SOLVED: yet another hesitant misbehaving engine

[Cruz]

In a morning the van is chuggish when cold on both fuels

The van has been hesitant when cold for a while but recently once I get going I'm having serious hesitations in all gears too as well as a lack of power that suddenly clears at high revs but returns once I change up a gear. I can also feel the engine missing as I am cruising. This happens using both petrol and LPG

Sprayed the carb with WD40 this afternoon to see if the revs changed due to a leak but nothing.
So I did the suck test on the pulldown unit and the choke flap didn't move. I assume the pulldown unit being goosed isn't helping the situation at all?

I'm booked in to the garage in a couple of weeks so I've been trying to see what I can do to make my life easier between now and then.

Is there a step by step guide to changing the pulldown unit with the carb still on (is this even possible)

Ta

[ghost123uk]

There is so much it could be, but I have just popped in to say that the pulldown unit doesn't operate the enrichment choke (if I am reading your words correctly) - It operates the secondary throttle valve ("butterfly") - the one at the lowest point of the rear most of the 2 carb intakes as you are looking at it, so it's actually the intake nearest the front, if you get what I mean !)

Kev is the carb expert, I bet he will be along soon

~~~~~~~~~~~~~

Aside = I wish the 2 main air inlet "tracts" on carburettors where not referred to as "chokes" (primary and secondary). It can cause confusion with the cold engine enrichment "choke" (flap)

[Cruz]

Cheers. It can't harm to change the pulldown unit as it's not working when I suck on it.

Just seen that it's a case of removing the little roll pin to remove and the gap is adjusted using the screw

Also noticed there are two units 025-129-220 and 025-121-220B

I can't assume that the carb is original so I'll have to double check which one I need when I get back to the van

Also the little black pipe from the pulldown unit to the carb has seen better days. Where sells them?

[ghost123uk]

a lack of power that suddenly clears at high revs

pulldown unit as it's not working when I suck on it.

OK, you say it clears at higher revs, but if the pulldown unit was not working, then the secondary butterfly would not open and it would be at high revs (and load) that the engine would be down on power and it would be ok at low revs (and low load).

E D I T = unless the mechanism is sticking and suddenly opening the secondary butterfly "late" = slightly possible.

E D I T 2 = Best ignore the above as reading Kevs post below I have been confusing the actual vacuum unit that DOES operate the choke with the "secondary vacuum unit" (I just looked it up ) which is the one that controls the secondary butterfly.

[Cruz]

tbh ghost it's all over the place. I have explained myself badly as it's low on power at high revs and low revs with the occassional brief regain of power, until say I release the throttle then when I depress again it's lost it's ooomph.

I can still drive it but it's frustrating

[kevtherev]

reads more electrical than fuel related cruz.

the pull down only works when cold and you have to really suck hard

[Cruz]

Rotor arm looks ok as does the cap. Plugs are new and gapped to .6m.

Worth replacing the leads? They are about 2.5 years old

[ghost123uk]

the pull down only works when cold and you have to really suck hard

In my post above I was getting my vacuum units mixed up wasn't I
I have edited to post to indicate it is duff information !

[Cruz]

reads more electrical than fuel related cruz.

the pull down only works when cold and you have to really suck hard

I think it is electrical too Kev as LPG seems more suspect that petrol.

I'm going to recheck the dizzy and rotor arm again, in the daylight this time ) as well as swap the leads for a spare pair I know are good.

On the subject of the pull down unit I sucked like a backstreet lass, when cold after closing the flap, and nothing happened. I couldn't suck any harder.

Does this mean it's toast?

And if so how do I know which one I need to replace it with, early or late? No markings other than pierburg on the front and no idea if the carb is original

[kevtherev]

On the subject of the pull down unit I sucked like a backstreet lass, when cold after closing the flap, and nothing happened. I couldn't suck any harder.

Does this mean it's toast?

And if so how do I know which one I need to replace it with, early or late? No markings other than pierburg on the front and no idea if the carb is original

pull downs do not differ whatever the year.
ok if you were sucking that hard then it is
There is a restrictor in the vac pipe to the pull down, if you put your tongue over the pipe end after every suck it should open, if it is not holding vacuum then the unit is shagged.

[Cruz]

I'll try again. I'll suck, block the pipe, then suck again etc etc

Is the flap supposed to open slightly when you suck?

[kevtherev]

Is the flap supposed to open slightly when you suck?

yes... or at least move!
It stops overfueling during warm up, over fueling causes hesitation (among other things)

[Cruz]

Cheers Kev

[Cruz]

Just an update. Can't believe how "blonde" I have been recently. I am rather embarrassed with myslef (even blaming doing things in the evening by torch light is no excuse)

I removed the dizzy cap again, which was fine, and re-checked the rotor arm in the light of the kitchen. The curve of the rotor arm contact had a noticable flat spot on it once the slight carbon deposit was remove. So I changed it for a used spare I had in better condition, as well as changing the leads for a spare set and it was like getting my old van back. "Hopefully" that's solved by running issies

Started fine from cold this morning, choke came on, no chugging, no flat spots, no kangarooing, just plain sailing. So from that I assume (maybe wrongly) that the pulldown unit is working but I'd still like to see it for myself. So I will continue below

-------------------------------------

I've not had chance to test the pulldown unit again from cold but I found this video on another topic

http://www.youtube.com/watch?v=OngFIfT9 ... e=youtu.be" onclick="window.open(this.href);return false;

I know that is what the flap is supposed to do but in that video it seems it is easy for him to suck the flap open. Is that because there is no restrictor present? Is the restrictor in the pipe or the unit?

[kevtherev]

in the pipe