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Xl600r dual carb issue

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Hi all, I "inherited" an 85 xl600r which I can get running, but won't idle at operating temps. I pulled the carbs and cleaned them, and used the book to sync them. Jets are slightly richer than stock and I am at 5k ft . The idle adjust has to be adjusted all the way in in order to idle, but once good and warm it sputters and dies. It won't start with choke and any choke kills it. I was thinking it was rich. Air screw has little effect... All the way in and the bike still runs (slightly slower.) I even removed it and bike still ran. I tried several steps lower pilot (58) with no effect. I am thinking I am not even engaging the pilot circuit when I run it. The carb is not the same as the one the book shows for an 85, but is more like the 83 one. Is there possibly a critical air passage way that I missed getting cleared in the pilot circuit? Any help would be appreciated.

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So your right carb has a serial number that starts with ph60a? The easiest way to verify the pilot circuit is to remove the carbs, pull off the left carb bowl, turn the air screw out almost all the way and spray carb cleaner in the inlet hole using the little straw that comes with the can of carb cleaner and see if the carb cleaner comes out where it is supposed to. If i remember right it will come out the pilot jet and inside the carb bore kind of under the slide.

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If you look at the primary carb from the intake side you will see the various ports. There are two that i would check out specifically, the one at the 6:30 position is the pilot/air screw circuit under discussion. The other inlet to check out is the one located at the 3:00 position, that is the air cut off valve circuit. To check this, seperate the carbs and pull the little plate off the right side of the primary carb and remove the acv diaphram and spring. Now when you spray carb cleaner through this port it should come out the little hole behind where the diaphram lives. This is also a good time to hold the diaphram up to a light and inspect for pin holes.

Keep in mind that these are strictly air passages and it is fairly uncommon for them to clog if you have been running an air filter. Check them out and see if all looks good.

Was the previous owner at a similiar elevation to you? And what exactly is the current jetting? Any mods? Exhaust?

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Thanks guys. The previous owner had broken the original carbs at the tab were they connect. The new carb is one presumably bought used with unknown history. Current jetting is 65pj, 125mj, 120 secondary. The bike looks stock and is at 5k ft. I did set the float height. I will take them off again and see if I find any issue with those ports. Thanks

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I wondered about that, I have another 600 and am running a 58 pj in it, so I tried the 58 and it made no difference to my problem. According to my Honda manual the 84 bikes came with a 65 pj stock, so I am not sure about it. The carbs are also slightly different on the exterior. I do have a question about a couple of ports on the side of the carb that look like they need to be plumbed to something... I will try and post photos

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Should the black tube connect to something? How about the silver port coming straight out the left side?

1399090580766.jpg

1399090882752.jpg

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Strange choke for an XL..that's early twin carb XR style..Black tube..no..silver thing..hose to dirt.

 

What's the numbers on the side of the carb.???.can't quite see them..PD----

Edited by Horri

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i agree , looks like an xr choke. An 83 xl600 carb will be a ph60a and it looks like that says ph51a. niether my honda or clymer manual say anything about a ph51a so i have no idea what bike that is off of.

Those are both overflow/breathers and are usually just plumbed down by the swing arm with the other breathers and such and are open ended.

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Dunno how I got the PD,,must be going blind..Looking at my records of twin carbs those carbs are from an 83-84 RFVC 500 (PH51A)..They

also seem to come with a few different carb numbers if my files are to be believed,,2-3 more different types actually.

Not really sure what size the 500 carbs are nor the 600 XL tbh,,Can't help trying to jet carbs that are maybe a different size than they're

supposed to be..Needles are probably different as well as the jet sizes..A 65 is normal for the XL,,the other jets are in the ballpark as well

for sealevel jetting..My 86 XL twin carb ran a 65 and a couple of 125s or 128s.

 

Have those carbs got any other air/fuel screw on them than the one on the right in the second picture. Some of the twins

have a screw in the middle bottom of the carbs between the two bowls,,Anything like that there. ???You'll need to get down

on the ground and look up underneath the carbs to see it if it's there..

 

New info..

83-84 RFVC XR500..two 28mm..
83-87 RFVC XL600..two 30mm..
85-87 RFVC XR600..two 28mm

 

Couple of mil doesn't sound much. Not sure how you'd go jetting the 500/600 carbs to suit the XL.,Up/down,,who knows??

Edited by Horri

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I ran a 28 mm ph52a set up off an 87 xr6 on my 83xl6 for a short while. It ran good but it felt held back and was just a little tough to start cold. It was jetted small at 45 pilot, 122 & 122 (i was in a pinch and knew it was a proven setup in my old motor). Like i said it ran good. Now same bike, same motor, same everything, i put on a set of 30mm ph60a's and holy cow! To get it to run right i am jetted 60 pilot, 125 & 128. At just over sea level.

After this experience i feel pretty confidant that two mm actually makes a big difference and i would think 65 pilot on 28mm carbs at an elevation of 5000 feet would be really rich. But hey, these bikes are all a little different and my experience may not be normal.

