honda trx 250 carb ajustment

JerseyTrueBlue · #1 02-03-2011, 02:10 PM

So I'm guessing this isn't the stock carb since it's super clean and doesn't have the infamous "D" shaped air/fuel screw. Problem is, I've been having trouble with my atv running lean (no airbox and coreless stock muffler) so I put on a new filter and plug but this seemed to make the issue worse. It has trouble holding idle and every few seconds it pops like a misfire, plus it pops a lot on down rpms. I decided to mess with the air/fuel screw to see if I could make it better. I turned it in until it started to choke, then started backing out until it idled good but no matter how far out I turn it the poppin from the down rpms never stops though it does get slightly better. I'm thinking maybe something else needs to be tuned but I'm not sure what number one and three are? Also the screw gets so loose after about a turn out that the vibrations just make it turn, could I solve this with loctite?

JerseyTrueBlue · #2 02-03-2011, 02:49 PM

Also could not having an airbox and having the muffler gutted essentially mean that I need a larger main jet? Maybe it's just from average wear but my old plug was kinda black but not really bad, does this mean I'm rich instead of lean? It gets worse when I make it more lean so I would think I need more fuel, unless the air/fuel screw is an air screw rather then a fuel screw and has me all ass backwards lol. If anyone has any tips on how to make the screw stay put I guess I will just find an okay spot and keep it there since I really don't want to have to rejet right now.

Here 2 help · #3 02-03-2011, 03:11 PM

Number 1 is the idle speed screw and #3 is the float bowl drain. Obviously it's not the stock carb for an 06 TRX250EX. I'd like to see more pics of the carb (both sides), brand name (if any) and any numbers it might have on it.

You didn't say if the "popping" was out the exhaust or through the carb?

I suggest you check for a vaccuum leak. If none found, take the carb off, remove the float bowl and find out what size pilot jet the carb has in it. You most likely need to change the jet. Also, engines run best with some exhaust back pressure. You may need to put the core back in the muffler or buy a performance muffler.

JerseyTrueBlue · #4 02-03-2011, 11:27 PM

Thanks man, I'll get more pictures tomorrow. The popping is out of the exhaust, just like a car it just pop pop pops on the down rpms after a high rev or slowing down in gear, sort of like a 2 stroke. It's not bad but I've heard this isn't supposed to happen and I've sure never heard it before. No vaccuum leaks and I guess I'm gonna have to rejet the carb anyway. How do I find out what jet I have and what one I need? Whats a good kit to get that's not really expensive? Also more info on the muffler, it's a stock muffler with the stock tip and that core thing that goes behind it removed. It has one of those cheap ebay tips on it now and a screen spark arrestor. If I look in the muffler it goes a few inches back to a wall and then there is the hole for the pipe in the top right corner so I think it has enough backpressure. Also I don't have the piece that's missing I bought it like this, just going by what I've seen on BikeBandit.

JerseyTrueBlue · #5 02-03-2011, 11:28 PM

Also do you know why the air/fuel screw is loose or how to fix that?

Here 2 help · #6 02-04-2011, 12:47 PM

Popping out the exhaust is due to a lack of back pressure and a lean low speed fuel mixture. It won't hurt anything, just annoying, but normal for unrestricted exhaust. Some carbs have what's called an air cut valve on the side of the carb. It cuts the air to the idle circuit to enrichen the mixture during decelleration to reduce (or eliminate) backfiring out the exhaust. Your carb doesn't have one. Having the stock carb might help.

By the picture, your carb has a fuel screw. If you were to take it completely out, you might find it is missing something. It is normally "held" in place by a spring. Many times people remove the screw and lose the spring. Find out what kind of carb it is and a replacement may be available.

Jet kits are worthless. Just take the carb off, take it apart and see what kind and sizes of jets are in it. To buy a jet kit, you need to know what kind of carb you are working on. See the thread Carburetor Basics ( Thanks to Saber6) - it will explain it all without me having to echo it.

Hope this helps. Worse come to worse, you could send the carb to me and I could check it for you.

JerseyTrueBlue · #7 02-04-2011, 11:51 PM

Thanks a bunch man, I guess what I'm gonna do is one try and figure out what type of carb it is, and two pull that screw out to see if there is a spring. I don't think I'm gonna worry about the jets since the plug didn't show any extreme conditions of lean or richness. It makes since that it would pop without the quiet core in it so I'm not as worried about it as I was. The body on this atv is crap but the motor is in really good shape and always fires rightup so I'm just trying to keep it running good.