Topic: Am I tuned properly??

[toycollector10]

My 1969 K0 starts first jab, idles well, pulls well and shifts up with the usual ker-lunk when hot. Problem is, if it is a problem, is that when I am just tooling along at 30 MPH at 2000 RPM  in top gear it sort of "burbles" if you know what I mean. It doesn't really run 100 percent, maybe 90 percent. Should I blast the carbs with cleaner?  Points?  Plugs?  Any ideas guys??   Thanks.

[Bob Wessner]

I've a K0 also. Though it will idle down to 1500 in 5th and pull smoothly from there, personally, if I were tooling along at 30 mph, I would probably be doing it in 4th to keep the revs up a bit.

[Jim Shea]

Do you mean it dies when you quickly open the throttle?? Mine does that, I can pull away from 30mph in 5th, but if I open it up quiclky it will die.

[TwoTired]

Since your carbs have twist grip actuated slides, it is really more meaningful to note at which throttle opening you are experiencing symptoms.  This will determine what part of the carbs are dominating the mixture.

How confident are you that the carbs are well synched?

When was your last complete and throrough tuneup?
I wouldn't change carb settings until the whole tuneup regimen met book values.

Cheers,

[750goes]

Let me borrow it for a test spin and I promise to let you know after a few thousand clicks what I think is wrong with it, but no guarantees whether I can shed any light on the subject.

[lassenc]

Do you mean it dies when you quickly open the throttle?? Mine does that, I can pull away from 30mph in 5th, but if I open it up quiclky it will die.

Mine does the same, maybe it would be an idea to enrich the mixture!

[Jim Shea]

I am loathe to enrich the mixture as the bike runs well otherwise; how much do you enrich it??

[Gordon]

Going against my better judgement, I have to agree with Bob on this.   Get that thing out of top gear at 30!  Depending on the conditions of the road, you should be in either 3rd or 4th at that speed.  Over 3000rpm is where the engine is meant to be run at. 

[theunrulychef]

Yep, 30 in 5th is a gearing issue.  Your bike isn't even in it's power curve at 2000.  Don't be afraid to scare the neighbors - rev that sucker up a bit.

[csendker]

Don't want to hijack the thread, but...do these RPM's apply to a 550 also?  I tend to shift at 2000~2500 RPM.  Is there an optimum RPM to shift or run at?  I've never seen any power or torque curves for these.

[lassenc]

I am loathe to enrich the mixture as the bike runs well otherwise; how much do you enrich it??

Well, does it have the issue in neutral? Cause it shouldn't if it's a mixture problem you have.
Of course all testing must be done on a warm engine, what's the point in a adjusting a cold engine?

[Gordon]

Don't want to hijack the thread, but...do these RPM's apply to a 550 also?  I tend to shift at 2000~2500 RPM.  Is there an optimum RPM to shift or run at?  I've never seen any power or torque curves for these.

A similar but smaller engine (ie. the 550) has to rev a little bit faster than it's larger 750 counterpart to make it's power.  So if you want to get into the power band, rev it up a little higher.  It all depends on your personal riding style and preferences, but for normal accelleration I tend to shift my 750 somewhere around 3000 to 3500 rpm, so I would imagine the 550 should be up at least that high.  On the 400F I didn't shift until almost 5000, but then the redline was 10K. 

[MetalHead550]

I also vote that there is nothing wrong with your bike(though you may want to make sure everything is properly tuned) and that you are simply riding completely out of the powerband.  Like others said these motors are designed to run at high rpms, they love it.  My 550 doesnt seem to hit its powerband until around 4500rpm or so.  Definitly picks up after 5k though.  On my 550 I select a gear that keeps me around that powerband so if Im cruising through town at about 30-40, Im in 3rd gear.  Im in better control of the bike because when the rpms are up you can use that for both engine breaking and quick acceleration.  I use the gears as much as the throttle and break to control speed.

[TwoTired]

I am loathe to enrich the mixture as the bike runs well otherwise; how much do you enrich it??

If you want to enrich your low speed mixture for better twist grip response from low settings, turn your idle air bleed screws CW (all four) in 1/8 turn increments and drive for effect.
If you get improvement, repeat the procedure until you get no improvement in low speed throttle response.  Then go back and turn them back out 1/8 turn, as you have reached the limit of effectiveness on that adjustment with your current jetting.
If your intake and exhaust system are stock you'll find the book settings best,  With changes to these items, other air bleed settings may be beneficial.
This assumes you do NOT have accelerator pump type carbs.

