XR600R Big bore, what carb?

[96xr600rSM]

I have a 1996 xr600r with a 654cc big bore kit and stock carb. I just bought it last week and the guy I bought it from said it needed a bigger carb(he suggested one from a CRF450) to run right. Right now for it to run without giving constant throttle, the idle has to be way up. Otherwise it coughs and backfires and dies. Once im giving it gas it runs fine though, which is why I'm skeptical about it needing a bigger carb. I'm new with bikes so what do you guys think?

[FORMA MOTO]

I have a 1996 xr600r with a 654cc big bore kit and stock carb. I just bought it last week and the guy I bought it from said it needed a bigger carb(he suggested one from a CRF450) to run right. Right now for it to run without giving constant throttle, the idle has to be way up. Otherwise it coughs and backfires and dies. Once im giving it gas it runs fine though, which is why I'm skeptical about it needing a bigger carb. I'm new with bikes so what do you guys think?

Sounds like the pilot jet is clogged. Replace it.

FCR 39 or 41 will work great, but I'd go with the Mikuni pumper kits, with the jetting already worked out, available from XR's only, Thumper Racing, and other companies.

[96xr600rSM]

Sounds like the pilot jet is clogged. Replace it.

FCR 39 or 41 will work great, but I'd go with the Mikuni pumper kits, with the jetting already worked out, available from XR's only, Thumper Racing, and other companies.

Do you think a bigger jet than stock would be good because of the big bore kit? I'm not sure what the stock size is. And you recommend the mikuni because of the same reason? What all can I do to make it run better without spending a lot on a whole new carb? Replace the pilot jet like you said, maybe adjust the low speed screw on the carb? Also would a xr650 carb not fit? or just a xr650 main jet? I thought i read somewhere that it doesn't work

[FORMA MOTO]

Do you think a bigger jet than stock would be good because of the big bore kit? I'm not sure what the stock size is. And you recommend the mikuni because of the same reason? What all can I do to make it run better without spending a lot on a whole new carb? Replace the pilot jet like you said, maybe adjust the low speed screw on the carb? Also would a xr650 carb not fit? or just a xr650 main jet? I thought i read somewhere that it doesn't work

You are bouncing around a lot of questions.

The issue is the carb design, not what bike it came off of.

If it's not a pumper carb, it will never run will from idle to WOT, and be linear. Different loads and temps will just make it always changing. Jet it so it never stalls, then it's anemic.

A modern pumper carb will allow you to use the throttle like a dial. Dial in the power slow or immediate, with always the same results.

There are thousands and thousands of posts in the XR section about how to jet your stock carb.

A big bore does not mean it needs to be richer, cause you are pulling in more air at the same time.

Just change your pilot, put in a fresh fuel screw oring, and adjust it properly, or, go pumper.

[TheRockiT]

I have a 1996 xr600r with a 654cc big bore kit and stock carb. I just bought it last week and the guy I bought it from said it needed a bigger carb(he suggested one from a CRF450) to run right. Right now for it to run without giving constant throttle, the idle has to be way up. Otherwise it coughs and backfires and dies. Once im giving it gas it runs fine though, which is why I'm skeptical about it needing a bigger carb. I'm new with bikes so what do you guys think?

Bigger won't mean better... it's all about getting the right settings, and yes if you go bigger you can gain more power but again you have to set it up to get the most out of it...

Just finished rebuilding a engine for my XR600... used a NX650 engine with a XR600 head/cover, the NX cilinder been re-bored to 102,41 (675cc) and used a (XR650L) Wiseco piston.. changed the Cam. with a HotCam, replaced rockers (XR600) and tuned the ports, polished the valves and dome... Used stock carb (XR600) with a open air-filer (TwinAir).. carb. got 160/60 jets (i've used before on stock XR600 engine) and reactest the same on this engine as it did on the stock engine..

Cold start (with or without choke) one kick and it runs (idle speed OK) warm start it idles very low (1100) but again starts with one kick, also when you play a little with the trottle it goes up (1600), play again and it goes down again (1100) and once in a while a backfire when you play.. so it seems the (idle) mixture ain't right.. So before i start playing with the mixture screw first make sure it got plenty of air..

Been told this got to do with the air(box) what needs more air intakes (even with stock carb.) so gonna do some test with a old site-panel then modify my new panel... Could just drill some holes but its better to use a filter and now busy making it, use 2 big rings, one on the outsite, and the other one inside trapping a fliter..

Will post results...

[96xr600rSM]

You are bouncing around a lot of questions.

The issue is the carb design, not what bike it came off of.

If it's not a pumper carb, it will never run will from idle to WOT, and be linear. Different loads and temps will just make it always changing. Jet it so it never stalls, then it's anemic.

A modern pumper carb will allow you to use the throttle like a dial. Dial in the power slow or immediate, with always the same results.

There are thousands and thousands of posts in the XR section about how to jet your stock carb.

A big bore does not mean it needs to be richer, cause you are pulling in more air at the same time.

Just change your pilot, put in a fresh fuel screw oring, and adjust it properly, or, go pumper.

