Mac Exhaust Installed. No Power, Terrible MPG

Just installed a MAC 4-2 Baffled Slash Cut exhaust. New O rings, synced, colortuned. Idles great. Sounds great. I also have an UNI Air Filter installed, so its a liiiitle higher flow than the stock paper filter.
SO! My problem is that all my power is below 4k now. Great pick up, but as we all know these bikes power bands are like 6-9. At about 5k in second gear she looses power and sounds like the exhaust is stuttering a bit. No jerks or bumps in the ride, no real popping, just no power and slow RPM rise.
Also i went 70 miles on a FULL TANK OF GAS! Thats like 22mpg!! WOW!
SO! If it was running lean, wouldnt she run like a scalded cat and be popping a lot? Loud too? I thought this MAC exhaust would make it lean since its so open, no collector Box. But, stuttering, bad MPG... Rich mixture????
Anyone have any suggestions???? I'm "Baffled" Ha ha
-Chris

 

Rejet? I don't know much about but Im under the impression that if you change the flow on either side, intake and/or exhaust you need to rejet.

Len has a formula to figure all that out in the catalog.

 

You'll need to rejet if you have stock jets installed. I have a similar setup on my XJ1100, it needed 2 sizes larger mains and stock pilots. With your mileage so bad is there a possibility the float levels are too high? Could be high and being sucked out of the bowls. I've seen it happen.
Check your plugs for color, might give you some hints on whats happening.

 

I would agree with the consensus here,,, you need to rejet as your air/fuel mix ratio has changed.

 

Checking those float bowls sounds like a real good place to start. I hadnt really thought of that. Cause that makes a lot of sense. Getting up to speed, and then its starving for more gas, so no power. I could see that. I'll be sure to look into that before I decide on a jet change.
I remember reading on Lens catalog that for a custom 4-2 you need to go up 2 main jet sizes.
I think I'm runnin 110 mains. So I'd need to upgrade to... Does it go by 5s? So 115 or 120 right?
-Chris

 

Besides bigger main jets, you'll probably need to raise the jet needle. If they're aftermarket needles, they may have an E-clip and several adjustment slots; in which case you can move the clip down one or two slots. If they're stock needles, you may want to go for a Dynojet stage 1 kit, or you can get a small washer from a hardware store and put it under the needle to lift it a bit.

 

Definitely check the float levels; and then I'd begin by rejetting in accordance with Len's "guidelines" and go from there. Len also has needle shim washers.

You've discovered exactly how much of the "magic" was in the collector box, and how important exhaust tuning can be to moving the powerband around. Trying to "out-engineer" Yamaha isn't always a bolt-on proposition, as you're beginning to find out.

One additional point: That UNI filter flows considerably more than the stock paper one; you probably need to factor that in with your jetting choices. If it were me, I'd go back to the paper filter and get the carbs sorted for the exhaust first.

But start with doing the float levels right.

 

I'm wondering whats happening behind the bike?

 

Fitz THAT was my first thought. Go back to the paper filter to try and even it out. When I did my float levels last summer they were spot on, and had no troubles till now. But hey maybe its a liiiiitttle too low. I'll be sure to double check. Definatly.
And Rob the same thought crossed my mind and when riding with a buddy yesterday I asked him if he saw any... smoke, pops, flames, anyhting that looked or sounded out of the ordinary. He Just shook his head and said "Only when you're gettin on it like you said, she sounds like shes trying too hard."
SO! First, float levels, then paper filter, rejet to 120, and needle shims. Sounds like a hefty shopping list

 

Hey, you're the guy who decided you'd like to try to out-think Yamaha. You didn't really think it would be that easy, did you?

