Help with string trimmer engine

[Kosmo]

Having problem with and older Ryobi 790r string trimmer. Amazingly this trimmer has been trouble free for many years but this year have been having trouble keeping the engine running. I rebuilt the carburetor and have been trying to get the jets tuned right. This is an older model which has access to the jets without a special tool. After the rebuild, I was able to get it started but it would not start with the original jet settings after removing the screws, cleaning, and setting them back to the original settings. Again this was a complete teardown of the carb with thorough cleaning and new gaskets, needle valve, etc. So I started from the beginning with the normal procedure of backing the High and low jets off 2 turns and then adjusting the low jet at idle and then the high. I've gone through this procedure several times and seem to get it running well for about 10 minutes, but then it starts to have problems bogging down when I hit the throttle, and stalls. I am able to start it again at idle, but again can't get it to throttle up without bogging. After about 5 minutes more, I can't get it started at all. If I let it sit for an hour or so, it will start but the same thing will happen after it warms up again. Wondering if you all think this is an ignition coil problem or what. Thanks for your input.

 

[Tjdux]

Could be an air leak with a gasket that didn't seat right thats leaking after everything gets warm. Especially if its running weird before dying or surging.

 

[Tractorable]

I've never been able to tune carbs on small, under 50cc, engines. I don't know what it is, they're just finicky as all get out. Can you just buy a new carb? Or would that cost more than a new string trimmer?

Try removing the string head and see how it runs with no load. My Husqvarna string trimmer runs fine with the string head but if I put a blade or blower on it it bogs out and dies.

 

[sidemouse]

Having problem with and older Ryobi 790r string trimmer. Amazingly this trimmer has been trouble free for many years but this year have been having trouble keeping the engine running. I rebuilt the carburetor and have been trying to get the jets tuned right. This is an older model which has access to the jets without a special tool. After the rebuild, I was able to get it started but it would not start with the original jet settings after removing the screws, cleaning, and setting them back to the original settings. Again this was a complete teardown of the carb with thorough cleaning and new gaskets, needle valve, etc. So I started from the beginning with the normal procedure of backing the High and low jets off 2 turns and then adjusting the low jet at idle and then the high. I've gone through this procedure several times and seem to get it running well for about 10 minutes, but then it starts to have problems bogging down when I hit the throttle, and stalls. I am able to start it again at idle, but again can't get it to throttle up without bogging. After about 5 minutes more, I can't get it started at all. If I let it sit for an hour or so, it will start but the same thing will happen after it warms up again. Wondering if you all think this is an ignition coil problem or what. Thanks for your input.

It depends on whether it's worth fixing...

Could be the fuel lines / fuel filter as well, things such as a tiny pinhole leak will make it do that.
There's a decent chance there's a crack in the line right past where it hooks into the fuel filter.
Could also be a leak where the lines go through the tank, not sure if there's some sort of a grommet there or what.
Or where they hook onto the carburetor, or in between...

If that doesn't fix it I'd either order up a new carburetor, the gasket(s), and like I said replace all fuel lines (inside and outside of tank) and the fuel filter.

Again it depends how much it's worth to me.

 

[weathda]

My 14 year old cub cadet cc 3000 string trimmer just started exhibiting the same problem this past week. I replaced the fuel lines about 3 years ago as they were disintegrating. I replaced the spark plug on it last night. Took the air filter off which was replaced recently. Starts great, idles great, but stalls when I run up the RPM. The carb kit is $22.80. New carb is $46. But, it needs a new bump head and the shaft is bent from me bumping it too hard to get string out. I don't think I'm going to dump anymore time or money into it.

I'm going to try to pull out the spark arrester to make sure it's not plugged and if that doesn't work, then it's headed for the scrap heap. Everything has a life...

 

[Maxify55]

Dude, have you checked your exhaust screen?
It sounds to me like you've not checked the spark arrest screen.
Take it out/off.
Grab your torch. Butane or LP, either is fine.
Burn off the excess carbon and you'll be back in business.
The unburned carbon from 2 cycle oil builds up there and clogs the exhaust from the engine.

Hope this works for you. Older 2 cycle equipment needs more lovin' but works just fine with some well intended caressing.

Come to think of it, the Mrs. isn't much different but I digress.:confused3:

 

[RandyT]

Some of those older ryobi trimmers also had issues with the cylinder mounting screws coming loose, and allowing an air leak

 

[Gary Fowler]

Dude, have you checked your exhaust screen?
It sounds to me like you've not checked the spark arrest screen.
Take it out/off.
Grab your torch. Butane or LP, either is fine.
Burn off the excess carbon and you'll be back in business.
The unburned carbon from 2 cycle oil builds up there and clogs the exhaust from the engine.QUOTE]I had the same thing happen to me. It would run fine at idle but wouldn't get up the rpm. Finally took it to the shop and it was the muffler stopped up with carbon.

 

[MossRoad]

As others have mentioned, did you replace the in-tank fuel filter and the fuel line? Its a cheap fix... a few bucks and can't hurt on an older machine.

 

[Newtocvt]

My trimmer did the same thing and it was the exhaust screen. Got the torch and cleaned it. Works like a champ.