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rich or lean at full throtle?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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ok heres my problem , my bike has loads of bottem end power an great
acceleration up to about half throtle, then it just starts to strugle and wont accelerate anymore. it dosnt backfire either so im thinking its lean? any help would be appreciated
thanks guys
 
lean to a certain extent will make more power...but get really hot.

what you can do is sit on the bike, and warm it up. hold the clutch, leave it in neutral, and rev it up to over 7,000 RPM. hold it there for a second (8000 would work) then kill the power to the bike. pull a spark plug, or two, or all of them, and check the condition.

do you know how to read plugs?

for those who dont, it's your best friend to tuning. you want to look at the base of the plug, where the small electrode sticks out. around this electrode there is a ceramic part...which will change in color depending on how the engine is running. black is rich, white is lean, brown/coffee color is what you want.

hope this helps,

~Adam
 
Re: rich or lean at full throtle?

Youre lean. Try synching the carbs to 10 in hg (25cmhg) @1200 rpm.
That should do it, but if it doesnt, you can always raise the needles 1 notch.

Earl

pete_holden said:
ok heres my problem , my bike has loads of bottem end power an great
acceleration up to about half throtle, then it just starts to strugle and wont accelerate anymore. it dosnt backfire either so im thinking its lean? any help would be appreciated
thanks guys
Click to expand...
 
thanks alot guys ill definetly try that in the mornin,
thanks again
 
Does it work ok at full throttle? It is always best to get the main jet right first before playing with the needles.
The plug colour will tell you what the mixture is running at.
 
saaz, i have to disagree. you are riding on your needle more then you are riding on your main jet. main jet is only used from 3/4 to WOT. the needle covers most of the useable range on the engine.

~AOD
 
You are correct in that the majority of mixture requirements for average riding can be handled with needle adjustment. (assuming the main jet is close to the required size in the first place.) However, Saaz is correct in that the proper proceedure is to size the main jet first (WOT setting) and then adjust the needles accordingly.

Earl


AOD said:
saaz, i have to disagree. you are riding on your needle more then you are riding on your main jet. main jet is only used from 3/4 to WOT. the needle covers most of the useable range on the engine.

~AOD
Click to expand...
 
earlfor said:
You are correct in that the majority of mixture requirements for average riding can be handled with needle adjustment. (assuming the main jet is close to the required size in the first place.) However, Saaz is correct in that the proper proceedure is to size the main jet first (WOT setting) and then adjust the needles accordingly.

Earl


AOD said:
saaz, i have to disagree. you are riding on your needle more then you are riding on your main jet. main jet is only used from 3/4 to WOT. the needle covers most of the useable range on the engine.

~AOD
Click to expand...
Click to expand...

http://www.factorypro.com/tech/carbtun.html
 
Exactly what I was trying to say OldRider. There is a difference between "can be" and "proper". The site says it much better than I. :-)

Earl


OldRider said:
earlfor said:
You are correct in that the majority of mixture requirements for average riding can be handled with needle adjustment. (assuming the main jet is close to the required size in the first place.) However, Saaz is correct in that the proper proceedure is to size the main jet first (WOT setting) and then adjust the needles accordingly.

Earl


AOD said:
saaz, i have to disagree. you are riding on your needle more then you are riding on your main jet. main jet is only used from 3/4 to WOT. the needle covers most of the useable range on the engine.

~AOD
Click to expand...
Click to expand...

http://www.factorypro.com/tech/carbtun.html
Click to expand...
 
Not to argue anyone's way of jetting, but I have installed mains that performed perfectly and then found the needle circuit was too lean.
I then raised the needles to get them correct according to plug reads and performance but then found the combination of the raised needle and same main jet supplying too much fuel for the cylinders to burn during normal roll-ons. The bogging can be anywhere from mildly bothersome to real bad. Decreasing the main a full size usually gives good results.
For this reason, I've found it easier to get the needle set right and then see what mains I can use. Just my experience.
 
KEITH KRAUSE said:
Not to argue anyone's way of jetting, but I have installed mains that performed perfectly and then found the needle circuit was too lean.
I then raised the needles to get them correct according to plug reads and performance but then found the combination of the raised needle and same main jet supplying too much fuel for the cylinders to burn during normal roll-ons. The bogging can be anywhere from mildly bothersome to real bad. Decreasing the main a full size usually gives good results.
For this reason, I've found it easier to get the needle set right and then see what mains I can use. Just my experience.
Click to expand...

Had this discussion with an experienced mechanic recently. He reckons if the procedure doesn't work for CVs then one cause - if there's nothing else wrong - can be incorrect size carbs. Don't understand how this could be so on a stock bike :!: Certainly possible on a modded engine.
 
Either way can work in practice. I have found getting the main right means you can then concentrate on the needle/needle jet and pilot circuits, as these circuit all overlap (I won't go into the slide cutout!). I am just going through the fine tuning of my low to mid throttle reponse at the moment. Of course, getting the main right is best done on a dyno or racetrack of course :)
 
Not to sound completely stupid but what exactly are you guys refering to when I read " raise the needles up a notch"....
Are you all refering to the air adjustment screws on the engine side of the CV carb???? I'm just trying to understand what is happening cause my 550 is running lean on carb 1 correct on carb 2 rich on carb 3 and lean on carb 4. So by raising the needles up a notch is that turning the airscrew out 1 full turn or something?????
 
Raising the needles is referring to the needles that protrude from the bottoms of the slides. (The slides are the pistons inside the carb body) Those needles have grooves and circlips that fit into the groove so as to hold the needle extended a set amount from the bottom of the slide. As the slide raises, the needle is withdrawn from the main jet, letting more fuel flow, or less fuel, depending on the adjustment.

Usually, the needles would all be set the same and all four carbs would have the same burn color on the plugs. In your case with different cylinders showing different symptoms, I would first set the float heights in the bowls and do a good carb synch with vacuum guages. I believe that will cure your problem.

Earl


Wigglespank said:
Not to sound completely stupid but what exactly are you guys refering to when I read " raise the needles up a notch"....
Are you all refering to the air adjustment screws on the engine side of the CV carb???? I'm just trying to understand what is happening cause my 550 is running lean on carb 1 correct on carb 2 rich on carb 3 and lean on carb 4. So by raising the needles up a notch is that turning the airscrew out 1 full turn or something?????
Click to expand...
 
Earl,
Thanks so much for clearing that up for me. I have all my floats set the same but I have yet to sync them. That is next on my to do list....
 
If you have CV carbs (1980 and later) the needles will not be adjustable unless it has an aftermarket jet kit. Stock CV needles can be raised by adding small precision washers under the needles.
 
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