engine and drivetrain Carburetor problems, part deux...or tres

[Mike Self]

Here's the setup: 73 2002 with Weber 32/36, manual choke, M10 with about 20k miles on a rebuild, 9.5 pistons, 284 Schrick. Carb freshly rebuilt, no obvious vacuum leaks (tested with carb cleaner and propane). Correct dwell, timing and point gap. No spark miss; good plug wires. Accelerator pump delivers a nice healthy squirt of gas when I work the linkage. Choke goes completely off when the knob is pushed in.

Symptoms: horrible flat spot when accelerating. From a standing start, unless I rev to about 2k before releasing the clutch, the engine will actually stall. Boggs very badly when I shift gears----and if I let off the gas and then accelerate again. The flat spot nearly disappears if I pull out the choke partway.

Idle varies between 1000 and 1500 rpm, a little lopey but mainly too fast. Haven't messed with mixture or idle speed screws yet.

Suggestions? I'm running out of ideas and V@V is approaching.

TIA

mike

[Guest Anonymous]

Here's the setup: 73 2002 with Weber 32/36

Symptoms: horrible flat spot when accelerating. From a standing start, unless I rev to about 2k before releasing the clutch, the engine will actually stall. Boggs very badly when I shift gears----and if I let off the gas and then accelerate again. The flat spot nearly disappears if I pull out the choke partway.

Idle varies between 1000 and 1500 rpm, a little lopey but mainly too fast. Haven't messed with mixture or idle speed screws yet.

Suggestions? I'm running out of ideas and V@V is approaching.

TIA

mike

Mike:

With respect to your flat spot, I would first 2x check that all jets are snug and clear. This includes idle jets. Next, consider my previous post re: loose or ill-fitted auxiliary venturi. http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,290341/

Respecting your idle, why haven't you messed with the mixture and idle screws yet? Haven't you written a column about this yet?

[jp02ti]

Mike,

if it gets better when the choke is on slightly, then it suggests a lean condition when running. do the plugs support this?

perhaps the fuel pump is dying, or the fuel filter may be clogged? I've heard from several sources that our modern fuel may be eating the stock lines up and creating "goop" in the carb bowls and filters. have you had a peek in your tank recently?

I'd hate to suggest this, but i've heard (from a reliables source!) that most carb issues are actually timing...is it safe to assume that you've checked and re-checked the timing?

Jon

[Gthielen]

Mike,

I second the aux venturi tube alignment...I had the exact same symptoms...but I suspect that you have already checked that. Also, improper valve adjustment can do weird stuff too...

George

[Napes]

Mike;

Maybe you have most of the adjustments too close to perfect. Seems like our cars like to have something a little "off" to run well. :-)

Seriously, hope you sort it out soon.

Bob Napier

[brianstj]

Webers run mostly from the low speed (idle) circuit. If everything else is adjusted as you say, then it is time to follow the low speed adjustment procedure (available from Redline Weber) and get the carb set up correctly.

[c.d.iesel]

your in need of new tiny rubber o-rings for the idle mixture screw,

idle jets, and cleaning the primary side jets and passage ways