[Bombadoo]

Ok, so I am about ready to drag my 1990 f300 ourtrax out in the back yard and let mother nature take over.
The bike is running very poorly. VERY poorly! Black smoke and sputtering like crazy at all rpms. I installed new rings (a buddy said he really doesnt think that was the problem, but i done it any way. he was right). I cleaned the carburetor first time around. Second time, following as many you tube videos as i could find, I installed a carb kit and cleaned like crazy. Still exactly the same.
I tried new plugs before all of this obviously. The black smoke seems to indicate too much gas? So I am wondering could it be electrical in nature? A bad coil...cdi? Its almost like its firing every second time? It misses at idle and at every rpm above it consistently.
This bike is pretty much retired now, and is going to left at the cabin for a back up machine, but i just dont want it to die.....many memories.

 

[fishfiles]

The first question usually goes , OEM carb or Chinese carb!

I would ask , choke plunger and cable , are they the correct ones for a 90 ? short plunger is a 90 or an OEM replacement longer plunger with an adaptor at the carb

is the diaphragm split or have a hole in it ?

is the tank , petcock and carb really clean , with good fuel ?

did you set the timing right of the cam when you done the upper ?

where you at , how much you want for it ?????

 

[Bombadoo]

Original carb. I did change the choke needle with the larger nut adapter. (It was the second thing I tried after the spark plug. Forgot to mention it)
The large rubber diaphragm looks ok but I did not check it throughly.
The gas is not old and flows fine. Too well I think.
Pretty sure and confident I got the timing correct. Runs the same as before I did the rings tho.
I did change the muffler out to a tractor muffler. Original was rusted out and it was a temporary thing until I get it welded up and back on. Bike ran good for the longest while and slowly got worse and worse. I know it’s free flowing exhaust but would not think it would cause it to run so bad??

 

[fishfiles]

something else that will make it run bad , the boot between the carb and the head leaking from a split , hole or loose clamp , can be checked by spraying starting fluid around the boot , if the idle jumps up then you have a leak

did you do a compression test , you could be fighting a losing battle

 

[alloutdoors]

I would not give up on the unit. The issue is likely fuel/air and confident here we can get it resolved.

 

[Carolynskii]

Is there any gas leaking out of the bottom off the carb? Also pull the oil dipstick and see if it smells at all like gas.
My guess is that fuel is in the oil causing the smoking which is easily fixed by changing the oil then buying a new carb to stop it from happening again.

Its usually the brass seat in the carb body that the float valve sits in that causes it not to shut fuel off like it's suppose to which means you'll need to buy a new carb because the brass seat can't be replaced.
But the fuel gets in the engine/oil because the little overflow pipe in the bowl is clogged.

 

[Off_Road_Al]

I agree with gas in the oil. I’d change the oil and try a new carb. Also worth mentioning I’ve had the choke butterfly come off inside a carb before. No amount of adjustments can fix that. Might be worth checking your choke is working correctly and in the correct position

 

[fishfiles]

Also worth mentioning I’ve had the choke butterfly come off inside a carb before. No amount of adjustments can fix that. Might be worth checking your choke is working correctly and in the correct position

Al , a 300 carb doesn't have choke butterfly , choking is achieved by the enrichment valve

 

[alloutdoors]

As fishfiles suggested, a compression test would be worth it to verify where you stand with the unit. Given the age, memories and "need to be a backup", I would just get a genuine Honda OEM new carburetor for the unit. Before installing, I would verify the compression and then completely clean the fuel system (especially the tank) and replace all fuel lines. The lines/boots, etc., where produced well before ethanol fuels and ethanol can eat away at linings, so I would just upgrade the lines...

 

[Goober]

Check compression. If you’re absolutely sure the top end is tight then you might suspect carb.

You changed a couple things I didn’t quite understand. Choke needle, larger nut??
Change it back I’d say.

Will it start with choke off?
Is your plug fouled? That would cause the stumbling you mentioned.

Then I think your starter valve is not seating and the enrichment feature is always enabled (choke on).

 

[Bombadoo]

The starter enrichment valve was replaced. That was one of the first things I tried (came with the larger spacer nut). It’s what the bike sounds like running. Like the choke (enrichment) is always on. I was suspicious of it cause the bike always started right up, even cold.
I have a new second bike coming for the “family”, so this one is strictly a third, hardly ever used unit. But I still like to have it running. I

 

[misterclean59]

Turn the fuel off while running in neutral. If it runs better as it starts to run out of gas then it is running rich. Many have good suggestions here. If you have changed the oil, made sure the enrichment valve is not stuck and you have run it with the air filter and it's cover off then the needle jet and jet/needle may be worn out. I don't know if the needle jet is replaceable or not. If not replace the carb with a good used one or new OEM. Chinese knock offs are not recommended by many here who have tried and failed. Some got lucky and it worked tho

 

[JohnnySolo]

Take diaphragm off, give the rubber a slight pull to see if it's torn anywhere.
Take float bowl off, pull float up and turn petcock on. If gas flows out still then you got a worn seat and need new carb.
Check the throttle needle, be sure it's seated in. If you can take picture of inside carb through air intake and show us.
CHECK OIL!! RUN COMPRESSION TEST! That needs to be done.
What does air filter look like? When taking it off to look at throttle take picture for us.

Get back with the results when you can. You can fix it!