After upgrades, Top Speed only 60mph Hawk 250

[DustyRJ7]

I bought a 2019 RPS Hawk for 1k. 3k Miles on the Odometer.

After upgrading to Shinko 705 tires, adding a JFG exhaust, and installing JT 17/45 sprocket combo, my top speed is only 60mph. Also added an iridium spark plug, didn't seem to make a difference.

I checked the oil with the dipstick while the bike is upright, oil level is correct (Shell rotella t4 15w-40)

Everyone claims their hawk does 75mph with these upgrades.

I have not checked the valve clearance, I plan to this weekend. Assuming that the valve clearance is correct, does anyone have any clue as to why a rider at 145lbs is only topping out at 60mph?

My carb is stock, is that what's wrong? Should I order a new engine?

I would really appreciate your guys' input, I am not very knowledgeable when it comes to motorcycle mechanics.

[Bill Hilly]

Originally Posted by DustyRJ7

I bought a 2019 RPS Hawk for 1k. 3k Miles on the Odometer.

After upgrading to Shinko 705 tires, adding a JFG exhaust, and installing JT 17/45 sprocket combo, my top speed is only 60mph. Also added an iridium spark plug, didn't seem to make a difference.

I checked the oil with the dipstick while the bike is upright, oil level is correct (Shell rotella t4 15w-40)

Everyone claims their hawk does 75mph with these upgrades.

I have not checked the valve clearance, I plan to this weekend. Assuming that the valve clearance is correct, does anyone have any clue as to why a rider at 145lbs is only topping out at 60mph?

My carb is stock, is that what's wrong? Should I order a new engine?

I would really appreciate your guys' input, I am not very knowledgeable when it comes to motorcycle mechanics.

If you have a stock carb, WITH STOCK jetting, then you definitely need to do something about it. The exhaust is apt to even make it leaner. Seeing that you bought it used, it may either have been rejetted, or possibly replaced with a Mikuni style VM26. With a bike that's broken in, and the sprocket gearing, it should be able to run 70, and still be a little under 8,000 rpm. If you expect these stock bikes with higher gearing ,to gain top speed quickly on flat ground, they don't . Oh yeah, definitely check, and adjust the valves. Do it while the motor is completely cold, as in sat all night, and keep in mind that when you read post, especially on the Facebook groups, a lot of them don't specify Metric, or SAE( Imperial). .002" is inch, and .05mm are common settings for motors that are broken in.

[ProDigit]

I have a feeling with these pushrod engines, if speed is what you want, after properly jetting the carburetor, all you really need is to get as tall of a gearing possible. Biggest front, smallest rear sprocket. Then just tuck (or draft another car) and they should top out in the high 70s mph.

[krat]

"Everyone claims their hawk does 75mph with these upgrades."

Yea, and I have a pig that flies and the women can't keep their hands off me!

I did all those upgrades too, including a replacement carb and tuning the crap out of the unit, and my CG 250 tops out at 60 due to the fact that it only has a specific number of RPM in it and can't mechanically do any more! What "everyone" does not tell you is "everything" they do to that engine or how much they actually spent.

And I know that we have people on this forum that claim every Hawk or CG they throw a leg over will do 75mph. Sorry, it's not real.

There are only three ways a CG250 is going to hit 75MPH.

1. Spend as much on aftermarket parts and machine work as the bike originally cost.

2. Put a 75 pound 14 year old girl on it riding downhill with an 80mph wind behind her.

3. (and most likely) Put it in the back of an F150 pickup.

[Megadan]

Originally Posted by DustyRJ7

Everyone claims their hawk does 75mph with these upgrades.

I have not checked the valve clearance, I plan to this weekend. Assuming that the valve clearance is correct, does anyone have any clue as to why a rider at 145lbs is only topping out at 60mph?

My carb is stock, is that what's wrong? Should I order a new engine?

I would really appreciate your guys' input, I am not very knowledgeable when it comes to motorcycle mechanics.

Everybody claims 75mph. Everybody is full of shit. 75mph on a stock speedometer is 70mph in reality, and 70 is about the absolute maximum you would see out of your mods and sprocket setup. 68mph is pretty average for most riders with an exhaust and 17/45 sprockets.

My Hawk will do 75mph, but it has a 292 cam with aported head and 70mm bore cylinder from motocult. My carb is a VM26 30mm clone, which is basically the same as a stock carb, but with Mikuni jets.

Speaking of jets, did you jet the stock carburetor at all? They are notoriously lean on the main jet out of the box. With an exhaust on the bike, you are reaching "melt a piston" levels of lean at wide open throttle. You need at least a 110 main jet, usually a 115 is better with an exhaust on the bike, especially at lower altitudes.

If not, that will definitely explain your lack of top end power.

[Megadan]

Originally Posted by krat

"Everyone claims their hawk does 75mph with these upgrades."

Yea, and I have a pig that flies and the women can't keep their hands off me!

