J1MS wrote:A longer inlet manifold might help a little, thats if its possible to fit one?
A dellorto may be a better option here, and maybe with a powerjet.
Pinking at high speed with barely open throttle
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soulsurfer
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A dellorto may be a better option here, and maybe with a powerjet.
Turn On, Tune In, Cop out!
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sean brady scooters
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junk the mikuni and get a delly........and get it set up on a dyno........ 
Sean Brady Scooters - 01765 690 698
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ArmandTanzarian
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Swapping the carb may not be entirely straightforward.sean brady scooters wrote:junk the mikuni and get a delly........and get it set up on a dyno........
Its currently running a TM24 on an LTH Reed manifold. JB Tuning suggested it would work a lot better with a 30 mm delorto but by then I'd already bought the LTH and so swapping it all over might prove a bit pricey. I suppose I could change it all and sell the bits but at this rate I'll be needing to sell a kidney!
I've done about 100 miles on it since the rebuild, I'll try and get a few more on it and then get it over to John's to get set up properly. The clutch needs work too as the 5-plate can't cope with 23HP with SX Sprockets.
Meus Lambretta est non infractus. Is est quietus.
Electronic power jet would be nice, but you would have to change your electrics, but can be done.soulsurfer wrote:J1MS wrote:A longer inlet manifold might help a little, thats if its possible to fit one?
A dellorto may be a better option here, and maybe with a powerjet.
I was thinking of the cheap easy fix... But I think you might be right, a Dellorto carb would usually be my first choice as well.soulsurfer wrote:J1MS wrote:A longer inlet manifold might help a little, thats if its possible to fit one?
A dellorto may be a better option here, and maybe with a powerjet.
But the inlet tract length on a Dellorto can alter the carbs performance, where the slide is positioned in relation to the piston skirt (distance) and not just overall length of the inlet can and does alter low speed running, and off throttle conditions so varying inlet length could still be an advantage depending on setup...
Power jets don't usually work much below Half throttle as they enter the top half of the venturi and work on slide position and air speed, so closed throttle coasting down hill might be a challenge for a power jet however its been fitted and to whatever carb you might try...
Basic Carburetion:
If the bike is too lean, it will rev but will have no grunt, and it will run good on the first lap then gradually get worse.
If the bike is too rich, it won't rev, will have good mid-range, and be stronger later in the race rather than earlier in the race.
How do you tell if it's rich or lean? Look at the following:
Plug readings. How do you read a plug? If you look at the ground electrode, it should burn white to within two-thirds to three-quarters of the distance from the tip towards the body of the plug. You can also look at the steel body of the plug around the outer diameter, and that needs to run biscuit brown to light brown, depending on the oil that is used.
You can look at the piston, and read the top of the piston. You should see a nice deposit of carbon on the top; the color will depend on the type of oil and fuel you are using. The piston should be dry with two small areas of bare aluminum exposed at either side of the exhaust port at the front, with slight traces of dampness. You don't want to see any detonation-this is erosion of the piston through pre-ignition caused by being too lean or too advanced or running too high a compression.
You need to see a burned oil deposit the size of a dime on the underside of the piston. The size of this deposit will depend on the temperature at which the oil burns, i.e., it depends upon the type of oil that you use. You can also measure the exhaust temperature, and you can also log the maximum rpm, using data acquisition.
You can look at the exhaust gas temperature, the cylinder pressure and such like. You can also use a detonation counter. This counts the detonations per kilometer. That, basically is how you read the carburetor.
Generally, the back-of-the-piston readings denote the carburetor on the needle. The airscrew and the pilot system work right through carburetion from no throttle to full throttle. Most people use standard pilot jets and airscrew settings, but if they have problems with the performance of the bike, and their riding style, this may have to be changed.
Some riders may spend lots of time off the throttle, which will load the engine up with unburned fuel, and to compensate should run either a smaller pilot jet, or the airscrew will have to be wound out.
Likewise, some riders may find that they need a richer pilot setting for sharp response off the bottom of the rev range. The needle can affect the mid-range performance of the engine and different riders prefer different needles, again it depends on what kind of power delivery the rider needs from the bike, and entirely depends on their riding style. Some people run lean needles, some people run rich needles, quite often, riders tend to run too lean a needle, because they will carburet the bike on the throttle on the stand, and when the engine sounds sharp and feels crisp, they will go with that needle. But in effect, the needle will be too lean and under load won't deliver enough fuel to give good drive out of the turns. But again, a lot depends on the riding style of the rider.
The main jet needs to be the right size to make the engine rev, and over-rev. Over-rev being between 12,000 and 13,000 rpm. The power jet switches off on the standard bike at 12,200 rpm, and is important for the mid-range. Most riders do not change the power jet, and they would only change the main jet, leaving the power jet as a constant.
