After changing parts, WOT is slow, and sound louder

geoldr · Jul 19, 2011

Hey guys, so I finally got my bike up and running. I did a few modification to get back in working order.

1) I bought a new muffler, bought a regular black muffler, same as I had before.
2) Bought high temp gasket paper stuff from Autozone and created my own exhaust gasket.
3) E-clip in carb broke, so I fixed it and put it all back together.

Now when I ride, if I go WOT, the engine doesnt even rev that high and it tops out at 22. Before, at WOT, it would get so high I thought it would explode, and id hit around 25-26.
Before, I would be coasting and hit this RPM. But at WOT it would be much louder and faster.

And now hill climbing is a pain, its super tough for the bike.

When I made the exhaust gasket, I dont think I made the hole the same size as the one on the motor. Could such a small thing like that cause these problems?

Also, it seams "louder" and as if it backfires sometimes, but thats just the noise, I don't think its actually backfiring althought I have no idea what that sounds like.

Besides that, it runs great.

Im using NGK BP6HS spark plug,
regular 66/80 CC Chinese HT
upgraded plug wire and boot
Regular muffler, regular head.
32:1 fuel mix.

Also, I'm not sure, but I think my bike goes through gas quickly. Although I have nothing to compare to. I have a regular 2 liter tank, and I get maybe 20-25 miles to it. Not sure if this is normal. Although my computer on the bike is a piece of walmart trash, and keeps dying and resetting. But ive been keeping track and adding it up.

biknut · Jul 19, 2011

Assuming you don't have any exhaust, or intake leaks, the problem is probably your new muffler. Open it up and check to make sure it's not too restricted.

Here's a look at mine to see what I'm talking about. Your muffler may be a different one but it still might have the same kind of problem.

This is what I did to fix it. It's not loud at all.

Goat Herder · Jul 19, 2011

What notch setting did you put the carb metering rod needle clip at? Most folks do well second down notch from the top one.

geoldr · Jul 20, 2011

Goat Herder, that is the notch that I am using and have been using for a while now. Ill check the muffler tomorrow when its light outside

BTW, do I just take the muffler cap off and ill be able to see that?

biknut · Jul 20, 2011

geoldr said:
Goat Herder, that is the notch that I am using and have been using for a while now. Ill check the muffler tomorrow when its light outside

BTW, do I just take the muffler cap off and ill be able to see that?

Different China girl mufflers are slightly different, but basically most have 3 chambers. In the pictures I posted you're looking at the top chamber closest to the header pipe. The 2 small pipes you see run down to the bottom chamber, so in this case you would be able to see those pipes from the end cap too, but it would just be from the other end.

geoldr · Jul 20, 2011

I took the bottom cup off the muffler that broke, here is what was inside.

geoldr · Jul 20, 2011

I looked into the muffler today, and the gasket. The muffler is the same as the old one. Since it looks completely different then the one posted, I'm not sure what to do about it.
Also the exhaust gasket looks like its having an exhaust leak?

biknut · Jul 20, 2011

geoldr said:
I looked into the muffler today, and the gasket. The muffler is the same as the old one. Since it looks completely different then the one posted, I'm not sure what to do about it.
Also the exhaust gasket looks like its having an exhaust leak?

Just based on the pics of your muffler, it doesn't look like that would be causing the problem you describe. Your exhaust gasket does look like it's leaking a little, but that's probably not causing it either.

Is it possible you could have a leaking head gasket?

geoldr · Jul 20, 2011

How can I check to see if the head gasket is leaking?

biknut · Jul 20, 2011

geoldr said:
How can I check to see if the head gasket is leaking?

Other than taking the head off to look at the gasket I'm not too sure. Normally you check the compression.

The reason I mentioned it is because it looks in the picture like there's oil on the top fin. Usually when I get any leaks in my china girl motors oil starts leaking out of the leak.

Maybe someone with more experience with these motors will offer some advise.

Pilotgeek · Jul 20, 2011

I know when I tried riding once without my muffler cap, it ran like poop because I have it jetted for the amount of back-pressure when the cap is on. The new muffler may has less restriction, so you may have to change the jetting seeing as it happens at WOT. Even though it looks similar, the number of baffles and such internally could be different. The fact that it's louder also goes with my theory of it having less restriction.

Do a plug chop. Go full throttle for a distance, then kill the engine and pull in the clutch. Coast to a stop, let the engine cool off, remove and then check the color of the plug. If it's running too rich, it will be oily and dark.