Completely off the subject, does anyone know why the main jet in the primary carb is usually larger than the main jet in the secondary? It seems counterintuitive that the carb that usually opens at higher rpm has a smaller jet. For example stock jetting for an 83 xl600r (non california) is pilot 55, primary main 125, secondary main 112. That just sounds backwards to me. Maybe someone can enlighten me on why honda and or kehin did this.

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Thanks Guys,

yes, the carb I have on there is a 51A. There is no other air/screw adjustment that I can find, and I have the carbs off and apart. I also have the carbs that were supposedly on it before (with the broken connection tabs) and they are marked 68B. Is that correct for a '85 xl6? I am really tempted to try and get them working again if I can't get the 51A to work.

Back to the 51A, I do have a small hole in the air cut off diaphragm. Can someone explain to me how that works exactly and will it cause a big problem? if anything, it seems that it might lean the mixture? The other thing I am struggling with is when I shoot carb cleaner through the intake port which the air screw controls, some goes into the air cut off and some to the pj, but I am really not seeing it come out in the bore any where. Does anyone recall WHERE exactly it should come out? That seems like a pretty big issue. Also, my air screw does not have any oring...not sure if it should have one to prevent air leaking out? Am I correct in thinking that turning it counter clockwise leans the idle mixture?Thanks so much for all your help guys. There is a wealth of knowledge here.

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Yeah a PH68 should be the correct carb for the XL600,,I have them down as being for an 86/87..I don't have the B listed but a CA,,G,,and  an H.

There;s a few others I have listed for other year XL600,,eg..PH60A,,PH64A,,PH66A.Close enough I guess,,my records aren't precise per

the exact year.

How bad are these tab things broken,,any chance of a picture.??? You may be able to do a semi repair of them.

They aren't that vital,,a mickeymouse type repair may work..NZers are famous for them..

 

I can't explain ACVs workings..If it has a hole in it you can try and repair it,,some here do,,maybe they'll chime in. If

the repair option isn;t what you want buy an ACV from a single carb XR600 and use it..it'll do the job.

 

I have no idea where your squirting stuff is supposed to go when you put it through the holes.

 

That Airscrew on the side of the carb..There's two sorts..Ones short and stubby and comes with only a spring..The other is

long and slinny with a fine point..It has a spring a metal washer and a rubber o-ring on it..Sounds like your bike has the short stubby

variety..I need a picture of the current one to be certain..

 

Turning it in I guess would cut/lean the air getting to the carb I think..What's not really right here is the XL600 normally have the

screw in the bottom between the bowls or on the side close to where that one you currently have on the bike..Those are normally

classed as a fuel screw and are the long skinny variety,,yours being back where it is and if it;s short and stubby makes it an airscrew..

Slightly difficult trying to tune carbs that aren't really the same in Fuel/Airscrew design as each other as well as being a different size

than the originals.

Edited by Horri

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Sounds like you have an air screw so yes, counterclockwise makes the idle mixture leaner.

As for checking the pilot circuit with carb cleaner, you may have to turn the carb upside down and tip it away from you a little so that gravity can help. It will come out the tiny hole in the bottom center of the bore directly under the little notch in the slide. Not much will come out but if any makes it through then i would belive the circuit to be good.

1399215739954.jpg

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In that pic, the hole the carb cleaner will come out of is dead center right in front of the needle.

Some guys smear silicon or some other goop on ACV's to patch pin holes. I like new parts. You never know when honda will stop selling these little odds and ends type parts so if i can put something new in and not have to think about it for 25 years, I'm in!

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Well, I robbed an acv from my broken carb and did finally get the cleaner to run out the 6oclock hole that you described. The bike seems to be running better, although I still can't get it to die with the air screw all in, although it definitely idles rougher at that point. Leaning the air screw really doesn't do much. My idle is still set too high, so I'm thinking my pilot is still way off. I set the linkage per the book as far as throttle opening and sequence, but since the carb is meant for another bike, I may have to tune things some more. Thanks guys for all your help in this

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Horri, I think I could fix the busted tabs on the broken carbs, so I may just try and go that route... Not knowing why they were removed in the first place, there may be issues there too

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Horri, I think I could fix the busted tabs on the broken carbs, so I may just try and go that route... Not knowing why they were removed in the first place, there may be issues there too

Yep..If there's anything left of the metal connection points you could just use some smallish holes and some self tappers on them to hold

them together..I'd be able to give you a maybe better idea if I saw how bad they are. Even some JBweld may be good enough formed and drilled;

Chances are the p/o just busted them off somehow trying to get them apart..The internals may be fine..and yep,,the ACV from those 600 carbs

should be fine in the 500 carbs..Those ACVs are pretty much the same for the twin carb and the singles in XL/XR600/XR650R.

 

The main bit you want intact is the plastic type pipe which connects the 2 carbs together..It's shortish and has a rubber o-ring on

each end..O-rings you can get from a bearing shop or motor parts type shop..Can't imagine much else being wrong with them

apart from the pipe and maybe some gaskets for the bowls..Any jets in them???,,Slides and needles still in there???

Edited by Horri

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