What are all possible causes of a lean condition?

[Jethro]

Cannot believe that I still have stark white plugs after installing Mikuni 160 main jets and shimming my needles about 5 mm below the lowest notch on my DJ needles. How could this ever happen? Bike runs like crap like that, but I'm dying to see at least a little bit of tan or soot on the insulator! No such luck, white as snow.

Anyway, I'm 100% convinced that it's not the carbs now. Can anyone suggest a possible cause for this? Here is what I have thought of for possible lean running casues:

1. Air intake leak
2. Exhaust leak
3. Float heights
4. Poor timing
5. Gas cap vent
6. Vaccum line broken or not hooked up
7. bad petcock
8. poor valve clearances
9. undersize jets
10. needle too high

Can anyone suggest other possible causes? Or does my bike just run so freakin' clean that my plugs don't get any soot on them whatsoever? They look like they are right out of the box, except the electrode end has a off white glaze on them. The insulator is clean as a whistle.

The bike also seems to run pretty cool. Maybe my oil temp gauge isn't working right, but it rarely gets over 160. Yesterday, although pretty cool out (50F) I rode for an hour and a half and could put my hand on the outside of the block no problem. Very strange.

People must be sick of my constant b!tching about this.

[Anonymous]

carbs

one thing a found on my 1000 with vm carbs was that the petcock has a small vacum one way valve in it that stops the fuel cut of diagram, from pulsuing with the engine vacuum pulse, it was bad and was straving the engine for fuel, checked ok with a vacuum pump for fuel flow, but when hooked to the engine the pulsing that is normal, combine with the bad one way valve in the petcock was only allowing enough fuel for engine operation but could not keep the bowls at proper fuel height, and my plugs kept coming up white, you may also have the wrong needle jet holders? if you have the needle up 5mm and not .5mm then you need to start over from the beginning. or your doing some thing wrong with your assm. of the units, also use NGK plugs,

[Jethro]

Yup, got NGK plugs BR8ES as called for stock.

I'm pretty sure that I have the jet needle right- I have (from the bottom of the needle) a small spring then a small flat washer, then the e-clip, then another flat washer, then the small delrin or plastic spacer that comes with the stock needle on top. Is that all correct?

[crag antler]

Yup, got NGK plugs BR8ES as called for stock.

I'm pretty sure that I have the jet needle right- I have (from the bottom of the needle) a small spring then a small flat washer, then the e-clip, then another flat washer, then the small delrin or plastic spacer that comes with the stock needle on top. Is that all correct?

Here is the page from my CD parts manual. Hope it helps
[img]http://groups.msn.com/_Secure/0WgCRAqYbhgY2TEjE!wtUA*j1md6tRWAEjpvw3wkOZ1HUCnpqY yp*kVUadoGofCs1RSjKRYNBXyV*U7D5ETKAwOQq9UaPdVfSViq XbTnZVV6oAT*vuvdFVCjxOrlnQQzlIqo1*iiPCVo/jethro%20carb%20picture.JPG[/img]

[AOD]

Jethro, do the carbs have an air screw setting like the VM carbs? I know some will argue it's used only for idle, but it could affect things.

You raised the needle and the main jet which is 40% throttle and above for the most part...but does it run lean at idle too? I think that will help you answer how 'big' the problem is, and maybe which direction to go.

On your idea of tracking an air leak, your idle would be increased if you had a leak, and a quick check can be made by spraying some WD40 (or if you're nuts, propane) around the intake boots. Any change in idle speed means you have a leak, careful not to get it in the filters.

~Adam

[Jethro]

Jethro, do the carbs have an air screw setting like the VM carbs?

I do have an air screw on the CV carbs, and at idle the burn seems ok. But whenever I take a plug reading at 3500 or above, I'm crazy lean, no matter what I do.

The is no air leak at all. I went so far as to spray carb cleaner on the boots 8O just to ensure there isn't an air leak. I was convinced that was the problem, but no change in idle at all.

I'm confused, and am gonna have to pony up the dough to have it dyno tuned. I can't stand having someone else wrench on my bike

[earlfor]

Re: What are all possible causes of a lean condition?

Which bike is it? You running pods and a V & H 4 into 1? The plugs for my 83 1100 are NGKD9EA. You're running hotter plugs than I am if you're using 8's.

Earl

[pano]

Have you tried running the bike with the petcock in the prime position? Any difference?

[Anonymous]

It is highly unlikely that there is an air leak in all four cylinders. The problem is something that all four have in common if, that is, you are finding the same problem in all four plugs. A gas station may be able to put an exhaust gas analyser up the pipe and give you more info to chew over but its hard to do that under load which brings you back to the dyno.

Don

[AOD]

I just remembered someone saying a test you can do is put something over the air filter, like a towel...something restrictive, but not choking, and run the engine up over 3500 and see what happens.

~Adam

[earlfor]

Have you checked that the float bowl vent tubes are open to atomsphere?

Earl

[Anonymous]

A couple thoughts:

1) Good list of possible lean causes. I haven't been following this saga too closely, but are you sure the top end of the motor is sound?

2) Is there something other than a lean condition that could be causing your plugs to come out white? After all, I think that if your engine is running better with the smaller jets, and any size jet gives you white plugs, there is something we're not thinking of.

3) Have you thought about getting a hold of a Colortune kit? I really want one of those things, they look very useful for situations like this.

[Anonymous]

Only two reasons for a lean condition//// Too much air or too little fuel

[Anonymous]

Sorry, I apologise.

[scotty]

2 things that i used to modify the needle setting are small washers above or below the whatever to push the needle down and i believe that i once filed the plastic spacer to allow more travel down((i had a rich condition)). the suppliers like murdoch usually sell asjustable needles so you dont have to buy a jet kit. I woild supose that grinding a few thousands off the needle tips would do the job.
just wild guess that i have tried from time to time.