******HELP!****** Theories as to why my bike is running lean?

[Egaeus]

Okay, I'm about to give up.  I just don't understand.  My bike is showing all the symptoms of running lean due to poor fuel flow.  It runs fine for a bit, starts sputtering at speed, and both spark plugs are white. 

I figured that it was a constriction in the fuel lines.  I checked.  The flow seems sufficient.  I thought that maybe it was a problem with the float valves.  Nope.  The carbs were cleaned out right before christmas to try and fix this, and I cleaned out the jets before I rode it last weekend to try and diagnose it.  I even took videos of the fuel flow out of each carburetor with my phone.  The videos work in quicktime, but I don't know what else they work with if you don't have it.

Video 1 (right carb)

Video 2 (left carb)

I mention in the video that I thought the flow out of the left carb is less.  I now disagree with that assessment.  Oh, and I have a cold, and I sound like it.

[rob1bike]

Isn't there a screen or a filter in the stock petcock? I thought I remember someone taking it apart and cleaning it.... Vacuummmmmmmmmm leak? Not pulling enuff vaccuummmmmm?

[Egaeus]

If it was clogged, there wouldn't be enough fuel flow. 

Switching the petcock to PRI doesn't help the situation, so it's not a vacuum problem.

[tussey]

Hey Eg, hope you're not selling the bike, oh yea my neighbor doesn't have the money to buy it. He never did.


GL finding out why it's lean. 

[tussey]

try backing the fuel mixture screws out a half turn.

I went through this and finding out why mine was rich. Turned out the mixture screws were out way too far.

[Wrecent_Wryder]

I4

[Egaeus]

The question is, do you guys think the fuel flow is insufficient?  That's kinda' why I took the videos.   I think it's fine, but I may be wrong.

I will check all your suggestions when I get home from work assuming it doesn't rain today like they're say it might.  I'm also going to remove the fuel filter to check whether it is clogged. 

Edit: And yeah, tussey, my bike's still for sale, but I'm going to at least try to ride it before it goes away.  And I'd hate to be that bastard PO who gave someone a bike that wasn't running right.

[Wrecent_Wryder]

I4

[Susuki_Jah]

could it be somthing with valve adjustment. where the engine is bringing in to much air for the amount of fuel?  what exhuast are you running? I had a problem with my car one time that was like this. no matter what engine I swapped in it (3 to be exhuast USDM and JDM)  it always ran lean ,,, too lean . needless to the say all three engines bit the dust and I couldnt ever figure it out.  Untill I figured out what they all had in common. the header on the motor, it wasnt properly designed and I was hard on the car My father can explain it to me again, I'm no engineer but it was causing major problems with the engine.

its just an idea. I could be way off but I thought I would share.

[dgyver]

How fast the fuel flows out of the carb bowl drain has nothing to do with how fast the carb bowls fill.

[Egaeus]

It does after a while.  It can only flow as fast as it can fill.

Edit: I reread my post, and yeah, it does seem like that's what I'm saying, but believe me, I let that thing run for several minutes.  I got at least a pint of gas out of one carburetor before deciding that the flow wasn't going to slow down, so it's running into the carb at least that fast.

[Egaeus]

Yay!  Good weather and a day off so an update:

I've done some experimenting this morning.  The petcock and fuel filter do restrict the fuel flow significantly.  So to eliminate that possibility. I ran a line directly from the reserve to the carburetor and plugged the other line.  No change, and that flow will drain the tank in minutes, so we know that's not the problem.  It flows constantly, and the problem manifests itself almost immediately, so there's no vacuum forming in the tank,

The next experiment, I unhooked one cylinder at a time to see how each is running individually.  Running on the left cylinder, it backfires significantly, but otherwise it runs okay. 

Running on the right cylinder, there was no backfiring, but that could be because it was run first, and the left exhaust wasn't hot.  However, this cylinder was the one giving me the problems.  It's missing fairly severly on that cylinder.  It's causing the jerkiness that I feel when riding. 

The fuel level in the carbs is even with the float bowl gasket on the right, and about 2 mm above on the left.

That's all I've checked so far.  Next on the list is checking the timing (unlikely but easy), the mixture screws, adjusting the right fuel level up a bit.

[tussey]

the mixture screws

I put my money on that.

[Egaeus]

The timing is fine.  I adjusted the right fuel level to be very close to level with the left.  I checked the right carb jets, and they're clean as a whistle.  The mixture screws were both 3 turns out, which is what I've been running since I got the bike. 

So how much money did you put on it? 

[werase643]

Really important question.....

is it running lean at idle... or half throttle..... or WFO.....?
it sounds like at idle only......
what size idle jets are in there?
do a compression test.....just cause I asked
sync the carbs also......same reason as above
and 1/4 turn more open on your air bleed screws


re read first post....
what size mains also?
stock air box?
stock pipe?

[Egaeus]

werase643: Read my signature for most of your questions.

Correction on the problem description.  Rerunning my test last night with each cylinder, the right's running fine, and the left is running badly. 

I think I may have found the problem though.  I got so excited that I didn't fix it yet.  The part of the float with the o-ring has a passage that's supposed to be open.  It's clogged.  It might not be drawing fuel fast enough in that one.  I'm going go clear it out and go for a test ride if the rain doesn't hit first.

Compression was checked as one of the first things, sorry.  The cylinder that's running right has worse compression than the one that's running badly, but they're both within spec.  Don't remember the exact numbers ATM. 

The carbs were synced.  I thought that was initially the problem.  I'll adjust the screws if I don't fix it, but 3 turns worked for several months.

[werase643]

i was going to ask about the o-ring around the float needle seat, next

the right is trying to do more work to compensate for the left
after you clean/fix....probably have to resync the carbs to get the cylinders pulling air in together

[Egaeus]

Well, I put it together and started it before the rain hit.  It looks like it's going to get bad soon on the radar, so I'll wait until afterward to test ride and resync the carbs.  When I started it, it didn't seem to be missing anymore, so hopefully that's done it.  I'll let y'all know.

[Egaeus]

So I caught a break in the rain, and took it for a spin.  The purpose was to warm it up for rebalancing since I'd had the carbs apart and cleaned that bit of gunk out, but I couldn't help but notice that the symptoms were the same, or worse.  I had to keep reminding myself not to panic. 

So I got it home, balanced the carbs, and went back out before the serious rain got here.  It runs great.  Doesn't miss a lick.  Just in time for the rain.

[tussey]

So I caught a break in the rain, and took it for a spin.  The purpose was to warm it up for rebalancing since I'd had the carbs apart and cleaned that bit of gunk out, but I couldn't help but notice that the symptoms were the same, or worse.  I had to keep reminding myself not to panic. 

So I got it home, balanced the carbs, and went back out before the serious rain got here.  It runs great.  Doesn't miss a lick.  Just in time for the rain.

So you fixed it? Clogged carb hole? Badass Eg, good troubleshooting!!