I did all those upgrades too, including a replacement carb and tuning the crap out of the unit, and my CG 250 tops out at 60 due to the fact that it only has a specific number of RPM in it and can't mechanically do any more! What "everyone" does not tell you is "everything" they do to that engine or how much they actually spent.

And I know that we have people on this forum that claim every Hawk or CG they throw a leg over will do 75mph. Sorry, it's not real.

There are only three ways a CG250 is going to hit 75MPH.

1. Spend as much on aftermarket parts and machine work as the bike originally cost.

2. Put a 75 pound 14 year old girl on it riding downhill with an 80mph wind behind her.

3. (and most likely) Put it in the back of an F150 pickup.

1. More like $500 if you buy the Motocult stage 3 kit (Currently $489). That's cam, ported head, and properly machined 70mm cylinder all together. That's about a third to a quarter the cost of the bike. Toss in those cheap exhausts, jets, and sprockets and maybe $700 total and that Motocult kit comes with a flywheel puller and a few other additions that make it really nice. Even has jets and an adjustable needle for the stock carb.

2. 260lb 6ft 4in tall grown man me has done it on flat ground. Just can't have too much head wind lol.

3. Agreed, for most of them.

[Megadan]

Originally Posted by ProDigit

I have a feeling with these pushrod engines, if speed is what you want, after properly jetting the carburetor, all you really need is to get as tall of a gearing possible. Biggest front, smallest rear sprocket. Then just tuck (or draft another car) and they should top out in the high 70s mph.

There is a point of diminishing returns. On an otherwise stock engine with just an exhaust on it, the absolute fastest I have ever seen anybody post was JerryHawk250 right here on the forum. If I remember correctly, he managed to get 73-74mph with a 17 front and 39 or 40 rear sprocket, and that was on level ground with no wind, at near sea level. He would have to chime in to correct me for sure, but I know it was close to that.

At one point I ran with a 17 front and 43 rear, and with my giant self on my bike, only an exhaust and pod filter for modifications, managed to occasionally clip 71mph in the right conditions, but you really start to lose climbing and acceleration at that point, especially if you are over 200lbs.

I do know that small guys with sprockets like the ones that Jerry ran with my engine mods have actually hit 80-82mph confirmed with GPS. That is the fastest I know of any Hawk actually going.

Me, I don't care about top speed really. I love all the torque I have at the back wheel, and my bike still cruises at 60 to 65mph all day long. 17/45 sprockets with a fully upgraded engine is a great combo.

[JerryHawk250]

On a stock engine with the mods you have done with properly inflated tires, Tune carb with proper jetting and valve adjustment, you should be able to hit 65-70mph. My mike wasn't stock. I could consistently run 72-75mph and comfortably run 65-70 mph all day. I only weigh 175lbs. Yes I've hit 80 a couple of times but didn't feel safe at those speeds. These bikes aren't designed for high speeds. Stars must be aligned with the wind in your back on flat land. lol

[Texas Pete]

It’s kind of like the blind leading the blind with all the claims on forums that all the usual suspects grab bag of bolt on parts you buy and install will make big performance upgrades on small CC motorcycles. All backed up by the best scientific “butt dyno” testing evidence posted in the replies that something actually happened afterwards.

Smart money leaves the bike stock using it for what it was designed for and saves all the wasted doo-dads money and buys a bigger bike if you want a larger increase in power. There is simply no replacement for displacement.

[bigdano711]

50-55 mph on a pretty serious uphill, 4th gear wound out. Pretty impressive for a little bike, actually. After cresting hill and getting into 5th, 60-65 all day, which is more than enough. The only time I get this bike close to 70 is on the downhill with wind at my back. There is a video of a guy on one of these small bikes and he hits a pothole at speed that sends him into a speed wobble and crash. Just rolling over road snakes at 60 makes my Hawk want to speed wobble. 75 mph is a fool's errand.

[Do©Hawk]

I think a lot of high speed claims come from inaccurate speedometers. My EFI Hawk has the digital dash display and is within 2mph of GPS all the way through. I don't believe the analog gauges are as accurate.

My EFI Hawk with sprockets and an NGK plug hasn't hit 70mph. It is my understanding that the stock EFI Hawk performs similarly to a carb Hawk with all the normal mods.

I would also add that top speed isn't my goal, but I like to know what the Hawk can do. The Hawk is also a little scary at those top speeds. It doesn't feel very stable.

[DrewsBrews]

My xf200 with taller sprocket, a cam, aftermarket muffler, a few holes in the airbox and appropriate rejetting does 75 pretty easily on a good day. I also have a much taller front tire. When I go past the speed radar traps it is pretty close (within ~1mph of the speedo). With the small stock front tire it was badly overrating the speedo.

Rejet is necessary. Since you are flowing more air through the engine it needs more gas to compensate. More air plus more gas equals more power. It is elevation dependent though. So Somewhere like Denver you will be inherently making less power due to thinner air.

[alex_in_az]

I self limit to 75 because the bike is not very stable past that. I run 17/40 gearing and am pulling a little over 7K at 75 with more to go. It might hit 80, but I'd rather not risk it