Topic: Engine Pulls Hard up to 5.5k RPM Then Not So Much

[Tracksnblades1]

We have the rumble strips in the breadbasket..
The shoulder strips are understandably avoidable.
However the centerline rumble strips are interesting at the very least when trapped behind slow moving machinery, disabled vehicles, or police detained vehicles…

Always wonder what the states feed back has been on the center strips..It’s pretty intense in a modern low aspect ratio tired auto..😳

[PeWe]

CB750 shop manual K6:
Front 32PSI / 2.2BAR
Rear 40 PSI / 2.8 BAR


The earlier had lower. I guess the tires developed or experinces of the bike in general.

[Finnigan]

Tires inflated to 40 PSI didn't do much for the handling, accepted I'll have to swap them out...gonna miss the high sidewall look!

Bike was running very well last couple of days (250 miles on the new engine build) and decided to try to put in the +3 degrees of timing again per Yoshi catalog.  Again the engine struggled to rev to 8k, it did with some tailwind but nothing like when it was set normally.

[PeWe]

Is the +3* timing really the ignition, not the cam?

My bikes runs best with ignition F at 1100-1200 idle.
Advancer springs cut 1 wound.
This made full advance to happen at ca 2600-2700rpm.
Idle is more stable too with cut springs.

I have tested to advance ignition during dyno runs. Less power. Risk for pinging too when compression is raised.

I have verified where T is at true TDC.
If advancer has a play before tighten the small nut, set it max counterclockwards, T and F will be correct.
Same on both my bikes.

If max clockwise, it will advance the settings.

[Tracksnblades1]

I have verified where T is at true TDC.
If advancer has a play before tighten the small nut, set it max counterclockwards, T and F will be correct.
Same on both my bikes.

If max clockwise, it will advance the settings.

“Advanced” In relation to actual ignition time vs indicated time by the F mark…”taking up full clockwise index pin and hole slop”.

[Finnigan]

Is the +3* timing really the ignition, not the cam?

My bikes runs best with ignition F at 1100-1200 idle.
Advancer springs cut 1 wound.
This made full advance to happen at ca 2600-2700rpm.
Idle is more stable too with cut springs.

I have tested to advance ignition during dyno runs. Less power. Risk for pinging too when compression is raised.

I have verified where T is at true TDC.

If advancer has a play before tighten the small nut, set it max counterclockwards, T and F will be correct.
Same on both my bikes.

If max clockwise, it will advance the settings.

Hmm you're probably right about the cam, I always assumed it was the ignition.  I assume I need to pull the motor if I want to change that now.

[HondaMan]

Hmm you're probably right about the cam, I always assumed it was the ignition.  I assume I need to pull the motor if I want to change that now.

It is do-able with the engine in the frame, but complicated, sorta like this:
1. loosen all 4 carbs' air intake pipes, or just remove the 2 airbox bolts so it can move a little forward.
2. Remove the exhaust pipe(s).
3. Pull all the engine mount bolts except the bottom rear one: loosen it instead.
4. You might have to loosen the drive chain if it has less than 1.5" slack midway between the sprockets. Otherwise the engine won't pivot downward very far.
5. Remove the [center top] breather cover.
6. Remove the cam cover's screws (BTW: this is one reason why so many racers used Allen-head screws in the cam covers...) and the breather hose.
7. Remove the sparkplugs (makes the engine easier to turn by hand).
8. Finagle the cam cover upward and forward: it should let you tilt it toward the front. This is/was how we changed cam cover gaskets that leaked (K0/1 engines mostly). This will give you [tedious] access to the 2 cam sprocket bolts.

If/when you turn the engine to get to the other cam sprocket bolt, DON'T turn the engine backward with the big nut by the points, or you will bend the shaft the spark advancer is mounted to. This makes the timing 'jitter' back-and-forth, seen best with a strobe timing light. Then you'll have to straighten it (again?). I just 'bump' the engine with the electric start or use the kickstarter if possible, the alternator rotor bolt is the best bet (but then you're also taking off the alternator cover to get to it).

Easy peasy? Beats pulling the engine, but it's still most of the same work! This is why the 'frame kits' became popular.

