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GS650 - can't go faster than 50mph - what gives?

  • Thread starter Thread starter Fenixgoon
  • Start date Start date
F

Fenixgoon

Guest
Took my bike out today over to my brother's house after getting it running (i still need to carb sync, i know i know :( :( :() and while I was riding I couldn't go faster than about 50-55mph even with full throttle (though I do need to play with the cable some). If I clutched my revs would go through the roof unless I made sure to have the throttle in the right position. I thought maybe it was maybe the brake pads being too close and rubbing the discs, but the discs were only moderately warm - sensible given the amount of braking I did.

Battery is new. Plugs are new. Carbs are cleaned (but not yet synced). Air screws are on the farther side of out than they are in, but they gave a nice startup the other day. Any ideas? :eek:
 
On my 650g I went 2.5 turns from lightly seated - what are your's at?
 
Could be anything, one GS1000 I bought would only do 50 on a long downgrade, barely ran on level ground. Had a heck of a time riding it home, all on backroads which I did not know. Checked everything, and a lot was wrong, ignition timing, valve timing, etc. I noticed even with a 4-1 and stock jets it was really rich, and really quiet too? WTF? The main culprit was inside the exhaust collector, someone had stuffed a huge wad of steel wool, almost completely blocking the airflow through the pipe. Just check everything out, you will find the problems.

Most of the bikes and cars I have had that were severely down on power had some form of blockage or restriction in the exhaust, you might want to start there.
 
lilbilly said:
On my 650g I went 2.5 turns from lightly seated - what are your's at?
Click to expand...

probably really far out (i still have no idea what lightly seated means. is it when the screw first contacts the bottom of the carb?)

the heads of my idle screws are just below where the threading starts on the inside of the carb body. i imagine that means i am running quite rich, but it was giving me much better starting than before.

as far as exhaust blockages - there are none that i know of. i will definitely check it out when i get back home.

for the ignition timing - it's supposed to be preset and non-adjustable on the GS650. do i still need to check that out?

my airbox is on though it isn't fully sealed because the retainer clip was busted. whoever had it before me drilled some holes in the box and held it together with zip ties, so that's how i currently have it. i cleaned out my air filter using engine oil. apparently it still had a good bit of oil soaked in it though when I put it back in :\

and yeah, it's real fun on the backroads. it's even better when you have to go on the highways where the speed limit is 55. luckily i had a good tailwind and a few hills to help me :rolleyes:
 
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Fenixgoon said:
and yeah, it's real fun on the backroads. it's even better when you have to go on the highways where the speed limit is 55. luckily i had a good tailwind and a few hills to help me :rolleyes:
Click to expand...

I would not be riding that thing any more than is necessary to trouble shoot, engine parts are expensive as are hospital stays.
 
tkent02 said:
I would not be riding that thing any more than is necessary to trouble shoot, engine parts are expensive as are hospital stays.
Click to expand...

unfortunately the only way to find this out was to find out the hard way :( all the roads around my house are 40mph, so I would have never hit the 55 "barrier"
 
the air filter shouldn't be overly oiled. I used a couple tablespoons on mine and put it in a plastic sandwhich bag and squeezed it around to spread out the oil. possibly not getting enough air of course getting your carbs synched up should help to.
 
I would re clean the filter and use filter oil. That could be part of your problem - running way to rich
 
Engine oil is fine for the filter but you don't want very much; blot out the excess oil using paper towel. Another thing is that bike bike won't run right if the exhaust and/or the airbox system is modified unless the carb jetting is changed.
 
Nessism said:
Engine oil is fine for the filter but you don't want very much; blot out the excess oil using paper towel. Another thing is that bike bike won't run right if the exhaust and/or the airbox system is modified unless the carb jetting is changed.
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yeah i'm gonna clean out the filter shortly. I know for sure that I had *way* too much oil still soaked in on it.
 
Address your airbox condition. Not being sealed properly will make the bike run poorly.

Mine had a nice size hole I plugged up with some JB Weld......:eek:

It works great !!
 
Larry D said:
Address your airbox condition. Not being sealed properly will make the bike run poorly.

Mine had a nice size hole I plugged up with some JB Weld......:eek:

It works great !!
Click to expand...

alright i'll give that a shot. i did clean out the excess oil from the filter and set the air screws 2.5 turns out from "lightly seated" but apparently that did not help.

valve clearances are on the tight side of things - 0.04 - 0.05mm, but within spec.

i got home ok, though not before running out of gas <1 mile from my house :o trip total comes out to roughly 10mpg :eek:

is there a good way to test the coils, check the timing (despite clymer saying it's not adjustable), and do a compression check? i may end up putting it on a truck and taking it down to a guy i know (he specializes in harleys, but he had some old and new yamahas in his shop as well)
 
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I think I have 2 extra metal clips for the airbox cover if you want them. I ordered them and lost them, then re-ordered some new ones and after installing, unlost (found) the lost ones. :o Let me know if you want them and I'll check to see where they're at - I may have re-lost them.
 
Sounds like you are running on 2 cylinders only. Maybe the coil connections got bumped off or a wire is loose. check the coil connections. Use a wet paper towel on the exhaust pipes when you FIRST start it to see which ones are cold, chances are you will find two are not running.

The pipes are around 1000 degrees when hot so be careful and only do this on an overnight cold bike,

An inductive timing light is great for quickly verifying you have spark. Black wet plugs are another indicator.

If by the rare chance the ignitor or pickup coils are bad (highly unlikely) I can help you out with one as I have a few lying around.
 
well, I cleaned off the connectors to the ignition coils. I guess they had dielectric grease on them or something? It was pretty nasty looking, kinda powdery/gunky. I also sanded down the leads on the coils to expose some fresh metal.

I tried taking pictures of my spark plugs, but it didn't work out too well, so here's the best description I can do by words:

Plug1: light, off-white colored coating on top of some black stuff (presumably carbon buildup?)

Plug2: virtually pristine. only a minor amount of carbon buildup

Plug3: much stronger white coating than plug1

Plug4: almost pristine, minor carbon buildup

Finally, and this is probably the dumbest thing of all.. I want to check to make sure I have the right coil connectors going to the right plugs.


Left side of bike
Right side "connected"
Come to think of it, I should have taken the same picture of the left as I had of the right, but they're wired the same. The outermost high tension lead for the spark plug goes to the outermost cylinder
Thanks again, everyone!
 
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well i found out cylinders 2 and 4 are not working properly - the exhaust pipes are cold (well, ambient temp) once the engine is running.

what kind of things should i be checking now?
 
I think your last note indicates the problem. The coils are supposed to fire 1&4 and 2&3 together. If you have 1&2 and 3&4 on the same coils, you're only firing on two cylinders. Switch the wires for 2&4.
 
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