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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
So, I have this '86 Trans Am with the 5.0 in it. I bought it about a month ago with just under 27K miles on it. Driving it 4 hours home, I noticed no power and a hesitation when coming off of idle. I figured the accelerator pump was old and dry, and the whole carb could use a refresh.
Well, I had just purchased the car and wanted to drive it. So, in addition to getting a rebuild kit for it, I ordered a re-manufactured carb from an ebay seller who had a good reputation. Now, I have plenty of experience with non-ccm carbs, and rebuilding them. I used to rebuild engines for my old Pontiacs way, way back (2nd gen firebbirds), but when I looked at everything you need to do with the ccm version, I figured I would give a rebuild a shot.
So, when I put the reman carb on, the performance is top notch. But, when I am idling or driving around 800-900 rpm, the engine shudders like it wants to fly apart. When it's in drive, it runs about 650 rpm, and has a tiny stumble. I checked for vacuum leaks, and couldn't find any. Now, this isn't constant. It only happens about half the time. The other half, it runs smooth as can be. When I put the old carb back on, there is no shuddering, I lose all performance, and the hesitation when coming off idle is there.
I have swapped the carbs several times, replaced hoses, cleaned things meticulously, and I get the same results each time. So, any ideas what to check next? Can I rebuild the old carb without having all those special tools, like dwell meters and all that stuff to check the electronics? I'm getting old, arthritic, and cranky! I had an '81 Corvette with all the computer stuff taken off, and I had it purring like a kitten. I am not relishing the idea of swapping to non-ccm stuff without going ahead and doing a motor swap. Ideally, while I slowly build a small block over the next couple of years, I would like to keep the cruise and overdrive tranny. Heck, I'm getting 26 mpg on the highway!
Driving me crazy! I would blame timing, but with the old carb it idles fine. I did take it out this morning, and drove it around. The idle in park was 1k and in drive was around 750 or so, and I had no trouble. The car felt like it had a little bit of a cam in it while sitting at a light, but I don't think that's the case. Later on, I drove it again and it idled in park around 850 or so and in drive around 600 and shook like a wet dog. I haven't touched the idle screw.
It's like to computer is hunting for proper timing - maybe, but only with the reman carb.
Other than the shaking and once in a great while dying, it runs great.
Well, I got a little adventurous today and decided to rebuild my old carb. I did the top end, anyway. I also discovered that one of the hangers on the secondaries was bent way up, so the metering rod was actually up even when the secondaries were closed. I carefully bent that back into its proper shape.
Car runs great, now. Well, as great as 150hp can run. It's very civilized and doesn't try to shake itself to death under 1000 rpm. I still don't know what was going on with the rebuilt one, but at least I no longer have the problem.
09-10-2021, 02:51 PM
