Help Acceleration Issue - 1990 ZXR250R

I thought the sp carbs were 32mm inlet diameter so how will a set of 30’s fit the inlet manifold ?

I’d be looking at the slides , at 6000-7000rpm, you are on the main jet with the slides coming up , where are your needles set to ?

 

Please explain “where are your needles set to ?”, they are held in the slide by the spring, I haven’t made any changes to them.
The slides are free and I have checked the diaphragms for leaks.
These are my first CV’s, any guidance is appreciated.
I still believe that there’s something going on with the slides, I just don’t know what.
As you know, you can get to 7k with very little throttle opening, so I’m not sure that I’m getting on the mains fully.

 

Sorry , are the needles shimmed ? Ie has some used washers to raise the needle height ?

 

Standard ZXR 30mm carb needles are non-adjustable. No clips. You can only shim/space them to run richer. In the event you need to lean it off, it's either find a set of adjustable ZXR needles (rare) or change the air jets, which are pressed in.

I have a set of adjustable needles I got off @sharky some time ago.

 

Yes, clear

Yes, all good (Litetek seals )

 

Same part number.
Carb spigot O.D. Same

 

This sounds like it could be a CDI/TCI issue, i.e., the spark is too short when the rpm reaches a certain point so the spark is too close to the top-dead-center, like trying to run the engine backward almost. I have no idea if this bike used a CDi or TCi but the TCI as far as I am aware enables a longer spark at higher rpm. Older engine systems would just need the spark advanced more to enable smooth running as rpm increases. Maybe worth checking I guess?

 

the symptoms are the same as my old zxr250 where the fuel inlet t piece seals had failed.


I would be check the carbs for leaks , put the airbox on and spray some ether ( we have stuff called start you bastard) around the fuel inlet t piece , just a small spray and make sure that t piece is sealing correctly , if the revs rise then there is still a leak.


I have doubts it is the tci, but never say never

 

Update:
I believe that the issue WAS, running out of fuel.
The tank had been cleaned numerous times, but when I filled it, I discovered a few pin holes in the front of the tank. It had some little spots of rust inside, so I decided to line the tank with Caswell’s tank epoxy.
Upon removing the petcock, I noticed the reserve filter screen had some rust particles, which I believe were restricting the fuel flow. So, I sealed the tank, cleaned the petcock filters, and replaced the fuel line with clear fuel hose ( for visual inspection). The spare Igniter box came in, so I went ahead and swapped it.

The fork seals had been leaking and I had previously ordered new seals and bushings.
The parts were here, so I decided to rebuild the forks while I had it on the lift.
While there, I installed some billet clip on’s to give me some adjustment for a better ride position.

I just took it for a ride up the street, it has the noticeable hesitation/sputter at around 7k that most people have mentioned, but it clears up and smooths out and revs out great.
This is the first time that I have ridden it.

My impression so far: It revs to the moon, sounds really good, but I’m a bit disappointed in the power.
My KR250 would outrun it. Next, I have to get it registered and I will be able to get it out on the road.
Thanks to everyone who helped.

 

Might want to dyno-test to confirm AFR and power-output.

My CBR250R MC19 was pretty anemic when first getting back on road. After having carbs professionally restored by Gordon @ https://customcarbservices.com , it ran A LOT better. Checking with wideband-O2 showed lean spot in mid-range and super-rich high-end. Ended up shimming needles 0.75mm and going down main-jets 1 size. Still super-rich in high-end at 10:1 AFR, but will put off downsizing mains again until I get on dyno. Looking to get MC22 exhaust with smaller tubing first.

My sponsor Spears immediately downsized mains on my track Ninja 250 before dyno-tuning. After initial pulls, he downsized once more. That's with Tyga full-exhaust and free-flow intake. Ended up with +22% more power than stock. That's 22% more airflow than stock to match 2-sizes smaller mains. Still pig-rich @ 11:1 AFR.

Nice bike BTW!!!

 

Wow! 22% is amazing.
Fortunately,
The Barber Vintage Motorcycle Festival is next week.
There will be a mobile Dyno there. (Halls brothers)
I plan to get it there and get a baseline run.
Should give me enough information to start.
I’ll take some shims, just in case. These carbs aren’t as easy to access as my other bikes.
May take the KR too.
Thanks

 

Well,
Got the bike on the dyno, whopping 15 hp!
Air/fuel ratio was 13:1 all the way through the rpm range.
On the way home, it died at a stop.
Restarted, then wouldn’t rev past 3000 rpm, even full throttle.
I have parked it until I can set some time to investigate.
Oh yeah, the KR250 got 41 hp at the wheel.

 

Compression test:
#1=150 psi
#2=125 psi
#3=150 psi
#4=125psi
Interestingly, #1& #3 plugs were wet (fuel).
#2 & #4 looked to be running clean.
Checked the service manual, acceptable range is 143-218 psi.
Thoughts ?

 

I think their consistent afr reading sounds suspicious. But it is speculation. The wet plugs don't match the coil, so I can't blame that. Unless the leads were on wrong way around, but you sound too knowledgeable for that.