GS450 Carb Unbalanced after rev

[Guest]

I have a '81 GS450T - After making a homemade manometer I synced the carbs at idle. However after reving the engine the right carb pulls much harder than the left and the carbs are no longer in sync until I let the bike idle backdown. I have the right idle screw backed most of the way out and the left screw most of the way in, that seems strange. I'll have new intake boots tomorrow and have already replaced the intake o-rings. Any advice? Thanks for looking.

[Larry D]

Which screws are you adjusting ? You should be adjusting the locking nut that controls the butterfly opening and closing, NOT the idle air screws.

[spyug]

A couple of things:

Does your manometer have restrictors in the tubing? If not your fluid levels are going to bounce all over making accurate reading nie on impossible. Restrictors (smaller diameter tubing) should be placed about 6" from the ends or the tube ( the ends that go on the vacuum barbs). Cut off about 6" on both ends and find some smaller diameter tube (plastic metal whatever) and insert it into the maintube and the pieces you cut off. You will have 2 of these one for each end.

When balancing the carbs there is only one adjuster you will be dealing with on a two carb setup. It is the screw in the linkage held fast by a lock nut. The other screws you fiddled with are the airscrews and they should be set identically at around 2.5 turns out from seated. Turn them both back down until lightly seated then back them both out 2.5 turns. As the screw heads are slotted one turn out is flipping the screw slot 2 times so count 5 flips of the slot to get 2.5 turns.

To do this easily it is best to remove the gas tank and run a small remote tank to supply fuel as you will need to get to the center part of the carbs. You will need a long shafted blade type screw driver and a wrench to fit the locknut 10mm I believe. MotionPro makes a tool specifically for this which makes it so much easier as it is a screw driver and socket wrench in one.

Start the bike without manometer connected but vacuum barbs still plugged off. Now using the idle adjustment knob ( big thumb screw knob sticking down between carbs) adjust the idle to around 1500 rpm. shut down bike and attach manometer ( make sure to plug off the vacuum port on the right hand carb). Start it up and see where your levels are. Chances are, they will be way off and as you mention one side will pull way higher than the other.

To get them levelled out, unlock the locknut and dial the screw in and out until they are more or less equal. You will likely not get them 100 % exactly the same so don't kill yourself.....just close enough for government work. When satisfied, holding the screw, tighten down the locknut. This is the hard part and it may take a few tries as things tend to wander. Once set check to see that the levels remain roughly the same. Using the idle knob, back the idle down to about 1200 rpm and you're done.

If, when first doing this, one side pulls but the other doesn't show any movement run the idle (using the knob) up to 3000 or 4000. The other side should then pull. Do the adjustments as stated above and then back the idle down to 1200 rpm.

Before attempting this you should, of course have a) cleaned and rebuilt carbs b) installed new intake boot o-rings and c) adjusted valves other wise its kind of a waste of effort.

Give it another try and let us know how you make out.

Good luck,
Spyug.

[thevillaindylan]

Thanks for the input fellas. Yes, I placed brass restrictors about 6 inches from the end and the 2-stroke oil I used doesn't jump too much. I had performed a bench sync and got the butterfly valves close, but not close enough apparently. I'm gonna make a makeshift gas tank to perform this while the bike is running.

Also, I haven't checked my valve clearences yet. I haven't yet purchaed the Suzuki feeler guage that the Clymer manual recommends. The manual says that the Suzuki kit contains "feelers" that are smaller than normal kits. Do I need the Suzuki one or can i pick one up at my local auto parts store?

Will I have to replace the valve cover gasket and do I have to put any sealant on the gasket? Additionally, if you have any other tips when doing this that would be great as this will be the first time I have ever checked valve clearences. Once again thanks for the input.

[chef1366]

Try again with the new boots.
If a no go try a bench sync and ride.

[Larry D]

Any feeler gauges will work. Yes, a new valve cover gasket will be needed and NO, NO, NO sealant. Of course, clean the surfaces very well after removing the old gasket. You can put a very thin layer of your favorite grease on the new gasket, I mean a thin layer, not globbed everywhere. This will make it probable that you can re-use the valve cover gasket a couple times. I'm not certain if RealGasket has one for your bike or not. If they do, I'd recommend that.

http://www.realgaskets.com/

[BassCliff]

Hi,

Yes, you do need to ensure that the air intake system has no leaks. New boots and O-rings should take care of that. Same goes with the airbox, air filter, and airbox boots. You want no leaks in the air intake system.

I always sync my carbs at about 2000-2500 rpm rather than at idle. It seems to work better. I don't know exactly why but that is how Mr. rapidray taught me and I trust him.

Valve clearances should be checked before syncing the carbs. You can get a decent metric gauge at just about any auto store, or order one online if you must. I found one at the local Pep Boys that starts at .04mm and goes up in .01mm increments. Save yourself some confusion and get a metric gauge rather than an SAE gauge with metric equivalents.

On my website there is a link to a video showing how to adjust the valves on the GS twins. You'll find other helpful stuff there too. Please feel free to stop by.


Thank you for your indulgence,

BassCliff