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Old 02-06-2010, 09:33 AM  
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Default Is a 40mm CV carb more fuel efficient than the stock unit?

Title pretty much says it all.


I'm just wondering if a standard tune Harley CV carb install (40mm) is more/less thirsty than the 1990 factory carburetor? What figures would we be talking, or will it be much of a muchness?


I'm looking to improve on my current 12 kms per litre economy - factory claims are 25mpg... which is around 9.5km/L. The CV carby is wrapped as more efficient alternative - should I 'expect' or 'hope' for better mileage from this easy mod?


Obviously driving style has a lot to do with things, but if I could get 400kms (250 miles) outta one tank of fuel i'd be wrapped.

Last edited by che_guitarra; 02-06-2010 at 09:38 AM.
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Old 02-06-2010, 06:35 PM  
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In a word... yes.
I did two CV conversions, each with 44mm HD Screamin Eagles and they both raked in a clear 30mpg. The power and throttle response was also overwhelming. Going HD will always get my vote.
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Old 02-07-2010, 12:29 AM  
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i have no experience with this, but i would say it comes down to how u drive. if you have a lead foot, probably not. the fuel efficiency probably comes down to not having to push the accelerator in as far to make it go.
as i said i have no experience with this sort of thing, but to me that seems logical
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Old 02-07-2010, 02:15 AM  
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Quote:
Originally Posted by Billjohn View Post
In a word... yes.
I did two CV conversions, each with 44mm HD Screamin Eagles and they both raked in a clear 30mpg. The power and throttle response was also overwhelming. Going HD will always get my vote.
Can you expand on this a little more? What carb(s) did you install? What is "CV" and "HD"?
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Old 02-07-2010, 03:55 AM  
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HD is harley Davidson
CV is constant velocity

If you have a properly tuned stock carb on a stock samurai, then it will get better mileage than the CV carb. The CV carb will give you more volume of fuel/air mixture so if you couple it with a header and larger exhaust, you will get a considerable increase in power. On the downside, The CV carb is not regulated with an O2 sensor. They are very efficient when properly jetted, and if you drive a specific way you won't need to rejet them. They will need to be rejetted for different driving styles/conditions and altitudes however. I had twin dual mikuni side draft carbs on my rig and they were jetted for sea level highway use. I ran them for 8 years. The additional power was great but it did wear on the engine more and I did go through a couple U-joints and a motor mount.
After 4 years, I was starting to get blow-by pressure build up in the crank case. It gradually got worse over the following 4 years untill it was venting out the dip stick and PCV valve. Last year I took them off and went back to the stock carb so that I could preserve my engine. I just didn't have the budget at the time for a rebuild or replacement and didn't want to push my 160K mile engine.
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Old 02-07-2010, 07:53 AM  
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PW CV Carb

Here is one of the write-ups.
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Old 02-07-2010, 02:45 PM  
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Those are pretty slick. Thanks for the additional info. Price is a bit steep but still not too bad. Something to definitely keep in mind as it would be nice to have the extra acceleration.
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Old 02-07-2010, 02:51 PM  
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Just remember that performance comes with a price. As Baratacus mentioned, it will take its toll on the motor. Be prepared to beef up the motor to handle the stresses that will be added.
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Old 02-07-2010, 03:45 PM  
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I don't think our Sammy motor is as tired as I initially thought. When I did the first compression test the motor was cold and had about 90PSI across the board. Tested it again recently at operating temp and it was 135-140PSI. Off road it seems fine. But accelerating up to highway speed is where I would like some more pep. Still probably not a good idea to put extra stress of those carbs on my engine not knowing how many miles it has on it. Odometer shows 183,000 miles. Have no idea if and when it may have been rebuilt.
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Old 02-07-2010, 06:39 PM  
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my thoughts... cv carb is great! adjustable, easy to work on, extra power. I went through the trouble of putting one on my 94, lots of work since it was efi from S.O.J..
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