accelerator pumps on Zama carbs

taxidermist · Sep 8, 2010

I have had about 3 stihl string trimmers in the shop that have a accelerating problem. I thought the throttle shaft was worn I sprayed a little carb cleaner around the shaft and it ran better. With the price of rebuild kits for these I have just replaced the whole carb for a few more $. Tonight my fs55 1 year old string trimmer starts to do the same thing....well I know its not wore out so I tear out the throttle shaft and find a accelerator pump. I google this and find out the A P o rings are going bad on these carbs.

Is there a fix to these or are we stuck replacing the carbs.

Rob

Stumpys Customs · Sep 8, 2010

opcorn:

parrisw · Sep 8, 2010

Yes they do go bad, I too would love to know a fix since I have a bunch of bad ones.

1steve · Sep 8, 2010

the accellerator pump galls the body which causes o-ring to fail, looks like replacement only but someone else might have a fix

parrisw · Sep 8, 2010

1steve said:
the accellerator pump galls the body which causes o-ring to fail, looks like replacement only but someone else might have a fix

Wonder if you could hone or polish the body? Then new o-rings.

lcso10 · Sep 8, 2010

The FS-55 has a 2 year homeowner warranty.

With the retail price around $30.00 for most current trimmers, it almost pays to just replace them. I mean, by the time you get the kit and count your time putting it in and it still not working right!!!

1steve · Sep 8, 2010

parrisw said:
Wonder if you could hone or polish the body? Then new o-rings.

you might be able to but it might just be a temporary patch if it worked at all.....any polishing or honing would increase the bore.......nothing to loose trying though. good question

parrisw · Sep 8, 2010

1steve said:
you might be able to but it might just be a temporary patch if it worked at all.....any polishing or honing would increase the bore.......nothing to loose trying though. good question

Ya, ture. What I've heard actually is to just eliminate the pump circuit, just block it off with JB weld or the sort. The problem is the pump leaks by air causing a lean condition, that's why they fall on their face when you rev them up. I got like 4 or 5 200T cars here with that problem, and they are real expensive to replace around here. Last one cost $140, so you can see my incentive to fix the old ones.

How do you get acess to the pump anyway? I've never taken on that far apart? Take out the throttle shaft?

1steve · Sep 8, 2010

parrisw said:
Ya, ture. What I've heard actually is to just eliminate the pump circuit, just block it off with JB weld or the sort. The problem is the pump leaks by air causing a lean condition, that's why they fall on their face when you rev them up. I got like 4 or 5 200T cars here with that problem, and they are real expensive to replace around here. Last one cost $140, so you can see my incentive to fix the old ones.

How do you get acess to the pump anyway? I've never taken on that far apart? Take out the throttle shaft?

i understand completely, $140 is a very good incentive.
yep remove throttle shaft
last 200t carb i priced was $80 C1Q 61E i think thats the latest one out, suppose to be better
pull one apart sometime see if your idea will work....be great if it did, keep us posted on it

parrisw · Sep 8, 2010

1steve said:
i understand completely, $140 is a very good incentive.
yep remove throttle shaft
last 200t carb i priced was $80 C1Q 61E i think thats the latest one out, suppose to be better
pull one apart sometime see if your idea will work....be great if it did, keep us posted on it

Sure thing, thanks!

Zombiechopper · Sep 9, 2010

I have three dead ones as well. I'm planning on trying to epoxy one at some point when I get some time.

1steve · Sep 9, 2010

Zombiechopper said:
I have three dead ones as well. I'm planning on trying to epoxy one at some point when I get some time.

keep us posted........we need a fix, shoe boxes full of bad ones out there

Zombiechopper · Sep 9, 2010

1steve said:
keep us posted........we need a fix, shoe boxes full of bad ones out there

I will for sure if I ever get to it! Never enough time

parrisw · Sep 9, 2010

Zombiechopper said:
I will for sure if I ever get to it! Never enough time

Ya, likewise.

angelo c · Sep 9, 2010

I got a crap load of Redmax trimmers that do the same thing. Been through each one many times and never figured out the issue. Mine think they have spa memberships they are in the sonic cleaner so often.

A

taxidermist · Sep 9, 2010

lcso10 said:
The FS-55 has a 2 year homeowner warranty.

With the retail price around $30.00 for most current trimmers, it almost pays to just replace them. I mean, by the time you get the kit and count your time putting it in and it still not working right!!!

I just checked and I guess I have had it for 3 years with about 1 hr run time. JUst my luck!!!!

parrisw · Sep 20, 2010

Ok, got a 200T carb apart, throttle shaft's out. Now I've never had one of these apart before, so what am I looking for, for the pump circuit, is it the little brass jet looking think in the middle of the carb body? How do I get it out?

1steve · Sep 20, 2010

parrisw said:
Ok, got a 200T carb apart, throttle shaft's out. Now I've never had one of these apart before, so what am I looking for, for the pump circuit, is it the little brass jet looking think in the middle of the carb body? How do I get it out?

No, accelerator pump piston is activated by throttle shaft. See plug on carb body next to butterfly? Thats where piston is located

parrisw · Sep 21, 2010

1steve said:
No, accelerator pump piston is activated by throttle shaft. See plug on carb body next to butterfly? Thats where piston is located

Ahh, ok, I'll take another look. Looking in the complete wrong location.

Thanks

1steve · Sep 21, 2010

no problem, let me know how it goes :cheers:

accelerator pumps on Zama carbs

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