 

Ha with this lil girl NOTHING is easy. First bike anyways! So got lots of time to play trial and error.
And dont get me wrong! I didnt get the new exhaust for Power or to increase... anything really! My stock was beat up pretty bad from my two wrecks and it was time for a new one! Liked the look of the slash cut. Wish it was larger like the Vulcans!!
So When I get around to finishin the cosmetics she'll look purty good
Figuring it out is the fun part
-Chris

 

Reset the float level this morning from 20.0mm to 24mm and she took a while to fire up after I filled the bowls. Ran great, Idled great. Sounded good. No pops. Revved right up to 8k rpms, getting me to 65 pretty quick. Still no pops or probs.. But the float height seems too high for me... Doesnt feel right. I need a colortune and a plug chop to really find out whats going on.
Cant seem to find my stock height. I want to say the dry float height is 17.5?? So if Im right, then Im set WAY to high.. But shes runnin good. Baffled again.
I need to purchase more carb drain screws to be able to do the clear float tube method to see where Im at. I'll send an order in for em now so I can get on that

 

Ok if the stock float height is 17.5 from the carb body to the bottom of the float correct? If you raise the float height to 20 or 24 are you not making the level lower in the float bowl? which in turn would make the bike run lean?

 

Wow so Im a dumbass... My spec float height is 16mm.. Hmmm so why was she running poor at 20mm, and good at 24? Oh well. I'll reset the float height to 16mm tomorrow morning and repost

 

Dry setting is only a starting point anyway; just take the time to fix the float bowl drains and do it right; then it'll be done and you can cross it off the list. Right now you're just pounding your head against the wall, and will be until you "wet" set them.

 

Got needle shim and float drain screws and a stock filter in. Installed stock filter, no change at all. Adjusted the floats to 16mm. No change at All. Still stutters at 5k.
Also installed 2 shims in the float needle to bring it up to the FIRST notch.
<====)=)0 First from left to right.
Made it a million times worse. Stutter from 1000-3000, catches, fires up, then stutters again at 5k again. Dropped the uni filter in as well and she just idles a little better with it. I'm going to bring it to the second notch on the needle just cause I can and report back.
Sounds like new main jets are in order. Still gotta install drain screws. But adjusting from 20mm to 16mm had NO effect on it at all. With stock filter and with Uni.
Guess I'll go get dirty again
-Chris

 

One shim was a little better. But still awful... Sooo rejetting is indeed in order. Accorrding to the rough chart, I should go up 2 sizes on the main with stock intake. Or 2 up on main and 1 up on pilot with the Uni filter.
Shoulda stuck with the stock set up
Just sayin

 

OK...
Update
Installed 110 Jets with the stock filter. Same 5k prob. NO difference except for the pickup is nice. Until 5k...........
Its either gotta be floats.. Again.. Which, I replaced 2 drain screws, the other 2 I'm gonna have to find a way to drill out.
I tried several TCI units, no change.

The only other thing I can think of is that Maxine has 650 coils on her from a parts bike I acquired. Think those wouldnt crank out enough juice??

I'll be taking carbs off and somehow trying to get those drain screws out. Again. And I'll wet set the two I have.
-Chris

 

I doubt the coils would be the problem.

Any chance you can get the bike on a dyno so you can see what's happening to AFR at 5K?

 

Since the procedure is most easily done with the rack off the bike, you can simply swap the two good float bowls to the other carbs and set them, then put everything back where it's supposed to be afterward. Or, you could do like the PO of one of my bikes, and leave them all mixed up with some of the drain ports facing inward...

 

Just wondering. You said 2 wrecks. How fast were you going? Was the bike running well after the last one and before the new exhaust?

 

Oh yeah. SHe ran great after both wrecks. Not much can stop these. Ran AMAZING before the exhaust swap. And as soon as I get out there I will do that Wet set fitz

 

Alllrighty... SO!
Here we go again
Floats are 100% correct. Checked em all, and they ALL, with the clear tube method, check out. -1mm below the bowl lip. STILL having the 5k stutter.... Now the UNI Filter is in, gonna switch to stock just to try it. Running Stock pilots and 110 Mains.
I'm baffled...
I might be picking up a complete parts bike next week. New carbs and comes with rebuild kit, new seats, yadda yadda, gonna be fun actually. So i'm going to rebuild the spare set, and put em on with the 110 mains and see what happens... Put the 700 coils on too. Like I said I've got the 650 coils on right now but I dont think it really makes a difference.
I mean... I've had NO change since the beginning.. Maybe its the coil wires? Or something..
I do have the shims for the needles still. Maybe drop one in each with the new mains. Now for the shims (Just to clarify) you unscrew the needle from the diaphram and slide the shim over the needle and seat it as far as it will go up the needle, correct?

