lean running , may need rejet?

hi, I'm nearing the end of my "3 year" rebuild, and trying to get the bike running right. I rebuilt the carbs last year, cleaning all passages with carb cleaner, and changed all the throttle shaft seals ,fuel rail seals.
I bench sync'ed the butterflies, set pilot screws at 2 turns out, wet set floats at 3mm.
I started the bike today "with difficulty" and after about one minute running ,the header pipes were glowing red hot.
stopped bike immediately
mods are-- 4 into 4 stainless steel header pipes, with 4 after market silencers with some baffeling around outside, open in centre
boots and airbox retained but with modified filter housing ,(ran without filter for first trial)
so, would this be a definate rejet or could it "lean up" by adjusting the pilot screws ,blocking the "straight through" bit in the silencers, and fitting the air filter, or lifting the main jet needles a notch.
Haynes is very confusing, as it gives two different values for needle notch #3



any practical help greatly accepted.

cheers
stu

 

Nice bike, what model and year is it, btw?

 

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Nice bike, what model and year is it, btw?
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its in my sig. 1991 xj 600 euromodel

 

Oops sorry I was too excited to see it !

 

Beautiful build. But with all those mods I suspect you are running very lean. If you had a colortune you could see the flame and determine if it's lean or not. Even though, getting the pipes glowing that quick would worry me unless the pipes are very thin.

 

Holy cow! You cant ride that!
It'll get dirty!

Seriously though
+1 on the colourtune plug, invaluable if your not a super duper carb setting mechanic with a good ear.
Your only dealing with the idle 1050RPM and getting that correct to then get the carbs sync'd correctly.
I use an electronic carbmate thingemie to sync which works really well (it has a happy face under the sync light which makes me happy of course).
http://tecmate.com/products/carbmate/

Messing with the needles is for when you get the butterflies open and are out of the idle range.

So, idle mix and sync before anything else! and now the fun really begins

 

sorry in my original post ,I meant to richen out.
yes I have a colourtune but I daren't start the bike now to use it.
I also have a pair of sync gauges but this thing is obviously much too hot to run it.
the pipes are stainless steel but not double walled.
stu

 

Wet set your float levels, double check all passages in those carbs. When you run the bike to sync , use fans to blow lots of air on the engine to keep it cool as possible.

MN

 

If the pipes aren't double wall I would not be surprised that they glowed. It's hot right out of the cylinder. I use an a/c squirrel cage blower to keep my bike cool while tuning. You didn't say how you had the pilot screws set, but perhaps you should open them about 1/2 turn, hook up your colortune plug and take a look. Remember that the engine is running primarily on the pilot system from idle up to about to 1/4 throttle, so you should be able to richen it enough with the pilot screws to at least get it synced and set for idle. If you can't get it to run richer at idle with the pilot screws then you'll probably have to do some serious re-jetting. That's the reason I keep my bikes stock. Good luck.

 

What's modified about the air box? Regardless, the change in exhaust probably means bigger main and pilot jets at least... maybe raising the needle as well. The pilot screws help set idle mixture, but don't have much effect on mid-band or WOT. I just got some jets for my Virago from JetsRUs. You might want to ping them to see what they'd recommend for your setup.

 

ok, thanks guys, made good progress today ,and bike is now starting and ticking over really good.
1- I put the modified air filter back in the airbox
2- I put some penny washers in the silencers , to block the "straight through" pipes
3- I turned the pilot screws to 3 turns out instead of 2
then she started straight up, adjusted idle to about 1200, put vacuum gauges on and they weren't far out, but tweaked anyway
colourtune on all four is now mid blue but with flashes of orange?, which would indicate a little rich- wouldn't it?
have to try it at higher revs now and under load.

mods to airbox are
cut filter housing away from airbox

make a mounting plate and fitted new round filter inside airbox




oh, and thanks for the tip with the cooling fans

 

Sounds pretty good. Now I would ride it at highway speed and come back and read the plugs to make sure you are not lean at higher speeds when the pilot system has less influence. Hope you get it right 'cause the bike really looks good.

 

yeh , thanks v much, that's tomorrow's job. but next door neighbour don't like me makin a noise, and this thing was really loud. the penny washers have quietened it a bit.
i'll see how it goes
regarding the colourtune, would the flashes of orange still indicate a rich mixture, can't get a solid blue, no matter what the pilot screws are at.
but hey-ho , I'm mega happy with todays results.
here are the silencers, i'll make a permanent job of those if everything works out


cheers
stu

 

Fabulous work on your bike I must say. Your air filter setup is very nice.

 

Flashes of orange indicate a mixture that is rich. Are you seeing alternating flashes of orange and blue? That may indicate that you have a vacuum leak (or other issue) that is leaning things out intermittently.

 

How's the build going? Just picked up a pre div myself and fancy a cafe scrambler type build

 

build is now finished, bike appears to be running ok. things are on hold now till weather improves. done about 50 miles on it , not enough to colour the plugs yet.
gonna start a build thread in "modifications" soon.
time now taken up cos I bought another to do up a couple of weeks ago .here it is, but this one runs and rides ok.
stu

 

The exhaust system is really bitchin'!

As is the airbox.

Exceptional efforts.

This could actually be due to a LEAN condition, here's what happens:

a) 1st intake cycle introduces a VERY lean mixture, it doesn't fire (so no color flash at all). Exhaust stroke does not purge all the (unburned) fuel out.
b) 2nd intake cycle introduces a VERY lean mixture. Same results as happens in "a" above.
c) 3rd intake cycle introduces a VERY lean mixture. Now, the accumulated results of the previous remaining lean mixtures are to the point where the plugs can fire the mixture, and now it's a bit RICH (orange), and you see the spark.
d) repeat over and over sometimes it will get rich enough on the 2nd intake cycle, sometimes, the third, etc.

This is assuming that the electrics are strong enough to fire the mixture, i.e. coils and especially plugs.

TEST: bump the choke on just a bit, see if you get more consistent flashes of color on the colortune plug. If so, then it points to a very LEAN pilot fuel circuit, either due to jetting issues, partially plugged internal passages, or mixture screw adjustment (or other) issues.

 

I love the work you do. Can't wait to see your next project!

Cheers!

 

I have two questions:

1-what is the main reason why you modified the airbox? more room below the seat? easier to remove the carbs and put them back?
2-how did you make the washers stay in place in your mufflers?