Air Leak? (loss of engine power)

Elitefr · Sep 12, 2010

About 2 months ago I bought a Skyhawk GT5 66cc and it ran great until yesterday, and after reading numerous posts I think its an air leak but I'm not exactly sure.

So first let me start off by saying that I was never able to run the engine (with strong power) with the choke fully disengaged, the engine would just not produce enough power. So instead I ran the bike with the choke half-engaged and that gave me tons of power and speeds up to 25-30 mph.

After two months of everyday use I decided I would run a little check-up on the engine. No scratches on cylinder, piston was clean, carb was clean, and everything was nice and tight. So I put everything back on the bike, took it back out and immediately noticed a complete difference. The bike wouldn't even get me around without the choke fully engaged. The bike idles completely fine but its just when I disengage the clutch it seems that the engine has trouble getting me around.

Also the engine can run at high RPM's when idling, but it would take about 2 seconds of pulling the throttle with the choke disengaged for it to finally take effect, but with the choke engaged it would rev right away... weird.

So what the **** is the problem? its buggin me...

r00t4rd3d · Sep 12, 2010

Where the carb connects to the intake is the most common spot for an engine robbing air leak.

Take some starter fluid or WD-40 and spray a small amount where the carb connects to the intake while the bike is idling. If it wont idle , hold the throttle so you get a low , steady rpm. If you have an air leak at that spot the engine rpms will change , starting fluid they will increase , WD-40 and they will decrease and the engine may sputter.

2door · Sep 12, 2010

r00t4rd3d said:
Where the carb connects to the intake is the most common spot for an engine robbing air leak.

Take some starter fluid or WD-40 and spray a small amount where the carb connects to the intake while the bike is idling. If it wont idle , hold the throttle so you get a low , steady rpm. If you have an air leak at that spot the engine rpms will change , starting fluid they will increase , WD-40 and they will decrease and the engine may sputter.

I concur.
It sounds very much like a vacuum leak in the induction system. Either carburetor to intake manifold or manifold to cylinder. The kit supplied intake gaskets are notorious for early failures so I recommend making a new one from a good quality gasket material available from any auto parts store.
Take a close look at how the carb is sealed to the intake manifold. The slots in the carb throat that allow it to be clamped to the intake need to be sealed as well as the throat itself. Many rely on silicone based gasket sealers but most silicone products are not compatible with gasoline (read the lable). I've been using Seal All and have not had any issues since switching from silicone products. I like to rough up the surface of the intake and make sure that both the carburetor and intake are free of any oil residue before using any sealing product.
Get back to us if these suggestions don't help.
Tom

Elitefr · Sep 13, 2010

I sprayed WD-40 all along the air intake pipe at both ends and the exhaust started emitting white smoke but the engine didn't die, but i'm pretty sure the WD-40 caused the white smoke.

I was pretty busy today and didn't have time to stop by an auto parts shop, but when I got home I tried to fix it with some electrical tape. (lol) First I wrapped the intake pipe where it meets the carb, put the carb on, and wrapped tape around that, making sure everything was nice and tight. On the other end I just tightened the bolts making sure the gasket was on there tight.

So I took the bike out and I still get the same thing... except I have more power than yesterday and some weird engine struggling, but I still couldn't run the bike with the choke off.

When I tried running the bike with the choke off sometimes it would spark, and some times it wouldn't, It kept pulling me forward and backward, but as it was doing that I would immediately turn the choke on and the engine would spark... what the heck?

killercanuck · Sep 13, 2010

Sounds like you're lean on top of a mild air leak, what's your metering clip set at? You might just need to richen the needle. If it runs good with the choke on, you're definitely lean in your carb. If you're already on your bottom knotch, you may need to enlarge your jet(much simpler than shrinking it). [Easily found with our Google search at the top of the page, they link back to this site, if you can't find, let us know.]

What I do for my mild leak, is take the carb clamp completely off, wrap everything with some plumbers tape(or electrical tape if you can't find plumbers) and put the carb clamp on over all of the tape. Alot of guys use gas resistant silicone, but that's alot harder to take off.

r00t4rd3d · Sep 14, 2010

You have an air leak at your intake if you hit it with WD-40 and white smoke started to come out the pipe.

High heat silicone , o-ring between the carb and intake , MM intake. All options to help seal it up. Electrical tape is not gonna cut it and will melt and make a mess.

I personally would take some sand paper , lightly scuff up the end of the intake , apply a light amount of high heat silicone evenly around the last inch of the intake , reinstall the carb and let the silicone dry overnight. You can get high heat silicone at any hardware store.

killercanuck · Sep 14, 2010

What do you think of the stretchable plumbers tape? Is supposed to be good for gas lines, and Coolant hoses. I prefer that over electrical any day, but hey, if electrical gets you to work that day.... eh?

I like about 4" of plumbers tape stretched out around my intake before I put the clamp on. Any more than that, and the clamp won't slide on. For me, it lasts as long as I need to take it off again(in other words never).

thoughts?

r00t4rd3d · Sep 14, 2010

They make a couple different types of plumbers tape. You can tell what is what by the color of the spool.

