BACKFIRING ISSUE

[soysss]

Hey, my bike has been running great except for one thing.  Its been backfiring after i let the throttle out.

I have K&N lunchbox, 152.5 main. 40 pilots. 2.5 turns. One washer under each needle. Straight pipe with small muffler.

Too much gas is what I think, what do you guys?
Im gonna try turning in the mix screws a little. or could get 150 mains.

-erik

[The Buddha]

I dont ever think you need larger than 150 mains. However 1 person I set the carbs up with 150 had an issue and swapping to 152.5 got it right. 1 in ~100 I have set up with 150's.
Cool.
Buddha.

[soysss]

K thanks, will swap em out tomoro and see.

-erik

[yamahonkawazuki]

IMHO it seems the mains a re a hair too large, try 150's first, and tehn mess with screws if still problematic

[soysss]

k changed out the mains for 150's it still backfires on throttle down but not as much.  It also isnt picking up fully at WOT. I guess ill mess witht the mixture screws andneedle washers.

do you think it needs more or less gas? or maybe needs to be balanced real well?

-erik

[The Buddha]

You running K&N and shortie pipe ??
You lost power on 150 from 152.5 - Sure about that
The reason I ask is, throttle opening problems are usually too rich, and steady throttle problems are too lean. But you miss by more than 1-2 jet sizes, too lean will act up all the time, and too rich will bog all the time.
If you are sure you lost WOT performance as you open to WOT and not when its steady rpm at WOT, then try 147.5's I guess. If its at steady WOT (after accelerating and its at steady rpm at WOT) and you're having it act up (it will rev up and rev down all by itself - AKA lean surge) then do 155's. Very very rare you need larger than 150's man. Your floats set right, not too low I cannot help but think some else is off.
How is the plugs (however you have to do a high rpm run and plug pull at WOT after it gets to steady rpm ... 6th gear WOT till it hits its steady rpm and then plug pull and test. Not easy.
Yea the 2 carbs should be equal and have the exact same butterfly opening etc etc (synch it)
Cool.
Buddha.

[soysss]

it just doesnt get power when i crank it open at around 5-6k rpm.  I usually cruise at 5-6k and when i go wide open the power just isnt there until over 8k, then it picks up again.  it feels really rough when i WOT until 8k rpm. 

yeah K&N lunchbox and a shortie muffler.

-erik

[The Buddha]

5K to 8K opening up doesn;t make good power. But clears up after 8K
OK needle, put washers under the thing you got 1, put 1 more, you have none, add 1, you have 2 add another ... but you have 3, dont add more, problem has to fixed another way.
Cool.
Buddha.

[soysss]

k ill add more today and im gonna change the oil too.  Im pretty sure i have 1 washer under each so ill try 2 then 3.   ill post my findings. thanks again.

-erik

[The Buddha]

dood ... check floats, check synch and then try more washers, dont just start modding before checking for correctness. You mod it to fix a problem guess what, when your problem gets accidentally fixed later, you have another seto of figuring out and Unmodding to do.
Cool.
Buddha.

[soysss]

k its not backfiring anymore but i went to check the vacuum sync with a hose, atf fluid,a dn a ruler taped together like other people have done.  The left carb draws all the fluid.  It goes straight up into that side, i cut the engine before it sucks it all in.  I tried messing with the mixture screws but couldnt get it to stop going into that carb. 

which way on the mix screws will increase/decrease the vacuum for that carb?  I havent taken the washers out yet, but now i will and try to tune again.

the problem now is that it just doesnt pick up between 5-8k rpm in gear.  when it sits in neutral its fine and i can crank it without any roughness but when i go in gear between thos rpms at WOT it is rough.

idk

-erik

[soysss]

bump

[The Buddha]

k its not backfiring anymore but i went to check the vacuum sync with a hose, atf fluid,a dn a ruler taped together like other people have done.  The left carb draws all the fluid.  It goes straight up into that side, i cut the engine before it sucks it all in.  I tried messing with the mixture screws but couldnt get it to stop going into that carb. 

which way on the mix screws will increase/decrease the vacuum for that carb?  I havent taken the washers out yet, but now i will and try to tune again.

the problem now is that it just doesnt pick up between 5-8k rpm in gear.  when it sits in neutral its fine and i can crank it without any roughness but when i go in gear between thos rpms at WOT it is rough.

idk

-erik

Right aint got no vacuum waaaaaay out of synch take em off and eyeball it and synch that way.
Now under load you cant make 5-8K but in neutral you can ... dead giveaway sign ... you have a tear in the diaphragm. Tiny ass tear.
Lets try this and you tell me if this is what happens.
Neutral, 10K+, 1st gear 10K max, 2nd 9K max, 3rd 8K max, 4th 7K max, 5th 6K max, and 6th gear 5K max. Definete pin hole in the diaphragm. Take em off and look at the sun.
Air screw does not touch vacuum, opening the air screw retracts the cone shaped obstruction in a fuel passage and lets it get more fuel per amount of vacuum. It does not touch your vacuum which is created by the engine, and it there fore creates the vacuum in the carbs and as the butterflies open it manifests as velocity in the venturi and that makes the air get sucked out of the 2 holes in the bottom of the slide, that in turn causes the slide to rise because the low pressure above the diaphragm causes a suction that counters the spring force and that creates a smaller and smaller obstruction in the emulsion tubes by pulling the neddle up and up.
Anyway, you have a problem somewhere.
Cool.
Buddha.
Cool.
Buddha.

[soysss]

damn new diaphragms for the slides right?  ahhh. lol
ther goes another $40

im gonna try some more stuf today before i buy them but most likely will anyway.  It gets through all rpms in all gears to redline but is rough from 5-8k

-erik

[The Buddha]

$5 a diaphragm Good used ones. $2 mailing.
Cool.
Buddha.

[soysss]

k ill take 2, how do I pay you?, i have paypal.

-erik

[The Buddha]

Does this mean you checked it and both are bad. Cos this is not like O rings, its not a wear item.
I also have 4 or more of these, and they all have F&*ked up slides ... so these are basically orphaned IMHO. So they not going anywhere. make sure they are bad, then buy it.
If bad, I'll PM you my paypal ID.
Cool.
Buddha.

[soysss]

yeah i spoke too soon.  I checked both in the sun and found no hole or wear.  So...I took off carbs checked the butterflis for even openng, which was fine they both opend at exactly the saem time.

I also checked the slide to see when they opened(with it still on the bike), and they opend at the same time with throttle. 

So i took out 2 washers from each (1 under each now) and did 3.5 turns out, and switched the slides with diaphragms from one side to other.

seems to run just fine now through all rpm range in all gears.  idk but i guess it worked itself out after resetting all those things.

thanks for all the help, if i get the same type of trouble in the future i know where to come.

-erik

[The Buddha]

Ha ha ... you prolly had a kinked spring. Try swapping it back, and not stuffing springs in crooked.
If not, it automagically fixed itself.  Just like the bike just fell over right there ... I didn't crash it.
Cool.
Buddha.

[starshooter10]

check your plugs?

im running 150's and i have one plug thats BLACK and the other thats white...

i think i need to take my carbs apart and clean them (one is going dry) and rejet down as one is black....

im running a Uni filter and a WELL drilled out pipe.

i on occation shoot 3 or 4 foot flames out my tail...

notrmally while engine brakeing down hills. at around 6k