2010 at the Hammond Barn

[Phil Waterman]

Originally Posted by Bob Carriere

Encountered a slight technical difficulty on SUnday while driving my C15a chassis.

AS you know Rob and I have had our stock Rochester B carburators rebuilt and flow tested by the Oak brothers in TO. Both our vehicles now run so ever much better...... and they look brand new.

Well I was driving mine in the back field using just a fast idle setting when I decided to see if it would climb the steep...45 degree... pile of wood chip located in a corner of the back field. Amazing.... in low gear.....few times and noticed that at a steep angle the carb was flowing raw gas ...literaly dripping gas...... not a good thing if all those fumes could collect inside the engine compartment......did not seem to affect engine performance...

I raised my problem on the Stove bolt site and CarbKing confirmed that I may have exceeded the design of the civilian Rochester B carb which is intended for flat street driving. .... He recommended sourcing a military carburator that would have been original on a GMC 270 engine.

Phil have you had any similar experience with your new 261/Rochester combo?

...
Bob

Hi Bob

Interesting issue, maximum angle of operation for Rochester B Carb. First I'll have to do some checking in Chev parts book remember seeing that 261 engine was fitted in heavy 4x4 Chev trucks. I'll look to see if a different carb or float setting is listed.

I have another NOS B Carb on the shelf I'll hook it up to the electric fuel pump and see what happens at various angles. Problem may be something stupid like that the current electric fuel pumps put out a little more pressure than the stock manual pumps as originally equipped. I'll check numbers but I think it is putting out 2-3 PSI more than needed.

Did discover something that you may want to take into consideration if you are going to operate your 261 at extreme angle, keep an eye on the oil pressure. Discovered recently that my 261 at full song going down the highway is pumping so much oil up into the engine that if you hit the brakes going into a sweeping left hand turn the oil pressure will suddenly drop from 42 PSI to under 5 PSI momentarily.

I have the 261 4x4 sump oil pan but it doesn't have the lower baffle found on the military 216. My surmise is that when you hit the brakes and turn left the oil sloshes forward away from the oil pickup allowing it to suck air for a moment. This doesn’t show up on the normal instrument panel gage which are slow reading due to their small tube size on my CMP with the standard 216 oil gage that reads 0-30 SI it is pegged almost all the time. I installed a second fast reading pressure gage which reads 0-80 PSI this one shows the pressure fluctuations. Got to do some more research on this issue.

I have done some studies on what grade and side angles the original 216 systems could work at, I’ll have to put the pictures and notes together and post them.