OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Two Stroke Trimmers & Brushcutters fs 55 stihl

Giday all, ihave a fs55 stihl that I just can't seem to get right
When I got this machine it was hard to start and when you throttle up it just died. I have cleaned the carby ,let it soak in dishwashing detergent overnight put the needle wire in every little hole a good blow out and now it starts after about three or four pulls ,it hits high revs no worries if you pull the trigger quick and drops to a fairly good idle. If I slowly pull on the trigger it picks up revs and about a third of the way up it starts to bury and if I hold the trigger there it will die but if I give the trigger a quick pull it will get past this point no worries . So it seems to be all good except it has a flatspot .What ould the cause of this be?ps this post wouldn't let me choose ussb for photo,sorry don't know how to fix this either. Cheers

The setting should be either UBBCode or HTML and UBBCode roebuck - I've changed your post from HTML to HTML and UBBCode to fix the image problem.

Flat spots such as you describe are nearly always caused by lean mixture. In your case, it sounds as if your carburetor cleaning process has not been completely successful. My guess as to the reason, is that your dishwashing detergent did not do an adequate job of cleaning out the progression holes near the throttle plate, and one of the holes is still partly obstructed. Frankly, I'm surprised that the detergent worked even that well. The quickest and easiest way to clean out the passages in a carburetor is generally, to use carburetor cleaner. In the case of small orifices that can't be accessed directly, it is just about the only way. Also, I suggest in future you avoid putting wire or needles into progression holes since they are very finely calibrated and easily damaged in the soft aluminium.

I find a good carby cleaner and compressed air works good for me,I also pull the fuel filter and blow it out clean,blow out fuel line also....It looks to new to need carby kit but in saying that if it has ever been run on fuel with ethanol in it might need a new kit, ethanol does all kinds of bad things to diaphragms in hand held 2T carburetors especially if let sit on the shelf with ethanol fuel in the tank.....

Ok thanks a lot Grumpy and Chris, I gave it another clean with carby cleaner and a little compressed air but no needling with wire ,but it back together and now it runs perfect and starts easily know and no burying whatsoever.. No needle wire no more ! Nice little machine thanks again.

I forgot to ask what is good and safe to soak the carby in to aid in cleaning /carburetor metal parts only.

I'm not sure you can remove some of the plastic parts roebuck, and that is the main reason I greatly prefer a brief squirt with fairly strong solvent (carburetor cleaner) followed by blowing the solvent out with air pressure, before it has a chance to eat the plastic.

You can soak the carburetor in a light oil-based solvent such as kerosene, mineral turpentine, white spirit etc. They are much the same mixture of substances as petrol, which the carburetor is designed to be exposed to. You will need to blow out the solvent when you finish the soaking, to get rid of whatever it has dissolved. Many years ago I used to try to clean carburetors that way, but the effectiveness was quite marginal. It will not dissolve gum, which is usually the main problem.

Thanks Grumpy',I have kerosene and thinners 3parts kero and 1 part thinners to soak and clean engines with would this be ok for carby soak overnight or to harsh .I ask because it does an ok job on parts but I want to be carefull with carby in particular.

Either kerosene, or mineral turpentine (which they call something else in the US, I don't recall what), is in effect extremely low volatility, low octane petrol. Neither substance will harm a carburetor intended for petrol, even with quite a long soaking. I don't know if you mean mineral turpentine when you say paint thinner. For example, traditional automotive lacquer ("Duco") was thinned by acetone, and you shouldn't put that anywhere near a carburetor that has any plastic or elastomers in it - and just about all of them do. There are other exotic solvents used for thinning some types of paint, none of which should be used on carburetors.

So, if you mean mineral turpentine, go ahead and soak the carburetor in it. It won't do much of a job of cleaning the internal passages, though, since it will not dissolve gum. And for Pete's sake don't try to run an engine on it - Joe Carroll has described what happened when he tried it once. You can't expect even a low compression engine to run for long on fuel of well under 60 octane. Joe's blew spectactularly and irreversibly.

People are getting good results with Ultrasonic cleaners for fiddly carburetors like this..They are a cheap thing to buy now days and if you work on a few carburetors they can be a handy thing to own you just have to get the appropriate cleaning solvent for the job at hand...

Thanks heaps , I have a little jewelery cleaner and I will try this next time .you all have been a great help. I would be lost without such great advice cheers roebuck.