White plugs AND poor fuel economy

What might cause lean-looking plugs but very poor gas mileage? Perhaps the two symptoms have unrelated causes. A little info on what I and my bike have been up to: valves in spec, cold cyl compression ~130-135 across the board (that's low, but in spec), single K&N filter in airbox, 42 pilots (smaller jets required mix screws to be out 5+ turns), 122 mains, fuel level wet-set at 3mm, vacuum synched, colortuned to just outside of blue (mix screws are out between 4.25 and 4.75 turns). I thought I might have an air leak somewhere, so I replaced manifold gaskets and bolts, applied rtv around joint, sprayed starter fluid around intakes while running and there was no indication of a leak. The bike idles steadily at ~1000, no hanging rpms, no surging while cruising. The bike shifts smoothly and has plenty of power. It rides great. BUT I'm getting about 24 mpg! and my plugs are white! Also, I thought I might be dumping fuel into the crankcase, but my oil level has not been rising and the oil does not smell at all like gas. Oh, yeah, I also rebuilt the petcock and replaced the fuel and vac lines. The wheels move freely, no rubbing of rear tire on shaft, breaks not sticking. I forgot to mention that I rebuilt the lower end of carbs using metal tipped valve needles.

 

5+ turns? 8O That ain't right. That's extra rich, so you're blasting the engine with fuel, hence bad mileage. Should have black plugs.

I can't comment too much, but I am looking forward to the feedback you get in the next 24 hours. This is one of the best mysteries I've seen all season.

One thought, besides the obvious red flag of your mixture screws - inaccurate mileage reading, making your math wrong. 24 seems weirdly low, unless you are dripping gas down the highway.

 

As ColoradoDan said, 5+ turns would be rich. But you said its running lean. A lean running engine is actually being starved for fuel, so at higher speeds and rpms you actually need to give a more fuel to get the same results as a tuned engine

 

Thanks for your interest in helping me, ColoradoDan. During the colortune, I don't begin to see the blue fade out until after 4.25 turns out, and the truly yellow doesn't come on until almost 5. I know my plugs should indicate this supposedly rich mixture, but they don't. My poor fuel economy does indicate rich, though. I'm getting a little over 80 miles out of a tank.

Thank you as well, MarkV. I'm a bit confused, though, by your last sentence. Can a "lean-running engine" eat more fuel and still be lean? I don't get it. If it's using the fuel, then it should not be lean, correct? I might be misunderstanding a lot of things here.

 

At 5 they are not really doing anything then. The hole is wide open. Optimum I think is under 4, if everything else is good.

Give it a few hours - there's a handful of members here that will have great suggestions.

 

What type of spark plugs do you have in?

Also, is it possible that you overestimated the amount of fuel you're burning to do 80 miles?

 

That's what came to my mind first. Original spec plugs,plug wires and caps (w/resisters) and coils, or have they been upgraded?

 

#42 pilots are bigger than stock (40's) plus your way out with the pilot screw.
the 122 mains are ok at 1 size over.
like quebecois59 said, maybe check that mileage again.
maybe you ride like a wildman

 

po removed the springs out of my pilot screws and 5 turns is the only way it will start. still runs lean, but gas mileage is like 52mpg when i have checked it. ordered new carb stuff for winter project-thanks len @ xj4ever

 

My plugs are NGK standard BP7ES, new aftermarket coils (same as OEM) with 15K ohm wires, new 5k caps. Regarding the fuel volume estimate, I fill the tank to the top and run until the fuel light comes on. The last two tanks have lasted only about 80 miles.

 

@Polock, Yeah, I had to increase from 40s which were in the carbs when I bought it in July. Those 40s were too lean, as were the 41s I tried next. If I'm out less than 4.25 on the mix screws, during colortune it's pure blue and there's hesitation off-idle. The screws at between 4.25 and 4.75 are just off pure blue in colortune and off-idle is nice. The bike seems to run very well, aside from the white plugs and bad mpg. As for aggressive riding, I've been careful to not crank the throttle when I'm riding because I thought I may have been wasting gas with too much throttle.

@Kennyhartman, my mix screws, springs, o-rings, and washers were all replaced in August.

I don't understand why the plugs are bright white (indicating lean, a rapid, hot burn) when my fuel economy suggests rich.

 

i wouldn't trust that light. do a fillup to fillup, gal vs miles.
i don't think this 10% gas does the old fashioned plug color, at least not very quickly. how many miles on those plugs?

 

Yeah no kidding.

You're not getting accurate fuel economy numbers.

Every time you get gas, fill the tank to the same point as closely as possible. Stick to either sidestand or centerstand fueling and match the levels on the neck from fillup to fillup.

Get a receipt from the gas station. Write the odometer reading on it.

Save at least three receipts. Do the math.

My 550 Secas have an actual fuel gauge; I can piss it off just by hammering second and third; then bring it back to half a tank by grabbing the front brake.

Light, schmight. Phooey. Do some record keeping and see where you're really at.

 

Okay, guys, thanks. I'll post the stats after I've collected them. But I'm still concerned as why the colortune doesn't show yellow coming on until 4.75 turns out. Anyway, thanks for the advice.

-Nate

 

Float levels or you missed something in the pilots. New o-rings on the screws?