Carburation

I am at the point of carb's rebuild. Going with K&N Intake Breather and Dunstall exhaust. Should I make any carb changes (needle groove, jetting, Etc) ?

Moose
What carburation system are you using?
CNN

Likely the k/n will flow as well as the good ole air box so mainly the freer exhaust is what might lean mix more. You can go by guess and by golly via plug chops and symptom list of lean vs rich behavior, or put on CHT & EGT meters or buy some dyno time to guide you. General questions only has general answers.

I am going to clean the carb's and keep everything original. when I get it running do the old can't go wrong check of the color/carbon on the plugs, had no idea how simple these Amal's are until I took them apart. Hope I do not need to adjust float level's, that looks like it could be the biggest pain. Likley if i t ain't broke it should not need fixing! (Nobody previous hopefully has screwed with it)

If using Dunstall Decibal silencers I believe you need to go up 1 main jet size, a plug chop on full throttle when ridden & reading will show if the jet is correct.

If the pilot jet screw can't adjust to good idle, then diddle the float level till it does, though a bit high on level helps the initial suck up idle response.

Another real adjustment that will effect general operation is the needle position. If you will be channeling a higher rate of mix due to a fresh motor, better air intake and a draw from a better exhaust then dropping the clip (raising the needle) by one groove may be required.

If you find that you cannot get what you need from the needle position than a slide shange may be in order. What direction you will need to go in will be dependant on your testing results.

You can go up a size or two with the main but that will only effect WOT responce and economy.

All this being said, the addition of enhanced componants may bring a functionality to your motor that may take you in another direction. I would try what you have been running before making changes.

As you say Amals are pretty simple. The needle height has only three positions on a 750 more on those other Nortons. What I find provided you have the idle set correctly, open the throttle slowly in gear if you get rough acceleration move the clip to another notch. If you feel the Dunstall exhaust is breathing better than what you previously had put the clip in the next notch down the pin again only if it doesn't run to your satisfaction where it is.

I suggest you need to recognise what the provisions are for changing the jetting at various throttle openings. The needle positions and needle jet sizes are critical when riding around roads with a lot of bends . If the motor coughs as you are using about 3/4 throttle, you need to raise the needles or fit larger needle jets. Setting the main jet is important if you are doing a lot of high speed riding using full throttle. That is when you need to do plug chops, and look for the black ring in the spark plugs. If it is not there , you can do damage to pistons and valves . Setting the idle is not really important to performance, but the slides must come to the top of the carb bores at exactly the same time when you open the throttle wide. The motor should need choke to start when cold, and if it is lean enough, it should spit back through the carbs a bit, until it is quite warm. Lean is good, but your bike will go best just before it self-destructs.
The place to start is to get the slides opening precisely together then adjust the needles and needle jets, you should try to get the motor to cough at 3/4 throttle by lowering the needles, then raise the needles one notch. If the carbs are too rich at 3/4 throttle, the bike will be sluggish to ride. Then do your high speed runs in cold weather, and do your plug chops and set the mains.

mooskie said:

I am going to clean the carb's and keep everything original. when I get it running do the old can't go wrong check of the color/carbon on the plugs, had no idea how simple these Amal's are until I took them apart. Hope I do not need to adjust float level's, that looks like it could be the biggest pain. Likley if i t ain't broke it should not need fixing! (Nobody previous hopefully has screwed with it)

Click to expand...

You might want to spring for rebuild kits which include Stay Up Floats among the usual gaskets, needle valve, ect. The new floats are much easier to adjust. They also include needle jets, which don't last forever. I recently swapped out a needle/needle jet set out of my Mikuni with big mileage on it. The throttle response up to WFO was transformed and the gas mileage went up around 8mpg.
You don't say where you're from and what gas you have available but carbon/color ain't what it used to be, as far as jetting goes. This is a good article on it.

http://www.dragstuff.com/techarticles/h ... plugs.html

BTW, over on the VFR list a reliable source had it that the stock paper air filter was less restrictive than the K&N. No references.

Youd raise the needles a notch , and go up a size or two on the main jets . for a start .

Seen posts on float level set up ? CHECK . dont be scared of that . Can be done with capilary tubes . . .