Running WAY too rich.

[sacook542]

(How did you get Brad Pitt to post with your CBX???)

He owed me since he married one of my old girlfriends...

[Larry Zimmer]

I knew I was going to like you, Scott. That was good!!

[daves79x]

Scott:
Welcome and sorry for not replying sooner - been away. Nice CBX you have there. As others have suggested, perhaps the choke shafts are not opening completely. Could be cable installed incorrectly, binding, or some binding in the choke shafts themselves. The only way to really check that is to pull the carbs.

As for the jetting, it is very possible to mix up a couple (or all) of the primary and secondary mains. They will interchange and if you get one or more of them mixed, mileage will drop dramatically and the plug/plugs will be very sooty. That's the easy thing to check, but again, the carbs must be off.

The by far the most common problem is a PO drilling out the #35 pressed-in pilot jets to a bigger size. This will drop mileage also. You will need a wire gauge or jet gauge to check them. K&L makes a nice set of gauges and the smallest is a #35. I've found quite a few carbs with drilled-out pilot jets. They can be extracted and replaced.

You are correct - your bike should get at least 35mpg. Check the above and let us know what you find.

Dave

[Don]

Nice looking bike - Can't say the same for 'the woman' though ;)

Dave has probably forgot more about CBX carbs than most of us ever knew . . . . but I would alter his 'at least' to 'very near' 35 mpg - You gotta have a pretty well tuned '79 to see an actual 35 mpg out of it . . . . certainly possible on a good day if you're not twisting the snot out of it, but (IMO) 35 mpg is about optimum for a '79 . . . . something to shoot for, but don't be disappointed with two or three less

I guess it could be that I've never gently ridden mine 100 miles or so to see if I can do better . . . . but 32/33 seems about the norm for mine, and Dave did my carbs . . . . twice

Don

[EMS]

Aren't you running a 17" rear wheel, Don? A 6% smaller rear wheel could account for 1-2 MPG.

[sacook542]

I'm taking the carbs off as we speak.
At least now, I've got a couple of things to check without relying solely on the shop manual.
Thank for the suggestions guys. I'll keep you informed with my progress or, lack thereof.

[spencer]

Don't forget to check the air cut diaphragm too.

[sacook542]

Ok, time for me to show my rookieness...
Primary and secondary jet plugs are switched.

I know...

[Larry Zimmer]

Don, you sure you're not dragging your heels. My 82 gives 40: fast, slow, up hill, down hill, into wind, with wind, hot day, cold day, duffle/no duffle, etc. That's stock gearing, carbs (with pilots backed out an extra half turn), exhaust.

[steve murdoch icoa #5322]

Ok, time for me to show my rookieness...
Primary and secondary jet plugs are switched.

I know...

You are a good man, Scott.
I usually blame the previous owner when i screw things up[and trust me there have been plenty of oppourtunities].

[Don]

Aren't you running a 17" rear wheel, Don? A 6% smaller rear wheel could account for 1-2 MPG.

Rear *wheel* size shouldn't be a factor in my case - It's possible for the tire on a 17 inch wheel to actually be larger in circumference than the tire on an 18 inch wheel, depending on the tire sizes. Mine aren't, but my larger rear tire is much closer to the stock tire's circumference than 6%

When computing gas mileage, the overall circumference of the *front* wheel/tire would be much more important, since that directly affects the distance measurement of the odometer which would affect things lots more than any minor changes at the back. My slightly smaller front tire circumference makes the odometer lie to me, telling me I've gone a little farther than I actually have, which makes my gas mileage figures a little more optomistic than they really are

Don, you sure you're not dragging your heels. My 82 gives 40 . . . .

Yup Larry - ProLinks do get significantly better mileage than '79's . . . . many '81/'82's do get about 40, but that's pretty much impossible for a '79. Not sure exactly why, since they weigh more. Must have something to do with the carbs/valve timing/aerodynamics. Dave will fill us in on the particulars

Anyway, for a '79 the 35 number is something to shoot for - Low 20's definitely means there's carb work to be done. Something a bit over 30 would be the norm . . . . 35 on a well tuned bike on a good day is certainly possible

Don

[NobleHops]

Ok, time for me to show my rookieness...
Primary and secondary jet plugs are switched.

I know...

You are a good man, Scott.
I usually blame the previous owner when i screw things up[and trust me there have been plenty of oppourtunities].

LOLOL

Nice one Steve. Confession is good for the soul. That is of course the origin of the acronym DPO, where PO stands for 'Previous Owner'.

Scott, Boorah for closing the loop. If you search the archives you will find a dizzying array of really dumb mistakes I made during my restoration. Having learned many hard lessons along the way, I'm looking forward to helping you avoid them with yours .

N.

[Kool_Biker]

Ok, time for me to show my rookieness...
Primary and secondary jet plugs are switched.

I know...

Welcome on board Scott and don't worry! Admitting mistakes is very cathartic around here and in fact is appreciated by its many good people.
Please check my thread "I think, at last, I am on to something", for the mother of all rookies !!!

Best, Aris

[sacook542]

Interesting turn of events.
While I'm pretty new to diving into my bike with a wrench, I'm definitely learning every day. Reading the shop manual, going through all of the interesting discussions on this board and, getting my hands dirty. I'm really getting good a R&Ring the carbs too.

Long story to short:
After installing new jets (all), experimenting with different mixture settings, configurations inside the airbox and other-ways, I hooked up some new throttle cables from Louis and, voila!
The old cables were so crappy and stretched out that, at any speed the throttle butterflies weren't opening all the way. Too rich at slow speeds and lean/no power at higher speeds. Almost like the choke was partially closed all of the time. Running great now and, heading to Fort Myers tomorrow for a test run.

Anyway, might be something to put on your checklist when you're not getting good throttle response. Throttle cables...

Kinda makes sense, don't it?

[sacook542]

P.S.
Was 19mpg, now 34mpg.