Choke/Carb question 1600

[ARowe84]

Hi all,

I’ve got a 1600 roadster. In regard to choke usage can somebody help me understand the following. Should pulling the choke just a little increase the idle without increasing mixture (ie without lowering the jets). Is this what’s called fast idle. Or does pulling the choke start increasing mixture right away.

I have used a carb sync at idle and then readjusted the dog bones to sync at 2000 rpm.

Thanks for clarifying,
Andy

[jrusso07]

There is a fast idle knob in the upper left hand side of the dash, by the headlamps. The choke knob is in the center dash. Not sure which one you are pulling...? The fast idle changes the throttle plate where the choke lowers the jet.

In general, If the carb jet is properly aligned in the seat, and the needle is positioned correctly, when you pull the choke, even a little, it should lower the jet and increases the mixture. Typically, this also causes the idle to increase. If not set up correctly you may get a different result. Make sure all the throttle and choke cables have the proper clearance and are not interfering with one another. Fast idle cable connects to the mechanism as the accelerator cable

Here's a great write up on the carbs in the Tech wiki on this site. There is a lot of good info on the carbs there ("Carbs-Fuel")https://www.311s.org/pmwiki-311/pmwiki. ... sNewSuTech

[ARowe84]

Thank you, I read the tech wiki article many times and it was helpful. We also have a mgb and a Bugeye sprite which have variations of SU carbs both of which do not use a wishbone design and increase idle without lowering the jets when you first pull the choke. Thanks for help with the wishbones. And I’ll continue to use the throttle hold cable to warm up without using the choke. The MGB does not have the throttle pull cable but the way those SUs are designed it’s unnecessary. As you can fast idle with the choke before the jets drop to increase the mixture.