81 GS850G Won't Rev over 4000 RPM

[Guest]

As stated above.

Just bought this bike off a guy who said he only rode it occasionally.

He told me he:
Rebuilt the carbs 3 years ago
Put the stock jets back in -115 mains (bike came with 130's not installed)

Bike had holes in H pipe in exhaust, was popping. Ran poorly.

Work I have done:

Replaced H pipe on exhaust
Replaced all gaskets on exhaust from head on back
Cleaned K&N air filter (Single in stock air box, was on the bike)
Replaced spark plugs
Check and set timing, was off a little, now dead on
Pulled, cleaned, bench sync'd carbs
Set float levels
Checked voltage at battery, 12.5v regardless of engine speed

Since all this work, it starts better, runs smoother, quieter

STILL NO REV'S BEYOND 4000 RPM Same as the day it came home.

Today, for the hell of it, I put the 130 Jets back in, NO CHANGE

What am I missing?

[gustovh]

Pull the valve cover, check the cam timing. When your r limit is sorted read your plugs to determine if your 115 jet will be rich enough, it might be a bit lean but then again might not.

V

[ShadowFocus603]

Next time rev it ill it bogs and shut key off without releasing throttle until the engine shuts all the way down then check your plugs. This will tell you if you are lean or rich. I suspect lean. Try resealing your airbox with foam weather strip tape and check the orings on the intake boots where the bolt to the head. Id replace them regardless how they look. Cycleorings.com. order the orings and the stainless cap head screws. Get the orings for the carbs as well. Look for rips in the intake boots and replace if they are or if they are super hard. Also replace the boots between the carbs and airbox if they are hard because they shrink and cause poor sealing. Once you're totally airtight I gaurantee you'll be good to go. Sync the carbs and call it a day. And if you haven't yet adjust the valves.

[GS850GFan]

Next time rev it ill it bogs and shut key off without releasing throttle until the engine shuts all the way down then check your plugs. This will tell you if you are lean or rich. I suspect lean. Try resealing your airbox with foam weather strip tape and check the orings on the intake boots where the bolt to the head. Id replace them regardless how they look. Cycleorings.com. order the orings and the stainless cap head screws. Get the orings for the carbs as well. Look for rips in the intake boots and replace if they are or if they are super hard. Also replace the boots between the carbs and airbox if they are hard because they shrink and cause poor sealing. Once you're totally airtight I gaurantee you'll be good to go. Sync the carbs and call it a day. And if you haven't yet adjust the valves.

OK, I will get seals between head and carbs.

I forgot to mention I did replace all 4 of the rubber seals between carb and air box.

The K&N air filter does NOT fit very well in the air box. Should I scrap it and get a stock filter? or get weather striping?

Not sure which items these are? "order the orings and the stainless cap head screws."

[GS850GFan]

Pull the valve cover, check the cam timing. When your r limit is sorted read your plugs to determine if your 115 jet will be rich enough, it might be a bit lean but then again might not.

V

I will have a look at the cam timing after I replace the intake rubbers. Thanks

[wymple]

OK, I will get seals between head and carbs.

I forgot to mention I did replace all 4 of the rubber seals between carb and air box.

The K&N air filter does NOT fit very well in the air box. Should I scrap it and get a stock filter? or get weather striping?

Not sure which items these are? "order the orings and the stainless cap head screws."

I use a heavy piece of weather stripping on the K&N, works fine.

[ShadowFocus603]

I use a heavy piece of weather stripping on the K&N, works fine.

I second this as well.
Carb O-rings

http://cycleorings.com/#BS_Series_O-ring_Kit

Intake O-rings
http://cycleorings.com/intake.html You need the 38mm O-rings
Order page

http://cycleorings.com/order.html

If you scroll down further you will see the cap head screws as well. To remove the old philips head hardware an impact driver (screwdriver you hit with a hammer to break screws free without stripping) is invaluable. Also helps with engine side cover screws. You are almost there especially since you have already got the airbox to carb boots done. Keep that chin up soldier. It does pay off lol. http://www.thegsresources.com/_forum...7-Black-Magick Link to my build so you can see I started off worse shape than you and managed to get a daily rider out of the mess I bought to start with.

