850 loses power at high speed after heated up.

[redfenix]

Okay, so I've had my 1980 GS850L for about a month now. I was having issues with the cylinders 2 & 3. I checked compression (was at low end of spec), and verified spark. I determined since 2 & 3 run on the same coil, I would replace the coils. So, to be thorough, I replaced the coils/wires with Dyna greenies and 7mm wires. I also replaced the plugs with new NGK Iridiums. Power is now MUCH better and all the exhaust headers heat up equally.

Since then, a few times now, the bike loses power at high speed, especially after it's been running on the interstate for 20+ minutes. Usually what triggers it is when I hit a solid headwind, go uphill, or try to pass traffic. At this point I lose the ability to accelerate and downshifting doesn't regain anything. Here are the interesting points to this condition:

- Sometimes, I get a little "blip" and lose power for a split-second, then it comes back. This is sometimes a harbinger of more trouble to come.

- At its worst, the condition continues for 5-10 minutes and then eventually power is restored and everything is okay again (for a while).

- When in this condition, throttle response is VERY sluggish and if I let off the throttle completely, the engine will die. It's unable to hold an idle by itself.

- During this condition, if I am in neutral (or have clutch pulled in), when I open the throttle, the engine revs up sluggishly until it hits 7-8k rpms, then it fully engages until I close the throttle again (I didn't try this for long, but wanted to see if it were a fuel issue.)

So, from reading other posts on here, I'm wondering if the Dyna coils are arcing back to the tank or frame. When I put the Dynas in, they were a VERY tight fit. However, it seems that they should be getting enough air flow to keep from overheating as they're pretty open on the bottom side. Do I need to cover the primary coil screws?

Also, I do still have the old dreaded 80 vacuum petcock on here. I haven't noticed any fuel leaking down the vacuum line when I've taken the tank off. Is it possible that the petcock is somehow playing a part here? I've tried running the bike in PRIME and RUN, and this same condition has occurred with both settings.

And the carbs were supposedly rebuilt by a shop to some extent before I purchased the bike a month ago. I even have the receipt for it. However, I don't know the shop or have any idea how reputable they are. Is it possible that this is a carb problem somehow? If the float bowls become depleted, how long does it take for them to refill?

All in all, it seems to be difficult to reproduce without a significant amount of riding. It hasn't stranded me YET, but I feel I can't trust the bike until I can know for sure that this is fixed.

[tom203]

redfenix said.....

"Also, I do still have the old dreaded 80 vacuum petcock on here. I haven't noticed any fuel leaking down the vacuum line when I've taken the tank off. Is it possible that the petcock is somehow playing a part here? I've tried running the bike in PRIME and RUN, and this same condition has occurred with both settings."
It doesn't necessarily have to leak to be declared defective. It might not be delivering fuel consistently- maybe the diaphragm is struggling to stay fully open at times or maybe there's gunk floating around in it. Just replace the petcock and rule it out as a problem - then you will just have to determine how good the "carbs were rebuilt by a shop to some extent".

[razor02097]

When I worked at a shop checking for leaks and where the levels were before installing a rack of carbs; I remember it taking between 5 and 7 seconds for 4 carbs to fill from empty.


I does sound like you have a fuel problem. If you do not know the history of the carbs it might be a good time to either service them yourself or take them in for service. Many shops that "rebuild" carbs just take the bits out and soak them in a tank for a few hours up to overnight. A proper cleaning involves a lot more work.

Has the fuel line ever been replaced? What is the condition of the tank inside and has it ever been coated?

[850GT_Rider]

My bike was doing the same thing. Acted like it was running out of gas (cough, sputter) then dead. Had spark when I checked it. Knew I had plenty of gas, but turned the petcock to prime and waited a few minutes - bike would re-start and keep running as long as I left it in prime.

Replacing the petcock with a NEW one from Suzuki solved the issue.

[Dogma]

The petcock on that thing has a selector valve made of plastic. Basically, the difference between run and prime (the only settings) is that prime should hold vacuum once applied. on the run setting, vacuum is lost almost immediately.

After 30 years, the plastic valve parts have degraded and shrunk so that it can't hold a proper vacuum at either setting. At least, that's the state mine was in. With insufficient vacuum the carbs are starved. These effects can also be exacerbated by a leaky vacuum line back to #2.

Your symptoms sound an awful lot like mine before I replaced the petcock. A new one from Z1 or PartShark (with a new vac line) will be bullet-proof reliable for a couple more decades. So don't succumb to any pressures to find a manual petcock that will fit the oddball bolt spacing. It's expensive, and you have to remember to shut it off.

[bwringer]

In addition to the above, how are your valve clearances?

[redfenix]

Thanks for all the good advice. I will definitely be replacing the petcock soon. As for the valve clearances, I must confess that I haven't checked them yet. However, I will do so post haste as I just recently joined the forum and learned of the importance. I'll probably also order a new valve cover gasket as well (and possibly the half-circle cam plugs too) as I'm getting a small oil leak in that area.

Looks like I'll be putting in an order to Z1. I'll let you know when I get the order in and have some results.

As for the carbs, I'm going to try this petcock thing and the valve clearances first. I just started a new job at Garmin and am pretty busy right now. Do you think the carb rebuild can wait until winter if things are running sufficiently?

