Carb rebuild questions:

supasamurai · 04-23-2009, 02:06 PM

So I just got my first ever motorcycle. It's great, I love it, but it doesn't run. It's a 2000 Vulcan 750 and with just a little rust on the chrome, I paid $400 for it! Unfortunately the carburetor came in a hundred pieces in a box. The guy that sold it to me pulled it from the shop because he didn't want to sink anymore money into it and I get to rebuild the carb in order to get the bike going.

So the long and the short of it is that while I've got no problem figuring out how to put a carb together, I realize that there are a few things I need to know. I have most of the parts, missing a few hoses and such and those aren't free, but that's ok. The the box held two keihin cvk34 carbs.

There's a light layer of varnish which I know I need to clean, and the jets look good. I need to replace the air cut valve diaphragms on both sides and I think that was why the carb had to get worked on. Also the vacuum valve diaphragms don't seem to fit in there right and there's a layer of fine rust particles on it in places like the guy that took it apart left it out in the rain for a minute and just let the water evaporate out of it. It seems to wipe right off though.

My questions are:

1.) Do I really have to pay $45 apiece for air cut valve diaphragms and $95 apiece for vacuum diaphragms or is there a cheaper way? Seems like I could mosey down to the junkyard and buy a new set of carbs for cheaper than $300, you know?

2.) Why can't I find a dang carb rebuild kit? The o-rings for this thing are gonna run me like $28 per carb if I buy them separate. Whats up with that?

3.) Barring buying new o-rings, how can I tell if the old ones are still good? Should I just assume that they aren't? Could I use rtv sealant or something like that instead of o-rings? Could I just go down to the hardware store and fine some rings that seem to fit right? It it that big of a deal?

3.) Whats with the screw thats attached to a cable and has a knurled nob one the end of the cable, is that the idle stop screw? Which screw do I use to "set the idle"? How do I tune these bad boys?

4.) Finally, like a good puzzle, the pieces seem to go together easily, but I have no clue as to how much to torque things. Which screws are the ones I use to adjust things? Do I screw every screw/jet/bolt etc in till they stop? I learned from rebuilding cars that for small aluminum pieces you should screw until you see the tendons stand out on your hand (which I take to mean a normal person, as I'm a big manual labor type I do it till just before that point), but is that right?

Also, why in the heck did the guy tear the whole carb apart? Maybe there is a rebuild kit and I'm just not finding it. I partially rebuilt a carb on a 65 ford big block and it seemed to have all kinds of fun stuff in it.

Sorry for the length but thanks for the help!

yozalo · 04-23-2009, 05:26 PM

Maybe it's worth buying a brand new carb on ebay. It will cost way cheaper if you do so.

katoranger · 04-23-2009, 06:15 PM

Quote:

Originally Posted by yozalo

Maybe it's worth buying a brand new carb on ebay. It will cost way cheaper if you do so.

Yes. You may want to consider a new or a use carb from a running parted bike.

Or even a carb that is all together, but needs a rebuild.

Great buy on the bike though.

Allen

AZ200cc · 04-24-2009, 12:35 AM

Were You on bike bandit, Maybe they are cheaper than if You were at a dealer...

http://www.bikebandit.com/houseofmot.../m4539sch73344

Link to the parts

forchetto · 04-24-2009, 10:28 AM

Should be able to find anything you need at either of these two sites:

http://www.motorcyclecarbs.com/

http://www.sudco.com/Carburetor01.html

Weldangrind · 04-24-2009, 10:42 AM

Good score!

I recommend two things:
1. Buy a shop manual. It doesn't really matter if it is Clymer / Haynes / whatever, but Haynes is my personal favourite. Around here they're about $25.
2. Buy an o-ring kit. I'll bet that Harbor Freight has them for cheap. I bought a very comprehensive o-ring kit for $10.

The manual will tell you everything you need to know, including torque values and preliminary carb settings. I would stay away from RTV inside the carb.

Cheers!

knothead · 04-24-2009, 07:56 PM

When I had my Yamaha TDM the diaphragm/slide assemblies were $135 each, turns out that a Suzuki DR650 had the exact same diaphragm and they were only $20. Look for a bike with a similar carb (the TDM had Mikuni BDST 38 downdrafts, the DR has a BST 40). It might take some hunting and it helps if you can look at the diaphragms side by side. Having a good relationship with a local dealer helps!

The Kaw dealer should carry all of the o-rings you need for your carbs. Don't be scared to go in and price the parts. Bike bandit wanted over a dollar each for the o-rings I needed, the dealer prices ranged from ten cents to fifty cents... I got everything I needed for less than $10, including the gaskets. I was too late in matching up the diaphrgams though! The Harbour Freight o-ring kits won't have everything you need.

That Vulcan 750 should make a good first bike. They are a little underpowered, low and docile. Good things when you're learning.

