TRX 300ex Backfireing/Popping

[Brian_300ex]

Hi, I have a 2001 Honda TRX 300ex. It has a white bros. e-series exhaust system, a K&N air filter system, and a dynojet jet kit. I believe it now has in a 124 jet and the stock jet was 122. Even before I bought the dynojet system, it was just popping non stop. It pops even when you give it 1/5 steady throttle and it isnt a small pop, it is EXTREMELY loud.
I bought the atv with the pipe and air filter already on it and it was backfiring since the day i got it. It has in the original NGK plug (DR8ES-L) that comes with the atv stock. Also, what i find is that, if i start up the engine for the first time for the day, at least 3 seconds after it is started, the header gets WAY WAY WAY TOO HOT. The thing left a scar on me after 3 secs. of startup and i barely touched it !!!

1) What can I do to stop the backfiring ??

2) The (DR8ES-L) is an original spark plug. I would like to change this to the iridium plug. What is the iridium version to this plug and where can it be purchased ?

3) How do I repack the exhaust and what packing should i use and where do i get it ?

4) Where can i purchase Jets for the carb (stock carb) because someone lost my jet kit.

5) Are the dynojets the same size as the ones that come stock in the carb ?

6) Where can i set the air screw and which way makes it richer, turning it in or out ?

Please, just answer what you can
Thanx,
Brian

[GPracer2500]

Originally posted by Brian_300ex
Hi, I have a 2001 Honda TRX 300ex. It has a white bros. e-series exhaust system, a K&N air filter system, and a dynojet jet kit. I believe it now has in a 124 jet and the stock jet was 122. Even before I bought the dynojet system, it was just popping non stop. It pops even when you give it 1/5 steady throttle and it isnt a small pop, it is EXTREMELY loud.
I bought the atv with the pipe and air filter already on it and it was backfiring since the day i got it. It has in the original NGK plug (DR8ES-L) that comes with the atv stock. Also, what i find is that, if i start up the engine for the first time for the day, at least 3 seconds after it is started, the header gets WAY WAY WAY TOO HOT. The thing left a scar on me after 3 secs. of startup and i barely touched it !!!

1) What can I do to stop the backfiring ??

Sounds like a lean pilot circuit and probably too lean jetting all the way around. Adding a pipe and air filter will let it breath quite a bit more than stock. Assuing those are Keihin jet sizes you mentioned, going up only one size probably isn't enough.


3) How do I repack the exhaust and what packing should i use and where do i get it ?

Drill out the rivets, dissassemble the pipe, repack (cut out an appropriately sized sheet of packing material, wrap it around the core, secure the wrap with some masking tape so it doesn't unravel during reassembly), and rerivet the pipe.

My favorite packing material is M/T Pro Power Pack. I get it at my local shop but I'm sure it's available elsewhere, including online venders.


4) Where can i purchase Jets for the carb (stock carb) because someone lost my jet kit.

It's nice to find a local tuning shop that stocks Keihin jets. My local tuning shop lets me trade jets when I need different sizes. Call around or order them from an of a number of on-line venders.


5) Are the dynojets the same size as the ones that come stock in the carb ?

No, they use a different scale from factory Keihin jets.


6) Where can i set the air screw and which way makes it richer, turning it in or out ?

It's a fuel screw on that carb not an air screw. For a fuel screw--in is lean, out is rich. See HERE (http://www.exriders.com/vbb/showthread.php?s=&threadid=225191) for best procedure for setting the pilot jet and fuel screw. Alternatively, 2 1/2 turns out is a pretty regular setting, but that only holds if the pilot jet is the correct size.

[Brian_300ex]

WOW... Thanx alot, i'm gonna just order some jets and get started right away. But just two more questions.

The lowest that I run at is sea level and the highest is 5000 ft. above sea level. I usually leave my house which is about 100 ft. above sea level and we ride up to aprx. 5000 ft. Bare in mind my modifications. I just want 1 jet to run the whole day with. I just want to make sure that I am running safe and that I wont blow my engine due to leaness at these higher altitudes.

Also, due to my overheating, which oil should I use, 10W40 or 20W50 ?

