Newbie looking for help with Honda GX240 that won't run

[PDX Man]

My tuppence worth,

Do you leave the fuel tap on while not in use, ? What I'm about to say, can happen quicker if the tap is left on while not inuse, but can also happen but slower if the fuel tap is switched off after use.
The old carb, have you taken the bowl off, ?? If you have/haven't what does the inside look like? The reason is because when fuel sits around and evapourates, it leaves a varnish like substance. This. Can be cleaned off with a green scrubby thing. This varnish does flake off and can block the main jet, or in your case partly block it, and by using the choke. You richen the mixture and it will start but opening the throttle the air flow increases but the fuel does not.

So get a flat head screw driver and take out the jet and make sure it's clean you can use a thin bit of wire to poke out any crud or a blast of air but the wire is what I've used before.
As for you new carb, I don't think it's set up properly

I hope this helps
If you'd need help in locating the main jet. ask, but you should be able to see it in the manual

Ps I've fixed a few engines with this problem of a blocked jet

Thanks for the info. I have to admit, I usually don't turn off the fuel flow. I'll have to start doing that. The bowl has signs of corrosion, but I don't see any varnish or flaking. I'll try cleaning the bowl anyway and the main jet.

 

[Fish]

 

[bill saf]

sorry that I did not reply sooner but was out of town. Ok so you have good flow of gas! so the screen in the gas tank is ok. Yes you clean the mags only in fly wheel and the bottom of the legs on the coil and where the coil bolts to the engine. when you reinstall the coil us a business card to set air gap. set business card over mags under coil legs and bolt down coil. the sliver box for the oil alert is just behind your kill switch if the electrical components are starting to go bad inside when they start to heat up not by the engine temp but from electrical power they will short out and kill the spark if the box is ok then I would look for a pinched or rubed wire form the switch to coil. or you could have a coil going bad that is it for the electrical . did you down load the pdf file I posted?
Its the shop repair man for that engine it will give you all of the specs on that engine and info on Troubleshooting. the man is 218 pages long right from honda.



this shows the insulator behind the carb it has two gaskets that insulator can crack and will cause stalling when you hit the gas.

 

[woodtool89]

I installed a Chinese replacement carb for my neighbors gx390 generator, I could never get it to run right, he bought it because the bowl on the original was pitted bad and had a pin hole, I ended up cleaning the original one and just taking the bowl off the replacement to put on the original carb then trashed the rest of that junk carb...they look similar on the outside but the internals and bore sizes were way different...
id try to clean the old carb and see if that works

 

[chipper1]

Pretty sure it ain't the valves, if I'm wrong, I'll eat crow I guess.
Go with the KISS system before tearing into the inside of the engine.

I pulled the fan shroud and there is definitely rust. Where, though would rust be a problem? Just on the magnet? Or on the whole flywheel outer rim? Here are pictures of what I have:
View attachment 77032 View attachment 77033 View attachment 77034

This looks like it could be a part of the problem, but I'm not convinced it's all of it.
Pull the muffler and check for anything plugging it.
Being a Honda, even an older one it should still start on the second pull in those circumstances, if not there is a problem.
Squirt a little starting fluid directly into the carb with the air filter off with the choke open, then close the choke, if it fires first pull you problem is still in the carb area.
Hope this helps,
Brett

 

[Fish]

Valve adjustment is simple and routine Maintenence.
Takes about 5 minutes or so, and costs nothing. I think that a peek at the valve train is needed, rust on a flywheel is not anything to worry about. Now rusty coil laminations, not allowing a good ground, yes, that could be a problem.

 

[Fish]

Watched the movies again, am more convinced that your trouble is valve related, after you finally get it started, it soon dies and will not restart, and looks like it has little or no compression.

 

[PDX Man]

...

this shows the insulator behind the carb it has two gaskets that insulator can crack and will cause stalling when you hit the gas.

Thank you for your help. I did finally get the insulator off and the gasket was brittle and broke apart. So I guess that could have been the problem. The gaskets that came with the new carb are cardboard and I don't have a lot of confidence in them. Anyone have a source for a good set of gaskets for this carb?

I did put on the new insulator and the new carb and the behavior is pretty much the same as before.

I did clean the ignition coil and magnet and set the gap. I also checked the resistance of the coil. It was hard to get a measurement on the primary - the reading would jump around a bit, but I think it was close to the .8 ohm spec. Sometimes it read .8, sometimes 1.2 ohms. The secondary was about 17 K ohms, which is more than double the spec of 5.9 to 7.1 K ohms. DO I need a new coil?

 

[PDX Man]

Watched the movies again, am more convinced that your trouble is valve related, after you finally get it started, it soon dies and will not restart, and looks like it has little or no compression.

Sorry for the delay, I wasn't ignoring your post about the valves, I had already pulled the ignition coil and wanted to get it put back together. Thanks for all the info. I will check the valves next and report back.

 

[bill saf]

The gaskets that came with the new carb are cardboard and I don't have a lot of confidence in them. Anyone have a source for a good set of gaskets for this carb?


I cut my gaskets just go to the auto parts store and get a roll of .020 gasket paper its like $12.00 and you can cut all you need and I run the old gaskets over a flat scanner and use a glue stick to hold the copy till Im done cutting the gasket then remove the copy and install.


I did put on the new insulator and the new carb and the behavior is pretty much the same as before.

I did clean the ignition coil and magnet and set the gap. I also checked the resistance of the coil. It was hard to get a measurement on the primary - the reading would jump around a bit, but I think it was close to the .8 ohm spec. Sometimes it read .8, sometimes 1.2 ohms. The secondary was about 17 K ohms, which is more than double the spec of 5.9 to 7.1 K ohms. DO I need a new coil?

how di you check the coil with the spark plug cap on or off? if on it is a false reading you have to check coil with no spark plug cap. the cap has specs to 7.5-12.5 anything out side of the its bad. if you did the coil with out the cap and got your readings of 17K then is bad any thing out side of the spec's is junk!