Blue - water
Yellow - natural gas
Pink - heavy duty

I havent had good luck with plumbers tape and gas/heat. Its just not meant for this type of application. In a pinch , sure. Some pink hd stuff would be a great addition for a break down tool bag (giggidy). Long term I dont think its a good option.

killercanuck · Sep 14, 2010

By the colour of the spool? Mine is white and its rated for gasoline and high pressure radiator coolant hose man. It cost me $15 so it should be, eh.

I'm just saying their are options to the "Gooping it up" approach.

But I guess in the long run, wouldn't a proper sized gasket be better? Can we use Gasket-Paper for this?

Elitefr · Sep 16, 2010

I gooped up both side of the intake pipe, head gasket, and replaced the exhaust gasket... still the same problem, except that the engine had gained significant power.
After a frustrating ride on my bike I looked down at it and noticed a small pool of gasoline on top of the crankcase, could this be a sign of a crankcase leak? I'm certain that it was not gas from my carb

r00t4rd3d · Sep 16, 2010

Its gas from the carb. Either from the little pumper primer thing or from a leaky bowl drain screw.

If gas is flowing out your primer the floats are probably sticking.

If its from the drain screw put some type of thread sealer on the screw.

Wipe your finger on the bowl right below the drain screw. Gas ?

charles kohler · Sep 17, 2010

add an o ring that fits tite inside the carb & push it up on the intake then tighten the carberator clamp on carb , my delroto carb has one in it.
carb may have the slots cut too far in to the carb.try it it works.
i have worked on small engines for over 60 yrs.
by the tinman.

Elitefr · Oct 1, 2010

Sorry its taken me so long to reply but I've been pretty busy.
It ended up being a problem with the float bowl, and the engine runs better now, but there is still a problem.
When I come to a stop with the engine (at an idle), I have to put the choke on mid-way to start back up. Once I accelerate to the maximum speed that it will allow me, it will sounds like the engine is struggling, so then I take the choke completely off and the bike goes off like a dart.

However, if I try to start accelerating from an idle with the choke off, the engine will still run, but it will bog so much that im barely moving... what the heck????
The bike seems to bog a lot more when the engine isn't warmed up all the way, but that seems normal.
It's just a pain in the butt that i have to keep messing with the choke as im riding my bike

Also, i've noticed that its having a harder time going up hills, but my bike still easily goes 30 on flat

Any help or suggestions would be great

EDIT: Also, my float bowl leaks while I run it, but nothin major at all. The gas can be seen at the screw points, primer and under the float bowl, it doesn't exceedingly drip gas.
I have the head gasket, carb, and injection port siliconed up

r00t4rd3d · Oct 1, 2010

First off bog is too much fuel not enough air.

What exactly did you silicone on the carb. I wanna see pics.

charles kohler · Oct 1, 2010

Do you have fuel filter between the tank & carb, if not you may have have a small speck of dirt between the float needle valve & the seat , i hope you did not put any sealer on your gas line fittings . remove carb & check if the needle is seating in the brass seat.

Elitefr · Oct 2, 2010

Couldn't a bog be caused by too much air too? (not enough gas)
Yes, I have a filter from my gas tank. What do you mean by gas line fittings? I put silicon at the front and end of engine intake pipe.
I opened the float up, found some very small specs at the bottom of the float but nothing major... i cleaned it out.
The engine runs good, its just annoying to have to keep messing with the choke, I might have to make a cable run up to my brakes.

EDIT: Sorry, I know what you mean by gas line... DOH. No I have clamps on the gas line

Elitefr · Oct 2, 2010

I didn't mean for the pictures to be so big...

gunslingerburrito · Sep 10, 2012

First of all, I know this thread is a few years old. But, i just came across it, and I noticed some striking similarities to what I've experienced.

I have been messing with my first build for almost a year now, and I am also running the exact same speed carb.

First thing I noticed is that you had the exact same fuel drip as I did. Mine came from a bad seal from the fuel line to the shutoff. But, I'm curious what that buildup has done to the seal in that area.

Second, I have had to do the same thing with my choke up until recently (now, I can put on full throttle and I just cant seem to get the engine to accelerate).
It seemed like once I could get it revved up and rolling at the mid to top end, it would run great. But, if I came to a stop, i had to hope I could get it to jump back up.

I just replaced it with an NT carb, and i still have to kill an air leak, replace the plug and see if I can get it to work.

I hope you got yours worked out (and I'd love to hear how you did it)

garreth · Jan 6, 2013

My motor has just developed a problem and might not be related to this link as i am a new user to motorbicycling.com. . . my problem started when i gave my motor a little service ie. change the sparkplug which was a BP6HS to the same one but new then i changed my fuel filter. took it out for a ride yester day and it wont get above 40 kph as apposed to my top speed of 52 kph this is a stock motor. please if theres is anyone who knows of a problem like this or experienced it themselves please give me a reply or PM mehttp://motorbicycling.com/images/smilies/Waa.gif

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Air Leak? (loss of engine power)

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