Engine idles but bogs and has no power when throtle is opened

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Flyinggrape

New Member
May 27, 2011
9
0
0
Ocoee, Fl
Hope somebody can help. My 12 year old son wanted to motorize his bicycle. He saved up his money and I matched it. We purchased a boygofast 68 cc bicycle engine kit. We installed it and had it up in running in not time with no troubles at all. It ran great for a couple of months. He went to ride it one day and it was to start and didn't have any power. Now it will crank up and sort of idle. You do have to keep reving it to keep it running but it eventually bogs down and shuts off. When you let the clucth out it doesn't have any power and bogs when you give it throtle. I have been through the carb. Replaced the intake to cylinder gasket and put sealer on the carb to intake joint to prevent any vacuum leaks. Nothing has changed. I hope someone can give me a clue as to what it is before I tear down the negine looking for something else. Do these things have reed valves? I have plenty of experience with 4 cycle engines but know hardly anthing about 2 cycles. :-||
 

DuctTapedGoat

Active Member
Dec 20, 2010
1,179
10
38
38
Nampa Idaho
Sounds like a CNSv2 carb. Is it's air filter cover square and red?
I'm not sure what's up with those things, and I can't justify the cost of buying one to tinker with. The one time I've encountered one, it felt like a choke problem in that it was like it was literally starving for air.

I'd suggest a new carb - the NT carb works great and without a hitch. It's the one with the black air filter cover that is kinda shaped like a skull.
 

nate-m

New Member
May 24, 2011
13
0
0
Georgia
Remember the three important things your engine needs to start and run well:

1. Spark. You need a eletrical spark to start the motor.
2. Gasoline. You need the proper amount of gasoline to mix with air in the right ratio to form a combustible fuel.
3. Air. Your engine needs to be sucking in air and pushing out air properly in order to mix with gasoline to form a combustible fuel.

You have all three of those things and you have a running motor.

Your missing one of those three.


First thing to do...

1. SPARK!

A new spark plug is always a good thing to try. When a spark plug fouls it will simply stop working. Like somebody flipped a switch. Putting a new spark plug will help tremendously if that is the case.

I always carry a new spark plug with me whenever I ride 2-stroke bikes. It's kinda stupid not to as it's cheap, easy to replace (with the proper tool), and small to carry.

2-strokes foul plugs. It should happen rarely and only when the plug is worn out if the bike is properly tuned, but most people will foul plugs time to time. 4-strokes tend to not have as much issues and on automobiles you have multiple cylinders.


When you replace a spark plug you can check two more things:

A. See if it is getting gasoline. Try running it a bit before changing the spark plug. When you pull it out and you cranked it over a bunch of times without starting then it should be wet and you should be able to smell the gasoline very strong out of the spark plug hole.

It's not a very good test, but it's easy if you remember.

B. See if it is getting spark.

The idea is that if you put the spark plug into the spark plug boot, but don't plug the spark plug back into the hole first you can place the tip of the plug against the engine block and turn it over and you should see the spark. It should be fairly bright and blue, but you'll have a hard time in direct sunlight.

But that's hard on these bikes since you need to be pedaling it first. :) You'll probably shock yourself and it's painful and scary. But it won't damage you much.

I'd just try it with the new spark plug first without testing the spark, but it's something to keep in mind.

If your not getting a spark then it's probably a lose connection somewhere. Trace the wires, make sure that they are firmly in place.

Connections come loose, they corrode and form to much resistance. Your kill switch can be broken and be killing your motor even when your not pressing it. The spark plug can be lose. The spark plug wire can be lose. The CDI black box can be bad.


B. GASOLINE!

If replacing the spark plug does not work and you know your getting a strong spark then it's time to check the fuel.

It sounds like your engine is running very rich or you have water in the float bowl.

I'd check:
* Make sure that you have gasoline,
* make sure that the filter is not plugged up, (fuel flows through the fuel line.
* Make sure that the float bowl is filling up with gasoline.
* Make sure that it's not filling up too far with gasoline and flooding the motor. (that your float bowl floats are working...)

I think that it is likely that you have water in your float bowl.

Water and gasoline don't mix. But... water can get into the fuel tank. It doesn't take much. Riding through sprinklers or even just high humidity can do it. The gas caps on these things are pretty lousy.

When water gets in the motor will run very well. The water gets shaken up into particulates... like tiny bubbles of water in your gasoline. This gets sucked into your motor and evaporates very rapidly and doesn't usually cause problems immediately.

But what happens is that when you turn off the motor and let it sit then the water collects at the bottom of the fuel bowl on the carb. The water bubbles collect and form a puddle that sit underneath the main jet. This will allow some gasoline to get past occasionally so you can get it to sort of run, but it will die if you try to give it lots of gas or if your trying to go up a hill or something like that.

Enough water will simply stop the motor running at all.

To check for water requires a visual inspection of the float bowl with gasoline in it. Take the carb off, take the bowl off and then look for a puddle or bubbles underneath the gasoline. Thats water.

If you have water then clean out the bowl, empty out the gas tank, and put fresh gasoline in. Add alcohol to soak up the remaining water. Alcohol binds with water, but gasoline doesn't. The alcohol binds with the water and eventually gets sucked into your motor and burns away harmlessly.

Ethanol gasoline is helpful. Also you should buy and use anti-gas line freezing chemicals at the auto part store. That is mostly alcohol.

Stuff like Iso-heet. Use as indicated by the bottle. Don't overdo it.


If it's not water then it's likely your jets are clogged and fuel isn't getting through to the engine.

