Club 80-90 Forums

I have a gunstones gas anilizer if you want to borrow it .... I'm not that far away
It was checked against a calibtared one only a few weeks ago so I'm pretty confident it accurate as far as it goes

Thanks for the offer - I'll see how I go. I had success with the LT carb I tried by just winding the CO2 screw in until the revs started to drop and then winding it out half a turn. That seemed to get pretty close.

I took the van out for a drive, just to make sure all the remedial work on my 'normal' carb was ok, and that the Powerspark vacuum advance unit works ok. Once warm it drives perfectly again. So I pulled up onto my drive and decided to go for it with the 'test' carb. After I'd swapped everything over I fired it up - it ran for a moment then died. Fired it up again, it died again. Then it wouldn't start at all. Tsk.

Let's just say that an empty fuel tank wasn't the first thing I thought of . A bit of an unlucky coincidence. And after I poured my lawnmower unleaded supply into the tank, it still wouldn't start because I'd flattened the battery. Oh how I laughed.

After I'd got it started again I iterated a bit between the CO2 screw and the idle speed screw until it was about right, but by then it was warming up, so I can't say what it's like from cold yet. But on the road, in this pre-warmed state, it drives perfectly. No hesitation at all when pulling away, no roughness under a trailing throttle, and nice smooth acceleration everywhere. So far so good.

I should have set the fast idle speed screw while it was warm, but I'd had enough by then, and it's an awkward thing to get to. So next time the engine's cold I'll see how well the choke works, and then when it's warm again I'll set the fast idle screw. I know the screw engages with the stepped cam at the right points (another adjustment that I'd made earlier and forgot to document), but I don't know whether the fast idle rpm is set properly yet.

Ran out of petrol...you couldn't make it up.. LOL

Your results are most encouraging.
Hats of to your diligence.
Is there a possibility you could condense what you did into a list?
With some parameters please.

Yes, that's a good idea. I'll do that in parallel with giving my 'normal' carb the same treatment. I've had a quick look this evening and it's clear that the fast idle cam isn't setup properly - that probably explains why it's always been a bit hit and miss. I recall that some of the levers were a bit bent when I fitted the service kit a couple of years ago, and all I did then was bend them back into the right approximate shape. I now realise that the position of all these rods and levers is quite important.

I can finally come back to the original purpose of fitting this 'test' carb - which was to run my new plastic parts for a while to see how they perform. I'm happy that the stage 2 throttle piece works as intended, and the adjustment of the u-bracket around the short lever is something that would need doing even with an original part. I'm slightly less happy about the remaining lash in the choke piece, since this compromises the stability of the choke flap during the warm-up period. From what I've seen it doesn't 'flap about', but when the manual says to set the gap to 2.5mm +/- 0.2mm then the lash really ought to be less than 0.2mm, which it isn't. I think a couple of turns of PTFE tape around the spindle would take out the lash, but if I ever do another batch I'll make that hole a fraction smaller again.

I fired it up from cold this morning, and it behaved impeccably. Two stabs on the throttle to set the fast idle, then I turned the key with my foot off the pedal. It fired first time and the revs rose smoothly to a sensible fast idle speed - I haven't checked the rpm but it felt 'right'. I drove off immediately to see how it felt, and it was perfect. No hesitation, rough running or kangaroo juice. And best of all the first use of the throttle pedal didn't kill the fast idle completely as it used to do (when it worked at all) - it just dropped it slightly to a speed that kept it turning over nicely while it warmed up. I drove around for a bit and can't say that I noticed the choke coming off - it just kept running smooth and clean the whole time.

So rather than being a black art I think this shows the value of just setting it up by the book and making sure all the parts work as they should. I'm going to order another refurb kit for my 'normal' carb and do the same to that one.

I think the adjustment of that accelerator pump is the key to curing the hesitation issue. I took the van out for a long drive yesterday, and once it got fully hot I was noticing just a hint of hesitation again. I'd already adjusted the cam to give me the maximum fuel volume (1.175ml, just inside the spec of 1.35ml +/- 0.2ml), so I thought I'd have to live with it.

But by chance, when I stripped down my 'normal' carb (ready for having the body vapour blasted), I noticed that the accelerator pump diaphragm in my 'normal' carb has a much stiffer spring behind the ball bearing.


I thought that was odd, since the one in my 'normal' carb has been fitted to the van and in regular use for a couple of years, whereas the one in my 'test' carb had only been fitted a year ago and the carb had never been used until my recent testing. So I removed the diaphragm from the test carb, and I noticed a bit of delamination in the rubber too.


I don't remember where I bought the refurb kit that I put on the 'test' carb, but I guess they're not all created equal. I guess the ill-fitting needle valve should have been a clue.

I fitted the diaphragm from my 'normal' carb into my 'test' carb, and rechecked the accelerator pump. With the same cam setting that previously gave me 1.175ml per stroke, I now got 1.58ml per stroke - a third more. So I adjusted it down to about 1.4ml and reinstalled the 'test' carb into the van. Took it out for long enough to get it hot and the hesitation has gone completely.

So if your engine seems to hesitate, or has a flat/dead spot, when pulling away from stationary, I'd definitely recommend taking a look at the spring in the accelerator pump diaphragm, and trying to get the fuel volume close to the centre of the spec. For what it's worth, the two refurb kits that I've just bought from Brickwerks were not only cheaper than anywhere else but they also seem to have good strong springs in those diaphragms.

Hello all

I’m still having problems with the choke on our T25! CJH’s lever fitted and works fine; it now appears that the Bi-metal choke unit (Pierburg part no. 4.07262.54.0) is only working intermittently. Does anybody have one for sale, please, or know a likely source of one? Thanks again!

Ian.

Take off the housing and heat the spring with a hair dryer
https://youtu.be/v0zY8Mi3ZH8" onclick="window.open(this.href);return false;

If yours does this then it's ok
with springs they cannot be "intermittent"

Where is the suffix letter on the carb body positioned?

What are the significant differences between suffixes?

025 129 015 A is the early carb and H and J suffix are the late
Minor changes in jetting from early to late, also some other small differences, hole in choke flap for example, looks like a different float and needle valve in at least some earlys I have read.

kevtherev wrote: If yours does this then it's ok
with springs they cannot be "intermittent"

But the electrical connection to the heater element can be.
Does it take too long to come off choke sometimes?
Or is it failing to apply choke from cold?

itchyfeet wrote:025 129 015 A is the early carb and H and J suffix are the late
Minor changes in jetting from early to late, also some other small differences, hole in choke flap for example, looks like a different float and needle valve in at least some earlys I have read.

Would you consider the parts interchangeable?

My gut feeling is yes top and base could be swapped from different versions but I never tried it.

What are the commonly used torque spec for the three carb clamp down nuts?

I followed CJ's adjustments to the letter and have removed my carbs hesitation, stalling on pulling away.

All that's left is a little flat spot/stutter at 2500 rpm.
This happens on gas too so ...I'll be dismantling the distributor later