# Ryobi 990r 4 cycle trimmer adjustment



## dji (Feb 11, 2005)

Is the method for adjusting a 4 cycle trimmer the same as a 2 cycle? I have replaced fuel lines, in tank filter, primmer button, clean carb and exhust. I can get it to start but it won't idle without me having to use the throttle. The engine hesitates and stalls also when depressing the throttle. I roughly adjusted the carburetor like on a 2 cycle 1-1/2 turns to start with and have try to fine tune it but without any luck so far. Any ideas or commets.


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## scrench (Dec 8, 2004)

"hesitates and stalls" open the low jet but be sure you set the carburator with the air filter on it ,,,

turn the idle up then tip the engine on its side the same side as the jetts @ idle , if it tries to die then its too rich , turn it in till it idles smoothe and dont hesitate when you gas it , after you set the low then set the high dont get it too lean or you will burn it up fast , you might have to kinda jump back and forth from high to low a little ,. to get it right also set the high with the line all the way out on the spool dont set it with no line ,, also might want to be careful with the throttle trigger they break pretty easy good trimmer though good power kinda heavy but good


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## bugman (Aug 12, 2004)

yes true try it with the air filter, i've seen even 2 cycles that would not run full throttle and hesitate and die till i put the filter on and usually i would up the screws a tad when they do that for a 2 cycle, same for a 4. but yeah those things are heavy but they give some good power. not as fun to rev though


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## dji (Feb 11, 2005)

Yep, I need to put the air filter on...and the bottom cutting shaft too. My heart isn't into fixing this trimmer. They are way too heavy. I been messing with it for a few weeks. Lot of little neglect problems. I am not sure why anyone would buy a 4 cycle trimmer. I will get it running smoothly tomorrow. Thanks


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## bugman (Aug 12, 2004)

well the reason why is they last sometimes if taken care of they last longer then your average weeder 2 cycle but if a 2 cycle is taken care of then they might last longer. but the main reason is they give lots of power and they can take attachments on most like tillers hedgers etc. on most models that allow em


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## scrench (Dec 8, 2004)

dji said:


> Yep, I need to put the air filter on...and the bottom cutting shaft too. My heart isn't into fixing this trimmer. They are way too heavy. I been messing with it for a few weeks. Lot of little neglect problems. I am not sure why anyone would buy a 4 cycle trimmer. I will get it running smoothly tomorrow. Thanks


 
fix and sell the name of the game


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## bugman (Aug 12, 2004)

scrench said:


> fix and sell the name of the game


  you got it. if you got it back running good and reliable and it looked in good shape, you might get 80 bucks or more for it. but make sure it looks good, some people want em to look good, they usually don't care engine wise because they usually don't care about the engine. me i care about both, more engine then looks but i keep the body and all in good working order and fix the rust or scratches. like i say for my riders and pushers, take care of the engine and the deck and you'll have a mower for years with little to no probs, and i mean keep the engines practically spotless. no oil leaks or misbalanced blades or which i hate most of all, cleaning the filter, which most don't or never even replace, but selling it is the name of the game. make you a couple bucks:thumbsup:


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## hankster (Jan 1, 1998)

Two things to look for. First is a plugged muffler screen. Second is make sure the idle is set high enough... best bet is to adjust the idle high so it will run by itself and then start backing off. But these things are almost impossible to set properly without the lower shaft, head and string. If you rev them up without a load you'll float the valves for sure... most times it won't hurt them but it sure sounds nasty!


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## dji (Feb 11, 2005)

The muffer screen is clean and I have try to set the idle high. I can get it started and it will run for about 20-30 seconds but with full throttle only? Then it dies. Can't get it to idle long enough to make any adjustments. I need more hands... I am starting out with the low and high jets open 1-1/2 turns. FYI, I am using the old plug (looks ok) that was in it. When I took the carb apart to clean it I used the same gaskets when i put it together, like I always do..


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## bugman (Aug 12, 2004)

ohh you might should look into new gaskets etc, and maybe a new plug


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## hankster (Jan 1, 1998)

Two other places to look into is compression and valve lash.


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## scrench (Dec 8, 2004)

"I used the same gaskets " it is money well spent to just buy a kit ..i never clean a carburator without putting a new kit in it , sounds like the diaphragm on the needle valve side might be the problem , ,, or might still be dirty ,, but when you are running it at high rpm you are creating a pretty big ammount of vacuum and causing the diaphragm to work like it should ,then @ idle the crankcase presure is low and wont open the needle , i am going to say its the diaphragm ,, it might be sucking air arround a crank shaft seal , or the carburator adapter or cyl gasket but if the diaphragm is stiff it wont run right @ all , might also check the impulse hole and make sure it is not stopped up in the carburator adapter , and that the gasket is good and not leaking ,,, what kind of carburator is it ?


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## bugman (Aug 12, 2004)

yep thats what i was thinking scrench, carb kit and rebuild


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## dji (Feb 11, 2005)

Everyone, Scrench thanks for the information on the workings of a diaphragm..I think you have found the problem..the diaphragm isn't as fexible as it should be, it didn't look that good when i had it apart.. I always use a new carb kit when i am fixing my own things but I am doing this for a neigbor. He brings me various lawn equipment he finds at the dump and I "quickly" try to get them running again. I try not to spend much time or money on them since I don't get anything for do this.. I do it just because i enjoy taking things apart and seeing how they work, especially things that aren't running . The things i own I maintain so my stuff last me a very long time and I never get the chance to really rip into them. When I was younger I use to take apart brand new things just to see how they worked but I am wiser now after learning the hard way a few times..Its a great hobby..


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## dji (Feb 11, 2005)

I forgot to say the carb is a Walbro 332..Also this is the first walbro carb that i have worked on that has a 3/8" dia spring on top of the fuel diaphragm?


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## scrench (Dec 8, 2004)

nothing like the feeling you get when you get something running ... i also fix alot of things for people and dont charge . its just a good feeling you get when you help someone. my opinion walboro is the best carburator made , but i like tillotson too, pretty easy to get 75 to 100 bucks in something now days . thumbs up



that carburator has what i think they call a Needle Limiter Cap in it


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## bugman (Aug 12, 2004)

yep walbro is the best, last long and are easy to fix. and cheap


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## tgann (Apr 3, 2007)

*Ryobi 990r*

Can anyone take me from start to finish in adjusting the 990r carburator.
I recently rebuilt the carburator and replaced the primer bulb.
I adjusted the valves to .152 clearance as stated in the manual. I could get it to run for a short while and had it adjusted or I thought.

It just keeps falling on its face. tried to make adjustments and have just gotten lost on it.

I prime it and I have gass leaking somewhere now. Looks like from the low and High idle mixture screws. When I have it on level ground the primer bulb gets a lot of air in it where I have to tip it up to get a firm bulb, my line maybe to short.... plenty of gas in the tank. good compression.

Can you tell me the initial turns to set the low and High idle. I do not have the limiter caps on the screws so I do not know the initial setting for the screws. The 990r was given to me so I am not sure what happen to them. 
I am ready to sell this thing....


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