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| trying to adjust idle mixture https://slantsix.org/forum/viewtopic.php?t=36114 |
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| Author: | 00spy [ Sat Jul 04, 2009 11:48 am ] |
| Post subject: | trying to adjust idle mixture |
I read some articles on adjusting the carb at idle, and I turn it in until the rpm drops and then turn it out, but the rpms never seem to drop .I turned it 13 1/4 turns and still no rpm drop. I am using my timing light , which shows rpm also, it kind of jumps arund alittle. I am not sure if it is suppose to or not, but still by listening to the engine it doesn't drop in rpms. Thanks for any replies Dave |
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| Author: | SlantSixDan [ Sat Jul 04, 2009 11:57 am ] |
| Post subject: | |
Many carburetors made after 1967 have idle circuits designed such that they cannot be richened beyond a certain degree by means of the idle needle. With those, you have to do a one-sided adjustment by reference only to the lean drop-off point. Carburetor operation and repair manuals (and some training movies) as well as adjustment procedures are posted here for free download. |
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| Author: | 00spy [ Sat Jul 04, 2009 12:08 pm ] |
| Post subject: | |
Thanks Dan , have you used the Colortune , it looks like something to get. I have also noticed when reving up the engine some ,the rpms drops kind of slowly, I will have to figure that out also. would dropping the gap on my plugs a little below .45 help. Dave |
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| Author: | SlantSixDan [ Sat Jul 04, 2009 12:12 pm ] |
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Changing spark plug gap won't alter the speed at which the engine returns to idle. Perhaps your carburetor is equipped with a dashpot. |
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| Author: | 00spy [ Sat Jul 04, 2009 12:15 pm ] |
| Post subject: | |
My carb is a Holley 1920 #7585 , and have you used the colortune before. Dave |
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| Author: | SlantSixDan [ Sat Jul 04, 2009 12:18 pm ] |
| Post subject: | |
So no dashpot on the carb. Fortunately for you, that 1920#7585 is highly tweakable to get it to work just the way you want. See the 1920-specific threads linked off the topic I linked above. Colortune: Yes. It's a good way to dial in the adjustment, and to check cylinder-to-cylinder mixture distribution. |
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| Author: | Aggressive Ted [ Sat Jul 04, 2009 4:32 pm ] |
| Post subject: | |
I have a R7585 EconoMaster also and it idles great at 1 7/8 turns on the mixture screw with a #56 jet up to a #612 jet. You may have a pretty bad vacuum leak throwing it off. Be sure you have the correct carb to manifold gasket. Take a look at my plugs on the red link below. That picture is with the #56 jet. |
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| Author: | 00spy [ Sat Jul 04, 2009 5:52 pm ] |
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I did find that one of the bolts that hold on the carb was not all of the way tightened down,I guess it works its way loose over time. I am not sure if that is the problem , but was a problem. Thanks for the replies Dave |
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| Author: | Aggressive Ted [ Mon Jul 06, 2009 10:02 am ] |
| Post subject: | |
Get a grade 8 lock washer or even a star washer and put it under the hold down nuts. The base gasket will shrink over time. Makes for a nice little vacuum leak and rough idle so you tend to richen up the mix over time. Just keep the 9/16 box end wrench handy and check it now and then. |
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