Alternative Carburetors?

[J32]

I'm looking for alternative carburetors that are out there on the market that can be bought from the factory and with a little adjustments work on the bike without having to pay $$$$

Maybe something around the $$ to $$$ range. I keep seeing 34mm carburetors on Amazon like this one Carburador Vergaser TM24 TM28 TM30 TM34 TM32 TM38 Flat Slide Spigot Compatible For MIKUNI Carburetor 50-650cc 2/4-Stroke Engine I know this would obviously work because, it says 650cc in the description.

Now what really gets me confused is that why do most motorcycle carburetors have almost the identical size, still be 34mm, but only rated for 150cc? Such as the PWK 34mm Carburetor Motorcycle Racing Carb Universal why wouldn't this be able to work with a 650cc engine?

 

[Adamc]

I'm looking for alternative carburetors that are out there on the market that can be bought from the factory and with a little adjustments work on the bike without having to pay $$$$

Maybe something around the $$ to $$$ range. I keep seeing 34mm carburetors on Amazon like this one Carburador Vergaser TM24 TM28 TM30 TM34 TM32 TM38 Flat Slide Spigot Compatible For MIKUNI Carburetor 50-650cc 2/4-Stroke Engine I know this would obviously work because, it says 650cc in the description.

Now what really gets me confused is that why do most motorcycle carburetors have almost the identical size, still be 34mm, but only rated for 150cc? Such as the PWK 34mm Carburetor Motorcycle Racing Carb Universal why wouldn't this be able to work with a 650cc engine?

My guess is its to do with the standard jet sizes installed
But the Carb Gurus here will have a better understanding.

 

[46th Georgia]

I'm looking for alternative carburetors that are out there on the market that can be bought from the factory and with a little adjustments work on the bike without having to pay $$$$

Maybe something around the $$ to $$$ range. I keep seeing 34mm carburetors on Amazon like this one Carburador Vergaser TM24 TM28 TM30 TM34 TM32 TM38 Flat Slide Spigot Compatible For MIKUNI Carburetor 50-650cc 2/4-Stroke Engine I know this would obviously work because, it says 650cc in the description.

Now what really gets me confused is that why do most motorcycle carburetors have almost the identical size, still be 34mm, but only rated for 150cc? Such as the PWK 34mm Carburetor Motorcycle Racing Carb Universal why wouldn't this be able to work with a 650cc engine?

Stay away from those PWK's. Contact Gary at Hoos Racing if you want different carbs. He'll set you up with complete kit of high quality Mikuni VM's with cables manifolds and filters. He's a great guy.

 

[jpdevol]

The original carbs work very well when properly cleaned/rebuilt. Replacement alternatives will likely cause additional tuning issues without any performance gains. Replacements made specifically for the XS650 will likely need re-jetted and generic carbs will need extensive trial-and-error rejetting, if you can get them to work at all.

The genuine VM34 Mikuni's and the original OEM carbs have an extensive knowledge base applied to the XS650; anything else and you're strictly on your own and breaking new ground (fat chance)

 

[JJames]

Just curious why you're looking for carb alternatives. Performance? Old carbs in disrepair or missing? Etc. Etc. And how much is $$$$?

 

[J32]

Just curious why you're looking for carb alternatives. Performance? Old carbs in disrepair or missing? Etc. Etc. And how much is $$$$?

Manly just to upgrade, I'm redoing all the wiring the previous owner put in and I wanted to see what else is out there on the market that could possibly work better than the Mikuni VM34's that I have currently (which seem like their in decent shape) this is my project bike for getting back and forth to work someday.

The Mikuni VM34's I have are working, it seems like I can only get it up to maybe 50mph before it starts to bog down though. After it warms up the idle is high and there is quite a bit of popping coming from one side's exhaust -I have yet to open them up and clean them out.

 

[J32]

Stay away from those PWK's. Contact Gary at Hoos Racing if you want different carbs. He'll set you up with complete kit of high quality Mikuni VM's with cables manifolds and filters. He's a great guy.

Thanks, I'll send him a message if I cant get NV34's working properly.

 

[Raymond]

The Mikuni VM34's I have are working, it seems like I can only get it up to maybe 50mph before it starts to bog down though. After it warms up the idle is high and there is quite a bit of popping coming from one side's exhaust -I have yet to open them up and clean them out.

Those symptoms suggest you need to strip and clean the carbs. Clean working area, be methodical, keep all the parts together - otherwise easy to lose all the small bits. Note all the jet sizes - this is basic information you will need. Compare with the sizes recommended on this forum - after cleaning the carbs, the bike might well need further tuning. What exhaust are you running? What air filters? These affect the mixture you need.

Also, the bike won't right unless all the basics are right - valve gaps, cam-chain tension, clean & correct plugs, spark timing at idle and advance.

