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5000 rpm "wall" .....

  • Thread starter Thread starter jaywelchy
  • Start date Start date
Do the carbs and valve adjustment. And don't sorta do the carbs. Take them off and soak them and make ABSOLUTELY SURE that all the passages are clear. I'm sure that many here that had to do their carbs multiple times will admit to not doing a complete job the first few times, then broke down and did it right. You've got to tear them completely apart and soak them and clear all the passages and then replace all the o-rings with the right pieces, not just some junk off ebay. If it's still pouring fuel out the carb, you've got a float valve not doing it's job. Could be it's just got a piece of gunk in it. The floats and float valves are the only thing I didn't replace on mine, but I've done this a hundred times and understood the chance I was taking. It worked out ok. My carbs worked great the first time. Don't get scared off by the valve adjustment, follow the directions religiously and you'll be fine. You may only have to buy 1 or 2 shims. You can check the cam timing while you're doing it, and eliminate that from your list of possible causes. Then I'd forget trying to decide whether ignitor is bad and spring for the Dynatek EI and new plugs. The best $150 you'll spend.
 
HOw did you get the engine so clean? Mine looks like yours did and it looks like you got the cooling fins nice and clean. You use something in particular?
 
For all you newbie guys...please check the link in my signature about common newbie mistakes. Incomplete carb cleaning is at the top. Also, the "ceiling" issue is often caused by the jetting being too lean (such as trying to run the bike without the airbox or filter). There is tons of info in the archives and stored by basscliff, so you guys need to dig in and do some maintenance.
 
Lots of great posts ..

So to clear some things up..

The carbs no longer leak fuel .. the pilot jet was too large, and was gushing fuel in at idle .. and only idle, causing the fuel to pour out. I replaced with factory size pilot jets, and thats cured.

I agree on the "complete" carb clean .. I know I went through the carbs rather lightly, and the bike shop synced and played with floats .. no parts replaced.

The bike will rev out fine in neutral .. but thats a no load situation, and tells me nothing. The "wall" is under power, and under load.

I have O rings ordered and on the way ... I have factory 92.5 main jets on the way (in case originals were drilled out ... )

The plan is to gather the O rings, jets, and needles IF I can find them, and print out the tutorial on CV rebuilds from Basscliff's site. Then to rebuild like it should have been done the first time. ( I am guilty .. have gone through lots of carbs "lightly" with wonderful results. Not these!)

I am not discouraged, but rather interested .. in the bike, and the work that needs to be done.

Valve adjust will be on order also.

As far as brutal honesty .. I crave it! Bring on the thoughts and honest opinions :)

I am excited to get this little bike running well ... should be a fun ride.

And again, this is my first exposure to the old GS bikes ... and once I bought and paid for this 550, I did a ton of research on parts availability, which introduced me to the history and the GS 1000 ... which I really, really wish I had. Love the Cooley bike, but the Red with white #34 race replica ... THATS the bike I want to build!!

One project at a time ...... still scouting for the bigger GS ... ;)

Jason
 
Pilot jets, regardless of how large, can not make fuel pour out of the carbs. You have a stuck float needle and/or a petcock dumping fuel down the vacuum line.

Good luck and glad you have turned the corner and are getting serious.:)
 
Pilot jets, regardless of how large, can not make fuel pour out of the carbs. You have a stuck float needle and/or a petcock dumping fuel down the vacuum line.

Good luck and glad you have turned the corner and are getting serious.:)

yea what he said,lol... I was scratching my head at this thinking why would a pilot overflow fuel...
 
Hmm .. maybe I need to be more detailed. The pilot jets (idle circuit, yes?) were a few sizes larger than stock. Bike fouled plugs quickly at idle when I bought it, AND when it sat and idled, raw fuel would drip out rapidly, almost pour, where the airbox boot and carbs come togethor. Obviously there were no clamps on the boot/back of carb joint, and the extra fuel was not being drawn in at idle...hence the leak.

I hope this makes sense, and if not will be good for a quick chuckle! Ha! :D

Jason
 
Hmm .. maybe I need to be more detailed. The pilot jets (idle circuit, yes?) were a few sizes larger than stock. Bike fouled plugs quickly at idle when I bought it, AND when it sat and idled, raw fuel would drip out rapidly, almost pour, where the airbox boot and carbs come togethor. Obviously there were no clamps on the boot/back of carb joint, and the extra fuel was not being drawn in at idle...hence the leak.

I hope this makes sense, and if not will be good for a quick chuckle! Ha! :D

Jason

Your leak theory is wrong. The floats are letting too much fuel into the float bowl so it's over flowing. Or the petcock has failed and fuel is flowing down the vacuum line. The pilot jets have nothing to do with it.
 
Hmm .. maybe I need to be more detailed. The pilot jets (idle circuit, yes?) were a few sizes larger than stock. Bike fouled plugs quickly at idle when I bought it, AND when it sat and idled, raw fuel would drip out rapidly, almost pour, where the airbox boot and carbs come togethor. Obviously there were no clamps on the boot/back of carb joint, and the extra fuel was not being drawn in at idle...hence the leak.

I hope this makes sense, and if not will be good for a quick chuckle! Ha! :D

Jason
It doesn't make sense cause that's not how they work brother.

