2 Cycle Engine Running Problems


Old 04-16-04, 09:26 AM
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Gas Trimmer cut off

My Ryobi 2 cycle gas trimmer model 725r is 4 year olds. New spark plug, cleaned the air filter, put in new gas & oil mixture, adjusted the idel speed screw several times and the engine cut off when the level was switched from B (Partial Choke Position) to C (Run Position).

Before I performed all of the above services, the gas trimmer is hard to start and will cut off at either B or C choke position.

Could you please provide advises on 1) how to keep the engine running, 2) adjusting the idle speed screw "when it was turned all the way in clockwise" to "the proper position" and 3) where is the carb?
Old 04-16-04, 09:47 AM
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OK. Your carb could need a good cleaning. To get to the carb, you must remove the air cleaner, then you can get to the carb. Now, here is something to let you in on. Those cheap trimmers only last about 50 hours or so. You said this thing is 4 years old. This may be the limit. However, clean your carb with Automotive Gumout Spray, and reinstall the carb and lets see what happens. If this thing still does not operate in the run position aftor you clean the inside of the carb really good, and you know for sure you are getting spark, and you have tried different adjustment settings, then you may have to give it up. Let us know how it goes.

My guess is that you either spent 90 or 150 for this trimmer right?
Old 04-16-04, 10:38 AM
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Where is the carb and how does it look like?

Is the "thing" where the idle speed screw and choke level (A,B,C) connected to is the carb?
Old 04-16-04, 10:53 AM
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Hello mnnhk5. Welcome to the Small Engine forum.

The carb is the part the air filter is attached to.

>Yes.< The part with the speed and carb adjustment screws and the choke is the carb.

Having to run the choke to keep the engine running is an indication the carb is fuel restricted internally. In this case the carb needs to be cleaned out.

Based on the information provided, the internal carb fuel ports and passages are plugged up. The problem description it appears to be a fuel related problem. Fuel not getting into the carb or flowing to the carb from the fuel tank.

B4 removing that card, try this.
Buy a can of carb cleaner at any auto parts store. Remove the two carb adjustment screws.

Insert the plastci tube that comes with the can of spray cleaner into the holes where you removed the two adjustment screws from. Blast with cleaner into those holes.

Also clear the center extension orifice and any other ports in this location. Use the plastic extension tube provided with a can of automotive carb cleaner.

Check and clear the air intake vent hole on top of the carb bodies upper half. The hole is extremely tiny but must be opened. It allows air to enter the carbs fuel bowl or diaphram area depending upon which type of carb it is. All carbs have one.

Use EYE PROTECTION during this procedure.

Another possible problem could be a restricted exhaust system and or muffler. Removal and internal cleaning is required.

There may not be a steady and or full volume flow of fuel into the carb. Remove the fuel line hose at the carb and allow fuel to flow out for about 1/2 to 1 minute.

The flow rate and volume must remain constant. If there is any slow down in the rate during this time, remove the fuel tanks cap and note any difference.

If the flow rate continues to remain slow or stops, there is a restriction in the tank, fuel line or the vent hole in the fuel cap is plugged and or restricted. Removal of the cap will allow full flow to return to full flow.

At this point in time, in my opinion, removing the carb to disassemble it is not needed. If you do remove the carb and are not totally familar with how it works or how to disassemble or reassemble it, avoid these mechanical repairs.

Another possibility is very low compression due to normal usage and engine wear over the years of usages. But for now, we will not deal with that aspect.

Check back on your question several times over the next few days for additional replies.

Small engine repair parts, generic repair manuals and additional help are all available at all local small engine repair shops and or lawn mower repair shops in your area. Shops and dealers are listed in the phone book directory.

Regards & Good Luck. Sharp Advice.
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Old 04-16-04, 04:53 PM
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Try this first!!!

