What is typical on freeway

Don't worry about the RPM's, these 650's love the upper range. I bought one new in 77 and when it was stock I almost always shifted at about 9200 RPM or so and after hopped up I shift at around 10500 when I'm getting on it. I've hit some water doing a burnout and pegged the tach. They make most of their power in the upper RPM range. I run a 17/41 on my hot 650.
Mark

That's pretty high gearing, Mark. You got a short back wheel? Hell, I put a 16-inch wheel on our 650 to help get it low enough for Kim, and put a 17/42 on it to tone down the revs on the highway and keep her out of trouble while learning. Ran good, but was a bit boggy out of the hole for me. Now have a 15/42, and make lots of tire smoke and wheeliesB)

tjk wrote:

That's pretty high gearing, Mark. You got a short back wheel? Hell, I put a 16-inch wheel on our 650 to help get it low enough for Kim, and put a 17/42 on it to tone down the revs on the highway and keep her out of trouble while learning. Ran good, but was a bit boggy out of the hole for me. Now have a 15/42, and make lots of tire smoke and wheeliesB)

I have a 18' rear wheel and it's a little boggy but my motor is a little boggy at lower RPM's with the cams so I slip the clutch a little starting out anyway. My bike pulls that gearing no problem, it pulls the front wheel with ease and when I used to smoke the tire it did it all the way through second and got a little rubber in third.
Mark

I had a 15/42 for a few years but first gear comes and goes so fast it was tough to ride. The 16/42 is much better for me. :blink:

I've got a 17 front and 41 rear sproket my self wich is a 2.42 gear ratio, and its good. I can let of the clutch slowly and it will stuble away. I dont have a tach or speedo yet, but it feels like Im going 35 before hitting next gear.

Someone had a chart on this about almost 2 years ago. It had gear ratios, speed, and you could even change the numbers around to see were you would be.

SO, I did a search on the forums and found someone said that below 130psi for compression and things are not responsive, 130 to 160 is ok and above 160 things are snappy.

If this is all true, how can I get my compression up there? Can I just slap a new set of rings in or do I need to have the engine bored and put in oversize rings?

Thanks.

Well, your compression figures would suggest rings would certainly help but I was under the impression that 130 was your magic number for turbo applications. Maybe I'm wrong there. I'm sure someone can shed some solid light on it.

Get your compression too high and you'll have issues as well. Notably, preignition.

I think you can still get some good life out of what you currently have, honestly.

aarons80kz650 wrote:

SO, I did a search on the forums and found someone said that below 130psi for compression and things are not responsive, 130 to 160 is ok and above 160 things are snappy.

If this is all true, how can I get my compression up there? Can I just slap a new set of rings in or do I need to have the engine bored and put in oversize rings?

Thanks.

Yes Dynamic compression is the efficiency factor in these and other engines. Any engine below 130 is not going to be responsive. A lot of people base there compression on static wich is the piston, combustion chamber, stroke, deck height. The problem with this is that it does not take into consideration cam or cam timing. So it is posisble to have a static compression of 14:1 and only have 160 psi of cranking compression so it can still run on 87 octane.

If you want to raise your compression slot your cam gears and advance them 5*. This will raise your comp 10 points.

I have 155 cranking compression and I have shaved my cylinder head(only cause I have it off at the time). I shaved it using a straight peice of wood and 80 grit then finishing with 180. I took it down to the vaves, and used a graphite gasket and coverd it with copper spray. This was 11 years ago. Shaving the head will cause your cam to retard. In the future I am going to slot my cam to advance the timing 5*. :evil: That should raise it to 165 . Perfect compression for these engines in my book:) . You dont want to go too high with these engines cause they are air cooled. So maximum I would have to say is 175 or maybe 185.

My SR650 has 16/41 sprockets and I am guessing that is stock.

Update. I've been cramming 5's in the tool box under the seat for a year now. With all that green I finally ordered the Dyna-S ignition, new dyna 3.0 ohm coils, new copper wires and a Clymer manual. $295.72 from Z-1. It all came in today so I was out in the garage until about midnight hooking it all up.

The bike does seam to run smoother. I did the static timing method described with the dyna install instructions. I put the timing light on after starting it up and the line matched up with the F mark like it is supposed to. Unlike last year when I tried to time it now the line is not jumping around. Smiles from ear to ear.

So Its cold outside and dark thirty but there are shiny new coils on board so I had to take it for a spin. Unfortunately my high speed,5th gear on high way, didn't seem to improve.

I found on page 42 in the clymer manual that compression should be 170psi +- 15 psi. So with my compression at the low 130's I'm back to my question from last year. And I ask this because so many of my coworkers have said they just slap new rings in their dirt bikes and are off and running again. Can I just slap new rings in? Like take the engine apart and hone the cylinders and clean it all up and put in new rings? or is that a recipie for disaster? Idealy a top end bore and oversized rings and the works would be the way to go.

I'm going to start cramming $5.00 s in the tool box again. Maybe next year I can do some more good.

A quick note on the clymer manual. I was expecting something like a Haynes repair manual for my car that doesn't tell me much except to take it to a mechanic. I was pleasantly suprised. There is a lot of good information in there.

"Thumbs-up" for the successful Dyna install man

You deffinately can hone and put new (whatever acceptable size required) rings in your engine! That is completely up to you.

Yes, it will improve things in your case. But... lets be rational here, and save some of your stash whilst you can.

Make sure you perform ALL of the maintenence operations in your Clymer Manual in order first. Especially valves!
Its super important for all these things to be as close to spec a you can resonably get them.
Lots of places can to the manometer balancing if you cant borrow one. Just have to call around for a bit.

When your certain all these tasks have been completed effectively, and you are still not satisfied with your top end... $$$ is pretty much the only way.

Good-Luck! and Cheers!

J. :lol:

PS. I love dem bike manuals too

As for gearing as far as I know all 650 B and C models as well as the F1 run 16/42 stock (although some came with a 16/41).

The D (SR) models came with a 16/40 gearing, though I think some of them might have come with 16/41 too - B, C, D and F1 all run a 530 chain.

The F2-F4 models run a 13/33 gearing and 630 chain, same setup as the 750 fours.

I have no info on Ltd (E) and CSR (H) models.