3.0CS car bogging down at around 4k rpm

[Dick Steinkamp]

I had a weird situation with my Webers. One day getting on the freeway, the car was accelerating hard in 2nd or 3rd gear but would suddenly start bogging. I could repeat the problem. I had good fuel flow and was confident with the ignition system so I pulled the tops off the carbs, The needle that controls the fuel flow into the carb has an actual spring loaded needle on the tip that, I guess, helps control flow into the carb over rough roads. I have the same thing in the carbs on my old motorcycle. With one carb, that spring loaded tip was stuck in the extended position. This effectively lowered the fuel level in the float bowl to the point that the jets would be uncovered under strong acceleration and that carb would stop working. I freed it up, then disassembled and cleaned both carbs. On these carbureted engines that aren't operated enough, the fuel evaporates and leaves a varnish like residue that can clog things up.

 

[bluecoupe30!]

I experienced a "hiccup" at highway speeds, checked everything again and again. Traced problem to gummed up mixture screw on back carb. Was so ineffective that the turns of the screw did nothing. Removed carb, chased/cleaned the threads in the base of the 32/36, reassembled, re set. Problem solved and has never idled so strong. Hiccup gone.

 

[JAB]

I recently had a 123 distributor installed and am experiencing the exact same issue. At 2000-3000 RPM I get a misfire and the car hesitates and stutters. Idle is fine and above 4000 RPM is fine. We also rebuilt the zenith carbs at the same time......so don't know if it's a timing issue, carb issue, spark plugs/wires, of fuel issue.

 

[Arde]

... (ALL cars run on good used parts )

That is really a great point!

 

[JAB]

I recently had a 123 distributor installed and am experiencing the exact same issue. At 2000-3000 RPM I get a misfire and the car hesitates and stutters. Idle is fine and above 4000 RPM is fine. We also rebuilt the zenith carbs at the same time......so don't know if it's a timing issue, carb issue, spark plugs/wires, of fuel issue.

 

[JFENG]

Late to the discussion: how you’ve already solved the issue.

if the engine is misfiring when you try to go over that 4000rpm ‘wall’ then I’d do the obvious ignition checks: gap too big, bad coil, iffy condenser, arcing in the cap, old wires/connectors shorting to the head etc.

If the engine runs and sounds ok but simply won’t go over 4000rpm, I’d suspect an over rich condition (carb jetting). If you hear pinging (preignition) a you try to go over 4000rpm, they you’re prob too lean (carb jetting).


I hate to sound like a broken record but I think $200 for a wide band AFM is one of the best investments in tools you can make if you have old cars with carburetors, or old FI without O2 sensors. It will not only save U lots of time and $, but you’ll be almost as popular amongst your classic car pals as if you had a trailer. $200 for an AFM is relatively cheap in the grand scheme of things … about the price of a good floor jack or set of wrenches.

Ignition is relatively easy to setup and check on stock E9’s with a adv type timing light. Carb and old FI adjustments are much harder and fewer shops are good at it. (And not that many were actually really good even back in the day).

 

[Breiti]

I'm totally da cor with @JFENG .
You can install the gauge hidden if you don't like the not original look.
I already done that at my Mercedes and I also will install on in the e9 as well.

If you use a2 channel system, it will be easy to tune in each carbs or determine the problem down to 3 cylinder.

Breiti