engine and drivetrain Car "Chokes"

[Utah02]

Hey guys,

I've got a problem with my 02. So when I'm accelerating and hit about 3500 rpms, my car becomes noticeably slower. I have a constant acceleration then it hits that point and takes nearly twice the time it would take to increase 500 rpms. Then when I hit about 4k rpms it won't accelerate any more. 90% of the time at 4k rpms it will "choke" too. It's almost like it loses all power and decelerates. It does that for about a half second and then works it's way back up to 4 and does it again. It can also do it when I'm accelerating fast and dump the clutch and apply a lot of gas. It will choke for a second and then begin to accelerate. Is the engine losing fuel for a second? It's like it's starving. I have a weber 38/38 carb on an e21 m10. Could it be the carb is too big for the engine? Should I switch to a 32/36 carb?

Thanks for the input

Utah02

Edited May 5, 2015 by Utah02

['76mintgrün'02]

It does sound like a fuel starvation issue.  There is a screen on the pickup in the tank which could be clogged.  The lines which come out of the tank were originally cloth covered hoses, which can have cracks under the cloth and allow air to be sucked in.  If they are cloth, replace them with new rubber, for good measure.  I assume your fuel filter is clean, but that could be a fuel limiting factor.  The pump itself could be unable to deliver sufficient fuel, I suppose.  There is a small screen behind the inlet on the Weber, which you could check.  

 

Aside from those things, the float level and proper jetting come to mind.  I dunno tho.  Just trying to help.

[Hans]

I'd start with the gas tank/pick-up strainer. Shien a flash light in the tank to look for crud.Either get anew sealer ring or let teh old one sit for 24hrs

[Mike Self]

check that your accelerator pump is functioning properly.  With the engine off, look down the carburetor throat while quickly opening the throttle by manually moving the accelerator linkage.  You should see a squirt of gas emerge from a nozzle or orifice in the primary barrel.  No squirt = malfunctioning accelerator pump and probably a bad pump diaphragm.  Easy fix--check archives for how-to's, which will depend on whether you have a Solex or Weber carb.

 

mike.  

[Buckeye]

Give this a shot.

Remove secondary idle jet, clean orffice and matting hole with carb cleaner. Put back together,go for drive and let us know

[AustrianVespaGuy]

That definitely sounds like an issue with the main jet circuit, so I would start there.  If the car idles OK, probably nothing wrong with the float levels or idle jets.  Could also be a blockage problem that ends up starving the car of fuel for sure, but I also doubt that this problem would be due to an issue with the accelerator pump circuit.  Accel pump only does anything when the pedal is actually moving: if you've got your foot down on the floor from 2k up to 3.5k rpm, the accel pump isn't doing anything anyway.  Last possibility is if there's a problem with your distributor timing and it's not advancing properly, but I think this very unlikely compared to the previously mentioned fuel issues.

 

-Carl

[dlhoovler]

What if there's a rev-limiting rotor in the distributor that's malfunctioning in some way? Is it possible for one of those to fail such that it cuts out fuel at a lower RPM than spec'd?

 

-Dave

[Chris_B]

It would help if you described how/when this behaviour started (e.g., did you buy the car that way; did it start after the car sat for 5 years; or did it just suddenly start behaving that way...?). Are you saying that when you are driving, the car simply won't accelerate beyond a certain RPM (in which gear?)? No, your carb is not too big for your motor.

 

Carbs have float bowls in them to prevent fuel starvation when the demands for fuel increase, such as in the situation you describe. If your carb is in gross condition (if the car sat for years and years, or you somehow got dirty fuel that managed to make its way past your fuel filter, the filter in the carb, etc.) you might want to be pulling and inspecting your jets and looking inside the carb. If this is just a momentary pause, at 3-4K RPMs it could well be being caused by the transition between the idle circuit and the main jet circuit, but that is usually not so pronounced.

 

Also, check your fuel pressure at the carb- should be 3-4PSI.

[Utah02]

It would help if you described how/when this behaviour started (e.g., did you buy the car that way; did it start after the car sat for 5 years; or did it just suddenly start behaving that way...?). Are you saying that when you are driving, the car simply won't accelerate beyond a certain RPM (in which gear?)? No, your carb is not too big for your motor.

 

Carbs have float bowls in them to prevent fuel starvation when the demands for fuel increase, such as in the situation you describe. If your carb is in gross condition (if the car sat for years and years, or you somehow got dirty fuel that managed to make its way past your fuel filter, the filter in the carb, etc.) you might want to be pulling and inspecting your jets and looking inside the carb. If this is just a momentary pause, at 3-4K RPMs it could well be being caused by the transition between the idle circuit and the main jet circuit, but that is usually not so pronounced.

 

Also, check your fuel pressure at the carb- should be 3-4PSI.

I went ahead and switched to a 32/36 carb and it still bogs. In every gear right at 4000 rpms. Thought it could be a rev limiting malfunction so we switched from pertronix back to point and after even switched the distributor all together. Not the carb. Not the distributor. Not the fuel pump. Not the timing. Not the ignition coil.

I purchased the car like this. Wasn't expecting it to be too difficult but here I am. Stumped.

What if there's a rev-limiting rotor in the distributor that's malfunctioning in some way? Is it possible for one of those to fail such that it cuts out fuel at a lower RPM than spec'd?

 

-Dave

I swapped out for a working distributor and it didn't seem to work. That thought came to mind.

[Chris_B]

That was helpful. Wow. Would you pls describe this "bog" in a bit more detail?

 

Probably time to fall back on the basics: fuel pressure; compression check;  Charging system (system charge state); valve adjustment; the rest of the ignition system (wires, plugs)...