Wolf
25th January 2005, 14:13
Perhaps someone here can give me a fresh perspective on this problem:
When my LS400 started seriously acting up, I located a second-hand engine for the GSX250 I had been given (the bike was in great order except the chain had jumped the sprockets and locked up the engine, shearing three teeth from the front sprocket and seriously mangling the inside of the gearbox. As it was given to me to convert into an Electric Vehicle, I hadn't been concerned about the engine.)
The engine I located was a couple of years older than the original but it was pretty straighforward to put it into the frame and put on a new chain.
The bike started but ran like the proverbial haunted shit-house. I managed to limp into work and back a couple of times then it died on me a couple of minutes up the road and I couldn't even crash start it, had to push it home.
I thought it was carburettion and so I stripped and cleaned the carbs - several times. When I first put the bike back together it took 45 minutes and several blood sacrifices to Epona, Goddess of Motorcycles, to get the carb in. It now takes under 2 minutes and I could teach "Bloodless GSX250 carburettor maintenance" at University level.
Still couldn't get it to run on 2 cylinders 100% of the time and it still died after 2 minutes.
I bought a good second-hand carburettor and installed that and put some fuel and carb cleaner in the tank for good measure (dispite the fact that I had already taken the fuel tap out and checked that the filters were not clogged and that there was no water in the tank).
Still ran for only two minutes then would not start. Figured that - unless GSX carburettors are prone to that sort of failure - it was not likely that I'd have two sets of carbs with precisely the same problem.
After a while it occured to me that the fault might be in the electrics. Tried switching the plug leads over and switched the wires on the coils so that the right-hand coil was firing the left-hand cylinder and vice versa - this made absolutely no difference.
A friend suggested that sender unit for the CDI might be stuffed so I went back to the wrecker to get the original sender unit from my old engine and discovered that the sender plate and actuator looked totally different to the ones in the replacement engine.
The replacement engine had a centrifugal assembly on the actuator to adjust advance and retard, the original was a fixed actuator. (Seems advance and retard is handled by the electronics on the later model). Fortunately, when I unbolted this assembly the original part bolted straight on to the shaft.
Suddenly we had progress. The bike fired up and ran on both cylinders. Revved up and down really well and ran like the proverbial Bondi Tram...
For 2 minutes.
Had a friend follow me up the road and tried to jump start it when it died - we had the output of the car's alternator pouring into the bike and when I tried to turn it over it sounded like I was trying to start on a dead battery - scarcely could turn the starter over.
Thought that it still might have been fuel causing the problem - the GSX has a vaccuum hose off the carb that opens a valve on the side of the fuel tap so that petrol will flow. As I had replaced the hose I thought it might not be supplying enough suction to open the valve sufficiently (enought to run at low revs but not enough to replenish the fuel at full noise).
To rule this out, I tried running it in the "Prime" position which is a straight-through flow - still the same probelem.
It seems that the problem must be something that suddenly happened when I was heading to work - I had managed to limp to and from work twice, despite the fact that the centrifugal advance/retard was causing the engine to run ragged. That was using the original carbs and running on "Prime" (didn't have the vaccuum hose set up). So that would suggest that the problem is not carburettion or fuel supply.
The dying after 2 minutes first occurred before I put the proper sender plate and actuator in the machine and had not been improved or worsened by that.
When it is cold I get good healthy sparks, the engine turns over well and it runs nicely. It goes great for about 2 minutes and then if I throttle back slightly the revs drop to zero, no about of playing with the throttle helps - then it won't turn over, will not fire even if crash started down a long, steep hill and is basically dead until it cools down again - whereupon it will start.
Any idea what could be acting up to cause that behaviour?
When my LS400 started seriously acting up, I located a second-hand engine for the GSX250 I had been given (the bike was in great order except the chain had jumped the sprockets and locked up the engine, shearing three teeth from the front sprocket and seriously mangling the inside of the gearbox. As it was given to me to convert into an Electric Vehicle, I hadn't been concerned about the engine.)
The engine I located was a couple of years older than the original but it was pretty straighforward to put it into the frame and put on a new chain.
The bike started but ran like the proverbial haunted shit-house. I managed to limp into work and back a couple of times then it died on me a couple of minutes up the road and I couldn't even crash start it, had to push it home.
I thought it was carburettion and so I stripped and cleaned the carbs - several times. When I first put the bike back together it took 45 minutes and several blood sacrifices to Epona, Goddess of Motorcycles, to get the carb in. It now takes under 2 minutes and I could teach "Bloodless GSX250 carburettor maintenance" at University level.
Still couldn't get it to run on 2 cylinders 100% of the time and it still died after 2 minutes.
I bought a good second-hand carburettor and installed that and put some fuel and carb cleaner in the tank for good measure (dispite the fact that I had already taken the fuel tap out and checked that the filters were not clogged and that there was no water in the tank).
Still ran for only two minutes then would not start. Figured that - unless GSX carburettors are prone to that sort of failure - it was not likely that I'd have two sets of carbs with precisely the same problem.
After a while it occured to me that the fault might be in the electrics. Tried switching the plug leads over and switched the wires on the coils so that the right-hand coil was firing the left-hand cylinder and vice versa - this made absolutely no difference.
A friend suggested that sender unit for the CDI might be stuffed so I went back to the wrecker to get the original sender unit from my old engine and discovered that the sender plate and actuator looked totally different to the ones in the replacement engine.
The replacement engine had a centrifugal assembly on the actuator to adjust advance and retard, the original was a fixed actuator. (Seems advance and retard is handled by the electronics on the later model). Fortunately, when I unbolted this assembly the original part bolted straight on to the shaft.
Suddenly we had progress. The bike fired up and ran on both cylinders. Revved up and down really well and ran like the proverbial Bondi Tram...
For 2 minutes.
Had a friend follow me up the road and tried to jump start it when it died - we had the output of the car's alternator pouring into the bike and when I tried to turn it over it sounded like I was trying to start on a dead battery - scarcely could turn the starter over.
Thought that it still might have been fuel causing the problem - the GSX has a vaccuum hose off the carb that opens a valve on the side of the fuel tap so that petrol will flow. As I had replaced the hose I thought it might not be supplying enough suction to open the valve sufficiently (enought to run at low revs but not enough to replenish the fuel at full noise).
To rule this out, I tried running it in the "Prime" position which is a straight-through flow - still the same probelem.
It seems that the problem must be something that suddenly happened when I was heading to work - I had managed to limp to and from work twice, despite the fact that the centrifugal advance/retard was causing the engine to run ragged. That was using the original carbs and running on "Prime" (didn't have the vaccuum hose set up). So that would suggest that the problem is not carburettion or fuel supply.
The dying after 2 minutes first occurred before I put the proper sender plate and actuator in the machine and had not been improved or worsened by that.
When it is cold I get good healthy sparks, the engine turns over well and it runs nicely. It goes great for about 2 minutes and then if I throttle back slightly the revs drop to zero, no about of playing with the throttle helps - then it won't turn over, will not fire even if crash started down a long, steep hill and is basically dead until it cools down again - whereupon it will start.
Any idea what could be acting up to cause that behaviour?