cough, sputter, pop
 

I ran this post on The Samba, I was hoping someone on this Forum might have additional ideas. I'm out of ideas.

Here's the problem:

My stock, '64 ragtop sputters, coughs, and pops when accelerating and at speed, otherwise it pulls well and is very strong. All systems (carburetor, fuel pump, distributor, ignition settings, valve settings, compression) check out fine, and were either recently rebuilt or replaced. I replaced the vacuum advance distributor with a mechanical advance unit (both Bosch originals), and the timing advances well. The plugs and wires are new. The engine had a rebuild 10,000 miles ago. The car sits in heated storage 9 months of the year, and has never had this problem of coughing, sputtering, and popping.

The only symptom I can pick out is that the heat riser heats up to hot on the driver side (#3 and #4), while the passenger side (#1 and #2) heat riser is only warm after driving 10 miles. According to John Muir's Compleat Idiot guide, April 1973 edition (page 239-240), a blocked heat riser can lead to bad things including poor performance. The Clymer Shop Manual (Feb 1984) indicates that missing at speed and under load may signal an intake manifold leak. Before I tear into things, I would like to hear from folks who have had a similar experience with an all-stock engine sputtering and popping at acceleration and at speed, and how they resolved the problem. When I searched prior posts, I've read of everything from bad plugs, shorted condenser wire, points mis-adjusted, faulty plug wires, distributor caps, etc. I am pretty sure my problem is beyond those things, and I would like your learned insights.

If I need to clean out, open up, the heat riser, is there a magical way to get to the heat riser without removing the fan shroud and generator? I would like to avoid dropping the engine.

Thank you in advance for your help.:)