Choke pull-down diaphragm pipe - 1.9DG

[y30man5]

Hi all,

I just took the Choke pull-down diaphragm pipe off to do the "suck test" on the unit and noticed a hole in it... so I need to replace it, but I don't know what type of pipe to get... this might sound like a stupid question ask, but I thought it best to check... I'm getting a pull down unit from brickwerks, so is there any pipe on there that would be appropriate?

Also, one of the nuts holding the pancake appears to be cross-threaded... how can I get this off and do I need a special type of nut to replace it?


Thanks in advance.

[kevtherev]

The pipe has a special valve in side which must be refitted if you replace with a different type of hose.
The nut needs to be a flanged type



you'll struggle to get one new one but you may have more success at a breaker

[y30man5]

Thanks for the quick reply...

I just had a look at my pipe and there's nothing inside it... I can see right the way through

you'll struggle to get one new one but you may have more success at a breaker

The pipe or nut?

[kevtherev]

the nut

[kevtherev]

Thanks for the quick reply...

I just had a look at my pipe and there's nothing inside it... I can see right the way through

[

the valve is missing then
Let me check the spares and see if I have a pipe

It's not actually a valve more of a restrictor to stop the pull down unit snapping open too much

[y30man5]

the valve is missing then

OK... well I hope it's not too vital, if it's missing.

Just spent the last couple of hours tryin to get that nut off without any luck... Guess I'll have to get a nut splitter tomorrow and give that a go, although I'm not sure there's enough room around it.

[kevtherev]

it is vital
or it wouldn't be there
The pull down unit opens the choke when you accelerate. If it opens too quick the engine will stall.
the restrictor opens the choke slower

[mblake4u]

Hi Kev,

I wonder if you can comment on my choke pull down unit. My T25 lacks power going up hills so I've been testing most things, and found that when I suck on the pipe of the choke pull down unit the diaphragm moves which in turn moves the butterfly in the venturi.

What happens though is you have to give it a strong suck - it moves the butterfly but the butterfly moves back to its original position, so I think there must be a leak in the diaphragm unit somewhere (the pipe is new)? Is this how it should normally work, or is the butterfly supposed to stay open until the pressure returns to normal?

You mentioned that there's a valve in the pipe from the carb to the unit. My old pipe didn't have a valve but there's something restricting the airflow in the metal pipe of the carb. Compared with the other metal pipes coming out of the carb (eg dizzy vacuum advance) the amount of air you can suck through is much less. In fact I find it hard to believe that the vacuum through such a small hole can move the diaphragm/rod and butterfly.

Thanks in advance, Michael

[kevtherev]

yes it is a strong vacuum isn't it.
OK remember the vacuum would be constant at tickover then increase with opening the throttle.

The restrictor is to stop the unit snapping open, and without acceleration vacuum it returns to the start position. (3mm gap)
It should really be viewed working in situation or using an adjustable vacuum pump.

This pull down unit only opens the flap when the engine is cold.
once warmed up the flap is wide open.
As I have said before if you can constantly suck air through the diaphragm or the flap shuts with you sucking the flap open and then sealing the pipe with your tongue... then that is an air leak into the mixture.

Most T25's (DG 1.9's DF 1.9s CS 1.6s CU 2.0s and some diesels) lack power on hills mate.
I fitted a 2.1 to give me 30 more horses and some hills STILL slow the van up.

Make sure the wheel & tyres are correct overall diameter, too big a diameter and you get a tall gearing effect which will have you stirring the cogs in the box.
Correct Diameter is 654mm use your school boy Pythagoras (Pi = 3.142) to work out your correct circumference

[mblake4u]

Hi Kev,

Thanks for the reply. I'm almost sure there's less power than there should be so I'm going to do a compression test tomorrow. Sorry, after posting I found one of your other posts where you mentioned that being able to continue sucking on the pipe means the pull down unit has gone.

As I'm living in South Africa and it doesn't usually get too cold here I'm wondering if I can work around this issue until I can get a replacement.

What I'm thinking is:
1. block off the pipe so the carb doesn't suck in the extra air.
2. adjust the choke housing so that there's a minimum 3mm gap.

My question is will this have a negative effect on things when the engine is warm and with the general performance of the engine?

Cheers, Michael

[kevtherev]

what's your ambient temp there at the moment?

[mblake4u]

11pm, 2nd day of spring, 20C / 69F.

Mid-winter during the night can go down to about 5C in Cape Town.

[kevtherev]

20-25C ambient the flap will be quite well open anyway.
Disconnect the pipe and block it off.
You can adjust the choke to be fully open at these temps by using the housing adjustment if you want to be particular .

Might be interesting to do a gas test (CO) before and after the pipe is blocked

[mblake4u]

Thanks Kev, at least that's one problem solved for now (well not solved but a work around).

Yeah, good idea.. it would be useful to know how much leaner it runs when it sucks in that extra air. Added to my list of todo's!

[Mickyfin]

Great thread for reference, I too am experiencing my choke not functioning, thus resulting in low tick over, and hesitation. I will get the pancake off tomorrow, and inspect things to see whats what. As usual, its great to see Kev helping others!