William
Cant Get Enough
Finally got my xs to fire after a two year build! Only concern is it revs super high after start up and freaks me out so i kill it and it lopes at idle for a short bit before dying! Carb adjustment maybe? So pumped!
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High Rev!!
- Thread starter William
- Start date
CDNTX650
XS650 Guru
timing? throttle screw all the way out?
William
Cant Get Enough
no idea about timing or how to check it. Just pumped it finally fired. The butterflies arent pulled at all from the tension on the cable. it idles and sounds so good after key is turned off! I have to twist the throttle to kill it!
William
Cant Get Enough
Lowered the idle with the screw but it stays revved after throttle twist so pretty sure it's a manifold! Just super stoked I can go out and crank her. Thanks a million for everyone that helped!
Rexxis
Almost there...
I'm having the same problem Will. Did you get it figured out? I'm suspecting my old as dirt carb boots as well..
Tron
Bearded Sheep Whisperer
Sounds like a lean condition. Leaks most likely. Any airbox mods or exhaust mods to these hot rods?
Rexxis
Almost there...
No mods between carbs and head, original boots. Open filters, no airbox, open pipes, 750 kit. I stepped up 2 on the mains and one on the pilot. Can the carbs themselves pull in air around things like butterfly shafts n stuff? I think I read that somewhere..
Oh, and mine dies soon as I hit the kill switch, doesn't come down to normal idle rpm's.
Oh, and mine dies soon as I hit the kill switch, doesn't come down to normal idle rpm's.
Rexxis
Almost there...
It's a '79 w a pamco, Hugh's Pma and capacitor.
Springs on my advance snap back cleanly and advance rod is lubed and turns freely. I ordered some cheapo boots off eBay today, hopefully that will stop the issue and get me through sept as JBM is out of stock on the boots till then.
Idle is adjusted as per the amckay guide. Diaphrams are in good shape.
Anything else than can make the bike nearly redline like this?
Springs on my advance snap back cleanly and advance rod is lubed and turns freely. I ordered some cheapo boots off eBay today, hopefully that will stop the issue and get me through sept as JBM is out of stock on the boots till then.
Idle is adjusted as per the amckay guide. Diaphrams are in good shape.
Anything else than can make the bike nearly redline like this?
Tron
Bearded Sheep Whisperer
Your running no airbox, and open pipes.
Its probably running lean.
Its probably running lean.
Rexxis
Almost there...
You think it's still running lean withe 2 sizes up on the main jets and 1 up on the pilot?
Rexxis
Almost there...
Running the 750 kit w open intake and exhaust. Nearing the end of my build and this is the first time the bike has ran since I bought it. Bike revs crazy high on start-up. No tach but I'd guess it's around the 5k range.
Throttle cable is good and slides are sitting at bottom and return when pushed up. Diaphragms are good and slides fall slowly when the crescent shaped port at top of intake bell is covered. Idle screws are turned 2.25 turns out. Factory setting for my year. Any other settings I should be concerned with?
Jet sizes currently
Main 140
Pilot 30
Originals for my bike('79 XS650F)
Main 135
Pilot 27.5
I checked and the bike was previously using the factory size jets so that means I definitely only went 2+ on mains and 1+ on pilot. I was worrying that maybe a PO had already upped the jets and I was upping it even more but this is not the case.
The change in jetting wouldn't cause such a drastic increase in RPM's would it? I would think that changing the main by two sizes might increase the RPM's a little but to nearly what I would guess is around the 5k range.. I think something else is going on. I really don't know though as my experience is next to nothing.
Could a vacuum leak cause such a drastic response to RPM? My carb boots were abt as hard as rocks.. New ones just arrived and will replace soon as air barb plugs and proper hose clamps arrive. I've got the gaskets between head and boots but I didn' use any gasket glue, should I use some kind of gasket glue? I just hate scraping gaskets so when the carbs have to come off again(which I know they inevitably will), I didn't want to have to scrape and replace the gaskets every time.
I'm hoping one of you gurus will see this soon and maybe be able to get me pointed in the right direction. I'm pretty much stumped right now and I have a feeling the new boots aren't the solution, but hey, I needed new ones anyway.
