81 GS850G Won't Rev over 4000 RPM

[GS850GFan]

I'm with gustovh on this. Valve timing first thing to check if a new to me bike was not revving out especially if changing mains made no difference.

OK, it's on the "The List". Can I check the valves with the engine cold?

Since the tank, carbs and air box are coming off today, I might as well do it now.

[GS850GFan]

Click HERE to see a current eBay auction that has some decent pictures.


It is not an item that you can order separately from any dealer. Your best bet would be to find a used box online or maybe someone here has a spare.

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OK, gotcha. Thanks for the picture. There is an AMAZING motorcycle junk yard not far from me. Guy has been there for 25 years, parts piled to the ceiling. That's where I got my exhaust parts.

Tri-County Motorcycle Salvage in Ventura, Ca.

I'll stop there today and have a look.

[Brendan W]

OK, it's on the "The List". Can I check the valves with the engine cold?

Since the tank, carbs and air box are coming off today, I might as well do it now.

That's the way I always do it - nice and cold. Opening it hot could expose children in earshot to words they haven't heard before.
For a check that isn't going to cost anything except time it's well worth doing if just to eliminate it. Just so there is no misunderstanding you're going in to check timing but while you're there might as well check the clearances as well. Only saying because when someone says check the valves I assume they mean clearances - but that's just me.
Happy hunting.

[GS850GFan]

That's the way I always do it - nice and cold. Opening it hot could expose children in earshot to words they haven't heard before.
For a check that isn't going to cost anything except time it's well worth doing if just to eliminate it. Just so there is no misunderstanding you're going in to check timing but while you're there might as well check the clearances as well. Only saying because when someone says check the valves I assume they mean clearances - but that's just me.
Happy hunting.

I'm with you on that. Might as well check it off the list. I have to order the parts today, will probably take a day to get them, so cam timing and valve clearance will be tonights job.

This is my first GS and I have felt the power, even for just a moment. Really looking forward to getting this worked out and ready to roll.

[gustovh]

I only mention valve timing because, if you have one too many pins between the intake and exhaust cams, no matter what you do on the carb side, the engine will not rev beyond a certain point, period. I spent 3 months chasing the problem that you have. I could be wrong though.

V

[GS850GFan]

I only mention valve timing because, if you have one too many pins between the intake and exhaust cams, no matter what you do on the carb side, the engine will not rev beyond a certain point, period. I spent 3 months chasing the problem that you have. I could be wrong though.

V

Oh man...that doesn't sound fun....well, there is only one way to find out!

[GS850GFan]

All parts ordered, be here on Saturday!

[GS850GFan]

Weather striping in the air box!

[gustovh]

Well how about an update, the suspense is killing me.

V

[GS850GFan]

Well how about an update, the suspense is killing me.

V

I wish I had something to report. Still waiting on parts, should be here on Saturday. I haven't taken the valve cover off yet as I want to verify that I have the correct gasket before I take it apart.

I did look into the snorkel for the airbox, the junkyard didn't have it. I'm going to hold off till all this other stuff is done.

In the box of extra's that came with the bike, I did find some small bags from the carb kit the PO did and it had all the old O rings, so at least I know those are new.

Other than that, I have been cleaning and preparing for work on it this weekend.

[londonboards]

Anything like this:

For me the problem was the needles incorrectly installed in the throttle slides. Main jets not able to deliver fuel.

See my blog posting: Who put these main jets together?

And also the needle valves in the floats needed replacing.

Just another idea.

Greetings

[GS850GFan]

Anything like this:

For me the problem was the needles incorrectly installed in the throttle slides. Main jets not able to deliver fuel.

See my blog posting: Who put these main jets together?

And also the needle valves in the floats needed replacing.

Just another idea.

Greetings

Wow, that was an interesting read. I have had these carbs off and on a few times looking for problems but haven't pulled the needles out.

I didn't mention before that in neutral the bike will rev to redline it's only under load that it will not pass 4,000 rpm.

