Bike no run without air cleaner installed?

[SixteenValve]

Hi, 81 GS750. Has anybody else found that their bike will not start if the air cleaner/housing has been removed?

[Agemax]

not surprising really! you need to re jet the carbs for a start and you shouldnt really run it with no filters at all. the bike wasnt designed to run with out a filter or housing unless you modify it to suit.
welcome to the site by the way

[SixteenValve]

thanks

thanks for your welcome agemax. the only reason i asked that question was the bike started and ran fine in the past with the housing removed, just quick winter starts to get some oil into the top end. but the bike just had carbs rebuilt, and i noticed it would not start without the housing in place. anyway thanks

[Big Rich]

If it started and ran at all without an air filter and now wont run, then your carbs are gumming up.

And starting up a bike to just "oil the top end" isn't a good idea. That's a lot of dry starts and the motor doesn't get hot enough to boil any moisture out.

[Agemax]

if you just had the carbs rebuilt then something is wrong if it ran ok before. strip the carbs again and check over everything to make sure they are all correct

[spyug]

It may be that the carbs are not properly clean but it could also be that the "butterflies" are jammed shut. Did you make sure to adjust them as per the tutorial. They should sit open about the width of a paperclip wire when at rest.

On a couple of occassions, I've had carbs that wouldn't fire after a rebuild and I found they needed to be "tricked". On the suggestion of a member hear I learned to cover the mouth of the carb with cling film (i.e. Saran wrap or the like) and poke a small hole in the center. This gives the right amount of air restriction/flow. Once the bike fires and runs you can remove this as it then tends to cause too much fuel to flow and you may get gas peeing everywhere.

You may also need to crank it over a it longer than normal to get it to suck the fuel in. For this I find a second automotive type battery attached to the bike battery works wonders, giving lots of cranking power. If its still in your car make sure the car is not running or you will cook the bikes electronics.

In my experience, all bikes will run with the airbox off but it is not recommended and they are, of course, designed to run with them.

Hope this helps.
Spyug

[850 Combat]

Does it normally run the stock airbox and filter? If so, it should not run without the airbox, unless the choke is on. If you run pods, properly jetted, it should run without them.

For what its worth, if your "quick starts" don't last long enough to heat the oil and the exhaust system to normal operating temperature, they will help the exhaust system rust out from condensation. If you feel the need to lube the top end, consider putting some oil in the cylinders, and/or crank the starter without starting it.

[Steve]

Actually a properly-running engine should be able to start and idle without the airbox.

Just don't expect too much response if you blip the throttle.

.

[SixteenValve]

results

thank you all for your suggestions. i put the air cleaner housing back on, put the petcock on prime, it started right up. so i guess with the housing off the number two carb could not generate enough vacuum to get the gas flowing. bike is running great now, thats a good feeling as i'm sure you all know!!

[Steve]

thank you all for your suggestions. i put the air cleaner housing back on, put the petcock on prime, it started right up. so i guess with the housing off the number two carb could not generate enough vacuum to get the gas flowing. bike is running great now, thats a good feeling as i'm sure you all know!!

If #2 is not generating enough vacuum, you have other problems.

Since you put the petcock in PRIme position to start it this time, it still doesn't prove anything. It might have started with it in PRIme with the airbox off, too.

By the way, if you have the airbox off again, and find the need to go for a quick test ride, fold a shop rag in half, drape it over the carb intakes, clamp it to the outer carbs with hose clamps or zip-ties. This is good enough for a quick ride, but is not good enough for jetting checks.

.

[SixteenValve]

follow up problem, white smoke

here is the whole story, any ideas would be appreciated. bot the bike 81 gs 750ex in may. 24k miles. bike ran strong, great power. battery kept dieing. researched internet, found out the stators and rectifiers go on these bikes due to poor design. checked stator and rect, indeed they were burnt. the guy who sold it to me of course did not tell me this, he had been riding it by charging the battery every time he went out on it. i changed the stator and rectifier, got good charging readings. at the same time, however, the bike began to smoke. white smoke. didnt smell like gas, didnt smell like oil. the valve cover and piston head gaskets were leaking so i assumed they were leaking oil into the cylinder heads, and it was burning oil. had all top end gaskets replaced, carbs rebuilt by local shop. it looked like he did a good job but the smoking didnt go away. bike "runs" great, great power, no stumbles or stalling, but still smokes. goes away after warmup a bit, but still is smoking. any ideas?

[bccap]

If your bike started on prime. Make sure you do NOT leave it on prime, when the engine is off, and the bike is parked.

[BassCliff]

Greetings and Salutations!!

Hi Mr. SixteenValves,

It's possible that the valve seals are leaking a bit. Or, if the bike has sat around for a long time, a stuck ring which could be un-stuck if it's ridden aggressively for a little while. Have you done a compression test or leak-down test?

It concerns me when I read about one of these vintage bikes being taken to a shop or dealership for repair. I've read literally hundreds, maybe thousands, of horror stories here in the forums. Good mechanics who really know these bikes, and enjoy working on them, are few and far between. We're a bunch of DIY guys around here. We can help you learn to work on your bike. That way you know it's done right.

So let me dump a TON of information on you and share some GS lovin'.

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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 Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. 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

[SixteenValve]

basscliff appreciation day

basscliff i am so glad you sent me a message, your basscliff page with all those tips and manuals, etc has just been fantastic for me. so helpful! and you are right, i have had so much trouble finding a good GS mechanic, it is quite painful (and expensive) to have someone working on one's bike that does not love it as much as I do. so i've had to learn to do it myself and you've really helped that process. thank you.