Weber experts - Plea for help

[Super_Rich_Bernie]

Driving along some favourite road, on a sunny sunday a couple of weeks ago, just when I wanted the car in the rudest of health it decided to play up.

 

As soon as the revs reached 3500rpm a misfire set in. A quick check in a layby revealed that all wires were secure, and the carb jets under the little brass cover were all clear.

After a slow trip back to London I investigated a bit further and found that one of the venturi (the one in front of the main choke tube, first one in from the air cleaner) is loose.

 

There is a grub screw and locknut under the carb which looks like it secures this in place.

 

Questions are:

 

Is this grub screw all that secures it?

 

Can I just tighten it up, or do I need to align it somehow?

 

Would this cause the misfire above 3500rpm? I can't see anything else wrong. And if so will it have caused that cylinder to run without mixture - or could it have meant that the cylinder was flooding with fuel? If the latter I guess an oil change is in order.

 

Any help appreciated. I have been away a few weeks and would like to get the car sorted for the Lydden Trackday.

 

thanks

 

 

Jonathan

[Roger King]

If the venturi rotates, it stops the main jet on that cylinder from supplying fuel. This is not a problem at lower revs and throttle openings because you are running on the slow run jets which are not affected.

 

On the face of it therefore, you have identified the problem correctly.

 

You will need to retighten the locking screw and nut (if they haven't been lost), but it is important to line the venturi correctly before doing so.

 

Remove the locking screw and look up the hole with a mirror. The venturi has a small depression in it at one point that lines up with the hole. Rotate the venturi until it comes into view. All you need to do then is refit and tighten the locking screw and nut. Check the others too!!

 

The above assumes that you have 40s and not 45s which are a bit different (two locking screws and no lock nuts) and really need lockwiring.

[Super_Rich_Bernie]

thanks Roger - sounds like I'll be raiding Sara's make up bag for a suitably small mirror.

 

Jonathan