BUT, since I have to deal with the carbs again I will have a look to verify I don't have the same problem.

The guy I bought the bike from was a nice guy, but not a great mechanic. I have found nuts and bolts loose all over the place (clutch cable lock nut, choke cable lock nut, air box mounting bolts, headlight mounts). Old rubber parts that should have been replaced (like intake manifolds and air box tubes). But they used it a few times a year on vacations. They put it on the back of their camper. I understand that he probably didn't want to spend the money to fix all this stuff. So I am doing it.

I only paid $750 for the bike and i think when all is said and down, it will work out to the right amount of money for the bike and what I have spent

Thanks for sharing this thread!

[GS850GFan]

OK, Here's how the weekend went. Got the gaskets and intake manifolds on Saturday.

Installed the new intake manifolds with new O rings
Re-Installed original 115 main jets
Replaced bowl gaskets
Had to replace all screws on float bowl because they were warn out and the heads were stripped
Cut drilled and shortened stretched out intake boot clamps. Before they wouldn't tighten all the way, not there is 1/4 inch left after they are tight.

I DID NOT adjust valves because I realized I didn't have my torque wrench here, I lent it to a friend.

The finished product:

Not too different! It will still only rev to 4,000-4,500. But what IS different, if I let up on the throttle just a little it will then go to 5,000 rpm.

Tomorrow I will get my wrench back and do the valve adjustment and check cam timing. I'm also going to check the ignition timing again with a dead light, not just with the timing light.

Maybe the ignition mechanical advance?

Here is the plug:

20140907_153840.jpg

[ShadowFocus603]

Plug is showing lean but the caveat is did you actually do a chop or just let it idle then shut off? If the latter then the plug doesn't tell you much. When you cleaned the carbs did you uncap the fuel mixture screws and remove them before dipping the carbs? If no that would be the next course of action. You will have to remove the carbs anyways if you got the o-ring kit from cycleorings. Be careful as the screws tend to be stuck. Once you get them out dip the bodies again and reset the needles to 2 1/2 turns out. Doing this and installing the new o-rings will remove two more links in the chain and get you that much closer to finding the culprit for being lean. By the by, if you have a thermometer of the laser variety you should temp all four head pipes at idle and see if they are all around the same temp. This will give you some indication if you have any spark or carb issues as well.

[GS850GFan]

Plug is showing lean but the caveat is did you actually do a chop or just let it idle then shut off? If the latter then the plug doesn't tell you much. When you cleaned the carbs did you uncap the fuel mixture screws and remove them before dipping the carbs? If no that would be the next course of action. You will have to remove the carbs anyways if you got the o-ring kit from cycleorings. Be careful as the screws tend to be stuck. Once you get them out dip the bodies again and reset the needles to 2 1/2 turns out. Doing this and installing the new o-rings will remove two more links in the chain and get you that much closer to finding the culprit for being lean. By the by, if you have a thermometer of the laser variety you should temp all four head pipes at idle and see if they are all around the same temp. This will give you some indication if you have any spark or carb issues as well.

I did ride the bike about 3 miles and it runs great below 4,000. Best it's ever run...

Which brings me to this...

As previously mentioned...The bike came with a small box of parts, carb kit bags with the old O rings, a set of multi air cleaners, a set of 130 main jets, a box with the K&N cleaning kit and in the bottom of THAT BOX I found some tappets and a tappet tool!

So someone was in messing with the valve height.

As previously mentioned in this thread "Check the Valve Clearance". So tomorrow I will be doing that. I ordered and have the valve cover gasket and tomorrow I will go pick up my torque wrench so I can put the valve cover back on right.

According to the "Official Manual" page 3-5 which talks about tappet / valve adjustment and that if the tappet height is to low, you have a low power situation, basically the valves aren't opening wide enough.

Either way, I'll be going over your list above, checking the tappet / valve clearance and reporting back!