Loosing Power

aaronbentzel · May 20, 2012

Hey Guys

I just noticed the other day when I was riding my bike that when I hit its top speed, or when going down a hill my motor makes real loud choppy noises, and it loses a little speed when this happens. One day I was going down an especially large hill and this noise and small loss of power happened and I held the throttle to see if it would go away but I then lost all throttle response. When I got home, I found that the carb had blown right off the intake pipe! It was an easy fix, but I dont know what would cause this stuff. It works fine in the low and mid range, but once it is at its max, it starts doing weird things!! I have a CNS high performance carb (the one that comes with the grubee skyhawk kitt 2011) and it is only about 2 weeks old. Help!! zpt

rustycase · May 20, 2012

the small loss of power when running WOT might have been the piston seizing in the cylinder from getting too hot. Hope it's not that!

...loud choppy noises??? four stroking? is it running too rich?
What does your plug look like after a speed run?

Carb coming off the spigot?

Well, that's just another day in the life with a chinagirl!

I suppose you could use some shimstock in there, or lockwire the carb forward, to keep it from drifting back... just don't overtighten it! Then they just break!

It seems your list of things that should get regular attention just got added to...

Best
rc

david jeffries · May 20, 2012

the loss of power is probaly due to the crappy tuning of cns carbs. never had one myself, but heard a lot about the problems they come with. some claim they are able to tune them and they work great. others say they are a continual headache. best to get an nt carb if you can find one, or an rt carb from dax. i will be getting an rt carb myself when i have the money. i currently have an nt carb and its ok. as far as the carb blowing off the intake pipe, you gotta torque that sucker on there. the bolt that was on my carb didnt get tight enough for me, so i replaced it with a longer bolt. i tightened it as tight as i could, no more air leak or sliding around on the intake pipe.

Bikeguy Joe · May 20, 2012

david jeffries said:
the loss of power is probaly due to the crappy tuning of cns carbs. never had one myself, but heard a lot about the problems they come with. some claim they are able to tune them and they work great. others say they are a continual headache. best to get an nt carb if you can find one, or an rt carb from dax. i will be getting an rt carb myself when i have the money. i currently have an nt carb and its ok. as far as the carb blowing off the intake pipe, you gotta torque that sucker on there. the bolt that was on my carb didnt get tight enough for me, so i replaced it with a longer bolt. i tightened it as tight as i could, no more air leak or sliding around on the intake pipe.

He has the cns, you say you have the nt. Rustycase, who has both types says "don't overtighten the carb they break".

Don't over tighten the carb.

Bikeguy Joe · May 20, 2012

Going down hill, the engine unloads and will usually four stroke, which is completely normal. It is normal for the engine to four stroke when at cruise as well, though usually it will break back and forth between a two stroke and a four stroke sound....once again, normal.

I am wondering how you got home if the carb "blew right off the intake"? How did the engine run like that?

More than likely, it vibrated loose, and didn't blow off, right?

Greg58 · May 20, 2012

The most common problem with the cns is the spacer, some like mine get hard and start falling apart. I made a copper spacer almost a year ago, my carb is still tight on the manifold.

rustycase · May 20, 2012

Yes Joe, there's a number of members here who have broken the petals on the carb mount.

then again, there's others who have had the intake spigot drop off at the weld!

it's all fun!

Really never know what will happen with a chinagirl...

lol I've made the mistake of telling people to do something tight before... so they had their one-eyed gorilla snapping bolts off and ripping thread!

I think Alf has some torque specs posted somewhere... I would go by that, and if there is a continued problem, replace the machine screw and nut, or the pvc adapter, or shim it, or go with a copper spacer... maybe even put a little bit of rtv red on there...
...just a little!

Best
rc

young grease monkey · May 20, 2012

i had the same problem, but there is an easy fix. people always say cns is crap, its not true! at high rpm, the carb shakes a lot and causes the fuel to foam up and you get lean mix. this is because of the plastic spacer isn't very rigid. you can either add braces to the carb so it doesn't shake, or a metal spacer like greg58 did. I got an old brake cable and put it around the back of the slide and choke thing, then used the head bolts to keep the cable tight. Cured the problem and it goes top speed smoothly as long as i want. it didn't look nice, so i will make a new spacer and use a different brace

dragray · May 21, 2012

it's jetted too lean or it's developing an air leak at w.o.t. which is what is giving you the loss of power.
the carb blowing off the intake is not uncommon for the cns carbs.
the plastic ring inside the carb is a bad design, and it will never grip the intake manifold tight enough as it is to stay on.
your best bet is to go with a re-jetted and tuned nt or nt "speed" carb.,
the cns carbs are nothing but headaches.
I had ONE cns carb, tried it out for about 2 days, took it back off, and put my re-jetted and tuned n.t. carb back on.
the cns was nothing but a headache, they are very tricky to tune, and at higher rpms, the plastic intake spacer will fail to keep the carb from falling off of the tintake.

dragray · May 21, 2012

Bikeguy Joe said:
Going down hill, the engine unloads and will usually four stroke, which is completely normal. It is normal for the engine to four stroke when at cruise as well, though usually it will break back and forth between a two stroke and a four stroke sound....once again, normal.
QUOTE]

if this is normal for YOUR 2 stroke, then you obviously don't know how to tune and jet a carb correctly.
a 2 stroke should never 4 stroke, and a 2 stroke will never 4 stroke if the carb is jetted and tuned right.

rustycase · May 21, 2012

I disagree with the 'never' part, ray...

it's not a perfect world in HT land.

