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Bike running lean? GS850

  • Thread starter Thread starter jlmoulto
  • Start date Start date
J

jlmoulto

Guest
Losing power (surging) when at crusing speeds, say anything over 70km/hr. This is after the engine rebuild and a carb clean. The only real difference is that a proper air filter has been installed. Prior to the engine work the bike appeared to run fine. I am about to search for anything on fixing this but if someone can help point me or can find a link to a previous message explaining how to fix this I would greatly appreciate it (Got to hate dialup!)
 
So I found the air screws were 4 1/2 turns out, pretty much the same on each carb. I thought they should be closer to 2 turns? Anyone's thoughts on that? I am going to try them about 2 turns out to see what the plugs look like then. As for a sync, the tool is going to take 2 weeks(roughly) so I'd like to get it reasonable until that time if at all possible (local garages have close to the same wait as it is peak season).
 
4 1/2 turns out is too much. Someone may have tried to compensate for the possible lean problem by adjusting them out. I would put them to about 2 turns out.
You're running lean or you have a fuel flow problem.
Did you replace the o-rings in the rubber manifolds? Are the rubber manifolds in good condition? Are all the clamps tight? Do you have an idle that rises several hundred rpm as it warms up? Or if you DID have a high idle, did you adjust it down but now the bike won't idle until its warmed up?
Do you have a stock airbox with its lid on?
Did you replace the vacuum line to the petcock? Did you clean the gas cap vent? Also the petcock? Did you use 5/16" fuel line? Did you install an in-line fuel filter? They may cause flow problems.
 
I'll try to answer best I can:

Changed to 2 turns, symptoms worse with respect to surging and idle. Lots of power on the bike, immediate as soon as you twist the throttle. However, leave throttle in one spot and eventually (i.e. two to three seconds maybe as high as thre or four) the surging will take place, mosatly about 50-60KMs or so.

Did you replace the o-rings in the rubber manifolds? Are the rubber manifolds in good condition? Are all the clamps tight?

Yes to the above...everything looks OK there.

Do you have an idle that rises several hundred rpm as it warms up? Or if you DID have a high idle, did you adjust it down but now the bike won't idle until its warmed up?

Haven't adjusted the idle screw yet, but with 2 turns out it is now struggling to idle (really low like maybe 600-700) Hope to adjust that screw this morning. Only noticed the idle last night after I returned home.


Do you have a stock airbox with its lid on?

Yes.

Did you replace the vacuum line to the petcock?

No

Did you clean the gas cap vent?

Yes

Also the petcock?

No

Did you use 5/16" fuel line?

Didn't change it but I will try o check the size.

Did you install an in-line fuel filter?

No but in checking these it this silver one on the line. Should I remove it completely?


Would synchronization cause this the lean issue? How can I determine if it is fuel vs running lean? Plugs are pretty "white". I don't know how to read color but I couldn't see any trace of brown.
 
The results from adjusting your mixture screws in was expected. They are much closer now to where they're supposed to be. Compensating for the real problem always creates more problems. I think your screws are now within 1/2 turn either way of stock.
It's hard to tell a lean mixture from fuel starvation sometimes. If you had a float bowl measuring tube, you could immediately see if the bowls are filling up, and KEEPING a good level. This would narrow down the possibilities. Without it, I can only suggest you check everything that's related to fuel flow first. This would be the gas cap vent, the tank itself (rust/dirt inside), the petcock filter and internals- especially the diaphragm, removing the in-line filter, replacing the vacuum line unless you're positive its not leaking. I just don't think in line filters are necessary. The petcock screen is very fine and does its job. If there is rust or something that makes someone install a filter, then the real fix is to repair the tank. But it's easy to check if this is your problem by just removing your fuel line and filter and installing a new fuel line.
If you still have the problem, then it's the carbs. You say the carbs are clean inside. I'll assume you did a good job. How much did you tear them down? Did you disturb the diaphragms/needles, etc?
Yes, a good carb sinc may help. If they're off enough, you can have major mixture problems. In this case, I would recommend a carb sinc after the fuel flow checks and before getting into the carbs again.
You say this happened right after the engine rebuild/carb cleaning and the bike ran fine before this work was done. I'm trying to think of things you could have disturbed. Are you positive the air box is sealed well? I would do the above checks and the carb sinc. Do you have a vacuum tool and a manual? At least do the carb sinc manually.
Again, please fully explain what you did during the carb cleaning.
 
Thanks for your help Keith and I'll try to explain what I (We) did.

I had a friend who helped with the carbs and we followed the info found on the site for the carb cleaning. May not have been perefect becauase I am an amateur and my friend has never worked on a GS model before (He is a fairly good all around mechanic but certainly no expert...He helped me with most of the engine rebuild. Everthing went back where it should have, I think!

I may not have stated, but when we stripped the engine down, the air box was actually stuffed witha towel instead of a real filter. We installed a proper filter and there doesn't appear to be any air leaks. Someone mentioned spraying wd-40 around the intakes and stuff to see if things improve, which would indicate a leak. Does this make sense to you?

As for gas in the bowls, I am not 100% how we can test. Any ideas without the tool you mention? We were able to confirm there is gas in the bowls by removing a screw in each one and they all had the same amount of fuel as we measured it.

Do you know how many turns would be normally on the throttle screw (I think that is what you call it...in the centre of the four carbs?) Also, on the tank in front of the petcock, there is a circular thing with a pipe coming off it that appears like it should be connected to something, however it never was on this bike. Am I missing something critical or is this a vent with no consequences? Couldn't see anything in Clymer's on it.
 