As biknut said, it would also be a good idea to make sure your head doesn't leak. At the very least, make sure all the head bolts are properly torqued.

geoldr · Jul 20, 2011

Ok, so today I took off the head and cleaned everything, after putting it back on and tightening the acorn screw I went for a ride. I have to say, that was the smoothest ride I have ever had on this bike, but after looking at the motor, id say the headgasket is leaking. One one side it looks like the gunk is coming out.

The headgasket was good, no bends no cracks or anything. Whats the deal with this how do I fix this?

Ill examine the spark plug tomorrow by doing what you suggest Pilotgeek, and ill let you know. Id do it now, I just have to go to work

Goat Herder · Jul 20, 2011

You will prolly have to take the cylinder head and or mebbe the top of the jug as well. Start with the head first. Get something very flat like a pane of glass lay some 400 grit sand paper on it. Start moving the cylinder head on it alternating the way you hold the cylinder head. So as not to favor sanding to much at any one side.Check to see if it is perfectly flat at the gasket mating surfaces.

bairdco · Jul 20, 2011

i think the real problem was the exhaust gasket you made. backfiring and poor performance is caused by a leaking gasket. you should open it up the same size as the exhaust port, and you can grind the exhaust pipe flange out to match, too. or, almost match, anyway. there might not be enough metal to make it match exactly, but get it as big as you can without compromising the strength.

now that you've messed with the head, you'll have to do like Goatherder typed. it's "lapping" the head to make a perfectly flat surface. you may have torqued it down wrong and warped it.

if there's any kind of "gunk" coming out inbetween the head and the jug, it's leaking, and if you continue to run it that way, you'll probably end up destroying your motor.

droc089 · Jul 20, 2011

bairdco said:
i think the real problem was the exhaust gasket you made. backfiring and poor performance is caused by a leaking gasket. you should open it up the same size as the exhaust port, and you can grind the exhaust pipe flange out to match, too. or, almost match, anyway. there might not be enough metal to make it match exactly, but get it as big as you can without compromising the strength.

now that you've messed with the head, you'll have to do like Goatherder typed. it's "lapping" the head to make a perfectly flat surface. you may have torqued it down wrong and warped it.

if there's any kind of "gunk" coming out inbetween the head and the jug, it's leaking, and if you continue to run it that way, you'll probably end up destroying your motor.

What would happen if you ran it with a leaky head? Mines kinda leaky, I did tighten the nuts down and notice a difference in performance. Still leaks, still can see a seam between the head and gasket. I plan on taking the head off in the next couple days to check the head gasket, and do some sanding of the jug (I guess that's what it's called) and the head if needed.

bairdco · Jul 21, 2011

loss of compression, for one. it'll also create a hotspot where it's leaking due to the extremely hot charge blowing out, which can lead to more warpage, piston heating, etc, and can possibly seize the engine.

most likely, if it's a small leak, it'll run like crap for awhile, then blow the gasket out, then quit running.

if you're lucky, it won't do any major damage.

Ckbente · Jul 21, 2011

im having a similar prob. I had two intake gaskets break or crack on the top only, i made a new one. now i cants make top speeds like i use too and when it is wot it vibrates like mad, and the carb backfires. wtf is going on? im so stuck and starting to lose the faith in these ****ing chinese build machines. it was the answer to all my problems for two months, now im bumming rides again>>> no good. please help. fuel mix is 40:1 is that it? but downhill it goes kinda fast maybe not top and will backfire a bit, but low speeds are a *****, it backfires a lot and i constantly think ill be late for work if i come to a hill. what do i do

geoldr · Jul 21, 2011

Wow ok, now that I know I can ruin my motor from this leaky head im worried. Ill check tomorrow if its the head thats leaky, or the exhaust just spreading the stuff everywhere.

I hope its the exhaust, seems like a much easier fix then sanding down the head of the motor. Ill prolly end up breaking it even more if I have to do the sanding, I am not sure how to even do that correctly.

Is there anyone in the Bay Area, CA who is good at this kind of stuff?

bairdco · Jul 21, 2011

if there's "gunk" on the fins in the middle, it's most likely the exhaust. if it's from the headgasket, you'll see burnt marks between the head and the jug, as well as some oily residue.

sanding the head is simple.

tape a piece of wet-or-dry 400 grit automotive sandpaper to a piece of smooth glass (like an old window pane, glass table, or a mirror.)

sprinkle some water on it, then sand the head in a circular motion until it's shiney all around the mounting surface.

after a few seconds, you can see where the high-spots are because some parts will be sanded clean and some will have the original dirty surface. keep going till it's all sanded clean.

it takes 5 minutes and it's a piece of cake.

droc089 · Jul 21, 2011

Thanks bairdco, will definitely be fixing that if its the problem.

After changing parts, WOT is slow, and sound louder

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