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Old 01-06-2014, 08:46 AM   #1
KxRuss OP
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what carb for klx650?

I would like to try fitting a different carb to my klx because its a bit of a slug. Im thinking about trying one off a kxf450. Has anyone got any suggestions on what would be a good carb for the bike?
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Old 01-06-2014, 08:57 AM   #2
sandwash
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Get a pumper carb,that would to the goods.
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Old 01-06-2014, 09:02 AM   #3
Wansfel
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One possibility is a Mikuni direct pull like the VM38. No diaphragm, no butter fly. They drop easily into a KLR, don't know about the KLX. They will give much better response and are highly/easily tunable. Many of them out there and the cost is really reasonable as they have been a mainstay of the large MX bikes and more recently in snowmobiles. Big in the Harley crowd as a replacement as well. I swapped one on my 2000 KLR last year and will never look back. I have a second one that is going into my 2002 KLR (2nd bike) this winter. See link in sig line.
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Old 01-06-2014, 10:22 AM   #4
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Why don't you set the good old CVK40 up properly with good jetting/slide drilling and the adjustable needle from the KLX-R ?
You'll be very happy. The damage is less that $40.
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Old 01-06-2014, 10:59 AM   #5
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I agree with the above poster. I also kept my stock carb because I think they are more forgiving of elevation changes.

Not to be an ass, but filling out a profile is helpful to determine just where you are going to be riding this bike. Since there are 2 KLX 650s with quite different carb jetting, it would be nice to include that info also.

There is a dedicated ADV KLX 650 thread which could get you better responses from people who own this bike, http://advrider.com/forums/showthread.php?t=159970 and there is a dedicated site: http://autos.groups.yahoo.com/group/KLX650/messages. In addition there is an inmate who goes by Fogo in Australia regionals on ADV who can answer just about any KLX question, as he builds and races them.

What size is a Kawasaki 450 carb? The 40 in CVK40 is the diameter size of the carb mouth. That influences how much air flows through the carburetor whether it is a CV or not. On a CV carb, vacuum and atmospheric pressure also controls fuel flow via vacuum actuation of the slide. A smaller carb will improve low rpm response and lose top end power.

A lot of pumper carbs have a slide directly controlled by the throttle. Too much throttle and the bike bogs. That is the reason for the pump.

You can tune all that out, resulting a faster throttle response, but I would at least look at a pumper carb the same size or larger than stock. 96-2004 1500 Vulcans have a hybrid 40mmCV carb that includes a pump function.
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Old 01-06-2014, 11:38 AM   #6
KxRuss OP
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the main reason i was thinking about fitting another carb is to improve the throttle response. If i can get more power that would be a bonus. I live in the uk so running well at altitude is not necessary. At the moment the bike wont even try to lift the front wheel. Now I realize its a heavy old beast but im used to mx bikes and this is more cement mixer. My old husaberg 650 would lift its front wheel in 3rd but this wont lift in 1st once you have pulled away. It does have mega torque low down and looks cool so it would be nice to make it quicker opposed to buying a quicker bike

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Old 01-06-2014, 03:07 PM   #7
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The KLXc model weighs 378lbs wet and makes about 39 stock rwhp. Don't set your expectations too high, that is KLR range. The one thing over the KLR is a better flowing head, so it does respond to jetting and exhaust modifications.

I have a big bore, the typical CV mods and an exhaust that I have tuned and it still won't lift the front on throttle alone. It will stay with a X Challenge or KTM 640 adventure in a roll on contest in 5th gear.

Frankly it is too heavy for single track, but works just fine for open desert or a typical fire road. Not much need to wheelie where I ride it. If there was, a pumper probably would help, so would the shorter swing arm off the R model and/or just gear it down.
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Old 01-06-2014, 04:27 PM   #8
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Like itsatdm says, it'll help if you let us know what bike you have and how it is modded. Edit your signature, please.

