Topic: High altitude 73 CB500 daily driver ( 5/20/17 update )

[Desert Dan]

   So I have re-fixed the leaking #2 carb issue, I pulled the float needle valve out and polished the end of the needle that blocks off the brass portion of the inlet valve as it had developed a ridge on the end of the needle seat. So far the fix has worked so Im crossing my fingers that the problem wont resurface for another few thousand miles.
   

HP loss of these carb'd engines is about -1% of total output per 1000 feet altitude, all else being equal. So, by 8000 feet, the 500 is typically running about 32-ish HP at 7000 RPM. Higher-compression pistons (if they are NOT forged pistons) will reduce this effect by about 50%, as the efficiency stays higher. This is why the "Gentleman's Express" version of these bikes (590cc, made with 750 pistons) has been popular for many years. Way back when, Action Fours used to make some 1mm oversize 10.5:1 pistons for these bikes, and if the owner stayed with the stock cam this made for a mighty torquey 500, indeed! Then, the rear sprockets would lose a few teeth to make them smoother 80 MPH tourers, too. But, those who decided they wanted a "big cam" to go with the pistons discovered the efficiency was very low until 7000 RPM, so the bikes became a nuisance to ride. (Something to ponder...).

   Mark, Im intrigued by the " gentleman's express" modifications you described in an earlier post, could you elaborate on what modifications have to be done in order to fit the 750 pistons and make the engine a 590cc. Boring the cylinders out on the 500 from 56mm to 61mm seems like a lot would it be better and or possible to get my hands on a 550 cylinder block and do the boring on that?
   And my last question pertains to ride-ability, right now I believe Im running the stock sprocket combo but I was wondering if there is a better sprocket combo that would be more efficient on the little four. Right now in 5th gear at 65mph the bike runs at 5400rpm and at 80mph it is screaming at 7000rpm.

[calj737]

7,000 is not screaming with a redline of 9,500. These are small motors with tiny pistons that require revving to extract power from them. If you want a lower torque band, you'll need to move up to a much larger displacement motor that reclines closer to 6,000.

[Desert Dan]

7,000 is not screaming with a redline of 9,500. These are small motors with tiny pistons that require revving to extract power from them. If you want a lower torque band, you'll need to move up to a much larger displacement motor that reclines closer to 6,000.

I figured the torque of the engine would be the primary limiting factor, I just feel a bit guilty when I hold the engine in the higher rpm band for extended periods of time.

[HondaMan]

7,000 is not screaming with a redline of 9,500. These are small motors with tiny pistons that require revving to extract power from them. If you want a lower torque band, you'll need to move up to a much larger displacement motor that reclines closer to 6,000.

I figured the torque of the engine would be the primary limiting factor, I just feel a bit guilty when I hold the engine in the higher rpm band for extended periods of time.

Don't feel quilty about that: this is exactly what Sochiro and Company had in mind for this bike. When it came out, the US speed limits were 70-75 MPH, and the tires and gearing it came with put it right into the upper RPM powerband these engines have. My brother toured next to my 750 for 8 years with his, and it never missed a beat, nor cared. The top speed of his grew from 102 MPH when it had 1000 miles on it to a little over 112 MPH when we last 'played' together when it had about 28k on it. (On that trip, it blew the whole core of the #2 muffler out onto the hiway near Fort Collins!)

[SOHC4 Cafe Racer Fan]

From the mouth of Hondaman -- so it is written, so shall it be done!

Yes, 7K is not that high on the revs, even for sustained periods/miles. 

[Desert Dan]

Well if Hondaman and two other really old timers say so, it must be true. My guilt has been abolished, I was just worried I was over working the bike holding 7k rpm for sustained periods.

[calj737]

stop holding it at 7,000. Try 8,800 for more fun! 

[SOHC4 Cafe Racer Fan]

Yeah, Dan. Ride it like you stole it! Wring its neck a little!

[RAFster122s]

Just don't take it up to redline in 1st gear, that could be a very hard shift...
Going up to 8800 and above is going to take you to some fun speeds so, exercise judgement to gauge police presence.
David

[Desert Dan]

For the most part I keep the rpm's right around 4k but Ive been known to get it right up to the red line on occasion. On a related topic thats out of purely academic curiosity is it possible to do a wheely on a 500 or does it lack the required torque?

[SOHC4 Cafe Racer Fan]

For the most part I keep the rpm's right around 4k but Ive been known to get it right up to the red line on occasion. On a related topic thats out of purely academic curiosity is it possible to do a wheely on a 500 or does it lack the required torque?

You can do a wheelie on a 50cc bike.  A stock CB500 will not generally power wheelie.  With a big bore kit, cam, ported head and CRs you can get the front end to lift using a 1/4 turn throttle.  If you know how to wheelie, you can get a stocker to do it.  I'm not really a wheelie kind of guy.  I've power wheelied powering out of turns on my modern bikes, but I don't try to wheelie.

[Desert Dan]

You can do a wheelie on a 50cc bike.  A stock CB500 will not generally power wheelie.  With a big bore kit, cam, ported head and CRs you can get the front end to lift using a 1/4 turn throttle.  If you know how to wheelie, you can get a stocker to do it.  I'm not really a wheelie kind of guy.  I've power wheelied powering out of turns on my modern bikes, but I don't try to wheelie.

Thanks for the wheelie education, what sparked my interest was I'd notice the front end would get light on hard  acceleration which seems to me to be the first step to doing a wheelie. I think Ill hold off on doing wheelies on the cb500 and practice on a dirt bike or something in the meantime.

