prutser

How is the float height of the carbs? I ve had similar issues with my 1981 gsx750, having a weak spot around 3-4k. Found out one carb was having a low fuel level. Running a 4-1 exhaust with stock airbox and stock jetting by the way. Once warmed up it pulls smoothly through all the rev range.

Which gsx750 are we talking about? The first generation 16valves (ET/EZ/EX models, built till '81 or '82 i guess) has mechanical advance at higher Rpms. At least my 81 EX does. If i recall correctly, the '82 550m has "full electronic ignition" meaning it has electronic advance, correct me if im wrong. Mixing mechanical with electronic advance will advance way too much probably? The 2nd gen 16valves (ES, EF, 1983 and up) moved on to fully electronic as well, i assume. But, to confuse all of the above even more, the first gen 16valves were still called GS in the USA, but GSX in pretty much anywhere else in the world.

Well, in the end I decided to not take the head off (yet) but try cleaning it first. Instead, gave it another blast with brake cleaner first, trying to get the sticky oil out of there, so any dirt would be blown out easier with compressed air. Then another round with carb cleaner. (People say it works on carbon deposit as well.) Eventually, valves didn't sound crunchy anymore! Funny thing is: once I poured some new oil down the plug hole, some crunchiness came back here and there. I suspect the 'crunchy' sound might have been some oil being squeezed between the valve and seats. (?) But whatever: after having adjusted the valve clearance, mounted the whole lump, carbs, exhaust, etc back together and gave it a shot. It fired up straight away at first try. Immediately running smooth on all four cylinders. Sound is comforting. (The previous engine use the have a light, mysterious, erratic, 'tinging' sound that used to come and go, which I never managed to trace, but which just might have been an unhappy big-end bearing ?) Have ridden it a couple of dozen of km's by now, runs smooth, can idle below a 1000 rpm, so far so good. Haven't rev'd it above 5000k rpm yet, though. Gave the outside a good clean today, to keep an eye on any oil seeping out of old gaskets and O-rings in the coming time. No major oil weepings so far.

Anybody has a clue what could have caused this residue in the carb? It came of a recently running bike, its in number 3, so i dont think it is related with the vacuum-hose (which is on 2). Fuel bowl is clean inside, other carb bodies clean as well. It is white/greenish brittle powderish stuff when removed with finger, tho some of it is stubborn sticky gunk. Looks like something has been trapped behind the butterfly, with the bike on sidestand (residue is towards the left side). Maybe float needle not seating well, so last bit of fuel in the line after the vacuum petcock drains here, slowly overnight? However it doesnt look like regular petrol residue to me. Or is it? I always use E5 petrol, never E10. Or simple oxidation from rain infiltration?

I was afraid of these answers, but it does make sense. As matter of fact I happen to have a third lump laying around, with a thrashed head, but a decent lower end. If the head of the con-rod ejector is still usable, these two could make one solid engine after a proper reassembly. I was hoping to cut some corners and get back on the road in little time, and then have a nice relaxed winter project with the two cripples. Any other specific wear-points to check while the cams are out? I always take a measurement of the camchain stretch. The chain guides look a bit worn in already.

Long story short: the katana-styled make-shift all-road GSX750E ejected a con-rod through the crank case recently, so I bought a similar replacement engine of a local bike shop. It had been laying dry on the shelf for god only knows how many years, so the first thing to do was to clean the outside of the head, then pour a bit of oil in the plug holes and over the cams and valves, and then crank it by hand. It turned over alright, without any noticeable hard or rough spots, but it made a rather "crunchy" noise every now and then, which seemed to come from the valves. So to rule things out I lifted the cam-shafts to move pistons and valves independently: - as expected the pistons go up and down smooth like butter, no weird noises at all. - some of the valves make a "crunchy" sound sometimes when seating again after being compressed. Of course, during the storage years some debris could have easily have gotten in there, that now gets trapped under the valves. Or could it just be some carbon deposits that got loosened up? I tried blowing whatever could be in there out of the cylinders by pushing down individual valves and blowing compressed air down the plug hole. Unfortunately, stuff is sticky in there because of the well-intended dose of oil. I'm thinking to re-install the cams to hold the valves open, and have a blast with brake cleaner or some other solvent and more compressed air. Or do people have other smart ideas? Here is a picture of the cute kat in merrier times, just for the sake of it.