Stick is sick...

[George]

After a few weeks of noodling and fussing, STick is no better now than she was when I got home from my last trip. I've fixed a few niggly problems, but the gas mileage is the main issue.

Worked over her carbs upon return home, next (299 miles) trip fetched 36.5 MPG, down 5 to 7 from her historic rate. Received the carbs off Will England's 93 via Turley, did a full clean and refresh per the instructions at ST-Riders and took her on another ride. Returned 35 MPG. Ugh!

So, further analysis needed. Did do a valve adjust check (worst was on #1 front intake, .001 tight). And, did an inconclusive compression test. Tho only read ~120 instead of the hoped for 160, I don't fully trust my compression tester. (Prolly ought'a check it against lipSTick.) Anyway, don't understand why lower compression reading would have that much impact against gas mileage, my max speeds are usually about 80, and that's at steady throttle.

Brakes are NOT dragging, bike seems to run well, all carbs are well balanced, etc.

Any tips or hints on what to check next? That gallon and half has to be going somewhere. (Deba did complain about gas smell in the garage when I got home on Thursday, but nothing obvious, no drips or puddles.)

Help! What do I check next?

 

[Uncle Phil]

Maybe a slight gas leak when underway?

 

[vinny]

Have they increased the amount of ethanol in the gas around Kingman?

 

[Reginald]

Get a good compression test. Check spark plugs. Check spark intensity ( http://www.skywaytools.com/products/2797-THX-458-Coil-On-Spark-Plug-Tester/ ).

 

[W0QNX]

Compression has a big effect on how well the gas mixture burns. If it is indeed low on two cylinders then I'm not surprised with the mileage results. Check it out better would be my first to try. 120 is getting pretty low.

Might read these pages and consider things.

http://www.linnbenton.edu/auto/perform/vacuum.html

http://www.linnbenton.edu/auto/perform/compress.html

Could be a head gasket? Are the two low cylinders the same side?

"If two adjacent cylinders have low compression it is often caused by a head gasket that is leaking between these two cylinders. If there is a very low first puff, and it gradually builds to an overall low pressure, that cylinder likely has bad rings or a worn cylinder wall. You can confirm this with a Wet Compression Test."

 

[George]

The plugs all look good. Could be a small gas leak, which adds up over time, but the gas odor is pretty minimal. Need a better compression tester, could probably borrow one at Auto Zone. Maybe over the weekend.

Rode lipSTick and Dr. Z today, both worked well.

 

[Don B]

I don't claim to be an expert auto or M/C mechanic, but my understanding is that an engines compression should be checked at normal operating temperature. I realize that many recommend not doing a R&R of spark plugs on anything less than a stone-cold engine if it has aluminum head(s), but if you don't have any problems removing the plugs from an already warmed engine, you may get more meaningful results than you have now. You can always let the the bike cool overnight before reinstalling the plugs.

 

[wjbertrand]

That sounds pretty low on compression, my 1300 is pushing 200PSI at 150k miles and its compression ratio isn't that much higher than the ST1100's. As mentioned before make sure the engine is completely warm and you're holding the throttles wide open.


-Jeff

 

[Reginald]

Could be a small gas leak, which adds up over time, but the gas odor is pretty minimal.

Could be your coils. An incomplete burn will cause this smell and mileage issue. A yellow spark from a plug is generally weak, a blue/white spark is generally good. To be sure you could use a coil on spark plug tester, they measure the voltage coming off the plug with the added benefit of no surprise shocks.

 

[dwalby]

Your compression numbers are very low, if the test was done properly. did you hold the throttle wide open so you could get a good charge of air into the cylinder? Low compression would explain the poor fuel economy, but its unlikely that more than one cylinder would lose compression all of a sudden. Did the mileage decrease happen gradually over time? If so then its possible all 4 cylinders have been gradually losing compression. If it happened suddenly then its not likely that more than one cylinder has lost compression. Compression and coils are the two things you need to check first, weak ignition or low compression will both decrease power and increase fuel consumption.

 

[George]

Maybe a slight gas leak when underway?

Phil wins the prize! Even tho, over the two test rides, I detected virtually no gas smell, upon arriving home from a grocery-getter ride the other day got a strong whiff of gas. Pulled the panniers, seat, side covers, and fake tank, found gas dripping at the recently reinstalled vacuum valve. Pulled it and installed another spare.

Ride on Saturday to 'Vegas and back returned 42MPG at speeds around 70-75. All is good again.

STick is currently up on Mohave County Craigs List for $1750, including STanley as a "spares" bike with many other parts. No calls yet.

Make me an offer.

 

[Uncle Phil]

Well, even a blind hog finds an acorn every now and then ...

 

[paulcb]

We have blind squirrels in TX!

 

[Jim Van]

After a few weeks of noodling and fussing, STick is no better now than she was when I got home from my last trip. I've fixed a few niggly problems, but the gas mileage is the main issue.

Snip ......

And, did an inconclusive compression test. Tho only read ~120 instead of the hoped for 160, I don't fully trust my compression tester. (Prolly ought'a check it against lipSTick.) Anyway, don't understand why lower compression reading would have that much impact against gas mileage, my max speeds are usually about 80, and that's at steady throttle.

Brakes are NOT dragging, bike seems to run well, all carbs are well balanced, etc.

To do a compression check on a MC with CV carbs, you need to mechanically open the slide ( and have the throttle wide open ) when cranking the engine over. If you didn't do this, you will get a low reading........... I got a similar low reading on a bike w/o CV carbs by not holding the throttle wide open, BTW.

You will have to pull the air filter off, and remove the carb "snorkels" to be able to open the slides by hand.

Are you certain you rear brake isn't dragging ?? Does the rear wheel spin freely when on the center stand ??