Substained high rpms

[kirkallen143]

Asking a question, once broke in is it safe to run these motors for long periods of time up to 6500 rpms (max torque), or even 7500 rpms? When I say long, I mean 20 - 30 minutes at a time, in warmer weather and without an oil cooler.

Appreciate all responses.

Kirk

[JerryHawk250]

I do it all the time. I've taken 45-60 minute rides running 60-70 mph which is 5500-6800 rpm range with the 17/40 sprockets. Higher rpms if I get lazy and leave the 15 tooth on.

[JerryHawk250]

If the carb is tuned so it's not running lean. Regular oil changes and good gas, the engine should run cool and have no problems.

[roundhouse]

Jerry got it handled. I do not do it for that long but 10 minutes at a time. I switched to rotella T-6 synthetic oil. It will not break down under abuse. I reckon that dino oil changed frequently would probably be OK but I swear (may be in my head) my hawk was smoother and maybe......just maybe I felt a wee increase in acceleration from 600 mile cheapo dino oil before.

Cheap insurance. It is about $6 more a gallon than T4 conventional.

[kirkallen143]

Great replies gentlemen. Yeah, I am going to switch my counter sprocket to a 13T from the 15T and was worried about the higher rpms at highway speeds (well, 55 - 60mph). That 15/40 ratio that I run now is just a tad too tall for the tighter trails around here. Anyways, most of the roads I take are county roads, 35 to 40mph so that shouldn't be a problem.
RoundH, once broke in, that's a good idea to switch to the T6, and smoother you say? How's that clutch feel with the synthetic? I know it might be too soon to tell, but my clutch action gets grabby after an hour or two of ridding with the T4. Maybe it's still part of the break-in, but we'll try the T6 after the 600 mile mark and see how that performs. Thanks a bunch!

Kirk

[Ariel Red Hunter]

Asking a question, once broke in is it safe to run these motors for long periods of time up to 6500 rpms (max torque), or even 7500 rpms? When I say long, I mean 20 - 30 minutes at a time, in warmer weather and without an oil cooler.

Appreciate all responses.

KirkYes, if re-carbed or re-jetted. Re-carbed is better for off road use, because you can tune the low end to give good response and pulling power in the low rpm range. Engine comes way over lean from the factory. Lean fuel mixtures burn much hotter than slightly rich mixtures. After 500 miles, I would change to a full synthetic wet clutch approved oil like Shell Rotella T-6, 5-40 grade. Synthetic oil deals with heat better, and works better in the transmission...ARH

[DualSport]

The only thing I've seen from complete carb replacement and modding is the ability to start in the cold.. Which is more of a mandatory assembly-upgrade since you'll stall out or flood trying to start otherwise maybe even in warm weather..

You need compression to support low gear ratios even if not on a grade. This is why you can't keep up with traffic on a 55MPH hwy without gearing down and making the engine scream while slipping clutch.. Japanese makers solved this with a sixth gear and liquid cooling on top of slightly better arm length and piston diameter.

[pete]

Something I was told years ago... And what I have always gone by
and have never destroyed a motor useing it...
It should beable to sit anywhere up to 80% of it's max revs all day..
so on a motor with a 7500 rpm red line that is 6000 rpm..give or take..
My XR250 would sit on 6200rpm all day at 100kmph...and still had
enough left to pass slower traffic...

But the best hint is that all Jap 250cc road going duel sports do somewhere around 6000rpm at 100kmph
I can't imagine they would gear the bike to stuff the motor at common speed limits..


..

[Ariel Red Hunter]

The only thing I've seen from complete carb replacement and modding is the ability to start in the cold.. Which is more of a mandatory assembly-upgrade since you'll stall out or flood trying to start otherwise maybe even in warm weather..

You need compression to support low gear ratios even if not on a grade. This is why you can't keep up with traffic on a 55MPH hwy without gearing down and making the engine scream while slipping clutch.. Japanese makers solved this with a sixth gear and liquid cooling on top of slightly better arm length and piston diameter.Really? You really believe that a fully re-jetted carburetor only helps cold starting? I have to wonder what engineering school you went to where you learned such non-critical thinking...ARH >:(

[DualSport]

Really? You really believe that a fully re-jetted carburetor only helps cold starting? I have to wonder what engineering school you went to where you learned such non-critical thinking...ARH >:(

You go too lean or too rich and you kill your valves.. It has too little effect on the power band..

I've tried a few jets on my magician and there is little to no difference in performance.. Idle circuit is the only benefit I've seen.

Again,,, just cause something has any effect doesn't mean it's the primary factor.. Like people saying valves have more influence over speed than arm-length and gearing and calling anyone who disagrees stupid..

[Tashka]

if your slow jet is right, and your main is off, you won't notice any performance differences. main jet definately changes performance at high rpms and full throttle.

on the road or by yourself it doesn't matter too much, the performance increase is like a couple bikes farther in acceleration. But the wrong jetting will cause hiccups and stutters which do affect overall performance greatly.

having the right slow jet gave me more power down low and I spent a lot of time getting my main weight for extended full throttle runs.

[Tashka]

Correct jetting on the hawk means the difference between 60 mph top and 75 mph top speed

[roundhouse]

Great replies gentlemen. Yeah, I am going to switch my counter sprocket to a 13T from the 15T and was worried about the higher rpms at highway speeds (well, 55 - 60mph). That 15/40 ratio that I run now is just a tad too tall for the tighter trails around here. Anyways, most of the roads I take are county roads, 35 to 40mph so that shouldn't be a problem.
RoundH, once broke in, that's a good idea to switch to the T6, and smoother you say? How's that clutch feel with the synthetic? I know it might be too soon to tell, but my clutch action gets grabby after an hour or two of ridding with the T4. Maybe it's still part of the break-in, but we'll try the T6 after the 600 mile mark and see how that performs. Thanks a bunch!