Hi. Use a fine mist water bottle to listen for intake leaks. The rpm's will drop a moment if there's a leak. Make sure the motor is warmed up first. You did say the manifolds and their o-rings and clamps were good though.
As for setting the ide, you should set the idle to about 1,100 rpm with the idle adjuster screw or knob.
I don't know what you're describing that's in front of the petcock. As far as I know, there's nothing else near the petcock.
I'm wondering about your carb work. You said the bike ran fine before the carb work, correct? I would still do the things I suggested before getting into the carbs, followed by at least the manual sinc.
If it's inside the carbs, it sounds like the pilot circuit in one or more carbs may not be clean. It could also be the needle circuit. I know many people install the diaphragm assy' incorrectly too, which will cause vacuum/mixture problems. The diaphragms have to be installed just right. The jet needle and ANY SPACERS have to go back exactly in order.
I'll be out the rest of the day. If needed, I'll try to help you more later. Good luck. :)
 
Hi, jl
I think the round object ahead of the petcock that you refer to is the tank vent fitting, and it should have a hose about 18-24" long which would be fed out past the carbs and aimed in the general direction of the rear wheel where it can't do any harm. Put some air to it, or a vacuum pump - it should be unrestricted. I believe it's redundant to the cap vent but I'm not sure. Keith and Earl, any comments?
 
Bike ran fine, except (I should have explained this before maybe!) she was only runnning on three cylinders. Compression was very low, which was solved with new rings on all four cylinders, and cylinders were honed, valves lapped and new valve seals. Don't remeber exact copression numbers after rebuild but do remember all cylinders were even.

Did adjust the idle and air screws again...seems to be running a lot better than it was though not perfect. I am wondering if it simply is a combination of little things, based on the former owners attempt to compensate for the towel air filter. The sync is going to take another week or so before I can do it I guess to confirm that side of things.
 
Air Screws

Air Screws

One and a half turns is normal according to the book.
 
OK. I would do the checks I suggested because they should be done as normal maintenance anyway. Then sinc the carbs.
I think I know now what you were describing that's in front of the petcock.
This circular thing as you called it, is not really right in front of the petcock but in front of and on the inside wall of the tank, correct? This is the fuel gauge sending unit. The little pipe is for a hose. This hose is just a drain for fuel in the event the unit's gasket should leak. Put a new hose on it that's long enough to route fuel to the ground, away from the motor.
 
So a big thanks to everyone who gave advice. Finally, the bike is running near perfect (exhaust leak to weld tomorrow). The problem on running lean seemed to be a combination of settings and a carb sync. Now we are seeing a "slightly rich" condition on the plugs i.e. little bit of brown/tan coloring. No surging, only slight backfire on deceleration which I suspect is more of a result of the leak in the exhaust. Otherwise, I think I am finally putting the majority of the work behind me this summer.

I can only hope to get in some riding in the next few weeks before winter!
 
I spoke too soon :evil:

The surging has returned. So if anyone has anymore ideas I would be glad to hear them. Happens somewhere around 3000 - 4500 rpm...above and belwo the bike seems to run fine. Can't cruise at highway speeds at all but can certainly get up to 160KM/hr no prob.

Done so far, petcock cleaned, inline filter removed. Carbs synced and cleaned. Check for air leaks...none
Checked floats, needles,etc....everything appears fine.

Checked spark plugs...#2 and 3 lean, # 1 and 4 rich. This after they initially seemed to be running "slightly rich" i.e. tan color.

The only anomally we noticed is that changing the air mixture screw appears to have little affect on cylinder #3, but noticeable difference on the other three cylinders. I asumme this means a prob on this carb...anyone hazard to guess what?

I am getting to my wits end with this bike. The bike ran better on three cylinders than we can make it run on four. Makes me wish I didn't spend the $1,200.00 on repairs. :( In fact the way I feel at this point, if it ever runs properly it will probably be sold...I don't want a project bike, I want a daily runner. Cheer me up before I make another bad decision!
 
Sorry dude...bikes this age are rolling repair jobs.
It all depends on how it's taken care of and how much of an "Investment" you're willing to make for the love of the bike.

:)
Dm of mD
 
I didn't read the whole thread--just the first and last parts--so I don't know if this was suggested. Anyway... Have you thought of taking it to a shop? You've got so much into it that it seems worth it. I try to do a lot of the work myself, but sometimes it just makes sense to take it to someone else with a fresh perspective.

You know the best part about beating your head against the wall?

It feels so good when you stop.
 
There are only so many things that can cause your problem. It has to be something previously mentioned.
Have you tried running the bike at 3-4.5K with the petcock on "prime"?
Also, are your two floatbowl vent tubes clear and not kinked?
 
Yes to both questions.

I did find an anomally in the fuel line which was not readily apparent. When the tank was off everything looked fine, however when we installed the tank in a tucked away corner, the fuel line was kinking. I rerouted the line. I wasn't able to test fully last night, but it appears like it has helped. I might still have minor adjustment on the mixture screws but I am crossing my fingers.
 
Still cautiously optimistic....bike ran excellent again today. No stumbling at all.

Now all I need is an exhaust, left side cover and a self-cancelling turn signal module. Exhaust I have welded up for now but really needs to be replaced. The side cover was lost on the first run after the engine repair. The Self-cancelling...I can live without!
 
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