I'll take it you have the C model. Now, there are differently powered versions of that bike around. Are you sure yours is not power reduced?
It pays to have a maintenance manual at hand

33kW(45ps)@6500r/min(rpm) ,
(AR)20kW(27ps)@6000r/min(rpm) ,
(ST)20kW(27ps)@5000r/min(rpm) ,

Maximumtorque: 53Nm(5.4kgm ,39.1ft-lb )@5000r/min(rpm)
(AR)44.5N-m(4.5kgm ,32.5ft-lb)@3000r/min(rpm)
(ST)40N-m(4.1kgm ,29.6ft-lb)@3500r/min(rpm)
---
(AR ) AustriaModel
(AS ) AustraliaModel
(CA ) CaliforniaModel
(FG) GermanyModel
(GR) GreeceModel
(IT) ItalyModel
(NR ) NorwayModel
(SD) SwedenModel
(ST) SwitzerlandModel
(US ) U.S.Model

Which model did you say you have?

Throttle response problem is solved by the KLX needle mod.
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Old 01-07-2014, 10:42 AM   #9
KxRuss OP
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My klx is a uk 1995 c model and it has no airbox lid and a straight through exhaust with a 148 main and the standard needle lifted about 3mm. All my riding is at sea level.
cheers

Russell
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Old 01-07-2014, 03:54 PM   #10
Bell driver
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Well, you need to check the inner parts of the carb.
Who knows what a previous owner has done.

The parts list shows 5 possible main jets for that model, being 132, 135, 138, 140 and 142.
No 148 listed.

There are two possible needles, N1RD and N23RP.
The questions are which one do you have and which of the two restricts power?

The only way to find out, and I do that to all my bikes, is to install a bung for an O2 or Lambda sensor and gather some data on the air/fuel mixture.
I hate guesswork.

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Old 01-08-2014, 12:36 PM   #11
itsatdm
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Quote:
Originally Posted by KxRuss View Post
My klx is a uk 1995 c model and it has no airbox lid and a straight through exhaust with a 148 main and the standard needle lifted about 3mm. All my riding is at sea level.
cheers

Russell
The problem with trying to ID your situation, is that there is overlap between the changes. I didn't like the open air box mod, because I did not successfully get it tuned. I lost low rpm punch, the bike surged at steady state throttle, and I had to change the air filter after every dirt ride.

I probably could have got it right but I got tired of the noise and adding a restriction (baffle) in the exhaust seemed to fix it. Never did get rid of the suet on tail of the exhaust pipe.

If this is a new bike to you, the first thing I would do is see if the valves are in spec. They effect how much air/gas gets in and vacuum generated.

The carb has 3 overlapping fuel inputs. Low speed and idle is handled by a low speed jet. Other than changing, the only adjustment is the pilot screw located on the bottom towards the front. For emissions they are capped. I am sure some one has "adjusted" it. Turn it in until it bottoms. Turn it out 2-2.5 turns. If some one has turned out more than 3 turns, that circuit is too rich.

The needle adjusts fuel in midrange. It adds fuel to that already provided by the low speed jet. Shimming It is pretty common for non adjustable needles but 3mm is way too much. 1mm is about par for the course.

It is attached to and opens/closes by the vacuum operated slide. There is a hole on the bottom of the slide for the passage of air and the difference in air pressure causes it to rise and pull the needle up. Some enlarge that hole to speed up the process. 7/64" is the "experts" opinion on proper size. A potential problem is, air flows faster than gas so if it opens too fast you have a lean issue, too slow a rich one. If the hole is too big, vacuum won't keep it in place and it rapidly moves up and down.

I didn't know what that air was doing in the air box without the lid on it. I would put it back on and pull the snorkel.

At WOT the needle is out of the jet entirely. We used to determine that size, by going WOT is top gear until the bike topped out. If backing the throttle increased speed we were too rich. If the bike should go faster, but won't, too lean. Probably not acceptable anymore. If you can read plugs do a run at WOT and chop the throttle and check the plug.

The bottom line is if you make a change in one component, it effects them all. That effects pumpers too.

The stock MJ is 138 or 140 depending on emissions in your country. The carb is common and used on a lot of bikes so you can find needles of all sizes.

I have had your mod and didn't like it. My current set up is 2.5 out on the pilot screw. One thin (.03mm) shim under the needle. 142.5 mj, though I would go 145 to account for your exhaust. I also did the 7/64 enlargement of the hole in the slide.
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