Sorry for wall of text, just thought it would be easier this way instead of answering 99999 questions later.

So today I was going for a ride and had been driving around the area for 1 hour or so and set course for home. While rolling down a hill, I could suddenly feel the bike did a small "bump" or something, no sound, I just felt it in the bike, same feeling as when you get a really loud backfire all the way into the headers.

I tought it was just that, I had just let up the throttle, so I didn't think about it until I reached the bottom of the hill and applied the throttle again, then I noticed that the bike ran really crappy, lagging and coughing, so I pulled over to figure out what just happened.

The bike idled just fine, as soon as I applied throttle, it would cough and just die off. I managed to get it going like this and crawled my way in 1st gear at 3k rpm to try to get home (was only about 1km or 3/4 miles out) didn't want to push it all the way as it was all uphill. Managed to get like 1/8 mile in snail pace until I felt another "backfire" and then it just stalled out on me.

I could still start it like nothing had happened and it idled fine, it just died off as soon as I touched the throttle, so I had to push it the rest of the way. Did get a good cardio session tho...

So now it sits in my garage, starts an idles fine, cant get it to rev above 2k rpms unless I pull the choke lever/button thing, then I can get it up to 5-6k barely and then it just spits and coughs.

I have checked:

Spark plugs, they look ok and works
Fuel tap(?) under the tank, inspected vacuum membrane, looks fine
Rear carb, checked vacuum membrane, looks fine


Messed about with the carb pistons a bit to see if one of them would slide easier/faster than the other, they seem to work exactly the same, think that means the front carb vacuum membrane should be fine as well.

I also put some more gas in the tank just to make sure it wasn't close to empty and the fuel light had failed or something.
Vacuum lines also seem fine.


Has anyone ever experienced something like this?
Running out of ideas here, it really seems like there is a fuel/air related problem because of that choke thing.

Appreciate all suggestions and help, I'm quite new to this whole bike world.

 

Do you have manual or (stock) auto CCTs

 

Did the vacuum hose that leads to the petcock fall off? The petcock is vacuum operated. There should be a vacuum hose the leads from underneath the carbs to the back of the petcock, not to the bottom of the petcock. This could be possible fuel starvation.

What about your R/R (Regulator/Rectifier). Is it stock? Is it finned? This could cause these issues as well if it is on its way out. Check the R/R's connector for burnt wires. Are you handy with a multimeter?

Also, it might be a CCT (Cam Chain Tensioner) that let go and the timing chain jumped a couple teeth and the timing is off. But usually stock CCT's don't break and then keep a little tension. FYI, this is an interference engine, so your pistons will hit the valves if the timing is way off.

 

The CCT has already been swapped out by the previous owner, so that sould be ok.
All vacuum hoses were in place, petcock is the one under the tank, right?
One hose was broken off, it went straight into the tank and out under the bike, looked like it was just for ventilation or something, also from the looks of it, that hose had been off for a long time already, will try to find out what it's for tomorrow.

 

'99-'00 has the petcock attached to the tank. '01-'05 has the petcock attached to the frame.

What about your R/R? Look on the subframe on the bike's right side (just underneath and behind your right butt cheek, while sitting on the bike obviously).

 

RR looks fine as well, no crispy wires or sockets or anything. It's just flat on top, not finned, so it's probably the stock one.

 

 

That's the one I got

 

From experience I can tell you that should be on your short list of "change sooner rather than later". May not be your problem now but it WILL be eventually and usually at the worst possible moment, while destroying most of your charging system.
Plus don't make the mistake of just using the finned version in place of your non-finned version. At the very least go mosfet, do a search, there is quite a bit of info on here. May even be a stickie, if my memory serves me correctly.
Good luck with your bike.

 

I didn't know the RR was a weak spot, my bike has 34k on it (about 20k miles I think), should I worry about this anytime soon?

 

How many years does it have on it and yes.

 

Just a thought, but what if the previous owner didn't set the tension correctly on your manual CCT's and the timing did in fact jump a couple teeth? However, before tearing into your engine, check the simple things first. Follow the K.I.S.S. rule. Make sure your petcock is actually working correctly. Once you checked out your fuel system, lift the tank and open your airbox and take a look and make sure everything looks okay. Once you checked your fuel and air, then check the spark. Do you know how to use a multimeter?