We are operating a very small chinagirl across a wide range of demanding conditions and best practice is to use the fuel to protect the motor. This effectively will produce the conditions Joe described.

I do agree, a fire breathing zinger built for racing should never exhibit four-stroking when racing in it's powerband.

Best
rc

Greg58 · May 21, 2012

Since these engines don't come with reed valves some mid range equalizing I call it for lack of a better word happens when you are cruising, it does that on mine at 23 to 25 mph. A lot of people here have reported the same on their engine.

aaronbentzel · May 22, 2012

I am wondering how you got home if the carb "blew right off the intake"? How did the engine run like that?

More than likely, it vibrated loose, and didn't blow off, right?

Unfortunatly for me, it was a long bike ride home

The carb I guess fell off from vibrations, however I was not looking at it when it happened. The engine just lost all power and throttle response.

When you go down hills, do you pull in the clutch? I go faster and if I try to give it gas it just gets loud and choppy and bogs down and I lose power.

Also, once or twice when riding at WOT, the engine goes into a fit of reving and I have to kill the engine for it to stop. Do you think this is the carb is not opening and closing correctly? It fixes itself once I start the engine again.

Thanks again for all the advice.

My bike ride = start up, give gas, hit 25, engine bogs/looses power, let off gas, give gas, WOT, engine bogs/looses and gains power, hold it, engine goes rev crazy or carb blows off, shut down, pedal home.

rustycase · May 23, 2012

WoW!

Your last post does NOT sound good, AA.

It seems like there's a number of probs besides the carb coming off.

Secure that however you decide, but get that done.

also sounds like float may be adjusted improperly, or jet plugged, or petcock.
AND, you have a problem with jetting that you have not yet been able to get to!

I forgot. what carb do you have?
If it's NOT an NT, just stop everything and get one.
Your life will be simpler.

Everything else applies, but things will be simpler than also trying to tune a cns during the process.
If nothing else, it could be said that a cns is difficult to tune.
...and an NT is far less difficult...

IMO, you are just undergoing a kinda normal bunch of chinagirl probs.

some run dandy out of the box, after preliminary inspection and fixes, and carb jetting.

Others are a real bear.

But it's all for fun, right? lol

Good luck
rc

young grease monkey · May 23, 2012

If you just brace your carb so it can't shake on the plastic spacer, your problems will be cured. Shaking causes the fuel in the carb bowl to foam up and run so lean it bogs out, and gives you h#ll in mid to high rpms. Just try it, I promise it will be fixed! Worked great for me, now my bike pulls full speed for miles.

Longshot270 · May 23, 2012

aaronbentzel said:
My bike ride = start up, give gas, hit 25, engine bogs/looses power, let off gas, give gas, WOT, engine bogs/looses and gains power, hold it, engine goes rev crazy or carb blows off, shut down, pedal home.

Sounds like you need a smaller jet because of a rich mixture or to adjust the fuel float. It was a problem I had. Then it sounds like as the carb slips off, it gets an air leak giving way too much air causing it to over-rev.

Here is a tip, keep a small toolkit with you. Walmart and most other places that also sell bicycles have little tool kits like this one. They are a great investment at only ~$15. Also keep a long screwdriver, a 10 mm open ended wrench (mine also has a ratchet on the other end which is awesome), 14 mm wrench and maybe a 15 mm if you have bolt on axle. Between those tools you can literally fix any part of the bike, anywhere.

brian tedesco · Nov 29, 2014

I have a 2 stroke 80cc engine it is loosing power when full throttle and makes a noise what can i do to fix an what could be the prob its a new motor on my 4th tank of gas Im mixing 8 oz of oil to gas using full synthetic 2 stroke oil plez help

Greg58 · Nov 29, 2014

Brian welcome to the forum, people here will gladly help its just that this is a old thread and since its been 2 years since the last post a lot of members don't respond. Losing power at full throttle sounds like a main jet that is too large, most are rich for these engines. 8 oz of oil or 16/1 is way too much, try cutting that in half, that is 4 oz to one gallon of gas and see if that helps with any of your problems.

rustycase · Nov 29, 2014

+1

Greg is absolutely correct.

Yikes! That's a HUGE amount of oil, unless it's going into about 3 gallons of gas!

More than enough oil will make the mix too lean, causing the engine to knock from detonation. 8oz of 'full synthetic', well, I'm not sure how you can even get it to run!

Perhaps we should ask for more info???

Full synthetic oils are awful good! 50:1 should be a good mix.
...somewhere around 2 1/2 ounces per gallon of fuel would be close enough...

Best
rc

brian tedesco · Nov 29, 2014

Thanks guys ill try that and im looking fro mods i can do to increase Power or even mph any ideas

Loosing Power

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