First Time Build Thread

[Jim]

If you were to search this entire forum.... I doubt you'll find any (or damn few) instances of carb kits actually having the right parts...
Look for OEM from Partzilla.com and/or Nichecycle.com for genuine Mikuni parts.

Have you read the carb guide? It's pretty much the bible for carbs in these bikes.

 

[Jim]

Another good source for genuine Mikuni parts. Them and Niche both sell Chinese crap too. Make sure you get the real stuff (Mikuni)

https://www.jetsrus.com/

 

[Kevin Werner]

These seemingly complex carbs are desperately simple. The problem is that every couple years the whole jetting package changed. If you have 76 carbs, 75 and 78 parts are going to be wrong (IIRC) Stay with OEM Mikuni brass. If you have intake or exhaust mods slightly different jets may be needed. Mikuni jets at Niche are ~$10 a pair. But, endeavor first to get both cylinders firing good, carbs synced etc.
Gentlemen far wiser than I emphasize (and I learned from experience) that a real careful examination of your charging system is important. Make sure your battery is strong and when running at 3000 rpm is getting charged to ~14.4 volts. Variations in your battery voltage directly affect your spark and how the motor runs. Check that the charge system is good to make you life easier.
And welcome to the XS650 madness (sickness?)
Finally, there are some on this forum who believe that is the best "Blue" ever put on an XS650.
Cheers

 

[Junkyard Jake]

It's pretty much the bible for carbs in these bikes.

But, endeavor first to get both cylinders firing good, carbs synced etc.

I will dig into the carb guide and get the real parts needed to properly rebuild them. I’m thankful to have found the forum as I want to do this right and learn as much as I can. I appreciate everyone’s help and replies!

 

[Junkyard Jake]

Put the old needle and seat back in and it is no longer dumping fuel and is firing on that side now. Sounds and revs pretty good with the choke on, but with the choke off it pops and bangs on the right side. I’ve got some tuning to do.

 

[Jim]

With the hanging idle and the popping, it's lean... very lean....
Could be the pilot circuit in the carbs plugged or restricted... and could also be air leaks from cracked intake boots. Or both. have a look in TECH. should be some good info on cleaning the carbs.
For air leaks, spray some carb cleaner, brake cleaner or electrical cleaner on the carbs and boots.... something that's flammable and evaporates. Use the fine straw to direct the spray so you can tell where it's leaking. Any leaks and the cleaner will get sucked in and cause a rapid increase in revs. Once you find a leak, spray it several times to verify and isolate to a specific area.

You're making progress!!

 

[Junkyard Jake]

With the hanging idle and the popping, it's lean... very lean....
Could be the pilot circuit in the carbs plugged or restricted... and could also be air leaks from cracked intake boots. Or both. have a look in TECH. should be some good info on cleaning the carbs.
For air leaks, spray some carb cleaner, brake cleaner or electrical cleaner on the carbs and boots.... something that's flammable and evaporates. Use the fine straw to direct the spray so you can tell where it's leaking. Any leaks and the cleaner will get sucked in and cause a rapid increase in revs. Once you find a leak, spray it several times to verify and isolate to a specific area.

You're making progress!! View attachment 328373

Thanks for the great info and tips as always Jim! The bike didn’t have the air box or filters when I got it. I imagine that is going to play a big part also?

 

[Jim]

I imagine that is going to play a big part also?

Not a big part, no. Yes, no air filters will make you a tad lean, but the engine will basically run just fine without filters... as long as it was rejetted for the less restrictive intake air.
If you wouldn't mind backtracking a little, it's be nice to know exactly what jets you have installed. That would actually give you a good excuse to give the carbs another good clean.

Some good closeup pics of the carbs disassembled might give us some more clues as to what's up too.

 

[member43148]

Just a suggestion.
When tuning further it could be beneficial to use that Centerstand!
Get the carbs level and have an easier time accessing everything. Remove the tank ?
You can even create a temporary fuel supply by hanging a reservoir off the clutch side handlebar.
Make it easier

 

[Adamc]

With the hanging idle and the popping, it's lean... very lean....
Could be the pilot circuit in the carbs plugged or restricted... and could also be air leaks from cracked intake boots. Or both. have a look in TECH. should be some good info on cleaning the carbs.
For air leaks, spray some carb cleaner, brake cleaner or electrical cleaner on the carbs and boots.... something that's flammable and evaporates. Use the fine straw to direct the spray so you can tell where it's leaking. Any leaks and the cleaner will get sucked in and cause a rapid increase in revs. Once you find a leak, spray it several times to verify and isolate to a specific area.

You're making progress!! View attachment 328373

Here is a good carb cleaning video; it helped me anyhow.

 

[Junkyard Jake]

Not a big part, no. Yes, no air filters will make you a tad lean, but the engine will basically run just fine without filters... as long as it was rejetted for the less restrictive intake air.
If you wouldn't mind backtracking a little, it's be nice to know exactly what jets you have installed. That would actually give you a good excuse to give the carbs another good clean.

Some good closeup pics of the carbs disassembled might give us some more clues as to what's up too.

Ahh okay, good to know about the air filters. I assumed that was going to have a bigger impact.
I forgot to mention that the left side is dumping fuel now also. I think it's safe to say the needle and seat in those kits are junk. I'll be tearing into them again here soon and will be sure to get better pictures. I'm also going to order new jets and everything before then and make sure to get genuine Mikuni parts this time around. When I rebuilt them, I bought the big can of chem dip and let each side sit in there for about 30 minutes. I then sprayed out the circuits with a can of carb cleaner and a straw. I must not have hit all of them as well as I thought.

Just a suggestion.
When tuning further it could be beneficial to use that Centerstand!
Get the carbs level and have an easier time accessing everything. Remove the tank ?
You can even create a temporary fuel supply by hanging a reservoir off the clutch side handlebar.
Make it easier

I had the tank off for testing the coils etc. earlier but have it halfway on now for the fuel troubleshooting and tuning. I like your auxiliary tank idea better though. I appreciate the suggestions!

Here is a good carb cleaning video; it helped me anyhow.

Thanks for the video recommendation. I'll check it out!

 

[John Regular]

Sweet bike dude, glad you didn't chop it. I would recommend reading some of these guy's build threads in their entirety if you haven't already. You'll find answers to questions you haven't thought of yet. Welcome to the show,,,,