1981 GS 850GL loses power and dies in 5th

[dwickham]

Hi GSer's,
I had a 1980 GS 450 for a couple of years and it never game me problems like this 850. I have been riding the 850 around town for 3 months now and it never had this issue in the lower 4 gears. Twice now I have got it out on the open road up into 5th and 10 miles later the engine loses power, I down shift to try to maintain rpm's but it dies anyway. The first time no electrics came on when I turned the key so I thought it was an electrical issue. My friend moved the fuses around and it fired back up. Towed it home and saw that all the old glass fuses were 20's and 30's instead of 10's and a 15. The 15 mainline was super heating (melted the plastic a bit) using a 30 so my friend (the engineer) cut the whole thing out and swapped in modern weather proof fuses. I took it back out across town, through traffic, never got higher than 4th and it seemed fine. Fuses didn't pop and the lines didn't heat up like before either. Got back on I-5 the other day and same deal, got out of Portland but just shy of Wilsonville it died in 5th. Now I have no idea why. Does that sound like a carb issue, fuel line issue, or engine? Thanks for the help.

[Tom R]

Sounds like it's starving for fuel. Check the vent on the fuel cap for starters - if that's not it, check the petcock and the carbs. Fuel filter?

[Redman]

I would say the electrical problem you had is not related to the engine dieing at highway speed. THat sounds more like fuel flow not keeping up and the carbs starving of fuel.

If happens again (and seems like you can make it happen), do you have to wait a while then it will restart? Next time, right away, open gas cap, and then see if will start right away. If so then can suspect the gas cap vent problem.

.

[dwickham]

Gas tank and lines

Yes, I had to wait awhile before it would start again. Thanks for the heads up. I snapped off a bolt and got a drill bit stuck in the bolt when trying to change the cylinder head gasket. So I took it to a shop. They got the bolt out but broke my fuel line so they replaced it. Before it had this plastic thing that was in the middle of the fuel lines, now its just rubber hose. What was that clear plastic part for? They also dropped a bike on my tank which left one big dent and one small when they had it off so maybe the cap or the opening is damaged. They are getting me a new tank but its taking forever.

[keman]

I would check the petcock screen. Drain the tank, pull the petcock. Maybe enough debris in the tank will clog the screen at higher volume, but not enough to reduce flow at lower flow demands. After it sits, the debris will fall of the screen, so it seems OK. .. clean out the tank and seal it.


Edit, I see you have a new tank on the way. This problem may solve its self!

[BassCliff]

Hi,

I don't know why it should take long to get you a new tank. I saw several on Ebay yesterday.

Anyway, that clear plastic thing in the fuel line was probably a fuel filter. Inline fuel filters are not necessary if your fuel system is clean (tank, carbs, petcock, etc). Is the gas cap venting properly? Is the vacuum line to the petcock in good shape, no leaks? Is the petcock functioning properly? Is the air intake system free of air leaks? Is the air filter clean and very lightly oiled?

It sounds like you also need to clean every electrical connection and ground in the entire wiring harness. Thirty year old connections get corroded. Corrosion leads to extra resistance. Extra resistance leads to heat. Heat leads to melted connectors and insulation which leads to short circuits.

What maintenance have you done to your bike? Have you seen the maintenance lists in your "mega-welcome"? Most of these tasks are very critical to a well-running, safe motorcycle.


Thank you for your indulgence,

BassCliff

[dwickham]

venting test

The first tank the shop ordered the guy stiffed them on it so they had to dispute the sale. Now they are bidding on a second tank and I am sure trying to get it for as cheap as possible. I'll make sure and clean it with rusteco or evap o rust or something non toxic when it comes, take its petcock apart and clean it too. Besides riding it till it dies and then pulling the gas cap off, what other test can I do for the vent? Thanks.

[BassCliff]

Hi,


I hope your guys at the repair place can "shop victoriously".

Besides riding it till it dies and then pulling the gas cap off, what other test can I do for the vent? Thanks.

That's about the only way to effectively test. See if there is a suction sound when you lift the cap. That means there is vacuum building up in the tank and not allowing good flow. Or you could take a pro-active approach and just take apart the gas cap and clean it good.

Don't forget, there's a lot of other maintenance that has to be done to a 30 year old motorcycle.


Thank you for your indulgence,

BassCliff

[Dogma]

...

I'll make sure and clean it with rusteco or evap o rust or something non toxic when it comes, take its petcock apart and clean it too. Besides riding it till it dies and then pulling the gas cap off, what other test can I do for the vent? Thanks.

