Engine Sputtering

[Buster-boy]

Two weeks ago I replaced my plugs and had my carbs synch'd - 1981 GS850GX. It made a huge difference in the performance of my bike. The #1 slide wouldn't return causing #2-4 to stay open as well. The bike now idles just fine - usually around 1100-1500 rpm, depending on the moon, the sun, the gravitational pull of the Earth.

Anyway, since then (3-4 days after the synch) I've noticed that as I go through the gears the engine sputters - kinda like it would when you start riding and it hasn't fully warmed up. It does this the whole time going through the gears, but is most prevelant when you reach the point of an even throttle and no longer accelerating. As long as I'm accelerating it's fine. It's only at an even throttle that this occurs.

When I hit 5th gear and am cruising it continues to sputter, but as previously stated, as long as I'm on the throttle it goes away. Also, while cruising (no matter the speed, just steady cruising in 5th gear), it seems as though I lose acceleration.

Example - I'm cruising 45 mph, sputtering along, it will slowly decelerate to around 40 mph. Then I hit the throttle, sputter goes away, back up to 45 mph, cruise, sputter, decelerate, lather/rinse/repeat - you get the idea.

Although it's not too awfully bad, this has gotten progressively worse. I mean, I can ride it all day and it'll perform well, just not 100% and it's kind of a pain after a while.

Does this sound 1) Air/fuel intake related (carbs), 2) Electrical related (bad plugs), 3) Vacuum related (leaks), 4) Timing, 5) Valves

Give me your best guess but all suggestions very welcomed.

Thanks
Jim

[Steve]

My best guess is that it's a junk bike and you need to send it my way. After all, there are only THREE 850s in my garage, may as well make it FOUR.

Since you are not likely to accept that offer, let me therefore suggest:

1. Pull the plugs, check the color on the insulators. If they are white, you are running lean. A lean bike runs like you describe.
2. Have you checked the valves? They should have been done before the carb sync.
3. You did not mention airbox vs. pods or stock exhaust vs. header. Either one will affect jetting requirements.
4. If you have a stock airbox, it NEEDS to be well-sealed. Weatherstripping from Lowe's or Home Depot will work reasonably well.
5. Another common source of an air leak is the o-rings between the intake boots and the head. Since you have to take the carbs off to change these o-rings, might not hurt to clean them and install new o-rings in them, too.
6. If your airbox and exhaust are stock, you might get by with simply richening up the idle mixture adjustment screw. Stock setting is about 1 to 1 1/4 turn out to meet EPA regulations at the time, but they work SO much better between 2 and 3 turns out.

.

[Buster-boy]

Steve, you're not kidding when you say it's a junk bike. I've had so many problems with this thing that it's not even funny. I'll try to address the things you mentioned. 1) O-rings are new, 2) stock airbox but not the best condition - has rubber seals but I'm not sure they work very well, 3) Stock exhaust, 4) did not check valves before synch as this condition didn't exist before the synch

Maybe I just need an incindiary grenade?

[Larry D]

Check your plug caps. Make sure they are securely on the wires.

[Dave8338]

Jim... the fact that it smoothes out when you apply throttle suggests to me that it is NOT spark related as that tends to show up most when on the throttle. It does sound like you have a pilot passage or two that may be plugged slightly or that a bump to the jet needles may be in order.

One thought to the problem getting worse is that air temps have cooled and this alone will lean out a bike. Also, IF you've not done a valve adjustment recently, I would suggest that things may be a little out of spec on the intake side. Just a thought...

[Buster-boy]

Well guys, here's what I did tonight. I checked plugs #1 & #4. They were white. I cleaned them off and replaced them. I didn't do #2 & #3 because I'd have to remove my fairing to get to them, and I just didn't have that in me tonight - plus it's dark now, too (7:00 pm). First thing tomorrow morning though I'll get to them.

I took it out for a ride - about 5 miles or so and it ran a whole lot better. Still a bit of sputtering but maybe that'll go away when I do the other plugs tomorrow.

Steve, you mentioned this in your reply - "If your airbox and exhaust are stock, you might get by with simply richening up the idle mixture adjustment screw. Stock setting is about 1 to 1 1/4 turn out to meet EPA regulations at the time, but they work SO much better between 2 and 3 turns out."

I'm not real carb savvy. Where is this "idle mixture adjustment screw"? Is that the big honkin screw on the #3 carb or somewhere on the carb itself?

Anyone can jump in and answer that question, not just Steve.

Thanks for all your tips guys!!

Jim

[Buster-boy]

Dave, what you say could be true too. When I bought this back in April there was a ton of crud inside the tank. I could see it in the fuel line. There's an inline filter that caught alot of it but I'd imagine it didn't get all of it. I haven't seen any lately, though.

I've had the carbs cleaned and rebuilt since then, and the guy told me they were quite dirty, but as i said I haven't seen any since.

I'm going to repaint the bike over the winter and when I do that I'm going to clean and seal the tank. Either or buy another one - not sure which. I'll probably do the carbs again at that time too.

Thanks Dave!!

Jim

[BassCliff]

I'm not real carb savvy. Where is this "idle mixture adjustment screw"? Is that the big honkin screw on the #3 carb or somewhere on the carb itself?

Thank you for your indulgence,

BassCliff