Jetting recommendations for Weber 40 IDF's

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Post by Gabe » Thu Apr 20, 2006 7:23 pm

I appreciate the offer, but I think I might purchase a set anyway as I will eventually be moving up to a slightly larger motor and will want some extra jets for tuning in the future. Unfortunately, I no longer have the drilled 55's that came with the carbs available to try out. Even though an Air Fuel meter would be nice, I think I'd rather buy a couple sets of jets instead and just play around with them (and my wife would probably kill me if I bought some more tools. Jets are small: out of sight, out of mind 8) )

Top end is strong, though I've probably never gone above 4000 RPM with the new setup; I don't plan on racing the car, just looking for good acceleration and fuel economy which this setup seems to have. The flat spot seems to be down low around the 2000 RPM range, so I think I'll probably order a set of 52's first and see what happens. If no effect, then the 120's.

Thanks again for your help; without it, this would have been a very frustrating experience. :)


Post by 500LbGorilla » Thu Apr 20, 2006 7:59 pm

Thing is, it's very systematic, but depends on knowing what's causing things and knowing when things happen in the carbs. I'm not an expert, but I've spent a lot more time tuning them than a lot of folks. Not nearly as much as some others though. Not many folks really want to spend the time to talk about how to make them work right though. I don't get that.

Let us know how you get on.

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Post by Gabe » Thu Apr 20, 2006 8:15 pm

Thanks again. I just ordered a set of 52 idles and 120 mains. Anyone looking for some Italian NOS Weber/Dellorto parts at very good prices should check out the auctions by "alfa1750" on ebay. I ordered my 50 idles from him, and they were noticably of better quality than the idles that came from my carbs. Fast shipping also; took about a week and half from Italy.

Idles were $1.95/piece and Mains are $2.50/piece with $4.50 total shipping from Italy.

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Post by robbied31 » Fri Apr 21, 2006 10:03 am

alfa1750 is who I bought my Dellortos from a couple years ago. Then, when I melted my aux. venturis [overheated the engine], I bought the replacements from him also. His work is great and is to be trusted. I had to buy the vents from him because the Dell's I bought from him were basically only seen in Italy, [different venturi configuration]. It just takes a little time to get things from Italy to here. I wish he lived over here!


Leon van Zyl
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Re: Jetting recommendations for Weber 40 IDF's

Post by Leon van Zyl » Mon Dec 16, 2019 4:05 pm

Hi I'm new on this forum and I read a lot about u guys talking about carbs an problems. Now I'm from South Africa. I want to fit a 40 idf weber on my 1400 suzuki intruder. What is the right jetting for this mod
For now this scoot have two Mikuni carbs on

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Re: Jetting recommendations for Weber 40 IDF's

Post by ainokea » Tue Dec 17, 2019 8:50 pm

This may be of some help, if your engine bogs off idle when blipping the throttle, your venturis are to big. If when releasing the the throttle after reving and the idle stays high for a few seconds, your vents are to small. The float should have 30 to 32mm max drop and 10.5 just touching the needle. Regulated fuel pressure should not be lower than 2,5 or more than 3.5 PSI @ 3,400 RPM

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