Hi folks,
I've got a real problem with my baby at the moment.. I'll try and paint an accurate picture..
Last week, I took it for a good drive up Mt Mee (QLD), filling it with VPower Racing (that 100 octane ethanol blend from Shell) before the drive. It ran fine on the way up, but whilst heading back I found a flat-spot during acceleration around 3000rpm. It would get there, choke a little, then keep revving as if nothing happened. The problem presented about 35kms after filling up.
The next day, it was worse. It would reach this 3k flat-spot, but refuse to rev any further. Odd.
The following day it got stranger still; with the throttle open fully, it would rev to 3000, hold there for a second or so, then fall back to idle, then back to 3k, and so on. This is with the accelerator on the floor, with no movement. It would rev up, down, up, down.
Now, after a few days without looking at it, it will not rev without operating the choke. Any attempt to use the throttle stalls the engine. It will, however, rev happily to 3kish just on choke. A loud induction hiss can be heard when trying to open the throttle, with or without the choke being open.
My first thought was the fuel, so have drained it completely and put 5ltrs of of BP Ultimate (98 ), which is what it normally drinks. I'm confident the Shell fuel is completely flushed, but the problem remains.
I've had a brief look at the carb (which was rebuilt about 250kms ago, and was perfect until this drive), and everything looks fine. I've swapped several components with the old (pot and piston, needle, jet assembly, float/needle, etc), but no change.
All card gaskets are new.. the only original ones being on the inlet manifold (but they appear fine). All rubber through the carb was renewed when it was kitted. It's a 1.5.
I can't figure out what the problem is. My hunch is it is starving for air. The induction hiss is quite loud even when opening the throttle slightly, and results in an immediate stalling effect.
Any ideas would be hugely appreciated.. Heelp!
