Topic: Jetting and altitude

[Rocking-M]

Hey folks, I live at about 3000 feet. With each 1000 feet of altitude gain
I have read somewhere that jetting differences occur.

Does a stock jetted bike from sea level go lean at altitude or rich?

Curious because it would seem that thinner air with same jets would mean richer.

[johnny-from-bel]

You are correct, at altitude they go rich. So jet smaller

[Rocking-M]

Thanks Johnny, so I should be closer to the correct jetting with the Kerker since it should
lean it out a bit. What do you think? I'll do a plug check but that always seems hit or miss for me.

[johnny-from-bel]

Thanks Johnny, so I should be closer to the correct jetting with the Kerker since it should
lean it out a bit. What do you think? I'll do a plug check but that always seems hit or miss for me.

I am not a specialist on jetting. Axl Griessman from Germany is I'll send him a mail hand ask him to join in

[Master Ted]

I'm at 3-5k feet (average) in Central OR and am still stock jetted since getting bike together a few weeks ago. I've read my plugs several times now under a number of conditions.

I'm running a wee fat except when wringing out the rpms on a consistant basis. Since I don't intend to press my luck with a 35 year old motor I plan to keep the rpms down and drop the needles one position (assuming I can get off the bike long enough to get it done).

Post your out-come and I'll do the same. The main diff between our locations is no doubt humidity... I'm in the rain shadow on the high desert side.

Ted

edit: ps - I'm getting 38mpg with my 500 driving with haste around the village - 4 into 1, uni air filter.

[Gordon]

When I moved from near sea level to Denver, the 750 was understandably running too rich and fouling the plugs after only a few miles.  I swapped the idle jets with some meant for the 550 (38's I believe), replaced the paper air filter with a UNI foam one, and tweaked the mixture screws, and the plugs have been a nice tan ever since.  At 3000 feet, you may be able to get away with only adjusting the idle mix screws, though. 

[Rocking-M]

I just ran it down the road and back, and twisted the throttle to hear it sing.
She seems faster by the butt dyno sounds sweet too! I took out half the packing on
the baffle. I know she feels lighter, I need to weigh those stock pipes and muffler to see
just how much more they weight.

What is the correct way to do a plug test?

[Gordon]

You can get a general overview of how it's running by checking the plugs as they are now, but to get specific and really know for sure, you have to do some plug chops.

It's basically a matter of running the bike at a set throttle position, pulling in the clutch, hitting the kill switch and stopping on the side of the road to pull a couple of plugs to see what condition they're in.  You can do this at different throttle openings to find out how your mixture is throughout the entire throttle range. 

[seaweb11]

Reminds me of my ride through the mountains in Eastern CA, and OR a couple years ago.  I thought I was going to have to get off and push a couple of times at the tops of those mountains!!!!!!!! 

[Gordon]

Reminds me of my ride through the mountains in Eastern CA, and OR a couple years ago.  I thought I was going to have to get off and push a couple of times at the tops of those mountains!!!!!!!! 

I was worried about that the first time I rode up Mt. Evans (14,000 plus feet), but the 750 did just fine.  I figured if it started having problems I could just remove the filter for better air flow, and at worst, I would have to turn around and coast downhill until it would start again!