Any other suggestions would be greatly appreciated
-Chris

 

I don't think you should have to unscrew the needle. I may be misremembering how Hitachis go together, but in the Mikunis, at least, the needle just hangs in there... held in by gravity and a plastic disc that sits above it.

Basically (for the Mikunis) you remove the hat, pull out the spring, pull out the diaphragm and slide, turn the slide upside-down, and the disc and needle will drop out. Then you put a shim over the needle and thread it back into the top of the slide. Installation is the reverse of removal from there.

 

don't resist it just change the mains, two sizes at least, maybe three with the air filter
raising the needle adds fuel at a lower rpm when the engine isn't ready for it but overall it doesn't change the amount just when, mains change amount.
consider a size bigger pilot too, i think non-epa bikes had one size bigger

 

Float levels should be at spec. Changing the level for tuning reasons can create other problems.

I am trying to get one thing clear, was the bike running perfect and you ONLY changed the exhaust, and now it has issues?
If thats the case, then play with the jets.


If you have made mods to a bike with a running problem, you need to fix the problems, you wont tune them out.

I run a Mac 4 into 1 exhaust with standard intake and it performs acceptably with standard everything, so I find it surprising you have problems that noticable just from the exhaust change.

 

Inside the diaphram there is an allen head plastic nut that you unscrew to reveal the little tiny spring that pushes down on the needle. That pressure is what hold it in place.
Polock i went from stock 107 mains to 110 with no mid range change. If I am correct, above 3k rpms the pilot jets cut out, and are no longer used. No idle probs at all, but at 5krpm would that transfer over to mid range be stuttering because of pilot jets?
And no she had no problems at all. A nice pull from 2-5k, then the second band between 6-9 always ran great. No probs on the highway or nothin. And yeah me too! I didnt think itd be this tough.. I do very regular maintenance on her. Valve checks, syncs, colortunes, carb cleans, spark plugs, oil changes the works! Thats why this bugs me so much. Shouldnt be this tough

 

from a 107 to 110 i wouldn't think there would be much difference, someplace here i saw 110 and that would put you at 114 or 116 for 2-3 sizes and there i think you'll see a difference, unfortunately those sizes cost more..?
i see 36.5 for the pilot with 40 being the next bigger size, that might be a bit much ?
5K seems to be the # a lot of people have a hesitation at, my theory is thats when the scavenging effect starts to work and the engine wants lots of fuel, that would be the needle jet and the tapper on the needle, what # is on your needle?
it's easy to see a 650 needle is fatter than a 750 needle, i never saw a 700 but a thinner one might help the transition

 

I have Y-70 in each carb for the needles.
Well my favorite motorcycle shop owner said I should go with a 110 or 115 if I can get em with that Uni filter
I think she actually has 40 pilots in her.
Not sure bout the needles though. I think they would change fuel delivery at all times if I'm not mistaken.
Eh maybe I'll order some 115s for kicks and giggles. Drop that stock filter in tomorrow as well just to see.
REALLY need a new bike and leave tinkering to projects. I miss my power band

 

i don't see 115 on chacal's list only 116 and 118's, i might be tempted to do 118 but i'am a cheap sob
i'd have to look at the #'s on the needles to see which way is thinner, unless someone knows

 

Not sure on what the 700 stock jets are, but in our 750's the main jet is a #120 and pilots are #40. Jet Needle = Y-13

That's what i'm running with a MAC 4-1.

 

I'm not sure why no one has mentioned this, but if your new exhaust is more restrictive than a rusted/holed out stock then you may be too rich on the top end - even with a UNI plopped on there (air gets in, but too much back pressure wouldn't let it get out). That being the case, you'd be running too rich and not too lean as some of the symptoms seem to indicate.