[RAFster122s]

Being a little rough on the shifting of my CX500, I have been able to lift the front wheel on shifts but, not wheelie. My CB550 is still a project on hold.

David

[HondaMan]

Hey Dan: (or anyone else with 550 parts?)
Do you happen to have a leftover 550 set of cylinders? I need some for one of our members who's engine took a terrible hit in shipping here from NY. And, I need a tach drive for the head as well: his is broken in two.

Anyone?

[calj737]

Hey Dan: (or anyone else with 550 parts?)
Do you happen to have a leftover 550 set of cylinders? I need some for one of our members who's engine took a terrible hit in shipping here from NY. And, I need a tach drive for the head as well: his is broken in two.

Anyone?

Just the gear? I am pretty sure I have that. Sorry, no extra jugs though. Send me a PM with an address and I'll ship that off.

[HondaMan]

Hey Dan: (or anyone else with 550 parts?)
Do you happen to have a leftover 550 set of cylinders? I need some for one of our members who's engine took a terrible hit in shipping here from NY. And, I need a tach drive for the head as well: his is broken in two.

Anyone?

Just the gear? I am pretty sure I have that. Sorry, no extra jugs though. Send me a PM with an address and I'll ship that off.

Thanks for the reply, Cal!
This one's gear is OK, it is the housing on the outside of the head that got hit in transit, broke it right in two!  The tach cable is still screwed onto it, so it acted like a lever on the housing.

[Desert Dan]

I don't have much in spares, but I do have a spare tach drive housing. I won't be able to drop it off with you until the 27nth because Im up in northern Colorado for school and the drive housing is in my shop at my paren't place down south. If time is of the essence you could go to Steele's cycles, I bought the spare housing there for 10 bucks with the drive gear. Last time I was at Steele's two more 550 engines had been added to their pick-n-pull yard.

[HondaMan]

I don't have much in spares, but I do have a spare tach drive housing. I won't be able to drop it off with you until the 27nth because Im up in northern Colorado for school and the drive housing is in my shop at my paren't place down south. If time is of the essence you could go to Steele's cycles, I bought the spare housing there for 10 bucks with the drive gear. Last time I was at Steele's two more 550 engines had been added to their pick-n-pull yard.

Thanks, Dan! I'm not in a big rush for this: I have to find some 550 cylinders before I can move forward on this rebuild. It's a full-blown Gentleman's Express build on a CB500-4 like yours. The engine has less than 6k miles on it, but was parked then for 30 years and rusted itself tight.

[Desert Dan]

Sorry I can't help with the cylinders, but Ill drop the tach drive gear housing off with you sat the 26th or Sun the 27th.

[riverfever]

   

One of my favorite rides on a mountain bike was from Deckers to Buffalo Creek on this road and back. You could also jump on the Colorado Trail in that area as well. I wish they would pave the whole thing so I could take my motorcycle on it but I see that didn't stop you.

[Desert Dan]

One of my favorite rides on a mountain bike was from Deckers to Buffalo Creek on this road and back. You could also jump on the Colorado Trail in that area as well. I wish they would pave the whole thing so I could take my motorcycle on it but I see that didn't stop you.

It's one of my favorite rides too, and when Im not away at school it's only about a 15 mile ride from my house. The dirt parts aren't terrible by the platte, the bad part is actually all the paved corners where gravel has gotten spread on the road from anglers tearing out of the dirt parking lots. The two dirt roads that go from the Platte to Sedalia are a little more challenging on the CB's but it seems like when ever I ride those dirt roads theres always a guy on a giant harley hauling a$$ up them kicking up a huge plumes of dust behind him.

[riverfever]

Oh that really nasty dirt climb used to be one of my favorite hills to do repeats on. Sometimes I would take random trails in that area. I know of three grow camps back in there that got busted and I walked right into one of them. Took Jefferson County PD back to it later. They choppered out tons of weed.

[MJL]

I was hoping to hear more about a 590 build. I'll be watching this thread anyway.

[HondaMan]

I was hoping to hear more about a 590 build. I'll be watching this thread anyway.

I'm starting one for one of our other members: keep an eye out for it in the Build section.

[Desert Dan]

    So I finally gave up searching for stock 7.5k ohm resistor spark plug caps and installed the NGK 5k ohm resistor caps on the bike, I was worried the shorter spark duration might negatively affect the engine but after a few hundred miles I haven't seen any signs to justify my worries. I did notice that the engine's idle was slightly smoother now that all 4 caps have the same resistance.
    Im still on a quest to do the ton, but it seems no matter how well I have the bike tuned, 95mph is about all I can get out of it regardless of altitude. It's like there is some sort of invisible barrier right at 95mph.   The bike pulls well all the way up to 85mph then it slowly builds momentum and stops at 95. I think there may be 3 possible reasons I cant hit 100 A. The speedometer may not be accurate at higher speeds after 42 years of use B. the persistent oil burning may be making a few horses lame and C. the cam chain being a bit stretched may be costing me a few extra ponies. It could be a combination of the 3, but as of right now I can only check one, so tomorrow Im going to do a high speed run with my GPS strapped to my leg and see how accurate the speedo is.
    In the meantime Ive decided Im going to get a picture of the CB500 at every airport Ive flown into during my flight training, Ive been to a few already on the bike but I only just decided to start documenting each visit. A few are going to be pretty long trips, so Im going to need to hustle to get them all in before the snow starts falling. I rode the bike out to Fort Morgan airport (KFMM) this weekend, which is a small airport consisting of a single paved runway and is mostly used by crop dusters. Its roughly 60 miles from my apartment out to Fort Morgan and the bike did great running at 80mph the whole way out there and back.