rumpfy
12-07-2013, 04:43 PM
In my post about the cannister rebuild, (which occurred at the same time I renewed the BVV), I found later that the rebuild caused/exacerbated a flooding problem. On a cold start the TP started like a new car; BUT after driving far enough to get the car fully warmed up, and then leaving it for say half an hour or longer, it flooded and was VERY hard to start.
The problem was diagnosed as a build up of fuel vapour pressure in the fuel tank and coupling through the cannister to the top of the fuel bowl via the BVV. This pressure would force the fuel up to the low speed running jet, and cause the motor to flood. To test this theory, when I would stop for a time, I unscrewed the fuel filler cap to release the build up of vapour pressure. This always worked.
The problem was that the cannister was able to couple vapour pressure from the tank to the carby outlet.
I tested this by connecting a water manometer to the carby port, and by blowing in to the tank port, I could raise the pressure at the carby port to around 15 mm of water. I rekoned that the pressure needed to flood the motor was probably around 10 mm of petrol. 15 mm of water pressure will support a column of petrol about 22 mm.
I diss-assembled the cannister and made up a tube about 75 mm long. This tube was a piece of 25 mm electrical conduit. The inside was turned out to 22.5 mm at one end and this size fitted over the spigot inside the cannister.
After the mods, the test result showed by blowing into the tank port, the pressure in the carby port was only 3 mm of water (4.2 mm of petrol). This was a significant reduction over the standard cannister.
In the TR/TS models, there was a 2 way valve fitted in the fuel vapour line. I reckon that MITS found out after a few years of manufacturing experience that:
the fuel level in the bowl crept up due to wear and settling effects in the float valve, AND,
the cannister granules settled and compacted themselves and caused a higher level of petrol vapour feed through to the top of the fuel in the carby bowl.
To fix this situation, they just added the 2 way valve. I guess this valve has a initial pressure to overcome, and when the vapour starts to flow, the very small orifice in the valve allows the vapour flow to be VERY slow so that there is a small pressure build up in the cannister.
Anyway, after installing the modified cannister, there seems to be a very much reduced flooding. Although my nervousness on the problem is masking a sensible judgement, I'm sure the mods are good but I still think the fuel level is too high and to fix, will require the carby to be disamantled and more judicious bending of the float arm.
Just follow my posts and those of Coldamus. Together we did a fairly full examination of the beast and reckon it is now under control.
regards,
Rumpfy.
The problem was diagnosed as a build up of fuel vapour pressure in the fuel tank and coupling through the cannister to the top of the fuel bowl via the BVV. This pressure would force the fuel up to the low speed running jet, and cause the motor to flood. To test this theory, when I would stop for a time, I unscrewed the fuel filler cap to release the build up of vapour pressure. This always worked.
The problem was that the cannister was able to couple vapour pressure from the tank to the carby outlet.
I tested this by connecting a water manometer to the carby port, and by blowing in to the tank port, I could raise the pressure at the carby port to around 15 mm of water. I rekoned that the pressure needed to flood the motor was probably around 10 mm of petrol. 15 mm of water pressure will support a column of petrol about 22 mm.
I diss-assembled the cannister and made up a tube about 75 mm long. This tube was a piece of 25 mm electrical conduit. The inside was turned out to 22.5 mm at one end and this size fitted over the spigot inside the cannister.
After the mods, the test result showed by blowing into the tank port, the pressure in the carby port was only 3 mm of water (4.2 mm of petrol). This was a significant reduction over the standard cannister.
In the TR/TS models, there was a 2 way valve fitted in the fuel vapour line. I reckon that MITS found out after a few years of manufacturing experience that:
the fuel level in the bowl crept up due to wear and settling effects in the float valve, AND,
the cannister granules settled and compacted themselves and caused a higher level of petrol vapour feed through to the top of the fuel in the carby bowl.
To fix this situation, they just added the 2 way valve. I guess this valve has a initial pressure to overcome, and when the vapour starts to flow, the very small orifice in the valve allows the vapour flow to be VERY slow so that there is a small pressure build up in the cannister.
Anyway, after installing the modified cannister, there seems to be a very much reduced flooding. Although my nervousness on the problem is masking a sensible judgement, I'm sure the mods are good but I still think the fuel level is too high and to fix, will require the carby to be disamantled and more judicious bending of the float arm.
Just follow my posts and those of Coldamus. Together we did a fairly full examination of the beast and reckon it is now under control.
regards,
Rumpfy.