Topic: Whick jets for altitude?

[medic09]

I'm going to order some Keyster carb kits soon (I hope they have them!) from Sirius.  I figure I should also order jets suitable to altitude.  I've heard from mechanics around here that most of these bikes were sold with sea-level jetting; and nobody bothered to change them in most cases.

I live at 2100m/7000 ft.  Much of my time is spent at or above 5000 in any case.  When I take long rides, and drop down I figure I'll just have to live with it for that duration.

So, does anyone have access to Honda's recommendations for how to figure this?  I seem to recall that Triumph made recommendations based on increments of 1000 ft, starting above 3000.  I have that set of guidelines somewhere.  The physics are the same.  Would the recommendations be the same?  Not starting a comparison war here about Amals vs. Keihins.   

What so you guys *down* in Colorado?

Thanks!

[Jerry Rxman Griffin aka MuthaF'er]

What's your current engine setup including main jetting and needle clip position? Stock? Pipes? Air cleaner? Etc. It all depends on your plug readings! Get all your tune up stuff done, put in new plugs and do the plug chop (readings) at midrange & top end then go from there. Your stock jets (probably 105's) may be fine. If not then you'll have to get different size jets. If you have 105's, why not get an extra set of 100's and 110's so you can play with them. 

I'm in Colorado Springs at 7000ft. My bike 75 750F isn't stock. 810 & cam. Stock air box with K & N. Kerker with standard baffle. Dyna III ignition with Dyna 5 ohm coils. Had been running 110's. I've had the 110's up to 14,110 feet. I think (don't remember) my needles are in the middle position. Just put 115's in this year. That works for my Yosh Daytona race cam on top end but I may need to adjust my needles down 1 notch leaner to make up for the increased mains which also affect midrange.

Soooooooooo, it depends on what your bike needs rather than just elevation. Your current jetting may just be fine. I believe Hondaman had posted a rule of thumb pertaining to this sometime this past year or so. Ride on up to the Springs this spring and we can play with carbs. I-25 north to CO exit 151. 

[kettlesd]

Take a quick look around this site and you'll see that hardly two people can agree on what the best jet/needle settings are at ANY altitude!!!!!!!  Each person's machine is a rule unto itself!

With all the afore mentioned factors coming into play, i dont see how a standard set of tables can work.

[cb650]

When I move back to CO I put a header on to go along with the K&N in stock air box.   Asked everyone about the jets.  Stock with those changes is good was the standard reply.  Well when I started drag racing it got faster with smaller jets.  So far I'm 3 sizes (112.5's) small.  Dont want to go any smaller than that so thats where it stays.   Everyone has there own ideas though.  for a street bike I'd just go 1 or 2 small and call it good.



                                 Terry

[medic09]

Thanks guys.  I shoulda known that.

RxmanGriff,

I've been up and down I-25 quite a bit.  Never been to Colorado Springs.  Would that be near the exits for Colo Spgs ?   

[gregimotis]

Off topic, but you aren't that guy up off Pacheko near Yucca with the beauty bikes always parked on the curb are you?





BTW, I put D7EA's in to 'solve' my altitude problem and may be revisiting the jets later this winter.  I'd be interested to hear how it goes for you.

[Jonesy]

Look in the "Thoughts of Hondaman" FAQ section. He wrote a nice bit on jetting for altitude (He's in CO as well...).

[eldar]

one of the easiest things to remember though is that air is denser at lower levels. So at lower levels, you would generally want to enrich your mix with larger jets. At higher levels where the air is not so heavy, you would go to a lower jet.

[Jerry Rxman Griffin aka MuthaF'er]

Thanks guys.  I shoulda known that.

RxmanGriff,

I've been up and down I-25 quite a bit.  Never been to Colorado Springs.  Would that be near the exits for Colo Spgs ?   

Exit 151 is Briargate Pkwy on the north side of the Springs across from the Air Force Academy.

[medic09]

Off topic, but you aren't that guy up off Pacheko near Yucca with the beauty bikes always parked on the curb are you?

That would be Dave Liggon.  I actually bought my Honda from him while I was looking for something for my wife.  He said to her "you take the Yamaha at home, and buy this for him".  We did.  He's a nice guy. We go back and visit with him from time to time.  In fact, I've got a socket he lent me to work on the Yamaha, that I need to return.  The Honda has needed alot of 'refining', but that's okay.  It was all there, in reasonably good shape.  The rest is up to me.


BTW, I put D7EA's in to 'solve' my altitude problem and may be revisiting the jets later this winter.  I'd be interested to hear how it goes for you.
How much did that help?  I'm just running stock NGK D8EAs.

So Greg, where are you?  In SF?  We're just up off of Columbia.

[gregimotis]

I had fouling on the D8's and had to clean and/or change plugs every couple thousand miles.  The D7's seem to stay clean - so it solved a minor problem
I did a run through Arizona and Nevada last fall and didn't think the bike ran at all differently with the altitude changes.  Don't know if everyone has this experience.



I'm in SF as well - Kinda off Yucca.  Small world.

[medic09]

I'm in SF as well - Kinda off Yucca.  Small world.

What are you riding?  Since you're spitting distance, come by some time and show us your ride!

[TwoTired]

Just to state the obvious...

If you rejet your engine to run perfectly at 7000 ft, any operation near sea level is going to be too lean.  A hotter plug will exacerbate the situation.  There may be risk of overheating, preignition and detonation.  Some of which may be helped with conversion to premium fuel and/or an ignition timing change.

Cheers,

[gregimotis]

Just to state the obvious...

If you rejet your engine to run perfectly at 7000 ft, any operation near sea level is going to be too lean.  A hotter plug will exacerbate the situation.  There may be risk of overheating, preignition and detonation.  Some of which may be helped with conversion to premium fuel and/or an ignition timing change.

Cheers,

This is partly why I haven't rejetted yet (lazy is the other part).  I haven't decided on the ideal scenario - most of the weekend rides around here are 4000-8000 feet.



Mines a CB750F1 Medic, I'd love to get together and have a look are yours sometime - the avatar looks real nice.  I'll PM you after I get back from my holiday travelling.

[medic09]

Just to state the obvious...

If you rejet your engine to run perfectly at 7000 ft, any operation near sea level is going to be too lean.  A hotter plug will exacerbate the situation.  There may be risk of overheating, preignition and detonation.  Some of which may be helped with conversion to premium fuel and/or an ignition timing change.

Cheers,

This is partly why I haven't rejetted yet (lazy is the other part).  I haven't decided on the ideal scenario - most of the weekend rides around here are 4000-8000 feet.



Mines a CB750F1 Medic, I'd love to get together and have a look are yours sometime - the avatar looks real nice.  I'll PM you after I get back from my holiday travelling.

I've hesitated for similar reasons.

Dave Liggon has a Hondamatic CB750A in front of his house if you want to see one.  He's been trying to sell that and the Beemer for a while.

Happy Travelling!  We'll talk to ya later...

[gregimotis]

Just to spare the rest of the board, I've PM'd you Medic