671 blower twin carb initial set up
08-11-2009, 12:02 PM
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671 blower twin carb initial set up
I just rebuilt my twin engine set up, 530cu/in 671 blower twin holley carbs. This was a running system before the rebuild. I bought the boat without hearing the engins run(great deal, not stupid). I rebuilt the carbs last winter. I fired up the engines yesterday one Idles well but when you give it fast throttle it backfires. The other runs a little rougher. Timing is set at 26 deg untill broken in and then to 28 deg. I am familiar with useing a vacuum gauge to set idle mixture on a single carb application but with twin carbs I can't see it working. Any tips on setting the carbs up would be great. Andy...
08-11-2009, 12:19 PM
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Close the butterflies all the way. Open idles circuit screws to 1 turn from closed each. Adjust the idle from there. Let your air bleeds do their job. With 2 carbs, you shouldn't have to open the throttle at all. It will all be in the idle circuit screws.
As far as the pop, it is probably a accelerator pump out of adjustment. Check there first, then move to possibly the power valves if you have them.
The engine might not like a quick bump on the throttle. Most blower engines like a smooth rev.
If you can't get them in tune , then you might need to take all 4 of them off and send them out to a specialist like Nickerson etc.. and have them matched to your application.
It took me quite a few hours on the dyno to get both of mine adjusted out and in sync on the last engine that I built.
Good luck.
As far as the pop, it is probably a accelerator pump out of adjustment. Check there first, then move to possibly the power valves if you have them.
The engine might not like a quick bump on the throttle. Most blower engines like a smooth rev.
If you can't get them in tune , then you might need to take all 4 of them off and send them out to a specialist like Nickerson etc.. and have them matched to your application.
It took me quite a few hours on the dyno to get both of mine adjusted out and in sync on the last engine that I built.
Good luck.
08-11-2009, 02:31 PM
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There 671's unless 871's take the same parts, how do you tell the difference?. I have just put new seals,bearings and gaskets in them, orderd for 671's and everything fit. The engines are 525 cu/in approx 4.0 stroke 4.56 bore, tall decks oh yeah, thanks Jeff.
08-11-2009, 03:12 PM
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Just depends on how fast you plan on spinning them.
6,8,10,14 - 71 etc are determined by the length of the casing. Seals, snouts, etc, are interchangeable on a lot of them. I don't have one laying around, or I could give you dimendions.
6,8,10,14 - 71 etc are determined by the length of the casing. Seals, snouts, etc, are interchangeable on a lot of them. I don't have one laying around, or I could give you dimendions.