Kirk


Unfortunately the grabby clutch did not go away from me but shifting seems a hair smoother and i swear so does the motor. I mean it is still a single jug with not counter balance so it will never be smooth. Not that way but when I accelerate it seems to do it in a smoother manner. Maybe placebo effect of syn oil.

[pete]

If the carb is tuned so it's not running lean. Regular oil changes and good gas, the engine should run cool and have no problems.

meay meany moons ago I built a couple of air scoops/defelters on a 82 TT250
to direct the air flow comeing passed the forks into the motor...
don't really know if they worked..but they didn't make it run any hotter thats for sure.
got the idea from the XT/TT350 that had air scoops in the tank panels to direct
air down onto the motor.....
When you think about it the front wheel/forks/mud gaurd are all in the way of
direct air flow to the motor..
I bent them up out trail riding... so took them off...
If you only do mostly road riding... they could be worth looking into...

...

[Ariel Red Hunter]

[QUOTE=DualSport;292356]You go too lean or too rich and you kill your valves.. It has too little effect on the power band..

I've tried a few jets on my magician and there is little to no difference in performance.. Idle circuit is the only benefit I've seen.

Again,,, just cause something has any effect doesn't mean it's the primary factor.. Like people saying valves have more influence over speed than arm-length and gearing and calling anyone who disagrees stupid..[/QUOTEWell, valve timing Does have more influence on power output, hence speed, than any other single factor in design. In reality, to get good results you bring as many factors as you can to the design on the drawing table. I can assure you of one thing though. You let me pick the valve timing, and I can deliver an 80 mph 250cc motor cycle, assuming you don't go totally rabid on speed killing features. I don't have to break a sweat on this problem, as it was already accomplished 80 years ago. On a 6 1/2 to one compression ratio. 80mm stroke. Push rod O.H.V. air-cooled engine....ARH :hmm:

[pete]

[QUOTE=DualSport;292356]You go too lean or too rich and you kill your valves.. It has too little effect on the power band..

I've tried a few jets on my magician and there is little to no difference in performance.. Idle circuit is the only benefit I've seen.

Again,,, just cause something has any effect doesn't mean it's the primary factor.. Like people saying valves have more influence over speed than arm-length and gearing and calling anyone who disagrees stupid..[/QUOTEWell, valve timing Does have more influence on power output, hence speed, than any other single factor in design. In reality, to get good results you bring as many factors as you can to the design on the drawing table. I can assure you of one thing though. You let me pick the valve timing, and I can deliver an 80 mph 250cc motor cycle, assuming you don't go totally rabid on speed killing features. I don't have to break a sweat on this problem, as it was already accomplished 80 years ago. On a 6 1/2 to one compression ratio. 80mm stroke. Push rod O.H.V. air-cooled engine....ARH :hmm:

Totaly correct.... power is in the head & cam profile...
even the hawk with it's single lob cam..



.

[pete]

[QUOTE=DualSport;292356]You go too lean or too rich and you kill your valves.. It has too little effect on the power band..

I've tried a few jets on my magician and there is little to no difference in performance.. Idle circuit is the only benefit I've seen.

Again,,, just cause something has any effect doesn't mean it's the primary factor.. Like people saying valves have more influence over speed than arm-length and gearing and calling anyone who disagrees stupid..[/QUOTEWell, valve timing Does have more influence on power output, hence speed, than any other single factor in design. In reality, to get good results you bring as many factors as you can to the design on the drawing table. I can assure you of one thing though. You let me pick the valve timing, and I can deliver an 80 mph 250cc motor cycle, assuming you don't go totally rabid on speed killing features. I don't have to break a sweat on this problem, as it was already accomplished 80 years ago. On a 6 1/2 to one compression ratio. 80mm stroke. Push rod O.H.V. air-cooled engine....ARH :hmm:

ARH is totaly correct.... power is in the head & cam lob profile...


.

[Ariel Red Hunter]

[QUOTE=Ariel Red Hunter;292405]

ARH is totaly correct.... power is in the head & cam lob profile...


.I think these differing viewpoints all have validity. These discussions can only help those who have never thought about these issues before. So, I am not trying to shut anybody up. The more viewpoints out there, the more we all learn...ARH :)

[Ariel Red Hunter]

Something I was told years ago... And what I have always gone by
and have never destroyed a motor useing it...
It should beable to sit anywhere up to 80% of it's max revs all day..
so on a motor with a 7500 rpm red line that is 6000 rpm..give or take..
My XR250 would sit on 6200rpm all day at 100kmph...and still had
enough left to pass slower traffic...

But the best hint is that all Jap 250cc road going duel sports do somewhere around 6000rpm at 100kmph
I can't imagine they would gear the bike to stuff the motor at common speed limits..


..Pete is right on the money with this. When I worked for International Harvestor 85% was considered the absolute maximum engine rpm under load. A gasoline burning engine is only efficient between 75% and 85% of full rpm (governed). below 75% fuel efficiency is deficient, above 85% engine life is drasticly reduced at full load. ARH :doh:

[Sochin]

My Hawk at 17/50 gearing gets to scream a whole lot........but now with close to 2500 miles on it doesn't seem to vibrate as much anymore. After I put on the more efficient TT250 head and ported the stock header pipe (Still use stock exhaust with punched out baffles and cat converter) It can hold 60-65 all day albeit at 7000+ rpms. I use mine in the hills and far away since I'm smack in the middle of the Rockies..........I'm keeping my 17-50 gearing which works VERY well for what I do with my Hawk.