Hello all,
I am headding into south america and altitude soon. I bought my XR from a red-neck in California who had changed the pipe and re-jetted. Now it sounds great but it is running rich and I am concerned about it's performance at altitude. I have heard from a couple of mechanics that re-jetting is often not needed and the stock settings are usually the best.
If I get my hands on a jet-kit, can anyone clue me up on the stock settings or give general advice about carb set up and altitude?
Thanks,
Trys.

Try looking at thumpertalk.com. Those guys are always rejetting, adjusting etc. They have areas for diffrent honda's and one for jetting. It may be just an adjustment. Also look at your plug it will tell you a lot about how it is running. Also the dealer should know what jets are correct, but try thumpertalk first. It may be you just need to adjust something. Also what type of pipe is on the bike? Some pipes like supertrapp you can adjust bye putting in rings etc. Wish I could be more help.

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John

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John

Better to run rich than lean. At altitude, it will feel very sluggish, similar feeling to the choke being full on. You should down jet for height & up jet as you descend. This is a very rough guide & varies from bike to bike & the exact altitudes that you're travelling at.

Steve

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Hi Trys,

I think what your mechanic meant to say was "If the bike is stock, the stock jetting usually works best", which is usually true. Given the fact that the guy put that pipe on, I'm 99.9% sure that he also took the snorkel out of the airbox, took the smog control equipment off, made the typical carb mods like drilling holes in the slide, and rejetted. With those mods, you can _not_ run the stock jetting. The bike will run horribly, if at all. I would also guess that he didn't give you the old airbox snorkel with the bike.

Before you do anything, we need to know what your goals are. Do you want performance or best gas mileage? Do you want the quiet stock pipe or the loud aftermarket pipe? What Altitude are you doing to? What signs are you seeing that make you believe it's running rich? It'll be much easier to just fix the current jetting than to try to go back to stock.

My XR650L was quite resilient to high altitude - not sure if it was the CV carb or just the overall low-performance tuning.

Wright


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Wright Bagwell
http://www.geocities.com/wwbagwell/

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Wright Bagwell
http://www.geocities.com/wwbagwell/

Thanks for the help guys,

John,
The pipe is a Yoshimura. Also I have checked with an XRL user site called xrlug, they gave me the stock jet sizes but said I could be better off as I am. Also is the "plug" the screw on the bottom of the carb? Also the dealer took the jet out, whistled and said "grandé". He could not get the stock jets in less than a week. Also from what everyone has been saying, they may not be the way to go anyway.

Steve,
"down jet for height & up jet as you descend" - I wouldn't know where to begin mate! Way too scared to open up the carb without good help.

Wright,
I'm not sure about the snorkel but he did take the smog stuff off and rejetted. I don't know if he drilled holes in the slide or not.

I was talking to another overlander about general carb set up and he mentioned the small screw on the bottom of the carb. He said that, that should be out at least one and a half to two turns from fully tight. Mine is tightened right up at the moment. He thought that instead of rejetting again, I should just get the bike warmed up then try turning that screw while the bike idles. He said the revs should go up as I would be effectively making the bike run leaner. He said once I had ajusted the screw and the idle I should be OK. Is this a good starting point?

My goals? Er, just to make it to the end of my trip. I am planning to go into Venezuela next. That will bring the Andies and some altitue. Later, down the west side of South America which will include Peru and other places of greater altitude.
I am not too concerned about performance as long as I can still overtake trucks and other slower moving vehicles. I don't go fast as it is, I just don't want to be doing 30mph for days on end. Better gas mileage would be nice though!

Signs. It drinks petrol, really drinks it. I am told it somokes (dark) from time to time but not a great deal. And the loud pipe, well, I just love it!
Thanks,
Trys.

Hi,

By "plugs" - most people are referring to spark plugs.

