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Old 12-13-2012, 12:30 AM   #1 (permalink)
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dual vs single carb

I have seen many posts like this and still do not understand. I want to dual carb the '77 John Deere Cyclone 440 fc but ppl say that it wouldn't realy help on power. A liquifire has 58 hp and mine has 44, only dif is 2 carbs and liquid cooling? Is it a whole different motor? Bore and stroke same, comp ratio same.
I know there cast differently but same specs and 14 more hp?
Same drivetrain also.
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Old 12-13-2012, 01:12 AM   #2 (permalink)
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One big issue in making HP is getting rid of the heat. Liquid cooled engines are more effective doing that. If you can figure out how to get rid of the heat in the fan, then you could theoretically produce the same amount of HP with the same displacement/compression/carburation.
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Old 12-13-2012, 07:04 AM   #3 (permalink)
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You might gain a couple of ponies, but the biggest gain would be throttle response and the ability to jet each cylinder specifically to improve efficiency.

Since the PTO cylinder typically runs hotter, you could jet for that and run the other a size leaner as it runs cooler being next to the fan.
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Old 12-13-2012, 05:12 PM   #4 (permalink)
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Would this change the rpm power band? Without looking in manual, my peak hp in the mid 6K range while the liquifires is in the mid 7K area. I dont know if mine would tolerate mid 7K or would it? Maybe the liquifires are balanced better. I dont know, this is still a pipe dream, lots to figure out I guess. Someone on here must to have tried this.
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Old 12-14-2012, 08:14 AM   #5 (permalink)
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No, it would not change the power band significantly.
At the most, only a couple hundred rpm.
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Old 12-14-2012, 08:27 PM   #6 (permalink)
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The problem with adding 2 carbs is you also need to add more air and more room in the cylinder to put it all. That liquid engine was designed for 2 carbs, with a longer/bigger stroke. If you added another carb, you'd have to jet it super lean so it would not flood, to the point where you're pushing as much fuel as the one carb you had before.
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Old 12-14-2012, 11:14 PM   #7 (permalink)
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I thought bore and stroke were the same..
Not sure but going to abandon that project(dual carbs) I just thought someone on here did it and could post the results....
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Old 12-15-2012, 08:58 AM   #8 (permalink)
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I had a twin tilly set up on a old silver bullet. The thing was ridiculously finicky but the days that it would run right it absolutely ripped. Ended up going to a single carb in the end. The engine definitely generated more heat, and PTO side had to be jetted so fat that idle was almost compromised. It was fun though.


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Old 12-15-2012, 11:15 PM   #9 (permalink)
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I actually used to have a silver bullet. It was a 72 ski-doo 340 tnt. Not sure if its the same as what a real silverbullet is but everyone who saw said it was.
Not going to do it.
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Old 12-16-2012, 12:09 AM   #10 (permalink)
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Mine was a 294 I believe. Don't let me discourage you. Im sure if you took the time to dial in a couple of carbs you could get it to work right, I think my main issue was working with twin tillotsons. Mikunis seem more feasible


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Old 01-10-2013, 08:37 PM   #11 (permalink)
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You can't take what you know about 4 stroke engines like from cars and directly apply it to 2 strokes because they don't work the same.
The biggest problem with air cooling an engine is to balance cooling across the entire cylinder and head without having hot spots. Liquid cooling solves that problem handily. Since you don't have to worry about hot spots you can be much more aggressive with your porting, so more larger transfer ports which more effectively deliver the fuel/air charge from the bottom end into the cylinders, you can also run larger exhaust ports because you can keep them from burning away like they would on an air cooled machine.

So while the bore and stroke is the same its not like your engine is the same engine with just a cooling jacket wrapped around it.

Don't let that talk you out of dual carbs, many manufacturers did dual carbs on air cooled machines.
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