Dick R

Strange Jetting for a Single Barrel Weber Carburetor

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The 2002 that I acquired a few months ago came with a single-barrel Weber carb.  It ran very poorly when I got it – it was full of flat spots, wouldn’t get beyond 4,000 rpm, and the plugs read as white as could be. 

 

After going through all the usual suspects (ignition, fuel lines, pump, filters, valve clearance, and compression (all 155-160), I rebuilt the carb, and replaced the accelerator pump diaphragm.  None of that made more than the slightest difference. 

 

Then I started messing around with the carb jetting.  It had a 140 main and a 170 air correction jet.  While there is not much information on this site or other places about jets for single-barrel Webers on a 2002, there was at least one site that sells Webers that recommended that exact jetting combination for a 2002 - 140 main and 170 air. 

 

However, after several rounds of ordering and re-ordering various main and air-correction jets, the combination that worked by far the best was pretty much the opposite of the original  - 170 main and 130 air correction.  It seems to run quite well, willingly going to 6,000 rpm with pretty good power throughout the range.   The plugs (the recommended NGKs) burn a nice light tan.  The idle is good and at the recommended screw settings.  All seems fine.

 

Except that I don’t understand how the jetting could be so different than what the carb is sold with or what one carb seller recommends for a 2002.   One possibility is that there is some kind of vacuum leak.  However, I’ve checked the vacuum and it appears to be quite textbook in operation.

 

While the car feels pretty good, I can’t say that I’ve achieved optimum performance. The last time I drove one of these cars was when I traded in my 1969 2002 back in 1973 (for a 73 VW van in case you were wondering).  Far too many years have passed for me to have any kind of calibrated sense of performance.  

 

I’m just wondering if anyone has any previous experience along these lines or any thoughts about what is going on here.   

Edited by Dick R
punctuation

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If you have a vacuum advance distributor, the pod could be ruptured and that will create a vacuum leak.

It is easy enough to check, if you suck on the vacuum line, you should be able to rotate the points plate... unless it is stuck... like the one I just disassembled.  But you should be able to tell if it is resisting the suction in any case.

Tom

 

 

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I tried the 34 ICH carb on a 1600 at one time and remember that we could not get it to rev to redline. I'm surprised you got it working on a 2.0 L. If i recall there was discussion on these carbs being too small for our application. The Solex 38 pdsi was a much better match.  

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1 hour ago, Dick R said:

The 2002 that I acquired a few months ago came with a single-barrel Weber carb.  It ran very poorly when I got it – it was full of flat spots, wouldn’t get beyond 4,000 rpm, and the plugs read as white as could be. 

 

After going through all the usual suspects (ignition, fuel lines, pump, filters, valve clearance, and compression (all 155-160), I rebuilt the carb, and replaced the accelerator pump diaphragm.  None of that made more than the slightest difference. 

 

Then I started messing around with the carb jetting.  It had a 140 main and a 170 air correction jet.  While there is not much information on this site or other places about jets for single-barrel Webers on a 2002, there was at least one site that sells Webers that recommended that exact jetting combination for a 2002 - 140 main and 170 air. 

 

However, after several rounds of ordering and re-ordering various main and air-correction jets, the combination that worked by far the best was pretty much the opposite of the original  - 170 main and 130 air correction.  It seems to run quite well, willingly going to 6,000 rpm with pretty good power throughout the range.   The plugs (the recommended NGKs) burn a nice light tan.  The idle is good and at the recommended screw settings.  All seems fine.

 

Except that I don’t understand how the jetting could be so different than what the carb is sold with or what one carb seller recommends for a 2002.   One possibility is that there is some kind of vacuum leak.  However, I’ve checked the vacuum and it appears to be quite textbook in operation.

 

While the car feels pretty good, I can’t say that I’ve achieved optimum performance. The last time I drove one of these cars was when I traded in my 1969 2002 back in 1973 (for a 73 VW van in case you were wondering).  Far too many years have passed for me to have any kind of calibrated sense of performance.  

 

I’m just wondering if anyone has any previous experience along these lines or any thoughts about what is going on here.   

ICK!  

 

Get that carb off your 02, and put the single barrel Solex one back on!! You'll be happy you did.

Edited by arminyack

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1 hour ago, '76Mintgrun'02 said:

If you have a vacuum advance distributor, the pod could be ruptured and that will create a vacuum leak.

It is easy enough to check, if you suck on the vacuum line, you should be able to rotate the points plate... unless it is stuck... like the one I just disassembled.  But you should be able to tell if it is resisting the suction in any case.

Tom

 

 

 

Good suggestion.  However, the car has a non-vacuum advance distributor that seems to be advancing as it should.  No evidence of a vacuum leak. 

Thanks for the advice. 

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12 minutes ago, arminyack said:

ICK!  

 

Get that carb off your 02, and put the single barrel Solex one back on!! You'll be happy you did.

 

I'm with you on that, but the car came with the Weber installed and zero spare/old parts.  I've looked a bit on eBay and found some pretty gnarly looking Solex single barrels that were priced too high for what I considered a pretty high risk purchase.  I haven't looked all that hard, however. 

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The venerable Weber 34ICH.  I put one on my dad's combine, and it worked great with very little adjustment.

 

As far as a 2002 is concerned, if you put TWO onto a later manifold, you might get some entertainment.

 

But if it was me (and it was, almost 20 years ago)  I'd find a 2bbl manifold, put a 32/36 on top of that, and, now that

you've gotten the knack of jetting, and some jets that will work in it, spend your time getting the 32/36 going well.

 

If you MUST beat your head against the single bbl, I have a couple of old Solexes I'd stick in a box and mail 

to you for $50.  But you really don't want to do that.  I'd much more happily send you a 2bbl manifold...  

 

t

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The 34 ICH Weber is just too small for a two liter engine...especially a free-breathing engine like an M10.  Even the 1600 used a 38mm carb, and 2002s used a 40mm Solex.  If you remember your plane geometry, that 6mm difference in throat diameter becomes a significant number of square millimeters (pi R squared).  That size carb was fitted to a 1.4 liter Peugeot and a 1.2 liter Fiat.

 

The original 40mm Solex fitted to your car was bulletproof--the one on my '69 is original (224k miles) and has had nothing more than gaskets and an accelerator pump diaphragm in 47 years.  Still runs fine, and has always idled smoother than my 32/36 Weber, despite hours of messing with the Weber's idle jets and mixture screws. 

 

The Solex you need is very common and easily found for little money.  Find one, rebuild it with new gaskets and diaphragm, bolt it on and (given no other problems with the engine and ignition system) your problems will be over.  Or you can always fit a 2 bbl manifold and a Weber 32/36...

 

mike 

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