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Valve Clearances

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Valve Clearances

wernwilk
Hello all.

So  i am about to check the valve clearances on my 1978 CB750K and had heard a rumor that I first had to slacken off the cam chain tensioner, is this true?

Thanks.
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Re: Valve Clearances

rrgunslinger
Probably just that, a rumor.
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Re: Valve Clearances

seestheday
In reply to this post by wernwilk
Factory Service Manual that you can download off the front Page of this site should be able to tell you everything you need.

I actually forget if I needed to loosen the cam chain tensioner when I checked the clearances on my 81K.
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals

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Re: Valve Clearances

cdaiscool
When I checked my '81, I did not loosen the slack. The cam is at full up when you check it.

It's always a good idea to have it tight, however. So I would do it before you check the tolerances if possible. But it's not going to harm anything if it's not tight. As long as it's not so loose, it's falling off.
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Re: Valve Clearances

TOOLS1
Administrator
In reply to this post by wernwilk
NO!!!! You do not loosen the cam chain. You should adjust it before adjusting the valves. I do this by loosening the nut, and bolt on the tensioner. Then press down on the kickstarter until I feel good compression. then while holding the kickstarter I tighten the bolt on the adjuster, and then the nut.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
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It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
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1976 CB 750-A X 2
1977 CB 750-A X 2
1977 CB 750-K X 2
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: Valve Clearances

wernwilk
Ok, great advice fella's....i will adjust the tensioner before checking the clearances.
Any tips or tricks for checking clearances?
thanks.
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Re: Valve Clearances

TOOLS1
Administrator
Just go slow, and easy. Double check before closing.
TOOLS
Life is not about the number of breaths, you take, but the moments that take your breath away.
I don't have an anger problem. I have an idiot problem. Hank Hill
Never confuse education for intelligence.
Happiness is a belt fed weapon.
I just can't imagine what could go wrong.
No fire? No explosions? So whats the point of your story?
Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato
It couldn't be done, but the darn fool didn't know it, and did it anyway.
We all got problems. Ksharp
I like vintage bikes because they take me away from the clutter of technology that I work with everyday and back to a simpler time of mechanical elegance and simplicity.. "ninadm"
Darkwing Duck: The worst part of public transportation is the Public.

1976 CB 750-A X 2
1977 CB 750-A X 2
1977 CB 750-K X 2
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: Valve Clearances

wernwilk
so I checked the valve clearances, all good.
then checked ignition timing with the strobe, all correct plus the advance works.
Next I synched up the carbs using the correct gauges, then tweaked the air/fuel screws by ear to get the optimum revs at idle.

sounds ok except there is a stumble as i give it some gas, its almost enough to stall the engine.

I have been through the carbs twice and blown all through and checked float heights as a matter of course.

The bike was standing for a long time and did have some debris in the float bowls however as i said i cleaned the carbs thoroughly...twice!

I am running the bike on the bench using a remote resorvoir which rules out any tank or filter problems.

also, holding my hand over the exhausts there is slightly less gas out of 1 and 4 cylinders which made me think of a possible coil problem but it honestly feels more fuel to me....

any ideas people???

thanks.
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Re: Valve Clearances

rileyfowler
i have a 78 cb750a and the carbs have an accelerator pump to pump extra
gas in when you honk down on the gas
could it be the problem?
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Re: Valve Clearances

robs750
In reply to this post by wernwilk
Have you checked the gas flow from the accelerator pump in each carb?
Have you checked the compression?
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Re: Valve Clearances

rileyfowler
compression is good within a few pounds on all cylinders,
i do not see but one accelerator pump on my carb bank
this is a 1978 honda cb750a,

On Sat, Sep 29, 2012 at 8:33 AM, robs750 [via Honda CB750'S] <[hidden email]> wrote:
Have you checked the gas flow from the accelerator pump in each carb?
Have you checked the compression?


