gx200 lacks revs

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playnotwork

Member
got 2 gx200 on my twin prokart. initial run when put on kart disappointed a 48 second lap( did 48 with gx 160's) de-governed, advanced timing, changed air filter and a quick hone. unimpressed i decided to de-baffled exhaust, 1.3 ratio rockers, 14cc gx160 head (could be a bit tired) giving compression ration 10.4.. this gave me a 47.9 lap. only hit 5400 revs on the straight. gearing is the same as others who aim for 6000 rpm. did i expect to much, do i need more compression. can i just not build engines. any help appreciated cheers martin.
 
sorry got 18lb springs in. Will rev to 6400 if i blip the throttle ( is this a good idea). Heads are a pair of old t1's. Lapped the valves but not sure how well they seat. ( how can i test ?) keep making modes and test on track, only to be disappointed. is there any way to do a relative test without a dyno. cheers:cool:
 
normal pump gas. 78 jets, would settle for 6300. dont think got coil bind as free rev to 5400. slowly rises to 5400 not a sharp rise then stuck at 5400. should this config be quicker than a gx160 with minor mods.
 
If that head is 14cc and you have a .010 head gasket that is a lot more than 10.4:1 compression. In which case your fuel would need to be 110-112 octane
 
You're right, with those 2 numbers the compression would be over 14 – 1. He didn't say how far the piston was in the hole. He really needs to do a cc check.
 
dont think problem is to much compression. gx200 dished piston .035 in the hole. .010 head gasket. looking at compression tables gives about 10.4. was going to either deck block or have head skimmed to increase compression( head would be easier) or should i skimm original 22cc heads
 
basic cc head 3cc dished piston 3cc in the hole and gasket. original compression 22cc head (196 + 28) / 28 = 8. 14cc head 3cc dished piston 3cc in the hole and gasket compression ratio (196 + 20)/20 = 10.8. should this be high enough on regular petrol to give power increase. is my problem somewhere else ie valves rings etc
 
Going off my memory a 78 jet is equally to .030, if that's correct I would say your lean. I would bump it up to .036 to .038 for your main jet. Also drilling the low side jet out to .018 to .024 will help with idle and low end.
 
looking at spark plug a little bit oily so dont think on the lean side. how do i test not losing compression on piston rings and valve seats. bearig in mind it seems to be happening with both engines.
 
got a spare gx160 conrod that is 2mm longer than this rod. could i use that to raise piston in the block and use a gx160 gasket. .035 thou in the hole .045 head gasket gives .080 thou = 2.032mm is that enough clearance? or do i need to put a .010 gasket in as well?
 
Oily doesn't represent it being fat, that means your rings are not seated, or bad valve guides . You can use a leak down gauge that screws into the sparkplug hole to check if it's sealing.
 
oily/sooty certainly not lean. will try and get a leak down tester. over this side of the pond some people race sealed gx200 extreme engines. basically gx200 t2 with .065 skimmed of the head. i can not get anywhere near them, they go between 45-46s a lap i'm 48s and i dont drive that bad
 
Where would you get a Honda rod that was 2mm longer than a stock rod, we never found Honda rods to vary by .1mm (.003")
 
Kart43 said:
Where would you get a Honda rod that was 2mm longer than a stock rod, we never found Honda rods to vary by .1mm (.003")
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Actually, because I have a calculator that does all the conversions, to be more exact, .003937". Just having fun. lol But I have to agree, 2mm would be a big manufacturing tolerance.
 
WINNERSCIRCLE said:
If that head is 14cc and you have a .010 head gasket that is a lot more than 10.4:1 compression. In which case your fuel would need to be 110-112 octane
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110 octane is overkill for one of these basically stock engines, even if he had 14:1 compression. Better power could be made with 93 pump gas

If you have gx160 heads on these engines and those heads have not been ported, or are completely stock, you would make better power with the gx200 heads. Your giving up alot of flow by using the gx160 heads if they are stock....ill take flow over compression any day of the week. You can have all the compression you can get, but if you dont have the flow you wont make power
 
playnotwork said:
looking at spark plug a little bit oily so dont think on the lean side. how do i test not losing compression on piston rings and valve seats. bearig in mind it seems to be happening with both engines.
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If the plug is oily you need oil rings or need to check your gaps on the oil rings, you shouldnt be getting that much oil in the chamber
 
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