Scratching my head on this free bike. Bike idles but dies when given any throttle

[mossheart]

So I was given an xs400 heritage special by my dad who got it for free from a friend. When he gave it to me he said he hadn't done anything with it and was originally going to fix and flip but got busy with other things ..
So here I am with a bike that doesn't start and is leaking oil from one side pretty bad.

I rebuilt the carburetor. Put a new battery in her. Found that the starter only tries to work if the bike is in gear. So kick start only until I can get a neutral safety switch. And probably a new starter solenoid.

I determined the oil was leaking from the generator housing. The bottom hole was stripped so tapped and replaced it with a new gasket. Still leaks around the wire grommet but oh well...

I put some fresh oil into the bike and get her started. She idles ok.. kinda low. 1k ish rpm but she dies immediately upon receiving any throttle...
I've read a lot on here about similar issues but haven't seen many solutions... It's not the pilot circuit that's clear.. the carb shouldn't be the problem... When I start it I can pull the wires from the plugs one at a time. The left cylinder is weaker than the right when running on its own... Hoping I don't have to touch the points cause the cover is held on by a stripped screw from the original owner...

 

[CaptChrome]

She idles ok.. kinda low. 1k ish rpm but she dies immediately upon receiving any throttle...

I would recommend you check/set the valve lash to spec as a first step and then raise the idle speed and synchronize the carbs. Doing this should eliminate the left/right cylinder imbalance. If it doesn't, then you will need to check compression on both sides.

 

[tstidham]

The carbs can be finicky for cleaning them, I had to do mine three times, and the last time I used a single strand of multistrand copper wire to ream clean all the jets and passages. Then I bench synced the butterflies using a zip-tie to set both initial openings the same and started the idle mixture screw at 2.5 turns out. After adjusting each mixture screw and lowering the idle speed, I ended up at 3.25 turns out on each. It ran OK but lots of decel popping. Recently, I also replaced the shaft seals and now it really runs well, no more decel popping from all the air being sucked in through the 46 year old shaft seals.

 

[mossheart]

The carbs can be finicky for cleaning them, I had to do mine three times, and the last time I used a single strand of multistrand copper wire to ream clean all the jets and passages. Then I bench synced the butterflies using a zip-tie to set both initial openings the same and started the idle mixture screw at 2.5 turns out. After adjusting each mixture screw and lowering the idle speed, I ended up at 3.25 turns out on each. It ran OK but lots of decel popping. Recently, I also replaced the shaft seals and now it really runs well, no more decel popping from all the air being sucked in through the 46 year old shaft seals.

So I've had the carburetors in and out about 50 times the past few days... Trying different things... I re adjusted the floats so the fuel sits at a proper level. They were low before. All the jets have been replaced. I never separated the carbs so they should* be in sync. The only thing I didn't fully service on the carb was the choke. And the bike won't start with the choke open rn kicks over fine with the choke closed... I also landed at about 3.25 turns on the mixture screws. I will note I've been running the carb direct to air with no intake installed just cause I got tired of putting it on and off...

 

[MrStubb]

Hey Hi Howareya? One thing to keep in mind is that these bikes were designed to work with the restrictions of the air cleaner. When I had mine running the Air cleaners were Totally eaten up so I replaced them with a set of Pods. That was less restrictive but caused a problem with accelerating. I actually was going to change the jets in my carbs before it Died on me & other responsible things took priority. You might also have a leaking carb boot that sucks air enough to lean it out & die. Good Luck!!!

 

[mossheart]

Hey Hi Howareya? One thing to keep in mind is that these bikes were designed to work with the restrictions of the air cleaner. When I had mine running the Air cleaners were Totally eaten up so I replaced them with a set of Pods. That was less restrictive but caused a problem with accelerating. I actually was going to change the jets in my carbs before it Died on me & other responsible things took priority. You might also have a leaking carb boot that sucks air enough to lean it out & die. Good Luck!!!

Carb boots are on my list of things to order... They have cracks on the outside... But after inspection the interior is clean and crack free. I'm suspect that the vacuum line from the boot to the tank leaks a bit... I'll try putting the intake back together and actually clamp the fuel lines. Perhaps that will help things...

 

[mossheart]

I would recommend you check/set the valve lash to spec as a first step and then raise the idle speed and synchronize the carbs. Doing this should eliminate the left/right cylinder imbalance. If it doesn't, then you will need to check compression on both sides.

Not exact sure how to do this. Trying not to get involved with internals of I can get away with it. Not doing a full restoration on this right this moment just wanna make it go down the road.