1981 GS 850GL loses power and dies in 5th

[Steve]

In the very first reply, Tom R suggested checking the cap vent. Have not seen any reply about that. :-k

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?

Easiest way to check that is to go until it starts to lose power. Stop, open the gas cap. If you hear a "WHOOSH" as you open the cap, your vent is plugged.

.

 

[dwickham]

I just finished up recharging the battery but I have to cop to being lazy. Just need to convince my wife to drive behind me for when it breaks down. She hates this bike and wants me to buy a newish bmw oil head but I love the way these GS bikes look. That plus freezing my butt off while my bike wont start is depressing. I'll get to that sometime this week and let you know.

 

[dwickham]

So I took it back out today for a real short hop just to get gas moving through it, 4.5 miles one way. Went to pick up some new aftermarket brake pads and an inline fuel filter. By the time I got there it seemed good and warm. Pulled the gas cap and listened very carefully but heard no sucking sound from vacuum. I am guessing at this point its A. the petcock, B. the fuel line, C. the vacuum line, or perhaps D. junk in the carb getting moved around and clogging my jets? The shop says my "new" tank is on the way so I'll treat and coat the tank, check those lines and maybe check the carb while I'm at it.

One the way down, by the time I got there it seemed like it was starving for fuel again, died super fast when I pulled up before I even hit the kill switch. On the way back up it seemed fine.

Big T, its RoadHawk Cycle thats taken over 3 months to get me a new tank. Next time I'll try Vicious Cycle.

 

[dwickham]

So I took it over to my friends today and we took the tank apart and inspected it. Seemed fine with no crap coming out so the tank is pretty clean. We broke down the petcock and found nothing wrong, clean filter, all parts with very low if any wear. Inspected the gas and vacuum lines and they both looked good. They were new as of a month ago so I expected that. The last thing I can think of is the manifold boots. You guys all say replace them as a first step and these are old if not the originals. I'll order them, swap em' and let you know if it makes a difference.

 

[Dogma]

That inline fuel filter may make things worse. Since these bikes rely on gravity instead of a pump, a restrictive filter can create a fuel flow problem. There have been some people who had success with a high flow filter (For mowers, I think - also gravity-fed.). Most go with the factory configuration of no filter other than the petcock's screen.

In today's post, you mention cleaning a filter. Does it already have an in-line filter? If so, get rid of it and see if your fuel flow problem goes away.

 

[dwickham]

It had an inline fuel filter when I first got the bike but it hasn't had one since the shop I took it to,Roadhawk cycle, broke its gas lines and replaced them. I can't think of another reason besides loss of vacuum at the manifold boots that it would die in 5th gear. My buddy told me that the more I roll on the throttle, the less vacuum I have and the more gas I need. So by the time I'm in 5th and rolled all the way on it has almost no vacuum due to broken or poor sealing at the boots. Does that sound about right? Thanks for your help.

 

[banditom]

vac leak?

vac leak?

Hi,

If youre wondering about a vacuum leak, the quick way to tell is run the bike , and spray some carb cleaner or propane from an unlit propane torch around where you think the vac leak is, if it picks up engine speed immediately, that is the location of the vac leak. Most recommend changing the inlet o rings regardless, I believe the carb boots can be rehabbed on zukis similar to the yammies that Ive done with spray on rubber coating if the boots are actually worn thru the inner walls. Just because the boots may look cracked on the outside, is not proof that they are leaking on the inside. Take em off and look carefully. If there is any inner cracking whatsoever, its best to just get new ones, but spray on rubber coating on the outside may delay the need to buy new ones if you dont want to go the new route.

 

[Big T]

My buddy told me that the more I roll on the throttle, the less vacuum I have and the more gas I need. So by the time I'm in 5th and rolled all the way on it has almost no vacuum due to broken or poor sealing at the boots. Does that sound about right? Thanks for your help.

His reasoning is backwards

The more you open the throttle, the more vacuum is created. The increased vacuum lifts the slides more and more gas flows out of the jets

It looks like you need to go back to your Megawelcome and check the 10 common things.

New O rings in the carbs and at the head are manditory. New intake boots may be needed

However, I don't think your problem is fuel related. Looking over your initial post, the problem seems to be electrical due to the 30 amp fuses and such. I don't think changing the fuse box cured that issue.

