Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I have a strange problem with my Honda GX390, 13HP engine.  I replaced the carb. with a working one it did not help.  The engine seems to run fine in low RPM.  Once I open the throttle it dies.  No problem to restart.  Maybe there is an air leak but I can't figure it out where can it happen other than the carb.  The gasket between the carb. and engine is in good condition.  What else can I try?

Thanks

Bob

Sounds like you might have two dirty carbs.  Unless the new carb was on an engine that was running fine just before you did the swap.
What you're describing   "It runs pretty smooth in low RMP, not  just in idle position.  I can increase the RMP slightly without any problem.  I think I ran it slightly chocked (full chock to start) in low RMP. Once I open throttle fully It dies.  Sounds like it's starving for fuel, clogged main jet, stuck float etc.  You might also pull apart the fuel shut off valve on the carb.  Sometimes you can get a
restriction in the fuel flow through the valve because the thick rubber gasket starts to come a part.  It's got holes in it that let fuel pass when the handle/arm is in the open position.  You just take out the two screws on top of the valve holding down the plate.  But watch it there is a spring in there.   The part is just below part number #26 in the diagram I guess it's part number 29   .          Honda parts

The carb, I replaced came from my working pressure washer,  It works fine before I removed it and works fine after I put it back.  It has to be something else.

I will check the valve and spark plug tonight.

Check that the gas tanks cap is venting.  I once placed the plastic cap on the hot muffler, it melted the vent hole closed, and produced exactly the same problem you describe.   A clogged fuel filter will do the same thing.

If the air can't get into the gas tank fast enough the gas won't be coming out of the gas tank. 

Does it just cut out or chug a little before stalling??...if u had a inline spark tester u could hook it up and make sure your not loosing spark when it stalls...given that its not likely a carb issue its most likely a spark problem..u could disconnect the kill switch and the low oil switch see if it still stalls.. a spark tester would be of help...u could put a new spark plug just to rule that out.

niper99 wrote:

I came in from garage and saw this post.  It is exactly what happened.  I discounted the oil level switch and the engine ran great,   Do you think it is the oil alert diode or the switch.  I honest don't know what does the diode do.  I connected an ome meter from the switch to the ground.  It showed open in low RPM and jumped around when I increased the throttle. Looking at the ebay the part costs around $20.  I am glad I got this problem solved. 

I'm glad you made some headway on figuring it out. First things first, the oil level is OK, correct?

I had a Generac engine with a low-oil switch that had failed. It would start, run 5-10 seconds until the control board enabled the low-oil shutoff, then it would die as the control board killed the ignition. I took the switch off and found that the switch would electrically open/close (I think to ground; it only had 1 wire) if you pushed  inside the switch with a screwdriver. So the switch was free to move, etc. But it would not detect oil pressure, you had to actually push on it with something solid to make it register "pressure". I had a few guesses as to why, but never tried to cut it open. Replaced the bad switch, and it's run fine since.

But I'm admittedly unsure of why your switch would see *lower* pressure as you raise the throttle. I'm assuming that the oil level isn't low, and that the engine is on a level surface. If it has an oil filter, could you try replacing that? Maybe there's some kind of restriction in it? I'm sure someone with more experience can help shed some light on this. But I might not just leap to replacing the switch, based on the symptoms. Unless someone can explain why the switch would perceive lower pressure at high throttle, when I'd assume it should be higher.

The GX390 just has a standard oil slinger type lubrication.  It's not a pressure system.  As the rpm increases so does the agitation of the oil in the crankcase.  If the level is low it can
cause the switch to activate. Had the same thing happen on my Honda powered generator one time.  If the crankcase is showing full.  Try bypassing the little metal box the crankcase switch plugs into.
Or you can disconnect the switch all together and just check the oil every once in a while the way it was done for decades.

I don't have an oil filter.  The oil level is not all the way to the dip stick hole but it registers enough on the dip stick.  I will fill it all the way tonight and see if that makes any difference.

I have a generator uses Tecumseh 10HP engine.  The oil level switch has an intermittent problem also.  It shuts off after running for a few minutes when the oil gets hot.  I took it out and it looked exactly like my aquarium water level sensor.   It senses the level not the oil pressure.  I ran the generator with the oil level switch disconnected.   The Honda switch is only $6 here.  Pretty cheap.  http://www.smallengineequipmentparts.com/brand/16131/272/277 . The Walbro carb kit is so much cheaper too comparing to my local shop.  I will buy parts from them in the future.

jrtrebor, thanks for the clarification. For whatever reason, I was assuming this was a pressurized oil setup. For clarity, my Generac engine *is* a pressurized setup, has an oil filter, etc. So I was dealing with a different type of switch. Sorry for the confusion.

bcjm, double check the manual before you go adding a lot of oil. If it has a dipstick with markings, then go by that, of course. But different engines get filled to different points. My Generac has no dipstick, and gets filled until it's about to run out of the oil fill location. But other engines are very different (if I filled my Tecumseh until it came out the fill hole, I would have a very big problem on my hands). Too much oil can be Very Bad, just like too little. I'd just hate to hear of something happening to the engine due to accidentally overfilling it "all the way".

I believe Honda engines oil level suppose to filled all the way up.   I will double check.