Carb question

I have a '93 XR650L, with a supertrapp exhaust, K&N air filter, and the emissions equipment removed using a kit. The airbox also has holes cut in the sides and screen riveted over them. I had heard that the stock carb severely limits the performance of this bike, and have been looking at the mikuni flatslide listed on XR's Only's website. I've asked several experts their opinion, but they all answered that "yes the stock carb limits performance, but you should buy our super-duper 500.00 carb to replace it." I'm not looking at spending that much, as the carb I'm looking at only runs about 300.00. Any thoughts on this would be welcome.

is their a differance between the the r and L modle? i have the R and changed the carb boot to the wide open one, along with all the other stuff like air box and smog delet and have no problem with my stock carb, my bike out rides me most of the time. this question comes up alot what is the advantage of after market carb and what is the complaint with the stock. thanks for any help. sorry billyboy i probably did not answer your question one bit :)

The '93 650L is street legal. I've taken off all the emissions stuff, except for the carb itself. The bike is nearly the same as the '93 600R. (or so I'm told)

what is the advantage of after market carb and what is the complaint with the stock.

One of the biggest advantages of aftermarket carbs for the 'R' model is the addition of an accelerator pump. Take a trip back to the 60's and 70's when muscle cars were more common. These cars and many others came with pumper carbs. Sure they'd run without the accelerator pump, but the off idle and low end throttle performance was significantly improved with the addition of the accelerator pump. It was a nice improvement over carbs without accelerator pumps until fuel injection came along and now the accelerator pump function is programmed into your cars computer.

If you're new to bikes or have been a thumper rider for a while, then you likely won't notice any issues with the off idle performance and would likely think everything is normal, but the off idle performance can be improved with an aftermarket carb that features an accelerator pump (Mikuni TM40, or Edelbrock QwikSilver, or Keihin FCR). If you've come off a 2 stroke, then you're more likely to notice the lackluster low end throttle response. I've had people tell me their off idle performance is perfect until they actually rode my bike and then changed their opinion.

The fact is that most people are probably satisfied with the stock carb once its properly tuned, but an aftermarket carb with an accelerator pump will further improve the low end throttle response. When you quickly twist the throttle from idle to WOT, the stock carb will initially go lean (lack of Venturi effect) for a moment. Instead of relying solely on the Venturi effect to suck fuel from the jet, the accelerator pump is manually tied into the throttle action and immediately squirts in fuel with the twist of your wrist to significantly minimize this initial lean spot, thereby improving the low end throttle response. If you look at all the newer MX bikes such as the CRF, YZF's, WR's, KTM's, etc, they all come with pumper carbs and for good reason.

Another reason I bought the Edelbrock pumper is because its super easy to tune and I don't have to take the carb apart to tune it. It also features a dual venting to keep the air/fuel ratio the same between sea level and 10,000 feet (less fuss) and I don't have to rejet like I do with our other bikes when we ride at varying elevations. It also features an internal fuel cell that provides constant fuel delivery under the most demanding conditions. I can lay my bike on its side while twisting the throttle quickly and it still keeps running just fine where as the stock carb would die out and fuel would be spilling all over. I also don't have to go through any special starting routine after my bike has been dumped other than one swift kick after TDC. My bike is a one kick starter with this carb whether it's cold, hot or has been dumped and that's worth something to me, especially if I have to stop on the trail to help my kids or wife.

This weekend I was riding down a narrow sand wash in 3rd gear with scrub and cactus on both sides. There were many sweeping turns where I could throttle the bike and slide it to make the turn a bit funner at speed, but there were also several blind turns that came up very quickly. One of these blind turns that came up rather quickly in this narrow wash had an ugly channel in it and there was little time to react. I was able to give my bike a handful of throttle and quickly get the front wheel up just in time to make that crossing without any incident. The quicker throttle response of the pumper carb likely helped me to get out of that situation more gracefully than I may have if I was using the stock carb. I'm sure a talented rider could have used the clutch or better body english to deal with this situation much better than I could have, but I need all the help I can get nowdays and the pumper carb is has become a good friend :).

I later went on a trail ride with some friends of mine (Kawasaki quad, KX250, XR250) and the whoops were getting too nasty for me so I was getting ready to slow down from mid 3rd gear to ride at a more comfortable pace. All of a sudden there was a nasty looking rock sticking up in my lane at the bottom of a whoop and all I could do was shift my weight, gas it and hope for the best. I firmly believe the quick throttle response again saved me from hitting the rock square on and possibly damaging my bike and or me. The guy on the quad couldn't avoid it and bent his wheel badly and blew the bead on his tire. The XR250 now has a dented front wheel, bent bars and the guy on it was thrown, but not injured except for pulling cactus needles from his new pants and boots along with scratching his new helmet. The KX250 guy missed it by an inch or so where as I only hit the top left side of it (still a bit bone jarring). I really think the quick throttle response of the pumper carb along with my Scotts stabilizer saved my bike and my bacon in this instance. It's times like these where I'm really glad I spent the money for these products even though they seem unnecessary most of the time, but I'd buy them again for my next bike unless they came as standard equipment.

Thanks for the info, gadsan. That was interesting. I don't know how different the '02-''03 model is from my '93, but, It seems I've already made alot of those mods. Having done alot of research into this, I'm seriously considering shelling out the extra few hundred bucks for a pumper carb. Now the only question remains: Which one?

yea thanks alot :) now i have to convince my wife that i need a new carb. hopfully she buys off on the safty issue. but really thanks for the info, the only bike i have ever owned is my brp, and all buddys bikes are four stroks w/ stock carbs so you naild it with you would know it unless you tried it.

I have the Edlebrock Qwiksilver (w/pump) on my ' 01 XR650L & love it! Even with the stock carb recalibrtated there is no contest. Instant throttle response & torque. I used one on my '00 XR250 (sold for CRF 450) also and it woke that bike up like you wouldn't believe. Go for the Edlebrock.

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