Topic: '73 cb750 jetting needs

[mthonda]

New to me basket case project 1973 750.  This bike has set for a long long time.  Going through the carbs and would like direction on jetting.  Currently the bike has a factory air box and filter,  2 into 2 mac exhaust, and 110 main jets, 40 pilot jets, with clip set on fourth notch down. 

I plan on switching to pods and am running around 3000 feet above sea level.

Search and read a lot but didn't finding anything on elevation or 2 into 2.

Any and all help is appreciated.

[seanbarney41]

nobody knows cause it is different for every bike every time

pods?...how many times do you want to take your carbs apart to make it your bike ultimately run worse than with the airbox?

or, leave the airbox, leave the jets you have now, maybe try a couple different adjustments for air/modern fuel, and enjoy a fine running classic motorcycle

[flybox1]

nobody knows cause it is different for every bike every time

pods?...how many times do you want to take your carbs apart to make it your bike ultimately run worse than with the airbox?

or, leave the airbox, leave the jets you have now, maybe try a couple different adjustments for air/modern fuel, and enjoy a fine running classic motorcycle

+1
It can run well with whats there. 

[mthonda]

The pods are solely for looks. I don't want the bike to want run worse, but as good or the same that's all I'm looking for. Since its a non running a bike, possibly even from out of state; I don't know that the setup it has would be correct even with a factory or box for the type  of riding and at my altitude. During my search I found the chart in one of the threads that said Main Jet should be 120 and the clip should be on the second from the top as a factory set up. I don't remember what the primary was supposed to be

[TwoTired]

The air filter is a functional part, not cosmetic.  You can't turn it into a cosmetic part because of whimsy.  If you change the function, or root engineering, you also have to do the work of altering the basic function of associated parts that rely on what Honda engineered to work together.

Pods are not a paint or lipstick.  Further "Pods" is in no way any sort of functional specification.  They can operate differently among manufacturers and even within a manufactured product when they don't test or have any sort of quality control to ensure each example works the way it was intended.  They off load that burden onto the consumer who is looking for a style, rather than actual performance.  Fine if you park it in a museum.

You might also like the "look" of hexagonal or octagonal wheels as a style statement.  Tuning a suspension to perform as well as one with round wheels will be quite the challenge, I expect, unless you also manufacture roadways that conform to your style of wheel/tire.

3000 ft won't need any changing in stock settings if you use the stock parts.

Cheers,

[mthonda]

TT.  Thanks for the reply.  I value your opinion and have read quite a few of your contributions.  I understand what you are saying and for the most part agree.  In this particular build I'm leaning more toward looks than function and I'm willing to give more time to tinkering to make it run acceptable.  Oddly I enjoy this. The factory air box rubber tubes have shrunk enough one fell out during box removal so I need to do something.  If this was a long distant cruzer I'd get the factory box up 100% and maybe even spend the coin for a uni or k&n insert.  Right now considering pods with the additional foam sleeve to help aid a little in cutting down on the effect of wind turbulence.  Since my last post I did gleam some additional jetting info of a few other sights such as Honda Chopper http://www.hondachopper.com/garage/carb_info/carb_info.html and Do The Ton http://forums.sohc4.net/index.php?topic=104490.0.

[TwoTired]

Do you have access to a dynamometer to get a fuel/power map?  Or, a test track?  Are you able to read spark plug deposits?  Are you aware that fuel requirements change with engine loadings?

Are you willing to thrash on the machine repeatedly to determine what it needs?

Cheers,

[mthonda]

No. Yes. Yes. Yes. Yes.

[TwoTired]

Do you know how to do a "plug chop"?

[Yamahawk]

These guys are essentially correct in that the stock airbox is really good at what it does, and the bike will run the best as per stock jetting.
I have a 1971 CB750, and the PO had 'lost' the stock airbox and rejetted the carbs. I also have a 2-2 MAC type exhaust. My mains are 125, and the pilot is 38. Keep the needles at 4th clip setting from top (next to bottom) and as Lloyd said, do some plug chops. I am running the UNI pods, and they filter well, and the bike runs good with them. Fiddling with jetting is a time consuming chore, but it is a fun chore lol...
Charlie

[mthonda]

Thanks for the info Charlie. Your primary jet number sort of surprises me from what everything I've read. Good to hear that it runs out fine.

[Yamahawk]

Thanks for the info Charlie. Your primary jet number sort of surprises me from what everything I've read. Good to hear that it runs out fine.

Whatever pilot jet you have, use that one to begin with, and use the mixture screws to fine tune it and see if you need a larger ones or smaller ones. It is always easier to see if what you have will work, rather than replacing them and then finding out they were fine.
As for pods, stay away from the El Cheapo ones, as they are junk, and don't filter well at all. There is a fellow on eBay that sells velocity stacks with UNI filter cartridges in them, but they are a bit pricey at $38 each. BUT they look killer!! An engine needs a good filtration system, no matter which way you go. A stock air box won't be effective with a poor air filter, or no air filter. Now, the same thing applies with pods. You wouldn't run velocity stacks without some type of filter screen, to keep the crap out. A good set of pods starts at $40, and goes up from there, I am running the foam UNI pods, and they are washable, and you oil them each time, with air filter oil, or I believe 30w 'could' be used. I get the spray foam filter oil, and its easy to use. Hope this helps!
EDIT: Now I think on it, there might be 40 pilot jets in those carbs... I can't remember now lol...
Charlie