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What are some Good dual carb XR6ooR Mods?


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In the process of what i call "restoring" this pig. probably no real motor work yet, but mainly cosmetic. But i was wondering for future reference and possibly things i could do now while it is just the frame with everything removed. When it did run, i hit full throttle rev in 2nd or 1st gear and blew a little black smoke. probably running a bit rich. waiting for my service manual so i can get some literature to read up on. TIA, Mitch

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Because it's running a little rich at WOT? Talk about throwing the baby out with the bath water. Besides, the twin carb setup works better than the single and is not significantly harder to tune. In addition, the single carb airbox does not fit correctly around the twin carb frame's centered rear shock, the head bolts and dowels are different sizes, and the cam chains are different sizes. It's not a "get the single carb parts, slap them on, and Bob's your uncle" kind of swap and certainly not worth doing in lieu of changing a few jets.

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i'm not going to do anything to the motor, just tune the richness out of the carbs after i figure out how to do it with the twin setup. I'm talking about other things.....removing the kickstart cable, the airbox already has additional holes cut in it on the top, anything i can do to the stock exhaust. it is pretty loud, much louder than my XR650 stock exhaust. things like this.....

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Your stock silencer SHOULD be nice and quiet. Someone has probably just removed the baffle. Your best bet would be to put on a real silencer line an FMF Q4 or an XRs Only stainless.

As for the carbs, they're probably the best thing on that bike. Keep em.

The suspension is weak. You could replace the front forks with a CRF front end. It's not a direct swap out but not too hard either from what I've seen. Then replace the rear shock spring. If you plan on keeping this bike for a while and really enjoying it, you may just want to have the rear shock serviced at the same time.

With a fresh suspension, it will be a bike that is fun to ride ANYWHERE.

I had an XR600R dual carb and it just ran great. The transmission was super smooth and it had TONS of torque. What a beast.

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HeadTrauma and akarob know of which they speak.

I've swapped a dual-carb top end onto an XR650L bottom and as HeadTrauma said, you have to change a lot.

And, I don't know where this "hard to set up dual carb" thing came from. They're actually quite simple and work great.

I imagine the only reason they went away is because they weren't cost effective for Honda to keep producing. Why build two carbs when one will work?

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1.)removing the kickstart cable,

2.) anything i can do to the stock exhaust. it is pretty loud, much louder than my XR650 stock exhaust.

1.) Removing the kickstart cable is fine. It will make doing the starting drill easier.

2.) Like rob said, your silencer may have already been opened up if it is that much louder than your 650R.

As far as external power mods, you might consider looking for a used SuperTrapp or adapting a later silencer. Aftermarket headers for later RFVC 600/650s will, AFAIK, fit your bike with minimal trouble.

I also agree that the suspension could use attention, especially the forks. They are the old damper rod type and are not as nice as the later cartridge design. I don't think it would that difficult to install a later XR front end. The reservoir shock isn't so bad, but I believe better CR125/250 shocks can be adapted without much drama. You could also convert to rear disc with a little fabrication.

And, I don't know where this "hard to set up dual carb" thing came from. They're actually quite simple and work great.

I imagine the only reason they went away is because they weren't cost effective for Honda to keep producing. Why build two carbs when one will work?

It seems that jetting even a single carburetor throws many people for a loop. They probably assume that if tuning one carb is hard, then two must be impossible, even if they have never laid eyes on a twin carb bike. As for why the twin carbs disappeared, I said in another thread that many dealers can't get even a single carb sorted out, let alone two. BTW, the Suzuki DR750/800 Big used twin carbs all the way through '97. BTW2, based on the numbers I could find, the '83-84 "big port" XL600R had the highest power density of any of the big RFVCs from '83-current. Food for thought.

