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82' GS300 Carb/Fuel/Acceleration Issue

  • Thread starter Thread starter molsonrocks
  • Start date Start date
M

molsonrocks

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Wife bought a 1982 GS300. Guy she bought it from said to only run it on prime and that he had been putting Marvel Mystery Oil in the bike the whole time he had it. Bike was running "fine" at this point. Had a small gas leak around each bowl gasket.

We changed the plugs, oil, and ran 1/3 can of seafoam through the gas tank. Couple days after adding the seafoam the bowl gasket leak picked up. Leaking more gas, more often. Figured easy fix of changing the bowl gaskets. Replaced the bowl gaskets and no more leaking, but....... Now there is no acceleration through any gears on the bike and the air box is filling with fuel and dumping out an overflow line at the bottom of the bike.

Replaced the petpock. No more filling the air box with gas.

So at this point the petcock, bowl gaskets, oil, and plugs have been replaced. There are no gas or vacuum leaks around the carbs (checked with a butane torch). Put the plastic floats in a bucket of water to make sure they did not have any cracks in them. I am not leaking or overflowing gas anywhere, but I am still having the problem of no pickup/horsepower through any of the gears.

Friends and I have taken the carbs off probably 10 times. Everything looks cool. Nothing is sticking when moved by hand.

Since I have changed everything above the best the bike has ran is on prime, with the choke all the way out and the cap for the vacuum test nipple on the right carb off. It would accelerate nice and slow but if i pull the throttle back more than 1/3 or 1/2 a turn I lose any acceleration and the bike sounds like it is bogging out.

I am in the Asheville, NC area if anyone would want a case of beer to help me figure out what the f is going on here.

Thanks.
 
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Ideas on your GS300

Ideas on your GS300

Hint 1: Since the petcock would only work on Prime there is either something wrong with the petcock OR the vacuum line from the right side carb is not connected.

Hint 2: It is not the carb GASKETS that prevent leaks. It is the needle valves and their seats that shut off the gas as the floats rise. You should be able to leave the petcock on prime without carb overflow. It is the needle valve and the floats that determines the fuel level. Too high or too low can both cause non or poor running.

Hint 3: I think things like Marvel Mystery Oil, STP, Motorhoney and stuff like that will cause the clutch to slip. Most bikes have clutch plates immersed in the engine oil, unlike standard transmission cars whose clutches are "dry". Slippery stuff in the oil is bad.

Never underestimate the possibility of bad, loose, dirty connectors and switches. A decent meter to measure both voltage and near zero resistance helps. Two ohms is too much.

When you took off the carbs did you open them up and clean all the jets and blow out the internals?
 
You replaced petcock, so I assume you aren't using it on Prime anymore. If it's a vacuum petcock, you need to uncap the vacuum port on the carb and run hose to the petcock. If not a vacuum petcock keep it plugged. The behavior you are talking about does sound like fuel starvation (as well as other things maybe). Could the floats (as you were fighting leaks) now be set too low causing fuel starvation?
 
When you took off the carbs did you open them up and clean all the jets and blow out the internals?
Click to expand...

+1 on dirty jets

Could the floats (as you were fighting leaks) now be set too low causing fuel starvation?
Click to expand...

+1 float levels
 
This is the exact same issue im having,,

except my PO didnt use marvel whatever stuff and the bike has never leaked from gaskets

check out my thread at post name "petcock or carb problems"

by newGS300Lowner

some people have given me some sugggestions as of what to do

Hope this helps!

p.s i have also heard, that it might be a timing problem though it doesnt seem like it
 
Plugged vaccum port

Plugged vaccum port

I cleaned my eBay replacement carb well and the 1982 GS300L ran pretty well - on Prime only. Not a new story. In my case the new OEM petcock was good, the hose was connected (both ends) and open.

But I removed the vacuum hose from the petcock and tried to blow through it (back into the carb). On the GS300 (and I suspect all) it should easily let air through, like a straw. My problem was that the carb's hose connector at the top front of the right carb was plugged. I took a very small drill and by hand cleaned the tube out. Very fine gritty powder formed a tight little plug. Easy fix. Cheaper than a new petcock. Don't get grit into the carb itself.

Sad thing is that now I do not have any more engine problems to investigate.
 
Sorry for the late response on this one. Working on my Magna while waiting for valve cover gasket to show up for the GS300.

Running much better now..almost.

Carbs have been taken completely apart dipped for a few days in carb cleaner.

Put back together. Synced carbs. Made sure that float needle shut off fuel flow.

Got it up to 60MPH today in 4th.

Rough idle and the top end of 3rd gear feels like it starts to bog/hesitate. Does not shut off or lose acceleration. Can pull the throttle all the way back with no more acceleration than were it currently is speed wise.

Going to pull apart one more time and check everything over. Nice thing about these carbs is you can get them out in about 10 minutes tops, if that.

Have one question for everyone.

On the right carb there are two vacuum line posts, one on the forward facing side of the carb and one on the back. If I pull up the parts diagrams on the various part sites out there it shows three hoses coming off the carbs. One for fuel and one on each of the vacuum posts on the right carb. One obviously goes to the petcock, and the other........?

Prosolar: Yes on the clean the jets and blow them with air this time around. Also adjusted the float heights to 20.
 
On the right carb there are two vacuum line posts, one on the forward facing side of the carb and one on the back. If I pull up the parts diagrams on the various part sites out there it shows three hoses coming off the carbs. One for fuel and one on each of the vacuum posts on the right carb. One obviously goes to the petcock, and the other........?


The one toward the front goes to the petcock ..

The two inside ones should route back to a clamp in front of your airbox lid wingnut then off to the right along the outside of the frame (tuck in behind the battery box bracket) ..


Float height should be 21.4 mm plus or minus 1



molsonrocks said:
Sorry for the late response on this one. Working on my Magna while waiting for valve cover gasket to show up for the GS300.

Running much better now..almost.

Carbs have been taken completely apart dipped for a few days in carb cleaner.

Put back together. Synced carbs. Made sure that float needle shut off fuel flow.

Got it up to 60MPH today in 4th.

Rough idle and the top end of 3rd gear feels like it starts to bog/hesitate. Does not shut off or lose acceleration. Can pull the throttle all the way back with no more acceleration than were it currently is speed wise.

Going to pull apart one more time and check everything over. Nice thing about these carbs is you can get them out in about 10 minutes tops, if that.

Have one question for everyone.

On the right carb there are two vacuum line posts, one on the forward facing side of the carb and one on the back. If I pull up the parts diagrams on the various part sites out there it shows three hoses coming off the carbs. One for fuel and one on each of the vacuum posts on the right carb. One obviously goes to the petcock, and the other........?

Prosolar: Yes on the clean the jets and blow them with air this time around. Also adjusted the float heights to 20.
Click to expand...
 
One more thing. If I pull the spark plug wire on carb #2 while the bike is running the idle cleans up a bit. If I pull the wire for #1 carb the bike dies instantly. This is why I drink.
 
see if the breather tube is connected to the air box. It sounds like when you pulled the carbs out to do the gaskets, you disconnected that hose from the breather box.
I pulled the tank off of my bike to change the air filter and i accidentally disconnected
the breather tube from the breather box. I couldn't even make it up hills unless i was in second gear. I had my uncle chad come over and check stuff out. I thought my carbs needed cleaned. He noticed a hose floating around freely, so he connected It to the nearest random port that it would fit on. I got it goin' real fast in no time at all:) Also, disconnect the rectifier and see if that gives it it's power back. my rectifier's given me complete hell the whole time i owned my bike.
 
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