Topic: can't get her reving

[greg]

Hi all!
I'd like to get your advice on following issue.

I've rebuild a CB500Four K1 model to it's original state with candy gold paint.
Only a few days ago I started the bike and have now trouble to get it running (rev) properly.
It smokes like hell on all 4 pipes (keeps smoking even when I shut her down).
Runs well on idle and takes throttle well, HOWEVER she revs only up 5500rpm - 6000 rpm --> stutters there and dies then.

What have I done so far.
- motor was rebuild
- valves lapped & new seals
- Carburetor: floats set with clear tube method to be 2 mm under bowl
- main jet changed from #100 to #78
- needle set to lowest postion
- stock air filter in place
- ignition assy changed to electronic one
- coil resistance - OK
- measured the compression after warming up (#1-130 psi //#2-120 psi //#3-130 psi //#4-130 psi)
- spark plug #1, 3, 4 are black, looking wet; # 2 wet but very shiny
- sprayed the carb. with brake cleaner to see if there are air leaks - no air leaks, no change in rev.

Any advice on what to tackle next is much appreciated
Thank you all!
Gregor

[calj737]

- main jet changed from #100 to #78
- needle set to lowest postion

For starters, restore these to original positions before you undertake anything else. At #78 you are starving for fuel at WOT.

Needle lowest is full RICH. I’d bet your plugs look like crap.
Undo these two mistakes and you’ll be surprised how close you are to a good tune.

[M 750K6]

I agree with that advice. Especially as you're on a stock air filter. Stock exhaust too?

I struggled with rich symptoms (CB750) until I went back to the original needles, which I had replaced from a refurb kit. The replacements were a little thinner, causing rich mixture on acceleration. Once I'd done that, I put everything back to stock settings and it has run well since.

Other thoughts. I don't know if 2mm fuel level is right or not. Are you also measuring float height from the gasket surface (without the gasket), at the point the float tang starts to touch the sprung top of the valve needle? I also suffered with one of my floats being a little reluctant to move. I had roughness on the spindle that cleaned off, but also the floats were slightly twisted.

Have you checked your auto-advance is free moving? Is your points gap spot on? + have you checked the timing? Also worth double checking the valve lash / tappet adjustment.

Also, have you dismantled and carefully cleaned all the channels within the carbs?

[greg]

- main jet changed from #100 to #78
- needle set to lowest postion

For starters, restore these to original positions before you undertake anything else. At #78 you are starving for fuel at WOT.

Needle lowest is full RICH. I’d bet your plugs look like crap.
Undo these two mistakes and you’ll be surprised how close you are to a good tune.

Hi Calj737,
thanks for your reply.

I had the original position -> needle clip to middle position, jet #100.
The sparks were all black and lot of smoke (blue/white) came from the exhausts with the original setting. So too rich, right?
Next I went to the #78 jet und hung the needle the lowest/clip fully up (leanest).
also had the reving issue with the original setting.

basically nothing changed after going to #78 & needle the lowest.

anything else you can think of?

[Scootch]

I believe with the clip in the lowest position gives richest mix

[greg]

I agree with that advice. Especially as you're on a stock air filter. Stock exhaust too?
Hi  M 750K6,

thanks for thoughts!
--> Yes, stock exhausts 4 into 4

I struggled with rich symptoms (CB750) until I went back to the original needles, which I had replaced from a refurb kit. The replacements were a little thinner, causing rich mixture on acceleration. Once I'd done that, I put everything back to stock settings and it has run well since.

--> was thinking that too already. How is the general opinion on the KEYSTER (KH-1050NFR) repair kit?

Other thoughts. I don't know if 2mm fuel level is right or not. Are you also measuring float height from the gasket surface (without the gasket),
at the point the float tang starts to touch the sprung top of the valve needle? I also suffered with one of my floats being a little reluctant to move. I had roughness on the spindle that cleaned off, but also the floats were slightly twisted.
--> set it first to 22 mm and rechecked with clear tube

Have you checked your auto-advance is free moving?
--> yes, is freely moving
Is your points gap spot on? + have you checked the timing?
--> Have electronic one, The setting was doublechecked.
Also worth double checking the valve lash / tappet adjustment.
--> did that just before I started the motor, will double check again

Also, have you dismantled and carefully cleaned all the channels within the carbs?
--> carbs fully disassambled, ultrasonic cleaned and rebuild with KEYSTER kit

[greg]

I believe with the clip in the lowest position gives richest mix

thanks for the pic.

yes, we are on the same page.
Had it in the middle,position 3 and set it to position 1 for the trial

[newday777]

- main jet changed from #100 to #78
- needle set to lowest postion

For starters, restore these to original positions before you undertake anything else. At #78 you are starving for fuel at WOT.

