Carb issues 95 300 EXC

jeopardy98 · 07-26-2011, 02:40 PM

I have a new to me 95 300 EXC that fires up and idled pretty well when I bought it but overall it ran like crap. I am riding at pretty close to sea level in VA. The bike currently has a 45 pilot and a 180 main. It has a clean air filter and an fmf pipe and silencer.

When I took it out it fell on its face when giving it throttle from idle and then it would randomly kick in with serious authority. This was pretty scary since when it kicked in it would take off and often loft the front.

I took it home and tore it apart and realized a few things: 1. The airbox cover is missing and 2. the idle adjusting screw is missing the spring. I taped up the airbox cover except for about an inch across the back and I will get a spring for the idle.

I pulled the carb apart and made sure that the main and pilot were clean and then set the idle screw to 1.5 turns out as a starting point.

Once I got it all put back together and got it started I noticed a few more things. I could turn the idle screw all the way in and it would die but the idle adjusting screw seemed to make zero difference in idle. I screwed it all the way in and it idles okay. I know it should be idling very high at this point. I also noticed that the choke doesn't seem to make much difference in how it runs.

When I took it down the road it still ran pretty bad but seemed to be working some kinks out and started getting better. I took it through the woods and it seemed to start running better. It was more snappy on the throttle from idle and I could predictably loft the front with little effort.

About a minute later the bike went WOT all of a sudden and took off with me straight into a tree and continued to run at WOT. I ran up and checked the throttle and it was not stuck. Before I could pick it up it cut off and would not start back up for anything.

I pushed it home and now I am stuck as to where to begin with this.

Can anyone provide me with some suggestions as to how I can get this thing going? I'm pretty mechanically inclined but have never been really good at understanding how to jet the carbs based on the symptoms they produce.

Thanks in advance for any help. I'm going to post up in the classifieds and try and find an airbox cover and a spring for that carb.

PineyMountainRacing · 07-26-2011, 09:55 PM

Hope you weren't too far from home when you had to push. A lot of this sounds like air-fuel/carb, but you do have spark now, right?

jeopardy98 · 07-26-2011, 10:14 PM

Quote:

Originally Posted by PineyMountainRacing

Hope you weren't too far from home when you had to push. A lot of this sounds like air-fuel/carb, but you do have spark now, right?

About 3/4 of a mile but it wasn't flat and 95 degrees plus 80% humidity. It really sucked. I think a broke a rib when I went down too so that part didn't feel too good.

I think you are right about it being air/fuel/carb but I don't even know where to begin. I did realize that it probably wouldn't start again because it was out of fuel. This was after re-pulling the carb and re-checking all the jets. Put it back on and then realized the tank was bone dry. I'll try to start it again tomorrow but I still have no idea why it went WOT. I never even opened the throttle enough for the slide to hang so I know it wasn't that.

I am at a loss...

PineyMountainRacing · 07-27-2011, 05:42 AM

Ouch, didn't realize you got off when it surged. Too strange. Let us know if it fires after you fuel it up. It makes absolutely no sense to surge like that when you're at mid-throttle. Been a long time since I messed with any 2 strokes, but I'd keep looking at the carb.

Pushing is no fun in the heat. Awhile back when I was demo riding a 990 SM T I took it out for the afternoon in full leathers. I asked the salesman about fuel, he said he had just topped it off on the way to work. So I was headed back to the dealership after a couple hours and it started dying. Then it would restart. Each time I could go a couple tenths of a mile, and each time I could go a shorter distance before it died again. Probably happened 8-9 times, finally it wouldn't start and I was 1.4 miles from the dealer. Dealers phone was continuously busy so I started pushing. I swear it was all uphill, and just over a mile to the closest gas station. I was sweating - it's Florida after all. Put a gallon in it and rode the last .2 mile to the store. Turned out it did have fuel, but the valve between the left and right side of the tank was not fully open.

Anyway, let us know if you get it started today...

WoodsRiderParts · 07-27-2011, 10:33 AM

Let us know if that helped or not...

jeopardy98 · 07-27-2011, 10:41 AM

Well I put just enough fuel in it to fill the bowl and it fired right up and ran pretty good. The idle is a little high but it seemed fine. As soon as it pulled the last drops of fuel it went WOT again for about 5 seconds. Blipping the throttle made no difference except to make it rev even higher. Then it just cut off when it was out of fuel.

Why in the world would it rev like that when it runs out of fuel?

PineyMountainRacing · 07-27-2011, 10:56 AM

Quote:

Originally Posted by jeopardy98

Well I put just enough fuel in it to fill the bowl and it fired right up and ran pretty good. The idle is a little high but it seemed fine. As soon as it pulled the last drops of fuel it went WOT again for about 5 seconds. Blipping the throttle made no difference except to make it rev even higher. Then it just cut off when it was out of fuel.

Why in the world would it rev like that when it runs out of fuel?

I don't know if it's related, but on carbureted aircraft engines we shut them down by pulling out the mixture control to "idle cutoff" which basically shuts the fuel off, rather than by turning off the ignition (magneto). If the carb is set up correctly, you should see a 150-300 rpm rise on the tach just as the engine goes from full rich to lean to idle cut off and dies. Obviously, it is not enough of a rise for a long enough period of time to run you into a tree

. I know when I run the carbs dry on my bikes / quads / whatever if they are going to be stored for awhile, the rpm increases right before it dies. If you turn your bike off with the key, you won't see this. Makes me even more convinced the issue is carb related. I'll ask around...

jeopardy98 · 07-27-2011, 11:22 AM

I agree that it is definitely carb related. I got the idle cut way back now and when it does it, it is less severe but it is still enough to cause a problem if you ever run dry on the trail.

It seems to run pretty good otherwise with a dead spot at about 1/2 throttle in first or second. I assume that is jetting. It responds well off idle and once I get to just over 1/2 throttle she kicks in and roars.