Hello,

Was wondering if anyone could offer some insight.

I own a 2002 Big bear 400. It only has about 137 miles on it, I purchased new in April 02. I use it primarily for hunting and chores on my property.

Anyway, after not using for several months over this past spring, when I went to use it, it would not idle unless you leave the choke pulled out about 1/2 way.

I'm mechanically inclined, I worked as a car mechanic for years, and have always done all my own vehicle maintenance, cars boats, trucks, etc.

Here's what I've done so far:

Drained and refilled gas tank with fresh gas. (twice)
Removed carburetor, disassembled cleaned and reassembled
New spark plug.
Checked and adjusted valves within specs.
Adjusted "mix" screw on bottom of carb. This was 2 5/8 turns out when I first took carb off, and that's where I started out, then turned in in 1/4 turn increments, then out, and cannot improve performance.

Basically nothing I've done has identified a problem, nor have I changed the performance of the quad. The bike will not idle unless the choke lever is approx 1/3 to 1/2 out, even then it backfires alot.

The carb is a Mikuni BSR 33 ? That's from memory, so maybe I'm wrong.

Anyone that can offer some help?

I would take it to the dealer, but I live in South east connecticut and don't know of a good shop. I'm just afraid of paying mucho $ only to have no improvement.

Thanks

Loughman

 

Cleaning the carb should have done it. Using the 'choke' is actually a starter jet, which lets the motor have some extra gas when opened.
Sounds like either the idle speed is too low, or the idle circuit is still plugged up. When you cleaned the carb, did you remove the jets and blow out the passages? Also, look thru the pilot jet, like looking thu a straw, you should be able to see thru it. The hole is extremely small, and this is also why its the first to plug up. Sometimes the crud is so dried on, it takes a small wire to dislodge it, from the inside diameter of the pilot jet. One strand of 22 gauge stranded wire should do it. If it still wont clear out, you may need to just toss it and get a new pilot jet, about 4 bucks.
If you know its gonna sit for awhile , without running, turn off the gas, and run it til it dies, on the last shut off. This will empty the float bowl, and the plugging wont happen again. Its the constant, evaporation and refilling of the float bowl, that lets the crud build up.
Welcome to the forums.

 

Hondabuster,

Thanks for the advice. I did remove the jets and squirted Gumout through them as well as the passages in the carb. I looked and they seemed clean to me, but maybe I didn't look carefully enough. I will remove the carb and clean it again. I will also pass a wire through the jets as you stated.

My frustration is that I know it is the carburetor, but upon disassembly it looked clean, although I cleaned it anyway. I'll look at it again, maybe I missed something.

 

Theres also an air bleed for the idle circuit,... in the bore, facing the air filter. Its unlikely to be plugged, but could be. Its also a very small hole. But if you have a good air filter, dirt isnt likely to get to it.

 

Listen! Carb spray cleaners are only so good. More of a hoping for good luck deal. You can clean the jets just find with the spray but you are not getting inside the carb body well enough, guaranteed! Do what the shops at the dealers do. Soak the carb in parts/carb cleaner. It is a roughly one gallon can with a parts basket inside. Used to be called Hydro seal because it has a roughly 1 inch layer of water on top to seal the acid in underneath. You can get this stuff (now made by chem tool) from Autozone for instance for under $15. You will love your new weapon for dirty carbs and will find yourself soaking all your carbs on lawnmowers, chainsaws, minibikes etc. etc. Spray cleaner is just a beginning point. Not a true carb cleaning. You cannot physically see all of the cavities and orifice tunnels throughout the carb and a spray can is simply not able to clean those area which are just as imprtant as those highly visible jets you can easily remove from the carb for easy access. It is one of the most common bad myths out there in the mechanical field. Carb spray cleaners. They rae really only designed to clean the exterior of a dirty carb and choke butterfly plates and linkages. They are not designed for internally cleaning a carb. Carb soak does wonders. Sometimes it makes and amazing difference in the performance of a machine, especially 4 cylinder bikes etc. The can recommends 15 to 30 minutes. But overnight is even better. I can get rough running 4 cylinder bikes smooth as new by soaking all four carbs. (takes me 4 overnighters) and then after reinstallation I put my carb synchronizer on the bike sand sync all the carbs. People are always amazed at the smooth running, idling and the extra horses when hitting that throttle on the highway. It can make an amazing difference on these machines. If the carbs are just acting up slightly on a big street bike I simply do not mess around and I tear the carbs out and soak and sync them. Done deal.

 

 

Caution, forgot to add a comment. When you are going to saok a carb you must dissassemble it and remove all rubber. If you are only soaking for 15 to 30 minutes you can usually leave on the hard plastic components, but overnight you might not want to leave them on and take that chance. Now if a hard plastic part does not want to come off easily enough and you are worried about breaking the part then opt for the 15 to 30 minute soak. 30 is better than 15. When that happens to me I will monitor the part while soaking checking it every few minutes to see that it is not softening up the plastic. 1st check every 15 seconds per say when you 1st put it in just to be sure nothing is happening. Rubber will dissolve in just a few minutes and definitely in 30 so you can usually see what is going on. It is best though if you can remove all the soft parts and then throw everything in. Jets should be out. Idle screw and all other adj. screws to allow better access for the acid to the ports. The carb will usually look almost new too when done.