Troubleshooting a Honda Engine

A bandsaw owner asks for help with getting his motor running right. April 30, 2009

My Honda gx-620 presented this problem after sitting idle for two weeks. I started sawing last week again and I smelled rich gas. The carburetor was dripping gas onto the engine case from underneath. Of course the engine was running rich except at 1/2 to full throttle. I took the carburetor apart to find minimal residue in the float system and the needle flow plunger looked in new condition (rubber tip had no damage or ring marks and it's spring seemed fine). I am baffled by now since I couldn't find a single carburetor problem (engine is four years old). Recently I sawed a little SYP and there were no gas drips but now it doesn't want to idle and stalled when I returned the throttle back, so I ran a very small amount of choke and all worked ok. All my jet holes were very clean and no obstructions were seen anywhere. Temp at saw time was 40 deg. Any clues would help.

Forum Responses
(Sawing and Drying Forum)
From contributor D:
The stuff that is called gas today, doesn't store very well. Two months is about max it seems. I suspect a dose of carburetor cleaner will put your Honda back to its old self.

From contributor T:
I only use premium fuel in my Woodmizer LT40hdg. It runs cooler, with less wear and cleaner. Less dirt or deposits also. I think in the long run it will be worth the extra change that it costs.

From contributor K:
Check to see if the float has a pinhole leak. I had this happen on a Honda, and the float filled, sank and ran the engine rich.

From contributor M:
I have used this type of engine on fire pumps in the summer. I usually start by cleaning the air filter and checking the spark plugs. I then move on to the fuel to make sure it is clean and fresh. There are return lines and even vacuum lines on some of the new small engines (makes me wish for the old Briggs or Wajax with their deafening noise and simplicity). After checking all of the above I would move on to adjusting the low speed jet. The best advice I ever got from a mechanic was to start with the simple stuff no matter how obvious and always replace the cheapest part first.

Another thought is you might have got a shot of water with your gas. Try Isoproponal alcohol, it will bond with any water in your system and carry it through. Methyl hydrate will keep water from freezing but will not move it through the system (it also wipes the oil of the crank bearings in a two stroke motor).

From contributor O:
Sorry not to be able to connect this advice to your symptoms, but I agree strongly also with checking simple things like trying a new spark plug if you haven't, and carefully inspecting everywhere for possibility of a mouse mansion and chewed hoses or wires. Quite a surprise sometimes when one removes a filter or housing cover. Have had both plug and nest problems happen to Honda GX340 engines kept outside.

From contributor R:
I have been given the advice of only using premium gas in small engines. The up to 10% ethanol found in regular grade gas can attack seals and other components in small engines. Premium gas does not contain ethanol.

From contributor N:
It must have had a piece of debris hung up in the needle to start with, sometime a little tap on the carburetor will dislodge it and you won't have to take it apart. As far as not idling, did you get the gasket in right and the bolts tight? It sound like it might be getting too much air if you have to choke it at idle or the idle circuit is plugged in the carburetor. Sometimes you can take the idle mixture screw all the way out and give it a shot of compressed air and it will work again. Did you change the idle adjusting screw when you had the carburetor apart, maybe turning it out a tad might help.

From the original questioner:
All good points of interest for me to re-check. I just added about two gallons of fresh regular gas (this is all I have ever used from day one with very little issues). I add gas Stabilizer to all my stored fuels for keeping it fresh as possible. I will go and look for H2O in the tank too. The air filter is almost new and I cleaned that compartment well with compressed air before installation. Considering the run conditions it wasn't that dirty, maybe because I've added (six months back) a second thin pre-filter covering to catch the very fine wood dusts. There are no mix screws like air or high/low speed on this Honda carburetor (new EPA rules probably) only an idle screw that works off the throttle stop distance which I turned up 1/4 turn to see if a little faster idle would help the stall factor. There is a funny small screw at the very top of the carburetor intake side that has a restrictive movement of say 1/8" sort like an on or off but I have no idea what it does with this amount of small of movement.

I checked the float (plastic) and it had no gas in it. The intake flange gaskets (two green ones) were in new condition (only took the carburetor side one off) and the two long intake bolts were tightened firm. On other engines I have sprayed ether around intakes to see if the engine revs up and then I know there is a gasket leak. I did find some fuel gunk on the float bowl and the electric solenoid plunger shut off and I wiped it clean with gunk choke cleaner. When the power switch is off this plunger kills the gas flow into the main jet system off the float bowl and the engine stops in three seconds. I don't have a tester for the fuel pump but I could unplug it and use a jar to collect flow and if it squirts well all is well. I'll go back and re-check the easy stuff and pull the plugs and clean them (didn't do this clean then but did do it three months back). I may also pick the brain of my Honda dealer I got the engine from to see if he can give me a tip. Thanks for helping me brainstorm this problem.

From contributor M:
Don't be to worried about using regular gas. In my hill climbing snowmobile that is all I use. Most gas stations don't sell a lot of premium so they only fill their tank 1/2 full. The resulting air space in the tank is where the water condenses. I use regular and add octane boost or blend in 120-race fuel. Trust me you don't want to get a drop of water into an engine going 9000 RPM at 10,000 feet above sea level. The other point for regular fuel is it is fresher; they sell more so it's not sitting in their tanks for two months.

Quick question - when you clean your spark plugs do you check the gap? One other note, that little bit of green slime you might have found in you float bowl is a type of bacteria that lives in the fuel. When you shut down for a couple of days turn off the fuel at the tank and let the engine use up the remaining fuel in the carburetor. This will prevent the green goop and make life better when starting again.

From the original questioner:
This small amount of residue was the golden brown type and it only adhered to the shut off needle tip and a very small amount was on the float bowl insides which the gunk cleaner worked easy to remove it all. I soaked and blew/examined brass jets out too (low and high speed ran fine and had good power).There was nothing in the carburetor like I've seen in many old engine carburetors I've torn into. I've seen the fuel tar/brown looking varnish so thick and dried you would of thought someone was mixing wood varnish into the fuel.

You are right contributor M, don't let fuel sit in a float bowl for any length of time even with stabilizer mixed in the fuel. Two cycle fuel is even worse for setting up like glue over time. Diesel can grow stuff too so diesel users watch out for this growth. I am going to check the plugs and clean them and re-check their gap. I will also check for water in the tank (anything is possible), check fuel filter and pump action, all gaskets, bolt snugness, and maybe adjust that idle screw up some more.

From contributor O:
One problem I had was with a GX340 engine running well for several minutes (longer at idle, shorter at top speed) then dying suddenly. Spark plug seemed clean and fine but finally when I replaced it with a new one it fixed the problem. This is after probably seven hours of work and several weeks of misery.