New expansion chamber + muffler causing excessive low speed bogging. How to tune?

outatime88

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I just put on a cdh 66 expansion chamber and it seems that with a muffler on, I have tried both the stock china girl muffler and the other shown in the pic below, that at low speeds I get that back and forth bogging when you let off the throttle that is much more excessive than usual.

Without the mufflers it seems to be much better, but unfortunately this pipe is way too loud.

Do I need to tune the c-clip or rejet? Would I be looking to run leaner or richer? Or could it be the fact of my exhaust setup being too long or the way I connected the muffler with the hose? And please excuse the scotch tape, that is just for testing.

IMG_5262 (1).JPG
 
I'm no expert but I would suggest a high performance air intake to go with the pipe. Also have you or have you had any porting work done? If you have then definitely get a better carburetor and air intake system and yes you will have to re-tune your carb (jetting,needle position). Start with the most rich settings and work your way down. If you start too lean you are running more risk of blowing your motor. I will much rather run a little rich and maybe have a little smoke than run too lean and blow my motor. And on the other side of things if it is a stock motor then the expansion chamber is not going to give you much in performance. Read up on porting your jug and trimming your piston skirt. This is where you will see the most gains. When you do this you are allowing more air and fuel to come in as well as better flow out for the exhaust which equal's more power. You can also run a windowed piston with a reed system which is even better. But for a first step if your motor is stock I would be putting the stock pipe back on and port your cylinder "jug". As for a quieter expansion chamber type exhaust check out bike berry they have a few options with mufflers. the one you have is for racing and is meant to be loud because its basically allowing the most air out and is coming straight from the engine. When you muffle it you lose power. Kindove defeats the purpose in my eyes. I guess you could weld on some type of muffler if you are able, but I would go with a different option if you are worried about noise level. Some people unscrew the cap on your stock pipe and pull it out about 1/4 in. this will give you a little gain as well as be fairly quiet.
 
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I'm no expert but I would suggest a high performance air intake to go with the pipe. Also have you or have you had any porting work done? If you have then definitely get a better carburetor and air intake system and yes you will have to re-tune your carb (jetting,needle position). Start with the most rich settings and work your way down. If you start too lean you are running more risk of blowing your motor. I will much rather run a little rich and maybe have a little smoke than run too lean and blow my motor. And on the other side of things if it is a stock motor then the expansion chamber is not going to give you much in performance. Read up on porting your jug and trimming your piston skirt. This is where you will see the most gains. When you do this you are allowing more air and fuel to come in as well as better flow out for the exhaust which equal's more power. You can also run a windowed piston with a reed system which is even better. But for a first step if your motor is stock I would be putting the stock pipe back on and port your cylinder "jug". As for a quieter expansion chamber type exhaust check out bike berry they have a few options with mufflers. the one you have is for racing and is meant to be loud because its basically allowing the most air out and is coming straight from the engine. When you muffle it you lose power. Kindove defeats the purpose in my eyes. I guess you could weld on some type of muffler if you are able, but I would go with a different option if you are worried about noise level. Some people unscrew the cap on your stock pipe and pull it out about 1/4 in. this will give you a little gain as well as be fairly quiet.


I researched a lot about modifying the piston and ports for better flow a while ago, but usually most say to start with a better exhaust since the stock one is so restrictive. I have been using the thrust pipe before this new one which ran great and the new cdh pipe has made a huge gain in top end. It screams at WOT. It just seems that any muffler I use with this engine gives me some annoying low speed bog since its a little soggy down low now. Obviously with the clutch in the problem is gone.

I mean the NT carb should be good enough for my set up. I am just curious on where to go as far as tuning between the c clip or rejet. I'm not quite sure which is the more proper one to adjust or maybe just both? And I would think running richer would worsen my problem?
 
I just put on a cdh 66 expansion chamber and it seems that with a muffler on, I have tried both the stock china girl muffler and the other shown in the pic below, that at low speeds I get that back and forth bogging when you let off the throttle that is much more excessive than usual.

Without the mufflers it seems to be much better, but unfortunately this pipe is way too loud.

Do I need to tune the c-clip or rejet? Would I be looking to run leaner or richer? Or could it be the fact of my exhaust setup being too long or the way I connected the muffler with the hose? And please excuse the scotch tape, that is just for testing.

View attachment 83474
I would shorten the stinger to look something more like this. When I had excessive length in my exhaust system it ran rich. when I shortened it it cleaned up. You may also have to jet down a size or 2 . With the expansion chamber you are getting some of the unburnt fuel charge returned into the cylinder. !st pic. ran rich. 2nd pic. ran good.
View media item 60844
View media item 61474
 
I had to jet my bike waaaay down after I added a MZ expansion chamber.
 
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I would shorten the stinger to look something more like this. When I had excessive length in my exhaust system it ran rich. when I shortened it it cleaned up. You may also have to jet down a size or 2 . With the expansion chamber you are getting some of the unburnt fuel charge returned into the cylinder. !st pic. ran rich. 2nd pic. ran good.
View media item 60844
View media item 61474

Ah ok I see. You actually have a very similar setup that I have. My problem is my last resort is the cut the pipe, so maybe I can try to make it run leaner with rejetting it smaller as you said? Also is that the stock muffler in the first picture?

I had to just my bike waaaay down after I added a MZ expansion chamber.

Adjust what way down?
 
Ah ok I see. You actually have a very similar setup that I have. My problem is my last resort is the cut the pipe, so maybe I can try to make it run leaner with rejetting it smaller as you said? Also is that the stock muffler in the first picture?



Adjust what way down?
Modified stock muffler. Gutted with enlarged exit. Yes you can rejet it. Don't know if your results will be as good as mine was with that much exhaust after the chamber. The more pipe after the chamber the greater the back pressure. Worth a try. If you don't like the results you can always shorten it later.
 
Modified stock muffler. Gutted with enlarged exit. Yes you can rejet it. Don't know if your results will be as good as mine was with that much exhaust after the chamber. The more pipe after the chamber the greater the back pressure. Worth a try. If you don't like the results you can always shorten it later.

I just found a post that said the jet controls 80% to 100% throttle while the c-clip controls everything below that. Is this is true, then should I be adjusting just the c-clip?
 
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