power issue worsens with time/miles

[the2ndgeorge]

I believe crankcase blowback sludge in air box fouled my carbs when bike took a spill, creating rough idle (theory).
I sprayed carb cleaner into carbs while engine running (air box off), cleaned out the bottom of the bowls, and inspected the slides for operation.
Rough idle kinda went away, but now I have a lack of power issue that worsens as I ride.
It starts out being difficult to maintain 65 mph, then after ~20 miles its impossible to go faster than 55mph, then after 10 more miles it becomes impossible to go faster then 55 mph, gradually, as more time passes I'm barely able to go 45, and it will stall if I slow down to idle, at a light, for example.

The bike was running great before I took the spill. There was maybe <~50 ml of oily sludge in the air box.

I noticed that the fuel doesn't seem to flow consistently from the tank to the carbs (noticeable presence of air in the line and filter), although when the tank is off, gas flows fine through the line.

Also the diaphragms appear slightly wilted, but this is my first bike so my basis of comparison is limited.

91 gsf400, 30,000 miles.

any ideas?

[bsodders]

      Pull over when it starts to give an issue, open the gas cap and listen for pressure relief.  If you hear a hiss and then the trouble goes away for a bit, the tank vent is clogged.  It could have been pinched somehow when you dropped it preventing fuel from flowing properly.  The carb cleaner is a bad idea, it is detrimental to the diaphragms and o-rings which will cause unending headaches in the future.  You really want to avoid carb cleaner on any of the rubber parts in that carb.  Either way, the tank vent is a cheap fix, make sure it isn't pinched then clear it with compressed air. 

I'd probably start there.

[bsodders]

        Post a pic of the diaphragms, be gentle 20$ each and watch the little orings under the carb cap.  Also as a second thought, check the choke/enrichener cable for proper play and check the mechanism on the carb, it's easy to bend the shaft.

[the2ndgeorge]

So I went from power issues to no combustion at all. I have had tank issues in the past, (water in tank, faulty petcock passing gas thru vac line) but im pretty sure everything is in working order there. I fully drained the tank and filled up with name brand gas. I checked the coils for resistance and they checked out in spec. I tweaked the float levels to spec. Looked around for loose or corroded electrical connections. Finally, I reluctantly took my bike to a shop. So the shop discovered 50 psi compression in all 4 cylinders, and suspects the valves due to the fact the psi did not go up when a little bit of oil was added in each cylinder. This kinda makes sense to me. In the manual, valves out of adjustment is the 1st thing listed under possible causes of lacking power. Maybe my gradual loss of power, over the course of a ride, stemmed from thermal expansion, causing operational tolerances to become even sloppier, yielding poorer compression, therefore lower power. Additionally, when I was in Indiana, ~4500 miles ago, the first thing my cousin, a long-time rider, asked when he heard my bike was how long ago were my valves adjusted. Anyone else experience this?

[rider123]

I experienced something like that on an old '84 GS750EF that I bought that sat for years by the previous owner. Because it sat for so long some of the valve springs were tired and not completely sealing when on the compression stroke. This sort of thing will show up with a leak down test. No biggie tore it apart in the winter, cleaned up the head and piston crowns, popped in new valve springs and seals and put her back together and she ran like new! Was a fun winter project, but would have been a bummer in the summer. I guess I could have done the whole project in a day or two if I was hurrying. Thats why it's not a good idea to leave a bike or any vehicle parked for a long time even if you've drained the tank of fuel. Some of the valve springs will be compressed when the engine stops and if you leave it long enough they will tire from the constant compression. Hell even in the winter time I run the bike every 2 weeks or so for 10 mins to charge the battery and keep the juices flowing. Come spring she just starts up and goes as she's been semi-running over the winter.

However ALL the cylinders not sealing may be a serious problem, like a cam gone bad or something. Generally when the valves get out of adjustment or springs are tired it will be intermittent cylinder/valves that will go(ie 1 and 3 are bad). Since you have ALL the cylinders go tits up, there no question that top end has to come off. If you're lucky due to the amount of valves(16) you may have just fluked out and have at least one of the 4 valves on each cylinder just so out of wack that all they need is an adjustment. But if it's the cams gone bad, I would use that as an excuse to pop in the GSXR Cams from Holeshot, an extra 15 horsepower couldn't hurt. You will have to re-jet but it's a good excuse as any. It could be that the valve springs are tired and not sealing the valves.

However usually with a bad cam the valves aren't opening enough, not not sealing. You may be the flukiest guy in the world and beat all the odds and at least one valve on each cylinder is not sealing due to mal adjustment. If so you're fine. A quick adjustment and some new gaskets and you're off. Only way to find out I'm afraid is taking that top end off.

