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Not Ideally Running/ Bad Mpg In My 02

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I have searched the forum many times to try and solve the problems I'm having with my '75. I'm sure someone who's better at navigating this website will get upset at me for posting this, and tell me to look harder. But, I'm frustrated and I could really use some direct answers. 


I'll start with some background: My 2002 is a '75 with all of the emissions gear removed. It has a 0231176059 mechanical distributor, a black Bosch coil, and a Crane xr700 electronic ignition. I'm running a Weber 32/36 DGAV (the one with the water choke.) The engine has stock internals. I'm using Autolite platinum plugs with a .026 gap and Accel 8mm wires.


Now here are the issues I'm having: The engine will not run smoothly cold or when tuned below 1500 RPM, It's running far too rich, My fuel economy is <12 mpg even when I'm driving conservatively, When I turn off the motor after a drive, It shakes violently before sputtering to a halt, the engine misses and occasionally backfires.


What I have already tried: I replaced the cap and rotor, Rebuilt the carb, used the guide offered on how to tune the carb, Set the timing using a light, replaced the intake manifold gasket and used plugs to try and eliminate vacuum leaks, 


Clues as to what may be wrong: When playing with the distributor and carb, I noticed that the engine runs far smoother with the brake booster hose detached, It seems like the motor may be starving for air. The idle is effected when i screw the idle cut off solenoid in and out. I seem to be stuck in a loop: I can't get the carb to run leaner without the engine running rougher, and I can only get the engine to run decently smoothly when the carb is too rich. There's nothing wrong with the choke, during a warm start, I have to put my foot on the gas hard to get it to start. 


Questions I have: What else should I try? Is the engine starved for air? Should I just get a new carb? As far as the brake booster hose, should I remove the valve-type-thing at the end? Would that help? What plugs and wires should I be using? What gap and size should they be? (I want to replace them but I'm not sure what I should use because of the Crane ignition) I've seen some posts about a "shutter wheel" in the distributor, what is that and could that be my problem? HOW CAN I LEAN OUT THE CARB WITHOUT IT RUNNING ROUGH???


To all the '02 experts/master mechanics, I would appreciate any and all insight and suggestions.


Thanks in advance, 


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Some things to check...(sorry if some sound elementary, but I've overlooked some pretty obvious stuff myself!)


1.  When did you last change/clean your air cleaner?  If you're using one of those small chrome air cleaners on your Weber, they get clogged up pretty quickly.  The big factory air cleaners allow far more air into the carb--and are easy to adapt to the Weber with a few minutes work with tinsnips/Dremel tool.\


2.  With a high energy ignition system, your plug gap should be closer to .035-.040 than .026.  And conventional wisdom says that M10s don't particularly like platinum plugs. 


3.  Where did you detach the brake booster hose?  At the booster or at the manifold?  If at the booster or at the check valve, that won't make any difference; that's what the check valve is for (presuming it's functioning and isn't installed backwards).  Didja check for other vacuum leaks?  Unused ports in the manifold?  Loose carb?  Loose manifold?  Bad dizzy vacuum capsule/bad vacuum hose?   Leak in the round plate under the carb on the manifold that once held smog stuff?


Check those and let us know whatcha find...



'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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First of all, thanks for the reply! And don't worry about some sounding elementary, I'm a novice mechanic at best! I'm using the stock air cleaner with an adapter plate. I replaced the air filter anyway though. Unfortunately that didn't help. I replaced the plugs with NGK non platinum ones at about .036 gap. That didn't change anything either. I detached the brake booster hose at the booster and you were right, no difference. (I originally had it detached at the manifold.) I checked all of the manifold ports that I plugged, and none of them are leaking, including the round plate under the carb. (I used carb cleaner and listened for a change in idle, there was none.) The carb is not loose, I did notice that the manifold nuts were not fully tightened, so I tightened them down. That didn't change anything though. So no serious vacuum leaks as far as I could tell. And even if there was a leak that I missed, wouldn't that make it run less rich than it is? That leads me to believe it's not a vacuum issue. Is that logic correct? What do you mean by "Bad dizzy vacuum capsule/bad vacuum hose?" I'm fairly sure my distributor is only mechanical advance unless I'm missing parts. (I can post photos for confirmation if need be.) I'm starting to think the problem might be in the distributor or maybe the ignition? I didn't install the thing myself, the previous owner did. How can I check to see if it's working properly? I also ordered a stock type wire set to replace the aftermarket one. It's coming Tuesday, so I'll see if that helps. The engine has never idled/run very smoothly, but this whole crappy gas mileage/rich running thing has to stop!

