Gx160 motor problem

[Gx160Mini]

My motor has the following parts on it and only revs to ~4000rpm
GX160
Arc rod +.020
Flattop piston stock bore
File fit rings
CM pushrods
1.3 billet rockers
26lb springs(have duals but can't find someone to cut down the seat)
307 lift cam from nrracing (307lift, ICL 08, LS 07)
.045 honda head gasket
27mm intake/25mm exaust valves(3angle valve job) (very mild port job)
Old style gx160 head
Arc 6619 flywheel w/ stock coil
No governor
22mm mikuni round side(95main/17pilot, needle clip on one up from the bottom)
Agk 2stage exhaust

 

[Motra]

Probably timing or jetting.

 

[cheezy1]

Bigger jets...too small for your application.

 

[Gx160Mini]

My plug reads rich though

 

[cheezy1]

Do you have a real Mikuni? Or a cheap copy they sell everywhere?

 

[cheezy1]

Also like Motra said..timing can be a big factor

 

[Gx160Mini]

I got it from nrracing and I think my coil may have a rev limiter.

 

[vwfan79]

I would advance the timing 10° and put a 130 main and 12.5 pilot and see what happen, should spin pretty good. I have less mods on my gx160 and it will spin 6000.

 

[Gx160Mini]

Ok I'll try

 

[PacMule]

I would check your valvetrain to make sure your not coil binding. Your at about .400 lift with your parts list,that asking a bit much with 26lb springs.

 

[mikeholt25]

sounds like a timing issue check everything head temp spark plug gap, try .50 gap on your coil to flywheel u got the best committing, cheezy1 and vwfan79 they give good advise

 

[vwfan79]

Pakmule is correct, if you have coil bind and start getting more rpms you will start damaging stuff.

 

[Gx160Mini]

How do I check for coil bind an if there is any I don't have the tool or can't find anybody with the tool to cut the spring pockets down.

 

[vwfan79]

You will have to measure spring height when they are fully compressed and look up specs for at what height those springs bind.

 

[astrowrench]

or just turn it over until the springs are FULLY compressed and see if there is any space between the coils(push hard on it and see if it moves,put a feeler gauge between the coils,a piece of card- stock,or Look at it ,not to tough to figure out)

 

[Gx160Mini]

Ok I figured that is how you check it but what if there binding. What would I have to do.