Topic: Should I expect a higher top speed?

[Orcinus]

Breaking 85 while going downhill is ok, but HockersChoppers probably feels that unacceptable because in Kansas, downhills are limited to your driveway and the backside of Highway overpasses.  

Sorry Jesse, couldn't resist...  

[TwoTired]

You can put 530 oring chains on a 650?  Can't do that on the 550.  Grinds the cases.

Cheers,

[DammitDan]

Well, I THOUGHT you could....  Any other CB650 guys run o-ring chains?

[medic09]

Ahem, and I said I was CLOSE to 250...  But I'm also 6'3, so at least I can try to explain away my incredible mass.  Erm, I mean weight.  Damn, there are too many engineers here

You don't want me to get into the whole Body Mass Index thing, do ya?  (Maybe that poor bike just gets tired fighting the inertia of all that mass...)   

[DammitDan]

Hey!  It's weight, not mass!  I'm not fat, I'm just fluffy! 

Very heavy fluff.  Yeah, that's the ticket!

[Orcinus]

Hey, it could be worse... I'm close to 250 (coming from the other direction), I'm only 5' 8" (I'm not overweight, I'm undertall) and my BMI sounds like an engine displacement.  The only good thing I've got going is that I'm losing an average of 2 lbs a week, and at the rate I'm going, the bike and I will hit race weight at about the same time. (Late next summer  )  Oh well, it gives me something to work toward.

[Pinhead]

Personally I don't think it's your gearing. that's holding you back that much. But if you do change it, go with a 17t front and a 40 rear (at least that's what I've got on my '79 CB650; I don't know if the '82 is geared differently). I guarantee my '79 will easily do the ton with those sprocket sizes.

120 mains seem incredibly huge. I've got 102.5's and it still runs somewhat rich (I've opened my airbox, too). Do a plug chop to see if at WOT you're running rich or lean. I'm willing to bet it's more of an engine performance problem than gearing trouble.

A bad chain could hold you back quite a bit, too.

[Soos]

Personally I don't think it's your gearing. that's holding you back that much. But if you do change it, go with a 17t front and a 40 rear (at least that's what I've got on my '79 CB650; I don't know if the '82 is geared differently). I guarantee my '79 will easily do the ton with those sprocket sizes.

120 mains seem incredibly huge. I've got 102.5's and it still runs somewhat rich (I've opened my airbox, too). Do a plug chop to see if at WOT you're running rich or lean. I'm willing to bet it's more of an engine performance problem than gearing trouble.

A bad chain could hold you back quite a bit, too.

I replaced my gears with 16/38 and got a new chain last year, and got my '79cb650 to 120.
And I swear she could have done more.... but I was running with the original bearings, and figured I had tempted fate a little to much already to push it any more.
I tend to carry almost any tool i would need in case of a on the road fix is needed, so me plus tools/gear the bike was carrying 200+lbs.

l8r

[crazypj]

What will it do at redline in third?
Thats a better way to check it.
 It should be around 100mph or more with the gearing your running.
 If it goes slower when you change up its overgeared.
 My modified 550 would run 82mph in second gear and it still did 70,000 miles after modifications (see avatar)
As we go into carbs,(in more ways than one ) I was running 117.5 mains on 591cc motor. Forget the gearing though, eiher it would pull or it wouldnt.
PJ

[CharlieT]

Click on this link:

http://racingdownloads.com/racing_software-22.html

Down load the free program. Put in all teh data it asks for...primary ratio, internal gear ratios, Tire size, etc. I've used that program to make internal and external gear changes and have found it to be quite accurate. Compares fairly well with our onboard data acquisition.

Won't be 100% spot on, as it doesn't have input for things like weight, frontal are, degree of rider "fluffyness" etc. But it will get you i the ballpark.

[DammitDan]

My engine (I replaced the '82 standard engine with an '82 SC) runs stock 118s.  The jet sizes went up with the introduction of CV carbs.  http://www.myhonda650.com/cb650history.htm

I dunno what it'll do in 3rd gear at redline.  But I'm absolutely sure it's not 100mph. (considering I was redlining in 4th gear at almost 90).  And I finally thought to look on the Dennis Kirk order history.  Back when I still had the standard engine in I bought a 17 front (apparently the same sprocket size as stock!  ) and a 38 back (down from 39).  So it's not hardly as big a change as I had initially thought.  And I now have the same sprocket sizes for a stock SC engine (although I'm running a standard frame).  Guess that means it's probably not the gear ratio then.

But on the other hand, it did make a HUGE difference in the RPMs at various speeds...  It dropped them by 1k at cruising speeds!  I'm sure 1 tooth in the back wouldn't make that much difference, so I don't know what the hell to think anymore. 

[Ibsen]

You can put 530 oring chains on a 650?  Can't do that on the 550.  Grinds the cases.

Cheers,

The 650 have got 530 oring chain as standard.

[Pinhead]

Honestly, 1k RPM shouldn't efect you that much (from 100+ down to ~85).

