loss of power everywhere

[drivinmecrazy]

Hey all
Posting a new thread to get some help with my kid's bike. He's already got a thread going but I think the description of the problem is lacking.
Originally we started with a bike that stuttered at higher RPM's and was kinda flat on power. Fast forward from a winter in storage to the work we're been doing:

• Installed brand new coil
• Checked TCI components visually and used timing light to visualize spark - found a possibly bad plug lead so we replaced the leads with a different used set
• Checked spark with "new leads" and all seems good
• Advance seems to work fine

Took the bike for a spin but no power up near 5000 rpm (just layed over like it's running on one cylinder) and stuttering badly

• Removed BS34 carbs and gave them a very thorough clean
• Mixture screws set to 3 turns
• Carbs synch'd
• Idle set to 1200 rpm

Started the bike and checked voltage at battery

• Idling voltage is 12.3 volts and declining
• Stopped the engine but could not restart on starter due to low battery
• Charged battery for a couple of beers
• Restarted bike and checked voltage, 13.5 volts @ 2500 rpm, thinking battery might be pooched?? The voltage climbs when the engine rpm increases but the highest I measured was 14.1 volts @ 4000 rpm
• Shut the bike down and checked battery voltage, 12.5 volts

Cooled bike down to check valve lash

• Checked valve lash - all is good

Bike runs really nice idling in the driveway but you can tell there's something the matter when you crack the throttle because the engine sounds like it has no power. Took the bike for a spin with the battery still fresh from the last charge.

Now the problem is no power throughout acceleration. Small amount of throttle input will allow the bike to make a little power but anything more and the engine has no power.

Any suggestions because I'm running out of things to check

One question - what size are the mixture screw o-rings? I had to use what I could find, they fit but maybe a little fat. Theoretically the mixture screw needle should not be affected?

 

[thuban]

Sounds like it starts and idles fine? Simple things, check the vent hole on the gas cap to make sure it is open! Also, if the kill switch is dirty inside, it can cause the engine to break down and run on one cylinder and chug at speed.

 

[WideAWAKE]

From both of your guys run downs it sounds like fuel issues.

how clean is the gas tank/petcocks?

 

[Ratranger]

Does it have pod filters? Straight pipes?
The CV carbs don't always like pods, and the type of pod can make a difference. Not an XS, but on a fzr without some work it wouldn't rev up and the slides would flutter.

 

[Superjet]

Sounds like stock jetting, open exhaust and open air filters.

 

[drivinmecrazy]

Pulled the evil b*tch out of the garage and tested with air boxes installed. Also looked at the vent on the fuel cap - it is old but functional. Bike starts easy, idles ok but still has no power. Stock everything so jetting shouldn't be an issue. One thing I noticed is a lot of fuel pulling out of the bowl with the throttle wide open to rev up the bike. It coincides with the rough running probably because the engine can't handle the fuel load. then bike then starts to run rough becasue the plugs are getting fouled.
I'm about snookered on the old girl. I don't want to blame the TCI module but everything else seems to check out.

 

[drivinmecrazy]

More...

• Checked TCI module and it looks good, no cold solder joints and diodes meter fine. All connections are tight.
• Checked coil ground at and it's solidly grounded,
• Charged the battery to full capacity
• Checked voltage at coil and it's about 0.5 volts lower than the battery
• Checked spark with plugs out, OK orange spark while spinning motor with the electric starter
• Checked spark turning the motor over using the kick starter and it's a nice fat blue
• Mounted the stock air filters
• Started the bike and set mixture screws to 2.5 turns
• Ran the bike around the block but still the same feeling that the bike is laying over stuttering

We are going to change the gas in the morning because it seems to be the next logical thing to try (probably should have been one of the first) since it's last year's gas with fuel stabilizer in it. Maybe the gas won't vaporize properly.

 

[drivinmecrazy]

changed the gas but still won't accelerate properly
Idles fine but peg the throttle stationary the bike gets to 4500 rpm then just stutters. O can hold the throttle wide open and never exceed 4500 rpm in the driveway.

 

[carlm]

Hi There,
I have what sound like the exact same problem with my 83 XS starts and runs but 0 power.
I wonder if you found the cause?
thanks

 

[jetmechmarty]

Mine went through that. I sent my TCI to @rickthefix . He fixed it. It has been running fine since then.