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| Rough idle https://slantsix.org/forum/viewtopic.php?t=29339 |
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| Author: | NewSlanter [ Thu Jun 05, 2008 9:09 pm ] |
| Post subject: | Rough idle |
I decided to change out my thermostat for a 195 degree unit because I'm trying to improve my mileage. Much to my surprise, there was no thermostat installed! Now the heater blows nice and hot. Next I adjusted my valve lash. Runs much quieter now ( two or three valves were looser than my thickest feeler gauge will measure). The problem is, my engine (a 225 Super Six with an A904 trans) is idling really rough now. My timing is set at 10 degrees BTDC initial. I don't have a tach, so I can't say what the timing curve looks like. Should I play with the timing to try to smooth it out, or could the loose valves and lack of a thermostat have been masking some other problem (or problemS)? Thanks in advance, Nat |
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| Author: | Joshie225 [ Thu Jun 05, 2008 9:12 pm ] |
| Post subject: | |
If it wasn't running rough before the valve adjustment you've probably got some valves too tight. |
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| Author: | Aggressive Ted [ Thu Jun 05, 2008 9:35 pm ] |
| Post subject: | |
I will second that comment! I have made that mistake. It is easy to do. I run a little looser, .012 and .022. to be safe and the result is better mileage and torque with a smooth idle. |
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| Author: | SlantSixDan [ Fri Jun 06, 2008 8:43 am ] |
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Yup, it's easy to get crossed up when concentrating on getting the tappet clearance just right, and forget that the order swaps in the middle of the engine. Front to back it's E-I, E-I, E-I, I-E, I-E, I-E. See the valve adjustment procedure for more info. |
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| Author: | NewSlanter [ Fri Jun 06, 2008 7:18 pm ] |
| Post subject: | |
I re-lashed the valves to .012 and .022 today and it smoothed out quite a bit. There's still some improvement to be made, though. I have a correction to post; My initial timing is set at 12 degrees, not 10. Thing is, the timing bounces around a bit (maybe two degrees each way). My dizzy shaft doesn't seem loose, so I'm at a bit of a loss... I do have a vac leak at the throttle shaft (Carter BBD) I'm going to have that re-bushed, but I need to swap out my front end for a disc set-up first (so I can stop lugging two spares around). Could the vac leak be causing my iming dance? Thanks, Nat |
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| Author: | SlantSixDan [ Fri Jun 06, 2008 9:28 pm ] |
| Post subject: | |
Timing bounce-around at idle can be due to a sloppy or failing distributor drive pinion, a distributor cam that's loose on its pivot bushing, insufficient light-spring tension in the mechanical advance mechanism, improper vacuum advance hookup or operation, or timing chain/sprocket wear. Does the idle improve and the timing mark settle down if you disconnect the vacuum advance hose and plug the carb port? |
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| Author: | NewSlanter [ Fri Jun 06, 2008 11:31 pm ] |
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I was checking the timing with the vacuum can disconnected and the carb port plugged. Didn't try with it hooked up.... Thanks, Nat |
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| Author: | Charrlie_S [ Sat Jun 07, 2008 4:59 am ] |
| Post subject: | |
Excessive distributer shaft end play, can also cause timing to move around. This is a problem with most slant six distributers. Whenever I replace the gear, I usually wind up adding an additional shim between the gear and dist body. |
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