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Dito on dual carbs being better for performance than a single and not being any harder to tune. There isn't jack in the second carb except for a main circuit, the primary carb is tuned just like any other carb and the secondary is for WOT. One thing to mention is with two carbs to play with the main jets, the jetting can be more precise because you don't have to run the same size mains in each carb. Honda even used two different sized mains some years. You can basically tune to half sizes by only changing one, with a single carb the main jets offered are as close as you can get and may not be just right.

The fear of two carbs is perpetuated by people who don't know how to tune a carb in the first place. It is not just the dual carbs that alows for more power, it is also the more direct intake path to the valves because of it and the higher velocities. If you look at the single carb XRs, the mixture has to make a bend to the right to reach the right valve because the carb points to the left because it has to be angled to clear the rear shock and not to mention there is a divider in the path to split the flow, which just causes more turbulance. The dual carbs go to each side of the shock and each carb have their own deicated intake runner. Any time the mixture has to make a bend, there is a probability that the fuel will fall out of mixture during high speeds because it is heavier than the air that carries it.

The dual carb design is superior in function. I agree that cost was the main reason to go with one carb, just like the Honda rebel only uses one carb bolted to an actual Y intake manifold when Honda could redesign the head to use one carb without a manifold, but that cost more than using a manifold. Changing the head design on a Rebel probally wouldn't make much of a difference anyway becaue it is a low performance engine.

The dual carb 600 made more power than the single carb 600, but in all practicality any of the 600s are more than enough in the woods.

Suspension and brakes were the biggest improvments overall improvments through the years. Find a used late year XR600R or XR650L fork and that will make a noticable difference. A disc XR600R swingarm can be swaped out, but that is a little more involved. I don't know what type of swingarm your XR has but if it is steel a aluminum one is more rigid and much lighter. I would say whatever you do to the suspension, keep it supple and it will work better in the woods and almost anywhere excpet if your are jumping tables and doubles. The steel frames do flex and I don't think a stiff suspenion will help it any.

If you could find one of those old stainless Supertrapp mufflers, that would be awsome, but a intact stock muffler is about a quiet as you can get and is not going to hurt power for trail riding, the 600 has plenty for that.

After some fresh paint on the frame and a thourough going over, everything else you would like to do can be later without eating into your riding time to much.

Congrats on your project though, and I hope you are able to enjoy it for years.

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Find some 49 state XL600 carbs. They're around 4-6mm larger. The XR head will need some port matching or full porting to gain all that's available. XL and 83/84 XR500 heads have much larger intake ports than 85 up XR600 heads. Likely where the higher HP ratings for XLs came from. Check the air cleaner to see if it has the restrictive original element. Some early models had steel wool mesh, screen and foam elements that were okay at low to mid rpm but didn't flow too well at WOT. That alone could be the over rich condition. Later model free flowing elements are direct swaps.

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Thanks for all of the ideas guys. valvesrule already helped me out with a rear spring. how involved is a shock servicing? I'm probably gonna stick with the stock front end until i get a bit more $$. the later year XR/XL front end may be an option in the future though. my car goes down about every other week and has been eating my fun $$ lately. so i'm trying to keep this a bit of a lower budget project for now. One interesting thing i didn't know...the second carb is just a main jet huh? cool. I do have the aluminum swingarm, but i think that the because of the budget thing i'll just order up some new brake pads and call it good. braking is some 70% in the front anyways isn't it? I'll have to see what's inside the muffler. it doesn't really bother me any, its not gonna be on the streets legally, just off-road. Thanks for the ideas...off to the garage!

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Yup, the right carb only has a main. Most of the low-throttle fueling is done with it completely closed, so the pilot is only needed on the primary carb.

I've been snooping around and am beginning to think that the "small port" heads are not the restriction they outwardly appear to be, at least for most applications. I'll post something new in the "dueling dual carbs" thread.

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Since you already have the aluminum swingarm, not much need to change it. Disc brakes offer more feel and last longer in wet conditions, but that drum will work fine.

I'm fine with the drum...if i still have the bike......NM...i'll upgrade...the bike is already older than I am by 2 years......

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