Honda CBR XX Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1 (Edited)
I just bought this basketcase bike, it starts and idles just fine, but when you rev it up it growls, revs to 6K or so, then stalls - RPMs drop back to 1-2K and then it revs up higher, rinse repeat. Carbs have been cleaned several times. It almost feels like a spark-cut. It does occasionally shoot fireballs when it does it. It has new plugs, coils off a good running bike, CDI swapped, cleaned carbs, checked for air leaks, running off 2 different tanks, then an aux tank... still it continues. Carbs are not sync'd yet, but I have a hard time seeing a sync issue cause a stall-out. I'm running without the airbox, until I figure it out, as getting the airbox on has been a pain, often causing the carbs to pop out of their boots.

Here is a video of the problem:
 

·
Registered
Joined
·
1,868 Posts
Sounds like fuel delivery. Check and see if you have the vacuum hose on the correct spigot. See if there's vacuum at that hose. Or stick a hose on the petcock and create a little vacuum on it using a mityvac, or if you're old school and taste oil and antifreeze, just suck on it.
 

·
Registered
Joined
·
354 Posts
if your basket case has been stood a long time the petcock diaphram has possibly " melted shut " as the ethanol degraded the rubber
i had this and bought a kit and all was well
you can test for that by as Ixxion said sucking on the vac line ( horizontal facing the downward facing one is a drain and of no use and just confuses people ) with the tap knob arrow facing down
if gas gushes out then that is ok
if juut a trickle then you knwo where the problem lies ...
a hint always theck the simple stuff first , then move deeper saves me a lot of aggro
paul
 

·
Registered
Joined
·
8 Posts
Discussion Starter #4
It's doing this on an aux tank with the vacuum port blocked off, and I noticed it blows fuel back out the intake when revved up... is it possible it jumped timing?
 

·
Registered
Joined
·
334 Posts
I would start bike when motor is cold then quickly feel exhaust headers for a cold pipe(or use thermal gun). Perhaps I hear the clutch basket and disregard.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #11
I would start bike when motor is cold then quickly feel exhaust headers for a cold pipe(or use thermal gun). Perhaps I hear the clutch basket and disregard.
No, you year a hard miss/growl/exhaust leak. It's there. The #2 cyl is cold for a bit, then starts up. I ordered a new battery. My neighbor says it sounds like when his stator went bad.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #12
I ordered a battery, it'll be here Wednesday. I'm going to probe the stator and Reg/Rect, but I can just swap those out, I have spares. The Reg/Rect is off a bike that was running great before a crash.
 

·
Registered
Joined
·
7,826 Posts
If you suspect the stator you can do a AC voltage test. you should see about 24VAC at idle and at least 50VAC at 5k. it's getting to 5k so you can test it. but before you do those tests. What are you getting at the battery terminals at idle and 5k. You should see at leat 13.2 VDC at idle and no more than 14.7 to maybe 15 VDC at 5K.
What are valve specs at you may be hanging open valves. That would explain the low compression numbers as well.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #14
I've also just found out this is a former drag bike. When it's revving up it's spitting fuel mix back out the intakes as well.
 

·
Registered
Joined
·
7,826 Posts
Ok
So now your going to have to go to square 1. Your going to have to verify where cam timing, valves, jetting and ignition timing are at. For baseline then go from there. Lord knows where it's at
 

·
Registered
Joined
·
4 Posts
I had a similar problem with stalling around 6000 rpm, the air box was off. I was told to reinstall the air box and after doing that the bike ran fine. Apparently the air box controls the carb air flow and doesn't allow it to run to lean at higher rpm. The bike now runs to redline with no problems. It is a 97 carb model.
 
1 - 17 of 17 Posts
Top