back firing before it starts

[oldblue700rjo]

ok guys i have a problem i put a 105.5 big bore and ported my head from trinity also put new valve springs. ok i put the bike together and it ran good. I went the next day to start it and again it did good let it warm up and gave it alittle gas it made a tapping noise and shut off and now evertime that i try to start it and  it will back fire and pop the whole throttle body off. what the hell is gone on man i've got my valves set at .004 intake and .007 exhaust o yeah and i have a 12.5 compresion piston stage three hotcam and +5 stroker kit

[Spartan]

Did you double check your timing? If it's off a lot it will cause it to backfire...and is your fuel controller set correctly?

[devious700rSE]

timing and what fuel did you use as in octane?

[oldblue700rjo]

yes my timing is good and i use straight avgas 102 octane

[oldblue700rjo]

also do i need to andvance my timing with all my mod or leave it alone anything will help

[Spartan]

No do not change your cam timing on your 700 unless you know what you're doing and have the right mods...Double check that the cam timing mark is lined up with the crank timing.

[russ-russ]

This is just some friendly advice, so you can take it or leave it.  Avgas is not formulated to burn quickly enough to keep up with a motor that can turn 9000 rpm.  It is made for a steady even flame propagation in a motor with a max rpm of about 3500.  Sure, the octane rating looks inviting and the price is better than race gas, but it is not a good solution for cheap race gas.  Not to mention that it has additives that are less than kind to plastic and rubber over time.

Have you re-mapped your PC3 for the massive changes you've made to the motor?

[Spartan]

According to the PM I got from him he hasn't...so that sounds like the major issue now.

[russ-russ]

According to the PM I got from him he hasn't...so that sounds like the major issue now.

OK, so borrow somebody's map that is sort of close, and then get that sucker to a dyno.  Problem solved.

oldblue700rjo, where do you live and what is the altitude there?

[oldblue700rjo]

ok guys thanks for the advice i will not use the avgas and will get it to a dyno machine and i live in big spring tx alitude have no clue ok now i aslo took it all apart this morning and my left intake valve is bent again y did i only bend one and not both thats y it wont start . also there are no dyno places around my little ass town this suck

[1badazz_700r]

if you have over sized valves your JE piston will not clear the bigger valves. I know this from personal experience. the valve reliefs are not big enough. Or if you dont have oversize valves then it sounds like your timing was off.make sure when you put it back together and time it correctly,roll it over by hand a few times. this way if something is not right you will know and should not do any damage

[oldblue700rjo]

well i still run stock valves and ive been runnin a high dome piston for a while but this is the first time that i put it together and let it idle for an hour and then give it gas and bend the one valve should i set my clearance at .005 or .006 instead on .004 on that one intake so ill be sure that i dont bend it the next time cause my timing was perfect and i always hand turn my motor to check the timing and it sounded good nothing was hitting like i said it idled for a good while before i gave it about 1/4 throttle it should have bendt it as soon as i started it if it was off mybe the piston has is off alittle i dont know bud its weird thou

[Krandall]

You had the head off. Did you see any marks in the piston?

[oldblue700rjo]

yes a very small one i got it going againgot some racing fuel 110 octane and changed my clearance on valves but now i need a dowmload for a 105.5 ,ported head ,dcm daull exhaust, k&m intake and big filter,stage 3 hotcam  can anyone get close to that till i get it to a dyno

[oldblue700rjo]

thanks guys for all the help now i can go spank some ass around my little ass town lol