What do you mean by anemic?

Bigger won't mean better... it's all about getting the right settings, and yes if you go bigger you can gain more power but again you have to set it up to get the most out of it...

Just finished rebuilding a engine for my XR600... used a NX650 engine with a XR600 head/cover, the NX cilinder been re-bored to 102,41 (675cc) and used a (XR650L) Wiseco piston.. changed the Cam. with a HotCam, replaced rockers (XR600) and tuned the ports, polished the valves and dome... Used stock carb (XR600) with a open air-filer (TwinAir).. carb. got 160/60 jets (i've used before on stock XR600 engine) and reactest the same on this engine as it did on the stock engine..

Cold start (with or without choke) one kick and it runs (idle speed OK) warm start it idles very low (1100) but again starts with one kick, also when you play a little with the trottle it goes up (1600), play again and it goes down again (1100) and once in a while a backfire when you play.. so it seems the (idle) mixture ain't right.. So before i start playing with the mixture screw first make sure it got plenty of air..

Been told this got to do with the air(box) what needs more air intakes (even with stock carb.) so gonna do some test with a old site-panel then modify my new panel... Could just drill some holes but its better to use a filter and now busy making it, use 2 big rings, one on the outsite, and the other one inside trapping a fliter..

Will post results...

So you think I should get 160/60 jets and then make sure it's getting enough air? And yeah just lemme know how yours works out. Thanks both of you for posting! I really am a noob with this stuff

Edited October 8, 2012 by 96xr600rSM

[96xr600rSM]

Ok so I was riding today and noticed the headers were red hot when going at slow speeds. I researched this and found out it means the bike would be running rich...how does this make any sense with what my situation is? I'm now confused. So I guess this means I should be looking into airbox mods first as TheRockiT was talking about?

[ozmx]

Hotter than usual headers(unless its glowing red) means its running LEAN,not good.

Timing,incorrectly jetted carb or an air leak is present.

Does it glow red when you take it for a ride at night?

Edited October 17, 2012 by ozmx

[FORMA MOTO]

Ok so I was riding today and noticed the headers were red hot when going at slow speeds. I researched this and found out it means the bike would be running rich...how does this make any sense with what my situation is? I'm now confused. So I guess this means I should be looking into airbox mods first as TheRockiT was talking about?

LEAN, VERY LEAN

[96xr600rSM]

Hotter than usual headers(unless its glowing red) means its running LEAN,not good.

Timing,incorrectly jetted carb or an air leak is present.

Does it glow red when you take it for a ride at night?

Yes is was getting dark when i could actually see it. And i looked up what makes headers glow and everyone was saying its a misconception that that means its lean. People were saying its caused by unburnt fuel in the headers aka too rich

[96xr600rSM]

I see smoke coming from where headers connect to engine, does this mean air leak?

[TheRockiT]

Ok so I was riding today and noticed the headers were red hot when going at slow speeds. I researched this and found out it means the bike would be running rich...how does this make any sense with what my situation is? I'm now confused. So I guess this means I should be looking into airbox mods first as TheRockiT was talking about?

Low speeds (rev's) it's using the pilot-jet..(slow-jet) SEE BELOW: (from JustXR.com)

So you have to adjust the air-screw to get a richer/leaner mix... and YES leaner mix will result in higher temp..

First go back to default (factory) settings... first turn air-screw complete in, then 2.5 turns out...

More info: http://www.justxr.com/info/quickjet.html

I'm using a Trailtech Vapor and so can see engine temp (sensor).. my engine when warm runs between the 72 and 88 celcius when riding.. goes up to around 96-104celcius waiting for a red-light (idle) and drops back to normal temp as soon your riding again (and so gets air to cool)..

These (see link below) little R/C temp guns work also very good.. a cheap alternative..

http://www.horizonhobby.com/products/pe1-tg1-infrared-thermometer-temp-gun-PXTPE1

Should also replace exhaust gasket-rings (around 2 dollar)... to get rid of the leaking...

This weekend i'm planning to try some mods. to see if more air-inlets (site-panel) works or not...

When i've saved up again (ca 500 euro) i will replace the XR carb. with something bigger (Mikuni) but

HAVE to upgrade the headers also then.. and to get the most out of it, have to spend

money on dyno-runs..

What i said Bigger does not mean better, when the settings/setup ain't right it even could be

you have less power, it's a combination of Carb./air-box setup (in) and the exhaust setup (out) and so more (fuel-mix) in means more out BUT still getting the right back-pressure (resistance) from the exhaust system.. and because we mod. the engine (big-bore, hotcam, port-tuning) it means there is NO (plug & Play) default setting/setup you can use, and so have to find the right settings/setup for your (custom) engine..

First try to adjust air-mix and fix new exhaust gasket-rings, then have a look if you can find a place/shop where you

can do a Dyno run, the data from the run makes it a lot easier (for the Dyno bloke) to determine where there is room for improvement, you can ask for some advice what to do or let them do it for you (jetting)

[ffjmoore]

If the stock jetting is 152/62 why did you drop down to a 60 jet?