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Discussion Starter · #1 ·
After messing with the jets in my carbs for the last month or so, i've finally got my bike running top notch...only thing is it's still running a little lean. I had to reduce my pilot air jet by 5, increase my pilot by 5 and my main by 5. I live at sea level. I haven't touched the air/fuel mixture screws yet, and i was wondering if they have a major effect on how the bike is performing? Would turning them out (they're on the front of my carbs) richen the mixture enough to bring me where i have to be without changing the performance too much? I'm really happy with how it runs now...i got major pull right through the rpm range, and would like to keep it where it is if possible.
 

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The primary effective range of the screw is at idle....the more you open the throttle the less of an effect those screws have- by say 6000 rpms in neutral they have virtually zero effect, if you consider loaded-it is probably by 4000 rpms their effect is almost nill.

Your jetting though seems awefully pig rich-dropping the pilot air by 5 would net about 10% more fuel from idle to needle taper and then adding 5 to the pilot fuel---nearly 15% more fuel especially at idle but it will still carry more fuel-say 10% or more upto that 6000 rpm no load (about where the needle is finally on the taper)
What modifications have you done to necessitate such drastic jetting changes?
 

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Discussion Starter · #3 ·
Hey, thank you for the reply. I have 4-1 headers and a Hindle Stealth exhaust. My plugs were telling me the bike was running lean...this was the original thread...you can see a pic of the plug..they all looked like that.

http://www.sportbikes.net/forums/ge...-yamaha-fazer-750-wont-start-when-warm-2.html

After messing with diff size jets and needle heights and a lot of trial and error, i found the right combo (performance wise) to make the bike run great....although my plugs are still telling me the bike is lean. I had it out a few times now, and it runs perfect...better than perfect. I get great pull now from about 2000 rpm all the way through. Before the change, the noticeable pull came in around 5 or 6 grand.

I thought with the increase in the main and pilot and reduction in the pilot air, that it would def be running richer....not sure where to go from here...
 

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Hey, thank you for the reply. I have 4-1 headers and a Hindle Stealth exhaust. My plugs were telling me the bike was running lean...this was the original thread...you can see a pic of the plug..they all looked like that.

http://www.sportbikes.net/forums/ge...-yamaha-fazer-750-wont-start-when-warm-2.html

After messing with diff size jets and needle heights and a lot of trial and error, i found the right combo (performance wise) to make the bike run great....although my plugs are still telling me the bike is lean. I had it out a few times now, and it runs perfect...better than perfect. I get great pull now from about 2000 rpm all the way through. Before the change, the noticeable pull came in around 5 or 6 grand.

I thought with the increase in the main and pilot and reduction in the pilot air, that it would def be running richer....not sure where to go from here...


No way those minimal mods necessitated such drastic increases in fuel required.

Oh you are definitely running richer, probably so rich it is washing the plug clean would be my bet.....Get it to a gas anylizer I bet you peg the CO meter from idle to main jet. and your HC will be way high...of course it pulls hard to someone with no knowledge and experience in proper jetting-they always feel great when too rich-why do you think so many are too rich all the time.........but that isn't good for the engine, the environment or your pocketbook
 

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Discussion Starter · #6 ·
The jet sizes i settled with were not the first ones i tried. I've got a toolbox full of them now. I am new to all this, and really wanted to fix the bike myself. No one around here will work on a bike as old as mine, and those that will say they will "try" to get to it.

First i tried just the main jet increase by 5. Noticed a little difference on the top end, but it still popped heavily on decel. Then i tried shimming the needle jet + the upped main. Got rid of the decel popping, but the bike ran like shit.

I then tried putting the stock pilot air jets in, which manual says is a size 130, though when i bought the bike they were 125. Popping came back, and the bike still didn't run very well. Mostly around idle and up to 1/4 - 1/2, so i upped my pilots by 5 and took the bike out again. Ran better, but from 1/4 - 3/4 throttle it sputtered and hesitated.

So finally, i put the original pilot air jets back in, which were 125's, put the needle in it's original position, left the 105 mains in, and the 25 pilots (up from 20). The bike still has a little popping on decel, though not nearly as much as it used to. I just checked the plugs again today after driving it for a few days, and they're still pretty white.

I don't know where to take my bike that would have a gas analyzer...like i said before, no one will work on my bike, so i'm stuck figuring it out myself. Is there anything you can tell me to help me fix it myself? My bike is a 1986 Yamaha fazer 750.

I really appreciate your input...i have no prob eating my fair share of constructive criticism.
 

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I wasn't aware they made a fazer 750....thought only fazer 700's

no matter


one of the huge issues with that era of Yamaha was that the emulsion tube wears out....the needle pounds the shit out of it and it gets oblong shaped and they allow a shit ton of extra fuel to go by the needle

the only cure (unless you are like sub 5k on the carbs or possibly even 10k if it was ridden very gently) is to replace those.....there used to be a few aftermarket companies making them out of better material but not sure anymore.
I haven't seen one of these roll through in years....lots of years and the last FZ700 I saw had only 6500 miles and they wear worn out and I simply got new oem ones for around $60 for the 4 of them and all the problems went away.

I might still have a set of them brand new in the oem Yamaha parts box.

It is called??????????????? "main jet holder" I believe on the parts fische--it is pretty self explanatory really just knowing where the slide needle goes.

you could pull yours out and inspect them- I would be willing to bet they are not round anymore

But without a gas anylizer you really are shooting in the dark to a large extent.......plus trying to read plugs..........you are using leaded gas when doing this---because unleaded will read differently and they should look white.
 

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Discussion Starter · #8 · (Edited)
I use supreme gas in the bike, which has the highest octane, which is unleaded...they don't sell leaded gas in Canada any more...at least not in Nova Scotia.

I know when i stripped the carbs off the old FZ i bought for parts (carbs are almost exact same) the little needle housing your talking about was so weak then if i tightened it any more than hand tight, the top would snap right off with the slightest pressure.

I can pull the carbs off the bike again and snap a high res pic of them.
If you have a set of them brand new in your yammy parts box, i'll take them off your hands. I snapped 3 of them off the extra set of carbs i got and need them for a re-build.....Here's the part i'm talking about...
 

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Those are not the parts I am talking about


I will look in the morning and take a picture...
 
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