Gave you checked for spark when it died?

 

[dwickham]

The one thing I haven't checked I guess is the spark. I'll check them when I swap the new boots in this weekend hopefully.

The first time it died in 5th I couldn't turn the electrics back on, we cut out the old fuse box for modern water proof stuff. The second time it died the electrics didn't die and when I tried to restart it the motor kicked over till the battery died trying. I shouldn't have figured the spark plugs were good because of that and I'll make sure and check them.

My starter is weak and I was thinking of replacing it but my buddy said it was easy to fix an electrical motor. Easy for him as he is an electrical engineer, I'm just your average-to-low end mechanical knowledge type guy and that is way over my head. How hard is it to find new brushes to fix it instead?

 

[BassCliff]

Hi,

Many of the vendors in your "mega-welcome" sell starter rebuild kits. Some of those vendors specialize in electrical stuff.

Thank you for your indulgence,

BassCliff

 

[koolaid_kid]

His reasoning is backwards

The more you open the throttle, the more vacuum is created. The increased vacuum lifts the slides more and more gas flows out of the jets.

Not exactly. Yes, the vacuum lifts the slides. However, if one cracks the throttle wide open, the engine speed has not increased yet. So the air pump (the engine) is pumping the same volume of air through a larger hole. This decreases vacuum and is the reason the VM carbs hesitate if you go WOT immediately. The reason for gong to CV carbs is to lessen this effect by raising the slides slowly as the air pump slowly increases the volume it pumps by increasing rpm.

 

[Big T]

The one thing I haven't checked I guess is the spark. I'll check them when I swap the new boots in this weekend hopefully.

The first time it died in 5th I couldn't turn the electrics back on, we cut out the old fuse box for modern water proof stuff. The second time it died the electrics didn't die and when I tried to restart it the motor kicked over till the battery died trying. I shouldn't have figured the spark plugs were good because of that and I'll make sure and check them.

My starter is weak and I was thinking of replacing it but my buddy said it was easy to fix an electrical motor. Easy for him as he is an electrical engineer, I'm just your average-to-low end mechanical knowledge type guy and that is way over my head. How hard is it to find new brushes to fix it instead?

I'm guessing you have overheated the wiring harness and created a short that is then overheating components. Replacing the fuse box only solved a part of that problem

The starter is about as easy as you can get - 4 bolts. Take it out, pull it apart and clean everything and see what you have.

But, before you do that - what kind of voltage do you have at the battery when you press the starter button?

 

[dwickham]

The first thing that happened with the bike was it didn't charge. We routed the regulator/rectifier straight to the battery with a modern fuse in the middle to get around those extra and rusty connections. After that it charged at a higher than spec rate around 14 or so. After we cut out the old glass fuse box voltage at the battery dropped back down to factory settings of 12ish. I haven't measured exactly when I hit the starter button, I will do that and tell you what I get on sat.

The brushes, are they screw on or do they have to be welded? We don't have that kind of welding equipment and I can't tell from looking at pictures of the brushes.

 

[dwickham]

Installed new manifold boots and rings in today. While I was at it I looked at the voltage, upon start up it read 11.3, I disconnected the spark plugs, inspected them and they were all clean and working, and hit the start button again to get a reading that way. Volt meter read about 10.5.

When I pulled the old boots I saw that one was held together by gorilla glue or something similar and none of them had o-rings. I also replaced the screws that held them with zinc plated stainless steel hex head bolts. Right away it idled and had a strong cadence that it had never had before. Something else I noticed, it was cold and misty so I could see there are two exhaust leaks coming from under the body. Sooner or later I will need to find someone to weld them up I guess. Upon start up when its cold the engine or something makes snapping and popping percussive sounds into the airbox. It goes away after the bike has warmed up though. Does anyone know what causes the snapping and popping sounds?

I yanked the starter while I was down there and tried to get it open but the head of one of the long screws holding it closed sheared. I'll try and find a long bolt to replace it but if I can't get it apart I might just take it in for a full rebuild. Maybe on sunday I'll get up the nerve to take it out on the road and see if the new boots solved the dying in 5th issue.

 

[2BRacing]

The new intake boots with O-rings are going to make a big difference. You should also check the airbox-side boots to make sure they seal properly. Then make sure your airbox is sealed properly at filter to housing area and side covers to housing area. See BassCliff's site for tutorial.