[gs550marc]

Wow, you have just detailed the exact issue I've been having with my 1980 GS550L. As much as I didn't think it was a fuel problem, I will check my petcock. I did replace the petcock about 5 months ago so I wouldn't imagine it has to do with it.

It's funny because when I first because when I first bought the bike, the previous owner had installed a completely make shift petcock that worked well (on/off) position. I wanted the bike to look as "stock" as possible, so I got rid of it and bought a new original petcock which now seems to have been a bad idea?

[Dogma]

...
As for the carbs, I'm going to try this petcock thing and the valve clearances first. I just started a new job at Garmin and am pretty busy right now. Do you think the carb rebuild can wait until winter if things are running sufficiently?

As long as you're not running dangerously lean on one or more cylinders, the carbs can wait. "Dangerously lean" means burning holes in the pistons, so play it on the safe side. Any other state of maladjustment will just result in a lack of power and more junk coming out the exhaust than usual.

New cam cover gasket and half-moon plugs are very likely necessary. Almost certain. Order a very thin shim at the same time, because you may need it to make measurements on a very tight valve. It's also good to start with a spare shim once you start swapping things around, because you really don't want to turn the engine over with a missing shim.

[Dogma]

Wow, you have just detailed the exact issue I've been having with my 1980 GS550L. As much as I didn't think it was a fuel problem, I will check my petcock. I did replace the petcock about 5 months ago so I wouldn't imagine it has to do with it.

It's funny because when I first because when I first bought the bike, the previous owner had installed a completely make shift petcock that worked well (on/off) position. I wanted the bike to look as "stock" as possible, so I got rid of it and bought a new original petcock which now seems to have been a bad idea?

I'm glad you mentioned this, because it should be mentioned that similar symptoms can be caused by adding an in-line fuel filter. They're usually not necessary, and if they are, you have to get one that flows very freely. Do you have an in-line filter? How about a loop in the fuel line that trapped a bubble?

[Missile99]

I have a Visu-Filter on my fuel-injection grade hose. No problems. GS550marc, I replaced my petcock with a new Suzuki one. You should be golden there as long as you cleaned the filter on it before reassembling your tank.

Redfenix: Like Dogma said, wait unless you're lean. Do a couple of plug chops after you get it running again and if good don't worry about the carbs yet.

[redfenix]

So, still being a couple of weeks away from my first paycheck at my new job, any bike purchases will have to wait until then. However, I couldn't help myself and had to fiddle with it anyway.

So... Just for testing, I cut out the center of the vacuum diaphragm and installed an in-line fuel cutoff I had lying around. I still have a clear filter on the line, but I blew through it and the fuel line and there was minimal resistance. Everything seemed fine, so I took the bike for a short ride on the back roads to a friend's house (about 20 minutes away). Everything was fine on the ride over. I stayed for less than an hour, then rode back. On the way back, the bike threw its tantrums about 3 times. Again, during this period, the bike will not accelerate, and it won't hold an idle. In all cases, either within seconds (the first time or two), or after several minutes (the last couple of times), the engine eventually recovers. When it does, the engine regains full power instantaneously and continues to act completely normal for several minutes at least until it does it again.

On the last tantrum, I pulled up to a stop and let it cool down. I popped out my phone and took a video of it. Moments later, the engine recovered, so I took another video then too.

Tantrum video: Note that I show that I'm twisting the throttle completely open, but the engine is VERY non-responsive and it sounds like it's not firing (hearing compression without fire).

http://www.youtube.com/watch?v=Po8DN9jPqes

Recovery video. This was taken just moments after the first, when the engine returned to full power and I rode it the rest of the way home with no further incident.

http://www.youtube.com/watch?v=zrYS2nV3tQA

Audio note: The mufflers were replaced with aftermarket straight pipes.

The thing that baffles me here is that the engine remains in this state for several minutes, and then clears up as if nothing happened.

[Missile99]

Redfenix,

From here that thing sounds awful and leads me to believe it's carbs or bad fuel.
Your wait on rebuilding the carburetors until wintertime might not come true but before worrying too much I have a few questions:

What does the inside of your tank look like?

How old is the gas? The 10% ethanol crap is only good for 28 days max.

Try draining gas out of at least one carb into a clear container or cut up soda bottle. Do you see any particles or is the gas discolored?

[redfenix]

Thanks Erik,

It does sound awful when it's throwing its fit. However, when it recovers, I think it sounds ok. It does pop on decel, but that's probably due to the aftermarket pipes on it that the carbs were probably never tuned for.

The tank actually doesn't look bad to me. There are a few tiny rust spots, but in general the inside of the tank looks like clean metal in there.

As for the gas, none of the gas in the tank is over 2 weeks old. It was low when I started and I put more in when I left that evening (low octane at the Flying J).

To be thorough, I drained all 4 float bowls. The story was much the same in all of them. Some very tiny rust particles and sometimes some black particles, which may have been from the black gaskets around the float bowl plug bolts? Are the particles enough to cause problems with the carbs? Do you think a jet is sucking the particles in, filling up, then releasing the particles and recovering?

[redfenix]

Here's another picture of the gas from the float bowls.