Only a true plug chop at ~2/3-3/4 throttle will tell you, but around 5k it may be your main jets kicking in, flooding the mixture, and bogging it down. Raising the float heights, as far as you did should have leaned it out which may be why it ran better in that range afterwards (but still not acceptably; only correct jetting would have fixed that).

I may be way off base but sounds to me like you're too rich.

Go do some plug chops before you order more parts!

 

When you eliminated the COLLECTOR; you created the problem.
Now, you have a FREE FLOWING Exhaust System.
You eliminated BACK PRESSURE.

Back pressure is created by anything that restricts the exhausts flow.
This includes: narrowing of exhaust pathways, Bends, & Baffles.

In a perfect world, we want the ALL the intake charge [air/fuel mixture] to completely fill the cylinder.
To do this, we need to open the exhaust valve so the exhaust fumes can exit the cylinder, allowing the intake charge to rush in.
It needs to be done really fast!

That means the need to keep the Exhaust Valve OPEN [While] the Intake Valve is open, too.
Causing this problem: Because BOTH valves are open for (Approx 64-Degrees) some of the Intake Mixture escapes out of the Exhaust Valve, in to the Exhaust System, and often ignites. [Backfire thru the exhaust].

Having some Back Pressure helps keep the air/fuel mixture from rushing out. Having Back Pressure allows for some latitude in Valve Timing which has a direct effect on Performance.

With some Back Pressure engineered into the overall Tuning Process; the Exhaust Valve can be Timed to remain Open for a longer DURATION; increasing the Power of Intake Mixture by preventing it being evacuated by the Flow Inertia of a Free Flowing Exhaust System.
Having Back Pressure mean engineers can leave the exhaust valve open longer.

Back Pressure effects: Gas mileage, performance & emissions.

 

Love the wealth of info Thats why I came to this site.
So what you are saying is that I need to pop the head, loosen the chain, and rotate the exhaust cam backwork a few degrees. Not much, but a little. Now, in doing that, I wont bend a valve will I? Cause thats whats wrong with my XS1100, its got a bent valve and blows smoke everywhere
OR do i just gotta put a timing light on and adjust? Hmmms
-Chris

 

You can't just jump a tooth on the cam and clear up a back pressure issue. That's not so much the way it works. There's no adjustment for timing either :/ so a timing light is useless other than watching the TCI doing it's advance.

Of course running a more free flowing exhaust isn't going to take you from 50 mpg to 25 either. Something is REALLY a mis in your setup, we'll find it, eventually.

 

I was just thinking, have you taken a sheet of paper and stuck it in front of your headers to make sure they're not leaking at all?

Also, loving the shorts in that first pic you posted

 

Ha ha oh yeah thats my super sexy motorcycle assistant girlfriend. She lends a hand from time to time on various projects.
I like these better
http://i53.tinypic.com/2a5k3t.jpg
http://i53.tinypic.com/1z2m6hx.jpg
Yeah i didnt think so. Its never that easy, but Itd be a start.
Hmmm.. So is it even possible to adjust the exhaust valves a few degrees? Or should I look into selling more parts and getting a 4-1 system
And yeah one of the first thing I did when I installed the new system, looked for leaks. Replaced exhaust O rings. Checked for leaks again. I can recheck no biggy. Satisfy curiosity
-Chris

 

Going to make a tuneable baffle in my welding class on Weds. Using thumb screws, a metal disc, and a few nuts. Hey May work

 

*SOLVED*Mac Exhaust Installed. No Power, Terrible MPG

Backpressure issue.
Made tune-able baffles and installed in front of the muffler. Cant even see em.
I took 1/4" Thumb screws, welded them on a 1 1/2"x1 1/2" little plate and cut a straight edge slot at the top for a screwdriver. Drilled a hole in the back of the exhaust pipe, right in front of the mufflers and inserted with 2 washers and a lock washer, and two nuts. One on either end.
The baffle is now, tune-able! I set it at 90 degrees against the flow, and viola. Low end torque. Now I can only turn it about 45 degrees before I start having my backpressure again, but hey. Kinda cool.
I'm making a couple more a size up, and a size down, just to play with. See what works best. I'll take pics then.

Thanks Bigfitz for the Link
-Chris