| Carb versus timing [message #312148] |
Mon, 16 January 2017 09:53  |
kwharland
Messages: 246
Registered: November 2005
Location: Central Florida
Karma:
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A year or so ago I started a thread regarding problems I was having after a carb cleaning and rebuild and would like to offer a followup now that I've resolved my issues.
The backstory is that like happens so often, the coach sat too long and the carb was fairly gummed up from old fuel. I pulled it, gave it a good soaking and then reassembled with fresh parts. I also had taken the opportunity to remove the intake and perform all the tasks related to that plus drained and refilled the tanks with fresh fuel.
As part of the intake R&R, wires and hoses were disconnected and the distributor removed. The distributor got a new rotor and wires and the engine got new plugs. After putting it all back together, the engine ran terrible. It was hard to start and it stalled with the slightest of throttle. I went through all the obvious items, checking hose connections, vacuum, linkage, timing, accel pump, float level, etc and even replaced the fuel pump at some point.
Everything seemed to point to the carb but I couldn't discern that anything was wrong with it. No settings were changed, only confirmed as correct and reassembled with new gaskets, filter, accel pump etc. I also confirmed it was the correct carb for this coach. The coach was relatively new to us before being parked for too long but we drove it enough to know it ran fine previously.
Ater searching the internet for some insight and ending up on a Olds 442 forum, I read where several posters talked about how the 403 motors preferred lots of initial timing advance. So I started advancing the initial timing and as I approached 20 degrees, it began to respond better! I knew that couldn't be correct because in theory there would be too much total advance. I had already cleaned and lubed the advance weights in the distributor as well as confirmed that the vacuum advance worked so I dug deeper and mapped the advance curve, both mechanical and vacuum. It was then I determined that someone had replaced the distributor at some point with one that was not close to correct for this application.
Whoever had done that obviously set the initial timing at a point where it worked for that advance curve and the coach ran okay. But when I pulled everything apart, I wasn't aware of that so I naturally went back to the specs for this application. I'm lucky I didn't wear out the threads on the carb before finding the true source of the problem!
I ordered the correct weights and center piece and secured a correct vacuum advance can and put it all back together. Now it runs like it's supposed to!
The moral? Besides the obvious about don't assume anything, always double check the timing, both static and dynamic when troubleshooting a sluggish engine.
1978 Eleganza II
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