, tube, pipe or cracked gasket.
accelerator pump, on the carb, diaphragm split,
transfer jet blocked, on the carb, trapped grit causing poor function.

When you stamp on the accelerator, the engine tries to gulp in as much fuel and air as possible.
Pierburg carbs have a transfer jet to assist with this.
the carb has a little pump on the side that uses the accelerator cable linkage to work it.
you can see it here item No 6



when the cover is removed the diaphragm is inside there should be no splits in it

To test the jet you'll need an assistant to press the accelerator whilst you look down the throat. and look for a good squirt of neat fuel from the jet into the throat.
no good squirt means the diaphragm has failed or there's a blockage in the carb body or jet.

As for air leaks then try removing the pipe of the carb to the "Choke pull down unit" (Item No 2.) and suck... if you can suck and just keep on sucking then this unit has failed and is leaking air into the carb

[MrBeard]

Two reasons that I can think of...
Air leak, from a vacuum hose, tube, pipe or cracked gasket.
accelerator pump, on the carb, diaphragm split,
transfer jet blocked, on the carb, trapped grit causing poor function.

When you stamp on the accelerator, the engine tries to gulp in as much fuel and air as possible.
Pierburg carbs have a transfer jet to assist with this.
the carb has a little pump on the side that uses the accelerator cable linkage to work it.
you can see it here item No 6



when the cover is removed the diaphragm is inside there should be no splits in it

To test the jet you'll need an assistant to press the accelerator whilst you look down the throat. and look for a good squirt of neat fuel from the jet into the throat.
no good squirt means the diaphragm has failed or there's a blockage in the carb body or jet.

As for air leaks then try removing the pipe of the carb to the "Choke pull down unit" (Item No 2.) and suck... if you can suck and just keep on sucking then this unit has failed and is leaking air into the carb

I suspect it's an air leak. the air box has a crack and hole in it (so I shall need to replace) and there is a hose that needs replacing. I'll post a pic later today of the engine

I really hope it isn't the transfer jet, as you can tell I am not a master mechanic!
Cheers
MrBeard

[kevtherev]

yes eliminate the easy stuff, that hose might just be the one that's causing it.
Air leaks do weird stuff to engines

[MrBeard]

Well changed the hose and taped up the hole in the air box, and it's running better now.
I think It still dips a little when setting off, but didn't seem to have an issue once moving.

Fingers crossed

Cheers
MrBeard

[MrBeard]

Drove it 1.25hours today to nottingham, and it ran nicely.
The new hose and and taped up air box have smoothed out the engine and now it purrs.

It does still hesitate on hard acceleration, but normal accel. it is fine with and happily drove at 70.

Well. I can't do anything to the transfer jet or other areas until I get it back from Notts where it is having a new High top roof added. next weekend (21st ish)

Cheers
MrBeard

[MrBeard]

Right

So I now it has been awhile, but I have a problem with this transfer jet issue.
I have been on the phone to VWHeritage and they seem to think that there is no transfer jet on the T25 1.9 WaterBoxer.
There is an Acceleration Diaphragm.

Beyond that I am confused

[CovKid]

f you look between part 1 & 2 on the diagram, you'll see a small cone-shaped filter that tucks inside the fuel inlet pipe. If this is clogged it will restrict rapid demand of fuel. Common fault when you're belting along and power drops until fuel flow keeps up with demand again.