new piston, hard starting?


20 replies to this topic
  • danzick

Posted June 22, 2011 - 12:13 PM

#1

did some searches and didnt find much. i just put a new piston in my bike, and new tranny gears. and it starts 1st kick when its cold every time so far. but when it gets warm, i kick my guts out just to get it started. and it pops a couple times before it will start. check the clearances before i put the motor back in, and the clearances were pretty tight. right on the line of needing thinner shims. is it just going to do this until i get it broke in good or did i do something wrong? i made no adjustments from my old head, and it used to be very consistent in its starting.

  • Duner185

Posted June 22, 2011 - 12:27 PM

#2

My Yz450F is the same way when it is hot it will not start.

  • danzick

Posted June 22, 2011 - 12:33 PM

#3

well, might i add that i ported and polished the intake and exhaust ports. but, when its running, it seems very strong and i checked the seats before i put the head back on with some carb cleaner, and none seeped through in any of the ports.

  • grayracer513

Posted June 22, 2011 - 02:40 PM

#4

You're going to need to retune the idle circuit for the new piston and rings. Probably running a little rich if all the jets are clean.

  • danzick

Posted June 22, 2011 - 05:11 PM

#5

i thought thats what the hot start was for? i was told the hot start leans the mixutre out to start it up easier when its warmed up

  • RiderX

Posted June 22, 2011 - 05:54 PM

#6

i thought thats what the hot start was for? i was told the hot start leans the mixutre out to start it up easier when its warmed up


The hot start is for adding more air while starting hot, thus leaning it out to assist in starting, but if you are too rich it's not going to help like it's designed to. It doesn't correct a rich condition.

  • danzick

Posted June 22, 2011 - 06:02 PM

#7

why would my bike all the sudden be rich?

  • RiderX

Posted June 22, 2011 - 06:07 PM

#8

why would my bike all the sudden be rich?


Possibly from higher compression

  • danzick

Posted June 22, 2011 - 06:44 PM

#9

ah i see. well did the porting job have anything to do with it?

  • yz480doinwork

Posted June 22, 2011 - 08:16 PM

#10

Your leg just got weak while it was apart!

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  • danzick

Posted June 22, 2011 - 09:11 PM

#11

ohhh funny guy over here. got the paddle tire on the turbo yet?

  • todds924

Posted June 22, 2011 - 09:28 PM

#12

porting will affect jetting.............Improper porting will ruin a head.
I would double check your carb settings and make sure everything is 100 Percent cleaned proper. If it sat for awhile while you rebuilt it....The carb is going to be a problem.

  • danzick

Posted June 23, 2011 - 07:34 AM

#13

it sat for a whole like 2 weeks being rebuilt but i guess ill clean the carb. and there isnt much to screw up in these ports. alse i did was knock down the arches in the ports. and made the actual port bigger where it goes to the seat, but i checked the seats and they are good. like i said, it starts awesome when its cold, but as soon as it gets hot it struggles and it wasnt like this 2 weeks before i put the piston in it. stock piston by the way.

  • yz480doinwork

Posted June 23, 2011 - 07:50 AM

#14

Its not the ports. Its either carb or valve gap

  • danzick

Posted June 23, 2011 - 08:03 AM

#15

yeah i was messin with my fuel screw this morning and after warming it up it started in about 4 kicks. i think it will get better when we head down to the dunes cause the elevation is quite a bit lower.

  • todds924

Posted June 23, 2011 - 10:52 PM

#16

it sat for a whole like 2 weeks being rebuilt but i guess ill clean the carb. and there isnt much to screw up in these ports. alse i did was knock down the arches in the ports. and made the actual port bigger where it goes to the seat, but i checked the seats and they are good. like i said, it starts awesome when its cold, but as soon as it gets hot it struggles and it wasnt like this 2 weeks before i put the piston in it. stock piston by the way.

Uhhhh. These heads NEED the arches in the port and you cant just "make um bigger If you knocked down the arches I bet the flow is all messed up..............I have seen a CnC'd GYTR head compared to a stock head and there really isnt that much difference. The ports definitely are not BIGGER and the only real difference is in the bowl area under the valve seat and the intake manifold is matched to the intake port."
Go in and make sure that pilot jet is 100 percent clean........

  • jratcliffe3

Posted June 23, 2011 - 11:28 PM

#17

How long has it been ridden with the new piston? My 09 when new was hard to start when warm, but after a few hours it got to first kick hot or cold. It was similar when I changed the piston, but was OK after a couple of rides.

  • danzick

Posted June 24, 2011 - 10:26 AM

#18

Uhhhh. These heads NEED the arches in the port and you cant just "make um bigger If you knocked down the arches I bet the flow is all messed up..............I have seen a CnC'd GYTR head compared to a stock head and there really isnt that much difference. The ports definitely are not BIGGER and the only real difference is in the bowl area under the valve seat and the intake manifold is matched to the intake port."
Go in and make sure that pilot jet is 100 percent clean........


ok well i sumed it up. i didnt just "make the port bigger" i removed that lip that is right under neath the seat. and yes, it runs stronger than it did before.

  • danzick

Posted June 25, 2011 - 04:29 PM

#19

so i got some hours on it up here at the dunes and put a 40 pilot in it, and it starts right away now. as far as the porting goes, im running even with if not pulling on my buddys 09 yz450 with a 13.5:1 piston. its pulling really hard in 3rd now. very impressed

  • yz480doinwork

Posted June 25, 2011 - 10:09 PM

#20

It might pull my ported 06 off the line but it wont quite run with it on top





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