I also had a habit, (bad or good), of lowering the gearing up front by one tooth, a pretty big jump. I had to shift more, but it would get rid of the low end dead spots on my bikes and pull harder.

I've got a 1990 CR250. Brought a boyzen rad valve ($340) and a brand new genuine keihen carburettor ($600) and I will get the motor rebuild from the ground up. There's a dude 2hrs from me that has a good reputation of making bikes go hard. I will give the carb to the mechanic at the time of rebuild. I think the 4hr return trip will be worth it.

Mine too, and small engine mods with good jetting made it even faster. Coming down from speed on a bumpy straight, (which they don't have anymore), I have had that front end swap from stop to stop about as violently as possible. Stiffer fork springs and some body adjustment pretty much cured it. I am sure you bent a shock linkage bolt or two also. That was a problem with that bike. I used a better grade bolt and ended the problem for me.

its fresh. Just what she makes on my dyno. Our dyno is stingy vs most…

@@HPRaceDevelopment I have a dyno. A little "land and sea" water brake engine dyno that I made the drive system and water system for. I use it for small engines like around 30cc. One thing I have found is there is no real calibration for dyno's, and computer factors can be changed to make them read what ever you want also. I was actually able to calibrate mine is kind of a half azzed way, (by trusting the manufacture claim for one of their engines, which is probably accurate but I have no way to be sure). The manufacture claimed 2.8hp at 12,500rpm with no air filter and no exhaust at all. So I set up a new engine, broke in the ring, set the jetting (per plug color at wide open), as well as I could, and calibrated my dyno until it read 2.8hp with that engine. I keep that engine for calibration only. I had this bike, and with very little port mods, good jetting, the stock pipe, it was probably the fastest 2-stroke 250 I ever had, (including my stock 2019 YZ250 2-stroke), with awesome mid to top power. My bike had to be 45hp or a bit higher, (I think that is at the crank. It is typical to subtract 10% if a chassis driven rolling dyno.). But my main point is, because of a lack of calibration alone (not even counting the cheaters), way more often than not, when we see dyno numbers, they are not accurate to a small degree of error. There are huge swings with the same power plant from dyno to dyno.

There are some factors out of control in your knowledge of your history, like that KX125 was not running well (jetted very rich from the factory), and there is no calibration for dyno's, because I know 125's (properly running and properly measured), were making 30 plus HP at the rear wheel in reality by the mid 80's. Owned and raced them all? Really? I had a few 250's and some smaller bikes first in the 890's and 90's, my next to last being a 97 KX250. I think they were all faster than my stock 2019 YZ250 2-stroke. I think they YZ is the slowest 250 MX bike I ever had. But,---ahem,I did gain some weight over the last 20 years off a bike. :)

Those can easily cross 50

@@HPRaceDevelopment If this 50 hp is from the rear wheel then it’s not so much lower hp than CR 500 has. But that CR 500 has a lot more torque as it doesn’t rev nearly as high where it makes it’s hp peak. 250 revs much higher and even higher when modified. Actually piston speed in 250 is higher than in 125 as the stroke is so much longer (72 mm vs. 54.5 mm). If a 250 is at 10000 rpm when going above it´s peak hp then similar piston average speed 24 m/s for a 125 is at 13250 rpm. This was one of the reasons why I changed my TC 250 piston to a 1-ring Wiseco. It´s modified so it revs higher than stock.

@@jannep6772 Ahhh, you know something about engine building. :) Me too, and I know how dyno's are, (not calibrated). I doubt a 250 2-stroke MX bike running on gas is making 50hp at the rear wheel. That would be about 55 at the crank, (assuming 10% drive train loss). But, it is not that the engine can't make that much power. It is that much power out of a 2-stroke 250 gets too hard to ride on a MX track, of yesterday. But on the other hand. Today, the tracks are much faster because of the faster 4-stroke engine, so maybe they can use the peakier 55hp.

Eventually we will have a project on one but shop is too busy at the moment

Not in any faster amateur class, against 4-strokes on these faster tracks today. But I had this bike, and I know I can make it run with the modern 2-strokes with YZ suspension (suspension was terrible on that year bike) and a few motor mods and pipe. I got that bike screaming easily, with the stock pipe. Had to be 45hp plus at the crank, and I think it was the fastest 250MX bike I ever had,--including my 2019 YZ250 2-stroke, (which may be the slowest I ever had, stock).

she was done… it will rev more but not make more power well past the tuned length of the pipe

@@HPRaceDevelopment Measure it anyway. The entire curve.

@@EarthSurferUSA we did what you see is all she has

no but from what ive seen and heard it would likely make 22-24

I also feel confused. 35hp is level of air cooled CZ 250 from 70s

Our dyno is a bit lower than some. While I agree the 90s era crs will go what a yz will - this is all this bike had. Its in perfect mechanical condition - speaking with a friend who did a lot of these, he said its m in line with what he would expect on my dyno. On the same day we dyno this clients cr500 - later mellower year and it still put down 55 for reference.

@@inevespace Not on my dyno…people seem to really struggle on that. We feel our dyno is a very accurate to true wheel numbers. Most dynos are fudged a bit higher to more represent crank numbers.

@@HPRaceDevelopment People need to understand that you really cant compare results between different dynos. Only way to really make the comparison is to have both bikes ran on the same dyno...

@@HPRaceDevelopment so you give numbers on wheel, without recalculation to crank? I thought your setup gives "crank hp".

We did

Are you going to post it?

Yep!@@JohnJ77777

Awesome thank you!@@HPRaceDevelopment

Thats what we show

@@HPRaceDevelopment Ok that ain’t too bad. What did the 500 have?

@@TopRevs 55

@@HPRaceDevelopment Awesome

A good 125 back in those days could make 36hp at the wheel. This bike runs between 45-50hp at the crank. I had one. Did a tinge of porting myself, stock pipe, good jetting,---and it would smoke my stock 2019 YZ250. If his dyno has any kind of calibration, (They don't), I could build that engine for him (if we can still get parts) to test again. That bike was fast in the higher rpm's. Real fast.

Until you start riding it for more than 20 minutes. Those old bikes vibrate like paint shakers and the brakes are terrible by todays standards

@@OGLD No worse than my 2019 YZ250, probably less. The aluminum frame does transfer vibration more efficiently than chrome moly. The brakes in 88 were great. They worked awesome for the rougher tracks that were not road racing speeds like today. The 4-stroke tracks are at least 30% faster today and most of the bikes are still over 215lbs. Nothing on a dirt bike course but modern, MX needs brakes as big as my 2019 YZ250. The brakes are so strong today, you never need more than one finger on the front brake lever, and with many boots, you can't feel the rear brake pedal when touching it, (same with the shifter). I think I wold crash less with the late 80's brakes, and go just as fast doing it. :)

It definately doesnt make 52 at the flywheel. and good dynos - like ours - dont lie. Its why we own it. There is no hiding when you have to move mass. The mass never changes - and time keeping is pretty darn accurate and reliabke these days.

@@HPRaceDevelopment You should take a reading at the flywheel, that will be the true bhp...do that on your video and I'll subscribe. 👈

@@Workerbee-zy5nx Your subscription isnt worth that effort, sorry.

@@HPRaceDevelopment But even if it is a crank dyno, Like mine with a rpm reducing belt system, there are bearings and other friction losses that really are not measured. I don't know if there is a calibration method for your dyno, but I had to develop my own using a stock engine, and assuming the manufacture numbers are correct. I don't think there is any real calibration for dynos, and I bet you if you took the same engine set up to 4 different dyno's across the nation, the variance of the results would be statistically considered "out of control".