Do a plug chop to verify the tune of your carbs. While you're at it, make sure the ignition timing is set right and you're getting good spark up high. Have you replaced your stock ignitors? If not, they're probably starting to lose their performance.

17/40 on my bike seems perfect. I didn't lose any noticable acceleration and I don't even want to see what my topend is; I let off the throttle when I decided I'd had enough (100 mph +).

[Pinhead]

You can put 530 oring chains on a 650?  Can't do that on the 550.  Grinds the cases.

Cheers,

The 650 have got 530 oring chain as standard.

Carefull, Ibseen... You let out too much information about our beloved 650s and people will start to get jealous!!

[Ibsen]

Personally I don't think it's your gearing. that's holding you back that much. But if you do change it, go with a 17t front and a 40 rear (at least that's what I've got on my '79 CB650; I don't know if the '82 is geared differently). I guarantee my '79 will easily do the ton with those sprocket sizes.

120 mains seem incredibly huge. I've got 102.5's and it still runs somewhat rich (I've opened my airbox, too). Do a plug chop to see if at WOT you're running rich or lean. I'm willing to bet it's more of an engine performance problem than gearing trouble.

A bad chain could hold you back quite a bit, too.

I seem to remember that you have got the earlier PD carbs on your 650, while Dan have got CV carbs. If that is correct you can't compare the jet sizes used for the two types of carbs.

[Ibsen]

Carefull, Ibseen... You let out too much information about our beloved 650s and people will start to get jealous!!

Dan, when I wrote my reply about the gearing it was based on the info you gave; "I've got a larger-than-stock (+1 tooth) front sprocket and a smaller-than-stock (-3 teeth) rear sprocket."
If the correct change for the rear sprocket are 1t down from stock, the difference won't be so dramatic, although it will be noticeable.
With stock gearing on the Z models you will hit the red line, 9500rpm,  at 121.2 mph in 5th gear. (As far as I remember,124 mph was the best result achieved in a road test.)
And as written in a road test back in 1979:
""Although the CB650 pulls well from 6000 rpm on, the definite power band lies between 7500 rpm and red line at 9500."

Btw, if your engine have the detuned (50hp) camshaft it would make sense that your top speed wont go above 100mph. But I don't remember if that camshaft was an option on the US models.

[DammitDan]

I apologize for my faulty information...  I honestly can't explain my early days of motorcycle repair, mostly because I didn't understand half of what was going on!  But honestly, now that I know I bought the chain and sprockets back in Fall 2005 (!!), it's probably about time to change them (especially since I've put about 8k-10k miles on the bike in that time).

I'm thinking this definitely could be a chain-sucking-up-all-the-power issue.  But what was that about ignitors?  I noticed that I wasn't getting a great spark (bright orange) when I did the last top end rebuild.  Are you talking about coils, or about wires?  Or none of the above?  I'm not even sure what ignitors are...

[Ibsen]

>The ignotors are the two spark units that are located under your seat. This is how they look:

[DammitDan]

Would have a bad ignitor really cause problems ONLY on the top end?  The bike runs like a top, but it just poops out when it hits 85mph.  It charges fine, idles great...  Dan's getting frustrated again! 

[Klark Kent]

relax!

change the chain and sprockets because you know you need to do that anyway.  if that dont fix it then go on to the next logical step.  one thing at a time.  methodical troubleshooting is much less exciting than what you are about to do, but i think you would end up happier.  all im saying is theres no use what-iffing, change out the old parts and see what really happens.

repeat after me: all i need is a chain and some sprockets.  life is awesome.  women find me irresistible.
-KK

[DammitDan]

All I need is a chain and some sprockets.  life is awesome.  women find me irresistible. 

[Ibsen]

I agree with Clark Kent. Replace the chain and sprockets first. And buy the stock size sprockets. That is the best starting point.

And yes, life really is awesome.  And one day you will quit worrying about how fast the bike will go and just enjoy the ride.

[DammitDan]

Alright, so for a new question now...  Since I have an '82 SC engine in an '82 standard frame, it calls for different chain length/sprocket size specifications.

82 Standard:  17/39 sprockets, 104 link chain
82 SC:  17/38 sprockets, 106 link chain

Opinions on what I should get here?

[ieism]

All I need is a chain and some sprockets.  life is awesome.  women find me irresistible.

[TwoTired]

Hey DD,
Trying to rule out spark issues.
Can you achieve power at redline in ANY gear selection?  If so, it is unlikely to be a spark issue...unless your bike has an interlink between transmission or speedometer and your ignition system.

Speculation:
It is a fact that spark needs more voltage to arc as the cylinder pressures increase.  Higher engine loads or higher horsepower demands COULD make pressures exceed the capability of a weak spark producer.

One way to check the spark issue is to close the spark plug gap temporarily (perhaps .005 inch) to make the spark jump easier under high load conditions, top speed, top gear, and the "fluffy" wind drag.  If the engine behavior doesn't change, look elsewhere for your speed limiter.  Put the spark gap back, of course.

Life is awsome.  One woman finds me irresitible.  And, I don't need a chain and handcuffs, er, sprocket.

Cheers,