i am running the GX-5r in my Rc8t and i love it. plenty of power. so thats were i would go.

+1 GO PRO .21 5 PORT TURBO HEAD
match with 2072 pipe & o'donnel 97T plugs
the last 2 are RTR motors

+1 That a killer combo

Thanks for info.

If my engine is revving up and then dropping down to normal when i stop my car, am i still rich on the lowspeed needle?and when my car is on a half tank of fuel,idle suddenly rise like its gonna run away from me.

Engine coming in with a high idle then dropping down after a few seconds is the sign of a rich bottom end with the idle gap too wide.
With this situation you will need to have your top end set too lean to compensate, so this could be the cause of your engine reving up at below half a tank - as your mixture will have leaned out further as it is harder to maintain tank pressure as the fuel level drops.

Set your idle gap to .7mm, no more. Now if the motor won't idle at this setting, lean the bottom end to bring the revs up - DO NOT ADJUST THE IDLE SCREW to bring the revs up.
At the same time richen the top end needle half a turn (this may be too much but you need to start rich and work the other way).
Tune the bottom end for a crisp take off, then make small adjustments to the top end for nice clean running at WOT with plenty of smoke. If you needed to adjust (lean) the top end by a reasonable amount, then re-visit the bottom end needle, which you may have to richen slightly to compensate.

Be aware of the relationship between the idle gap and the low speed needle -
If you raise the idle you will richen the bottom end, and if you lower the idle you will lean the bottom end. Always make adjustments to compensate for this if you need to adjust the idle at any time.


The other possibilty with the motor reving up at below half a tank is that you have a split in the tank seam, which is causing an air leak and leaning the motor once the fuel level drops below the level of the split and air starts getting entrained onto the tank.
Get the tune right first. I think this is more than likely your problem.

Well I just bought one these GX-5R combos. I assuming the pipe that comes with it is a decent match.

if you bought the GX-5R combo then it came with the 2072 pipe. it is an awsome setup. I couldnt beleave how much power it has. more than my old .28 setup

+1 Nice explanation Grizz.

I see this far too often at the track, and also guys tryin to tune an engine when the linkages aren't set correctly also is a big problem I'v seen latelly.

Yes - I think the wide idle gap / too rich bottom end / lean top end senario would be the most common tuning fault out there. It crops up on here all the time too. Same symtoms, same answer every time.
Itīs also surprising how many guys don't realise the connection between idle adjustments and LSN position.

im using a go 7port(not the go GX series)on my jammin X1Xcr,power is great but seem to get very weak on the bottom after 2 to 4 laps on the track,i cannot do a quick simple 180 degree turn with it,i just want to have a snappy acceleration,im using a dynamite 053 pipe .5mm head shims,fioroni carbon clutch shoes and 1.1 clutch springs gearing on my buggy is 48t spurgear/14 clutchbell..any advice to make this engine more punchy on the bottom end?

Have a peek down the carb throat and tell us if you have the long or short low speed needle in your motor.
If you have the long needle, I suspect you are too lean on the top end.
This senario is well documented on here, as are the different needle lengths.
The short and long needle carbs tune quite differently. If you want more info PM me for details on needles and tuning.
Try richening the top end 1/4 turn and retune from there.

i have the carb with the short LSN.should i lean the HSN or the LSN?

just want an acceleration like this one the video although the engine on the video is a modified 7port.. my 7port can scream like that on the stretch but when it comes to a full stop and pulled the trigger oh my what a lazy acceleration it has.
http://www.youtube.com/watch?v=711GETlpCEc

Well there is something wrong somewhere, because a 7 Port with 053 should kick butt. Could be clutch. Maybe a broken spring or the wrong springs. 7 port is best with 1.1 and alloy shoes, they do not like an early clutch.
Otherwise it could be too rich or too lean. Hard to say without hearing it in the flesh.

it took alot of work to make the 7 port scream like that ! unfortunately a stock 7 port is never going to make power like the one in my video.... FYI I modified that particular 7 port.....