Hi list, my car hesitates when I accelerate from standstill and then picks up speed after slight coffing. I have carefully regulated and restored the carbs but I can't free my car of this problem. I installed new pump seals for the accelerator jets and tested volume correctly. My question is could this problem be due to low pressure from the fuel pump...? Thanks, Enrique
Mechanical Fuel Pump Pressure vs Accel Jets
- Thread starter RIQUE
- Start date
Malc
Well-Known Member
Hi Rique,
From what I remember the mechanical fuel pump is very suseptable to air leaks, especially on the suction side from the tank.
In addition:
Check that the diaphram is ok
Some pumps have a built in microfilter which can get blocked.
Some pumps the built in valves can wear badly.
The above might be causing your fuel delivery problems.
HTH
Malc
From what I remember the mechanical fuel pump is very suseptable to air leaks, especially on the suction side from the tank.
In addition:
Check that the diaphram is ok
Some pumps have a built in microfilter which can get blocked.
Some pumps the built in valves can wear badly.
The above might be causing your fuel delivery problems.
HTH
Malc
Honolulu
Well-Known Member
Don't think it's the pump
obviously your carb fuel bowls have enough fuel to run, so they ought to have enough fuel to supply the accelerator pump.
I would look into ignition timing first, followed by raising or lowering mixture richness.
This requires, of course that your plugs are good and point gap and dwell (which inter-relate) are properly set.
obviously your carb fuel bowls have enough fuel to run, so they ought to have enough fuel to supply the accelerator pump.
I would look into ignition timing first, followed by raising or lowering mixture richness.
This requires, of course that your plugs are good and point gap and dwell (which inter-relate) are properly set.
Malc
Well-Known Member
Rique,
Have you checked all your fuel lines for kinks, flat spots, other damage, and holes?
Have you checked the pickup in the tank? There is often rust and "crud".
Malc
Have you checked all your fuel lines for kinks, flat spots, other damage, and holes?
Have you checked the pickup in the tank? There is often rust and "crud".
Malc
Two other things to consider:
1. The ignition coil. My CS (with Zeniths) would cut-out/cough between 3-4k rpms when accelerating. Replacing the coil fixed this.
2. If running with Zeniths, they had a tendency to warp at the bottom of the carb where they mate to the insulating gasket. Flat sanding this usually helped.
1. The ignition coil. My CS (with Zeniths) would cut-out/cough between 3-4k rpms when accelerating. Replacing the coil fixed this.
2. If running with Zeniths, they had a tendency to warp at the bottom of the carb where they mate to the insulating gasket. Flat sanding this usually helped.
blumax
(deceased)
Hesitation at take-off--another possibility
pull the airbox--engine off with warm motor so flaps in carbs are fully open--press throttle linkage--do you see the little injectors--one in each carb spraying nice uniform delivery of fuel into carb throats--these little guys are key to a smooth launch and if clogged or not correctly aimed into the primary throats they can cause the symptom you describe. If not done--and most kits do not include same--I would replace them with new ones
If you plan to remove them to clean, adjust or replace--BE VERY CAREFUL--DO NOT DROP SAME INTO CARB THROATS--they are brass and can drop all the way into intake manifold and magnet won't help in retrieving same.
BTW--similar vintage early 1970's MBZ 250 and 280's were carbed with same Zenith carbs--MBZ dealers did have spares available at much friendlier prices than BMW.
HTH
pull the airbox--engine off with warm motor so flaps in carbs are fully open--press throttle linkage--do you see the little injectors--one in each carb spraying nice uniform delivery of fuel into carb throats--these little guys are key to a smooth launch and if clogged or not correctly aimed into the primary throats they can cause the symptom you describe. If not done--and most kits do not include same--I would replace them with new ones
If you plan to remove them to clean, adjust or replace--BE VERY CAREFUL--DO NOT DROP SAME INTO CARB THROATS--they are brass and can drop all the way into intake manifold and magnet won't help in retrieving same.
BTW--similar vintage early 1970's MBZ 250 and 280's were carbed with same Zenith carbs--MBZ dealers did have spares available at much friendlier prices than BMW.
HTH