Project Bought a ZXR250C.

I was thinking soldering iron as a possibility too.

 

That I can do as we have an abundance of blunt bits and a bench grinder.

 

Discovered a gremlin in the electronics.

When I switch from high beam to low beam, the bike will sometimes stall. It did this once when I pressed the horn with the indicators on, too. It only occurs at idle and at low revs, below 2,500rpm, and not consistently... sometimes it will happen, sometimes it won't. I can reliably get it to do so by flicking the switch a lot.

Thinking back, I have replaced the junction box with a new one. I have wired the stator signal to the junction box to provide the signal to operate the headlight circuit, and I have replaced the globes with the LED ones.

Stator, reg/rec and battery have been done and the bike sits on a trickle charger every night.

The only other thing I have done recently is play with the balance and the pilots again, I set them on the rich side. The manual states 2.5 turns +/- 1/4 turn. I'm at 2.75 turns.

Has anyone ever encountered a problem like this?

 

Had an issue with the LED globes this morning, the right hand one had no low beam. Combined with the stalling issue I decided to remove them and reinstall the original globes. Still no right hand low beam. High beam OK on both.

Set off to work to get stuff done to my bike and not even 1/4 of the way there the right low beam came back.

Once I arrived I rapidly flicked the high/low switch. Couldn't get it to stall.

In any case, here is the screen and the new bolts



The crack I had to deal with:



Now there were no worn out drill bits of a small enough diameter to sacrifice, so I went with the soldering iron as I wasn't going to wait for the crack to get bigger.

Heated it up and poked it from the inside on both ends of the crack, let it settle and cool, and ran a line of superglue down the crack. I let that dry and ran one more a bit later



At a later date I'm just going to replace the screen, and be very careful when tightening up the bolts.

My main task for today was replacing the airbox crank breather tube:



While I was in there, I decided to re-set the pilots once again. This time to the stock standard setting of 2.5 turns out.

Then the throttle cables needed re-routing, so carbs off.

I discovered one of the diaphragm cap bolts sitting between the carb manifolds... bingo - that's my persistent air leak.

Then I went and pulled the diaphragms out and did the mod to the slides everyone talks about. Based off another thread here, the existing hole below the needle is 2.5mm. I carefully drilled another 2.5mm hole near it on each slide.

I put the bike back together and warmed it up with the exhaust extractor on it, couldn't hear much but the throttle response was better. I had definitely been too rich at 2.75 turns out of the pilots.

Chucked my helmet on and went for a squirt around the block (westconnex construction site) and did testing of 'extreme' conditions to determine if there were any drawbacks to go with the potential improvements.

I was cruising along in 5th and 6th gear at low speed / low rpm (about 40-60km/h, lower than you'd want to be for those gears) and pinned the throttle. The result was a bog and stutter that didn't clear easily. I believe I could definitely feel the slides pulsing up and down against the spring.

Keep in mind that since I made adjustments and fixed another air leak, the low end tune/balance is still not perfect - but it shows that under certain circumstances there can be drawbacks.

As for positives, fixing the air leak has helped with the idle. It is much more stable and does not fluctuate a lot between hot, cold and when coasting to a stop, and being stopped for some time. There is no bog, lag, or stutter upon taking off at low RPM in the correct gear.

Once fully warmed up I packed my stuff away and started riding home, how I normally would. Which is fairly smooth and somewhat agressive in traffic (I like to keep moving as much as possible).

I found that there was improved throttle response between 2-6 thousand RPM. It definitely revs up slightly quicker. There is less burble after closing the throttle, coasting, and cracking the throttle open to cruising position again. When downshifting, the engine braking is smoother and less agressive (I wasn't banging it down too hard though).

Past 6-8 thousand RPM it feels as if there is no difference. At that point the ZXR is coming onto the cam and throttle response is great all the way to redline anyway.

When just riding around normally at my cruising speed/rpm (60km/h, 5th gear, between 4-8 thousand rpm) the bike feels fantastic, throttle response is awesome, smooth, a lot less burble and only the faintest hint of the 7k rpm flatspot is still present. I believe that tuning the pilots by ear/rpm change and then balancing the throttles again will make it disappear entirely.

Conclusion - Is it worthwhile drilling the slides? In my opinion, yes. However I would not go larger than 2.5mm when drilling a second hole. Enlarging the exisiting hole to say 3mm or 3.5mm may be an option, but I'd have to get another set of unmodified diaphragms and make the change, swap them out, and test again.

 

Not quite the way I understand it. Which is that the throttle grip controls the butterflies directly, which fuel circuits activate when is regulated by the lifting of the slide, which operates on vacuum. You can pin the butterflies open but the slide has to catch up while providing smooth throttle response and do so without bogging down. The spring and air speed/volume obviously have an effect on this.

With faster or additional airflow, a stiffer spring will be needed to regulate the action of the slide. Of course, this begs the question - how conservative or aggressive were the designers when they produced these bikes? Evidently, they were conservative to provide smooth throttle response under all circumstances, but not the best throttle response under normal conditions. The tradeoff.

The needle and taper provide fuel metering - the slide lifting faster provides more air to mix with the fuel circuits that are activating sooner with the faster action of the slide. At least, this is my understanding of how the system operates.

Since our bikes are high revving, they don't have much power down low. They were also aimed at those new to riding in the Japanese market. By slowing down the action of the slide, it provides extra time for the rider to react. Of course, we want the best throttle response possible because we're revheads so we drill the slides. The race prep manuals aren't providing instructions for nothing. There is an improvement to be had.

 

I'm still experiencing the 7k flat spot. I have replaced everything bar the airbox itself and the vacuum valve. I'm certain there are no air leaks. The tune is 95% correct.

Ideas? I'm thinking of ditching the vacuum valve and seeing if it makes a difference.

 

It has always occurred, it was worse when all the air leaks were present, couldn't get past it without downshifting.

Now it is a small hiccup when slowly accelerating or a bog when holding steady speed and suddenly cracking the throttle.

Once it occurs, immediately trying to replicate it results in perfect operation.

It also tends to get worse the hotter it is and also creeps upwards in the rev range when holding 100km/h in top

 

Some battle damage to the ZXR from the drags, bumpy and dirt roads... steering head bearing to be tightened again, needs an oil change again, and the plastic piece for the left rear indicator has split and flaps around in the breeze.

The wear and tear is getting to the point that I want to strip and rebuild the whole bike

Need another daily before I can do that... and a big fat stack of cash

 

Been feeling the bumps a fair bit and watching what the front suspension has been doing while on the road. Came to the conclusion that it was too stiff on compression based on the forks not compressing on small bumps, and I was right. Adjusters were at 4 clicks out, standard is 7. I have set it back to 6 turns and checked the rebound damping (std). Softer, but better.

Rear shock seems slow to rebound, ie it will pack in and not rebound enough. Probably time for a less worn out unit to be swapped in

Going off the amount of carbon on the exhaust tip it has been running rich, I guess a dirty air filter and high altitudes will do that.

Managed to blow the inline fuse for the charging lead stuffing around with a meter... 9 volt batteries aren't happy at 3.7 volts, but a quick zap with the 12 volt charger will keep it going for a while.

I'm up for a new set of tyres and time for a chain and sprocket kit too, put the word in at work so hopefully it'll all be there waiting for me when I get back to Sydney. Hope to have maintenance done this coming saturday (tyres, chain/sprox, clean air filter, adjust steering head again and scrub the bike).