04-23-2009, 02:06 PM	#1
supasamurai Join Date: Mar 2009 Posts: 4	Carb rebuild questions: So I just got my first ever motorcycle. It's great, I love it, but it doesn't run. It's a 2000 Vulcan 750 and with just a little rust on the chrome, I paid $400 for it! Unfortunately the carburetor came in a hundred pieces in a box. The guy that sold it to me pulled it from the shop because he didn't want to sink anymore money into it and I get to rebuild the carb in order to get the bike going. So the long and the short of it is that while I've got no problem figuring out how to put a carb together, I realize that there are a few things I need to know. I have most of the parts, missing a few hoses and such and those aren't free, but that's ok. The the box held two keihin cvk34 carbs. There's a light layer of varnish which I know I need to clean, and the jets look good. I need to replace the air cut valve diaphragms on both sides and I think that was why the carb had to get worked on. Also the vacuum valve diaphragms don't seem to fit in there right and there's a layer of fine rust particles on it in places like the guy that took it apart left it out in the rain for a minute and just let the water evaporate out of it. It seems to wipe right off though. My questions are: 1.) Do I really have to pay $45 apiece for air cut valve diaphragms and $95 apiece for vacuum diaphragms or is there a cheaper way? Seems like I could mosey down to the junkyard and buy a new set of carbs for cheaper than $300, you know? 2.) Why can't I find a dang carb rebuild kit? The o-rings for this thing are gonna run me like $28 per carb if I buy them separate. Whats up with that? 3.) Barring buying new o-rings, how can I tell if the old ones are still good? Should I just assume that they aren't? Could I use rtv sealant or something like that instead of o-rings? Could I just go down to the hardware store and fine some rings that seem to fit right? It it that big of a deal? 3.) Whats with the screw thats attached to a cable and has a knurled nob one the end of the cable, is that the idle stop screw? Which screw do I use to "set the idle"? How do I tune these bad boys? 4.) Finally, like a good puzzle, the pieces seem to go together easily, but I have no clue as to how much to torque things. Which screws are the ones I use to adjust things? Do I screw every screw/jet/bolt etc in till they stop? I learned from rebuilding cars that for small aluminum pieces you should screw until you see the tendons stand out on your hand (which I take to mean a normal person, as I'm a big manual labor type I do it till just before that point), but is that right? Also, why in the heck did the guy tear the whole carb apart? Maybe there is a rebuild kit and I'm just not finding it. I partially rebuilt a carb on a 65 ford big block and it seemed to have all kinds of fun stuff in it. Sorry for the length but thanks for the help!
	0

04-24-2009, 12:35 AM	#4
AZ200cc Join Date: Apr 2007 Location: Show Low Arizona Posts: 2,889	Were You on bike bandit, Maybe they are cheaper than if You were at a dealer... http://www.bikebandit.com/houseofmot.../m4539sch73344 Link to the parts __________________ <br />2001 Suzuki DR200SE<br />1997 Suzuki RM250 YIKES<br />1995 Yamaha Breeze 125 daughters<br />1991 Honda XR80r Restored<br />maybe a 2003 Yamaha TTR90
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04-24-2009, 10:28 AM	#5
forchetto Join Date: Jul 2008 Location: Gijon, Asturias,Northern Spain Posts: 396	Should be able to find anything you need at either of these two sites: http://www.motorcyclecarbs.com/ http://www.sudco.com/Carburetor01.html __________________ Jincheng Monkey JC50Q-7 (two of them) Skyteam Dax replica ST110-6 (two of them) Zongshen ZS125-43 Qingqi QM200GY-BA Super Motard Yamaha Virago XV1100 Triumph Bonneville SE Qingqi QM110GY PGO Bug rider 250 Buggy
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04-24-2009, 10:42 AM	#6
Weldangrind Join Date: Mar 2009 Location: Sardis, BC, Canada Posts: 25,977	Good score! I recommend two things: 1. Buy a shop manual. It doesn't really matter if it is Clymer / Haynes / whatever, but Haynes is my personal favourite. Around here they're about $25. 2. Buy an o-ring kit. I'll bet that Harbor Freight has them for cheap. I bought a very comprehensive o-ring kit for $10. The manual will tell you everything you need to know, including torque values and preliminary carb settings. I would stay away from RTV inside the carb. Cheers! __________________ Weldangrind "I figure I'm well-prepared for coping with a bike that comes from the factory with unresolved issues and that rewards the self-reliant owner." - Buccaneer
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04-23-2009, 05:26 PM	#2
yozalo Join Date: Apr 2009 Posts: 330	Maybe it's worth buying a brand new carb on ebay. It will cost way cheaper if you do so.
	0

04-24-2009, 07:56 PM	#7
knothead Join Date: May 2007 Location: In the land of the busted up ricebowl Posts: 815	When I had my Yamaha TDM the diaphragm/slide assemblies were $135 each, turns out that a Suzuki DR650 had the exact same diaphragm and they were only $20. Look for a bike with a similar carb (the TDM had Mikuni BDST 38 downdrafts, the DR has a BST 40). It might take some hunting and it helps if you can look at the diaphragms side by side. Having a good relationship with a local dealer helps! The Kaw dealer should carry all of the o-rings you need for your carbs. Don't be scared to go in and price the parts. Bike bandit wanted over a dollar each for the o-rings I needed, the dealer prices ranged from ten cents to fifty cents... I got everything I needed for less than $10, including the gaskets. I was too late in matching up the diaphrgams though! The Harbour Freight o-ring kits won't have everything you need. That Vulcan 750 should make a good first bike. They are a little underpowered, low and docile. Good things when you're learning.
	0