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Discussion Starter · #1 ·
I had no idea i would have so much trouble getting this thing to start...

This build has a kicker so there is only so much tuning i can do on the pilot circuit before i can't walk any longer.

Some help on getting the right pilot jet would be much appreciated.

I thought i knew about tuning a carb but i was proven wrong today. I cannot get this thing to start without opening up the throttle.
My build: 480 with CP 13.5:1, Ported head with +1 valves, 42 mm carb, FCI with no box, Dasa shorty exhaust, Vortex CDI. The carb has a powerbowl 2.

The carb had a 48 pilot jet in it to begin with. It would not start with that. Big bore has more vacuum so i went to 45 then 42. Wouldn't start. Tried a 50 just for the heck of it. Still nothing. All this with the fuel screw 2 turns out.

Needless to say, I'm hurting...

Like i said, i can get it to start with the throttle almost wide open, but i want it done right.

Anything i am missing? I want this thing to start up first kick!

Thanks
 

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I have similar motor minus the +1 valves and bored carb. so I guess not so similar but same problem. starts like a big dirty ass. mine does starts though via electric start. I'm currently at 45 pilot NCVQ needle 3rd clip. 172ish main (or 170). 2 1/2 - 3 turns out on air screw. hoping to get mine dyno tuned soon. I'm going to also double check my valve clearance before that because my head was fresh with all new valves and everything. I have to hold my throttle 1/4 ish open to get mine to pop off. probably wouldn't very able to if it was a kicker though. I'll post back if I get mine straightened out.
 

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Discussion Starter · #4 ·
I have similar motor minus the +1 valves and bored carb. so I guess not so similar but same problem. starts like a big dirty ass. mine does starts though via electric start. I'm currently at 45 pilot NCVQ needle 3rd clip. 172ish main (or 170). 2 1/2 - 3 turns out on air screw. hoping to get mine dyno tuned soon. I'm going to also double check my valve clearance before that because my head was fresh with all new valves and everything. I have to hold my throttle 1/4 ish open to get mine to pop off. probably wouldn't very able to if it was a kicker though. I'll post back if I get mine straightened out.
I had a 470 set up almost exactly, except the +1 valves and ran the folllowing

Needle - NCVQ, 3rd Clip
Main - 190
Pilot - 45
A/F - 2 1/4
Leak - 35
The 45 pilot did seem to run the best. I think i might have been able to start it without the throttle on the 45. I was trying to break it in, tune the pilot circuit, and flush the cooling system at the same time, so i had a lot going on. It ran for a good while on the 45 then shut off and i couldn't start it again.

The only other thing that would have an effect on this would be the fuel screw right?
 

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Kickers on a yfz are all about where you kick it in the stroke, not how many times you kick it. I ran a 38 pilot on my 513 when it was a kicker at sea level. Try a 40 and screw the a/f out 1/2 turn. Make sure you just slightly open the throttle too when you kick it. It works. Just a scosh to there you can feel tension on the slide. YFZs are finicky and this really helps.

When you kick it, roll the motor over a few times so you can feel the difference between upstroke vs down. Down will be exremely easy to kick.. no effort. Get it to TDC.. You'll be able to feel the compression and resistance on the upstroke. when it stops you should be about tdc, bring the lever up for a full kick. Open the slide a scosh and hammer a good kick. That's all it should take.

If its still hard to start, you may check your valve clearance and make sure its not too loose. Also the larger decomp pin like mentioned already works wonders if you know how to switch them. The dirtbike exhaust cam has the larger pin so if you can find a yz250 or 450 exhaust cam for cheap, its a worthwhile purchase to get the pin. Shouldn't have to spend more than 20-40 depending on location.

hope this helps.
 

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Discussion Starter · #10 ·
Yeah, all it needed was tuning. I found out about bringing the piston up to the compression stroke before kicking halfway through. It worked great! I used to have a two stroke with a kicker so i didn't have to worry about that.

