why the f is my mcx apex popping

[Jona$]

My apex with mcx pops one time in the middle when in wot, it just pops and goes beyond to full power.

had it to mcx for 2 days ago and changed the efi since it was faulty and changed head gasket since it was blown.

made some short runs and it seemed fine. but now home again its the same.
wtf can the efi already been blown?

i changed the titan exhaust for the steel a few weeks back, could be exhaust leak? but why in the same range. as for the donuts and the clamps they were changed at mcx and it did nothing.

this is the last thing to get it perfect but it makes me angry as hell and i cant just go back to mcx since its like 6hr drive one way and cost alot.. just last trip with fuel and their bill cost me like 2000 $

 

[Jona$]

The things i can think on
1.
Timing off, missed when putting top together, but shouldnt it run like crap then?

2.
a valve to tight or Open? Changed alot of the schims.

3.
Exhaust leak, changed to mcx steel exhaust.

4.
Overreving?
Stretched it from 121-144 but can it overrev just for a longer track?


Yeah that what im wondering to, but it never came to rev limiter as a 121" could it do that as a 144" ? Shouldnt it go lower in rpm since the longer track, or perhaps the power is to strong so it doesnt matter but it gets more traction.

Adding maybe 2-3gr on the supertip and see?

Becauase it only happens when going slow and Giving wot, not if you have a speed of like 30 and wot, but it doesnt like wot more like one fine tuned backfire, maybee ignition cutting for rev limiter ?

 

[paulharris]

rev limiter.

normal to hit it once in a while on the trail, or when you first hit the throttle, or in hardpack conditions. but when in deep powder it will not do it.

or add more primary weight.

 

[Jona$]

well thats in my mind aswell, but i ran dragrace,played in the mountains and aswell spunn on the slippery ice in the spring and never hit the rev limiter.

now as a 144 shouldnt it if any go lower in rpms as ordinary machines or is the strong engine with the longer track just making more traction

 

[Tarzannr1]

You say you had a exaust leak and now its alraigt. Have you checked the boost? Maybe you are overboosting?

 

[M5-]

It's probably bouncing off the rev limiter before the secondary has a chance to shift out and pull down the revs, my Nypex does that as well but once it shifts out it settles right down to where it needs to be. What happens if you roll on the power slower up to wfo instead of just hammering on it?

M5

 

[summitboy]

What is the rpm showing you ? Also how old is the kit ? Injectors color ? What clutching ?

 

[Jona$]

M5 im with you.
the kit is just a year old and had it to mcx 3days were it were mapped etc.

and yes it goes better if roll on wot in the mid range.

alot went away when i put on 3gr on the supertip. total 86gr

silver-yellow-silver primary spring with supter tip cam x 55gr from inner:
tungsten,tungsten. tungsten,4 shims. 3shims,3shims. for primary.

secondary:
org helix with the wite-wite spring that goes to 120deg put to 6-2 80deg.

the setup worked flawless when it was a 121, now as a 144 why would it need more weights etc?

the rpms tell me 10500 since i put on more weights, had it at 10800 before and the pop seem to be around 8-9000rpm if i can believe my eyes and tachmeter.

The donuts and the clamps holding them are spanking new, so are also the y-exhaust wich is steel.

 

[up-high]

The pop might have been at 10500(rev limiter). The tach has a hard time keeping up to the engine. Maybe the turbo is sensing more load from the longer track and spooling faster? What elevation are you riding? Try some more weight and see what happens.
If you want to eliminate the chance of donuts leaking, get a set of copper ones from Thistledoo.

 

[Jona$]

yeah believe it is something like that since i put on 3gr more it has been reduced alot.

Got a tip from a member to get a steeper helix, like 44/54 and dalton red spring to get more grip at the secondary.

Im running sea-level.

the donuts and clamps are brand new.

 

[julio]

pop

just a guess but if it didnt do it till you messed with the exhaust you probably had a crack before slowing down the spool, by fixing it you are getting boost faster and hitting the rev limiter. It doesnt take much of a leak to slow spool but will take a decent leak to cost you note worthy boost.. The tach does not keep up with the engine especially where you are getting the pop.. julio

 

[julio]

ps

if you still have the titanium ys look them over around where they mount to the tunnel and in the bottom of the v where the tubes come together, I bet you find a crack.. julio

 

[Jona$]

yeah Julio, both y-pipes had cracks in the v when doing a overview under the summer and changed them for the stainless one, so they are spanking new to.