150cc bogs after 1/2 throttle By backyardmech (Read 9,164 times)

[backyardmech]

Hi, new to forum and appreciate any suggestions!

Bought a used/abused go kart 150cc gy6. After much headbanging, I got electrical issues solved and good spark. Carb was trashed, so ordered new carb from ebay seller, cleaned tank, new lines, filter etc. Read about vacuum petcock so checked to see if fuel was leaking into vac and it wasn't. Fuel flow seems adequete at idle. Starts right up and runs good at idle.

So here is where I stand. Install new carb and Kart ran pretty good (I have nothing to compare to, this is my first gy6) for about an hour. After that I went to ride it and it has no throttle response beyond about 1/2 throttle. Still runs pretty good and sounds strong until then but beyond 1/2 it falls on its face. (no speed increase and maybe sounds like it drops rpms?)

I did notice that if I put it up on stands with no load on it, it sounds strong thru out the throttle range?

Also noticed the new carb seems to have a very small leak, maybe at the bowl but haven't taken it off yet to check anything as it voids the warranty in case I need to return it. But just don't want to play parts swap, shipping back and forth if the problem I am having is a known problem. Of course, I don't know jet sizing in it but was advertised as a direct bolt and go replacement.

I did check and adjust my fuel air mixture as it was shipped at 4 turns out and sounds better at 3 turns out at idle, but this shouldn't effect top end anyway...

Just wanted to start with as much info on my end as possible..thanks in advance for any help...

[beachbum]

Check to see if the carb bowl drain screw is loose. That's where the leak might be coming from. If that is not the cause of the bogging, then I would check for air leaks around your intake. I don't know what kind of filter you have, but see if there are cracks etc around it.
Check all your vacuum lines for leaks and if they are connected.

[backyardmech]

Hey beachbum,thanks for the quick response. The leak is up higher (below that vacuum thing on the throttle side is where I saw vey light wet dirt accumulation?) and so minor I don't think it relates to the problem (I literally rubbed my finger on side of carb to find it...not puddling anywhere.
I sprayed around intake and all is good.

Running a stock filter housing in good shape, no cracks etc. and same problem with or without it mounted.

Also ran kart with and without it mounted for that first hour when I first put the carb on and was testing it. At that point kart ran good either way.

[Alleyoop]

If it was abused check your CVT, Variator weights and belt, also take the top off the carb and check the diaphragm for pin holes or rips in the rubber, some of these carbs they sell have been sitting on the shelves in a warehouse for many years and rubber deteriorates.

The Fuel Ratio will effect top end if it to rich, after it is warmed up adjust the Fuel Ratio to get the highest IDLE(RPMS) out of the mixture.
What size carb did you get 24mm 26mm 30mm etc..
Also what kind of AIR FILTER do you have on there.
Alleyoop

[backyardmech]

CVT, Variator weights and belt

...is this inside the engine? I have a drive chain with a forward reverse looking transmission operated by a cable.

Sorry...this is all new to me. I build old school choppers. bought this for my kid and on a learning curve.

Gues I should check the rubber. Being a new carb I didn't want to void warranty by opening it up, but, hell I understand carbs and it was cheap enough so ....

One question I have is did they put different mains in different carbs and would it be unsual for my main to be to small? I mean were different mains in different applications of what looks like the same carb?

[backyardmech]

Hey alleyoop.....would it be the same to just put it up on stands and see if the slide is operating properly vs. pulling the diaphram?

...and why does it not seem to bog when on stands?

sorry...lots of questions, just trying to sort this out in my head after chasing so many other gremlins.

[beachbum]

You said it ran good for an hour. So, it seems like the jets are ok. Something went wrong. Definitely follow Alleyoops advice.

[beachbum]

Feb 9, 2013 12:03:34 GMT -6 backyardmech said:

CVT, Variator weights and belt

...is this inside the engine? I have a drive chain with a forward reverse looking transmission operated by a cable.

Sorry...this is all new to me. I build old school choppers. bought this for my kid and on a learning curve.

Gues I should check the rubber. Being a new carb I didn't want to void warranty by opening it up, but, hell I understand carbs and it was cheap enough so ....

One question I have is did they put different mains in different carbs and would it be unsual for my main to be to small? I mean were different mains in different applications of what looks like the same carb?

Cvt is the transmission: continuously variable transmission

[Alleyoop]

Yes that is on the LEFT side of the motor Take the CVT cover off and you will find a front pulley that is called the VARIATOR and the Rear PULLEY is your CLUTCH which actually in turn turns the SPROCKET that turns the Rear Axle.
Alleyoop

[backyardmech]

Ok, going to head down to mini storage and do that now.....

[Alleyoop]

Also here is how to take the Variator off and check out the weights and or replace them.
Alleyoop

[backyardmech]

OK, I didn't see that last video before I left (so i might have to find an impact driver depending on your response to the following)...however my visual observations were that as I increased throttle the belt did ride up on the variator (the rear half of the variator moved out) and as I decreased throttle it rode back down (variator moved back in).

But the other strange observation I made again was that while the kart is up on the stands vs. down on the ground actually riding it, it sounds great. You can actually hear and feel the continued increase in rpms beyond half throttle on up to full throttle?

so would this still be related to the weights even tho visually I can see the belt moving up the variator and it sounds great on the stands with no load or whole different problem???

[Alleyoop]

It could still be the weights, since you said it was in bad shape to start off with and probably the weights can be either to heavy or have really FLAT spots. With no load on it the motor will rev up easly. It could also be low on compression and not have the power to pull a lot of weight. You could also try adjusting the Valves Adjust them both to .004 inchs.

Does it have a tach on it, I always recommend getting even a cheap tach to see what the rpms are. A tach is very important in tuning a motor and it also tells you the PAST, PRESENT and FUTURE as a gypsy would say. Once you get it running good all you have to look is at your tach and if something is going on the RPMS will tell you right off the bat. Unless you have very good ears and are familiar with the sound your motor makes at different rpms you cannot tell if it dropped 500 or more rpms on you which would indicate something is either going south or something is wrong.
Alleyoop

[backyardmech]

yeah, at this point I'm just going by ear as being a go kart it has no tach. Guess I need to get an impact wrench as, even tho I can see the belt ride all the way up the variator, I should at least still inspect it.
I do have a compression tester and the ability to check valve lash...it just seems so strong on the bottom half of throttle tho. Do you know what psi range I should have if healthy?

BTW, when I first got this kart it looked good visually (not banged up, decent paint, fenders intact etc,) and I traded for it non running (didn't trade much haha), but the stator was shot, the battery was bad, the coil and wire was cracked up, the fuse was cut out, the 3 cdi boxes laying on the ground were questionable at best, the carb was corroded and thick with green gunk inside, slide frozen, many connections needed cleaning and the tires were bald and not all would hold air, so yes it was rode hard (out in the country thru creeks etc.) and apparently left outside when not in use...lmao. All of the above items mentioned have now been replaced and sorted thru. Oh, and the seat belts appear rusted in the closed position and I can't even free them up with pb blaster...haha.

[Alleyoop]

If healthy anothing over 120 is good, 150 is excellent anything above that is AWESOME.

Yea check the valves and adjust if necessary
Alleyoop