Poor running once warm

Well, I finally got time to take it out for a spin last weekend but something was not quite right.
Starts OK, ticks over nicely. As it had not been out in ages I took her out on the short stretch of motorway for a few circuits, nothing mad just a steady blast up and down. I was then going to drive to my girlfriends house, but it started to hesitate and and judder when accelerating. It is very embarrassing and kind of takes the shine off driving it.

It has new fuel lines and filter (less than 100 miles ago), the coil was replaced just before it was last used (Oct 2006). I think the leads are new also. I just fitted EI and set the timing. I set it to the right hand mark on the flywheel housing.

Any ideas/suggestions?

The single most likely cause is something in the carburettor causing a blockage of the jets - putting new fuel lines and filters in stops new crap getting in there but it doesn't clear out what is there already.

Take the jets and emulsion tubes out one at a time (so you don't mix them up) and give them a good clear out (blow through them, hold them up to a light source and see if you can find anything - then shine a light down the tube they come out of and make sure there is nothing sat in the bottom.

If it only happens when warm it will be because the fast idle circuit hides the problem while the engine is cold by providing an extra flow of fuel.

If it only chugs when you first hit the accelerator then it could be your accelerator pump is at fault - either the diaphragm itself has perished or the fuel circuit is partially (or completely) blocked.

If the problems persist after giving it a quick cleanout you need to buy some carb cleaner and follow the instructions on the can closely and keep doing it. The cleaner does work but it can take several tries and you might have to go through the jet cleaning process a few times.

If the accelerator pump has failed or you have to open the carburettor up to really clean it then you will have to buy in a service kit (they come in several parts so you need to get just the bits you need otherwise it can get a bit pricey), thankfully the kits should be pretty easy to obtain from Weber specialists like Southern Carburettors. Typically you will need the basic service kit which is the main gasket, accelerator pump diaphragm, a few seals and adjustment screws. Jets and emulsion tubes come seperately as does the float chamber parts, internal filter, etc.

If you don't feel comfortable pulling the carburettor apart get someone else to do it for you (an experienced old-school mechanic preferably) as it is tricky, requires a degree of knowledge and it is pretty easy to mess the settings up.

Ignition timing could still be playing a part but generally the problem would be more prevalent - still best to check the timing (use the marks on the flywheel for total accuracy). It is also possible that the cam timing is off, just 1 tooth difference won't feel noticible until you try to accelerate hard and then it will struggle.

Thanks Jimbro
I'll give it a try.
Dave

Did you cure the problem? I had a similar thing on an X1/9 I owned many years ago and it was down to a heatshield between the exhaust manifold and carb having rusted almost to nothing, causing the carb to get too hot. It's an easy job to replace and I'd certainly look at this before stripping the carb (which you've probably done by now!). I doubt the shield is obtainable any more though.

Hi Mark
No, I have not sorted the problem out yet. In fact I have not been out to it since.
I think the shield you mention is tossed. It was on my other one. I have a brand new one from a few years ago.
Thanks for the suggestion.
Dave

This is what killed my last X, at first i thought it was carb problems, but then a cylinder valve blew so i never found out what it was, very embarrasing driving along at 60-70 with engine burping like your gona stall it

should there be a metal heatshield on the exhaust? If so I am missing my one

There was a heat shield fitted originally but I've never yet seen one that still has it unless restored to concours condition