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| idle questions https://slantsix.org/forum/viewtopic.php?t=12728 |
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| Author: | Murch [ Sat Apr 23, 2005 12:36 pm ] |
| Post subject: | idle questions |
I replaced the carb (bbs) on my 170. I've got it running pretty good however I have 2 problems. I can't seem to get it to idle under about 850 rpm's and accelerating hard around 60+mph there's is detonation. I've converted to Pertronix and tried adjusting the timing as well as taking the distributor out and maxing out the adjustments at the bottom. It's advanced about 8-10 * based at the recommended specs 2*btdc. I can't seem to get it any closer. What sort(s) of problems should I be looking for? By the way on an incline it ran a little rough. I bought this carb and it was rebuilt. (the reason I replaced it was the previous carb was sucking air at the throttle shaft and I knew of no one to re bush it. Do you also think the float level is of? Thanks in advance for any help, Dale |
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| Author: | SlantSixDan [ Sat Apr 23, 2005 3:24 pm ] |
| Post subject: | |
Most rebuilt ("remanufactured") carbs you find nowtimes have severely worn throttle shaft bushings, 'cause rebushing is not a standard part of the factory remanufacturing process, though it should be. Hemmings Motor News is full of ads from companies that rebush throttle shafts. It's been years, but I used to use G&S Machine in Colorado, 303-795-1412. They did quality work and turned it around fast. Your reman carb is probably idling high because its throttle shaft is worn. Other causes of high idle include improper throttle plate/spark advance port positional relationship, other vacuum leaks (the BBS carbs like to warp between upper and middle body -- I always use two gaskets here) and using the wrong PCV valve (hard to find the smaller-bore one that was used with the 170 engines; most books specify just the one valve for all Chrysler engines of the era. You should use one of the following PCV valves: ACDelco CV1001C, Fram FV281, Standard V253, NAPA Echlin 2-9325. Detonation under hard acceleration indicates either overly-advanced timing or a lean mixture, or both. The timing could be overly advanced because the baseline timing is too far advanced (I can't quite understand what you mean by "It's advanced 8-10° based at the recommedned specs 2°BTDC"), or because the vacuum advance is not working properly, or because the centrifugal advance is not working properly. The mixture could be lean because the carburetor isn't properly jetted for your application, or because of a vacuum leak. Generally if the float level's low, what you'll get is a surging effect at high engine RPM and load as the float bowl repeatedly runs out of fuel. Detonation under hard acceleration can also indicate a restricted exhaust system, combustion chamber carbon accumulation, and/or engine oil burning. Also, what spark plugs are you running? |
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| Author: | Murch [ Sat Apr 23, 2005 6:43 pm ] |
| Post subject: | |
Dan, I sprayed silicone around the throttle shaft and by where you described as the common warping area, no differences which seems to be no leaks. I bought it from someone from this website. Aside from having changed over some of the linkage (choke) to fit my application, and re-install some of the incorrectly installed pieces it seems "all good". The pcv valve is a correct Napa part. I replaced the exhaust manifold not that long ago. After a few attempts I got it right -no leaks, binding etc...what a b.... That being said I'm doubting there's blockage at the spent exhaust (found a NOS and the heat riser works beautiful). There's also no oil burning (less than 60k and maintained, very good compression and no smoke or residue). I could be using the wrong verbage- when I'm checking the time at idle, neutral and under some load the timing mark doesn't reach 2btdc until I advance my light about 8-10*. Maybe I'm doing something dumb (I hope). But I'm getting a feeling it something to do with the distributor or maybe a stretched chain???? The carb not being jetted correctly does make sense. I used a vacuum gauge to adjust the air, fuel mixture (up to about 18). When I pop the accelerator the gauge goes plenty high and down to zero, which seems good. I may have to rebuild it and check it out myself. If you have any other ideas I'm all ears. Thanks for your input, Dale |
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