The small brass screw on the underside of your carb should never be fully screwed in. It is there to adjust fuelling when you go from a closed throttle to a partially open throttle i.e. how cleanly the revs pick up. My understanding is that if the screw is on the engine side if the carb, then it adjusts fuel, not air. 1.5 turns out from a fully screwed in position is a good starting point. Once the engine is hot, try adjusting it either way in 1/8 or 1/4 turn increments. If you open the throttle & suddenly close it & the revs drop very quickly i.e as if its going to stall, turn the screw out slightly to provide more fuel. If the revs pick up slowly, screw it in to give less fuel. This screw has no effect on jetting & running once you're past about 1/4 throttle

At no point should this screw be screwed in tight - gently turn it in until it stops, less than finger tight will do. You really don't want to snap or damage this screw or the thread in any way - pain in the arse to repair. I'd recommend carefully removing the screw, watch out as they're quite often spring loaded, & the grease it before replacing it.

The bottom half of the carb is detachable - normally held on a small screw in each corner or similar. There's a rubber gasket sandwiched between the float bowl & the carb body. Loosen all screws, then remove all of them along with the float bowl, placing everything in a clean container. Look up in to the carb - the largest of the brass "screws" with a hole in the centre is the main jet. The hole size determines fuel flow - bigger the hole, more fuel passes through & vice versa. It's normally numbered, bigger the number, bigger the hole - makes sense. Remember to lubricate the float bowl retaining screws & ensue that the gasket is correctly positioned (a smear of grease will help locate it) on re-assembly.

The top of the carb is attached either by screws or is a screw fitting itself i.e like a jam jar lid. Remove it & you'll see that the throttle cable is attached to the slide either via a linkage through the side of the carb body itself or via a cable that passes through the carb top itself. If you lift the slide out, you'll see a needle hanging below. You can push the needle up through the slide to remove it - a lot easier on some carbs than others. Be careful about loosing any parts. The needle position relative to the slide is determined by a small circlip around the needle. There are a series of grooves towards the top (blunt end) of the needle. If you have the circlip on the top groove, the needle will hang lower in the slide & carb itself, restricting fuel flow. If sited in the lowest groove, the needle sits higher in the slide, allowing more fuel to pass. If you take the carb apart, make a note of such settings & jet sizes etc for future reference. Raise the needle to allow more fuel by moving the circlip down towards the pointed end of the needle & vice versa to restrict fuel flow. Lube the carb top on re-assembly.

If in any doubt, get a mechanic to do it for you. Don't let any crap enter the carb & don't break any screws etc. Carbs are delicate instruments & are very expensive to replace.

At altitude, air is less dense, after a couple of thousand metres, the bike will feel sluggish because there's too much fuel for the volume & density of air, so fit a smaller main jet. Possibly lower the needle also? As you descend, air density increases, so re-fit the larger jet & raise needle if you've lowered it. All of the above is further complicated by the fitment of aftermarket air filters & exhausts.

If in doubt, always run slightly rich. Running weak i.e. not enough fuel, especially in high temperatures, can result in holed pistons.

This is not meant to be a comprehensive guide to carbs, just trying to help. I'm guilty of some of the mistakes I've warned you to avoid making yourself.....

If in doubt, watch someone who knows what they're doing.

Steve

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My photos: www.possu.smugmug.com

Tam,

Pull your spark plug and look at it. It will tell you if you are running rich, lean or just right. There is an article on thumpertalk.com about it.

Basically as you add more air ie open the intake ,go to lower altude etc you fuel air mix becomes lean. Also when you add a free flowing pipe it becomes more lean, but adds power to engine. What a lot of people do is put an aftermarket exhaust on, open the air box etc to get the bike to "breath better" When you do this you need to put in bigger jets. All this adds horsepower to the bike.