If your '81 has the T model tank, I know you can disassemble the cap and make sure everything is clear and free to work correctly. There is a little ball check valve inside the cap that could conceivably stick if corroded or something. If you have the X model tank, I'm not so sure it can be disassembled. I've never seen one of those.

I see the X model also has the screwdriver-only petcock. The plastic bit that forms the working part of the vacuum valve was bad on mine (T model). I don't think that's part of the rebuild kit. I see the price has gone up on that petcock since I replaced mine. Replacement was the cure for me, though.

Folks around here usually recommend not spending money on the rebuild kits. If the problem is just a pinhole in the diaphragm, then I'd think the rebuild kit should work.

[dwickham]

My bike has the 2 level seat so that makes it a GLT type right? So I should be able to take apart the cap if its a T, thats good to know. I'll check my manual and see if it has anything on cap disassembly.

[BassCliff]

Hi,

The GS850GLT is the 1980 model. The GS850GLX is the 1981 model. There is generally very little difference between the two. But I can't speak to any gas cap differences.

If necessary, you can pick up a new gas cap pretty cheap here: http://www.partsnmore.com/parts/suzuki/gs850gl/?filters ...but Partsnmore.com has a $35 minimum.


Thank you for your indulgence,

BassCliff

[Dogma]

When I posted earlier, I checked the parts fiche to see if the tanks were the same from '80 to '81. Both '80 and '81 parts fiches list both T and X parts. I'm guessing a significant number of X models were titled as '80, and a significant number of T models were titled as '81. If your tank has the square cap, that's the X tank.

The stepped seat makes it an L model, and that's that same across all years of GS.

[Steve]

If the installation of a "new" tank does not fix your problem, try one more thing:
before venturing out on the highway, put the petocock in the PRIme position, then go for your ride.

I suggest this in an effort to rule out a low-vacuum situation that might not be able to open the petcock.

With the bike in top gear, you will likely have to hold the throttle open a little bit farther, reducing the vacuum level in the manifold. That reduced vacuum might not be enough to keep the petcock open. Shifting down to fourth gear will require less throttle to maintain your speed. The combination of higher engine speed and smaller throttle opening will increase manifold vacuum levels.

If that "fixes" your problem, look for a leaky vacuum hose or a bad diaphragm in the petcock.
Dogma is right, though, the success rate with rebuilding a petcock seems to only be about 10-15%.

.

[Dogma]

...
If that "fixes" your problem, look for a leaky vacuum hose or a bad diaphragm in the petcock.
...
.

Steve, if riding in 4th does allow him to maintain highway speed, wouldn't that be a dangerously lean condition for more than a few minutes? Or is it going to be so lean that won't matter? I guess I can ask myself, since we're talking about testing for the same problem I had. If I remember correctly, once the problem appeared, 4th wasn't much better than 5th. In a downpour. On the way to have the front tire replaced. Back before I had any more gear than a helmet. And it was cold. Maybe your test should include maintaining speed in 4th before ever going into 5th. If there is a bad enough vacuum leak, even 4th may not be able to hold speed.

Maybe we should recommend a petcock vacuum test while it's still in the garage. Thinking back on this now, I remember that when I replaced the petcock on my 850, I compared the new petcock's ability to hold vacuum against the old one. I took the vacuum line off of the #2 carb and sucked on it. I could feel through the suction that the diaphragm had opened, but I had to pull pretty hard to keep it open. Luckily, my vacuum leak was in the valve instead of a perforated diaphragm, or I would have had a mouth full of gas. Didn't think it through, I guess. Ask a "friend" to do that test.

Anyhow, when I did the same test with the new unit, I could feel the diaphragm open more ... decisively. But I didn't need more effort that just inhaling to keep it open. One might want to have it off the tank and drained for this test. If you have to work hard to keep it open, there's a vacuum leak.

[Steve]

Steve, if riding in 4th does allow him to maintain highway speed, wouldn't that be a dangerously lean condition for more than a few minutes? Or is it going to be so lean that won't matter? ...

I guess my reasoning was this: if there is no improvement, the engine is going to stop about as soon as it did in 5th gear, so no problem.
If it does improve, it's at least getting enough gas to run for the duration of the test.

Unless he is doing full-throttle tests all the time, it probably won't be lean enough to matter.

The main concern was whether there was enough vacuum to keep the petcock open.

.