1965 C10 shortbed stepside: Freshly rebuilt 230 inline six - has been broken in, has about 300 miles since rebuild. All stock except a slightly more aggressive cam, and the block is from a 250. Also exhaust valves hardened for unleaded fuel use. As I mentioned in a previous post, I am experiencing a "stumble" upon acceleration. This is not so noticeable at high speeds, mostly just when starting out. Or if I am at idle and hit the pedal, there is a hesitation before the engine "kicks in." 1. Timing - specs call for this thing to be timed at 4 degrees. However, the engine runs optimally at 18 degrees?? The closer I go back to 4, the worse it runs. Near 4 I begin to get backfiring out of the carb. This is very strange and I am beginning to wonder if the engine rebuilders might have put on the incorrect dampener with the wrong marks. The engine rebuild was nearly completed when the original 230 block showed some cracks on the deck. So at the last moment, I had to run around and try to find a different block. I located a 250 block and they used that. Parts were all bought for a 230, and they should all be the same, but I wonder if the dampener might have changed between the two engines? 2. Vacuum advance - I am pretty darn sure the carb is right - like I said, I completely overhauled two of them and get the same symptons with both. The vacuum diaphragm module checks out OK, but I am suspicious of the operation of the vacuum advance in general. I bought a brand new distributer during the engine rebuild (from Chevy Duty in fact). I don't know if the slightly hotter cam requires adjustment to the distributer, but the guy who did the rebuild never mentioned it and he was a detail God. The carb(s) is an original from a 230. Is it possible to have a mismatched carb and distributer? Plugs are gapped according to specs. Coil (original) appears to be OK. This continues to be a most frustrating problem. I greatly appreciate anyone's feedback or suggestions.
wizdog, If you ever figure out the timing, let me know, I've got the same problem. I've got a '63 c-20, that originally had a 230. Somewhere along the way a early '70's 250 got put in, with the original 230 head. I rebuilt that motor (bored .40 over), and put it all back together. I could never get the timing set. It has always been WAY off by the mark. I do have the later model (big diameter) distributor like was in early '70's camaros (with a 250). I finally just gave up and timed it by ear. It was a little hard to start, and all the old guys told me it was set a little to early, so I retarded it just a hair and it runs fine. Then to add more to the saga, I was driving down the road, pulling an empty utility trailer and WHAM!!!!, all heck broke loose. The harmonic balancer came apart. Fortunately it did not go through the radiator. I got a new balancer, for a 250, from local auto parts store and the timing mark was in the same place as the old one. I beginning to wonder if the timing tabs are in different places on 230s and 250s, and different on early and late 250s. Maybe someone out there can tell us.
