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GS550ES won't rev out

  • Thread starter Thread starter p_s
  • Start date Start date
P

p_s

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300 miles on new rings. I had the cylinder measured and honed, but not bored. It had only .001"/.025 mm of wear on the bore.

155-160 psi hot compression on all 4.

Carbs adjusted and synced 5 miles ago. Valves adjusted to the tighter side of the spec 300 miles ago, but I can still hear them a little bit.

It runs as it should up to 6k or 7k and then it doesn't have the sudden jolt of power it should. It'll grudgingly hit redline in 1 and 2 and almost in 3. Top speed is about 80 mph in gears 3-6. It doesn't stutter or bog, it just lacks power.

I tried putting on the choke at those speeds and nothing happened. (I'm not sure the choke would do much anyways at WOT.) I pulled the air cleaner and it's worse.

Everything is stock. I swapped ignitors in case it was a timing advancer issue and it ran the same.

The plugs look good but I didn't do a plug chop.

The engine has done the same thing before when I used an EMGO air filter instead of the Suzuki one and another time when one of the airbox tubes was not snug. This time I have no idea what I could be. I guess an air leak somewhere?

I also cleaned the carbs in August and it was running fine then--I ran it to 105 mph. (Then I rebuilt the engine because the engine I was running had a bottom-end problem and I had another engine with a top-end problem.) The intake o-rings were new in August and inspected 300 miles ago.
 
hampshirehog said:
Just a quick thought - you could have timed the top end a tooth out when you did the rebuild?
Click to expand...
I took a real good look at that when I put it together but I guess that's possible. I don't know what else to do so I guess I'll tear down the carbs and intake rubber, and then look at the valves and timing if that doesn't sort it.

The airbox drain and crankcase breather hoses may be original, so I'll take a look at them for cracks, too.
 
I was thinking cam timing too... had a similar problem when I swapped in the yoshimura cams...
 
If the cams check out fine it sounds like your running too lean! if it only happens when a air filter is changed for a higher flowing one it is leaning out your mix.

Do plug chops it's the only to know for sure what and where the problem is.

Stick with only one type of filter when doing the chops and adjust your mix screws to see if it improves.

Hope this helps.
 
Yup, cams out a tooth. I had set it very carefully using the spark mark instead of the TDC mark. Oops. So that's what I've been fixing the last 3 hours. (Maybe maintenance would be easier with an older bigger engine!)

I'm glad it was that obvious though.
 
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