yet more running problems!

[jimllshiftit]

first of all thanks to anyone who has helped me with this poor neglected machine before now. youve all helped a great deal but its still not right.

the strimmer now starts ok and idles nicely but now when i start to give some welly it goes from high revs to really low revs (like about to cut out low revs) and then high again and low again etc etc until it dies.

it has done some work at high revs earlier today and was fine for about a hour so i think the high air speed setting is about right. i have ordered a new fuel filter but thats gonna take some time to get to me.

anyone know of anything else i can do i the mean time?

p.s its a stihl fs 76 strimmer

 

[billyjoejr]

Can you give us a list of things you have done to it, so we can rule things out that you have done or give other suggestions.

Rebuilt carb, new spark plug, new air filter, cleaned muffler screen, etc.

 

[ropensaddle]

first of all thanks to anyone who has helped me with this poor neglected machine before now. youve all helped a great deal but its still not right.

the strimmer now starts ok and idles nicely but now when i start to give some welly it goes from high revs to really low revs (like about to cut out low revs) and then high again and low again etc etc until it dies.

it has done some work at high revs earlier today and was fine for about a hour so i think the high air speed setting is about right. i have ordered a new fuel filter but thats gonna take some time to get to me.

anyone know of anything else i can do i the mean time?

p.s its a stihl fs 76 strimmer

Well you could buy a husky but that is just my opinion lol. It sounds like a metering problem
like bad diafram or the like

 

[jimllshiftit]

ok, from the top.

decoked combustion chamber and piston.

new piston rings.

new base gasket.

new spark plug.

cleaned carb and replaced diaphragm and gasket on bottom of the carb and the screen and gasket on the top of the carb under the squeezy thing.

once the machine was running nicely i set the high and low speed air flow which helped immensely.

and finally a new fuel filter.


so whats up with it? i managed to get it to do some work earlier today but then it started the high and low rev thing again and died. it seems odd that its fine at idle speed but just cant handle any throttle.

just about the only part that hasnt been either overhauled or replaced, in the top end, is the coil. when i take the plug out when the machines playing up its wet around the edge of the threaded part but not at the gap.

any ideas yet?

 

[jimllshiftit]

Can you give us a list of things you have done to it, so we can rule things out that you have done or give other suggestions.

Rebuilt carb, new spark plug, new air filter, cleaned muffler screen, etc.[/QUOTE

oh yeah. muffler screen was checked too. no problems there.

 

[Lakeside53]

It could be the carb.. or a leak in the fuel line, or a bad tank vent (undo the tank cap and try again... ).

or...

You have an airleak somewhere.. most likely a seal or around the carb block. You'll need to do a pressure and vac test to locate it...

 

[jimllshiftit]

we're nearly there

phew, ive had all day today to check the machine over and your suggestion of the carb is right. however, the problem is not yet solved.

if i prime the hell out of it i can get 5 mins work out of the machine, then it bogs and dies again. then the priming trick will get it going again.

i guess that means that its not an air leak but a blockage in the carb itself (please dont hesitate to tell me if im wrong). so what should i do?

if i keep doing the priming trick will it clear the blockage?

should i just go and get a brand new carb?

whatever it is im glad we are norrowing it down. its been a great educational exercise if nothing else. what other engines have i got that i can take apart?