Topic: High elevation jetting moved to sea level (little Confused)

[jeffg]

High elevation jetting moved to sea level
I bought the bike in 2006 as a second owner, and have been riding it since. I moved from Colorado where I lived,  was 8500 feet elevation. I have not taken the carbs apart to see what jets are in it, but I have been reading about the parts available for carb rebuilds. I know this is not a real common topic, so it is kind of tough to find the jetting recipe straight off for such an old bike.  When I used t to buy a new dirt bike, the Honda race guy would tell me buy this needle, put the clip in the third position, buy this number  primary, and this number secondary. Berry was always right on the money, all I ever had to do once I followed his suggestion was, some times change out my primary. I have noticed replacement needles, for when yours is worn. Is it necessary to get a different size needle? Or just change the clip position, and buy some mains?

[raymond10078]

What year/model of bike?

[scottly]

Hi Jeff, and welcome to the forums! The first thing we need to know is what year and model SOHC four you have.
 Edit: kandrtech beat me to it....

[jeffg]

hey guys thanks.

it is a 1978 cb750 four K
every year I ran the carbs dry,  in the fall; my tank is real clean. I only have 9k miles on it.

[flybox1]

Jetting for stock bike is 35 pilots and 110 mains with  appx 1 turn out of the fuel mixture screw.
Which model carbs do you have? This will help us answer the needle/clip issue.
We also will need to know type of air intake and exhaust setups...

[scottly]

Have you started, or ridden the bike since the move to sea-level?

[jeffg]

I have not started the bike since I moved to seal level felt that it would run too lean and hurt it.

I have the original exhaust, it is in above average condition for the vintage. I have put some JB weld on a few spots, and 1 diffuser I have re welded. I want to run those stock pipes until they become trash.

I really never looked at the carbs I just got the bike out of storage and am hoping to ride this year. I'll look at the carbs soon

[trueblue]

Go back to stock jetting then work from there

[70CB750]

Welcome, neighbor!

[lucky]

Honda does not use the same jets on bikes sold at high elevations like Colorado from the factory. They use richer jets from the factory. So if the bike was a Colorado bike make sure to take that into consideration.

The Clymers' workshop manual lists the jetting for bikes sold by Honda for high elevations.

[lucky]

I have not started the bike since I moved to seal level felt that it would run too lean and hurt it.

I have the original exhaust, it is in above average condition for the vintage. I have put some JB weld on a few spots, and 1 diffuser I have re welded. I want to run those stock pipes until they become trash.

I really never looked at the carbs I just got the bike out of storage and am hoping to ride this year. I'll look at the carbs soon

It would run way too rich. NOT too lean.

The air in Colorado would be thin and the air at sea level would be much more dense.

You might even be able to keep the same jets. You need to find out if that was a Colorado bike, (sold originally in Colorado).

I worked in Tucson ,Arizona at a Honda dealership. We would take bikes up to the top of Mt. Lemon and they would hardly run at all at 8,000 ft.
They were way too rich. As soon as we got a little ways down the mountain they would start running right again.

[jeffg]

your idea of running rich is a good one but it is only correct if you come from sea level, and never re-jet . yes the air pleasure is lower, by doing nothing it would be true that you would then be running rich. However to compensate for lack of air you must install a smaller fuel jet, then you balance air fuel. If now I do nothing I will have a lack of fuel and way to much air. Instead of fowling a plug  I could burn a ring, valve, or a hole in a piston.
It is setup for high elevation no mistake about that, I lived at 8500 feet for 17 years, and owned some 19 or so bikes. Yes it is set up for high elevation. It did get rejetted by the original owner, he bought it set it up then I bought it. I am not going to mod this bike just ride as a daily driver back and forth to work. I should get 3 ~ 5 years out of my OE pipes. Not going to put any KN air box just keep OE style.

Since this is an old bike not new I am trying to learn what would be a factory OE sea level set up

seams that the main is the 110 jet size, I am trying to learn about if the needle has a required size and clip position also. I guess I am looking for the secondary jetting size if needed as well.

Nice to meet you all thanks for the welcome, maybe I'll see some of you if your in the DC area.

[bjbuchanan]

The left search button is  your friend, use it

http://www.motorcycleproject.com/motorcycle/text/specs.html

[70CB750]

I know y2kcowboy is in DC and 333 is Fairfax I believe. I am further out in VA.

Honda chopper web page has a list of cb carbs and their parameters, you should be able to find what the factory jetting was.

I remember Hondaman in his book mentions leaning out the mixture to only 3/4 of the screw out or so while the setting is normally one full turn.  He is in Denver, with bit of luck he will pitch in on your problem.

[Xnavylfr]

Try this info> http://www.hondachopper.com/garage/carb_info/carb_info.html
  http://www.salocal.com/sohc/tech/carb/asmpg_mgs/jetgraph.htm


All kinds of carb info for you!!!

Xnavylfr(CHUCK

[jeffg]

wow looking good thanks a bunch guys! just got the bike from a storage area it is still on my trailer hope to get it down this weekend and wash it off some. my move and 1 year out doors cause the bike to get a little corrosion. It's to bad cause it was cherry, least I still got to keep it. I'll stay in touch and let you know how is going on!

thanks a bunch fellas!
any of you guy live in DC metro?
I did have the pleasure of meeting a nice guy who had an original naked gold wing over in Aspen hill.

[scottly]

Since it looks like you will have to buy new jets, consider that 10% ethanol fuel requires slightly richer jets, like 4.4% richer. In your case, based on a stock 35 idle, a 36 idle would be closer. A 110 main jet for straight gasoline would translate to about a 113 for 10% ethanol, but good luck finding a 113.