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Old 12-09-2007, 03:15 PM   #1
cyclewizard OP
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83 XL600R twin flat slide carbs

I got a 83 XL600 twin carb, I'm thinking of putting twin flat slide 32mm carbs on it. Anybody done this or knows of a site that has info for the swap?
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Old 12-09-2007, 04:07 PM   #2
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I havn't read of that swap yet, but this site or http://www.thumpertalk.com/ would be your best bet for the info in North America.
Here are a couple other sites you could search, but you might need http://babelfish.altavista.com/ to do some translating:
http://www.xl600.de/site/
http://www.hondaxl.it/
There is also some good stuff here:
http://justxr.com/justxr.html
http://www.xlintperformance.com/index.htm
http://www.oldrice.com/xl_page.htm
Good luck on your quest.
If you figure it out, please post a report here.
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Old 12-09-2007, 04:15 PM   #3
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Tough to change carbs on the 80s Honda XL

Quote:
Originally Posted by cyclewizard
I got a 83 XL600 twin carb, I'm thinking of putting twin flat slide 32mm carbs on it. Anybody done this or knows of a site that has info for the swap?
The main problem with this conversion is that the intake has two ports for each of the carbs--you will have to match the twin carbs to low and higher volume air. You might be better off modding the existing Honda carbs.
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Old 12-09-2007, 06:32 PM   #4
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I think it would be better to swap in a XR600R head and single carb from something parted out on Ebay but I am no expert.
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Old 12-09-2007, 06:36 PM   #5
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Quote:
Originally Posted by rdnakx250
I think it would be better to swap in a XR600R head and single carb from something parted out on Ebay but I am no expert.
Single carb heads are very difficult to make work on the XL600R frame because the rear shock is dead centre, with one carb intake boot on either side of it. Single carb frames have the rear shock offset a bit to one side to accomidate it.
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Old 12-09-2007, 06:44 PM   #6
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OOPS! My bad.
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Old 12-09-2007, 06:47 PM   #7
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carb mods

Is there any good carb mods I can do instead of swaping out for the 32's.
On my 83 model the primary carb has a 125 main an the secondary has a 112 main. Would 120 mains be better on both carbs?
How could I get the second carb to open at the same time as the primary carb? Also this bike has a reed valve, should I get rid of that?
It seems like you shouldn't need it since the 84 an up did not have one.
The bike runs great, But I would like to get all the performance I can out of the ole gal. I'm also going to get my exhaust jet hot coated.
For a 125.00 bucks I think it's well worth it.

thanks
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Old 12-09-2007, 08:08 PM   #8
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Quote:
Originally Posted by cyclewizard
Is there any good carb mods I can do instead of swaping out for the 32's.
On my 83 model the primary carb has a 125 main an the secondary has a 112 main. Would 120 mains be better on both carbs?
How could I get the second carb to open at the same time as the primary carb? Also this bike has a reed valve, should I get rid of that?
It seems like you shouldn't need it since the 84 an up did not have one.
The bike runs great, But I would like to get all the performance I can out of the ole gal. I'm also going to get my exhaust jet hot coated.
For a 125.00 bucks I think it's well worth it.

thanks
Pop's
What you have is a 2 stage carb, this allows for higher intake velocity (vacuum) and better fuel atomization at low RPM, (= better throttle response) while on the primary carb. As opposed to a single larger carb which would decrease intake velocity (vacuum) at smaller throttle openings, and give poor throttle response. You then have the secondary (right side) carb that starts to open at about 1/2 throttle. You end up with a larger carb at wide open settings than if you had a larger single carb. Trust me a single 60mm carb would not work as well as your 2 stage (dual 30mm = 60mm) carb. The reed valve between the two intake ports, function is to deliver an air/fuel mixture through both intake valves while on the primary carb. without it you would only be supplying air/fuel through the left intake valve from idle to 1/2 throttle. This would cause the right intake valve to run hot, because there would be no cooling effect of the incoming air/fuel mixture on the intake valve, and this would also not fill the big 100mm bore evenly. Also the jetting on each carb is different because each carb has to handle different throttle openings. There is some overlap in their operation. Essentially you have all the benefits of a large carb at full throttle, and all the benefits of a smaller carb from idle to half throttle.
I had an early "83" that I bought new, and could not get the bike off the dealers lot, due to persistent stalling at idle. I mean the bike would shut off if left to idle for 2 minutes. The bike would also stall when chopping the throttle approaching a red light. There was a technical bulletin on the "83" XL600R for "slow speed drivability". The update included if I remember correctly, new needles for each carb, a new insulator (intake manifold) which had a passage between both ports, a new CDI box with a different ignition advance curve. They then removed the limiter cap from the mixture screw and adjusted the mixture. These bikes were so lean they would not idle from the factory. I believe the bikes that received the slow speed drivability update from the dealer were to have a center punch mark on the engine next to the engine serial number. I dont know how many bikes were involved, but they were performing this update on "83's" in dealer inventory prior to delivery. Or at least they were supposed too. It was rather dangerous having a 600cc kick start only bike shut off in traffic. But the update combined with a supertrapp slip-on made a huge difference.
I hope this helps some......Tech23
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Old 12-09-2007, 08:42 PM   #9
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That's some great info, I'll check for the update an see if it was done.
Thanks for your help.