Whats the milage on the bike? Are you the first owner? If not, did the person you buy from appear to be a poser instead of biker?(ie drives twice a year then parks it) Do you know when the last valve adjustment was done? In the manual it says every 12K kms but thats a little much as long as it was within 15K is ok.

It may seems a bit strange but sometimes buying an old bike with very little miles on it is not such a good deal as one might think. Yeah some parts are un-used. But some will be extra screwy due to the long periods of inactivity. Imagine a guy rides his bike up until just before an oil change then it sits for 3 years before he putts around on it again. Even if he drains the float bowls and the tank, that contaminated oil will sit in the bike with the acids eating at internal seals and gunking up the inside with oil sludge, clogging oil journals, etc. Not to mention having the valve springs on some cylinders compressed if he doesn't manually crank the engine every 4 months or so. For long term storage(>year) you have to do quite a bit of preperation. While newer bikes are tougher than old why take a chance?

The best bike to get is one that has low milage that is reasonable for the year of the bike. So say the bike you want to buy has 15K miles on it and it's 5 years old. You know it's been driven at least a few thousand miles a year and probably has had oil changes at least once a year or so and hasn't been parked and has had at least one valve adjustment and probably a new set of tires. Also it's has fresh gas through it as well and chances are it runs. That's going to be a better buy really than a guy who has the same bike with 3K on it and says "Well I bought it then never got to ride it". You know its been sitting there for years with god knows what kind of shit in the oil, not to mention what the gas and carbs would look like if he didn't drain the tank and float bowls. Plus it may have dead valve springs. Chances are the battery is dead and it won't start. Also he'll want more money than the bike thats been running and been taken care of properly. Which one is the better deal?

[bsodders]

     Nevermind all that..  50 psi is bad.    I will gladly walk you through a valve adjustment.  If after that you have no compression then you either have 4 bent/burnt/cracked valves or cracked rings in all cylinders, 4 bad pistons, or a really bad head gasket.  Either way, that is an unusual problem but don't give up yet, the b4 does not reveal it's secrets easiy.


|Brian

[the2ndgeorge]

So I did a compression test (cold engine) and here are the results:
Cylinder 1: 100 psi dry, @ 12.82v (key in off position); 210 psi w/ ~5 ml of oil added into cyl, 12.66v;
Cylinder 2: 45 psi dry, 12.77v; 180 psi wet, 12.60v;
Cylinder 3: 50 psi dry, 12.72v; 170 psi wet, 12.52v;
Cylinder 4: 85 psi dry, 12.69v; 150 psi wet, 12.46v;
I'm kinda doubting the shop that did the compression test actually did the oil in cylinders check to differentiate between bad rings vs bad valves. (in hindsight, they didn't voluntarily say that they did the compression test wet as well, they just said yes, when I asked if they did it)

other notes:
at 23788 mi, I drained only 1300 ml of oil from engine (cold), then filled up w/ 2300 ml.
at 26226 mi, again, I drained only 1300 ml from engine (this time warm), then filled up w/ 2300 ml.
I found it odd that the engine only had 1300 ml both times that I drained the oil. (I did not keep record of the mileage of the oil change preceding the 23788 oil change.) Maybe there is a maximum burn threshold for the engine?? Assuming the oil consumption is linear, my burn rate was 390 ml per 1000 mi. From 26226 mi to engine death, I made an effort to add 200 ml per 500 miles, but in actuality ended up adding in increments of 150 or 300 ml (always correlating with mileage, I just wasn't always in a good place to stop at the 500 mi increments). At 23788 miles, I shoved off from Philadelphia. I made it up to Vancouver, BC, then down to LA and the shit hit the fan while riding out to Vegas. The engine was quite loaded at times: me, all my luggage + the Continental Divide, other climbs to 8000 ft etc...

I did a compression test (warm engine) 3 mos before the trip and these were the results:
cyl 1: 145 psi dry @ 12.69v; 215 psi wet 12.60v;
cyl 2: 155 psi dry @ 12.73v; 260* psi wet 12.71v;
cyl 3: 150 psi dry @ 12.83v; 205 psi wet 12.84v;
cyl 4: 160 psi dry @ 12.82v; 205 psi wet 12.80v;

*i think the oil, ~5 ml, went into cyl 2 most effectively "nothing but net". Oil was added via syringe, but the syringe was too wide to fit down into the spark plug hole, and i didn't have a hose small enough to plumb it directly into each cylinder, so I just aimed and squirted. In the other cylinders, the oil went into the plug hole, but also pooled in the general cavity. Cylinder 2 went straight in the hole.  (with this latest C-test, I used a hose to pipe the oil directly into each cylinder.)

also to note, I do have a spare engine already, I'd just like to learn what went wrong with this one.