Adjusting a pair of Weber 45s on VX

[Marius]

Some days ago I checked the spark-plugs of my modified 16v VX running on 45s Weber. I found that plugs of cylinder 1 and 3 were fine (brown) but cylinder 2 and 4 showed signs of coal. That should mean that the left part of each carb runs little too rich ??? Can I cure it by just turning the idle-mixture of the left part of the carb clockwise (weakens the mixture) or is it more complicated than I thought ????? Yes I know, TB´s are much better but still on my "TO DO"-list....

 

Thanks for your help !

Marius

 

[CHRIS CLARK]

Marius.

 

I have limited experience with these carbs (I'm on 'K' injection), but what I have found tuning other peoples is that the std. set up as supplied (normally) runs as yours does. You can only tweak the IDLE mixture so unless you spend all your time at tick over you are governed by the jet settings as supplied. Isn't there something to do with length of inlet tract too that can alter the required set up? By this I mean different jets for inboard & outboard on the same carb.

 

My thoughts are that you have an engine designed in the 80/90's running on carbs designed in the 30's (?). Bound to be some compromise!!

 

Think the above is right. If not I'm sure someone will correct me. Good Luckthumbsup.gif

[AndreK]

Maruis, I have a Vx with twin Weber DCOE's but it is the 1600 Classic, so they are smaller size. Tuning should be similar though. It may be best to start from scratch by balancing the carbs first.

You can either listen using a tube, ie stethoscope or piece of 6mm bore tubing or use a proprietary gauge (synchrometer). The aim is to get both throttle pairs on the two 'carbs synchronised. It is also possible to do this by unscrewing the cover to the progression jet holes, just behind the mixture screws and looking to see that the throttle butterflies are at the same position for both carbs. I found this less accurate though, and tricky, as the holes are very small.

To balance them, look to see which is the 'lead' 'carb and adjust the idle speed screw, 'throttle stop' (not the idle mixtures!)so that the engine is idling at say 1100 rpm, engine must be fully warm first. On my Vx Classic the left hand 'carb is the lead, the right hand throttles are connected to it. Then, using the tube or what have you, listen to the hiss from the trumpets on that 'carb and adjust the connection between the two 'carbs to make the hiss from the other 'carb's trumpets the same. This isn't a perfect science! The throttle butterflies in each carb work together on these side-draught webers, so you shouldn't notice much difference between the trumpets on a particular 'carb.

Having got them balanced, you can now adjust the four mixture scews one by one, in the directions you suggest, ie unscrew anticlockwise to richen, screw clockwise to lean. It is easiest if you have access to a large scale tachometer, rather then using the one on the dash. What you are looking to do is to set each idle jet so as to give the fastest idle speed, or as close as you can. You will need to go through the process of idle adjustment at least twice, getting nearer each time. Also, if the speed gets above 1200rpm or so at any time, re-adjust using the lead 'carb throttle stop only. finally when you are happy with the idle jet settings adjust the tickover speed back to 900-1000 rpm as you wish.

I hope that I haven't confused you so far. Part of this procedure is described in the Caterham Assembly Manual. On the www there are also sites eg Alfa Romeo Club of Oregon, Triumph Sports Car Club of America and others that give their variations on this method. Good luck, but be patient! thumbsup.gif Or there is always a rolling road and Sun Tune if you have the DM's!!!

[StewartG]

The colour of the plugs is determined by the idle jets if your plugs look black screw in the idle jet. Black plugs don't mean the engine's running rich just that it's idling rich, all you see when you take the plugs out is how the engine was running just before switch off, usually at idle.

[captain chaos]

Marius,

Stewart is right, the only way you can try to see how the plugs are running under normal conditions is to do a plug 'chop', which is to cut the ignition whilst the engine is running at say 3/4,000 rpm. Once again, this is not exact science but being a little rich at idle, particularly on just two cylinders, can be quite normal on some engines.

If someone with expert knowledge picks up this thread could they also comment on the set up of fueling, in particular, are some cars set up like alot of bikes where the inner two cylinders of a straight four often have different main jet sizes?

 

Thanks

[CHRIS CLARK]

Or................just fit a V/X (or'K') injection and forget about it and just drive!!!

[Marius]

Thanks guys, your comments stated what I thought about the thing, phhuu, relief! I´ll try to get the idle-mixture sorted today and will let you know the results of playing with the idle-mixture. I´ve got a balancing-tool for the carbs but it´s not this easy to use as the engine has to run on idle-speed of around 1.400rpm, exhaust-note makes it hard to hear the intake-hiss. I can´t put it on the rollingroad yet as I´m still about to run in the engine, would not be too wise to spend huge amounts on a setup when it´s not able (or allowed) to rev freely yet. I´ll definitly dump the carbs this year for TB´s, anyone a cheap pair of 45´s ???

Thanks again for all your friendly advises!

 

Marius

[Glenn Wheeler]

Before you start adjusting anything, make sure all the holes in all jets and tubes are clean, even with filters in the fuel line the holes can get partially blocked making fine tuning of carbs almost impossible.