If you go back to stock jets with aftermarket pipe, smog off etc you will probably run to lean, that is why you need to look at your spark plug aka "plug" to see where you are running. thumpertalk.com has experts and many articles about doing just that. Some pipes you can add or subtract disks at the end of the pipe to adjust how lean/rich you are running. Add disks and it runs leaner, subtract disks and it runs richer.(I think) Once you get your bike adjusted right it will add more horsepower, thus the bike will run easier if you are driving like a normal person. If you are a racer it means you do wheelies easier, pass more bikes, and go faster all the way. That is the basics. Hope this helps. BTW I am NOT an expert, so double check everything I said for mistakes. Hope this helps.

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John

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John

Thanks guys,
I have just had the plug changed and didn't notice anything interesting going on with the one that was removed. the bike is being repaired right now so I won't be able to play around with the screw on the carb untill the bike gets to Venezuela in the new year. I will follow your advice about it and let you know what happens.
thanks again
Trys.

You will need to open up the carb and see what main and needle jets are in it. From factory the 650L is on the edge of lean to begin with, and has a non adjustable needle. OEM is 152main and I had a 155 with just minor airbox mods @2000ft. If it has a Dyno-jet kit, the needle will have 5 grooves in it and can be adjusted (move clip up to lean mixture) and a 160/165 main jet are the only choices provided (with and without pipe). If the pilot's larger than 50, it's not stock, Honda's high alt adjustment is to turn the airscrew (on bottom )in a half turn

[This message has been edited by scooter1100 (edited 05 January 2004).]

Hi Steve!

I read one of your recent posts and liked how you wrote. You sound knowledgeable and know how to convey that knowledge.

I'm the owner of a 2008 XR650L. I love the bike, have done the off-road and highway runs with it and it is doing everything I wish, on and off road, with the capacity I expect from a bike heavy enough to manage 85mph without any problems, and agile enough to handle tank trails, fire roads, and moderately difficult off road riding</SPAN>.

The only gripe I have with the bike is the legendary Harley-esque popping with deceleration. My local motorcycle mechanic (and several TTers) have recommended the re-jetting and getting rid of the CA smog assembly. Noted.

I have also seen the Mikuni Pumper Carburetor 42mm Kit advertised by XRs Only.

I've been told, and it seems to make sense, that any rejetting must be accompanied by a new exhaust pipe assembly.

The de-smogging only worries me for the legality of the issue (though I haven't seen many California Highway Patrol stops of Dual Sports yet :-)

What I desire: A bike that has as much (or even more) power than it has now, but a bike that a) doesn't pop so much and b) that will maintain or improve engine life perhaps, say, by reducing operating temperatures. I add this last because everyone says the re-jetting, etc. drops the temps a bit.

My question(s) are these:

1) Would getting a Mikuni Carburetor along with a new pipe, say a Pro Circuit Type 496 Spark Arrestor Silencer take care of the popping issues?
2) Would the increased power trash the rest of the system? (I'm a relatively mature 44 y/o and try not to break my bones or others eardrums)
3) Is the smog removal important?
4) Should I stick to just rejetting and the Pro Circuit Type 496 Spark Arrestor Silencer?

All the other mods, including electrical, I feel comfortable doing. But in engine-land, I'm completely naive and the forums offer a lot of contradictory information.

I sincerely appreciate your time and advice! Sorry for running on-and-on but wish to make the situation as clear as possible so you have an easier time answering. All the information has me !!!

I really appreciate your time and sage advice!
Sincerely, Tony

If not order them here and not the dyna jets!
Carburetor Parts Warehouse
4207 Ridge Rd.
Cleveland, Ohio 44144
(216) 635-1099
carbparts@hotmail.com
FAX: 216 635 1431
Parts:
Main:
99101 - 393 - 158
99101 - 393 - 155

Pilot: (SHORT VERSION)
N424 - 26 - 055
N424 - 26 - 053

I would recomend you to unkork the bike and remove the ugly octopus(smog crap)
There is a nice xr 650 L group at yahoo with lots of tips and tricks dealing this
http://autos.groups.yahoo.com/group/xrlug/
Wich build year is yours?
Karl

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