Setting Idle on 89 honda trx300

clemsonfor · Feb 19, 2012

I had posted a thread about rebuilding this carb in the rural living forum, before i realized there was an ATV forum.

Anyway i put the kit in which i learned did not come with a float till i got it. So i put the kit in minus a few pieces i did nt feel like doing. New needle high and low jets. Float did not apear cracked and didnt have fuel in it that i remember.

Put it back togeather and runs way better. I just need to know which adjustments you mess with to get the idle set right. There is the place where it goes in the carb that can adjust, the knob on the carb that can adjust which is the proper one to get adjustment. Im thinking the knob as i adjusted the other place and it seems to be loosing as i test ride it and i am back to stalling as i guess it is idled to low. The know dont seem to be doing much.

Also this one revs a lot higher than the 98 trx300 i have ridden, on CHOKE. I dont think there is any adjustment on this is there?

And finially it seems to be backfireing (not while running in gear more when you rev it and let of the gas like at idle or if you come off of the throttle and coast is when it happens)a bit more than it should even warmed up, what would cause this, i bet i need a float as the fuel level isint right!! and this was a plastic float so you cant adjust anything without breaking the thing.

I may be way off on all this but this is my first 4wheeler or bike rebuild. I have been in Saws a few boats and many mowers.

clemsonfor · Feb 20, 2012

Found this last night searching the web. This may be a small part of the problem. I ran this screw all the way in when i rebuilt the carb. I will try and reset this screw today, this should help the idle being high with the choke on as it sounds like an air screw which will make it rich if to far in.

1988 TRX300 Idle(air) Mixture setting? - ATVConnection.com ATV Enthusiast Community

cropdusting · Feb 20, 2012

Alright I followed your post over here.

I asume the "kit" you bought had the same main and pilot (slow) jets and the same profile jet needle as stock or what the service manual recommends.

The idle adjustment will be a screw on the side of the carburetor somewhere near where the throttle cable attaches to the side, on that model it should have a black plastic knob to make it easier to turn with your fingers.

Setting the idle mixture is fairly straight forward, depending on how easy the (in your case) the "fuel" screw is to access. Watch this video as I explain and show how to set the idle mixture screw. FYI you have a FUEL screw the tutorial video I am demonstrating on a carburetor that has an AIR screw, it makes the same adjustment just oposite from a fuel screw. Don't worry I explain it in the video. Before doing this proceedure warm up the engine and set the idle around 1000rpm (or what ever feels like 1000rpm it is not that important that the idle be at that exact speed just not set at a fast idle before you begin).

How to: Idle mixture screw adjustment | The Junkman's Adventures on Blip

This may help or solve your backfiring on deacell. If not the backfiring on deacelleration is caused by a slightly rich condition somewhere in the main jet circuit. You can try a 1/2 step leaner main jet or raising the jet needle clip position (lowering the needle) so it opens the main jet later and closes it sooner, thus leaning the mixture slightly when the carburetor slide moves through its stroke.

Now I know from experience with CV type carbs that some backfiring once in a while on deaccell is normal as well as less than snappy throttle response on acceleration is normal because of the inherant design.

Also a side note. When was the last time you adjusted the valves? Proper valve adjustment and cam chain tention has a profound effect on overall performance. See my other video below for a tutorial on that.

http://teammgr.weebly.com/how-to-valve-adjustment-tutorial.html

clemsonfor · Feb 21, 2012

cropdusting said:
Alright I followed your post over here.

I asume the "kit" you bought had the same main and pilot (slow) jets and the same profile jet needle as stock or what the service manual recommends.

The idle adjustment will be a screw on the side of the carburetor somewhere near where the throttle cable attaches to the side, on that model it should have a black plastic knob to make it easier to turn with your fingers.

Setting the idle mixture is fairly straight forward, depending on how easy the (in your case) the "fuel" screw is to access. Watch this video as I explain and show how to set the idle mixture screw. FYI you have a FUEL screw the tutorial video I am demonstrating on a carburetor that has an AIR screw, it makes the same adjustment just oposite from a fuel screw. Don't worry I explain it in the video. Before doing this proceedure warm up the engine and set the idle around 1000rpm (or what ever feels like 1000rpm it is not that important that the idle be at that exact speed just not set at a fast idle before you begin).

How to: Idle mixture screw adjustment | The Junkman's Adventures on Blip

This may help or solve your backfiring on deacell. If not the backfiring on deacelleration is caused by a slightly rich condition somewhere in the main jet circuit. You can try a 1/2 step leaner main jet or raising the jet needle clip position (lowering the needle) so it opens the main jet later and closes it sooner, thus leaning the mixture slightly when the carburetor slide moves through its stroke.

Now I know from experience with CV type carbs that some backfiring once in a while on deaccell is normal as well as less than snappy throttle response on acceleration is normal because of the inherant design.

Also a side note. When was the last time you adjusted the valves? Proper valve adjustment and cam chain tention has a profound effect on overall performance. See my other video below for a tutorial on that.

