Topic: Are leaner than stock push in pilot jets available?

[hevykevy420]

I think my idle is too rich.  I belive my pilot jets are stock.  When warming the bike I have to raise the idle via the idle screw in order to start the bike.  The bike will not idle cold with full choke.  I’m getting a little bit of smoke out of the tailpipe when the bike is cold, and it smells gaseous. I know raising the idle screw is normal for starting these bikes from reading other posts, but I have to wonder if there is some adjustment I’m missing.  My bike runs and idles great pretty decent, so I’m hesitant to “fix something that ain’t broke”.  Freshly rebuilt and tuned up and synchronized…

When driving the bike with the wife, her hair smells a bit like gas, but I’m using #110 mains.  I’m hesitant to go to #105, would this make any difference in the idle mixture at all???

Is it possible to purchase leaner push in pilot jets anywhere? I started 1.5 turns out on the idle air screws, but now I am 2.5 turns out and the mixture STILL seems too rich.  Still smelling gas upon start up and have to turn up idle screw to get started!!!  If I have to raise the slides to let more air in with the idle screw, I am logically thinking my pilots are too rich.  Am I right or wrong???

[eurban]

Mr Kevy-  You didn't specify what year and which bike you have but I'm going to speculate based on your pic, on the pressed in idle jets and 110 mains that you have a 77/78 750 . . . . .On the accelerator pump type carbs with the pressed in idle jets, the idle mixture screw controls the bleed of fuel rather than air.  To lean out the idle mix you would turn the screw in (clockwise) and out (counterclockwise) to richen.  If you do indeed have the accelerator pump style carbs, then it would seem that your attempt to lean the idle mixture by turning the screws from 1.5 to 2.5 turns out was the wrong approach!   . . . . .Changing the main jet should not affect the idle mix.. . . .The pump carbs have a feature built into them that bumps up your idle speed when the choke is fully applied.  If this is functioning as it should, and your bike is in a good state of tune, then you shouldn't need to manually crank up the idle speed.

[crazypj]

common fallacy that changing mains doesnt affect off idle mixture. if it has no effect until 1/2 throttle plus, try removing main jets and see if it will run at anything but idle ( or even start and idle)
Main jets affect mixture just about everywhere.
PJ

[eurban]

Not sure of your point PJ . . . . idle mix is dominated by the idle circuit and to correct an idle mixture issue you would not change your main jet.  Perhaps the difference between a 110 main and a missing main jet could be felt just off idle, but you aren't going to fix a supposed rich idle condition by switching from a 110 to a 105 which was  the question.   

[eldar]

Nope, no change with main jets on idle.
Kevy, your idle is set too rich right now. Those screws eurban was talking about are supposed to be set at 1.5 turns as he stated. Once set there, you a shop tach or dwell/tach to fine tune them. Then on the carbs, there is a high idle adjustment that should be set. Now you dont NEED to set it but if you dont, then you need to either use the idle screw or the throttle to hold rpms up during warm up.

Just stay with 110 mains but you could, if you wanted to, go to 105 since the 78F had those.

[hevykevy420]

Eurban-  You are correct, the bike and carbs are a 1978 CB750 so I do have the accellerator pump type carburetors.

Boy, i feel like a tool having adjusted the idle screws the wrong way.  I just assumed that backing out the screw let more air into the mix, but I guess its the other way around!  I'll definitely adjust back to the stock 1.5 turns out, and probably go to 1 or .5 turns out to lean out the mixture. (it was running rich even at the stock 1.5 turns out.)  I've been hesitant to properly set these screws Eldar, because when I checked sears, the digital tachometers were a little pricey, my timing light does not have a tachometer setting, and i don't have a dwell meter.  I guess i'll use my own diagnostic tools for this setting primarily being my nose 

Eldar or Eurban-  where is this high speed idle adjuster on the '78 carbs?  I did not know that the choke automatically raised the idle setting at full choke, or that their was a high speed idle adjuster on the carbs. How does it do this?  I see how the choke restricts air with the butterflies closing the carb throat, but I don't see how the choke raises the slides.    If you guys could let me know where I can check for this, i'll definately do that as i'd love to not have to mess with the idle setting during every start!  The PO definately messed up these carbs, when i overhauled them the accel pump was disabled for some reason, so i wouldn't be surprised if this high idle was too...

Thanks for you advice guys!!! 

[eurban]

Kevy-  A proper manual for your bike would probably save you a good bit of time and frustration . . . Basically you adjust your idle mixture for max RPM so use your ears and the bikes tach to see if turning the screws one way or another raises or lowers RPM.  A digital tach would make this more accurate.  Engine is warmed up, use a fan, wear some protective gloves (heat) and a stubby screwdriver (unless you have the neato carb mix adjusting tool).  While you struggle away at turning the screws a buddy might be helpful to listen and look for RPM changes.  If your current idle mix is way off, it may make the idle too lumpy and erratic for this procedure so get your adjustments back to stock baseline first.  If your idle jets are clogged (probably not since you seem to be running rich) or have been drilled out by the previous owner then this procedure will be a waste of time.   As to the fast idle cam, it should be visible between the carb tops (tank removed).  It is a screw with a spring around it to keep if from jiggling out of adjustment.  Before spending time on this, make sure that your bike when it is warmed up idles correctly around 1000rpm.  Bike off; pull the choke knob all the way and adjust the screw so it just touches the cam on the throttle linkage.  Then push the choke off and then turn the screw in (clockwise) two more turns.  Now when you open you choke all the way you should actually see the throttle linkage bump a bit more open.  Good luck

[hevykevy420]

Eurban...well, I do actually have a the manual that comes with the bike, and a Clymer or Hanes (forget which one) but the manual has mostly pre 1977 pics and procedures, and what they do have for the 77 and 78 is confusing and pretty much usless sometimes.  Oh, and would it hurt soooo much to have a few pretty girls driving the bikes on their covers rather than some cheesy dude in red 70's leathers?     I don't think it would hurt their sales, yet I digress...

I'll follow you advice and reset the idle mixture screws back to the 1.5 and i'll go from there.  I'll see if I can "do it by ear" for now and look into biting the bullet and buying the digital tach for the best settings.

Thanks for the procedure on the choke high idle adjuster, I've overlooked this in my tune ups (and always wondered what that screw thingy was for) so i'll definately take a look at it and post results.

THANKS EVERYONE!!

[eldar]

Well I get a dwell/tach from sears for $50

The bike tach is very inaccurate at low rpm as much as 100 - 200 rpm off.
I also dont trust setting it by "ear".
A dwell/tach or O2 sensor or dyno are the best ways to do it.

[eldar]

Did you download the manual from this site?

[hevykevy420]

I just found them in the FAQ, but the links were bad.  Not sure if its my firewall here in Corporateland.  Not sure how ANY business would get done without that filter!!! 

I'll have to check back later and see if i can download.  Thanks for the tip!

[eldar]

Give it a shot. It is a large download but will help a lot. If you cant get it, let us know and one of us might be able to get you a copy on CD.

[hevykevy420]

Well- Last night I screwed the idle screws all the way in, then backed out 1 turn.  I waited until this morning with the bike completely cold to test the new setting.  I could not get the bike started, even with full choke, and finally turning the idle up.   

I'll guess I'll try 1.25 or 1.5 and go from there.