Needle lowest is full RICH. I’d bet your plugs look like crap.
Undo these two mistakes and you’ll be surprised how close you are to a good tune.

Hi Calj737,
thanks for your reply.

I had the original position -> needle clip to middle position, jet #100.
The sparks were all black and lot of smoke (blue/white) came from the exhausts with the original setting. So too rich, right?
Next I went to the #78 jet und hung the needle the lowest/clip fully up (leanest).
also had the reving issue with the original setting.

basically nothing changed after going to #78 & needle the lowest.

anything else you can think of?

Greg
You said you have rebuilt the engine to original specs in the original post.
And the blue/white smoke.
Did you put rings only in your rebuild? As in you didn't bore oversized with new pistons and rings? Or did you remove the cylinder sleeves and install new sleeves and bore to original pistons?

If you only put in new rings? Then I'm leaning to the cylinders are too big now...worn, and you get the smoke from oil burning( and giving you the black spark plugs). The fix? Reborn to Bigger pistons and rings.

[M 750K6]

Greg,
My replacement set for the carbs was Keyster, from David Silver. The needles were thinner than the old ones I took out. That caused my richness. Was sorted only when I took the Keyster needles out.

But, that's on a 750. I suggest it's worth checking the Keyster needles against your old ones. On mine the difference was visible, looking side by side. Nonetheless, I used a vernier calliper to prove it to myself. I also went back to the old emulsion tube and pilot jet, even though they looked the same as the Keyster ones.

I don't know what compression readings should be for a 500 / 550. If yours are in spec, it suggests not rings, but if the plugs are oily, not just sooty, it could well be, especially if white not black smoke. The smell is usually a giveaway, if it's fuel rich. Were your valve stem oil seals replaced?

I'd be double checking through the carbs and the ignition / timing basics again, before opening the engine up. Hope you find it. 👍

[calj737]

The sparks were all black and lot of smoke (blue/white) came from the exhausts with the original setting.

Black and dry,or black and wet? It matters and it points to different things.

For curiosity, what do they look like now with current tune?

[Deltarider]

Greg is in Austria, so his CB500 has the same #78 main jets my CB500 has. If run with the air duct, this is original. Had to do with air intake noise ruling in Germany. See the parts lists. They are all here: https://www.honda4fun.com/materiale/documentazione-tecnica
#100 main jets on our models bring nothing. Performance is the same as models that lacked the air duct and had #100 main jets. More roads leading to Rome...

[Stev-o]

You have Keyster jets? These are known to cause jetting problems. Get genuine Keihin!

https://jetsrus.com/

[Tom R]

Since you’re chasing a fueling issue it’s certain to be an ignition issue as your real problem.
Recheck ignition timing… one tooth off on timing chain? Proper valve clearance?

[greg]

- main jet changed from #100 to #78
- needle set to lowest postion

For starters, restore these to original positions before you undertake anything else. At #78 you are starving for fuel at WOT.

Needle lowest is full RICH. I’d bet your plugs look like crap.
Undo these two mistakes and you’ll be surprised how close you are to a good tune.

Hi Calj737,
thanks for your reply.

I had the original position -> needle clip to middle position, jet #100.
The sparks were all black and lot of smoke (blue/white) came from the exhausts with the original setting. So too rich, right?
Next I went to the #78 jet und hung the needle the lowest/clip fully up (leanest).
also had the reving issue with the original setting.

basically nothing changed after going to #78 & needle the lowest.

anything else you can think of?

Greg
You said you have rebuilt the engine to original specs in the original post.
And the blue/white smoke.
Did you put rings only in your rebuild? As in you didn't bore oversized with new pistons and rings? Or did you remove the cylinder sleeves and install new sleeves and bore to original pistons?

If you only put in new rings? Then I'm leaning to the cylinders are too big now...worn, and you get the smoke from oil burning( and giving you the black spark plugs). The fix? Reborn to Bigger pistons and rings.