Thanks again for the tips on where to start,



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I'd suspect carb , check float height & float valve , for leakage  making the engine run fat.12 mpg is mental rich , I assume it's a 4 speed car not an Auto . Swap carbs with a known good one if you have access . I have a good one for sale from a friends car that went to a single 40 Weber if you cannot find one locally , I'm in So Cal.

1970 4 speed 2002 (Daily driver/track car ) 
1974  Hybrid powered twin cam engine, Pig Cheeks , ( now a round tail.) Getting ready to Sell 

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  • 3 weeks later...

Did you buy the car locally? When you say you have leaned it out I'm assuming you are talking about "best lean idle adjustment" when you timed the car was the ball dancing or stable. If dancing toss the dizzy for a properly functioning unit, was your vacuum advance disconnected. I was getting 25mpg hwy with a 40dfav. Your gas mileage issue has nothing to do with your plug wires unless they are not conducting. What do your plugs look like? If you are running rich then you need to rejet the carb for altitude.

Carb rebuild kit.

Float level. Yes when the floats are up the needle valve closes but is the float open and close measurement to the base correct to maintain adequate fuel.

Valve lash adjustment

Timing, vacuum disconnected 1500 rpm to the ball or 37* total advance at 3500rpm to start. Altitude like a few degrees of advance but back off if pinging.

Best lean idle adjustment. Within 2 - 2.5 turns out. IIRC If not rejet idle. While it is called idle it controls the transition to the off idle circuit as well. Warm. Make sure the water choke is working correctly and opening full. As well as adjusted correctly for cold start.

Plug chop on new plugs.

Then rejet accordingly.

Stock mechanical fuel pump? Fuel lines newer ish?

At our altitude the decrease in atmospheric pressure will reduce a static compression test result by roughly .835

You can do this but it will mean chasing your tail. Might help to contact somebody local who can walk through some of this with you and the car.

Ben in denver has a 32/36 if you just want to see if it is your unit but you need to know if you are properly jetted for this altitude first.

Think more air not less fuel. Usually need larger air correctors

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I dont recognize your distributor as being a "mechanical" advance unit. Take a picture. Maybe you are missing the vacuum pot and are not advancing correctly at throttle. Those more knowledgeable on the board will know about your dizzy.

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.... I have to put my foot on the gas hard to get it to start...


That is part of the design of the carb, to actuate the choke mechanism. If you dont put your foot flat to the floor BEFORE cranking, the choke does not engage. But that does not explain the <12mpg.

Shaking violently when you the turn the key off is normally timing advanced too much, or too hot a plug.

I would also consider taking it to a good garage and getting them to check the CO2 reading of the exhaust, just to confirm your assumptions of rich running. They can also help diagnose timing, carb mixture while they are at it.

Just my thoughts. Beaner7102

1971 - 2002 RHD VIN 1653940. Agave (stock with Pertronix & 32/36 Weber) - "Cactus"

1972 - 1602 RHD VIN 1554408. Fjord (with 2L motor, 5spd & LSD - Weber 40/40 to come) - "Bluey"

1984 - E30 318i VIN WBAAK320208722176 - stock daily driver

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Yeah, you should floor it once before cranking then let off (which will set the chokes) and be ready to give it some pedal as it catches. 


My experience with an old weber is that the throttle shaft wears out, you get unstable idle from air entering via the worn throttle plate shaft.   But that didn't make it run rich, just an unstable idle condition.


Other suggestions include that your fuel pressure may be too high, jets not correctly installed (secondary main in primary position, jet missing or backed out and rattling around in the float bowl, something like that.  Easy enough to check if you take off the top of the carb and then you can verify how the carb is set up.


But get together with someone knowledgeable in your neighborhood if at all possible.  Feed they beer (after they help you with the car) or buy lunch, some appropriate gesture.  It sucks to help someone who only sez "yeah man thanks a lot" then goes on their merry way.

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  • 7 months later...

Thanks for the input everyone, but I got sick of fiddling with that stupid 32/36. I bought a 38/38 instead, and now the motor purrs like a smitten kitten. That is, until I took everything apart to replace all the front gaskets. After that project I'm going to look into the distributor situation and do a final tune on the carb. If things go as planned, I'm hoping to end up with a leak free and perfectly running motor...we'll see how that goes.

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