Weber carb jet sizes

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Beej
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Weber carb jet sizes
can anyone please tell me what the correct jet sizes are for a bog standard 1700 X-flow super 135 (supposedly) bhp. Its the idle jets that I am especially interested in. I can't get it to pull clean on a part throttle and I think a previous owner may have been mucking around with the jet sizes. Any clues?
Graham Sewell
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The official sizes are: choke 32 main 120 air 165 emulsion f16 idle 45F9 according to Dave Andrew's program (and proven on my car) choke 32 main 130 air 180 emulsion f16 idle 45F9 Other issues include the number of progression holes (should be 3) Light throttle resonse is always a little awkward as the ignition timing is not brilliant - but can only be improved with 3-d mapped systems which I am not prepared to go for (at this stage). Low tech luddite - xflow and proud!
Beej
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Thanks very much - thats really helpful. I can cross check this against the current settings. I strongly suspect they will be different - it just runs too lean all the time and spits like camel having a bad day at the office. Cheers
Beej
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Graham - it turns out that the idle jets are correct, BUT the chokes are 30s, the mains are 110 and the air is a max at 180. So I am not really surprised at it running lean but it doesn't explain the off idle problem. Any further thoughts?
Graham Sewell
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Working the other way, from Dave's program: For flexibility (rather than outright power) which should give good manners lower in the rev range: choke 30 main 120 emulsion f9 or f16 airs 170 idle 45f9 for a 1700 engine with a 6000rpm red line. In which case, try getting onto Burton for some new air jets. It looks as though the previous owner has probably grown the engine from 1600 and not completely recalibtaed the carbs. Depending on what you are after, the cost could be very reasonable (<£10) or serious! New chokes are not cheap. Low tech luddite - xflow and proud!
Beej
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Cheers, I bought the car specifically for track days so, although tractability is important, I don't want to lose out on outright power. My everyday car does tractability quite well (420bhp) but its too darned expensive to run on the track. I had planned on changing the mains to 130s, and if that improves the balance I would change the chokes to 32s. I am not sure about the origins of the engine, it looks like a totally genuine, straight out of the factory 1700 with all the right bits but I wouldn't rule out the 1600 theory. Either way I had planned on transplanting a twink head this winter so I'll probably have to rejet it again!!
Graham Sewell
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The 130 mains with 30 chokes will be over-rich. Remember it is the choke size that is the driving factor in setting up carbs. See Dave Andrew's Weber Site for more info. Also his jetting program can be found here Low tech luddite - xflow and proud! Edited by - Graham Sewell on 21 Aug 2002 08:20:23
Beej
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Graham, smee again! Need some more help. OK - I ran it with the 130 mains and it ran ok - certainly not too rich but definitely still not right. It was still popping and [email protected] at both ends.. which has totally confused me. I replaced the O rings with sandwich plates and reset the rubber bobbins at the same time. Everything else checks out ok.. BUT no matter how hard I tried it would not pull more than 5,000 rpm in 4th and dropping to 5th actually lost me speed. I was at least 20mph slower than most other cars down the back straight (still stuffed them thru the corners though!!!). Since then I have changed the chokes to 32s and I can now get 5500 rpm in 4th (indicated 110mph but probabaly less) - with possibly more to come but it was really struggling - and getting very hot. It is still spitting back at and off idle and clearly is not happy on the main circuit. I assume you can spin your 1700 up to 7,000 in all gears? Any ideas? Cheers
Graham Sewell
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I doubt that I have got my car above 5000rpm in 4th due to the paranoia of losing my licence - I only drive the car on the road and not track so these speeds are not available to me. The only time hat I have taken my car upto 6200 in 4th was on a rolling road where drag does not count Low tech luddite - xflow and proud!
eric
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Hi, me too I had hudge problem with Webers My car is a 1600 with A2 cam and I bought the Caterham Kit Main 120 Air 180 F16 iddle 50F9 (richer than 45F9 but now as std) pump jet 35, choke 30 mm The problem is that my head is non std Unleaded stage 2 Head and the car was poping from webers and exhaust (with flames ...) On the point to revert to the single Weber, I found the solution : the iddle jet was too small, now I have 60F8 and everything is perfect, the car is like a dream even with a 55F8, it doesn't work my jets are now : main 115 air 180 F16 iddle 60F8 chokes 30mm pump 40 (Ifound better response) spark plugs : NGK BP7ES (excellent), Aldon distributor 103FXYS It is a road car with some track days from time to time to meet friends From your side you could try to remove iddle jets for 55F8 or 60F8 You must adjust richness screw and see I hope it can help
Beej
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thanks eric, sounds like maybe my original idea (that the idle jets were too weak) was correct. I was a bit surprised to discover that the "correct" jets were fitted but because I assumed that Caterham did their homework when setting the carb specification I figured the problem was with something else. It may be that my engine is not exactly to Caterham 1700 supersprint spec and it does seem worth checking out a richer idle jet configuration. That being said, I am not too concerned about how the car behaves at and off idle because I tend to drive it flat out . So my primary concern was to understand why the engine would not pull more than 5000 - 5500 rpm in 4th gear (and less in 5th). I posted a comment on this on another thread and various people have commented that this seems normal for a 1700 SS - equates to an indicated 110mph max speed. If so, I may need more horsepower because my nearest tracks are Goodwood and Combe and I am used to hitting 135 - 140mph on the straights in my everyday car (although its obviously slower thru the corners). Before I catch upgraditis big time I just wanted some reassurance that I was getting the best out of the current spec.