You haven't given us the model, type and code, which makes it difficult. I'm guessing it will be old, and have a large one-piece Flo-Jet carburetor like this:

[Linked Image]

Initial adjustment (just to get the engine running) for all types of Flo-Jet, both main and idle jets, is 1.5 turns from fully screwed in. If the jets have been opened as far as you say it sounds as if the fuel system or jets have become quite clogged - if so it probably won't run with the correct initial settings Joe has quoted. The gravity fuel system and the FloJet should be easy to clean out and are pretty well bomb-proof, though the needle and seat may leak after all those years. If they do, please say so and we can talk about how to fix that problem, which is the only relatively difficult operation on a large Flo-Jet.

If it has the reciprocating weight type of balancer (Synchrobalance) it is quite common for the link pivot mechanism, and the crankshaft bearings that move the weights, to wear if the oil has not been changed regularly, causing a rattling/thudding noise. Usually if the wear is bad the crankshaft is worn as well as the link, and fixing it requires major work so the engine is often scrapped when the noise gets serious. If it goes away off-idle, yours doesn't sound as if it is bad.

[Linked Image]


As you can see, it is not a very lovable mechanism.

Last edited by grumpy; 26/10/12 04:51 PM. Reason: Add detail