Backfires, sputtering, and lower gas mileage

[Supa]

So, here we go. Constant issues first. I'm getting some backfires on cold starts even though the temperature is over 60° and even got one when the temp was over 80°. Once I hit 6k rpm in any gear, she starts to get loud. Louder than normal and doesn't sound like the usual chatter. 5-6k rpm has a bit of uneven power. Idle is no longer perfect (jumps about 200rpm every so often). Chain gets loose quick and after cleaning, sounds like it's scraping something. Gas mileage dropped from 50mpg average to 32 mpg.

Known issues: Small oil leak from valve cover gasket (new gasket en route). Chain is starting to show signs of wear despite both sprockets looking great (will be replacing soon). Chain guard is missing. Swingarm/adjusters are all screwed up from previous owner (welded adjusting plates to the swingarm and rounded the nuts with vice grips).

Recent relevant services: Bike is at 9500 miles/purchased at 6k. Valves checked at 7k, oil/filter changed at 8.5k, clutch adjusted at 8.5k, fuel lines replaced at 7k, rear tire changed at 6.5k, carbs cleaned at 7k. Battery is good, everything is stock except for lights. I added oil last week as it was low, same weight, different brand.

Planned actions: Fix oil leak (new gasket), replace fork springs (not really relevant), change plugs, switch to premium gas (did that this morning), possibly another oil change, check valve clearance again since I'll have the cover off. Any idea what else to look for?

What started it off was a nice planned ride last weekend through some awesome twisties. Started the bike up to an insanely loud backfire. I mean, ear ringingly loud. Let her warm up a bit after that to make sure it was OK. 45 minutes of freeway riding with lots of hills (lots of up and down), she started to sputter near the top of one long hill. Pulled off immediately and she seemed fine once I got to level ground and lower gears. Only 80 miles on the odo at that point. Puttered around a bit in lower gears listening for issues. Couldn't see or hear anything aside from the louder chatter that was blocked out by my ear plugs on the freeway. Didn't want to risk it so I took her home. No problem doing 75 on the way home. Put gas in the tank to be sire it wasn't low (only 1.75 gals needed). I chalked it up to gravity and big hills with not enough fuel in the tank... but that might be wishful thinking. She did seem to ride a little better on reserve this morning before I filled up with premium. Premium also seemed to help, but that was only a 10 mile trip. Probably too much info here, but she just doesn't seem right at the moment.

[bmf]

I think that keys are back fire and fuel consumption, I think that you are running way too rich and that fuel is leaking past the needle valves  getting everywhere including your exhaust where it lights on startup.

[bmf]

Stupid tapatalk, does your oil smell of gas?

[Supa]

Sorry for the delayed response, haven't had a chance much to get at the bike.

The oil definitely smells of gas. Quite heavily in fact. I also played with the mixture screw. I had originally set it at 2.5 turns out. When messing with it today, it was incredibly loose. I tightened it all the way, then turned it out 2.5 turns again, but it felt super loose, like it could just rattle free. Bike rode well enough for the first 20 miles or so, then started to act up a bit again. Valves are chattering quite loud and I got a couple more backfires (very light, but noticeable) after about 60 miles. I'm pretty sure the screw loosened up more, but I'm not sure that's my main issue. With the idle bouncing around a bit, I want to get in and check the valve clearances.

Any recommendations on getting the mixture screw to stay in place? It feels loose after a single turn out.

[Janx101]

Err. .. going on what you mentioned about the prev owner and slack adjusters,  plus the overall condition/adjustments of a few other things, if that screw seems to be rattly/ loose. .. it might be a good idea to remove the carbs and check that out visually!! Could be stuffed, worn, wrecked or wrong?! ..

I predict a extended maintenance/refit of several areas of your bike... I don't think the prev owner was a wrench wizard somehow?!

[Supa]

I predict a extended maintenance/refit of several areas of your bike... I don't think the prev owner was a wrench wizard somehow?!

Oddly enough, the guy was apparently going to school to become a mechanic  He made some terrible decisions with the bike though. I'm gonna pull her apart next weekend and do a thorough inspection. Gotta fix that valve cover leak anyway, might as well check the clearances again (due in 500 miles anyway) and inspect the carbs again. I'm assuming I should drain and replace the oil? Never had that issue before.

[bmf]

Change oil immediately, gas is a terrible lubricant.

[Janx101]

Heheh. . See that's the difference. . To BECOME a mechanic. .. not is a mechanic.. 

There are car/truck/general mechanics on this board though... that are still unfamiliar with bikes in general and the gs500 in particular. .. you see questions and comments on the situation semi frequently. .. goes to show that no matter what a person is good at... that there is always something new to learn or unlearn at times!

