Jetting help

[nick20555]

so is the idle screw increasing rpms as it is screwed in ?
you say it's only lifting it slightly ?.... enuf to increase rpms to beyond a normal idle ?
if not, what would it take to get the idle screw to lift the slide further ....longer screw ? lose the nut and go with a spring for retaining it's setting ?

No its not increasing the rpms because I don't think it's lifting the slide enough. It has a spring on the idle screw. Longer screw might do it unless...

I had a similar problem with a 35 pwk on my banshee. It ended up being a bad slide.

No matter what I tried , I could not get the engine to respond to the airscrew. Finally after messing with it for a week, I took the carb out, and looked inside and could see that the slide was not closing all the way.

Just something to check or ponder.

I think you might be on to something. Is the slide suppose to close 100% where all you see on both the engine side and airbox side is a flat piece? On the airbox side a small amount of the circle at the bottom of the slide shows and no matter what I do with the throttle cable it doesn't lower anymore. Is that normal? I may be able to take a picture tomorrow if what I am describing doesn't make sense.

 

[dirtysquared]

No its not increasing the rpms because I don't think it's lifting the slide enough. It has a spring on the idle screw. Longer screw might do it unless...



I think you might be on to something. Is the slide suppose to close 100% where all you see on both the engine side and airbox side is a flat piece? On the airbox side a small amount of the circle at the bottom of the slide shows and no matter what I do with the throttle cable it doesn't lower anymore. Is that normal? I may be able to take a picture tomorrow if what I am describing doesn't make sense.

A pic will definitely show if it was like mine was. But what your saying sounds a lot like what I dealt with. The slide should be closed except for what the idle screw is keeping it raised.

 

[nick20555]

Another thought though, if the slide wasn't going down as far as its suppose to then wouldn't it be really hard to keep the idle under control? I can set the idle low enough with the throttle cable that the engine will die, would it do that if the slide wasn't going all the way down?

 

[nick20555]

Here is my half throttle plug chop. What do you think?


And also about my earlier question

 

[dirtysquared]

Another thought though, if the slide wasn't going down as far as its suppose to then wouldn't it be really hard to keep the idle under control? I can set the idle low enough with the throttle cable that the engine will die, would it do that if the slide wasn't going all the way down?

Good point, if it wasn't closing all the way the idle should be high, you would think.

 

[nick20555]

After reading up on reading plugs, is my picture above too lean because it's black/grey? If so I need to go down a clip on my needle.

 

[Blaaster]

One clip downward should do the trick.

 

[nick20555]

One clip downward should do the trick.

OK, that's what I thought. Maybe I will see a little more power when I do that as well

 

[nick20555]

I guess I should go ahead and ask while I'm on it. When I did my half throttle pull down the road, I set my throttle stop screw according to the slide halfway open. Is that the correct way to do it so I know how my needle jetting is?

 

[Blaaster]

You were correct the way you did it!

I applaud you for listening to advice and then taking the trouble to do what is advised and reporting back with the problem,

 

[nick20555]

Haven't had time to mess with it. Had time away from work and school so I wanted to spend some quality time with my daughter before her mom took her on vacation. And now its corn planting time so I'm helping on our farm with that. Hopefully here in a the next couple days, I'll get a break and I'll mess with the jetting some and try and get back with another half throttle chop and possibly a full throttle chop.

Thanks for all the help so far guys

 

[nick20555]

Alright, finally got a few hours to work on the blaster. I managed to find what I think is the maximum idle with the air screw. Got it at 2 1/2 turns out with a 50 pilot. I'm fine with it being a little on the high turns out.

Did another half throttle plug chop after moving the clip one position down. Here is what I got. Is this still too lean?

 

[Blaaster]

Too lean for me, others thoughts may differ.

Did you apply the brakes some so that the engine was under load.

 

[nick20555]

Too lean for me, others thoughts may differ.

Did you apply the brakes some so that the engine was under load.

No, I just set my throttle screw to half throttle and did 1-6 gear half throttle pull. Is it make much of a difference if I apply the brakes while I do it?

Is taking the clip down one more position going to make me too rich?

 

[MercMenace]

that's a little lean for me. Certainly won't hurt to drop needle one more. rich never melts pistons.

 

[nick20555]

that's a little lean for me. Certainly won't hurt to drop needle one more. rich never melts pistons.

Ok, I just didn't know how much of a change one position on the needle is. I know with main jets you can go one size up and its only a minor change so you can get it dialed however you like it but didn't know if the needle clip positions were big changes.

@Blaaster Do you think me holding the brakes as well as going thru all the gears at half throttle will change the outcome of my plug chop?

I still haven't even attempted to do anything with the main jet yet. Will that have any effect on the jetting for my half throttle chops? The guy at Vito's acted like the main will effect it as well but from what I hear the main only effects 3/4 to WOT

 

[MercMenace]

pilot = idle
Needle + Pilot = 1/4 - 3/4 throttle
Needle + Pilot + Main = 3/4 throttle - WOT


give or take.

 

[MercMenace]

here's a couple good reads if you really want to learn to tune a carb.

http://www.duncanracing.com/TechCenter/KeihinCarbJetting.pdf

http://www.amrca.com/tech/tuners.pdf

 

[nick20555]

Here is my half throttle plug chop on the bottom clip position. What do you think on this one? That is one clip down from my previous photo. Do I need to go back up one more clip because that is too rich? I held the brake on this one for the full pull.

half throttle plug chop

• nick20555
• May 31, 2015

Half throttle plug chop on bottom clip position

 

[nick20555]

What does everyone think of my plug chop? I dropped the clip one more from the previous chop you can see above and I also held the brake the whole pull this time. The one before was very faint color and this one is clearly a lot darker. Which would be better to run, this plug chop or the previous one?