1980 GS450L stalls when throttle is opened even a little

[nabrams]

Hi All,

Before I tell you my problem I just wanted to say that this is a great site. Aslo, I've used the search feature to glean as much information as I could about my problem, but I still haven't solved it yet.

Here it goes (I apologize for the length):
I bought a 1980 GS450L with 5,800 miles on it. It had been sitting for a year. I put fuel stabilizer in the tank. There is a bit of rust in the tank, but it's not terrible. The bike started up great with full choke applied. The bike warmed up at about 1200 RPM for a couple of minutes. Then the RPM rose to 4000 for several minutes. At this point I gradually reduced the choke to the fully un-applied position and the bike idled fairly smoothly at 1000 RPM.
So then I twist the throttle just a tiny fraction and the bike stalls immediately - no sputter, no backfire - it just dies. At that point I can restart it with no problem with just a touch of the starter. But the problem persists after restarting.
So I cleaned the carbs to the best of my ability. I did actually remove them from the bike and take them apart and clear all the jets and various orifices with carb cleaner. There was not much dirt in there to begin with. Just a bit of varnish at the bottom of the float bowls and a miniscule amount of grit in one of the main jets.
After that the bike started and idled as before (and the idle was a drop smoother). But the "twist-throttle-bike-stalls" problem remained. This was all done with the bike on the center stand and the transmission in neutral.
I saw someone mention (in a different post) that the fuel flow from the fuel-valve should be checked. So I set the fuel-valve to the "RES" position and when I pull the thin hose, no fuel comes out. Same is true for the "ON" position. How do I create enough vacuum in the hose to see if the fuel is properly flowing? Also, when I set the fuel-valve to the "PRI" position and pull the thick hose, the fuel flows freely. I haven't tried to run the bike with the fuel-valve set to "PRI" because I was under the impression that this might mess up the carbs. Maybe I should try it anyway?

Thanks in advance for your advice!

[Billy Ricks]

As long as the float needles are shutting off fuel flow to the carbs using the prime position to get the bike started and to see if the bike will rev is not a problem. Just be sure to plug the vacuum line with something. You can attach a piece of vaccum hose to the vacuum fitting on the petcock and just suck on it to see if fuel flows.

It sounds like a mixture problem to tell you the truth. You could still have clogged jets or passages in the carbs. Did you remove the tamper-proof caps over the idle jets? If not, drill a small hole in them and insert a screw into the hole to pop the caps off. Then remove the idle screws and clean the passages up that deal with that circuit. Be careful with the o-rings that attach to the mixture screws. They will probably end up staying down in the carb and won't come out with the needle. There will also be a small washer. The washer goes on the needle first then the o-ring. The idle mixture screws control the mixture from idle up to about 1/4 throttle. Also be sure to check the float heighth. It is critical on CV carbs and the idle circuit is the portion most effected by fuel level in the bowls.

[jimcor]

Yes, use the PRI (prime) position to run the engine to determione if the problem is your carbs. Before I did this though I would put an inline fuel filter in the gas line. If you did not remove the rust from the tank you will get some particles of rust in the carbs without a filter. This won't cost more than 3 or 4 dollars. If the engine runs in the prime position but not in run or reserve the problem could possibly be the diaphragm in the petcock or dirt (rust) clogging the filter screen on the petcock. Remove the petcock and clean it carefully with the carb cleaner...but not the diaphragm some carb cleaners are reportedly detrimental to rubber. You might be able to buy an aftermarket petcock rebuild kit for your bike for about 10 bucks...if not Zooki thinks very highly of their petcocks (mine cost me 60 bucks ). Also clean your gas cap make sure the vent is not clogged. Good luck and don't forget the mantra..."I'm having fun working on my GS, I'm having fun...

[nabrams]

Hi Guys,

Thanks for your replies.
I'll try it on the "PRI" position.

Billy,
Rearding the "tamper-proof caps over the idle jets": I'm not sure where these are, but I'm getting a Clymer manual soon, so maybe it will tell me. Also, I know what the floats are, but I haven't got a clue what the float height should be or how to measure it. Maybe the Clymer manual will tell me.

jimcor,
I did take apart and clean the petcock (forgot to mention that). Those diaprhagms didn't seem to be dirty, but they also didn't seem to be porous, so I'm not sure how fuel is supposed to get through. If I can find a rebuild kit for only $10, I'll get it for sure. I did not check the gas cap vent (didn't even know there was such a thing! - I'm definitely a novice). I'll do that. Would running the bike with the cap off be equivalent?
Also, I AM having fun but my hands are taking a beating from all the spilled fuel and carb cleaner and cold weather (I find it impossible to work with latex gloves or any gloves in general).

I wonder if anyone else on this forum has had this particular problem.

[Billy Ricks]

Here is a link to a post I made concerning how to make sure the petcock is working right. http://www.thegsresources.com/_forum...454&highlight=

The tamper proof caps are on top of the intake side of the carbs. I don't remember if they are brass or a tin like material. You will see a portion of the carb that rises up from the throat that is about 3/8" in diameter and maybe an inch tall. There will be a cap in the center of it. That is the one you need to remove. Just make sure you lightly seat the needles to see how many turns out they were adjusted to. Usually less than 1 turn or thereabouts. Then remove those completely and thoroughly spray where they were removed.

Also on the mouth of the carb is a small pilot jet that screws out. Remove it and spray that passage good. It is part of the idle circuit as well. It would be a good idea to remove them before doing any cleaning.

I'm not sure what your float heighth spec is, but they are generally about 21-22mm. You should measure this distance from the base of the carb where the float bowl gasket fits to the bottom of the float with the carb inverted. Bend the tang on the float where it contacts the float needle to adjust the heighth. If the distance is less than it should be the float is letting too much fuel into the carb, too high and not enough fuel is getting to the carb.

[Billy Ricks]

By the way, the diaphram in the petcock should not be porous or have any holes in it. What happens is that vacuum pulls the diaphram and exposes a passage for fuel to flow.

[nabrams]

Hi All,

I feel really stupid for not checking the air filter element first, but that appears to be the problem - there is NONE!! - totally disintegrated and sitting at the bottom of the airbox.
On my 1977 Honda XL350 the engine runs decently without any air filter at all, so it didn't occur to me to check it on my GS450L.
I did a search in this forum and it seems that many think that for a GS the air filter is essential for any hope of reasonably normal engine performance.
Billy, what's your opinion on this issue?
Anyway, I stuffed a couple of old cotton undershirts into the airbox, and bingo! - the bike ran well through all RPM ranges while riding down my street in first and second gears.
Now I just have to find someplace that has the stock air filter or an aftremarket filter that won't require re-jetting.

Thanks

[Billy Ricks]

As long as it runs well now don't bother with carbs anymore. You do need to run a filter in the airbox to have it run right. As long as none of the debris clogged the pilot jets you shouldn't have to worry about anything. It probably got sucked into the carbs before the pilot jets could pick any up.