79 258

[mojobean]

I could use a little help.  i believe I have a vacuum leak.  The 79 258 should be timed at 4 degrees before tdc.  I cant get it to idle or start at 4 8 or 10.  It begins to run at 12 and runs best at about 20 before tdc.  I have at this point eliminated all vacuum except distributor at spark port.    The egr is running to the vacuum canister, the cto is being run to the air cleaner tac vac. I have torqued down the intake bolts, the carb bolts, rebuilt the carburetor, replaced the distributor and the ignition module, i have also fumigated any gap prone areas with propane to hear for increased rpm.  Nothing the I can find.  When I had a vacuum gauge attached at 12 before tdc, it read late valve timing / intake leak / leak at heat riser - the heat riser flap works just fine.

[BenM]

Maybe a stuck valve?

[Mernsy]

I wonder if the timing chain has stretched.

[mojobean]

I wonder if the timing chain has stretched.

I hadn't thought of that and checked the slop, it has 6 degrees of slop.  Thanks.  Looks like I'll be getting another chain.

[mojobean]

Maybe a stuck valve?

How does one check for a stuck valve?, is it just a matter of pulling the valve cover and rotating the crank by hand and checking for movement on the stems?

[Amc1320]

You can do a compression test on each cylinder, the one with the stuck valve will be way different than the rest of them

[IowaEagle]

I was thinking a stretched chain too.

[carnuck]

Or the mechanical advance is messed up in the dist.