Hi

no rebore was done. checked the ring gaps before re-installing - all ok.
I also checked the compression which was at 130 psi. Compression would be bad if not OK, right?

[greg]

Greg,
My replacement set for the carbs was Keyster, from David Silver. The needles were thinner than the old ones I took out. That caused my richness. Was sorted only when I took the Keyster needles out.

But, that's on a 750. I suggest it's worth checking the Keyster needles against your old ones. On mine the difference was visible, looking side by side. Nonetheless, I used a vernier calliper to prove it to myself. I also went back to the old emulsion tube and pilot jet, even though they looked the same as the Keyster ones.

I don't know what compression readings should be for a 500 / 550. If yours are in spec, it suggests not rings, but if the plugs are oily, not just sooty, it could well be, especially if white not black smoke. The smell is usually a giveaway, if it's fuel rich. Were your valve stem oil seals replaced?

I'd be double checking through the carbs and the ignition / timing basics again, before opening the engine up. Hope you find it. 👍

Hi!

Yes! got the KEYSTER kits....which is my main suspect at the moment.
I will check if I have the old needles still somewhere.

Thanks

[greg]

The sparks were all black and lot of smoke (blue/white) came from the exhausts with the original setting.

Black and dry,or black and wet? It matters and it points to different things.

For curiosity, what do they look like now with current tune?

Hello!

black and wet. my interpretation of that is too rich, right?

[greg]

Greg is in Austria, so his CB500 has the same #78 main jets my CB500 has. If run with the air duct, this is original. Had to do with air intake noise ruling in Germany. See the parts lists. They are all here: https://www.honda4fun.com/materiale/documentazione-tecnica
#100 main jets on our models bring nothing. Performance is the same as models that lacked the air duct and had #100 main jets. More roads leading to Rome...

Hello!
you are right, the pics show exactly the air duct I have on my model.

[greg]

You have Keyster jets? These are known to cause jetting problems. Get genuine Keihin!

https://jetsrus.com/

yes, Keyster is what I used.
Looks like i need to invest in proper jets...

[greg]

Since you’re chasing a fueling issue it’s certain to be an ignition issue as your real problem.
Recheck ignition timing… one tooth off on timing chain? Proper valve clearance?

Hi Tom,

I use an electronic ignition timing assy. I might go back and use the original one - just to rule the ignition timing out.
The valve clearance was adjusted and double checked.

[scottly]

The sparks were all black and lot of smoke (blue/white) came from the exhausts with the original setting.

Black and dry,or black and wet? It matters and it points to different things.

For curiosity, what do they look like now with current tune?

Hello!

black and wet. my interpretation of that is too rich, right?

Your spark plugs are fouled, and even after you fix the carb problem that caused it, will continue cause problems unless you either replace them or burn the black off with a propane torch. 

[calj737]

black and wet. my interpretation of that is too rich, right?

Not necessarily. Could easily be oil-fouled. Any chance you could perform a leak down test? Do you mind providing specifics of what head work was done? Valve seals, guides, valve seats re-cut?

[Tom R]

Plug wires screwed into caps properly? 1-4 and 2-3 wires to right coils? Fuel line blocked or kinked?
I’ve seen these simple fixes solve big problems in the past. Fast and easy checks.

[scottly]

black and wet. my interpretation of that is too rich, right?

Not necessarily. Could easily be oil-fouled. Any chance you could perform a leak down test? Do you mind providing specifics of what head work was done? Valve seals, guides, valve seats re-cut?

Oil doesn't burn black like fuel.

[scottly]

Since you’re chasing a fueling issue it’s certain to be an ignition issue as your real problem.
Recheck ignition timing… one tooth off on timing chain? Proper valve clearance?

If the spark plugs are black, it means there was spark to light the fire: no spark=no fire=no soot. If the plugs are clean and wet, it would indicate an ignition problem.

[Tom R]

If the spark plugs are black, it means there was spark to light the fire: no spark=no fire=no soot. If the plugs are clean and wet, it would indicate an ignition problem.

That would indicate no spark. But it’s possible they’re firing at the wrong time or only occasionally and weak.
If the carbs are clean and at stock settings with a stock configuration with no vacuum leaks….
Maybe look elsewhere. They’re easy to check and free.

There was a study published in the New England Journal of Mechanical Medicine that concluded if you think it’s fueling, check the ignition….
The symptoms of either have a fair bit of overlap….