mustard-z Posted October 14, 2002 Share Posted October 14, 2002 I am totally confused now. I bought some weber 45's with the following: 32 chokes 140 mains 170 airs 45f5 idles 50f9 pump I called Pierce Manifolds and they said I should run the following: 29 chokes 140 mains 170 airs 45f5 idles 50f9 pump Then I talked to Top End Performance and they said: 34 chokes 140 mains 170 airs 45f5 idles 55f9 pump The car is a stock l28 with a 260dur. 450lift cam and 2-1/2 exhaust(no header). What the hell do I do? I've already purchased the 29's and it runs like crap with no top end. I suspect that Top End Proformance is correct in the settings but at $21/ea. I need to be sure. Maybe someone here would be willing to let me try some the parts? Thanks a ton, Aren Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted October 15, 2002 Share Posted October 15, 2002 I love weber questions. You are correct in your assumption, to a point. The larger you go in choke size the more topend power the car will make. I usually ran 33 mm chokes in mine, but that is what I had. If you can get the idle circuit working properly, then going to 34's would probably give you a little boost in power. I had to prove this point to a friend of mine a long time ago. I ran a set of 28 mm chokes against a modded conquest tsi, and from a kick, the conquest could pull me. We went back to the shop, I put in 36 mm chokes, rejetted, and we went back out on the interstate, and I pulled the conquest slightly. What you will run into on the street is getting to large on the choke that your flow velocity thru the carb is not good enough to give decent drivability. Your 32's are fine, and if I was going to spend 24 bucks a hole, I would go up to a 36 or 38's. 2 mm isn't worth the money in my opinion. Quote Link to comment Share on other sites More sharing options...
Dan Baldwin Posted October 15, 2002 Share Posted October 15, 2002 Agree w/ lockjaw, 2mm ain't worth the money or the effort. The benefit of triples over SUs or stock FI is at high-rpm operation, so choking them down with 29s(?!), it isn't worth running them, IMO. I've got 38mm chokes in my 45mm triple carbs, and it runs fine around town. I'd be thinking at least 34s, maybe 36s depending on your intended usage (street/autoX, or roadrace?). The bigger the chokes, the bigger jets you'll have to run. Either rig up your own A/F readout, or go to a dyno and see where you are. I've got 165 mains (which are too big, I'm running rich), and just switched from 220 airs to 200 (was leaning out up top, going to 200s gained me 5hp from 4500 up). There is no "correct" choke size, any size within reason can be made to run pretty well (with bigger being better for high rpm, to a point). Whatever formula you use to size your jets, you'll have to check the A/F ratio throughout the rev range to know if you're OK. Jets aren't all that expensive, and it's worth the cost of dyno time to see the effects of changes on A/F and power. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted October 15, 2002 Share Posted October 15, 2002 Oh and I should explain my jetting philosophy too. I jetted my carbs to work with a certain set of chokes. Once there, swapping the carbs onto another engine rarely required a jetting change since the air flow thru the carb determines the amount of fuel the thing pulls anyway. I always try to tell my friend with a holley that just because you have a big engine doesn't mean you need to change the jets in your carb. It only flows so much air, and beyond that you are just making the carb run rich. A good starting point for the main and air jets is take your choke diameter times 4 and that is your starting main jet size. Add 60 to that for your starting Air jet. Also keep one thing in mind. The bigger choke you run, the bigger pump jet you need to run. The bigger your pump jet, the more gas it spews every time you move the gas pedal. May not make that much a difference, but it should have a negative affect on your gas mileage. I always got way better mileage with my SU's, but I sure did love the sound and response of the webers. There is nothing finer sounding that a straight 6 with high compression and a big cam going thru the gears with the webers singing the song only they can sing. Have fun with those things. Quote Link to comment Share on other sites More sharing options...
mustard-z Posted October 15, 2002 Author Share Posted October 15, 2002 well, after some checking I found a few things that can cause problems. First my unisyn was not giving acurate readings so I was having a hell of a time balancing the carbs. Second, the #2 sparkplug wire seems to be intermitent. Third I found abnormally low compression in #5. I've reinstalled and have the following setup: 32 chokes 130 mains 170 airs 45f5 idles 50f9 pump f16 e-tubes With my new Unisyn, I am hoping for better results, I'll see tonight. Also, it may be informative that I am at 3500ft altitude so maybe some of the numbers need to change a bit. I know generally everything will need to be leaner than sea level. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted October 16, 2002 Share Posted October 16, 2002 Get F11 e tubes. Quote Link to comment Share on other sites More sharing options...
mustard-z Posted October 16, 2002 Author Share Posted October 16, 2002 Success!!! After installing the 32's and using a "working" unisyn the thing screams!! I made a good run up though 2nd before my throttle shaft sheared and shut-down the front two carbs!! Now I gotta make a new one It sure is a lot closer to correct now! Thanks for all the help. Quote Link to comment Share on other sites More sharing options...
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