1982 GS300L Not Running Well

[Guest]

I’ve been a member of the forum for a couple of years but only lurking, thanks for such an amazing resource for manuals, troubleshooting, and parts. I’ve hit a wall on a project and have exceeded my skills and resources for a 1982 GS 300L (pic included). I bought this bike from the original owner in early 2021, after sitting in his garage for over 20 years. The motor has about 12k and is very clean. I grew up in the 80s, so I like to wrench a bit and thought it would fun project.

I got a battery, added oil, and new plugs and it ran. I notice an oil leak near the pan and replaced the gasket. The bike shifted ok but bogged down when you hit the throttle, so I figured the carbs needed cleaning after sitting so long. I got a kit and rebuild the carbs, added new tires and brakes while at it. This didn’t really improve anything. I have other bikes, so I stepped back and tried to read up on other possibilities but was stumped. Getting nowhere fast, I found an independent mechanic to take a look. Good dude, a former dirt track racer. He said immediately the carb needed new jets and adjustments, so we ordered the parts and he installed them. He also drilled out something in the bottom of the carbs for drainage I believe. I went to pick it up and he said the right plug was fouled with gas. It still ran on one cylinder, so he concluded it would need new values and guides, I paid him $450 because he sorted out a couple of other small things with the brakes and clutch cable. So I decided to take it back and look for parts. In hindsight, that was stupid, I should have paid him to hunt down the problem because it's another year later and I'm it's still not ridable.

So I hunted down both intake and exhaust valves and guides on eBay, stripped a few bolts on the head but recovered and removed the guides myself. I found a machine shop to install the new guides. I didn’t bore out the cylinders but added new rings and honed the cylinders while there. I adjusted the new values and got all this back together this spring but it still runs really rough. The compression is good now at around 150 on each cylinder. I don’t have gas in the oil but the plugs are fouled pretty bad. The idle is not great and sometimes it races up or just stalls out when you turn off the choke. Now that I’ve written all this out, something seems really off with my carbs.

I had bad thoughts of quitting and parting this out but came to my senses and decided to ask the forum for direction. I appreciate any advice on this and apologize for the windy description of the problem in advance. Fritz
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[tom203]

Nice looking bike….. when you were lurking, it would have been best to heed the warnings about typical issues with these critters. The carbs likely just needed proper cleaning….not replacement kits with likely inferior parts. As you already surmised, your mechanic did you no favors, sadly. Valve guides, rings at 12k miles….no way! I’d bail on this one to avoid further frustration. Start over with another project if you’re willing …..there’s plenty out there !

 

[rphillips]

Carbs need new jets, did he mention the reason? Maybe, if a screwdriver slot was stripped off or threads were buggered up, did he say you needed a different size? one thing for sure, they aren't worn out.... Seems like a nice little project, projects are supposed to have frustration. Thinking zero in on the carbs. Maybe get it running and figure which cyl. is running worse by pulling plug wires, one at a time, then dig into that carb. It could be worse, could have 4 carbs instead of 2.

 

[Guest]

tom203 I’m close but want to give it another shot. rphillips He didn’t say and has moved out of the area. I’ll give that a try next.then pull the carbs. I since found a good post over in carbs section with a methodical approach
https://www.thegsresources.com/_for...l-exhaust/57223-help-your-bike-won-t-run-well
Thanks

 

[rphillips]

Find a post, here at GSR, from Nessism or bwringer, at the bottom there should be a tutorial thing to click on. I'd advise reading it before you start....Maybe kind'f keep you from chasing your tail.

 

[unfocused]

Last time I worked on a bike with an increasing idle without touching the throttle on a lates 90's GS500 I had to physically drill out the pilot jets until it went away. This took multiple times but the customer was extremely happy when I told him he ran out of gas after riding it 120 miles without issues. He also didnt know he has a reserve. But needless to say, this was a learning project as the internet is full of similar issues on the GS500...

My suggesting would be start with the pilot circuit in your carb. Check vacuum and make sure the petcock is properly working - as you've mentioned nothing about it.

He probably drilled out the plugs that cover the mixture screws - anti-tamper device - comon practice.

 

[Suzukian]

It's a GS300 "L" model, try and get the scrap value. Even free, I wouldn't take that bike. Parts for bikes not worth it cost just as much foe bikes that are worth redoing. You can get the learning experience off of a bike that will run for a very long time, and maybe even get a return on your investment. Just so you know, if the Jets are Brass, you can solder the ends, and drill them out with a drill to match the size you going for. Just solder the hole, this can save you a lot of time, and once you get it going, go buy a nice new jet to get a good spray.

There's an engine for that bike on EBAY for $350 bucks. Also a complete carb set up for $99.95



engine: https://www.ebay.com/sch/i.html?_from=R40&_nkw=Suzuki+GS300L+engine&_sacat=0&_ipg=240&_pgn=1

Carbs rack: https://www.ebay.com/itm/1860247953...IxyQuBuBU+fA1K71jPEi9Cmw==|tkp:Bk9SR4jQ48XAYg

 

[tom203]

I admired persistence! My guess is your pilot circuit is not right…these critters spend a lot of time on pilot circuit before main jet takes over as revs go up. Hopefully, your buddy did not drill out the pilot, but who knows… start over, remove carbs and properly clean them. and check jet sizes! These carbs are tricky to understand how fuel gets where

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[Guest]

Thanks, tom203 that graphic helps. I'm headed back to the advice rphillips suggested and work it step by step. I did the test suggested by removing one wire at a time, and the right cylinder wouldn't run on its own. That's been the troubled side since the beginning. Everything looks clean and new main jets were installed last time. I did keep the old ones, they look identical except for the openings (see photo). I'm doing another complete clean tonight and then working on the step-by-step rebuild plan found in the forum. I discoverd I left off the spring that added tension to the slide on the left cylinder, which was running the better of the two. So we'll see. Thanks for the help all. Gotta...keep...going

 

[Guest]

Quick update, I went through the rebuild steps and found the rubber membrane of the diaphragm wouldn't fit snuggly on the right side. I noticed when reassembling that the right slide didn't have any resistance versus the left which moved down slowly. More to follow when eBay drops off my replacements.

