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Discussion Starter · #1 ·
Hi Guys

I need some help. I have a 2000 300ex and it is sputtering/running rough whenever I hit water. I feel that it is a mixture issue.

I bought this quad a couple of months back. I have rebuild the top end because it was popping back into the airbox. I thought it had a bad valve or cam. I realized after I tore it down the pilot screw was all the way in. Too lean causing it to pop back. I rebuilt it anyway since I had it a part so it is now bone stock 40 over 300ex. Once I got it back together I tried to adjust the pilot screw. The book says to start out at 2.25 turns out and back it out until it sputters/idle drop and the turn it in until it sputters/idle drop and then put it in the middle. I have not been able to make it drop by backing it out. I bought new jets and the same thing. The stock slow is a #38. I have tried a #40 and a 45 and the same thing. Anyway I set it to 3 turns out using the 38 and it runs good once warmed up.

Here are some symtoms/ possible issues.
1 It will always start without the choke.(I never had a quad that would do that)
2. When it is cold it will sptter and spit a little. (NBD)
3. When I hit water it will sputter and spit. It will also sometimes die and not want to restart right away. If I put the choke on it will start right up.
4. The plug looks like it is running rich but I have never done a plug test on a low speed jet/mixture.

I also have replaced and checked all rubber boots on the carb. I have tried the carb cleaner/water test. All is good on that front. I don't think it is electrical because if I put the choke on it will start right up.


Any help would appreciated
 

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Welcome to the forums. Have you tried cleaning the carb? It does sound like it might be running rich. I think most of those 300EX's have to be choked, when cold, and they have to warm up for a few minutes or they will sputter.
 

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Thanks!!!

I have cleanded out the carb. I also put new jets and new pilot screw.
I'm not as familiar with the sport models as I am with the utility models, but Moose or Billy should be able to help you when they get on here.
 

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I know you said you cleaned the carb, but did you clean the passageways out in the carb body? A tiny piece of debris can clog those up and make it not run right. To me, it sounds like you have some debris still in the carb somewhere, but I could be wrong.

If you ride through a lot of water, I would put dielectric grease on all the plugs and connections and also around the spark plug boot. It's a good ideal to do that, anyway, even if you don't go through a lot of water. It'll help prevent problems at the wiring connections in the future.
 

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Discussion Starter · #6 ·
Thanks for the tips. I do have grease on all of the electrical. What I fid confusing is that after I hit the water it behaves as if it is lean. When I start it cold without he choke is a sign of being rich. If I run at half or full throttle after hitting the water it is fine. On the pilot circuit it sputters until it warms up again.

Thanks again
 

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Sounds lean to me.It shouldn't spit much if it's rich.Did you put a new main jet in?And what number was it.Some used a 118 and some a 122.
 

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Discussion Starter · #8 ·
Hey Billy

It is a 122. It always runs great past 1/4 throttle. It always idles well if it is running. It runs rough from idle to 1/4 throttle when it is cold and when I go in water. I think the water is cooling it back to a cold state because it behaves the same as when I cold start it. It sounds like maybe I am lean on the pilot circuit.

I have cleaned the carb and I am running a 38 pilot. I started at 2.5 turns out and turned it in. It started popping back into the airbox at 1.25 turns out or so and the idle got slower. I backed it out and the idle increase up until about 2.25. After 2.25 turns I could not notice a difference. I went all the way out to 4 turns. Throttle response did not change past 2.25 and it never ran bad. My understanding is that I should be able to adjust the pilot to a point where it is so rich it will not run. Do you know if that is true? I tries it with a 40 and a 45 too and could never get it to a full rich condition.


It also pops a little out the exhaust on decel when it is cold.
Can I do a plug test on the pilot circuit by putting a new plug in and just let it until until it warms up?


I am lost at this point. I would think it would will be pig rich with a 45 pilot on a basically stock machine. (all stock except 40 over bore.

Thanks again for all the help
 

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The way you are describing it now, it does sound lean. Usually when you have to turn your pilot screw out as much as 4 turns, then you need to go up on your pilot jet. I believe you said you already tried that, though, but that's the reason why I asked if you had cleaned the passageways in the carb body. It sounds like there might be some debris still in the pilot circuit. When you turn your pilot screw out to a certain point, it should stumble.
 

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Discussion Starter · #10 ·
OK

I will try that. What do you suggest? Carb cleaner in that little passage way that the pilot screw plugs up when it is all the way in? It does sound like the pilot circuit is lean but one thing does not make sense. I can start it all day long without the choke when it is cold. Isn't that a symptom of being rich?