[johno]

For a lazy bloke like me that's all a bit too hard.If you used the standard cam marks only and didn't dial in the cam using LCL it will likely be close enough for spirited road blasting.
If you want to check the valve timing easy peasy way is take the two no1 tappet inspection covers off, set the lash clearance to something ie .040 thou or 1mm then use the TDC mark on points plate to identify where you are, dial gauge on inlet tappet ( or feeler strips if u don't have a dial gauge , rotate engine forward until inlet is opening and as soon as the valve starts to open mark the spot in the points plate. Then do same for on exhaust except mark the spot on the points plate as exhaust closes.
Compare the two Texta points to TDC.
If equal distance from TDC the cam will be set near enough o straight up, if the inlet spot is further from TDS than Exh then it will be advanced, if Exhaust is further from TDC then valve ting is retarded. If you have a good eye and ruler you will be able to tell exactly be turning the crank until both distances are the same and estimate the number of degrees cam is set at either advanced or retained etc.
Either way normally you would need a dyno to tell the difference as the cams characteristics dominate the bum feel lol
cheers John

[johno]

BUT now we have the valve timing all sorted I checked my  YOSHIMURA R&D of America " Daytona" Cam spec card as follows.
The cam overlap is split Evanly at 23 bftdc and 23 attic , also it States at bottom of card that the Ignition Timing needs to be advanced+ 3 degrees over standard.
So your probably on track bro.
ciao Johno

[scottly]

decided to try to put in the +3 degrees of timing again per Yoshi catalog.  Again the engine struggled to rev to 8k, it did with some tailwind but nothing like when it was set normally.

Try moving it 3 degrees in the opposite direction.

[Finnigan]

decided to try to put in the +3 degrees of timing again per Yoshi catalog.  Again the engine struggled to rev to 8k, it did with some tailwind but nothing like when it was set normally.

Try moving it 3 degrees in the opposite direction.

lol that's just crazy enough to work

When I dialed in +3 advance with the strobe it move the hash marks clockwise.  I assumed that was advance based on the strobe instructions.

[Tracksnblades1]

What side of the F mark was the +3 degrees timing you had that made it run worse..?
Was the case mark showing up a little off to the right side of the F…?
Or was the case mark showing up a little off to the left of the F mark,  in between the F and T..?

[Finnigan]

What side of the F mark was the +3 degrees timing you had that made it run worse..?
Was the case mark showing up a little off to the right side of the F…?
Or was the case mark showing up a little off to the left of the F mark,  in between the F and T..?

F was counterclockwise relative to the mark

[scottly]

Did you tighten up the springs so the advance has it's full range of travel?

[Finnigan]

Did you tighten up the springs so the advance has it's full range of travel?

Not sure what you mean, I left the springs the same after cleaning and lubing up the advancer.  Verified they snapped back to where they needed to be.

[Finnigan]

Pulled the spark plugs after a long ride yesterday, cruising and revving high on the straits (~8k)

1 looks dark and slight smell of gas
2 looks the same as 1 in good lighting but smells a little burnt (?)
3 looks lighter than 1 and 2 and has strong gas smell
4 doesn't look tan at all, it looks grey and light smell of gas

Questions I ask myself
- Which one is best? specifically tan or grey and why are they different
- These are very dark, should I go down one sized main jet or raise needle clip, or both?

[denward17]

Can't answer about the color, but what gap are you running?

[Finnigan]

spark plug gap is .029"

[scottly]

Just set your timing so it's at the F mark for now, but verify the advancer is free to move to full advance, and returns to the F mark with the springs. Both plugs are on the rich side, but not sure if that's the problem? What Dyna coils, 3 ohm or 5 ohm?

Spark set to 'F', made sure the advancer moves freely - snapped it a few times and confirmed it fires at 'F' again.

Got a timing light and was amazed how far off the advance timing marks were, several millimeters to the right at RPM.

I adjusted the plate to get 1/4 in and then the individual pickup for 2/3.  It still idles but the F mark for idle is far to the left.

Your original timing was retarded, causing your power loss at higher RPMs. The springs on your advancer are too weak, preventing the return to the 10* BTC point at idle. This can make it harder to set an even idle, but as long as the timing is set dynamically at the full advance marks, the top end performance won't be affected. You can try squeezing the eyes on the ends of the springs to tighten them up, or even resort to cutting a coil off each spring. The idea is to have the full range of advance the system affords. Now that you have a timing light, you can check what RPM the full advance comes in at, and tailor it to your needs. Once you get it sorted, you can try the 3* advance from the other thread.

[Finnigan]

Just set your timing so it's at the F mark for now, but verify the advancer is free to move to full advance, and returns to the F mark with the springs. Both plugs are on the rich side, but not sure if that's the problem? What Dyna coils, 3 ohm or 5 ohm?

