The Stovebolt Site Forums The Shop Area Engine Shop A Milestone...and questions

I haven't posted for some months, but have been listening. I just completed the rolling chassis for my 62 1/2 ton LWB fleetside. I gotta say, it looks great; everything powder coated, rebuilt or new. The crown though, is the 261/4 speed that came with the truck from the factory. The RPO codes are still marked on the firewall (293/4s). It even has the original larger Rochester B with tag! I had the machine work on the engine done by my local machine shop who is a party of one and knows his stuff. It was assembled by myself and my friend Mark (51bolt) who likes this stuff so much he is doing a 51 and keeping it all original too! Our two trucks going at once generates lots of fun and questions!! Anyway, I was originally going to soup it up a little and I have the M4F cam installed, but then decided to wait or even forgo using the Fentons and Offy that I bought with the cam. The day came last week and the engine started right up!!! I won't go into the next few hours of us scratching our head as to why the thing ran smooth for a minute and then backfired like it was wired backwards. Suffice to say that new AC DELCO plugs fixed it!
We ran the engine 2000-2500 rpm for about 20 minutes and it sounds great with no leaks, not even from the carb. Here are the questions: What should I set the timing at with this cam? Right now I am playing with TDC(recommended) and 5 BTDC. What can I expect to get for a livable idle after the engine breaks in? The book says 475 but right now 1000 is the happiest place. Speaking of which, it really likes running with the choke partially closed. I am using the original distributor, which I disassembled and rebuilt; it works well but at idle it seems to hunt a little, probably from the cam and its effect on vacuum....any thoughts? I also scored the original oil bath air cleaner and will use it(THANKS MARK). Last,I know I am wasting the benefit of this cam without more carb and exhaust, but will it negatively affect anything long term? It sounds great. I won't be able to drive it for another 6-12 months cause now its on to the body!

My bet is you have a vacuum leak.

Check all vacume lines, plug off one and note any change in idle. Check intake manifold, sealing rings installed?, re-tighten all bolts. Shoot WD-40 around mating surface/gasket, carb base, throttle shaft on carb and note any change in idle. If it changes, you got a leak.

Carb re-built? Internal air leaks can cause havoc with idle.

If no leaks, retard timing. Be sure Vacuum is plugged off to the advance before setting timing.

Howard's M4F is a good cam. It has a high lift but the overlap is minimal and would not cause the idle problem you have described.

The dual carbs and Fenton headers with the M4F cam will really wake your 261 up! Recommend Holly/Webber carbs from Stovebolt Engine Co. for dual set-up!

I would start off with 8-10 degrees of timeing.
A performance cam needs more timeing. Also our
gas is higher octane than back then. If it pings
on acceleration set it back a little.

Hotrod6, I was really careful on assembly making sure my manifolds were true, using collars and hightemp rtv along with torque wrench and sequence. I know I do have some wear on the throttle shaft, but could that minor leak cause the need for a little choke? How about the subtle hunting the distributor does at idle? I would think the higher idle is due in part to a tight new engine. I'm going to go ahead and set timing to 8 btdc Wrenchbender and let all know how it works. Thanks.