bike running bad HELP

[TheCafeKid]

You're getting into a bigger can of worms by eliminating the airbox...

If it's something you WANTED to do anyway, you can check Dynojet's site for a kit for your bike, but be warned, i couldnt find any kit for my 77 750, and if im not mistaken your 79 850 will still use the VM mechanical carbs, they may make i jet kit for that still, i dunno. Failing that, you can buy specific main jets from Z1Enterprises, i would advise using as much of your stock stuff as you can, however, meaning the bleeder jets and adjustment screws. You should replace the orings (www.cycleorings.com) and floatbowl gaskets (also available at Z1) If you get rid of the airbox, you'll need pod filters (K&N's are the reigning champ, but somewhat pricey, Emgo makes cheapies that will do a decent job, but can from what i understand be harder to jet for) you'll need to replace your main jets, and probably move the needle a notch or two, and to do that you can ask around with some of the other 850 owners here who may have rejetted, to find out which size jets worked for them...its a trial and error kinda thing but they can give you a good base to start from..Basicly you'll need to jet and tune your carbs for the pod filters...

But if you are thinking of getting rid of the airbox as a "quick fix" for not being able to find/make a seal for it, you'll be in for more work than fixing the airbox...ALOT more work.

[rphillips]

I'm with him, Keep it stock & get it running right. The weatherstrip stuff should make it pretty simple to get the box sealed. Removing the airbox & rejetting is a pretty big deal, and what if the airbox isn't your original problem?

[NelanCustoms]

weatherstripping it is then

[TheCafeKid]

Good idea..HOWEVER..were i you, i would still check the valve clearances, you dont know how long its been since they've been adjusted..if they get bad, you could be saying byebye to your GS's top end in short order. It's easy (yeah i was worried too the first time, but great ppl in this place helped me out..thanks Steve!) and it can be done pretty quick. If ya need some help, just ask...I or any number of other members would be happy to walk ya thru it, as no one wants to see a GS take a dirt nap. Also, replacing the carb orings and intake rings is a good thing to do...they are cheap bro..and will save you a million dollars worth of aspirin, trust me i KNOW this. www.cycleorings.com for both the carb rings, the intake rings and even some sweet stainless steel allenhead intake boot bolts. 15 or 20 bucks for all that tops...seriously consider it please.

[NelanCustoms]

i'll get the new parts asap, i have the repair manual, should be able to adjust the valves and replace the shims if i have to. i got a whole kit of shims that i got with the bike

[SPARKSS]

might be the carbs or shims?

when i am riding the bike when i let off the throttle then get back on it there is no throttle power and it randomly back fires. any thought what might be my problem? thanks 8-[

Just reading through your post and replies Nelan and really would need more info before offering much for solid advice. Does your bike start and run normally with good power except as you noted? If not, is there any other history to when this problems started......i.e. just after some other work performed or other incident? Troubleshoot logically and never throw parts at a problem.

[bwringer]

Just reading through your post and replies Nelan and really would need more info before offering much for solid advice. Does your bike start and run normally with good power except as you noted? If not, is there any other history to when this problems started......i.e. just after some other work performed or other incident? Troubleshoot logically and never throw parts at a problem.

Those are the first symptoms of an intake air leak. He's not just throwing parts at a problem.

[SPARKSS]

Those are the first symptoms of an intake air leak. He's not just throwing parts at a problem.

There.....problem solved I must admit my own experience has always been to observe all the symptoms, check the history, verify with testing, make repairs and then retest to confirm - a lot of friggin around I guess eh! One little method I don't see being mentioned in this site is to look for air leaks with a little gas (not gasoline....I generally use propane from a small torch - unlit of course) and watch for RPM change and/or mixture upset (a high impedance voltmeter and a used O2 sensor in a piece of ducting at the exhaust outlet will work). Of course, if the mixture is ideal or rich the RPM will decrease somewhat and if lean it'll increase doing this.

However.....I guess I was pondering that if the bike started and ran good otherwise, it's possible that he has hanging ignition advance (which may cause a backfire to occur on closed throttle).......I'd want to know more about the symptoms and previous history though first

[bwringer]

Perhaps I was a little brusque... let me explain my advice more throughly:

Every GS850 has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting.

It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years.

It's not like a newer vehicle, where there's generally one problem at a time.


These common issues are:

Intake O-rings (install NEW OEM or Viton only - common nitrile o-rings will quickly deteriorate from heat)

Intake Boots (install NEW -- these cannot be repaired)

Valve clearances (more important than most people think)

Carb/airbox boots

Airbox sealing

Air filter sealing

Petcock (install a NEW one)

On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)

On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.

Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.


None of these things can be neglected, worked around, or half-assed in any way. Once they are squared away, you most likely have a bike that runs like a dream -- these issues account for a very large portion of running problems.

If not, then you can pursue more exotic problems. For example, I have found incorrect float heights a couple of times due to a common misunderstanding in how these are best measured. But you can't uncover other problems without making sure the intake/exhaust paths are leak-free, the valves are adjusted correctly, and you're getting good spark.

[Mr. Brown]

I wanted to point out that Bwringer's "checklist" includes EVERYTHING I'm dealing with right now. I'm gonna print it out and post it on the wall of the garage. The PO of my '81 GS850 rode it around for a few weeks with no seal between the airbox and carbs. With only 3 cylinders working. The only maintainence he performed was to spraypaint everything matte black.

If you can't swear on the integrity of all of these points, it'll keep you awake at night. Trust me... I just wanna RIDE the sucker, and I'm screwing around with gaskets, shims, and broken bolts.

Almost there...

[TheCafeKid]

Mr Brown (Why Mr Brown?? It sound too much like Mr Sh1t...sorry Reseviour Dogs moment..lol) I TOO had all of the same symtoms on my 750, besides my carburation problems...and i can atest to the fact that if you dont fix those FIRST you will be miserably looking at your bike sitting in the garage for a while. Or riding it around, possibly, likely, doing damage to your motor. But me, i knew it was running bad, and even tho it started and ran and i could go places on it, it made me crazy to know it wasnt running right. For a while i refused to believe such a little thing like a leaky intake boot oring was part of the overall problem...but without fixing it i was just chasing my tail. Ive since replaced all the intake rings, rejetted my carbs, adjusted my valves and sextuple checked my float levels...Carbs are going back on this week hopefully with a vac sync, and with any luck, i'll be right as rain...good luck with fixing and repairing yours...ive learned alot, you will too, and you'll be alot happier knowing that with a lil help, you did yourself.

[Ironriot]

Please for the love of god change those O-rings behind the intake ducts that go attached to the head. I'm 99% sure that they're cracked. They'll cause you a world of pain if you leave em be