Help me figure out my crappy fuel economy!

Hey everyone...

Thanks to you all and Len, I've been able to get the bike running pretty well. However, my fuel economy is still crappy - I've been getting between 25 and 28 MPG. I'm calculating this based on my trip odometer and topping the tank off at each fill up. Not sure what's going on, and I could use some help!

I've done the following related services:

Replaced fuse box
Rebuild and clean carbs
Replace airbox boots
Replace intake manifolds
New plugs - NGK BP7ES
New plug caps
Checked coils/pickup coils for proper resistance
Valve adjustment
Checked Tire pressure
Fresh engine oil
Fresh final drive oil
Tune each carb using colortune plug to just barely on the yellow side of bunsen blue
Synchronize all four carbs using a glass baby bottle sync tool
Set idle to ~1100 RPM


Right now, the bike doesn't seem to resist me moving it at all when the transmission is in neutral, so that makes me think the brakes aren't rubbing. I have fresh pads and shoes installed anyway, and the caliper/drum were in proper working order. I am not getting any noise from the wheel bearings, but I'm not sure of the best way to check them, and would not be completely opposed to changing them out just for good measure as I believe them to be original. How should I go about checking them?

The bike seems to run great. The idle is smooth, it usually starts with just a little choke and warms up quickly, and seems to have plenty of power. But I can't figure out why I'm getting <30 MPG. I'm about 200 lbs, no windscreen, and ride fairly agressively but I would expect mid to high 30's riding it hard, and low 40's for easy freeway riding.

What am I missing?

Thanks!
Aaron

 

Also - I seem to remember reading it somewhere, but I can't find it again - When tuning the bike with the colortune, I usually take it for a 10 minute ride to get it nice and hot before I come back, park it in front of a large boxfan, and start using the colortune. That sounds correct, right? Then I sync it immediately after and adjust the idle as necessary...

Aaron

 

Plug chops are your best friend at this point.
you gotta see what the mix is like at load around 4k

 

Synch first, then colortune, and re-synch after each cylinder is colortuned. The adjustments you make while Colortuning will affect the synch.

Repeat this process twice and you're in Fully Tuned Heaven.

 

Sorry, but I'd have to agree about the plug chops... unless you have access to a dyno. Colortune at no load is only going to tell you about your pilot jet settings; it won't help you if your metering needles are too small or high, or if you main jets are too big. Plug chops under hard accelleration should give you a better idea if you're running too rich under higher loads.

 

The bike is completely stock, with stock jets in the carbs. Is it common to have to modify the jets as the bike ages? It's got 30K on the ticker.

For some reason I was under the impression that doing plug chops was more appropriate for bikes with modified intake/exhaust systems.

And are you all saying that having it not be in perfect tune would cause it to get 10MPG less than what is common? I had figured it would only be a few MPG...

 

in a finely-tuned swiss watch, one tiny gear will affect the entire watch significantly.

 

what plugs are you running? stock?

 

Yes, as I specified in my initial post, stock plugs - NGK BP7ES.

 

I missed that part

 

Are you the original owner? Is this low MPG thing a new development? If you're not the original owner, and the bike came with this problem, then there are still things that could have been done to the carbs. For instance, were there any washers under the needles? Could the main jets have stock numbers on them, but actually have been drilled out to a larger size?

And, yeah, if you riding it pretty hard, I could easily see an over-rich high load condition sucking down 10MPG.

 

I'm not the original owner, but the previous owner told me he was getting around 40 MPG before he stored it for two years.

These carbs, however, are another set I picked up from craigslist, so who knows... There weren't any washers under the needles, and the main jets LOOKED to be the same size as the set that was on the bike, but LOOKED is a pretty feeble comparison when you're talking minutia.

I'll see what I can figure out as far as plug chops, and if they look very rich, first think I'll do is replace all the main fuel jets with new ones. Does that sound reasonable?

 

you should compare the numbers stamped on them to make sure.

 

That only holds if they haven't been drilled out. Some people do drill them to save money and time. Ideally, if you drill them, you also file off the numbers, but you can't count on PO's doing the right thing.

What happened to the original carbs? If the bike was getting 40MPG with those, it sounds like a good cleaning for them might be a strong option as well.

Also, besides the jets, try to compare the needles to known stock needles.

 

Sorry, I wasn't clear. The numbers matched, but as to whether they had been slightly drilled out, I can't say. The did not look like it, but I suppose for the $12 for a new set of jets it's probably not worth questioning it.

 

Are you sure that your speedometer and odometer are accurate? Check them against another car or bike on your next trip to see if they ae close. You are right you should be getting in the upper 30s for mileage. Reading through the posts everything looks to be in place.

 

ride it like a cop is following you for a tank, well a half tank, and see what it does
the difference on mine is drastic

 

I tend to ride mine like I stole it... well, for the price I paid, I may have stolen it
:lol:

 

Could you elaborate on "drastic"...?

I certainly don't ride like a grandpa, but I'm not full throttle to 9K all the time either...

 

i don't really watch the gallons i watch the $ and sometimes it's a buck or buck and a half more
are the choke plungers all the way down, not even touching the lifting fingers