Xr600 frame compatibility

So I started with an xl600, torn seat, very rusted out gas tank, air box missing the cover which can't be bought anywhere, missing the plastics, seized carbs and a head with bent valves, very bad scoring on the cam center bearing, gouged rocker arms and a very badly worn, unusable cam, which also can't be bought, so needless to say it was in horrible condition

So I set out on a big project to rebuild it, but I'm really not a fan of the dual carbs, sure they're marginally better if you can tune them right, but I can never get it Perfect, and I hate taking them in and out, plus mine are bad.. so a few hundred dollars later I have a sweet black and red xr seat, a nice plastic tank, xr side plastics, xr air box, xr600 carb, and a fully rebuilt engine bored out to 101mm with entire xr head and xr650l cam.. but of course I'm stuck getting the air box around the shock, in the future ill upgrade the suspension but I wanna get it running first.. I'm thinking instead of fighting to fit the airbox in here I might be better off just getting an xr frame now

So I have a local option, I can probably get it for like $40 its a 1985 xr350 frame, there's also a 1987 xr600 frame for that price but it would be like a 6 hour round trip to get it.. I'm curious if the 350 frame would work? It looks the same, but could it handle the extra weight of a 600? I'm also liking the idea of a different frame as I've read the head tubes of mine will bend from hard jumping, which I wanna upgrade the forks to handle jumps

Also I thought they didn't go to a single carb till 88? So would either of these work? They look different then my frame a little, where the rear shock mounts, more like the newer ones, thanks for the help guys

No 350 frame won't fit a 600 engine..Not really any such thing as an 87 XR,,86 dual carbs,,then it's up to 88 and the single carb..87 may be the registration year but',,,,,,,,,,ggggggggrrrrrrrrrrrrrrr,,deletion bug..


87 is still an 86,,duel carb. What is the issue with the single carb airbox..Can you not get the hose around the shock??..Have you tried unbolting the front of the airbox and maybe moving it across to the right a bit so it clears the shock??

Have you tried unbolting the front of the twin carb box and bolting the single front to that. Making up a new front for those boxes would be pretty easy..main major part is the ridge on the inside which the filter fits over.,,that's the tricky bit and making sure the filter is not over too far to the right. Once that's sorted all you do is go to a wrecker and sort out some piping from some othr airbox he has in his pile of junk..Junk to some but vital to you in your mod..

Edited by Horri

So you bought a parts bike and now you need to get an 88 or later to use your parts on. Frankly many have tried this and by the lack of replies I would guess they had various degrees of success, gave up the project or are under lockdown for psychological evaluation. Simple answer sell all the dual carb pieces and get on with the late frame bike. And like Horri said a 350 frame will not work. You can't get a 600 motor in them.

Ya I think now I wanna go with later frame, for now at least until I find a frame, I'm just gonna run it as an engine, seat and tank, and a pod filter and stay out of the dirt, ya, originally it was a decent bike with a parts bike, fixed up the other one and sold it for an insane cr250, I thought it wouldn't be to hard to rebuild this one, and slowly got too into it, I'm debating if I just try to reweld the shock mount a little forward

Be good to see some pictures of the actual problem. I know I keep rattling on about shifting airbox fronts over but that's because I assume that is the issue..Airbox front at wrong angle to miss the shock..Is it actually something else like the single carb ends up to close to the shock that's the issue..??

Edited by Horri

Well I haven't put the carb in yet, I havent gotten to mess with it yet so ill do that after work today with some pics, so far I've set the engine and tried to get the air box in, the air box won't sit straight because of the shock, I haven't tried putting the carb on yet..

So here's how stuff is lining up, the side of the carb is hittin the edge of the spring, however, the carb looks Luke it fits deeper into the intake boot, I just can't get it in there, also I'm curious, to me it looks like the choke is on backwards? Shouldn't that small flap open the other direction?





mmm..Looks tight..I take it that's the single carb box..Have you got the double carb box??..Be good to see a picture of it in there to see how one nozzle of it would line up with that carb..Just wondering whether a 650L intake manifold would shift that carb down and out a bit to the right..may do,,They bolt straight on a 600..it's certainly a bit shorter than the 600r intake..I take it that in the picture of the carb meeting the airbox nozzle that the box is not actually in it's proper place..


Looks like you have no engine mounts in..May pay to put a couple of the rear and bottom front in just to make sure things are precise with the carb to shock thing..


Choke plates right,,though you would replace the entire thing with a homemade job or one from XRsonly or it may bust off and destroy the engine..

