turbo 1098 first drive - need help with carb
Turbo Mini Forums

Hi All, rebuilt 1098 in '65 Minor, return style fuel system with boost ref'd reg verified at 3.5psi static and rising 1 for 1 with boost, reference taken directly from compressor outlet. HS4 carb and intake off Morris 1300 - fuel bowl vent sees same boost signal as regulator, AAA and ABY needles tried with both yellow and green springs. No restrictor at mouth of carb like the metro turbo carb, instead relying on hobbs switch and fogger nozzle in intake delivering extra fuel 2psi and up. Tuning with Innovate LC1 wideband so have a good idea what it's doing.

My issue is that it goes lean WAY before it gets anywhere near boost - light cruise is at 20 inches of vacuum where it runs perfectly, but it will start to lean out under very light accel at 10 inches of vacuum, and gets steadily worse until by atmospheric it has pretty much fallen over - if i push it to boost and it gets the extra fuel from the fogger it goes well, winds out nicely, no detonation, with AFR about 11.5 to 1 - nothing earth shattering though as I'm only using 6 psi at this stage.

I realised that the carb would need compensation at positive pressure if I ran without a restrictor plate, but these issues while considerable vacuum is present have me stumped. The needles I have tried are way fatter than standard, and some of that's quite early on from stations 3-5 too. The problem is less severe the higher rated dashpot spring I fit. Am I missing something that needs done to the older HS carbs?

Cheers, Andrew

id get a sacrificial needle ,and file a load off it up just below tickover point and see if you can make it go rich ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

i found the hif polishing post and thought it would be of help that's if you still need it lol

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=159683

Edited by Turbo This.. on 4th Nov, 2012.

AAA and ABY are suitable for 50ish bhp 998s, your requirements are quite different.

Even on a 998 running 6psi of boost I used the metro turbo needle (BDD, but this won't fit your carb, as I assume you are using a 1.5 SU, going by the needles).

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

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