Now that intake system leaks have been taken care of, that part of the system will function correctly and help with further diagnosis if there are still problems.

There are 2 little holes in the bottom of the exhaust system for drainage of water. Before welding, first check to see if it is those holes, which do not have to be welded closed.

The snapping and popping sounds into airbox at cold startup only happen if you are opening the throttle. DO NOT, REPEAT DO NOT, OPEN THE THROTTLE AT ALL DURING COLD STARTUP. The correct way is to pull the choke about halfway and then hit the starter button WITHOUT TOUCHING THE THROTTLE. If everything is setup correctly (carbs clean according to Nessissm's tutorial; valve clearances adjusted; adequate voltage at coils; etc; etc) your bike will start and run. As the revs continue to rise, push the choke in slightly. After a minute or two while putting your safety gear on, the motor should now be able to take throttle input. If you open the throttle at any time prior to this point while the choke is out, this will actually "cancel" the choke enriching process.

I strongly recommend that you take the opportunity to learn the basic maintenance procedures required for your bike. All the information you need is right here on GSR - just spend some time reading all the info on BassCliff's site, as well as using the "search" function to read up old posts about specific problem areas. You say that you have mechanical ability - so delete "...I might just take it in for a full rebuild " completely from your mindset (you saw what happened when you took it in last time) and do it yourself. Besides saving yourself a lot of cash, you will get great satisfaction from doing the job yourself.

 

[Big T]

Your battery voltage is too low and your charging system output is low.

You need to read the Stator Papers and go through those steps. Charge your battery, which could be defective or ruined

Did you follow BassCliff's 10 steps?

 

[dwickham]

Nailed it down I think. Took it out today with my wife trailing me just in case. While I was warming her up I noticed the idle screw wasn't turned in far enough so I gave it a full twist and now it idles properly and doesn't die at the line like it always did before without rolling on a bit. Less than 2 miles onto US26 in 5th it started to die, but I remembered what you all said and fumbled around until I put it to prime. It powered back up like Mario getting a burning flower. And now that it has new manifold boots it accelerates like gang busters. So I am pretty sure its the tank. On prime it rode another 25 miles with no issues.

 

[Big T]

Do you have a new vacuum hose from the #2 carb to the petcock?

If so, then new petcock needed. If not, replace it and see what happens

Just go on the Beaverton Motorcycles website, find your bike order the fuel tap (petcock) and check the "I will pick it up" box


They will then call you in about a week and you can go pick it up (That's what I do)

 

[dwickham]

Big T, I have gone through some of the things on Bascliff's list. I still need to adjust the valve clearances, get new spark plug caps, and depending on the shape of the petcock on the new tank get a new petcock.

I do have a new vacuum hose. We took that petcock apart down to the metal wire piece that switches it from Prime to regular and the damn thing looked almost brand new, inside at least. No particulate, no rust floating around, no gunk, nothing. Still waiting on that tank from Roadhawk so I think I'll wait to take a look at its petcock and general condition. On prime, does too much gas get into the carb? I smelled gas after the ride. I charged the battery up and it started fine, I think I'll but the stator on the back burner until I get the starter sorted out.

2BRacing, thanks for the water draining tips, I had no idea. I had to turn the throttle in order to get it to warm up because the manifold boots were crap and the idle was set too low. Got those fixed now so it starts up and doesn't die while warming. There is no way I am taking my bike back to Roadhawk but I was talking about taking the starter to a shop that only does starter rebuilding. But I'll try my best to fix it myself before I take it to them.

 

[Big T]

The problem with your current petcock is probably a pinhole leak in the vacuum diaphragm.

Prime doesn't provide too much gas, but you have to remember to turn it off Prime when stopped

It's unlikely your starter needs to be rebuilt. It probably just needs a good internal cleaning and possible a new brush kit, both of which are very simple

You should also check the solenoid. Check it for voltage drop across the 2 big poles. You can (very carefully) pull the top up a bit, spray it with contact cleaner, check the contacts and screw it back together

What I'm saying is - a slow turning starter is just as likely to be caused by voltage drop as internal starter problems. So, start at the battery (the 10.5V you noted is low) and work your way towards the starter