If you reply to this email, your message will be added to the discussion below:
http://honda-cb750-s.456789.n3.nabble.com/Valve-Clearances-tp3972856p4030041.html
To unsubscribe from Valve Clearances, click here.
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Re: Valve Clearances

robs750
There's only one pump which feeds all the carbs via the tubes connected to each carb.
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Re: Valve Clearances

Lucky 1
In reply to this post by wernwilk
No that is not true.
Why not just read the manual instead of  checking out all of the wives tales?

You do need to take the slack out of the cam chain though.
But DO IT LIKE THE BOOK SAYS TO DO IT and not be sorry.
On a new adventure now.
A V Star 1100 adventure.
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Re: Valve Clearances

Lucky 1
In reply to this post by cdaiscool
The 81 DOHC is nothing like the HONDA CB750 SOHC.

Very important. Do the procedure like the book for your motorcycle tells you.

Do not just do what you guess to be right, then be sorry your engine is ruined.

Check the manual and do it the way the manual tells you.
On a new adventure now.
A V Star 1100 adventure.
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Re: Valve Clearances

Lucky 1
In reply to this post by rileyfowler
To check if that pump is working right ,take off the air filters and air box.

ENGINE OFF. Petcock on.

Look into the intake with a bright LED flashlight and turn the throttle a couple
times and you should see a squirt of gas come from the brass tube sticking up and the
gas should squirt into the intake.

Check all four of them.

If all 4 do not work you need to clean the pump and maybe get a new bottom plate and check ball.
If any of the four carbs DO SQUIRT gas then you just need to clean the feed tubes and brass squirt jets.

There are articles online showing how to do this, including cleaning the check balls.
There are two of those check balls, but the one in the bottom of the pump bottom plate is usually the problem.
On a new adventure now.
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Re: Valve Clearances

Lucky 1
In reply to this post by wernwilk
Yes.

Lets say you check the exhaust valve on a SOHC. The clearance with stock cam is .003 thousandths.

To see if you have the adjustment correct..... try to insert a .004 thickness gauge when you are done setting it. If the .004 goes in then you know the adjustment is off.


Same goes for the intake.
On a new adventure now.
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Re: Valve Clearances

Lucky 1
In reply to this post by wernwilk
Never listen to rumors.

Get the manual and read it.

Separate the wheat from the chaff.
On a new adventure now.
A V Star 1100 adventure.
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Re: Valve Clearances

Lucky 1
In reply to this post by TOOLS1
The crankshaft needs to be in the correct position on
the CB750 to do the cam chain adjustment.
It has nothing to do with compression.

From Clymers:

Rotate the crankshaft clockwise until it is 15ยบ after
top dead center for the #1 cylinder.
Figure #33 ( make sure to look at that drawing!

This position puts the cam chain slack at the rear of the
engine and duplicates running conditions.

Many people have noisy engines and this is the reason why.
On a new adventure now.
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Re: Valve Clearances

rileyfowler
In reply to this post by robs750
to all with a honda cb750a or cb750k,
if you are having trouble with the starter spinning but not turning the motor
i could be the bolt holding the rotor and starter cog whell on,
i took off the cover on the left hand side and found that this bolt
was loose, it should have been 90 ft lbs of torque, note this also
made the output of my stator erratic and sometimes the thing would
not charge, I tightened this bolt, but you have to put on the kick
start arm and hold it down while tightening the bolt to keep the
engine from spinning. to get the right torque.
this fixed the starter spin and also the charging system
Note, be very very careful of the the three stator wires and the two
field wires, do not pull on them and disconnect them.
or you will loose connection with the stator and the field and it is
a job pulling these wires out to reconnect them.


On Sat, Sep 29, 2012 at 8:33 AM, robs750 [via Honda CB750'S] <[hidden email]> wrote:
Have you checked the gas flow from the accelerator pump in each carb?
Have you checked the compression?


If you reply to this email, your message will be added to the discussion below:
http://honda-cb750-s.456789.n3.nabble.com/Valve-Clearances-tp3972856p4030041.html
To unsubscribe from Valve Clearances, click here.
NAML



--
Riley Fowler
3416 Ledford Mill Rd
Wartrace, Tn. 37183
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