Once you got the float bowl removed take out the jet. Inspect it and make sure that it's clear from debris. That's the smallest opening and if it's clogged it's probably going to be that. Just don't damage it when trying to remove it.

Also the idle circuit is probably separate from the main jet. So if you get the main jet cleaned out and it's working fine, but it's not idling right then the idle jet/circuit may be clogged also.

I am not that familiar with these types of carbs so I don't know for certain.

Once you get the jet cleaned out put a fuel line filter to stop other debris from causing problems. The gas tanks in these kits are very dirty and you will probably get issues if you don't put a proper fuel filter in place.


These are the most likely issues.


C AIR!

Air is very simple on these motors. Check the air filter, check the exhaust. If they are clogged then that will cause problems. There is no valve train like on 4-strokes so it's easy to troubleshoot this issue.
 

oldsub

New Member
Dec 9, 2010
20
0
0
Victoria
Here is something you may want to check, trace the cable from your choke control. It goes to the top of the carburetor along with the throttle cable. (If your carburetor is a CNS) lift the rubber insulator, it sit on the top of the carburetor and the choke cable goes through it, make sure the end of the choke cable is not sitting on top of the carburetor and it is well inside the hole for it on top of the carburetor. Just to explain this a little further. This has happen to me, because of vibrations or ???? this choke cable climbs out of the hole which it is made for, and your engine is getting choked at all times. If it out of the hole, just push it back, you may want to wiggle it a bit to make sure its at the bottom of the hole. Also check the screw on the control lever, (center of the control lever, choke) this comes loose all the time.

Best of luck
oldsub
 
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cejay825

New Member
May 31, 2011
1
0
0
Georgia
I had the same problem and everybody screamed CNS carb, CNS carb. I replaced the cheap factory plug with an NGK BP5HS and she was back up and actually better than before. Never had a problem with the CNS....once I found out the screw on the left is the air/fuel mix and engine idle screw is on the left....at least thats the way I treated them and mine screams!!!!
 

Flyinggrape

New Member
May 27, 2011
9
0
0
Ocoee, Fl
new plug, new coil. Has compression, fuel and air. replaced intake gaskets. Went through carb and the jet is in place and the float is not full of gas. It still will not run other than an anemic idle then dies. Anybody else? Everything I have done has not changed a thing.
 

Wm Holden

New Member
Jun 1, 2011
358
2
0
Ventura California
is it smoking?
I once added oil straight to the tank without mixing first...it went straight to the bowl and acted pretty much how you describe...
Did your son maybe add gas from an unreliable source?
unlubricated runs could have hurt the compression...or just be plain crappy gas...
just trying to help...

I leaned mine waaayyy out to get a good top end scream instead of blubbering along...and now it's pretty tough to keep it running at idle when its cold and first running...full choke...half choke for a couple minutes...then i can keep it running and all is well...finally kick off the choke and blast around the beach.
but not nearly as easy to start and keep running as when it was running rich as ****...
 

rohmell

Active Member
Jun 2, 2010
1,531
6
38
New York
You say that it used to run good, but now it's not so good, You mentioned new plug, new coil, but did you reuse the old sparkplug wire and boot? I would go through the entire electrical system, from magneto to plug. Use a little bit of sandpaper on the bottom of the magneto where the mounting holes are, and on the posts of the engine to which it attaches. Also a little sandpaper on the ring lug for the black wire to clean it up nice and bright so that you have good electrical contact.
 

Flyinggrape

New Member
May 27, 2011
9
0
0
Ocoee, Fl
the boot and plug wire are new because they are part of the new coil. The bike used to run fine. He shut it off and then it would hardly idle and had no power at all. I have been through everything I know and cannot figure it out. I haven't checked the electrical trigger device that make the coil fire yet. I cannot imagine what else it could be.
 

Wippenshox

New Member
Jun 12, 2011
18
0
0
Brazil
I'm curious about this problem. Any news on the engine, Flyinggrape?

One thing I noticed is that you mention you have air, compression and fuel. But you never confirmed/mentioned to us you have sparks. Are you sure the electrical system is working?
 

Flyinggrape

New Member
May 27, 2011
9
0
0
Ocoee, Fl
The electrical is working. I even replace the coil, plug wire and spark plug. It does run. It barely stays running. You pedel it up to start it and then it slows down and eventually dies.
 

DuctTapedGoat

Active Member
Dec 20, 2010
1,179
10
38
38
Nampa Idaho
Flyinggrape: What kind of carb do you have? Can we see a picture?

If you have compression and no vacuum leaks it's gotta be that you have a red filtered CNS v2 carb.
 

Flyinggrape

New Member
May 27, 2011
9
0
0
Ocoee, Fl
the carb has the black aircleaner cover that sort of looks like a skull. Round with two screws holding it inplace and 4 vent tubes out the bottom.
 

DuctTapedGoat

Active Member
Dec 20, 2010
1,179
10
38
38
Nampa Idaho
Sounds like an NT cover on a CNS carb - dunno if it's CNS or CNSv2/Gen B though off that.

Do you mind if I ask where you got it from?

At the carb outlet, is there a white plastic piece?
 

Flyinggrape

New Member
May 27, 2011
9
0
0
Ocoee, Fl
I ordered it from boy go fast. THe carb does not have a white piece on it. Looking at the air cleaner, the primer and idle screw are on the left. The choke and fuel line are on the right and the throttle cable goes directly in the top. The carb clamps onto a 2-3inch long intake tube that bolts directly to the cylinder.