You spoke of the "idle speed screw." I am not sure if you are familiar with ALL the adjustments on this carburetor, so, the idle speed screw is just that - it controls the engine RPM's at idle. The two screw you need to be concerned with are the High and Low mixture screws. They will have limiter caps on them. These are identifiable by a red and a white plastic cap over the two screws. They are generally on the right side of the carburetor (as viewed from the air filter). Take a small bladed screwdriver and turn these as far counterclockwise as they will go. This will richen the mixture. NOTE: They may already be open as far as they will go - don't force them - they only have about a quarter turn adjustability to them by design. Try this first before attempting a carb. rebuild. If you are not familiar with carburetors, especially small, two strokers, take Sharp's advice and have it professionally done. You should need only take the carburetor to the repair shop. Be sure, if you do this, to purchase a new carburetor mounting gasket. If you need to remove the carburetor for service, post back and we'll walk you through proper removal procedure.
Old 04-19-04, 12:04 PM
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I used the carb cleaner and cleaned the carb, pulled the two fuel lines and cleared the lines, and used a new gas cap. Now the top fuel line to the carb does not allow flow of gas (no gas go flow it).

Can the limiter caps for the high and low mixture screws be removed before I get to the two screws? I could not turn either the limiter caps over each screws.
Old 04-19-04, 01:56 PM
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You might have mixed up the two fuel lines. Try swapping them the other way. The one coming from the carburetor should be on the suction side of the primer. As for the limiter screw caps, you can either take a small flat blade screwdriver and pop them off or you can take some pliers and pull them off, that will expose the two small limiter screws. The one on the air filter side (the one that has the red cap) is the high speed screw. The other one is the low speed screw. To set the adjustment screws follow this procedure, set the idle adjusting screw so that the engine idles at a good slow speed but doesn't kill, then set the low speed screw so that the engine runs the smoothest at idle, then set the high speed screw when the engine is running wide open, when you turn it counterclockwise it will start to run rough (that means that the engine is running rich), then turn it back clockwise until the engine starts to run really smooth and fast (this means that the engine is running lean, but you can't keep it like this cause when an engine runs lean it is running hotter than normal and if left like this, the engine could overheat and sieze up), then turn the screw back counterclockwise just enough to where the engine is running just slightly rougher than it was when running lean, this will ensure that the engine isn't running to lean. Hope I explained it clear enough. Good luck!!!!!!

Last edited by mower17; 04-19-04 at 02:17 PM.
Old 04-26-04, 12:13 PM
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THANKS for all the advices.

I fixed my gas trimmer. There was not a steady full volume flow of fuel into the carb. I pulled the two fuel lines and cleared the lines, blasted carb cleaner into the two fuel holes on the carb, and used a new gas cap. Let the carb cleaner inside the carb dry out for 2 days.

Could you please let me know how to adjust the idle speed screw back to manufacturer’s specification?
Old 04-26-04, 01:36 PM
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Its very simple. All you have to do is start the engine, than let go of the trigger and turn your idle speed screw clockwise untill the engine revs at a steady RPM. If your engine dies right away aftor letting go of trigger, it don't matter, just adjust clockwise and restart engine. Do small incriment turns. Let us know how it goes.
Old 05-22-04, 12:12 PM
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2-cycle "ZEMA" carb - is mixture adjustable?

I have a Craftsman 2-cycle mini-tiller & cultivator model 316.29256 that now will only idle, and conks out when I open throttle. However it does run perfectly IF I hold the choke half way. I've read enough to know that this is a mixture problem - running lean I think. OK, I know that I should blast it with some carburetor cleaner, but here is my question:

This has a carburetor stamped "China" "ZEMA" . I see the idle screw, but no mixture adjustment. Looking towards the air intake, the carburetor has two plastic cams on the top left. One is red, and one is uncolored. They don't move with ordinary force. Do these have parts have anything to do with the mixture?
Old 05-23-04, 02:18 AM
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Yes they do.

Use some needlenose pliers and pull those red and white plastic caps off. They are stuck over the top of the adjustment screws. The screw closest to the air filter is the high speed screw, and you'll want to adjust that one. Unscrew it about 1/2 turn and see hoe it does. By doing this, you are compensating for another problem. Might just be wear on the engine causing a need for a little bit richer fuel ratio, which is not really a problem.

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