 

[Guest]

Got the diaphragms in finally and got the bike running yesterday, wont quite idle but stopped racing up and down by itself. The values are loud so I’ll probably need to revisit that too. One thing I can’t run down, when took the carbs apart to clean again, 2 small steel ball bearing popped out. When I got everything back together yesterday the choke won’t stay in engaged so I suspect that. I’ve search parts diagrams but don’t see where these go, anyone run into this?

 

[Gorminrider]

Those tiny ball bearings are probably for the "choke"(aka "enricher" for starting) ...there's a rod that goes across the carbs that activates this and the little balll bearings go into tiny holes (with tiny springs they sit on) on the carb body to apply friction to that rod so it doesn't spring back... You'll want to find those tiny springs on the floor with a magnet but otherwise, you'll need to tinker up some other solution...

 

[Guest]

Thanks Gorminrider lucky for me springs stayed in place.

 

[Cipher]

Got the diaphragms in finally and got the bike running yesterday, wont quite idle but stopped racing up and down by itself. The values are loud so I’ll probably need to revisit that too. One thing I can’t run down, when took the carbs apart to clean again, 2 small steel ball bearing popped out. When I got everything back together yesterday the choke won’t stay in engaged so I suspect that. I’ve search parts diagrams but don’t see where these go, anyone run into this?

They came out? Did you put them back? I wonder if these are passage blocks that are pressure seated to block open ends required to drill the various circuits?

my petcock has one ball in it iirc. But that would never get past the Needle valves.

 

[Guest]

Cipher I got them back in ok, it was directly under the choke bar. I’m on to adjusting the idle. Life would easier if I didn’t have to take the tank on and off. With the vacuum system on these carbs do you need to plug the smaller fuel hose to run off a bottle of gas?

 

[LAB3]

Cipher I got them back in ok, it was directly under the choke bar. I’m on to adjusting the idle. Life would easier if I didn’t have to take the tank on and off. With the vacuum system on these carbs do you need to plug the smaller fuel hose to run off a bottle of gas?

If the "Prime" function on the petcock is in working order it lets the fuel through without the need for vacuum. If you take the tank completely off you'll want to plug the vacuum lines to avoid trying to tune with a nasty vacuum leak (damn near impossible)

 

[Guest]

Thanks LAB3 I got it the external tank to work. I think the new diaphragms stopped the racing up and dow but still wont’t idle without the choke. I pulled each plug wire separately and cyl 2 wont run on its own, so I’m now focused on that wire, connection or both. I found another thread from a similarly frustrated gs300 owner with good tips. The best stating check the wire resistance, should be 10 ohms.

 

[Mr.Vroom]

Thanks LAB3 I got it the external tank to work. I think the new diaphragms stopped the racing up and dow but still wont’t idle without the choke. I pulled each plug wire separately and cyl 2 wont run on its own, so I’m now focused on that wire, connection or both. I found another thread from a similarly frustrated gs300 owner with good tips. The best stating check the wire resistance, should be 10 ohms.

I have been down the very same rabbit hole as you with my Gs250. If you are going to replace the ignition system, there is a video of a guy replacing his 450's ignition with a dynatek system. I did it to my 250. Its a great video. But before you do that check the intake boots, where the carburetors meet the engine. if they are cracked out, YOU NEED TO REPLACE THEM! Extra air gets into the engine, and it throws off your air fuel mixture. Cruzin' image just started suppling them. (I'm actually going to buy some for my 250 today).

Link to ignition video: https://www.youtube.com/watch?v=hTJQzBMd5GQ&t=833s

 

[Guest]

I ordered a petcock just to eliminate that issue. My valves are noisy so I was going to check them again while waiting for parts delivery. I looked everywhere to figure out the markings and owners Macaulay to figure out top dead center to adjust the values clearance. I settled on using a screwdriver in the spark plug hole. I checked them 2-3 times before putting everything back together and now wondering if that’s what caused the racket. Does anyone have a hint about how to find TDC on the GS300? Thanks

 

[LAB3]

I ordered a petcock just to eliminate that issue. My valves are noisy so I was going to check them again while waiting for parts delivery. I looked everywhere to figure out the markings and owners Macaulay to figure out top dead center to adjust the values clearance. I settled on using a screwdriver in the spark plug hole. I checked them 2-3 times before putting everything back together and now wondering if that’s what caused the racket. Does anyone have a hint about how to find TDC on the GS300? Thanks

Do you have manual? You're not looking for TDC you're looking for when the cam lobe is in the proper position. On my GS450 the cam lobe needs to be set parallel to the top of the cylinder head to measure, on the bigger bikes the lobe points away from the shim pad. Like I said, get a manual to make sure you got that right.