zama carburetor starts and idles great but dies when given throttle

[bikesandcars]

I rebuilt the zama carburetor on my old homelite ST185 trimmer, and thought I had it fixed.

After the rebuild I tuned the H and L needles and it was running fine..... actually suprisingly good.

Today (after sitting 2 weeks) I went to start it and it idles fine but falls on it's face when given throttle. very slight throttle will get the revs up a little but when given WOT it shuts off. No amount of coaxing or warming up would let it run on throttle...but it idled perfectly. I toyed with the H screw but it didn't change anything.

I rebuilt the carb because the trimmer was given to me, it didn't run right. The fuel system was full of old sludgy fuel, I replaced the fuel line, filter, carb gaskets, fuel bulb and cleaned it with brake cleaner.

I'm confused because it ran after the rebuild but now doesn't, and nothing happened inbetween.

Any thoughts / ideas? (yes it's full of fuel)

I visited Zama's carburetor website for some theory, but was hoping you wise fella's could help me cut to the chase.... all that talk about welch plugs got me nervous.

I'm guessing something in the H circuit, but I'm certain I cleaned everything.

 

[watsonr]

Clean it again, you may have dislodged some smaller pieces and they are now stuck inside plugging the high speed passages. Don't forget to remove the metering seat and make sure the passage is clear. By removing both sides of the carb and the metering needle, you should be able to see right through the passage. If not, use a small bread tie to open it back up, don't use high pressure air on it, it can damage the carb. CLEAN out the junk under the little screen also, that gets plugged as well, spraying carb cleaner the opposite direction through the screen normally works.

 

[half_full]

Make sure the exhaust port and screen are clean too. May not be your issue since it ran good last time. But, that one gets alot of folks.

 

[bikesandcars]

Make sure the exhaust port and screen are clean too. May not be your issue since it ran good last time. But, that one gets alot of folks.

Thanks and a great idea.

I gave it a double-barrel shotgun muffler mod and removed the screen... see what I"m learning from you folks already!