Another jetting Q??!?

[xjma]

So I've got my other blaster that hasn't started in years all put back together again!! Stock pipe, FMF silencer, boyesen dual stage reeds, UNI filter, no airbox cover, 240 jet, middle clip, 32:1 w/ block off, TORS brain disconnected (but all the other junk is still there, and I have the carb part plugged in).

I FINALLY had some time to mess with it. I've always been under the impression that the screw on the side of the carb is the air screw, and the one on the TORS brain is the idle. Some searching got me confused....am I correct here?? I figured out that the air screw should be 1.5 turns out (the one on the side of the carb). Now with the choke all the way out, it starts up and will run for a while, but it seems like when the motor warms up, it dies out. It will start and run for less time with half choke, and I haven't gotten it started without the choke on. Not sure to do with the idle screw...been messing with it for quite some time.

I just oiled up the filter, so maybe that could be an issue, but taking the filter off didn't do much, although it seemed to run a little bit longer. It's a new plug. 93 octane.......

Help? Thanx!

 

[xjma]

OK, I'm thinking maybe I just need to throw a bigger jet in there??? I wasn't expecting to need that big of a jet with a stock pipe, but???? I'll try a 270 or so tomorrow....

 

[yamahaman126]

Sounds like you have something in the pilot circuit if it only runs with the choke on. Clean your carb. You will probably have to set the main up since you are leaving the lid off. Clean your carb though and see if you can get it to run with the choke off before you go messing with the main. Then do a plug chop to see how the jetting is.

 

[xjma]

Ahh, good call....I actually didn't take the pilot out when I had it apart....where is it??

 

[yamahaman126]

It is a long small jet. The smallest one in the carb bowl.

 

[stephen12091985]

its a tiny hole in the carb by the main jet

 

[burnin'_oil_2001]

Anytime that I put on a different exhaust I up the pilot by one size and generally change the needle clip to one richer (drop one clip position). And I could see you needing a 270 main with that exhaust maybe more with an open airbox. Here is a little more info.....If you are more than 2 turns out on the airscrew setting then you need a bigger pilot jet and if you are less than one trun out then you have too big of a pilot jet. Builders have told me that Blasters tend to be lean in the middle and that many people burn pistons because they only adjust the main so I always richen the needle one clip to see how it runs- for the most part that is where it stays.

 

[yamahaman126]

If you are more than 2 turns out on the airscrew setting then you need a bigger pilot jet and if you are less than one trun out then you have too big of a pilot jet.

The only thing is that the air screw has three usable turns. The more you open the air screw the leaner it gets. So if you open it more than three turns then you need to get a smaller pilot. So if you close the air screw to a half turn open then you would need a large pilot.

 

[yamahaman126]

Jet for top end first, your main. Get it perfect and then check the midrange or needle and adjust. Then worry about the pilot circuit.

 

[xjma]

So to confirm, the air screw is the one on the side?? Where should I set the thing at the top, the idle adjust??

I'm thinking that maybe the pilot is clogged. Starts up just fine with the choke on, it just won't run without it.

It's a stock exhaust, just the FMF silencer....for fun. I had the stock silencer on my other blaster with the FMF pipe, and that one got stolen!!

This thing hadn't run in quite some time and I wanted to let it idle to break in the new rings I just put in....but it won't idle for long!! It used to run with open aribox and stock jetting before I got it. I guess it's gone through it's first heat cycle though with the amount that it has run with the choke on....which I don't think it a good thing. Oh well, I'll check the pilot and report back tonight.

 

[burnin'_oil_2001]

Jet for top end first, your main. Get it perfect and then check the midrange or needle and adjust. Then worry about the pilot circuit.

never jet top to bottom it is not the correct method. ask any reputable engine builder and they will tell you the same. even carb tuning manuals start at teh bottom and go to the top. every change in jetting affects other circuits and makes for a mess. here is a link to a great article on how to jet a carb....

Jetting From The Bottom To The Top! - Power Sports Tuning

look for-- jetting from the bottom to the top

 

[xjma]

So do people think that my issue with not running without the choke is a clogged pilot?

 

[burnin'_oil_2001]

I would take apart the carb and clean it and see how it runs. you may only need a 250 main (i missed that you only had a silencer on the stock pipe in my last post). check really well for air leaks and make sure that your filter is not over oiled. then let us know how it is working.

 

[yamahaman126]

I will agree with you on one thing, that if the pilot isn't adjusted first you will never get it to start. Your right their, so yes you have to start at the bottom.

Here is where I don't agree, midrange and top end jetting the gas is all drawed thru the main jet. The main jet screws into the needle jet, which is fine tuned by the needle position. So if your main is too small to begun with they you can't properly adjust the midrange. If the main is too small and you put the needle in the fifth position, the richest, and your midrange is now perfect. As soon as you change the main to get the top end right you will be too rich in the middle and will have to adjust again. Hopefully this makes since to you. This is how I was taught and have jetted many Blasters and Banshees with success.

 

[yamahaman126]

Straight from a Blaster cylmers manual, Chapter 8, page 218, second column: " Check jetting in the following order: Pilot air screw, main jet, and jet needle"

I'm not trying to start a fight I just want to make sure that the people that don't understand jetting that well don't burn down their engines trying to jet.

 

[xjma]

I just had the thing apart, cleaned it up and put a new gasket....I guess I forgot to take out the pilot jet though.

I've had luck tuning the carb before by just using the main jet and the needle clip....we'll see what happens when I clean this pilot. I think it's clogged with junk!

 

[yamahaman126]

Use compressed air and make sure air comes out the hole on the inside of the front of the carb. It's a tiny hole.

 

[2StrokeFTW]

1.)Check to see if your carb is clean inside and the pilot isnt clogged, (the pilot is located down that little hole next to the main jet.)

2.)Then be sure you have the correct main jet (more fuel for more air aka pipe,intake,airbox gutted) so you dont starve the engine for fuel when you ride.

3.)Start the bike and keep it alive blipping the throttle til it's warmed up and running.

4.)Pop your seat off and twist your idle air screw counterclockwise to bring the idle down and clockwise to raise it.

5.)Then ride and see how it performs remember if you have an idle problem it's probably something to do with the pilot jet if it's falling on it's face under wot pulls it's probably the main jet. Now there can always be something else wrong but that's a good way to start your diagnosis.
Hope you figure it out bro.

 

[2StrokeFTW]

Oh I see your in MA I used to live up in Southern Connecticut man I know it can get really cold up there in the fall/winter ,that way be making it tough to get the tuning right cause 2strokes and the cold dont mix that well. I'm sure if you clean it and get the proper jets in the carb you'll get it running nice.

 

[xjma]

OK, so I took the carb apart again tonight, actually found where the pilot jet was (down that big long tube, haha) and it was indeed all clogged up. I used gasoline, fire, and sewing needles to get it clean. Put everything back together, swapped in a 250 main for the 240 (for sh*ts and giggles), set the air screw at 1.5 out and it didn't change much at all!! I found that it would run a little longer with the air screw in closer to 1 or .75 turns out than it would at 2.5 out. I was hoping that the pilot jet cleaning would be the eureka!! But it wasn't . I did, however, get it to start with the choke off!! Depending on the air screw adjustment it will start better with the choke full on or off. So that is my only improvement. It runs for a minute or so and then dies. It can restart but not run as strong. If I let it sit for a minute or two and then fire it up, it runs longer. It seems like maybe it's just getting an initial burst of fuel and then dying out.....I'm not sure. It doesn't want to stay running more than 30 seconds max....

Help??