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Discussion Starter #1 (Edited)
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.
 

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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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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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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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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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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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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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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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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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going from throttle body fuel injection to CV carbs is O.K. going from MPFI to cv carbs is a step backwards. The 94 had TBFI not MPFI.
 

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suzuki efi is crap, my samurai surged at idle, lacked power/throttle responce, took forever to start up, and worst of all, i was getting approx. 15 mpg, after the p.w. c.v. carb my samurai was getting over 30 mpg, great power/responce, easy adjustabilty. I had to swap over the distributor to the old style, along with the pitails, and had to remove the intank pump, and replace it with a low pressure elec. FP.
 

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Discussion Starter #15
So considering this - i'm happy enough with the poke of the stock Hitachi carb. I'm not chasing a gain in horsepower as a primary motive for changing the carb - I just want a simpler (and more reliable) setup under the hood. I don't need a carb that self adjusts for cold starts or altitude and has a heap of vacuum lines to maintain - a manual choke is all i'll need.



Considering my original post and what i've just written, what HD carb should I be going for? A 40, a 42 or 44mm? Or is it much of a muchness?


PS - I don't want to install something that'll half the life of my engine... I still want to get 250,000kms out of a rebuild.
 

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If you don't mind the power that it's at, want to preserve the engine, and would like a simple, maintenance free set up...

I'd say go with propane. A propane regulator is simple, inexpensive, and the gas is really clean burning. Of course if you don't have propane readily available where you live then it's not exactly an option.

For a carbureted option, and easy on the engine, the 40mm carb would be enough. I had 40mm x 4 throttle bodies ported directly to the cylinders and it was rough on the engine. A 2bb 40mm shouldn't be too harsh on it. Make sure you run some headders and about a 2 inch exhaust to let the engine breath well. Don't go over 2 inches, or you won't have enough back pressure and you'll be popping and snapping lean on zero throttle decellerations. Also, get a Air/fuel gauge and hook it to the O2 sensor. The carb doesn't have a hook up for the O2 sensor, but you will be able to monitor the 02 levels with the gauge to see if you're running too lean or rich and where you need to make adjustments. Once it's all dialed in, you shouldn't need the gauge anymore, but it looks cool on the dash anyway. ;)
 

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Discussion Starter #17
LPG is the closest thing to propane in my neck of the woods with any widespread availability, but i've been quoted a $3000 installation cost - so cost vs benefit kinda rules it out... unless I was driving 1000 miles a week I just wouldn't reap the benefit.


I'm wondering if anyone with the CV carb installed has had issues with getting their cars registered, or if they can be registered at all? Will it pass emmissions testing?

Aussie regulation is similar to US law, so if it's legal over there, it should be the same here.
 

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LPG is the propane I was refering to. Gotpropane.com sells the complete kit (with tank brackets, but no tank) for the Samurai for $700 U.S.

Here it is legal in some states that have very loose emission standards to run aftermarket carbs. Any state that is California Air Resource Board *CARB* compliant will fail you if you have anything but the stock equipment that came on the engine. My work around was to swap the CV carb back to the stock carb every 2 years when I had to do my bi-anual inspection. It takes about an hour to swap the carb and intake manifold out once you get good at it. I've become quite proficient in the vacuum hose routing diagrams after 8 years of that. The CV carb will pass the emission test for the actual exhaust emissions, but it won't pass the visual inspection when they check to see if you've altered the equipment.
 

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Discussion Starter #19 (Edited)
My bad - LPG is just LPG here in Aus... we use the term propane as much as you guys use the word petrol!

With the LPG kit - it'd be ideal, but ultimately illegal in QLD Aus - all installs must be carried out / supplied by certified LPG installers... DIY installs won't be approved, which is a bore if you're a competent handyman - but the laws are laws and we must abide.

Anyhows, one installer (on the end of a phone) said a it'd cost $3000 tops for a nice neat intall. But another installer I quizzed said in 1500 installs he'd never done a hardtop Sierra before, and would doubt an install would pass compliance if I was to mount the cylinder inside the cab. Removeable cylinders are illegal too.


But even so - with the backseat already out I don't know if i'm too keen on losing cargo area to a big cylinder either - I gotta haul my drumkit and band gear around too so interior space is premium.


I'll just stick to high-octane unleaded for now.

And that said - a Screaming Eagle 44mm dual carb will only use ~8L/100K's (30MPG)? That's amazing - that's be 10MPG better than i'm getting right now... and i'm no leadfoot. How can it both be amazingly more efficient and well performing, yet still be illegal for a roadworthy? Damn law-makers.
 

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And that said - a Screaming Eagle 44mm dual carb will only use ~8L/100K's (30MPG)? That's amazing - that's be 10MPG better than i'm getting right now... and i'm no leadfoot. How can it both be amazingly more efficient and well performing, yet still be illegal for a roadworthy? Damn law-makers.
Actually, the multicarb setup doesn't use the Screamin Eagle big bore carb. The installation I showed above uses a single 44mm (or 40mm with a slightly different kit) Harley Davidson Screamin Eagle CV carb. But you are right, it is a shame when you can prove better performance and gas mileage - and still not be allowed to run it on the street (where you are). This is one of the reasons I would never move to California, or any other area where restrictions are stupid tight.
;)
 
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