GS850 Stops dead after hard acceleration

[GuardsmanUSA]

Attempting to bring back a GS850 from the depredations of a PO. Put stock pipes back on cleaned carbouretors per instructions on the site but bike would not run acceptably. took it to local shop to obtain some expert service and when I tried to run it home it ran better at idle but accelerating rapidly caused the bike to stop cold and not be able to restart for a minute or two. Back to drawing board, replaced ingition and coils, went through bike and replaced numerous wires, bike now starts and runs much better, accelerates hard but still falls on its face, however now it will stay running if you quickly back off on the throttle. Suspicion has now fallen on the airbox, the PO had cut a big hole in it so we sealed it back up with aluminum sheet and duct tape.

Question: is it possible that we have reduced the air intake too much and that is causing the sudden loss of performance? I am seraching for an intact air box the only one found to date is from an 78 GS 850, is it suitable for a 1980 GS 850 L ?

Thanks in advance for your support, this website and the Venture Rider site seem to be populated with genuinely helpful folks.

Howard

[BassCliff]

Greetings and Salutations!!

Hi Mr. GuardsmenUSA,

Yours is a story that has been repeated in these hallowed annuls countless times. New owners of vintage motorcycle machinery all experience many, very similar, seemingly mystical conundrums trying to enjoy their newfound mechanical Pegasus. At first they will dance, they will chant, toss beads, smoke pipes, and curse. After these efforts have failed they will resign themselves to actual, proven, time-tested repair procedures that have been performed on these classic steeds for decades. I am here to point you down the path of enlightenment. Any shortcuts from the path of enlightenment will leave you stranded on the side of the road of life. When you can snatch the valve shim from my hand, you will then be free to soar through this existence on your Suzuki GS. Now, gather up thy tools, gird thy loins, and steel thyself for copious amounts of GS knowledge.

Yes, the stock airbox must be sealed up and in good order. Some people will remove the snorkel to get more air into the engine. But like any other air leak, it wreaks havoc with the carb tuning. Carb jetting/tuning is dependent on the air intake and exhaust configuration. The air/fuel mixture has to be balanced in all carb circuits for the engine to run right. There are a couple of air intake repair guides on my little website as well as carb tuning and troubleshooting pages.

My first guess for your situation would be that the idle or pilot circuit is too lean. That's why backing off the throttle causes it to die. Since you say the carbs were cleaned according to the instructions on this site, I'm assuming that they were completely disassembled and dipped in carb dip for 24 hours or so. The idle mixture screws were removed so that those passages could get cleared also. (You have to remove the caps to get to those screws.) And all of the O-rings were replaced with a kit from http://cycleorings.com. If any of the above is not true, you could still have blockage in the small carb passages.

Then again, it could be something really simple. Where are your idle mixture screws set? How many turns out? Maybe you just need to turn them out another 1/4 to 1/2 turn. Usually we set them using the "highest idle method", which is explained on my website.

Anyway, let me dump a TON if information on you and share some GS lovin'.

I just stopped by to welcome you to the forum in my own, special way.

If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....

Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Rebuild Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. Now let me roll out the welcome mat for you...



Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[Redman]

A 78 850 will not be a GL.
Were not GLs untill 1980.
DOnt know if airbox same or not.
Welcome to GSR.

.

[tom203]

Hi Mr. GuardsmenUSA,

Yours is a story that has been repeated in these hallowed annuls countless times. New owners of vintage motorcycle machinery all experience many, very similar, seemingly mystical conundrums trying to enjoy their newfound mechanical Pegasus. At first they will dance, they will chant, toss beads, smoke pipes, and curse. After these efforts have failed they will resign themselves to actual, proven, time-tested repair procedures that have been performed on these classic steeds for decades. I am here to point you down the path of enlightenment. Any shortcuts from the path of enlightenment will leave you stranded on the side of the road of life. When you can snatch the valve shim from my hand, you will then be free to soar through this existence on your Suzuki GS. Now, gather up thy tools, gird thy loins, and steel thyself for copious amounts of GS knowledge.


BassCliff

I knew the radiation was going to have unforeseen effects - I hope it dissipates before arriving here.
GuardsmanUSA; also make sure your petcock is flowing consistently- even on prime they can get restricted with gunk and cause fuel starvation.

[SqDancerLynn1]

You reference to 78GS850 should be a 79GS850 and NO the air box is completely different to an L model

[JimW]

It sounds like a fuel starvation problem. A leaky airbox may affect the engine's performance but shouldn't cause a stall.

I'd recommend starting with the petcock. Is it getting a good vacuum signal (vacuum hose tight and not split, cracked, etc.)? As tom203 said, check the petcock for contamination/restriction. If you find gunk in it, I'd check the fuel tank and make sure it's scrupulously clean and rust-free. If the petcock checks clean, next step would be to check carb float levels.

[GuardsmanUSA]

Thanks for the suggestions, given that the engine shuts down dramatically and that we now have a confirmed sound ignition system, the petock seems to be the most logical point of failure, it is new but I am now suspecting that we may have tank contamination.

Oh the bike has a new starter a gel cell battery and has been extensively rewired.

[GuardsmanUSA]

GS850 Stops dead after hard acceleration - update

I have been seeking an intact GS850 L airbox - so far no luck. Will a 1980-1983, GS 1000 or 1100 non L versions fit my bike? There seem to be more of these available on eBay.

Also just picked up a second GS850 G - it runs well it is getting new tires this weekend with only 30K miles the L model only has 11K miles.

I appreciate the help.

[DanTheMan]

I have been seeking an intact GS850 L airbox - so far no luck. Will a 1980-1983, GS 1000 or 1100 non L versions fit my bike? There seem to be more of these available on eBay.

Also just picked up a second GS850 G - it runs well it is getting new tires this weekend with only 30K miles the L model only has 11K miles.

I appreciate the help.

Non-L versions will fit. G and L airbox versions are the same until about '82, but I believe even the '82 version will work. I've got a spare one ('82) without the cage if you want it for $10 + shipping. PM me if interested.

[Dogma]

The symptoms sound very much like a fuel flow problem cause by a defective petcock. Have you checked or replaced it? They can develop a vacuum leak after a few decades that prevent proper flow.

[Big T]

The symptoms sound very much like a fuel flow problem cause by a defective petcock. Have you checked or replaced it? They can develop a vacuum leak after a few decades that prevent proper flow.

See post #8

[Dogma]

See post #8

Yep. Went right past it. Sorry.

[cleiper]

My GS gave me the run around with a similar problem, and after much poking with spoons and getting nowhere, I accidently failed to push down the petrol tank cap properly after filling it up. The ride home was fine, no dying at hard acceleration.
Noticed the loose cap the next day, pushed it down properly and set off, only to find the problem was back.
After a wee scratch of the head in confusion I took off the petrol cap, put it in my pocket and gave the bike some WOT, it ran fine again. Back on with the cap and fault found.
Turned out the pressure relief mech inside the petrol cap was blocked causing a vacuum in the tank and fuel starvation to the carbs.
There must have been a small amount of air getting in cos it only happened when I was giving it big licks.
An easy check, and if it helps its running strip down the cap and get it working.
Good luck!

[hampshirehog]

Cleiper looks like he's on the numbers - exactly what I was going to say. Classic symptoms of the tank not venting.

[GuardsmanUSA]

Gentleman, thanks much that just sounds right! I have experienced that exact problem in automobiles.

Also Dan has provided me an unaltered GS850 airbox - Dan thanks for the assist.