Fuel is metered into the float bowls of the carbs by a float valve. It works much like your toilet tank does. Gravity and air pressure, combined with vacuum draw of the motor allow fuel to pass from the tank into the float bowls. When the fuel reaches a certain level, the float valve closes and the fuel flow essentially stops, or slows at least. Just like your toilet. The pilot jets in your carbs are actually fed through the main jet, and emulsion tube. (were you to open them, there would be, or should be, a rubber cap covering the actuall pilot jet. If not, you'll want to remedy that)

Now, even if the jet was massively too large, it may foul the plugs, but the float valves "should" prevent overflow of gasoline. If you've got that much gas leaking, you've got either shot float valve needles, leaking Oring around the valve seat (which since you said they've never been replaced, is likely) or a bad petcock, or all three. The performs equipt from the factory are designed only to flow when the motor is turning over, unless they're on the "prime" position (it flows freely then). If the petcock is bad, it may flow gas all the time. Try as they might, even float valves in perfect shape cannot hold back the pressure from a tank full of gas. They'll give up, and the gas will over flow into your crankcase. Which is bad as gas will wash the cylinder walls and crank bearings of oil, leaving metal on metal contact. I'm sure you know that isn't good.

I'd suggest, as has been already, tearing the carbs down, replacing the Orings after properly cleaning them, and replacing your 30 year old petcock with new. (rebuilds fail more than they succeed and are a waste of money...buy new a d don't worry about it for another 20 years)

The carb rebuild tutorial by Nessism and many others is quite comprehensive and thorough, and while daunting at first, they're quite easy to rebuild. Just be organized and thorough. Once you've done it, you'll be amazed at how easy it will be to get the bike to perform as it should.

There are no shortcuts brother. They end up being the long way around. And motorbikes are a lot like airplanes. When something fails, it's generally painful, and possibly fatal. If ya need some help, shoot me a PM, I'll pass ya my number and can talk you through as much as I can. Anything to help.

And to answer your question:
I absolutely LOVE my ZRX. Its everything I love about GSes, but better brakes, suspension and rubber. Oh, and a wee bit more power helps ;) Like a good friends brother used to tell him: you don't need 100+ horsepower to have fun on a bike......but it helps. :D
 
Do you have access to a decent compressor?

So far my first tear down, clean, and rebuild per the tutorial (without compressed air) is holding up ok, but I would have felt better with the higher psi that my new compressor is putting out.

I found cleaning the carbs on my 650GD that canned air worked ok, and carb cleaner was slightly better, but I just wanted more oomph in the stream to really clean out the small passages in the carbs.
 
As several have said, the jets won't make fuel pour out of the carb. It's the fuel level system that you need to check

1) You should check to make sure the floats are good. One or more of them may be cracked or saturated and no longer "float" in gasoline.

2) Check the fuel needle valve assembly. Look for scoring or crud on the pointy tip (top) of the needle. Check the little spring plunger on the bottom of the needle (where it contacts the float).

3) Pull the body (seat) of the fuel valve and check the o-ring. Be sure to look for a little filter below the valve seat if your carb has one and make sure it is installed properly when reinstalling the valve seat.

4) Reassemble everything and check the float height per the book.

5) Hook up gas to the carbs and verify one by one that the fuel flow shuts off when you lift the float. If you need more than the lightest pressure on the float, the valve pin or the valve seat is either dirty or damaged.
 
Understood. Thanks guys. I adjusted the floats to spec when I replaced the pilot jets ... so I guess I made a connection in my head .... wouldnt be the first time I was wrong :)

So all that aside, I got my O rings in the mail(Thanks Rob!), and new main jets. (I am replacing the main jets due to possibility of a previous owner drilling them out)

Yes, I have a full shop .. due to building an airplane in my garage :rolleyes:

Air compressor and the like. Got the tutorial downloaded and ready to print, and got to get some berrymans solvent for the dip.

I forgot to order up the O rings for the intake boot/cylinder head joint ... going to get them too.

CafeKid ... I will hit you up if I need some help.

Jason
 
I am a newb to GS's but had the same problem with my 77 GS550 cleaned the carbs myself and still 4000-5000 rpm it lost it. when i hooked up a vacume sync. it read late valve timing or intake manfold leak. after inspection i found i have 4 shims needing replacing and when i get that finished ill let you know if that helped my rpm's or not.
 
Or your cam chain could be off by one tooth. Check valve timing while valve cover is off.
 
Similar Issues!

Similar Issues!

Fellas-

I had similar issues with my Yammie. I could rev all day in Neutral, but, as soon as I hit the road, I had a rev limit, which in-turn gave me a speed limit of 70mph. This was last summer, and my bike was my only means of transportation at the time. So, I had to drive behind semis so my slow speed would not be noticed.

Anyways, I found out that the problem was a combination of improperly tuned carbs (wrong jet sizes), cracked intake boots, diaphragms that were improperly seated, and aftermarket pod filters that were ill-fitting, causing air restriction to the carbs.

I worked on each one of these issues one at a time, changing the pods lastly. I had this thing running like a raped ape in a cage until the engine seized up on me due to a couple factors.

Timing should definitely be ruled out as a factor. If your marks match up, that's one less thing you gotta worry about. Checking your valve clearances in another biggie!

My Yammie and GS will be my wintertime projects keeping me busy. Thank God for that, as my girlfriend and I just broke up.

Keep us posted.
 
Or your cam chain could be off by one tooth. Check valve timing while valve cover is off.


So if the timing is off a tooth ... it will start and idle perfectly?? And run out to around 5000 rpm perfectly??

Funny how I hear these things wont break down and just keep on running. Which is a good thing most of the time .. but leads to abuse and/or lack of maintenance ... which I think is what I am dealing with on this little 550. So many little things .. :o

It is 30 yrs old too ...
 
I'd check the cam timing just to be sure, but in my experience I've never had the timing off a tooth and have it idle worth crap. It sounded bloody horrible.
 
the exhaust is ... original, and has pin-hole leaks here and there .... I sure replacement wouldnt hurt ... but still think my carb slides arent coming up ... and a complete rebuild is in order ..
 
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