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most older cars had 2 adjustments , a air screw for enrichment and throttle screw for engine idle speed, later models did away with the enrichment screw, to adjust set idle screw to 600 rpm, adjust air mixture screw to fastest rpm , reset idle screw to preferred idle speed.
Most older cars had 2 adjustments , a air screw for enrichment and throttle screw for engine idle speed, later models did away with the enrichment screw, to adjust set idle screw to 600 rpm, adjust air mixture screw to fastest rpm , reset idle screw to preferred idle speed.
The carb mixture screw may add air or fuel, depending on the model. If the bike will idle it can be adjusted without knowing the factory setting. What you want is the highest idle that can be achieved using just the mixture screw, not the idle setting screw. Start the motor, then slowly turn the mixture screw in. If the idle speed increases, continue in that direction. If it slows and becomes rough, turn the screw back out until you reach the highest idle speed. That will the correct setting for the bike at your altitude.
Generally there are 3 adjustments depending on the model. An idle speed screw that controls the idle rpm of the saw, the idle mixture screw that controls the air/fuel ratio at idle speed as well as "throttle up", and the high speed mixture screw that controls the air/fuel ratio for top engine rpm. The mixture screws will usually be identified on by a "L" and "H". Hope this answers your question.
If its an old Homelite you should have 3 screw on the carburator.
First bigger screw for adjust idle on the butterfly.
The 2 other for the mixture. One screw is ''L'' for low rpm mixture an other screw is ''H'' for high rpm mixture.
First the idle screw. It should just open a little bit the carburator butterfly.
Second full close both ''L'' and ''H'' screws (turn clockwise).
After open both ''L'' and ''H'' screws 1/2 to 3/4 turn (conterclockwise)
Normally the saw should start. Tune the ''L'' screw to have the motor running at idle if idle is to fast at this point is not important. After motor is running by itself at idle tune the ''H'' screw.
Full throttle tune the ''H'' screw to be able to pass from low rpm to high rpm with no lag.
Than at full throttle open again a little bit the ''H'' screw to make the high rmp mixture more rich.
Becarful if ''H'' screw is not adjust correctly the mixture will be to poor and motor damage can occur.
It may be necessary to re-tune a very little bit the ''L'' screw and idle screw after the correct setting of the ''H'' screw.
If it still not working carburator kit may be needed,
On some newer model there is no adjusting screws in this case see if a carburator kit is available for your model.
The high speed mixture screw is initially set at 1 & 1/2 turns out. Then adjust it to give good acceleration and top speed, while not closing the screw more than you need to. The low speed mixture screw is set at 3/4 of a turn out. Adjust that, to give a smooth idle. The 3rd screw, the idle speed screw, is set to give a low idle speed without stalling.
Depending on the type of intake system, if it's a normally carburettored bike, there is an air mixture screw on your carby(s). Set this screw at one and one half turns out from being screwed to stop. Run bike till it is warm and set IDLE screw or throttle stop at optimum idle revs. Without using choke or throttle, turn the air mixture screw slowly in or out till revs build to highest level. Reset idle screw or throttle stop to set revs back down to optimum level as before. If this does not cure your problem, depending on if it's a 2 or four stroke, single or multi cylinder engine your problem may be one of many from fuel ratio, valve rocker clearance, ignition, plug range etc....specify make/model for proper info.
This is not the original carburetor that came on the bike. The orignial was a Kehien "butterfly" carburetor. This carburetor is a later "CV" version with the large square looking top on it.
I'll tell you how to access the idle mixture screw on each model. The "butterfly" carb had it's idle mixture screw in a "tower" on top of the carb just forward of the carburetor mounting flange. The square topped "CV" carb has the idle mixture screw underneath the carb at rear of the float bowl.
They both came from the factory with an "anti-tamper" plug of about 3/16 inch diameter (5mm) pressed in over the adjuster screw so that the owner could not mess with the idle mixture.
To get access to the idle mixture adjustment screw, you must drill a small hole in the "anti-tamper" plug. Be very careful not to drill too deeply or you will damage the brass screw underneath the plug. Drill just enough to go through the plug with a small drill bit. Screw a sheet metal screw or start a tap in the hole. If you use the sheet metal screw, use a pair of pliers or something to pull the plug out. If you're using a tap, once you get the hole tapped screw a screw into the hole and use the pliers to pull the plug out.
If your bike will idle at all, start the bike up and allow the engine to warm up. If it won't idle, screw the idle mixture in until it just barely "bottoms" in the hole. Back it out 1 1/2 turns on the "butterfly" carb and about 3 turns on the "CV" carb and start the engine. Adjust the screw to obtain the highest smoothest idle. Then use the throttle stop screw to set the idle speed of the engine. Once you're finished, put a small dab of RTV sealant in the hole over the screw. If you don't do this, water will seep down by the fine threads permanently seizing the screw making it impossible to adjust the idle mixture in the future.