FS400 Brush Cutter... Carb or seals.. Vaccum test.

[champagnecharly]

Hi,

 

I have an FS400 thats driving me nuts.. Got a new carb for it.. installed without filter etc let it run. Worked fine lef tit running for 20 mins and reacted well to throttle.. I left it on the side for 3 weeks and now the darn thing wont run with choke off. Also cuts out under throttle.

Compression is 70,100,120PSI on 1,2,3 pulls

I tried a pressure/vaccum test. holds .5bar vaccume and 1bar pressure for a good 10 mins but does seem to leaks very slowly on both.

Could this be my problem? I wasnt sure given that it worked before the hols fine.. had no further use and then didnt work parculiar and wondered if my leak was from my blanking card or tester and that the new carb was at fault. Fuel is fresh.

 

Also wondering what these should sound like as it sounds awfully tinny (from exhaust side) when it idles.

Edited August 4, 2014 by champagnecharly

[ukminch]

Have you adjusted the valves?

[champagnecharly]

Thanks for the input... fs400 Basic 2 stroke, no valves on this.

[Ray1]

Cheap carb from Hong Kong off Ebay?

[champagnecharly]

From US.. But cheap yes. Hence more reason for my suspicion..

Qu is should so little loss / slow of pressure effect running of machine?

[Ray1]

I like to make sure they dont leak at all or if they leak slowly find out where its coming from. Ive even been known to put a full engine in a bucket of water to trace a very slow leak.

[ukminch]

Sorry I was thinking of a blower which despite being two stroke has valves which are a pita!

[spudulike]

I usually pressure or vacuum the engine, turn it over very slowly one to three times and if there is no appreciable drop in pressure or vacuum, declare that a success.

 

I believe Stihl just give a percentage drop over a 20 sec period but if it is holding pressure/vacuum over a ten minute period and my method shows only a very slight almost zero drop then you are good.

 

Your issue sounds like an issue with the high speed part of the carb - if it has an H screw, remove it, blast some carb cleaner down there and reset the H screw.

[champagnecharly]

A bit of diluted washing up liquid showed that my seal to the pressure testing block (like carb) was bad. was just using a piece of card. Unfortunately this carb is idle adjustment only.. a real pain. Can the caps be taken out and screws put in?

[mikerecike]

If you take the caps off theres probably a screw head under.If not cut flat heads with a dremel or hacksaw blade.

 

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