Thanks again for all of your help guys
 

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OK

I will try that. What do you suggest? Carb cleaner in that little passage way that the pilot screw plugs up when it is all the way in? It does sound like the pilot circuit is lean but one thing does not make sense. I can start it all day long without the choke when it is cold. Isn't that a symptom of being rich?

Thanks again for all of your help guys
Yeah, that doesn't really make sense to me, either, but I would clean it anyway and see what happens. Take the pilot screw all the way out and try to blow air throw the passageways.
 

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Alright I have an idea.Did you change the needle setting any.Because anything different from stock they will spit and sputter from idle to 1/4 throttle.It should have the the c clip in the middle notch of the needle.Good luck buddy.
 

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Alright I have an idea.Did you change the needle setting any.Because anything different from stock they will spit and sputter from idle to 1/4 throttle.It should have the the c clip in the middle notch of the needle.Good luck buddy.
i was gonna ask that same thing billy..that..and did he by any chance loose the tiny o-ring that seats in the pilot needle jet hole ?.
 

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On the pilot screw is an o-ring if it has any nicks or cuts in it you won't see any change in the way it runs. with no internal mods i wouldn't run anything more than a stock slow jet and step up to a 130 main if you changed the needle setting change it back to the middle clip setting. Also if the clip is bent in any way you will get the sputter you speak of. the popping back could be an exhaust leak when you drop the throttle and it backfires check your exhaust for cracks and check the header bolts. the pilot setting is 2 1/2 turns from seat. if you install the new main back out the pilot screw 1/2 turn and reset the Idle.

But first and foremost as Helmut stated you do need to clean the carb real good. a can of carb cleaner and compressed air will do that. make sure you remove any o rings the carb cleaner will destroy them. Good Luck
 

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Discussion Starter · #15 ·
Thanks for the input guys. The e clip is in the middle position like stock and I have the washer and o ring on the pilot screw. This is a crazy problem. I also replaces the all the o rings, pilot screw and jets in the carb.

It runs great after it warms up and it would be a non issue if it didn't misbehave after cooling down from the water. I am almost poitive it has to be the mixture. Today I hit this mud pit/puddle. It had to be 100 yards long. I went through it hard. I was probally 1/2 throttle. It was running great. No issues. I then stopped to wait for my buddy. It idled fine but when I started again it started sputtering. If I could baby it up to 1/4 throttle it would wake up and be fine and once the engine got hot again idle to 1/4 was fine too. I know the jet is clean but not sure about the circuit passages. I will try to blow these out. I should be able to back out that pilot screw and make the engine too rich right? What are the symptoms to look for? Could I be too rich right now? The book says to start at 2.25 and I am at 3 turns. How many turns are you guys out?


Thnaks again
 

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Discussion Starter · #16 ·
Hi Guys

I took the carb apart this morning. I cleaned it out real good. I blew out the pilot circuit and it seems clear. I notice the little washer between the spring and the o-ring was bent on the pilot screw. I replaced it with the original one prior to the carb rebuild.


I put the pilot screw at 2.5 turns out. It has the 38 slow jet in it. I needed the choke to start which was a change. I ran it for a couple of minutes and it still wasn't very smooth from idle to 1/4. I warmed it up more and it ran smooth. It has to be really hot to run OK. I then raise the throttle screw a little and tried to adjust the mixture. I turned the screw in a 1/4 turn (2.25 turns) and the idle dropped and started popping(too lean) I then backed out the screw to almost 3.5 turns and it was no difference from 2.5 turns. Have you 300ex guys gotten your machines to run too rich on the pilot circuit? How does it behave? I am looking for poor throttle response.

I put a new plug in it and just let it idle. I pulled the plug and it is black as if it is rich. I ma not sure if you can do a plug test on the pilot circuit like that. I am so confused on this.

Thanks
 

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Discussion Starter · #17 ·
Hey Guys

Update. I think I have it. I took the carb apart again and compared the pilot screw from the original one that I replaced when I rebuilt the carb. It had a slightly different taper. I put the original one back in and now it reacts when I turn the screw out.


Thanks for all the advise. I appreciate it.
 

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Glad you got it.
 

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Glad to hear you have figured it out! I was really interested in hearing what was causing it! But I like when new problems are figured out on here so I can learn.
 

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Yeah, glad you figured it out.
 
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