I have a 1999 400 4x4 scrambler 2 stroke. It has V-force reeds, and a Hot Seat Gen 2 header pipe on it with the stock muffler. I am currently running a 250 jet in the carb and have no low end or high end power with the bike, I have to blip the throttle until the power seems to build. I can only run at about 1/2 throttle once I can feel the engine make power. The plugs are coming out black after I ride it for a little while. I am running the NGK BR8ES plugs which Hot Seat recommends. With this set up I am supposed to be running lean, but obviously am not due to the black plugs. The carb is clean, with no build up in it and I pulled the two drain plugs in the muffler last weekend and it is clear of any debris. It ran good last summer, then about 1/2 way through it started doing the same thing, so we played with jets and the aif/fuel ****, it would run good for one time, nice power and all, then the next time I rode it would be the same as before. What are my next moves so I can get my bike running like it is supposed to be? Any help would be appreciated.

Thanks,

Kyle

 

Yep, check your choke and make sure it is adjusted correctly and then check the oil pump and make sure it is adjusted correctly. Is the air filter clean/new? You may also want to check compression. Do you have the dtock piston? They are famous for breaking skirts and that can cause a slew of problems. Also on the carb, check the float level and needle valve and seat for damage. Make sure there are no air leaks and that the idle is adjusted correctly.

 

I checked the choke the last time we worked on it and it is adjusted with the correct amount of "freeplay" now, we also adjusted the idle too. The air filter is clean but it is discolored with a black hue to it and it smells like gas and oil. I ran it without the filter about 2 weeks ago and it really didn't do much for performance, this was just up and down the street to test it. I have the stock piston in it, but when running the bike sounds like it is supposed too, no unusual noises or pinging, it just does not seem like it wants to pull or have the power it should. Thanks, NC for your input on the situation and if anyone has anymore, please chime in. I want to get my 4-wheeler running the way it should since the trails are open now.

 

What pilot jet are you running and how many turns on the air screw?? Is oil pump adjusted right?? Sometimes the choke freeplay is not accurate. The best way to do it is to remove the carb enough where you can look in the front of it. Find the hole that coincides with the choke plunger. It is easiest to find with a flashlight and flipping the choke on and off. Now when you have the choke off, the plunger should be fully seated in the hole, half choke the plunger should take up exactly half of the hole and full choke the plunger should be completely out of the hole. I have had the problems you describe before and the choke was not right. I adjusted it at the lever as you are supposed to, but when I done what I just described, it was off. It is better to be sure that way than try to figure out how to compensate for it. The oil adjustment is also critical. Also, make sure none of your carb or gas tank vent hoses are clogged or pinched. One more question, are you running any of the same gas you had last summer and did you put any stabilizer in it?? It is definately running rich. Make sure the floats are adjusted right and that the needle seat is clean and not damaged.

 

with stock 34mm carb you must run 270 main with hot seat pipe,and i known what i'm talking about,i had 2 of their pipe in the past,did you get their clutch kit?
also if you're running stock air filter and box,there is the problem,
it need more air,take the airbox off or put in a k&n air filter.

 

I am not sure what pilot jet is in the carb right now. The main jet in the bottom is the 250 jet in the bottom of the carb. The guy I bought the 4 wheeler from last May had all the mods installed and it ran great when I got it. I am not sure if he switched out the pilot jet in it when he did the mods. I will have to see about the oil pump adjustment too, I am not sure if he did anything with that either.

I have the Hotseat clutch kit, Gen 2 pipe and V-force reeds in the bike right now along with the stock carb and air filter kit. When I called Hot Seat up they said something about checking the needle in the carb to make sure it isn't sticking and to pressure test it. I haven't looked at it yet. I am going off of the tech sheet hot seat sent with the pipe kit that specifies the jetting and it recommends the 240 jet in it now and when it is over 80 to run the 250 according to where I am at.

Right now the scrambler is at my parent's house and I won't get to look at it until next weekend so I am trying to get ideas of what to look at. It has to be tuning related or something small because it runs decent and doesn't make any weird noises or cut out. My main concern is that I don't have to rebuild it. Thanks for all the advice guys.

 

Yep, just check your oil pump setting and the choke adjustment. That is probably were your problem lies. I think you got it backwards...."I am going off of the tech sheet hot seat sent with the pipe kit that specifies the jetting and it recommends the 240 jet in it now and when it is over 80 to run the 250 according to where I am at." You have to jet down for warmer weather and up for colder weather.