Spark set to 'F', made sure the advancer moves freely - snapped it a few times and confirmed it fires at 'F' again.

Got a timing light and was amazed how far off the advance timing marks were, several millimeters to the right at RPM.

I adjusted the plate to get 1/4 in and then the individual pickup for 2/3.  It still idles but the F mark for idle is far to the left.

Your original timing was retarded, causing your power loss at higher RPMs. The springs on your advancer are too weak, preventing the return to the 10* BTC point at idle. This can make it harder to set an even idle, but as long as the timing is set dynamically at the full advance marks, the top end performance won't be affected. You can try squeezing the eyes on the ends of the springs to tighten them up, or even resort to cutting a coil off each spring. The idea is to have the full range of advance the system affords. Now that you have a timing light, you can check what RPM the full advance comes in at, and tailor it to your needs. Once you get it sorted, you can try the 3* advance from the other thread.

I think what I'm afraid of here is that the springs will be too strong for the weights to change the timing, I took your suggestion and ordered a new set of springs from Yamiya.  Should take the guess work out of all this

[Tracksnblades1]

Just set your timing so it's at the F mark for now, but verify the advancer is free to move to full advance, and returns to the F mark with the springs. Both plugs are on the rich side, but not sure if that's the problem? What Dyna coils, 3 ohm or 5 ohm?

Spark set to 'F', made sure the advancer moves freely - snapped it a few times and confirmed it fires at 'F' again.

Got a timing light and was amazed how far off the advance timing marks were, several millimeters to the right at RPM.

I adjusted the plate to get 1/4 in and then the individual pickup for 2/3.  It still idles but the F mark for idle is far to the left.

Your original timing was retarded, causing your power loss at higher RPMs. The springs on your advancer are too weak, preventing the return to the 10* BTC point at idle. This can make it harder to set an even idle, but as long as the timing is set dynamically at the full advance marks, the top end performance won't be affected. You can try squeezing the eyes on the ends of the springs to tighten them up, or even resort to cutting a coil off each spring. The idea is to have the full range of advance the system affords. Now that you have a timing light, you can check what RPM the full advance comes in at, and tailor it to your needs. Once you get it sorted, you can try the 3* advance from the other thread.

I think what I'm afraid of here is that the springs will be too strong for the weights to change the timing, I took your suggestion and ordered a new set of springs from Yamiya.  Should take the guess work out of all this

^^^^^He’s trying to help you..^

Attached is the Honda manual strobe light timing method he’s trying to get you to do..

** Notice**   Honda’s reference to the additional advanced (total) timing marks in addition to the F (static) timing he wants you to verify..  ^^^^^^^^

Read number 6, you’ll need to check and verify this with your timing light.. ^^^^what he is saying^^^^^

Since you have new springs on the way, cut a coil off the old springs like everyone is encouraging you to do..
Worst case scenario is your full total advance (23-26marls) won’t show up until 2750 rpms. As another has already indicated instead of the stock 2500rpm..

Everyone is trying to help..it has all been posted above…🤔🤔🤔

[Finnigan]

Not rejecting anyone's advice, excuse the previous comments if it sounded that way.

[Tracksnblades1]

Not rejecting anyone's advice, excuse the previous comments if it sounded that way.

Just trying to figure out whether you have verified your advancer’s full range of motion (advance) with your timing light above 2500rpm.. You should see it move from the F mark to the 23.5-26.5 marks…?

Did you tighten up the springs so the advance has it's full range of travel?

Not sure what you mean, I left the springs the same after cleaning and lubing up the advancer.  Verified they snapped back to where they needed to be.

I’m not sure by your responses whether you have actually verified your advancer’s full advance with your timing light..?

[Finnigan]

Yes, verified that full advance is spot on, even if the F mark is off as a result.  I mentioned in a previous post that it still idles fine after the full advance was adjusted to be in spec.

[scottly]

If you want to advance the timing 3*, the two full advance marks are 2* apart, so set the timing with the right side hash mark to the left of the case mark by 1 1/2 that distance with the motor revved. You might want to scribe marks on the advancer.
BTW, do not try to adjust the timing by rotating the points plate with the engine running. Always adjust the plate static, lightly tighten the screws, and then check with the strobe. If adjustment is required, shut the motor off, make a guess on how far to move the plate, snug the screws, and check again. When you are satisfied, tighten the screws fully