She's running LEAN ... what next?

[79XS11F]

I have come to the conclusion that the engine on my stock bike is running LEAN. She is VERY cold blooded and after any given run the tops of the headers of the stock exhaust pipes are gold colored.
The carb jetting is stock but the air filter is K & N in the stock box. should i increase the pilot settings or pilot jets? OR raise the needle setting one notch?
I can't find an article I read last fall but I am sure there is a "fix" for an engine that is cold blooded at start up followed by lean when warmed up. i just don't remember what it was they said to do.
Any input would be helpful
Rob

[s head]

Sorry I will be no help as I have the same problem on my midnight special,everything is stock so the only thing I can think of is the inlet boots are cracked or the rubber O rings under the pilot mixture screws are leaking?Maybe the carb balance caps are leaking.
When I removed the exhaust headers to weld the rusted out mufflers I noticed the valves had a white chalky colour which I think means it is running way too lean.Oddly enough it runs perfectly.

[TADracer]

If you are lean and you have no vacuum leaks then jet changes might be in order, especially if you have done anything over stock.

There is an article on recommended jets for modifications but I do not know where I saw it. You may need one step higher on the main jets. Pilot jets are usually stepped up or down based on 3 main jet size changes. Example, if you have 137.5 mains and have done enough mods to go to 145's then you might go up one pilot jet size.

Raising the needles one notch will not make your machine run richer overall but will bring on the fuel through the mains quicker under part throttle. A main jet up or raising the needles up a notch is worth a try. If you dont have the jets, I would try the needles first.

[DiverRay]

Lean at idle can be adjusted with the mixture screws. Add about 1/2 turn on all 4, and see if it helps with the morning starts. The '79 carbs use the main jets for the pilot circuit, so going up one size may make the difference. Make sure you install Mikuni jets, as some aftermarket jets have the proper number, but the actual size can be different.

[79XS11F]

It's not just morning starts it's anytime I start the bike even when it's 30 degrees outside. Need high chock followed by low chock and then rough idle until the engine is well warmed up or hot. I don't have any main jets on hand so I will try raising the needles because I can actually do that without even removing the carbs from the engine. I think my color tunes are at the post office and if that's the case I will check it with them before I proceed.
Thanks guys
Rob

[mro]

What Ray said.....

Normal to need to start with choke.
All my XSes if they set for more than an hour generally need the choke to start agin.
Can start em without but has to crank a bit...with choke starts immediately.


mro

[79XS11F]

Hey MRO .. I don't mind needing to "CHOCK" her to start her up but she runs rather rough until at full operating temp which I am not used to. And then as I was saying the headers are turning gold so I am sure that she is lean even if jetted to stock specs. Sometimes I wonder if the issue is the age of the carb diaphragms??? They are not torn but may not be working as they should or all working the same.
Could a lot of the carb issues I have along with others be related to OLD DIAPHRAGMS that just don't work like they should or all the same? I KNOW my carbs are clean, I have no intake leaks and the jets are stock units of stock size.
Rob

Originally posted by mro
What Ray said.....

Normal to need to start with choke.
All my XSes if they set for more than an hour generally need the choke to start agin.
Can start em without but has to crank a bit...with choke starts immediately.


mro

[mro]

All the carb diaphrams I've come across have been in very good condiction (over 16 sets) so have no experience with bad ones.

Have noticed that BS34 111's seem to run smoother with choke on than my BS3411's but have no problems with either.

I'd try as Ray mentioned, adjust out the pilot but I'd only try a quarter turn at a time and see if it makes a difference.

Still a problem then I'd try going up one on the main jet.

Would also go and run for a mile or so with RPM around 4,000.
Kill engine and check plugs before changing main jet.


mro

[79XS11F]

Thanks MRO ... Being that you must chock for all start ups how long does it take to warm up for you? Do you need full chock even on a very warm day if the bike has sat for 3 to 4 hours?
Maybe I am expecting too much from this old girl? I really can't remember how the bike behaved given that it's been 24 some odd years since I owned one of these puppies.
Rob

[mro]

Gets very very cold here!!!

Seldom ever gets below 40 degrees here and most of the time never below 50's.
When it's that cold out takes all of about 30 seconds on full choke.
Then half (generlly can take off then)

Bike setting for a few hours always starts better on full choke.


mro

[79XS11F]

Well here in Ottawa we do get some nice days and I still have to full chock for that same 30 some odd seconds followed by a few minutes of half chock and rough idle for at least 10 minutes of riding. That is even on days when it's above 90* F.
Rob

[mro]

and rough idle for at least 10 minutes

10 minuets is XSive.
Might re-check enricher circut.
Always re-check float height when ever bowls are off too.


mro
btw, even 1 mm float height makes a difference. 80G runs like $h1t when I went to 22 mm.

[79XS11F]

Hey MRO ... Now that I have color tuned it I am not sure that float height is an issue because she appears to be burning correctly in the 3 to 45 K range (Bunsen burner blue with light yellow during the twist and disappearing when a constant RPM is maintained. Changing float height would have an effect across the board right.
Given that the pilot screws needed to be turned out to 2 and 3/4 turns to get the idle mix right I may move up one size on the pilot jet if I have the carbs off in future. 2 and 3/4 turns is more the twice the factory start point on those screws.
Rob

[skids]

Raising the level might also be an option, depending on what kind of performance you get at wide open, steady state throttle. I have one with that sort of trouble. It is an 81H with older carbs. Shoot...it already has #45's in it and it is blue all the way until air gets in! No broken tips. That bike had troubles getting moving from a stop on top of Loveland pass (12,000 ft.) and usually high elevations will cause a rich mixture. I just don't get it.

Originally posted by 79XS11F
(snip) I may move up one size on the pilot jet if I have the carbs off in future. 2 and 3/4 turns is more the twice the factory start point on those screws.
Rob

[mro]

Changing float height would have an effect across the board right.

That's why I tried it. Yamaha book does say + or - 1mm....
The G after it's warmed up has what sounds like pre-ignician nock.
Changing the float height did cut the noise down but it also cut down on the power.

Color tunes seem to be pretty good from what I've read, but don't have one. Old method has worked for me.

Pretty sure that TC and a few others have there pilots screwed out like yours and are not having a problem. (I have no hands on experience with there bikes other than thru my key board tho)
I did rebuild a 79F a while ago which had straight pipes and as I recall had stock pilot which ran good out about 3 turns.


good luck

mro