Built gx200 not putting power I think it should?

[Bautbaut]

Hi all...

Sorry if this is incorrect spot, but I'm new.

Built my own go kart this spring for a new hobby and have tinkered since. Had a gx270 with a header, port and polish, air filter and Governor removed. Was happy as it hit 65kmh and killed it through the mud and steep inclines.... but wanted to build high rpm motor just because...
After reading up, gx200 seemed like good option... 20 pounds lighter and parts are half price over the gz270 since its so common. Sounds like pretty easy to get over 10hp from it...

Anyway, long story short... Built one but Im really disappointed with it. My gx270 was more powerful.

Here is list of what I did :

1. Removed governor
2. GX 160 head (14cc) - port and polished
3. Arc Billet flywheel 28° advanced timing
4. Arc Billet connecting rod
5. Comp super x cam
6. Billet lifters
7. 1.3 ratio rockers
8. chromoly rods
9. MSD 8.5mm outlaw ignition coil
10. 0.010 head gasket
11. Thin ring flat top piston
12. 24mm genuine mikuni flat slide carb
13. Custom header (muffler might be wayy to restrictive though)

Did I have too high of expectations for the build or what could be wrong that's robbing it of eating the gz270? Haven't tuned carb but runs great (no sputter or lag etc and plug after idle was bit rich but nothing crazy.


Any ideas?

 

[landuse]

Have you got some hard data from both to confirm that it is not putting out as much power?

 

[Bautbaut]

'seat of my pants' data...

Have a 'track' in my back field and it slows down up hills it didn't use to, feels slower of the line and doesn't hit same speed on the straights.

Can't help but wonder if it's valve related now. Got a much thicker valve guide plate.... Which raises rockers but rod is same length so wouldn't that give way less lift?

 

[mckutzy]

Off hand is sounds the cam and flywheel timing are not working well with each other?

 

[JTSpeedDemon]

^^that! Cams usually work with specific parts(flywheel, head, carb, valve springs) and run poorly without that specific setup. That cam should have come with a spec card. Read that and also contact CompCams and ask what the ideal setup is for that cam. Bigger is not always better, true engine building requires making the parts work synchronously, not just plugging in bigger billet parts like so many do.

 

[Bautbaut]

Flywheel is 28° and the cam specs say 30°...would 2° make a huge difference?

 

[vpd66]

Horsepower is just a bragging number. What your experiencing is less torque. Torque is actually what you feel (or seat of the pants feeling has you describe it). Your GX270 most likely made more torque then your built up GX200. There is no substitute for cubic inches. Even if your built GX200 made has much torque has the GX270 it would be at a very different rpm and might only hit it for a split second. Where has the 270 carried the torque number longer through the rpm range. Like JTSpeedDemon said your cam will dictate what your engine does for torque and where it happens. It would also take a very detailed build of the GX200 to make more torque then the GX270.

 

[Bautbaut]

So.. I should have just hopped up my gx270....

 

[vpd66]

If you would have put the money you put in the 200 into 270 I think you would have been happier. A GX270 is a big block. It shares a lot of the same parts the GX390 has. A quick upgrade would be a 390 carb.

 

[Bautbaut]

Thinking of putting it back on the kart and tossing the spare flatside mikuni I have.

I must have had too high expectation... More I think about it, I must've been dreaming as my 270 had filter, header, Port and polish and gx390 carb on it. Was most likely putting out 11hp already and better torque. Just wanted high rpm

 

[JTSpeedDemon]

You can also gear it down to get a lot of that torque you want.

 

[Bautbaut]

You can also gear it down to get a lot of that torque you want.

If I lower gearing, I lose top end speed. I can already climb any hill and go 50mph down the road.... Just the sweet spot

 

[landuse]

If I lower gearing, I lose top end speed. I can already climb any hill and go 50mph down the road.... Just the sweet spot

In that case, you aren't going to get any more out of it

 

[vpd66]

Tell us about what gearing you have? Are both engines running torque converters? Did you just swap the motor and use the same gearing? Do you have a tach? I've never heard of the cam you listed do you have the specs of the cam? You need to gear the kart so the engine stays in the power band of the camshaft. All camshafts have a power band of around 3000-4000 rpm. Meaning something like 3000-7000 rpm, 2000-5000 rpm, and etc. A lot of these aftermarket cams make the engine fall flat on there face when not in the designed power band.

 

[Bautbaut]

Both using same gearing and torque convertors yes. Literally just motor swap. My problem is I now know I overestimated what to expect and also forgot I had my gx270 already modded (filter/header/jetted gx390 carb/ported and polished) so of course it wouldn't be as torquey.

Where can I find a gx270 aluminum flywheel? Think I'm going to back to it, but want some more rpm out of it. Flywheels hard to find here in Canada it seems.

I think I'm going to swap the 98cc out of my mini bike and put the 200 in and watch my 12 year old enjoy

 

[mckutzy]

Here in Canada were just screwed for stuff like this... all the minibike/gokart major makers are from the states, so thats pretty much where you can get stuff like that..

 

[Bautbaut]

Ya.. That's what I have been doing. Dollar so low its just too expensive though and the shipping is usually unrealistic

 

[vpd66]

Personally if I were you I'd sell the GX270 and get a Predator 420. The only flywheel for a 270 is $195.00 US. That is already half way to the cost of a 420. Also if your using the same torque converter setup which most likely is a TAV30 you are over the horsepower and torque rating of that setup.

 

[Bautbaut]

It is technically over the rated hp, but I have yet to wear out a belt on the tav30 with the modified gx270 and I've gone in and through some pretty gnarly stuff with. I don't put a lot of weight on the 'rated' hp for these anymore. Gearing is a huge part of it and my kart is geared the sweet spot for the motor (still does 65kmh and no hill I can't climb)

 

[vpd66]

If it is easy and not too costly I'd still try regearing the GX200. I highly doubt you were getting in to the power band of the 200.