Cheers,

[BobbyR]

5th gear is essentially for highway cruising at stock gearing. Tooling down the road at 30MPH you are lugging the motor. Your engine braking and throtlle have a lot to do with your handling. You really want to keep the RPMs somewhere in the power band. If you want to save gas coast down the hills. 

[TwoTired]

Don't want to hijack the thread, but...do these RPM's apply to a 550 also?  I tend to shift at 2000~2500 RPM.  Is there an optimum RPM to shift or run at?  I've never seen any power or torque curves for these.

The red line on the tach is where to shift for max power/acceleration.

The red line on the tach is not to be feared.  But, the flashing red lights behind you can be distracting, disconcerting, even annoying.

The 74 CB550 owner's manual indicates a shift to second at approximately 10MPH.  The sequence repeating with subsequent gears.  This is rather lethargic operation, IMHO.  But, should be good for NOT waking your passenger.

[Gordon]

I paid closer attention to the tach today while riding, and it turns out I've actually been up-shifting more in the 4000 to 5000 rpm range for normal accelleration.  Higher if I really want to pull away from the traffic. 

[chippyfive50]

My 550 gets happy in the  6500-9k range....

[cd811]

patient says to doctor..."doc it hurts when I do this"
doctor says to patient..."don't do that"
 

[toycollector10]

Thanks for your input men..I took a 3 hour ride up into the hills above the city today, a sunny 22 degrees C and some great cloud buildups, little wind..Just hummed it up and down through the gears shifting generally between 3500-5500 RPM, I felt like a pig in sh*t.

Got on the urban roads home and took your advice to travel in 3rd or 4th which made me and the bike feel a lot happier.

Bike ran flawlessly until about three miles from home, I might have a sticking carb slide or something as the bike wanted to idle at 2000 rpm until I put it in gear with the brake on then eased out the clutch to load the engine which then put the idle back to about 1100 rpm. Weird.

I'm using 98 octane which I hear is good for your engine (does it clean carbs over a period of time?) so maybe that has affected the carb jets, cleaned and opened them up a bit so I might have to adjust the idle settings..

Anyway, I've had a great day out riding...except when granny decided to undertake me in the worst possible place and I wasn't checking in my rear view mirror, she came from nowhere. Now there's a cliche boys. Safe riding.

[HondaMan]

Honda's charts for the CB750 show that 5th gear should be used for 40MPH and higher speeds. The problem is that the slide-type carbs do not mix evenly when the air speed is low through the slides. You'll notice, if you pull the plugs, that they are going to be quite dark. This causes a slight misfire that shows up as irregular power at low engine speeds under load. The K0-K2 are especially susceptible to this problem.

At 30 MPH, consider using 3rd gear or less. The SOHC fours were all made for RPM and despise lugging. It will ruin the crankshaft if lugged for long, because the oil pressure will be too low for the loads. The oil flow reaches 70% at 2200 RPM, which should be your minimum cruising RPM.

[toycollector10]

Thanks Hondaman, excellent post....Just what I needed.

I nominate you for the "Master of the Four" award..

Novice?

Cheers

[Gordon]

I'm using 98 octane which I hear is good for your engine (does it clean carbs over a period of time?) so maybe that has affected the carb jets, cleaned and opened them up a bit so I might have to adjust the idle settings..

The only thing that high octane fuel will clean out is your wallet.  If an engine isn't designed to take advantage of premium gas, you will see absolutely no benefit from using it.  Stick with the regular.

[TwoTired]

I'm using 98 octane which I hear is good for your engine (does it clean carbs over a period of time?) so maybe that has affected the carb jets, cleaned and opened them up a bit so I might have to adjust the idle settings..

The only thing that high octane fuel will clean out is your wallet.  If an engine isn't designed to take advantage of premium gas, you will see absolutely no benefit from using it.  Stick with the regular.

Yes, I agree.  I understand that the extra additives used to prevent pinging, detonation in high compression engine with premium fuel just lead to increased deposits in the combustion chambers of lower compression engines that can't burn them off properly.  Eventually the deposits will build up, raising the compression ratio so that premium fuel is required to prevent pinging, until you decoke the engine, that is.

Cheers,

[toycollector10]

Are you saying that I should go back to 96 octane TT??