IMHO you have a far higher chance of getting the bike running right if you stick with the original carbs and get those sorted than buying some new carbs which are unlikely to be set up for your bike and you would need to start playing around to get it running at all.

 

[Charles13]

Manly just to upgrade, I'm redoing all the wiring the previous owner put in and I wanted to see what else is out there on the market that could possibly work better than the Mikuni VM34's that I have currently (which seem like their in decent shape) this is my project bike for getting back and forth to work someday.

The Mikuni VM34's I have are working, it seems like I can only get it up to maybe 50mph before it starts to bog down though. After it warms up the idle is high and there is quite a bit of popping coming from one side's exhaust -I have yet to open them up and clean them out.

Sounds like you have one or more air leaks

 

[JJames]

Ha

Those symptoms suggest you need to strip and clean the carbs. Clean working area, be methodical, keep all the parts together - otherwise easy to lose all the small bits. Note all the jet sizes - this is basic information you will need. Compare with the sizes recommended on this forum - after cleaning the carbs, the bike might well need further tuning. What exhaust are you running? What air filters? These affect the mixture you need.

Also, the bike won't right unless all the basics are right - valve gaps, cam-chain tension, clean & correct plugs, spark timing at idle and advance.

IMHO you have a far higher chance of getting the bike running right if you stick with the original carbs and get those sorted than buying some new carbs which are unlikely to be set up for your bike and you would need to start playing around to get it running at all.

Have to agree with Raymond. The first thing to do on a new to you bike is clean up those carbs. Take care to clean all the small passages and blow through with carb cleaner and air. Lots of how to on this site and you tube. None of the carburetors used on the xs were bad carburetors regardless of what some people will try to tell you. As Raymond said , note your jet sizes while you have carbs apart. If you have stock airbox and stock or close to stock exhaust you may be OK with stock jetting. Mods to airbox or exhaust you may need to go up a size or two on pilot and main. Tons of info on this site tech section. Or, if you are lazy like me, report your findings and wait for one of a handful of experts to give you a "recipe ". IMHO for dependability and ease of tuning ya just can't beat the stock Mikunis. I'd spend my$$$ elsewhere,Tires ,brakes etc. My two cents is free. Have fun.

 

[gggGary]

So he already has VM34's the goto aftermarket carbs. Just a matter of getting everything in tip top shape, correct brass etc. I put a lot of miles on VM34's.
They aren't top tier carbs, just simple, relatively simple to tune, fairly low cost replacement carbs. Since they've been used so much, tuning info is widely available.
90% of the time the carbs you have whether stock, or decent aftermarket, will be fine, it's just an investment in learning how they work, and getting them set correctly. With any carbs, you won't get the latter, if you don't do the former.

 

[toglhot]

I have VM carbs on my 74 TX, they work well. I bought them in kit form which included manifolds, rubbers and cables as well as carbs. Be aware that the manifolds locate the carbs right under the taps, It is a well known problem, most tilt the carbs over or use BS34 manifolds. BS34 manifolds are a couple of mms too large, but the carbs will fit cinching up the clamps a little tighter. I made my own manifolds to get around the poroblem.
You can get Mikuni flat slide kits with manifolds cables and rubbers. But they are more expensive than VM kits.
Be wary of knock offs, I've heard the jets for the knock offs have a different thread than Mikunis, so it may be difficult to get jets for them and parts may not be interchangeable???
All carb kits need tuning, there are manuals to tell you how to do it, but briefly read your plugs, that is the only way to do it properly. idle = pilot jet and airscrew. Idle to 1/4 throttle pilot jet. 1/4 to 3/4 throttle = needle and needle jet. 3/4 - flat out = main jet. However, there is some overlap.
In a nutshell, it aint rocket science, but you'll never know that, unless you try!

 

[JJames]

So he already has VM34's the goto aftermarket carbs. Just a matter of getting everything in tip top shape, correct brass etc. I put a lot of miles on VM34's.
They aren't top tier carbs, just simple, relatively simple to tune, fairly low cost replacement carbs. Since they've been used so much, tuning info is widely available.
90% of the time the carbs you have whether stock, or decent aftermarket, will be fine, it's just an investment in learning how they work, and getting them set correctly. With any carbs, you won't get the latter, if you don't do the former.

Oops somehow I read BS 34. Duh. Anyhow. Genuine VMs should be decent serviceable carbs. As stated plenty of tuning info from those ho have gone before.

 

[AUTOMAN]

VM's were the go to carb on Trumps.

FWIW

cliff

 

[jay760]

Anybody got any jetting numbers for dellorto phm38 carbs, I'm try to sort out a high revving misfire I have and think it may be my old carbs worn out, I've been waiting to try the 38s for a long time so nows the time I think