And can I run a colder plug ? (NGK 9 instead of 8)

[GPracer2500]

As you go up in altitude your jetting settings get richer not leaner. Think it through: as you go up there is less oxygen (air) available but the carb is delivering the same amount of fuel. The result is that the carb's jetting keeps getting richer the farther up you go.

You could run a tad lean at your lowest elevation. Then it will be less rich at your higher elevations. But don't go too far with that! Only go just barely lean down low. It's better (safer!) to run too fat than too lean.

A better way to help deal with a situation like that (big changes in elelvation) is to run with the airbox lid on at lower elevations and then take it off (strap it to your seat or something) once you hit the higher elevations. Taking the lid off lets more air in and helps get rich jetting back to correct again. Taking your airbox lid on/off is sorta like changing your jets--instead of manipulating the amount of fuel delivered you're controling the amount of air delivered.

Just to be sure we're on the same page; when I say "jetting gets leaner" or "settings get richer" I'm talking about the actual jetting of the carb, NOT which way you should change the jetting. High elevations makes your current jetting settings rich which requires changing to leaner (smaller) jets. Lower elevations makes your jetting settings leaner which would require changing to larger (richer) jets. Clear as mud??

You could run a colder plug, but there should be no reason to do so on a mostly stock engine. If anything, running a colder plug will only reduce your engines ability to tolerate rich running conditions.

As far as oil, let the tempuratures of your ridding environment dictate what oil you use. If your engine has an overheating issue, correct that rather than trying to deal with it by way of a different weight oil.

[Brian_300ex]

Ok, i get what youre saying about the elevation change. But which main jet should i start out with (Based on my altitude). Since you're not so familiar with the dynojet numbers, lets use the keihin numbers also.

Stock in my motor = 122 jet = (116 DJ)
On now with mods = 132 jet = (124 DJ)
Pilot jet now (also stock) = 38 jet
Result, no top end, and too lean everything (top, bottom, & idle) and EXTREME backfiring.

I am going to change my pilot jet from a 38 - 42. I'm not sure where the pin position is but i am going to move it to slot #4. And I am going to turn my air screw out 2 1/2 turns (it seemed to have been at only a 1/2 turn out before).

So which main jet should I be using based on my altitude.

Also, I am planning on using racing gas (leaded). Is this ok ?

Thanx,
Brian

[Aceman]

I would try a 40 pilot with the fuel screw 2-2 1/4 turns out to start with. Leave the clip in the middle position. Probably try a 128 MJ. I think this would be pretty close to being right for you.

Leave the plug stock you have no reason to go to a colder plug.

Do NOT buy race fuel. That is for higher compression engines and you don't need it. Some people think stock engines require premium as well but mine ran just fine on 87 octane from the factory.

[bwamos]

NGK's irridium plug for the 300ex is DR8EIX.
You could run the 9 for a cooler plug, but it will tend to get carbon buildup faster if you're running in the 13:1 range for max power.

FYI: a cooler plug makes your engine hotter. It transfers more heat to the case so the tip stays cooler.

Unless you're getting detonation, I'd stick with the 8.

If you want a cooler engine, an oil cooler helps a lot.

I agree.. a stock 300ex runs just fine on regular unleaded.. it has a very low compression.

Up wont need premium until you put a higher comp piston in (10:1 - 11:1). Race fuel is only needed above 11:1 on the 300ex. (under normal circumstances)

Also are you running airbox lid on or off?

Lid off, start with a 132main, Needle 4th slot (slot 1 on blunt end), screw out 2-3/4 turns. You'll need to adjust from there.. but that should be a start.

If you run lid on (and not punched) , you'll probably need to drop down a couple sizes on the main jet.

[Brian_300ex]

I currently run:

132(keihin) or 124(dynojet) On my main.

38 pliot/slow jet

Airbox lid ON

10w40 engine oil

Not sure where the air screw or pin position on needle is but i will definately set these to 4th position and 2 1/2 turns out.

I just ordered a 135 Main jet and also a 40 & 42 pilot jet. along with a DR8eix & DR9EIX.

I want to try the AVGAS (93 octane & leaded). It is cheap and much better quality than the 87 octane that my gas station sells. Is this ok or will it damage the engine ?

Which grade oil should I use, 10w40 or 20w50 ?

Also, I would again like to thank everyone here that answered my questions, I really appreciate it.

Thanx,
Brian