Thread: 2.25 petrol - poor running with Zenith

Originally Posted by Busted Syncro

G'day Will,

Start filing!. The thread is 3/16" x 32 UNS 60 degree Cheese Head Set Screw on a 29D. The centrifugal advance should spring back to zero. Maybe a broken spring? or jammed weight.

The normal way to determine if the inlet manifold gasket is leaking is use a vacuum gauge. You have a rubber hose on the vacuum advance and just need a 3 way connector (like on windscreen washer setup) and some extra hose to connect the gauge in. You can pick one up on eBay for $25 that does vacuum and fuel pump pressure.

Chris

Thanks for that - I'll see if I can source some. (I can only really work on the car on weekends, so I don't mind waiting a bit for stuff to arrive.)

Regarding the centrifugal advance, it springs back 90% of the way, it's just the last 10% or so that it can't do when stationary.

I looked into using a vacuum gauge for the inlet manifold, but I wasn't able to figure something out - there's always going to be one cylinder with an exhaust valve at least part-way down, so how do I know the leak is coming from the manifold and not that cylinder? I've have thought the cylinder with the open inlet valve will always leak a bit due to piston rings not being a perfect seal.

An update on this: all's well with the engine now, there turned out to be a pair of problems.

The (brand new) carburettor was bad, and the second problem was that it was losing spark after running for a bit. So, when I was testing the quality of the spark earlier, it looked fine, but if I'd left it cranking over long enough it would have disappeared.

Not sure what the deal is with the spark since I replaced the entire ignition setup (it was reasonably cheap to buy an entire aftermarket distributor and coil instead of messing around with the old-style screw-on leads on the old setup).