Tuning Dual Su4 Carbs

[finch661]

i am at the stage of tuning my 1275 twin carb (SU HS4) engine. i know the first stage is to check the valve clearances, then check the ignition timing. i need to get the idle time down to about 800-900 rpm, but i am finding that i cant the engine down to that speed without it stalling, even with the engine is up to normal temp. this is an important stage, hence i dont want to roughly set the engine. any advice for me (this is the first time i have tinkered with a dual carb system)

thanks

[Dan]

I have to say I think you’re going to have a lot of trouble getting a 1275 to idle at 800 on a pair of HS4s, they’re a bit big really. What’s the rest of the engine spec like?

Make sure the float level is correct, the float bowl angle is correct and that the jets are balanced. You may need a pair of custom needles for this.