Why is one idf barrel drawing less air ?

[grasshopper]

Hi all. I have my 40 idf Weber carbs balanced quite well. I am using a syncrometer. One barrel is drawing slightly less air. I've tried everything. I have even backed off the air correction jet. It is the barrel closest to the fire wall. Does it matter if it is pulling slightly less air than all other barrels ?

[AndyVAS]

Check your valve lash. The air flow should be near equal across all 4.

[grasshopper]

Thanks for the reply but checking valve lash may be a little too advanced for me. I was hoping for an easier option,,lol

[SteinOnkel]

You need to match the higher drawing cylinders to the lower one with individual throttle bodies. So you need to "bleed" the vacuum on the other barrels.

But as was already suggested, make sure the lowest cylinder is drawing as much as it can.

How far is it off by? It's never going to be perfect, especially not with this ancient technology.

[grasshopper]

The barrel closest to firewall is drawing slightly less. They are all drawing aprox 5 on the carb sync tool but the weaker one is barely reaching 5 but the guage shows slightly shaky not as steady as the other barrels. Other than that the carbs seem fine.

[SteinOnkel]

5 inches of mercury? That's pretty good. My 11.5:1 CR engine with around 190PSI across the board gets about 5.4 on the lowest.

My carb sync tool has a little adjustment screw to steady out the needles on each gauge. A welding tip inside the hose can also work to dampen the signal.

Have you measured the compression? I bet you that cylinder is slightly lower than the others, in which case it cannot ever match the others perfectly. If they are within 10% of each other, you are fine. That goes for both compression and what your sync gauges reads.

This is why you need to balance the higher cylinders to the lowest. A herd is only as fast as its slowest animal and so it goes with individual throttle bodies.

I wouldn't sweat it too much. Even on my 2001 engine with ITBs (efi) I can only get them within about 3% of each other and that's after hours of adjusting fuel, spark and the ITBs themselves. Does it make one iota of difference in how the car drives? Nope!

Cheers
Steiny