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Old 12-09-2007, 09:52 PM   #10
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A little tip from XRs Only.

Twin Carbs
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Old 12-10-2007, 06:16 AM   #11
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Behold, the beauty of the twin carb thumper.
It was a damnd shame they couldn't have tweaked the hardware a bit to make them a little easier to set up.
When they are working properly, they make better and more easy to use low end, while having a stonking good top end.
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Old 12-11-2007, 08:04 AM   #12
Tech23
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Quote:
Originally Posted by cyclewizard
That's some great info, I'll check for the update an see if it was done.
Thanks for your help.

Pop's
You are welcome, and thank you Gregster, for the technical features page from the back of the factory manual. I wonder what was different about the "84" that the reed valve cross port was eliminated. May have been the update manifold with the connecting passage.
If the update "kit" and/or the parts that comprise the kit are no longer available, and your bike was not updated... and you are not experiencing slow speed drivability/stalling as I described. I dont think I would sweat it. I would be curious if the bike fell into the VIN range for the update though. Some tech bulletins are handled on an "as needed basis". So a letter was not mailed to owners with the potential issue. These types of technical updates often have an "expiration date", as to how long the dealers will perform the work, and factory will issue the parts.

I had an obvious problem, that I was able to show the dealer repeatedly. I struggled to keep the bike running at delivery, and trying to be careful with how I was breaking in my new engine (with lots of moving parts inside). I rode down the street to the first gas station to top up the tank for the ride home. I had the engine stall when turning into the gas stations lot and coasted over to the pump. I started the bike, rode over to the gas station exit and it stalled again. I caught a red at the next light and again coasted to a stop. I turned around and went right back to the dealer. I started the bike, and let it idle on the kickstand for them to watch, and six times it shut down. I have to admit that I did not have to wait long for the phone call to bring the bike in for the update, so Honda knew there was an issue with their first year XL600R. The fact that I had a Yamaha XT500 prior to the XL, kept me from getting killed in traffic. I was most times able to refire it while coasting. Gotta love manual decompresors. So yeah, I was releived when the issue was addressed.

Also I would think the primary carb (left) would have the smaller main jet, and the secondary carbs. main would be larger. More air filling the big bore when the secondary carb is open. My shop manual went with the bike when I sold it.

After you research the VIN/update post your findings....I am curious.
Tech23.

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Old 12-11-2007, 12:15 PM   #13
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Also I would think the primary carb (left) would have the smaller main jet, and the secondary carbs. main would be larger. More air filling the big bore when the secondary carb is open. My shop manual went with the bike when I sold it.

no, actually, that's correct per what honda claims in the chop manual....the 125 in the primary carb and the 112 in the secondary. one major feature of drivability kit was richer pilot jet....sorry, don't recall exact #s but maybe a 65.

i'm about to find out effect of having em swapped, as i just learned on carb teardown that prev mechanic put em in backwards.

your reasoning is correct, tho....most multi-venturi carb arrangements (single carb or multis) use bigger throat in sceondary
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Old 12-11-2007, 01:05 PM   #14
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my '87 XL600R in all-stock form ran better than most XR650s Ive ridden. I kept my '85 XL250R, match ported it to accept XL350R intake manifold and installed an XL350R primary and XR350R secondary, I used XR500R float bowls, they have easy jet access/change "ports". the dual-carbed Hondas reved so high it was easy to meltdown and crack the head due to lean mixtures. I dialed mine in with an O2 sensor and LED mix indicator.
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Old 12-11-2007, 01:47 PM   #15
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Quote:
Originally Posted by cptoversteer
Also I would think the primary carb (left) would have the smaller main jet, and the secondary carbs. main would be larger. More air filling the big bore when the secondary carb is open. My shop manual went with the bike when I sold it.

no, actually, that's correct per what honda claims in the chop manual....the 125 in the primary carb and the 112 in the secondary. one major feature of drivability kit was richer pilot jet....sorry, don't recall exact #s but maybe a 65.

i'm about to find out effect of having em swapped, as i just learned on carb teardown that prev mechanic put em in backwards.

your reasoning is correct, tho....most multi-venturi carb arrangements (single carb or multis) use bigger throat in sceondary
cptoversteer....is that right? I did not intend to mislead, It is a wonder I remember any of this from 15 years ago. I cant even remember what I had for breakfast this morning. Thanks and ride safe......Tech23
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