Fs400

[aquatoo]

I rebuilt the FS400 that I posted about before and it now runs well but just doesn't want to tick over. If I keep the throttle open it runs okay. I have set the carb controls to the basic set-up position and have tried adjusting the idle screw.

Just so I don't waste a lot of time I'd appreciate any advice on the sequence of things to check.

 

Thanks in advance

[GardenKit]

The basic settings are just that, basic. A starting point.

 

Try turning the L screw out a little and see if it improves, if not, turn it in a little and see if it improves.

 

Then, if you can get a tickover, fine tune the L screw like this. Turn it in slowly until the revs just start to drop off. Then turn it slowly out, noting how far you are turning it. The revs should increase and then start to drop off. Note the position.

 

You will now have established the 'lean drop off point' and the 'rich drop off point'

 

Turn the screw very slowly in until the revs just pick up and runs smoothly. At this point it should tick over fine, and respond to the throttle opening without a flat spot.

 

Turn the tickover back to the correct idle speed, i.e where the head does not spin.

 

Then you should tune the H screw, but thats a different lesson.

[aquatoo]

Thank you Gardenkit. I'll have another go, following your advice.

 

Much appreciated

[spudulike]

I rebuilt the FS400 that I posted about before and it now runs well but just doesn't want to tick over. If I keep the throttle open it runs okay. I have set the carb controls to the basic set-up position and have tried adjusting the idle screw.

Just so I don't waste a lot of time I'd appreciate any advice on the sequence of things to check.

 

Thanks in advance

 

Sounds like issues in supplying fuel on the low speed part of the carb - I would normally wind the idle screw right in until it DOES idle but am guessing that this isn't working.

 

Try turning the L screw 1/2 turn out and the idle screw 1-2 turns out from fully in and try again - you may find it hard to start but the leaner mix may give you a better idle speed.

 

Failing this, you may have a bad fuel filter, bad or holed fuel line, a carb fault, leaking welch plug, air leak etc

[humpo48]

There is a very tiny fuel filter mesh inside the carb where the fuel feeds in. Check that if I where you that will restrict the fuel entering the carb

[spudulike]

There is a very tiny fuel filter mesh inside the carb where the fuel feeds in. Check that if I where you that will restrict the fuel entering the carb

 

Not being funny but that would be more likely to kill running at speed/load than idle....worth a check but it generally gives fast running issues:thumbup:

[aquatoo]

Sounds like issues in supplying fuel on the low speed part of the carb - I would normally wind the idle screw right in until it DOES idle but am guessing that this isn't working.

 

Try turning the L screw 1/2 turn out and the idle screw 1-2 turns out from fully in and try again - you may find it hard to start but the leaner mix may give you a better idle speed.

 

Failing this, you may have a bad fuel filter, bad or holed fuel line, a carb fault, leaking welch plug, air leak etc

 

Thanks everyone. I'll have another go tomorrow if it isn't chucking it down, as usual of late. Makes me glad I live on a hill.

[aquatoo]

I reset the basics as suggested and it starts but won't run and then it won't start again and appears to be flooded.

 

I'll strip the carb out and start and give it a good clean.

[aquatoo]

Thanks everyone for your help and advice.

 

Stripped the carb, cleaned it and then discovered that the valve lever was about 1/8" too high. Sorted it, put it all back and hey ho it starts and runs.

 

Now perhaps someone could tell me where to get a tachometer so that I can set the max revs correctly

[aquatoo]

Thanks everyone for your help and advice.

 

Stripped the carb, cleaned it and then discovered that the valve lever was about 1/8" too high. Sorted it, put it all back and hey ho it starts and runs.

 

Now perhaps someone could tell me where to get a tachometer so that I can set the max revs correctly

 

Okay I'll just set it so that it runs, picks up quickly and sounds all right without sounding like a demented banshee!