Carb Tuning, Who Undserstands Carburetors?

[space_weazel]

Tuning 101
OK new thread time, the old one was off track and I need to correct some info that I had misunderstood and misstated in my frustration, so new thread.
I am trying to lean how each part of a Carburetor works and how they interact.

91 fzr600, which was set up and running with the K&N dual port pod filters, and a Yosh slip on, my mechanic and I also think it has an over sized cam.

So after who knows how many years the boots on the K&N on the right side got so hard they would not mate to the carb body any longer, so I search for new pods, no one in town has them, but someone offers me N&N style individual pods for about $10 a pop, so I get those to give them a try.

I install the individual pods and take it for a test ride, the bike accelerates harder than before but at about 7k RPM it sputters and the revs will go no higher, I check the main jets and they are 130's I figure the new filters are giving me more air so I need more fuel, so I put in 135's and its basically the same, hard acceleration up to 6-7k in all gears but it sputters and will not rev past that.

I tried jumping the jet needles down one clip position(from position #2 from the top to position #3 from the top) on the advice of a friend who works at a shop, just to try it, as soon as I started it I could hear it was eating way to much fuel, as it started from cold without choke and sounded "throatier" (not a word I know) test ride yielded poor results.

so I drop the jet needles back to the original positions and changed the jets to 152.5's just to see if I would get a noticeable result, test ride and the bike runs out of revs at about 6k flat now so a little lower than when it had 135's in it but not a big difference. hmmmmmm......

Now I am wondering if perhaps the filters having a smaller cross sectional area are delivering less air since all the remedies for an abundance of air do nothing, should I try going the other way? say going down to 125's or 120's on my main jets? or are these pods just delivering to much air for this motor to be run across the power band?
I am thinking about just sucking it up and plopping down the $120 on two new K&N dual pods and going back to the original set up.

What to do?

Thanks everyone.

[ragedigital]

PODs.... no fun. I gave up on them. I actually felt I had a harder pull with a K&N filter in the stock airbox and running 130 mains.

If you want to keep the PODs, cover half of the filter with tape and see if that doesn't help. Work from there.

[reelrazor]

I'm with Rage...get an airbox.

[megaloxana]

His bike ran great with dual pods and you guys are telling him to go back to airbox? I cant stand this hatred for pods.
Anyway see if you can't get ahold of smaller jets. Really sounds like you're too rich, especially since you tried larger jets.

BTW it still doesn't rev past 7k even after being fully warmed up too right? And double checled the boots that the carbs fit into for any cracks and make sure the carbs are seating correctly in them.

[ragedigital]

His bike ran great with dual pods and you guys are telling him to go back to airbox? I cant stand this hatred for pods.

It's not a hatred, it's a misconception that PODs perform better than the stock airbox. Plus, since "weasel" does not have a firm grasp on carb tuning, it would be in his best interest to return to a stock airbox and be on the road again shortly instead of screwing with the PODs.

It's SPRING - time to be on the road and out of the garage!

[sweekster]

His bike ran great with dual pods and you guys are telling him to go back to airbox? I cant stand this hatred for pods.
Anyway see if you can't get ahold of smaller jets. Really sounds like you're too rich, especially since you tried larger jets.

BTW it still doesn't rev past 7k even after being fully warmed up too right? And double checled the boots that the carbs fit into for any cracks and make sure the carbs are seating correctly in them.

I'm not really a fan of pods but saying "get an airbox" doesn't help solve his problem. Pods or an airbox would require proper carb tuning either way. I'd go back to the jet size you had when the bike ran satisfactory through the power ban, resynch along with checking for any seal leaks and or vacuum leaks. But that is just where I would start. is this bike a Cali Exup model?

[yamaha_george]

Guys,
It is very simple without the air box and more air flow it actually makes the Carbs more efficient !!!

IE they suck up way too much gas from the bowl.

Lean the needle out slightly drop the main jet by a size down from standard.
Why did it work ok with Dual pods because you were sharing air and had some resonance & volume for the carbs.

Ok so in town they do not have doubled filters err you can email so use the modern tech to order on the internet jeeze as the oldest geezer round here I can manage that !

I even put a link on the WIKI tech page a few weeks back for these same double filters

[space_weazel]

Thanks ragedigital, sweekster, megaloxana, & yamaha_george

It is not an Exup.

I will not being going back to a stock air box, that's just foolish.
I got individual pods because they were less than half the price of the K&N's and I could try to make the bike work that day if I wanted to be out riding at all costs I would have just ziptie'ed on the old n busted pod and go for it, the way it had been; I am trying to learn about how carburetion works and frankly I want to see if I can get them to work just to prove that it can be done.....

I think I'll try going to a smaller jet and see what happens, or try to lean it out at the needle....

Any other Ideas, any one else try these and not have complete failure?

[DonTZ125]

I like George's thought - if you're actually getting a stronger signal to the nozzle, you need a SMALLER main jet. Don't bother with the needles yet; once you sort out your mains, you'll likely just be changing them again.

Have you thought about what I said on the other thread, about soaking the old double-pod rubbers (not the filter elements!) in hot coolant?

[Cursed94FZR600]

space be very careful when leaning the bike out. as was mentioned before a rich bike is a problem a lean bike is gonna break something. when you test the new needle settings listen, feel, every other sense you can and if something/ anything is wrong turn the bike off before damage is incurred.

other than that good luck and keep us posted

[DonTZ125]

What he said. That said, if a #130 is staggeringly rich, a #125 isn't going to blow you up.

Wild thought - have you checked / established what your fuel height is? Are your starter jets stuck on?

[space_weazel]

Thanks guys

I have not checked the fuel height, though I guess it could be, but the bike was perfectly functional right up to the minutes before I changed the filters.
I may try soaking the boots to soften them up but frankly these have been through a lot the previous owners have been hard on them, they are dented, bent, and the one with the bad boots is slightly crushed, so its time to replace them.

No worries I will be careful with running it until it gets sorted out.

Just for giggles I guess I'll go put the 130's back in and drop the old pods back on just to get a baseline and ensure everything is still running right.


I'll have to make a wiki article one of these days, to make up for all this help....

[yamaha_george]

Hi,
as you quite rightly say if it is way rich on the standard jets then dropping one size is not likely to make it grenade by being lean, watch your temp guage as lean conditions will raise the engine temp (the excess fuel is not cooling it ).

I have used individual pods on other model yamaha's and whilst never simple to tune they were easier than an FZR simply due to the pods location & tight spaces round the carbs for removal to change jets & needle positions

Good luck & if you are serious be sure to keep a note book & only make ONE change at a time before testing

I always thought that it was lack of experience and impatience that has stopped any one getting a good tune with pods it is very time consuming and lets face it we all want to ride rather than wrench.

I hope you do crack it & as a WIKI mod I will hold you to that wiki entry on how you did it :-}

[space_weazel]

By george, You`ve cracked it George!

I came home put in the 125 main jets, test rode it and it felt better, still a dead spot but better. popped the carbs out and leaned out the needles one clip position, and test rode it, and she ran right up the power band, tomorrow I`m gonna try to run up some brand new plugs and see if she is too lean / rich / just right.

Thanks again Yamaha_George!
Started taking pictures for the Wiki...

[sweekster]

By george, You`ve cracked it George!

I came home put in the 125 main jets, test rode it and it felt better, still a dead spot but better. popped the carbs out and leaned out the needles one clip position, and test rode it, and she ran right up the power band, tomorrow I`m gonna try to run up some brand new plugs and see if she is too lean / rich / just right.

Thanks again Yamaha_George!
Started taking pictures for the Wiki...

I'd synch them as well.