Edited by Horri

i am running a pod filter on my 93 xr600, i have the xr650l carb boot and a 41mm FCR :) 

Glad to finally see some pics of the problem. The 650L and 600R intake manifolds are the same as far as I know. The prolink lowers are different too so just repositioning the upper shock mount isn't going to work alone.

Edited by valvesrule

I'll use the correct terminolgy for what I regard as the intake manifold "Insulator"..The 650L one is slightly shorter than the 600r one. You have to use the 650L one if you are doing the FCR mod on a 600r..It moves the FCR in and down a bit to enable better clearance of the 600r gas tank so you don't need to do as much melting of the underside of it. Using the 650L insulator will certainly give you more clearance between the rear of the carb and shock though I expect this would be dependant on the length of an FCR carb and a 600r carb..I have a spare 37mm FCR carb if you require a length measure of it. Actually I have both carbs so I'll look at the lengths of them a bit later..I'd say it'd be no different in length than the 41mm I have on my current bike. Whether it'd move the carb out a bit more to the right from the shock to enable easier fitment of the airbox intake I'm not sure on,,you will gain clearance between the rear of the carb and shock and I'd say the part of the frame your current carb is close to... A 650L insulator is $65 new..What with all this mucking about I do wonder whether it wouldn't be easier to just buy a used 600r frame as Valves said earlier.

Edited by Horri

Right now that's the goal, I just wanna get an xr600 frame, but the only I can find is $200, so I wanna hold off a bit, the 1987 one I mentioned I was to slow on, I messaged him to late, he took the frame to the scrap yard that morning, plus I wanted to get an xr600 swing arm on this frame eventually anyways to be able to use a rear disk brake, and I believe its a little longer, for now, ill just see if I can fit a $5 pod with a sock on there and ill stick to the woods, this time of the year the leaves hold most of the dust down and there's no puddles to splash through

Oh and to your earlier message, I have the bottom mounts in, didn't get to the top ones yet, gotta get rid of the red paint first, and no the air box isn't where it should be, I actually don't know where it should be as the dual carb airbox mounts were in the way so I had to cut them off, once I got everything in I figured I could weld some new mounts on, ill get the old air box back in with pics tomorrow evening

Right,,fair enough..Anyway I say the job is doable if anyone wanted to put some proper effort into it..The 650L insulator is the key and modding the airbox a bit is the other bit that needs a bit of work on..Need to use the twins box and unbolt  the front of it and fab up another front from a hunk of alloy then sort out some sort of hosing between it and the carb and use a pod filter in the twins airbox .Sounds easy huh.. :thumbsup:

Edited by Horri


So is that an xl frame with the single carb? Looks like a single carb.. makes me think its an xr though with the disc brake in the back, but I like that look, so ill try that out first, or until I find a frame

I've done a bit of investigation for you on carbs etc..


If I was trying to do this and retain the XL airbox what I'd do is this..Get the 650L insulator..Get an FCR carb,,Those two things alone will give you ample clearance at the rear of the shock to mount an airbox nozzle to the rear of the carb which would then run to your modified XL airbox..With that you'd remove the two pipe system from the front..insert a sheet of alloy in the hole left fabricating a hole in that so your pipe from the rear of the carb goes into the box and mounts to whatever filter you want..Job done.


Measurments of  carb lengths.

FCR all,,80mm

XR600 carb..112mm

You have a 30mm gain there as well as what the 650l insulator gives you..Both would add up to ample room between the shock and rear of the carb to attach your pipe to. That'd be a 2inch approx gain in non metric speak.


sezltoads bike is an XR,,Can tell the jobs not complete as he has no cover on the side of the FCR carb because he hasn't melted the tank enough to enable fitting of the FCR side cover without it hitting the XR tanks underside..No airbox on a bike just isn't right to me..I'm a purest..A Dirtbike is a dirtbike..A Roadbike is a roadbike.,,no inbetweens.. :naughty::devil:

Edited by Horri

She wont see the dirt so not worried about that but I might trim the cover for a better fit

I wanted to get an xr600 swing arm on this frame eventually anyways to be able to use a rear disk brake, and I believe its a little longer

Got one cheap. PM if interested.

I'd also suggest trying an XR650L insulator.  If that doesn't move the carb far enough outward, make a wedge shaped spacer to go between the insulator and cylinder head, something the outline of a gasket but thick on the centerline side and thin on the starboard side.  If you'll run a pod filter, it doesn't much matter how far over the carb gets pushed, as long as it clears the shock.


Or if you're comfortable fabricating, just remake the upper shock mount to match the later single carb style.  They almost look as if the factory took an early center mount and then bent it over to one side.

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