What affects the carburetor? Several things. The weather: The air pressure, the humidity, and the temperature all affect the relative air density (RAD). The denser the air, the bigger jet is needed. The less the air density, the smaller the jet. Basically when the air pressure is up you need to jet up, when the temperature is down, you need to jet up, when the humidity is down you need to jet up.
How do you monitor the weather conditions? Many people use RAD gauges or will measure the air pressure, the humidity and the temperature, and work out the relative air density (RAD), and then will formulate some kind of a pattern as to what their bike needs. The length of the straightaway also makes a difference. On a short straightaway you will need a smaller jet to reach the most efficient combustion chamber temperature and exhaust temperature in such a short time. On a longer straight the temperature needs to be kept down, and you would need a bigger jet so that you still reach optimum temperature at the end of the straight. If you run too small a jet, you have problems with seizures, etc.
This is based on a RS125
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If the bike is too lean, it will rev but will have no grunt, and it will run good on the first lap then gradually get worse.
If the bike is too rich, it won't rev, will have good mid-range, and be stronger later in the race rather than earlier in the race.
How do you tell if it's rich or lean? Look at the following:
Plug readings. How do you read a plug? If you look at the ground electrode, it should burn white to within two-thirds to three-quarters of the distance from the tip towards the body of the plug. You can also look at the steel body of the plug around the outer diameter, and that needs to run biscuit brown to light brown, depending on the oil that is used.
You can look at the piston, and read the top of the piston. You should see a nice deposit of carbon on the top; the color will depend on the type of oil and fuel you are using. The piston should be dry with two small areas of bare aluminum exposed at either side of the exhaust port at the front, with slight traces of dampness. You don't want to see any detonation-this is erosion of the piston through pre-ignition caused by being too lean or too advanced or running too high a compression.
You need to see a burned oil deposit the size of a dime on the underside of the piston. The size of this deposit will depend on the temperature at which the oil burns, i.e., it depends upon the type of oil that you use. You can also measure the exhaust temperature, and you can also log the maximum rpm, using data acquisition.
You can look at the exhaust gas temperature, the cylinder pressure and such like. You can also use a detonation counter. This counts the detonations per kilometer. That, basically is how you read the carburetor.
Generally, the back-of-the-piston readings denote the carburetor on the needle. The airscrew and the pilot system work right through carburetion from no throttle to full throttle. Most people use standard pilot jets and airscrew settings, but if they have problems with the performance of the bike, and their riding style, this may have to be changed.
Some riders may spend lots of time off the throttle, which will load the engine up with unburned fuel, and to compensate should run either a smaller pilot jet, or the airscrew will have to be wound out.
Likewise, some riders may find that they need a richer pilot setting for sharp response off the bottom of the rev range. The needle can affect the mid-range performance of the engine and different riders prefer different needles, again it depends on what kind of power delivery the rider needs from the bike, and entirely depends on their riding style. Some people run lean needles, some people run rich needles, quite often, riders tend to run too lean a needle, because they will carburet the bike on the throttle on the stand, and when the engine sounds sharp and feels crisp, they will go with that needle. But in effect, the needle will be too lean and under load won't deliver enough fuel to give good drive out of the turns. But again, a lot depends on the riding style of the rider.
The main jet needs to be the right size to make the engine rev, and over-rev. Over-rev being between 12,000 and 13,000 rpm. The power jet switches off on the standard bike at 12,200 rpm, and is important for the mid-range. Most riders do not change the power jet, and they would only change the main jet, leaving the power jet as a constant.
What affects the carburetor? Several things. The weather: The air pressure, the humidity, and the temperature all affect the relative air density (RAD). The denser the air, the bigger jet is needed. The less the air density, the smaller the jet. Basically when the air pressure is up you need to jet up, when the temperature is down, you need to jet up, when the humidity is down you need to jet up.
How do you monitor the weather conditions? Many people use RAD gauges or will measure the air pressure, the humidity and the temperature, and work out the relative air density (RAD), and then will formulate some kind of a pattern as to what their bike needs. The length of the straightaway also makes a difference. On a short straightaway you will need a smaller jet to reach the most efficient combustion chamber temperature and exhaust temperature in such a short time. On a longer straight the temperature needs to be kept down, and you would need a bigger jet so that you still reach optimum temperature at the end of the straight. If you run too small a jet, you have problems with seizures, etc.
This is based on a RS125
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Is that Gordon Jennings?
Frank WrathallJ1MS wrote:Is that Gordon Jennings?
Thought he was a Four stroke man...
That was part of a write up on an RS125.J1MS wrote:Thought he was a Four stroke man...
This is good, if you have a spare day
http://www.datafan.com/TunersHandbook/2 ... tered.html Your man Gordon