Nikki Carburetor Problem

[Bushedman]

2nd choke not opening?
Max Revs 2500RPM
TB42/Y60 4.2 motor 1994

[Brett Bignoux]

Good day Nicholas !

Have you checked the small vacuum tubes on your carb for leaks ?
Is the vacuum booster for the second stage throttle working ?
How is your vacuum advance tube ? (may be split on one end where it pushes onto the little metal pipe).
Check any vacuum system blanking caps , they tend to split over time .
Is the linkage working properly ?
Has the throttle cable adjustment not perhaps vibrated loose ?
Check for an intake manifold leak . (sucking air).

I hope this helps you with your problem . Brett .

[Peter Connan]

If i remember correctly, only the first stage is opened by the cable and linkage. There is a cam on the linkage preventing the second throat from opening at small throttle openings, but the actual opening is done by a vacuum-driven diaphragm bolted to the rear side of the carb.

You need to check that the tubes going to that are in good nick and correctly connected, and that this diaphragm is not damaged.

Remove it, stroke it, put your finger on the tube. If it gradually returns to rest position, the diaphragm is leaking.