Carbs 1973 CB750

[shinyribs]

What does the pop sound like?

[Piute]

shinyribs wrote

What does the pop sound like?

                                                     Good question,

[rrgunslinger]

I don't want to say backfire but it probably would be considered that.  However it also happens at partial throttle but not under load.

On Sat, May 26, 2012 at 5:34 PM, Piute [via Honda CB750'S] <[hidden email]> wrote:

shinyribs wrote

What does the pop sound like?

                                                     Good question,

                            1977 CB750 F2 Super Sport
<LET THOSE WHO RIDE DECIDE><RIDE TO LIVE-LIVE FOR JESUS> 
Native American from central Cal,  Kickstand down in S.W.Missouri,
                                     Titled N owned;
 6 Harley's,2 Honda's,2Kawasaki's,2 Triumphs,28 vehicle's
 I used and abused them all,But Triumph's sold before could
 NOT A mechanic,          Custom Auto Body N Paint by birth
     But am An Elc oholic                                  >STOCK SUCKS<

                                                                                                   

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NAML

[Lucky 1]

Are the idle jets still #35's????

[Lucky 1]

Could be lean.

Make sure the idle jet is not clogged.
If the carbs are synced the slides should all be very close to each other.
Look into the intake and see.

[shinyribs]

I'm with Lucky on the possible lean condition.Mine would popple,backfire, whatever you would call it when it was running lean.Once I got it jetted properly it quit. It never did it idling or under load,just while coasting in gear either completely or almost completely off the throttle.

It was the same sound you hear when an old car has a set of glass packs and the exhaust back pressure is way too low. I guess the extra fuel creates a ''fuller'' stream of exhaust gasses in the exhaust system to  prevent the ''backfire''. That is my completely uneducated guess,btw.

[rrgunslinger]

ok, Life is getting in the way (sick for a week)  who has #40 idle jets for my 73.  

[shinyribs]

You know,I'm 99.9% positive that I had 40's in mine originally and swapped to 42's. I know I have them...locating them is a whooooole other thing. I'll look for them tomorrow when I get in.

You do have round tops,right?

[rrgunslinger]

yea, round tops thanks

On Wed, May 30, 2012 at 11:27 PM, shinyribs [via Honda CB750'S] <[hidden email]> wrote:

You know,I'm 99.9% positive that I had 40's in mine originally and swapped to 42's. I know I have them...locating them is a whooooole other thing. I'll look for them tomorrow when I get in.

You do have round tops,right?

Montvale,Virginia
 Piute said it best:  "wheres my 10mm?"
Hellbilly-"that is a great way to tell if you have come to your senses, when you start drilling random holes in things... "

LukeM-"Scooters rock, especially when they're in posse formation. "

Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato

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NAML

[Lucky 1]

WHOAAAAA....

That photo where you say you plugged vacuum holes is a big mistake!!!!

Those two hoses on each side if the throttle return spring are float bowl vent tubes.
By stopping those up you have caused the fuel to run low or stop.
It is like putting your thumb over a drinking straw full of fluid the fluid will not flow out of the straw(float bowl) until you take your thumb off of the top of the straw.

No wonder you could not get the carbs synced.

So the popping was lean from the float bowls running out of fuel.

[rrgunslinger]

Yea, kinda of figured that out. thanks

On Sat, Jun 9, 2012 at 3:11 PM, Lucky 1 [via Honda CB750'S] <[hidden email]> wrote:

WHOAAAAA....

That photo where you say you plugged vacuum holes is a big mistake!!!!

Those two hoses on each side if the throttle return spring are float bowl vent tubes.
By stopping those up you have cause the fuel to run low or stop.
It is like putting your thumb over a drinking straw full of fluid the fluid will not flow out of the straw(float bowl until you take your thumb off of the top of the straw.

No wonder you could not get the carbs synced.

1978 CB750K Completely restored cafe style

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[shinyribs]

Slinger,so sorry.I completely forgot all about these pilot jets. I ran across them tonight and thought 'oh no!'

I do have 40's,but I only have 3 of them.I forgot that I had broke one of them.

Sorry for the hold up.If you still need the 3 I have shout at me and i'll get them to you.

[rrgunslinger]

That's ok,  Don't think I need them. Was reading and I think I have to move the needles up,  It runs strong at full throttle and seems to idle ok.  I may even go to a bigger jet if moving the needles don't help.  That is what the article suggested.

http://www.salocal.com/sohc/tech/carb/asmpg_mgs/jetgraph.htm

On Tue, Jun 12, 2012 at 10:51 PM, shinyribs [via Honda CB750'S] <[hidden email]> wrote:

Slinger,so sorry.I completely forgot all about these pilot jets. I ran across them tonight and thought 'oh no!'

I do have 40's,but I only have 3 of them.I forgot that I had broke one of them.

Sorry for the hold up.If you still need the 3 I have shout at me and i'll get them to you.

Montvale,Virginia
 Piute said it best:  "wheres my 10mm?"
Hellbilly-"that is a great way to tell if you have come to your senses, when you start drilling random holes in things... "

LukeM-"Scooters rock, especially when they're in posse formation. "

Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato

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NAML

[CR125Honda]

If your pretty sure it's not an intake leak on that cylinder, I'd recheck the valve clearance, and give the ignition system a once over. Check resistance values on spark plug caps and coils. Correcting a similar issue with my 74.

Ken

[rrgunslinger]

Ok figured out what I did wrong.  Took the carbs off and checked the needles and I set two of them wrong.  Instead of counting from the bottom I counted from the top.    Anyway here are some pictures I thought yall might like to see.

[rrgunslinger]

 Slow jet

[rrgunslinger]

Looking inside the slide

[rrgunslinger]

This is in the wrong place!

[rrgunslinger]

Ok all back together.  It runs perfect! I am so stoked!    OK here is the story.  
This bike has a Mack 4 into one and pods.  It is a 1973 stock motor.  When I rebuilt the carbs I put the clips wrong on two carbs.  So when I redone them and raised the needles to the next to last slot that and  fixed my problem.  The carbs have stock mid or idle jet and the air screws are turned one turn out.  I changed the main jet from the stock 110 to 120.  That's it!  

It idle's at 900 rpm with no fuss.  Has 30,000 miles on the motor.  

Last pic putting new gas lines on.

[rrgunslinger]

Oh, By the way you can bench sync your carbs while they are on the bike!