For now i can kick it just fine, but i am getting a shorter kicker (thanks Chopp124!) to clear the rath nerfs. So i might need the bigger decompression pin later. Thanks for the tip on that!

This engine is so picky with the A/F ratio! I had it running in the shop, opened the garage door, and it died with the cooler air! Given it was probably a 30 degree drop, but it was still crazy to see. My stock engine could start up at any given temperature.

I love this engine though. and the smell of C12... haha. The Dasa shorty is way loud though!
 

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I'm a little confused by your chart. What did you end up with in the end for jets? I checked my valves today, their all good. Swapped the pilot out to a 42 and I did get it to start but not easy... I can't seem to get this figured out at all. I'm going to get it dyno tuned but I would like for it to atleast start for sure when I get there lol. Once it's warm it starts right up with a blip of the start button and seems to run pretty good.

Any other idea's to try?? I'm currently at 42 pilot (tried all adjustments on fuel screw), NCVQ 3rd clip down, and a 172 main. Stock bore carb (funding ran short). 04; YFZ 480 BB w/ 06+ OEM Crank, Head Ported, brand new OEM valves, Stock bore carb, full HMF exhaust, FCI, Cam mod, Fresh rebuild w/ CP 98mm 13.5:1 piston. I am also at 900-1000 ft elevation.

Not to jack your thread but thanks for the help.

Chuck
 

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Discussion Starter · #12 · (Edited)
I'm a little confused by your chart. What did you end up with in the end for jets? I checked my valves today, their all good. Swapped the pilot out to a 42 and I did get it to start but not easy... I can't seem to get this figured out at all. I'm going to get it dyno tuned but I would like for it to atleast start for sure when I get there lol. Once it's warm it starts right up with a blip of the start button and seems to run pretty good.

Any other idea's to try?? I'm currently at 42 pilot (tried all adjustments on fuel screw), NCVQ 3rd clip down, and a 172 main. Stock bore carb (funding ran short). 04; YFZ 480 BB w/ 06+ OEM Crank, Head Ported, brand new OEM valves, Stock bore carb, full HMF exhaust, FCI, Cam mod, Fresh rebuild w/ CP 98mm 13.5:1 piston. I am also at 900-1000 ft elevation.

Not to jack your thread but thanks for the help.

Chuck
Sorry i didn't see this sooner

The chart shows my Pilot, The Idle Air Screw Position (how many turns out), and the Fuel Screw (how many turns out).

The more you turn out the Idle Air screw (black knob on the carb), the more it closes the throttle slide position (less air flows through at idle). The more you turn out the Fuel Screw, the more rich (more fuel) the your air/fuel mixture becomes.

The chart shows i started with a 45 pilot, The Idle screw all the way in, and the fuel screw 2 turns out. With that combination, I could get it started. So i had a good enough air to fuel ratio to get it started. The problem was, it idled way high because the Idle Air screw was all the way in, meaning it was opening the slide more (more air= higher idle). So i lowered the idle by turning out the screw but that also meant i had to give it less fuel as well to keep the air/fuel ratio at the right place. I did this until i ran out off adjustment on the fuel screw. This meant i had to go to a smaller pilot jet because i could not lessen the fuel anymore. I redid the procedure with the 42 pilot until my idle was satisfactory

I ended up with a 42 pilot, Air screw 2 1/2 screws out, and the fuel screw 2 1/2 screws out.

Try putting the Fuel screw 3-4 turns out (helps if you have a flex jet from R&D). Turn you Air screw all the way in (all the way clockwise) and then turn it out to 3-4 complete rotations. If it starts easier then, go up to a 45 pilot and start at 3 complete turns out on the air screw and 2 1/2 turns out on the fuel screw. Once you get it started, Set your idle with the (air screw) as low as you can without it dying. Then set your fuel screw to keep the mixture right. You will have to go back and forth between the air screw and the fuel screw until you can get your idle set and you Air/Fuel ratio right.

This is the way i did it. Hope this helps
 
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