SRX stumbles at 7000 rpm

MURDER YAMAHA

MURDER YAMAHA

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Ok, having an issue with my sled, first time I have ever run it. Plug was wet on mag side, but did have spark. wouldn’t get past 7000 rpm, seem to have a ton of torque down low though. Idles and revs well.

It’s low miles(2100).
Bone stock with power inc pipes and silencer.
Jetting is 151.3/150/150
Here what I have confirmed so far.

1. Checked wiring harness for rub through.
2. Fully rebuilt carbs, new o rings everywhere, jets clean, floats good
3. Checked head gaskets, appear not to be leaking
4. Checked crank phase, good.
5. All reeds are new

Any ideas?
 

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Power valves adjusted correctly, installed correct way, and verified operation of servo? Also clutches seem to be operating smoothly, stock clutch setup?did you clean the top of pto piston?
 
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Try spraying some carb cleaner or starting fluid behind the primary when it is running and see if the motor changes. That's a quick check for the crank seal since it looks to me like the pto is a little leaner than the other 2 but I am not an expert on piston wash. Easy check. If the power valves are all good it could also be a clutching issue. My experience with valve issues is it will rev to over 8000 and then drop back down to 7500 give or take. My experience with clutching when it bogs like that is a problem in the secondary. Not saying any of that is for sure but just my experience. What's the compression look like? I saw on the other thread (which by the way that is a good looking sled) that the motor was locked up so maybe its possible the rings are stuck? Also was this done on the stand or actually riding it?
 
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Power valves are installed correctly and spotless.
Not sure if servo motor works, but I have a tool to test them, will try tomorrow.
I have not cleaned any pistons, or head. Mag is real dark, center is medium color, PTO is really light colored.
Sled has never made I’d past around 7000 rpm riding it.
Compression is 121 on all 3.
Motors was stuck for maybe a couple weeks. Was free before and after.
Both clutches setup as per Mr. Viper setup.
 
You can check servo operation just by taking the cover off the servo and working the choke to make it run below 900 rpms and it should turn and not studder.
 
My first check would be servo opening the valves also. Like Drew said, remove cover and then start sled. Open the choke so that the rpms drop below 900 and the servo should move. It should move smoothly and not be twitchy.
Sounds strange, but I've seen top rpm issues from mice building nests in the exhaust and creating blockage.
Restricted air intake from some kind of blockage will also cause it to not pull top rpms. Did previous owner put in new foam that is too dense?
"Top Hat" filters are clean? I know you said carbs have been gone through, but these get missed by some.
That one piston is leaner than I would like on my own sled. Is it jetted too lean on that one or not firing all the time (unburnt fuel "washing" it)? Trimming the spark plug wire back a bit and throwing a new cap on is quick and cheap.
 
OK, checked exhaust pipes and silencer, all clear there.
Disassembled carbs again, all is good there.
New head gaskets go in tonight even though they didn't appear to be leaking.
Will also check servo motor tonight, along with rust on flywheel.
Im thinking this sounds like it could be the culprit, as it must have had a lot of moisture from sitting on garage floor for a bit, to the point that it actually seized the motor temporarily.
So, must have been enough moisture to rust the flywheel pretty good as well I would think.
 
Another observation.
Noticed when I disconnected fuel lines from carbs, they just kept dumping fuel out.
Have never noticed that on any of my other sleds.
Is that normal ? Or is the fuel pump shot ?
 
Checked harness by CDI, all looks perfect.
Checked servo motor without it running using test plug, nothing happened, then I turned it by hand and tried again, It then would return to the same point on it's own when power was applied. I assume that's what is supposed to do?
Took recoil off, very minimal corrosion on flywheel. Is this enough to be a problem ?
 

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MURDER YAMAHA said:
Another observation.
Noticed when I disconnected fuel lines from carbs, they just kept dumping fuel out.
Have never noticed that on any of my other sleds.
Is that normal ? Or is the fuel pump shot ?
Click to expand...

Aside from residual fuel in the lines, a continuing streamof fuel does not leak from the lines of my SRX when I pulled the carbs.
High head pressure from a full tank level may produce enoughflow to start a syphon effect but I think the check valve in the pump shouldstop that from happening.
In other words, I don't think that's normal.


 
MURDER YAMAHA said:
Checked harness by CDI, all looks perfect.
Checked servo motor without it running using test plug, nothing happened, then I turned it by hand and tried again, It then would return to the same point on it's own when power was applied. I assume that's what is supposed to do?
Took recoil off, very minimal corrosion on flywheel. Is this enough to be a problem ?
Click to expand...

It returns to the home or closed position when started? I would rule it out for sure. Never used the test plug before so I wouldn't know how it works. I'd just idle it down and watch it, then run it on stand and do the same, but I've never been accused of being smart lol. Some people won't run them on the stand.
 
Head is off, pipes ect. so that is the only way I could test it. Just wasn't sure that's what was normal for testing it that way.
Seems to move and sound nice. I think its working. I am just going to keep throwing new parts at it until it works. lol.
New head gaskets are in, flywheel is 100% clean, just waiting for new stator.
Fuel pump concerns me, but must just be a check valve. Too much fuel from the pump really cant hurt anything, as the floats should only allow so much in anyways I would assume.
 
New stator? Did it test bad or sled was exhibiting some electrical issues?
When my stator went out on my viper it caused me to get a bog around 7000rpm and wouldn't pull any higher. This only happened when a lot of load was on it, like when the hand grip warmers were turned on (which wouldn't warm up either). Turn warmers off, no bog and pulled peak rpm, turned them back on and bog...
 
That's what mine is doing, although I didn't realize at the time, it could be electrical.
So did not get to try turning off all electrical to see if it improved.
My hand warmers really didn't get warm, but thumb warmer seemed to work.
 
Fuel shouldn't keep coming out the 3 carb lines. I would put money on a failed fuel pump diaphragm. Check the pulse line from the pump to the bottom end, should not have fuel or oil in it.
 
OK, easy enough to check, will do this evening.
But, would a failed fuel pump cause the bog at 7000 RPM and limit it from going any higher?
 
I don't know. Mine had low end bog as well when the fuel pump failed. I had a bog a few years ago, was the stator. But before I came to that conclusion, I went through just about everything else. Worth a read to help you troubleshoot Here's the thread on it https://totallyamaha.net/showthread.php/76280-bog-rub-through Also I should note, the bad stator passed the electrical test that the service manual had me do.
 
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Got the flywheel off, looked really clean except for one spot on inside
 

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