[Supa]

Well that's one problem solved. Drained the oil, added synthetic for the first time (just wanted to try it), and really played with the mixture screw until I got it just perfect. I didn't realize how out of whack that thing got... and also never knew the process to get it just right. The only two times I've messed with it before, I just set it to 2.5 turns out and left it. This time, I warmed up the bike, let it idle, and then played with the screw. I went too rich and listened to it bog down, then went too lean and listened to it bog down. Then adjusted back to peak RPM and went 1/8-1/4 turn rich from there. Ran like a dream this morning after I readjusted the idle back down to 1200 RPM.

I do still need to fix my valve cover leak (gasket just came in the mail... yay!) and fork seal leak (also arrived, but still need to figure out how I'm going to disassemble the forks entirely to get my new sonic springs in there too). Anyone know where I can get this "special" tool for an '06? Is it even necessary?

After that, it'll be time to replace the chain and sprockets which are starting to show some wear.

Thanks for the help.

[ragecage23]

Quick question about the mixture screws, is one side for air and the other for gas? Or are they independent to their respective carbs and should be adjusted to the same turns out?

[Supa]

Quick question about the mixture screws, is one side for air and the other for gas? Or are they independent to their respective carbs and should be adjusted to the same turns out?

Independent per carb. Each should be tuned individually.

Here is one of my favorite responses from an old post:

There's a little terminology involved here.

There are two forms of idle mixture control:

1)  Idle air "pilot air"

2)  Idle mixture

Idle air screws adjust the idle jet emulsion rate.  They let air into the metering system, and more air means less fuel.  Therefore, turning the adjustment clockwise enriches the mixture, turning counterclockwise leans it.

Idle mixture screws adjust the mixture directly.  Idle mixture screws have a needle valve on the end that directly limits the fuel flow.  Turning clockwise leans the mixture, turning counter-clockwise enriches it.

As far as adjustment is concerned, the best way is by feel and sound.  Start at a predetermined setting (2.5 turns from closed on the GS).  Start the engine and slowly close one or other of the air screws.  As the mixture gets richer the engine will start to labor, the exhaust note getting a little deeper.  Now turn it out slowly.  As the mixture gets leaner you'll notice the engine RPM increase slightly, then drop off.  Going even leaner, the engine will start to misfire and stumble.  The exhaust note will also sound a little more hollow.

The correct mixture setting is just rich of peak RPM.  Once both carbs have been roughly set, go back and re-peak the first carb.  Then the second again.  This is just for accuracy, as it can be difficult to be precise when one carb is out of tune.

[ragecage23]

I'm going to have to try this after I adjust my valves. Thanks for the info!

[Supa]

Well, today ended in absolute frustration. Got the bike all apart yesterday, valve clearances were good, cleaned the valve cover and replaced the gasket. Everything was looking good. Except that I noticed that the two screws holding the right intake manifold were gone and there was nothing holding it in place! No wonder she wouldn't idle properly. I'm amazed she ran at all. Anyway. Fixed that, added a couple new racing plugs, put it all back together again.... And it wouldn't start. Dumb me forgot to open the tank petcock and I couldn't figure why it wouldn't start. After checking the carb drain, I realized no fuel. Duh, open the petcock! Did that and she still wouldn't start. Battery had started to die so I left her on a tender for about 3 hours. Came home and tried again. Nothing. She turns and turns, but won't kick. I played with the throttle, choke, and idle screw (which was screwed up from before). Finally got her to kick once but was insanely rough. Some backfires, poor idle, wouldn't stay alive. Sputtered out after 2 minutes of struggling for dear life with me trying everything I could think of. I swapped the plugs again and haven't been able to get her to kick again. Close a couple of times, but not enough to get running. Battery is still mad at me so I've got her on a tender for the night and I'll try my luck again tomorrow. If anyone has any insight, let me know. I made sure to reassemble properly, adjusted mixture screws to 2.5 out, and double checked all my hoses.

[ragecage23]

Do the spark plugs have the correct distance?

[Janx101]

After opening the tank petcock .. Did the PRIme setting on frame petcock get used? ... Wondering if little dribbles of fuel might get down there but not actually fill the bowls?

[Supa]

Yes to the Prime. Filled and emptied the bowls to check, though that will be my first check again today as I feel like it's fuel starved. Might be a pinched or clogged hose.

Plugs are Brisk (no gap) racing plugs. And I tested with the previous plugs as well which are still good. Just wanted to try the Brisks.

[Supa]

Well, I officially believe in gremlins. I took it apart again. Entirely. Adjusted everything the exact sane. Reassembled the exact same... And it started, no problem. I'm at a loss here... No idea what happened. However, I did tighten one of the oil filter cover bolts and it snapped  . So now I gotta see if I can fix that today.