Quote from: Alan Drover on Sep 08, 2023, 02:46 PMZenith every time. My 2.5 runs extremely well on my Zenith 36IV which has Solex stamped on the float chamber. It's the original carburettor that was factory fitted.
Webers strangle the engine in the misbelief they deliver better fuel economy but to make any decent progress you have to keep your foot flat on the floor. With mine once I 've got to the speed required I can back off and drive on a light throttle.

My 2.5 engine still has a weber as factory fitted- ETC6350 and runs very well, I was told these were standard on the 2.5 engine when fitted to early 110's
I think this is a much better carb than the much cheaper weber as seen on many 2.25 S11 engines

Quote from: Alan Drover on Sep 11, 2023, 11:50 AMI can't think of anything else that would cause that problem unless the air bleed screw pointed end is damaged.

Attached is a pic of the screw. The one on the left is the new one that came with the kit.  I opted to reuse the original one because it looked okay to me and the new one had a different configuration.

The second pic shows the new one at the top with one from a donor carb on the bottom.

Perhaps I should try the new one.

Quote from: diffwhine on Sep 11, 2023, 12:19 PMO ring quality? Breaking down due to ethanol content? That could create the same effect.

Hmm... used a brand new O-ring when I rebuilt it back in August 2020.  Unless our gas station is sneaking ethanol into the gas I don't use gas with it in it. 

But... I don't trust our gas station either. Unfortunately it's the only one around for 20 miles.

Try the new screw very carefully. The original looks though it might have a groove near the point but can't be sure.

Quote from: Alan Drover on Sep 11, 2023, 07:33 PMTry the new screw very carefully. The original looks though it might have a groove near the point but can't be sure.

Out of ignorance... why "very carefully"?

So you don't damage the point when it has gone in as far as it will go.

Quote from: Alan Drover on Sep 11, 2023, 08:44 PMSo you don't damage the point when it has gone in as far as it will go.

Gotcha.  I thought maybe something due to design.

In the Zeniths I've rebuilt I haven't yet found a carb body that the new air bleed screw fits into. The new screws all seem to be the wrong thread to me.
I always end up using the original again.

Craig.

Well... we are waiting to see what happens. Found out what the timing issue was... the nut used to clock the dizzy in position was loose. Before messing with the carb we thought we'd check to make sure the timing was better first.  Engine fired up immediately and idled very well for over 20 minutes and the RPMs were right at about 525-550.

No that that's taken care of I'm going to wait ans see what happens.

We did look at the screws again though. So.ething just doesn't look right about the new ones.  If the carb starts running rich again we will try one of them.

Is there a way to tell if the screw's spring could be worn out?

So here are my further trials and tribulations with the new carb.
I fitted the Britpart zenith carb.  Nice easy fit and install as it goes the same was around as the old weber.

Started first time without any adjustment
Played with the idea mixture screw to get a lovely smooth idle
First test run - amazing! landcover pulled like a train - nice smooth transition from no throttle to small opening.
No heat soak or vapour lock like the weber - so very pleased.
After a day or so idle started to falter and revs dropped. Tried to compensate with idle speed screw but idle still really lumpy.
Played with the idle mixture screw but now it seems to do very little - idle is really lumpy and engine seems to be rich. Pulled out the mixture screw and gave it all a blow through  - no change
I have closed the garage door for another day as the frustration is getting to me
I can already hear some of you saying "I told you so about Chinese copies!" However, it was running unbelievable smoothly for a day
If you have any sensible suggestions then please let me know
Frustrated of Essex
Steve

Send it back. I had similar problems with a nasty Chinese Zenith and returned it to the supplier. I fitted an old Zenith I had lying around and all was ok again.
I've now had a BFS remanufactured Zenith on the 2.5 in my Series 3 for about 13 years now and once set up it's never needed adjustment.

I'm afraid I've had the same issue as well. Starts off well and then pretty much unusable within a few days. Throw it back at the supplier...

Seems odd that it would go wrong after working properly - and it was perfect
Must be dirt/swarf in the idle circuit
Steve

I think you will find that of you pull it apart, it will have warped. As it cools it sometimes comes back into shape, but they just don't seal properly. You can get the odd good one, but not worth wasting time on in my view. You can tell by the price. £60 for a carb from Paddock. How do you make that and make a profit for that sort of money?

My cheapo Chinese junk one never worked properly at all.
Don't pull it apart, get on to the supplier and insist on your money back as a replacement will likely be just as bad.