 

[PDX Man]

Watched the movies again, am more convinced that your trouble is valve related, after you finally get it started, it soon dies and will not restart, and looks like it has little or no compression.

Take off your valve cover, and the spark plug out. Find TDC and snap a pic.

I am guessing that one of your valves has little or no clearance.
...

Here is a pic:


Both the valve clearances seem like they are a bit more than the spec or right at the edge of the tolerance. I don't have an angle feeler gauge, so I was having a hard time getting the straight blades in, so I'm not 100% sure of this, but:

Intake spec is .006" +-.001
The .006 and the .007 blades went in easily. The .008 went in, but felt tight.

Exhaust spec is .008" +-.001
The .008 and .009 blades went in easily. The .010 went in, but felt tight.

 

[PDX Man]

Pretty sure it ain't the valves, if I'm wrong, I'll eat crow I guess.
Go with the KISS system before tearing into the inside of the engine.

This looks like it could be a part of the problem, but I'm not convinced it's all of it.
Pull the muffler and check for anything plugging it.
Being a Honda, even an older one it should still start on the second pull in those circumstances, if not there is a problem.
Squirt a little starting fluid directly into the carb with the air filter off with the choke open, then close the choke, if it fires first pull you problem is still in the carb area.
Hope this helps,
Brett

Is the muffler really likely to be the problem? I am reluctant to touch it because exhaust parts get so hot, they get corroded and everything gets stuck together and I might break something while removing it.

 

[PDX Man]

how di you check the coil with the spark plug cap on or off? if on it is a false reading you have to check coil with no spark plug cap. the cap has specs to 7.5-12.5 anything out side of the its bad. if you did the coil with out the cap and got your readings of 17K then is bad any thing out side of the spec's is junk!

I checked with the spark plug cap on - I didn't know it came off. I looked at several youtube videos and they measured from the core to the inside of the spark plug cap.

 

[woodtool89]

running only when the choked is closed and stalling when opened has absolutely nothing to do with spark...
my guess is old carb needed a cleaning/rebuild, and the new carb is either jetted wrong for that engine or like I said before, its just junk...

 

[Fish]

How does the compression feel by hand? Pull the rope and watch with the valve cover off. Go ahead and try to start, and watch for compression leaking, also watch the movement of the rocker arms, etc..

 

[chipper1]

Is the muffler really likely to be the problem? I am reluctant to touch it because exhaust parts get so hot, they get corroded and everything gets stuck together and I might break something while removing it.

No, the muffler is not likely to be the problem(but bees/mud dabbers have been known to build nest in them and then they will have similar problems), neither are the valves or compression in my opinion.
I still think you have a fuel problem as woodtool is saying. I've bought hundreds of honda products not running properly and very few ever needed much more than a good carb cleaning and to be run.
I'm far from an expert on repairing the internals, but the reason I buy and sell honda products is because you rarely need to work on the internals of them.
Did you pull the air filter and spray starting fluid in the cab with the choke open, and then close the choke and give it a pull, do that and then post, that will be very telling as if it starts right up you have a fuel problem.
Start with the simple stuff.

 

[bill saf]

what I see here are 3 things / #1 hard starting, #2 stalling, #3 dying on its own. and all 3 can be a cause of the coil for one reason or another. #2 weak spark, spark timing, bad ground,# 3 spark plug going bad, spark plug cap going bad, coil going bad. all of this will have the same symtoms of gas starvation to a point and not always so you just cant rule them out. now add in the wire going to the kill switch ( dying on its own ) is it grounding out?? is the switch bad?? is the coil bad??

just my .02 worth

 

[woodtool89]

what I see here are 3 things / #1 hard starting, #2 stalling, #3 dying on its own. and all 3 can be a cause of the coil for one reason or another. #2 weak spark, spark timing, bad ground,# 3 spark plug going bad, spark plug cap going bad, coil going bad. all of this will have the same symtoms of gas starvation to a point and not always so you just cant rule them out. now add in the wire going to the kill switch ( dying on its own ) is it grounding out?? is the switch bad?? is the coil bad??

just my .02 worth

spark/coil automatically gets ruled out when the engine will only run with the throttle and chock in a certain position, and then immediately stalls when either throttle or chock position is changed (fist video)
the second video is with a aftermarket carb that hasn't been tuned (straight out of the box) so you cant really use that for any type of diagnosis of the initial problem.
its 100% a carb issue...

 

[woodtool89]

also the valves being a couple thou out of adjustment may make it sound a tiny bit rough when running, but it wouldn't keep it from running.
clean that old carb up set mixtures screws to ~1.5 turns out and throw it back on, I bet it starts right up...

 

[Wonkydonkey]

Another way, to find out if it's a fuel starvation problem, (as I said before could be semi blocked jet) is to get some fuel in a spray/mister bottle and start the engine and while it's running spray some fuel into the air intake (no air filter) and open the throttle bit by bit while spraying fuel into the air intatake. If it revs up each and every time you spray and then starts to die once fuel has been used.

Then it's fuel starvation, and you have to trace backwards or forwards, ie from air Venturi fuel mix, or from the tank to the carb

The way I check fuel starvation is to open throttle whilst restricting the air intake, but it's tricky to get the right amount of air to fuel ratio and it dies quick if to much air gets in.

Anyhow, I'm sure everyone will want to know what the cause was/is and that what solved it
Cheers