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Snaithoss1710

38mm VS 36mm Carb + Lectron or Smart Carb

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Hey!

Just want to make it clear that money is not an issue.

Can someone tell me the difference between 36mm carbs and 38mm carbs.

Furthermore, have read a tonne online and looking at Smart Carbs and Lectron carbs but still unsure which to buy. I hate tuning - period! Which should I buy???

Cheers :)

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The smaller the carb the better the part throttle response is. At the expense of top end power. As for what to buy, I'd ask the guys who make the carbs what they recommend. And think about why you're wanting one in the first place.

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Just now, nobade said:

The smaller the carb the better the part throttle response is. At the expense of top end power. As for what to buy, I'd ask the guys who make the carbs what they recommend. And think about why you're wanting one in the first place.

Thanks for your reply. By throttle response, do you mean the bottom end power or how quickly the throttle responds to a quick 'blip' of the throttle. Cheers.

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Yes to which part, the bottom end power or the quickness of response?
Both. You'll increase torque at part throttle openings, which of course make it respond faster. And make it work better in tough conditions that require precise throttle control. As an example, my KTM 200 came with a 38mm carb. Great for the MX track with lots of top end power. But hard to dial in on the bottom, I had to get on it harder than I wanted to to keep it running, but that makes it tough to avoid spinning the tire. When I went to a 28mm carb, the throttle became almost like an electric rheostat where I could dial in whatever amount of power I wanted without stalling the engine. It may have lost some power on top, but not enough to tell, it's still way too fast to be getting on the pipe in the tight woods.
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Just now, nobade said:

Both. You'll increase torque at part throttle openings, which of course make it respond faster. And make it work better in tough conditions that require precise throttle control. As an example, my KTM 200 came with a 38mm carb. Great for the MX track with lots of top end power. But hard to dial in on the bottom, I had to get on it harder than I wanted to to keep it running, but that makes it tough to avoid spinning the tire. When I went to a 28mm carb, the throttle became almost like an electric rheostat where I could dial in whatever amount of power I wanted without stalling the engine. It may have lost some power on top, but not enough to tell, it's still way too fast to be getting on the pipe in the tight woods.

Thanks a tonne mate. Awesome. I think I'm going to go a 36mm carb. Now I need to decide the Lectron or the Smart Carb :D

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I had a lectron 44MM on my kx500 and really liked it.  Tuning it was so nice not having to change jets.  If you're on the fence I would go with the smaller size.  Lectrons come with a power valve that you can tune independently for the top end.  I know my bike suffered some noticeable bottom end loss after going to the big carb.  Top end was on another level though.  Really depends on how you ride and what you're looking for.  I got mine from Packard Racing, and Todd was a big help getting it dialed in.       

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20 minutes ago, Snaithoss1710 said:

Thanks a tonne mate. Awesome. I think I'm going to go a 36mm carb. Now I need to decide the Lectron or the Smart Carb :D

What is your bike?

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Just now, yz250f 78 said:

What is your bike?

KTM 250 EXC 2007, going to a 2014+ Ktm 250 EXC though hopefully in the near future. I do very diverse riding - not MX though.

With carb choice, top end should be kept in mind however not necessary. Lots of gnarly single track and open tracks / dirt roads in between the single track. 

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26 minutes ago, Snaithoss1710 said:

KTM 250 EXC 2007, going to a 2014+ Ktm 250 EXC though hopefully in the near future. I do very diverse riding - not MX though.

With carb choice, top end should be kept in mind however not necessary. Lots of gnarly single track and open tracks / dirt roads in between the single track. 

Is the exc just a woods version of the sx?

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Just now, yz250f 78 said:

Is the exc just a woods version of the sx?

Sorry - Aussie version. It's the XC-W I believe you call it. 

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1 hour ago, Snaithoss1710 said:

Sorry - Aussie version. It's the XC-W I believe you call it. 

A 38mm keihin pwk airstriker performs so well on a 125 giving it nice pulling power down low and all the way up I would think it would perform great on your bike not losing any characteristics of your 36mm and actually gaining everywhere with the 38mm

 

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If its a 250 the 36 will be the best, try to get an OEM KTM one with the square top cover (shortbody).

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When you need to adjust your metering rod in either the Lectron or Smart Carb (you will despite what manufacturer's say) then at least the Smart Carb is externally adjustable unlike the Lectron where you hafta pull the slide from the carb to adjust the metering rod.

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Cool. Might not change anything for me... I want more low and use a green spring. Get a 36 and go yellow or red and probably still have more top end. 

 

Thanks. 

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I'm my testing the spring colour hasn't changed the power ,it makes no difference once you tune each one

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Thanks so much for all the responses. I’m thinking of going for a Smart Carb 36mm. It’s for a KTM 250 XC-W, so if anyone thinks I’ll have a problem please drop a reply :). Thanks a tonne everyone!

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