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Ignition timing and black plugs - cb750c 81

riderideride

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Hey my first project a cb750c 81 is almost finished and i'm test riding to fine tune everything.
The bike is running ok but it need some improvements. Maybe you guys have some tips :)

I'm playing al little with my ignition.
So if i understand the tuning with the timing light.
The arrow has to be between the 2 '' on top off the f mark.
If i want to advance my timing i put the arrow on place 1 of my drawing under here?
But if i Retarded my timing to the 2 mark of my drawing my motor is running stronger at idle. -> Is this saying something to you? Is there something wrong?


2----------1
---------V
---------' '
S -------F--------I--------T


The second problem is that my plugs are coming out black!
So i think i'm too rich. But if i read on the internet i find a lot off good reviews from this combo off jet upgrade.


I'm running

Pot filters :(
Main jet 120
pilot jet 80
pilot screw 2 turns out

Carbs are cleaned and synced

I know its almost impossible to fine the potfilters with cv carbs :(

Thnx!
 
75-115 jet and the 75 is not pilot, it's primary, pilot is 38. If the motor is down on seal due to valves not being set it will run the plugs black because the slides don't open fast enough. A compression test tells all. The engine MUST be well sealed with pods or runs worse.
 
Thnx @amc49
Yes sorry 80 is the primary main.

Compression is good.

My valve clearance is in spec but a little on the tight side.
I heard loose is better?

When the gap is bigger between the shim and the camshaft then the valves are seating better?
 
They will solidly and with no question burn valves at a measured .002", you tell me. BTDT, the explanation is not that simple but yes.

'Compression is good.'

If you only know how many times I have heard that then helped somebody for a month of mis-spent money to then realize it was crap. Give numbers or say nothing about compression, likely it's NOT good. Most have not a clue what good is. No insult intended but it is what it is.

Every engine on the planet speeds up at idle when you advance the timing, it being a physics thing.
 
A 0.003 can just fit between the tightest ones but that is still on the tight side. I will set them a little looser!

The strange thing is that if i turn my pulser plate counter clockwise the engine speeds up.

Counter clockwise more to the s sign is retarding the timing? like nr 2
And clockwise more to the I sign is advancing the timing? like nr 1

2----------1
---------V
---------' '
S -------F--------I--------T
 
Think...............clockwise on the plate is advancing the timing. Crank is turning CCW on that end.

If you want a clearer idea of where the valves are at then subtract .002" from any number you get with a feeler. It is not real world there if engine is running. So, your 3's are actually 1's. Trust me on that. Honda's service manual number is WRONG. You want to kill for .004"-.006" as a running range using feeler gauge. Nothing less than 4 should be left alone. That is why so many of the bikes run like crap when sold, nobody sets them and then the valves close up and the numbers not being real make it worse. Then everybody puts a finger over a plug hole to say the compression is 'good' when it's dead and burning valves right then.

120 psi minimum on the compression and if you want it to run like a striped -ss ape then no less than 150. 170 is the spec.
 
Ok thanks for the advise. :thumbsup:

Ill will set my valve clearance tighter this week.

I keep you posted with the results!
 
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