The International CBX Owners Association

Got a '79 CBX that's looks great cosmetically.
Just got the carbs back on after as good a cleaning as I could give and, it runs much better. Nice idle and, pretty smooth acceleration up to about 4800 rpm then, starts to sputter a bit. Here's the kicker: I'm getting about 20mpg on mostly highway riding. (I know).

What are the top 5 things to look at/tweak to lean the mixture and get my mpg back up? Hint:
I'd settle for 35mpg...

Welcome to the ICOA Forum, Scott!
We have several carb gurus here who have worked on these things for themselves and others and will most probably render excellent advice.
In the meantime, I would start with some basics. (Assuming you have not changed any of the jetting) Those things should have been checked with the carbs off the bike, because it is difficult if not impossible to do this with the carbs installed and the airbox in place:
Check whether your choke butterflies open completely. Maybe they are closed partially. It seems to me you are running on choke. Only thing you can do now, is see if the linkage returns all the way when you close the choke lever. Beyond that it requires to take the carbs off again and check the choke mechanism and butterflies for proper function
Also, your idle micxture screws should be 2 1/4 to 2 1/2 turns out.

I am sure more detailed and better advice will follow.

Hope everything will turn out

Did you check to see that all the slides moved up and down smoothly before you mounted the carbs?

Yep.
Double-checked all the slides and, they all check-out.
As for the choke... I'm not sure how you would go about making certain that the control arm was working properly unless you could actually see it at the bottom of it's action. Hard to do with the bike intact. Do you think you could see the choke valves if you looked through the airbox with the filter out and you had a flashlight and maybe a stick-mirror?
I only ask because the choke suggestion kinda makes sense and, I'd sure like to do as much as I could to diagnose the problem or tweak it before I took those carbs out again.
Thanks for the quick responses.

So,
I took out the filter and peeked into the private parts of my bike. Working the choke lever closed the butterflies but, apparently they did not open completely. ( a little less than parallel).
Hard to imagine that would be the cause of such horrible mileage but, worth further investigation.

Hopefully, Dave McMunn will get to this one soon, Scott. He and Mike Nixon are god on this stuff. I agree with your assessment of the chokes. I'm wondering about float levels causing too high fuel level in the bowls. A seeming sidebar, how does compression check? Any severely leaking valves? Valve clearance? I ask this, because, something wrong here might cause you to be operating at a significantly greater throttle opening just to get power in the higher rev ranges. Again, Dave and/or Mike would be the gurus for this. Much luck.

This is probably too obvious, but what kind of shape is the air filter in?? Sometimes a paper filter can look relatively clean but be matted due to previous exposure to gas and/or oil, or somebody blowing the hell out of it with compressed air.

I'm no help other than to say welcome to the site, and we will enjoy helping get your bike running well. Photos are crack here, let's see your bike!

N.

NilsMenten wrote:I'm no help other than to say welcome to the site, and we will enjoy helping get your bike running well. Photos are crack here, let's see your bike!

N.

Doesn't hurt to have a hot looking woman sitting on the bike either.

oilheadron wrote:This is probably too obvious, but what kind of shape is the air filter in?? Sometimes a paper filter can look relatively clean but be matted due to previous exposure to gas and/or oil, or somebody blowing the hell out of it with compressed air.

It's the stock filter, (foam sleeve around the metal mesh cage). And, it looks old but clean and clear. I'm looking at the choke mechanism right now nd, trying to figure out how I can open the butterflies more without dropping the motor...

I'd buy a K&N, plug it in, and see what happens!!

Jeff Bennetts wrote:

NilsMenten wrote:I'm no help other than to say welcome to the site, and we will enjoy helping get your bike running well. Photos are crack here, let's see your bike!

N.

Doesn't hurt to have a hot looking woman sitting on the bike either.

Yes, yes, hot women too. Get busy new guy!



N.

If there is any doubt about the airfilter, run without it for a bit. Should definitely notice some difference if it is that. I doubt that's it, though. Worth a try.

As requested...
gallery/image.php?album_id=22&image_id= ... w=no_count

Here is what you do, Scott: You go to the gallery and open your picture. Underneath in window it says [album} 4609{album].
You highlight this and click on copy, then go to your post and paste it into it and it will show up like this:
(How did you get Brad Pitt to post with your CBX???)