mikuni carby problems

[troopy94]

Ive fitted a mikuni 2 barrell carby to my g13a motor and its started to play up a bit lately.The carby is off a early model mitsubishi colt and previously it was running perfectly on the zook but now it seems when in cruising down the road at around 90kph and then put my foot down the car starts to missfire and surge.Ive tried changing the timing without any change so them i stripped the carb and cleaned the jets and that made no difference aswell.The secondries are opening fully and working properly so i removed the vacume line to the actuator for the secondries and it improved and stopped the missfire but the motor was down on power.Im thinking now that it could be a fuel starvation issue or if anyone has any other suggestion it would be most appreciated

[dank]

Mechanical fuel pump on its way out.

This happened to me. You'd give it some stick and a flogged out diaphragm in the pump can't keep up with the higher fuel demands. It was a frustrating thing to troubleshoot as it was the last thing I thought of. I thought it was carby issues but it was definitely the fuel pump. I ended up running an electric low pressure pump for a few weeks as I was going to rebuild it anyway. This isn't recommended though as a flogged diaphragm will allow fuel to mix with the oil in the head if you don't bypass the pump and this will most likely screw your engine.

Almost 100% this is it. I reckon every zook owner with an original g13 should be checking their fuel pumps or replacing them around now, the engine are getting old, anywhere between 10 and 23 years old now.

From talk on this board its not a very expensive part to replace. If you haven't done so for ages go replace the fuel pump, water pump, thermostat and fuel filters as part of your next service, it'll save headaches down the track.

[troopy94]

Thanks for that I was thinking it could be a blockage in the fuel line restricting flow or a dodgey fuel pump.I replaced the pump around 6 months ago with another i had that looked new but it i think you are right so ill put an electric on there and see how it goes

[dank]

Mate I'd defintely stick with the stock mechanical pump. Don't bother screwing around with the electric pump. As I said it was only a temporary setup on mine for a few weeks before the rebuild.

You will pay probably around 50-70 bucks for an electric pump and a mechanical fuel pump is probably not much more. If your pump diaphragm is broken it will be leaching raw fuel into the head....a bad combo mate, even if you whack on an electric pump. Keep it stock.

[jonno_racing]

new fuel pump is around 50 i think.. i have 2 spairs for some reason! i keep them in my tool box.. although they are now irelevnt due to efi.

[troopy94]

Thanks guys I plan on keeping the standard pump i just wanted to try the electric pump to try and trouble shoot the problem.I fitted the electric and it made a little difference and will now rev to 4200 before it starts to missfire.I checked the flow of the stock pump before removing it and it looked to be flowing quite well.I recently replaced the leads and plugs aswell as the dizzy cap when it first started to play up.