i am running 36 dells 30 mm venturi how big can i go can i get 36 mm the opening is 44 mm

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drive it like you know how too fix it

36mm are the butterfly .and you need a venturi smaller then the butterfly to speed up air &fuel .You my be able to make them 32mm at a local machine shop.

Heres a little section about venturies:
Venturi selection - For engines that rev pretty high (6000-7000 rpm), you are best off choosing vents that are about 2 to 4mm smaller than your intake valve size.

For engines that are set up for torque, like bus engines, and other torque-happy applications, you can go a little smaller on the vents and get better low end response. For these, I'd recommend 4 to 6mm smaller than your intake valve size.

So what happens if your vents are too big? You'll have reduced air-speed at low RPMs, which makes tuning harder. Air speed is one of the things that tells your different fuel circuits when to start to come on. It will be soggy down low.

So what happens if your vents are too small? The undersized vents will restrict your engine's ability to breathe at higher RPMs.

How critical is it? Not terribly, but if you're way off it will matter, and you will feel it. Putting 40 vents in a set of 44 IDFs with 40mm intake valves will be pretty soggy down low. Sticking with the 36's would be about right. Putting 28 vents into a set of 40 IDFs on an engine with 40mm intake valves will limit your top end noticeably as well. A set of 44 IDFs, for example, can me made to work on many engine sizes with the standard 36 vents, but you might find that you could optimize them better if you are willing to spend the money and try some different vents that would be ideal for your application.
Hope this helps.

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When in doubt, hit it in second gear!

thanks for the info i thank valve size is 40x35.5 venturi are 30 mm 140 main jet 60 idle jet it has all the bottom end you need just like more on top .the way they aer made can not machine . try a set of 40 idfs on it ran like different motor thought bigger venturi would help had to put 40 back on brother-in-laws motor thanks again

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drive it like you know how too fix it

You are an the right track. I don't know what is available for the 36mm Dell but it might be worth checking in to. Try CB Performance. I bought some Dellorto venturi's from them about a year ago.

Just remember that if you increase the size of the ventiri........... you will lean out the fuel mixture automatically. You may have to adjust for this.

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