Valve Adjustment tutorial - The Junk man

Thanks for your response. I think that may be the vid i watched before.

This "kit" was for a stock 89 trx300 so it should be the same jets, they looked similar. I have found the idle screw on the side and been fooling with it. Also i adjusted that air screw or whatever on the bottom of the carb and that took 98% of the backfire away. I have ridden a 98 trx many hours before and realize that backfire once in a while are just a given, but this was going like crazy when cold and when warm.

I will watch your vid when i get a chance today to see if its the same.

Thanks for your time.

Oh and the valves, not sure if or when they were adjusted. I just got this thing a week ago with the junked up carb where it was running so bad you could hardly drive it from the coughing and sneezing and hesitation.

cropdusting · Feb 21, 2012

Well sounds like you are on the right track. When I asked if they were the stock jets I meant the stock size, factory settings are a 115 or 120 main jet and a 35 or 40 with the fuel screw baseline at around 1 3/4 turns out. Depending on your altitude, air temperature, and air density/humidity you may have to adjust up or down (rich/lean). Typically the service manual settings are good for around 1500 feet above sea level.

Valve adjustments on that engine are easy and performed exactly as shown in my video. You won't nessisarily need the special valve adjustment tool I show in the video as the set screw can be held with either a 3mm wrench or a needle nose vise grip (just be careful) However the tools make it so much easier and aren't that expensive. You will need angled feeler gauges though.

Intake: .003~.004
Exhaust: .004~.005

[ame=http://www.amazon.com/Allstar-Performance-96421-FEELER-ANGLED/dp/B003TPMMIG]Amazon.com: Allstar Performance 96421 FEELER GAUGE ANGLED: Automotive[/ame]

Motion Pro - Tappet Tool Set

clemsonfor · Feb 21, 2012

cropdusting said:
Well sounds like you are on the right track. When I asked if they were the stock jets I meant the stock size, factory settings are a 115 or 120 main jet and a 35 or 40 with the fuel screw baseline at around 1 3/4 turns out. Depending on your altitude, air temperature, and air density/humidity you may have to adjust up or down (rich/lean). Typically the service manual settings are good for around 1500 feet above sea level.

Valve adjustments on that engine are easy and performed exactly as shown in my video. You won't nessisarily need the special valve adjustment tool I show in the video as the set screw can be held with either a 3mm wrench or a needle nose vise grip (just be careful) However the tools make it so much easier and aren't that expensive. You will need angled feeler gauges though.

Intake: .003~.004
Exhaust: .004~.005

Amazon.com: Allstar Performance 96421 FEELER GAUGE ANGLED: Automotive

Motion Pro - Tappet Tool Set

I want to adjust the valves on it. Thats once i take care of the neglect. I need to rebuild the front master cyl and to get pressure and onece i have fluid to the wheel cylinders i hope to have brakes. I have not pulled the drums yet to see what i have in there yet i just have my fingers crossed now. HAHA i am familiar with the front brakes as i had to bleed the crun/water out of my uncles 98 trx as well as free up his adjusters and then adjust the shoes up to the drum so i am not a newbie there. Well rebuilding the mstr cyl, yea.

As far as altitude im at about 700-800ish feet above sea level. Im here in the south so humidity can be awful most times.

cropdusting · Feb 22, 2012

Even though your familiar with brake systems. Here is a video of an easier way to bleed and flush all in one step that you may not have heard of. Of course this is once you get your rebuild kit in the master cylinder.

How to: brake bleeding flushing tutorial - The Junk man

clemsonfor · Feb 22, 2012

cropdusting said:
Even though your familiar with brake systems. Here is a video of an easier way to bleed and flush all in one step that you may not have heard of. Of course this is once you get your rebuild kit in the master cylinder.

How to: brake bleeding flushing tutorial - The Junk man

You obviously know way more than me about bikes, but im curious why dont you just gravity bleed them, seems easier to just keep topping up the master cyl till it runs clean out the bottom than the syringe method? Is it to keep the crud out of the wheel cylinders or calipers? Just curious?

cropdusting · Feb 22, 2012

Well as I said in the video there is several ways to do it, and none of them are wrong. I prefer this method with motorcycle/atv brakes because the master cylinder piston is so small that it doesn't push much fluid very far with each stroke (unlike an automotive/truck system) thus since air bubbles can compress sometimes it is nearly impossible to "push" an air bubble down against its natural tendency to float up. Basically it comes down to efficiency, with the syringe method I describe, filling and bleeding the system can be done in about 2 minutes reliably and without chance of accidentally pulling more air into the system during the process.

I guess the real reason I prefer doing it this way is when I was racing there were times I would need to change the brake fluid between races/motos because I was so hard on the brakes I was boiling the brake fluid making it necessary to change the fluid between races and typically I only had 30 minutes or less sometimes to do this.

On a side note this is how brakes are bled on mountain bikes with hydraulic brakes as their systems are so tiny (to save weight) that they hold only a few ounces of fluid and can't be bled the conventional way.