[GS850GFan]

I use a heavy piece of weather stripping on the K&N, works fine.

Will do, thanks

[eil]

The K&N air filter does NOT fit very well in the air box.

I don't get this... I have a K&N filter that fits just fine in my 850 air box. Are you by chance missing the metal cage that it attaches to?



If I recall, weather stripping goes all around the metal piece shown. (And unfortunately, I don't remember whether this is top or bottom.)

[rustybronco]

Metal is the top.

[GS850GFan]

I do have the cage and there was some sad worn out rubber weather stripping, but it was very deteriorated. I guess I'll be looking for more.

So, through this discussion, I am learning that everything from the intake (obviously) all the way through the air filter has to be a sealed system? Only breathing through the hole in the bottom of the air cleaner box.

If so, then the Positive Crankcase hose from the valve cover to the airbox must be clamped and sealed (It's not)

The clamps on the intake to the carbs are iffy and the same with the clamps to the air box. Old and stretched.

[Steve]

ISo, through this discussion, I am learning that everything from the intake (obviously) all the way through the air filter has to be a sealed system? Only breathing through the hole in the bottom of the air cleaner box.

Might have to define that "hole in the bottom of the air cleaner box" just a bit.
Some air boxes have a vent or drain hole in the bottom left corner. That should have a drain tube attached. There is a slot at the rear that might be about an inch high and four inches wide, but that should have a snorkel attached that reaches up over the battery box. THAT is where the airbox breathes.

If so, then the Positive Crankcase hose from the valve cover to the airbox must be clamped and sealed (It's not)

It's not a "Positive Crankcase hose", it's just the crankcase breather hose. DO NOT clamp it, it needs to breathe.

The clamps on the intake to the carbs are iffy and the same with the clamps to the air box. Old and stretched.

Your clamps are not old and streched. Your intake boots are old and SHRUNKEN. They are also probably hard as rocks (well, at least as hard as plastic). Replacing them will restore proper sealing and will also fill out the gaps in the clamps. Unless you just like the look of a new, shiny clamp, there is no reason to get new ones. Be prepared, though, the boots on the airbox side will run about $45 or so (for the set of 4), but the boots on the engine side will set you back about $130. WELL worth the expense, and you won't have to worry about them for another 25 or 30 years.

.

[GS850GFan]

Really good info right here...thank you....

Might have to define that "hole in the bottom of the air cleaner box" just a bit.
Some air boxes have a vent or drain hole in the bottom left corner. That should have a drain tube attached. There is a slot at the rear that might be about an inch high and four inches wide, but that should have a snorkel attached that reaches up over the battery box. THAT is where the airbox breathes.

It's not a "Positive Crankcase hose", it's just the crankcase breather hose. DO NOT clamp it, it needs to breathe.



Your clamps are not old and streched. Your intake boots are old and SHRUNKEN. They are also probably hard as rocks (well, at least as hard as plastic). Replacing them will restore proper sealing and will also fill out the gaps in the clamps. Unless you just like the look of a new, shiny clamp, there is no reason to get new ones. Be prepared, though, the boots on the airbox side will run about $45 or so (for the set of 4), but the boots on the engine side will set you back about $130. WELL worth the expense, and you won't have to worry about them for another 25 or 30 years.

.

I will take a picture of the airbox tomorrow. The back bottom of the box has a square out of the back of it. It's not hacked, so there must be something missing. No snorkel. Any pictures of what it is?

Yes, crankcase hose must breath. But it needs to be replaced. I was asking if it should have a hose clamp at each end.

I bought the airbox boots, just need the intake tubes. If the clamps are cheap I might pick up a set. Mine are worn out and bent from being over tightened.

Good to know these parts won't need regular replacing.

[Brendan W]

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.

[Steve]

I will take a picture of the airbox tomorrow. The back bottom of the box has a square out of the back of it. It's not hacked, so there must be something missing. No snorkel. Any pictures of what it is?

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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