Topic: better mileage, high altitude settings

[HairyPotter]

Hello,
I have a 1976 cb750k. I live at 7500 above sea level. I recently tuned the bike up, set the valves, adjusted the timing, cleaned and synched the carbs. I'm getting around 38 mpg around town. I've been careful not to engine brake or gun it around too much. Not my normal riding style.
I have stock gearing, 18 front, 48 rear sprocket. My jets are the stock  #40 slow, and #105 main. My exhaust is stock as well as the the airbox. Air filter is clean. The bike is running very well. Good pickup, etc. The plugs look good, I have them gapped at .032 the tips are clean but the insulators are a light tan.

I also have the Hondaman ignition.

From what I'm reading on other posts, I'm thinking I should be getting better than 38 mpg with careful driving.

Am I still running too rich? I have my needle valves set at one down from the top, (nearest the clip).
Should I drop it to the top slot or should I change to a smaller jet size on the main?

Any other suggestions without going into the engine and doing something to the inner workings?

Thanks
HP

[jaknight]

Hi HP,

At 7,500 feet up it sounds to me like you're doing great.  That is a nothing to sneeze at gas mileage even "down" here in The Valley Of The Sun.

The plugs are supposed to be gapped at .024 to .028 if I remember correctly.......?  Others join in here if I'm wrong.

Say HP, I live in Phoenix.  Just made a trip up north about a week and a half ago.  I got up to 7,500 maybe 8,000 feet up.  My bike ran like crap...... was afraid it was going to die and stay up there.  Made it out though........ was more than a touch scary.

~ ~ ~ jaknight ~ ~ ~

[HairyPotter]

I'm actually up in Flagstaff, before that I was in Kingman, at 3500 ft.
I read on these posts that setting the plug gap wider helps with mileage. So far it hasn't seemed to affect the bike negatively and I'd say it did make a difference. Before I was running the at specs. I was only getting 32 before I changed that, and reset the needle settings for the higher altitude.

[Jerry Rxman Griffin aka MuthaF'er]

Sounds like your setup is pretty good. 38 around town isn't so bad. I'm at 6860', 812 cammed engine, 115 mains, 18/48 and my last tank on I-25 at 80mph most of the way came in at 43mpg.

If your plugs look good I'd leave it alone. However you didn't mention if you did a plug chop at around town rpms, high rpms, etc. Don't make any changes unless your plug chop readings tell you to do so.

[Bodi]

Plug chop:
Do with used plugs, new ones won't read well.
Take your plug wrench and ride to a long stretch of highway with little traffic and no radar traps.
First try full wide open throttle if you're doing a carb jetting - this isolates the main jet circuit and gives you a starting point. Otherwise set the throttle whare you're seeing a problem like stumble or missing. It's a good idea to mark the throttle handgrip and switchblock with tape so you can hold the throttle exactly the same spot on repeat chops (after adjusting the carbs).
For WOT tests you will (hopefully!) have to be going an illegal speed in top gear. Hold wide open for as long as you can, at least 30 seconds to a minute. At full throttle, simultaneously use the kill switch to stop the motor and pull in the clutch. SHift down through the gears while slowing but do not let the clutch out and rev the motor.
Stop on the shoulder and sitch ignition off and kill switch back on.
Remove a plug and inspect the centre electrode.