Boxer carb tuning

I guess this runs on from the compression test thread but is different enough to be warrant a new thread.

I have been setting up my 365 Boxer carbs and used the Daytona procedure in the 'Technical Articles' section. Using a 'Uni-Synch' type meter I have balanced each choke on a carb to pull the same flow of air and then balanced each carb to be equal on each cylinder bank, and then finally balanced each bank so that all four carbs were pulling the same amount of air. On my guage this was showing as 3.5kg/hour at a tickover over 900rpm.

I then used a Colortune plug to set each barrel's mixture. Finally, I reset the balance on each choke of each carb so that the whole system was again balanced.

The car runs great and a test drive shows no problems.

Then I remembered JRV's advice to check that no fuel was being pumped into the cylinders when the ignition was on but the engine was not running. I took the air filter covers off and checked this.

To my surprice the chokes on cylinders #3 and #9 where both had fuel dripping in to them with the ignition on and teh engine not running.

So I gues that the float level needs setting on these chokes. What is the correct setting for the floats on these cars - the manual shows 13.5-14.00mm without the gasket, but I know the manuals are notoriously unreliable in this area.

Is it just coincedence that it is the same cylinder on each bank that has this problem?

Any comments or advice welcome.

My BB manual states 13.5-14 mm, in TWO different places......hence, probably correct. Check the mm on a float where the carb does not leak, and compare.

If the float is set there, then possibly bad float (filling with gas), or bad needle and seat.

Simon,

OK ....yes it's imperative to check for dribbles. The other thread I was writing on had different carbs though. The dribbing can have two root causes. Your particular problem I would suspect based on your description is an ACC Pump check valve sticking problem or ACC Pump actuator rod lenght improperly set.

Do you have the Float Gauge Tool and the Injection Quantity Tool?

Even without, stroke the trottles to check for Injection Acuation and Shut Off throat by throat to see if there are differences.

HTH's

Simon,
On my 365, I set the float levels to 13.5mm, using a Weber reference tool which bolts to the top of the carb, once the cover is removed...

The two barrels you reference do not "share" float bowls with the adjacent cylinders, so the needle valve float concern is real. On these carbs, the float are brass, and usually don't sink. The needle valves, on the other hand do tend to stick and wear out over time. I had a problem with fuel leaking into the barrels after shutdown, without the uel pumps running. I believe JRV is referring to the accel pump check vavles which secure the pump nozzles into the carbs...I have found the check vavles to stick (remove and shake...should hear tiny ball rattle) or that they are just loose. Try to wiggle a pump nozzle with your finger (no need to disassemble to check)...If the nozzles seem loose, hot fuel will seep between the copper gasket and the nozzle...and untimately into the motor. Simply remove the carb top cover...and clean/replace/secure as needed...

I have hard parts for these carb, if you need anything....


Regards,

David

Spot on David. Loose Acc pump valves. A quick tighten with a screwdriver seems to have cured the probblem. Interestingly enough quite a number of the others were slightly loose also. I must keep an eye on these in the future but for now I have no more drips, hot or cold.

What a great place this board is :-))

Excellent...Glad to hear you're all set.
Now, if I could just get my carbs set up properly!
Seems in the midst of tuning (and with a zero hours engine rebuild) she just fouled a plug...

This truly is a great board..Real people, real car talk...and folks that actually have an idea of what their doing. How refreshing! And no talks yet about "the best" wax!