Throttle cable is good and slides are sitting at bottom and return when pushed up. Diaphragms are good and slides fall slowly when the crescent shaped port at top of intake bell is covered. Idle screws are turned 2.25 turns out. Factory setting for my year. Any other settings I should be concerned with?
Jet sizes currently
Main 140
Pilot 30
Originals for my bike('79 XS650F)
Main 135
Pilot 27.5
I checked and the bike was previously using the factory size jets so that means I definitely only went 2+ on mains and 1+ on pilot. I was worrying that maybe a PO had already upped the jets and I was upping it even more but this is not the case.
The change in jetting wouldn't cause such a drastic increase in RPM's would it? I would think that changing the main by two sizes might increase the RPM's a little but to nearly what I would guess is around the 5k range.. I think something else is going on. I really don't know though as my experience is next to nothing.
Could a vacuum leak cause such a drastic response to RPM? My carb boots were abt as hard as rocks.. New ones just arrived and will replace soon as air barb plugs and proper hose clamps arrive. I've got the gaskets between head and boots but I didn' use any gasket glue, should I use some kind of gasket glue? I just hate scraping gaskets so when the carbs have to come off again(which I know they inevitably will), I didn't want to have to scrape and replace the gaskets every time.
I'm hoping one of you gurus will see this soon and maybe be able to get me pointed in the right direction. I'm pretty much stumped right now and I have a feeling the new boots aren't the solution, but hey, I needed new ones anyway.
Running the 750 kit w open intake and exhaust. Nearing the end of my build and this is the first time the bike has ran since I bought it. Bike revs crazy high on start-up. No tach but I'd guess it's around the 5k range.
Throttle cable is good and slides are sitting at bottom and return when pushed up. Diaphragms are good and slides fall slowly when the crescent shaped port at top of intake bell is covered. Idle screws are turned 2.25 turns out. Factory setting for my year. Any other settings I should be concerned with?
Jet sizes currently
Main 140
Pilot 30
Originals for my bike('79 XS650F)
Main 135
Pilot 27.5
I checked and the bike was previously using the factory size jets so that means I definitely only went 2+ on mains and 1+ on pilot. I was worrying that maybe a PO had already upped the jets and I was upping it even more but this is not the case.
The change in jetting wouldn't cause such a drastic increase in RPM's would it? I would think that changing the main by two sizes might increase the RPM's a little but to nearly what I would guess is around the 5k range.. I think something else is going on. I really don't know though as my experience is next to nothing.
Could a vacuum leak cause such a drastic response to RPM? My carb boots were abt as hard as rocks.. New ones just arrived and will replace soon as air barb plugs and proper hose clamps arrive. I've got the gaskets between head and boots but I didn' use any gasket glue, should I use some kind of gasket glue? I just hate scraping gaskets so when the carbs have to come off again(which I know they inevitably will), I didn't want to have to scrape and replace the gaskets every time.
I'm hoping one of you gurus will see this soon and maybe be able to get me pointed in the right direction. I'm pretty much stumped right now and I have a feeling the new boots aren't the solution, but hey, I needed new ones anyway.
The usual suspects for a hovering high idle are: air leaks, sticking ATU,carbs not sychronized. Its important that both butterflys in the carbs can go fully closed.
I recently had my rpms hovering high, and found that one carb had a worn out O-ring on the needle jet. Once I replaced the O-rings with new ones, I no longer have the hovering. I was able to actually see raw gas being sucked up around the needle jet.
The picture shows the 70 to 79 needle jets. The groove is where the O-ring lives.
Leave your air box/pods off, and with engine idling, use a mirror to view the needle jet.
The O-rings may or may not be your problem, but if they are original, then they are worn out and should be replaced anyway.
Also, you don't need to take the intake manifolds off each time you want to remove the carbs. Just undo the clamps and take the carbs out of the manifolds. Remove the dipstick, the camchain adjuster nut, and the throttle cable bracket on top of the left carb. Its a little tight but the carbs will then comeout on the right side. Lubricate the rubber intake manifolds (I use dielectric grease) and they will pop in and out quite easily.
