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Lawnmower carb on 302

Mightyfordranger

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alwaysFlOoReD

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I've been seeing this pop up on my YouTube feed all the time. I was ignoring it figuring it was click bait. I'm pleasantly surprised. I'm interested in the mpg.
 

Mightyfordranger

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I've been seeing this pop up on my YouTube feed all the time. I was ignoring it figuring it was click bait. I'm pleasantly surprised. I'm interested in the mpg.

Same man. This dude's crafty
 

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Roert42

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I watched about a minute of it and had to stop. He thinks it's "dialed in" and it's got a 1/2 second hesitation when he spikes the throttle. The fan shroud is missing and overall it looks like a rolling demo of poor workmanship. The chain holding the engine down is similar to Chevy's fix in the mid 60's for their break-prone engine mounts that pinned the throttle wide open so I'll let that go. I ran a 302 with a 490 cfm Holley and then swapped on a 600, power, throttle response, and mileage all improved. Too small a carb doesn't mean better mileage, it means restricted power. 14.7:1 is the important equation.
 

Roert42

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I watched about a minute of it and had to stop. He thinks it's "dialed in" and it's got a 1/2 second hesitation when he spikes the throttle. The fan shroud is missing and overall it looks like a rolling demo of poor workmanship. The chain holding the engine down is similar to Chevy's fix in the mid 60's for their break-prone engine mounts that pinned the throttle wide open so I'll let that go. I ran a 302 with a 490 cfm Holley and then swapped on a 600, power, throttle response, and mileage all improved. Too small a carb doesn't mean better mileage, it means restricted power. 14.7:1 is the important equation.
I don’t expect this to improve mpg at all, and he doesn’t claim this makes the engine run better. It’s more of a let’s see if we can make it work at all.

However it’s pretty impressive what he does to get it to run so well for such a restricted carb. He basically makes his own ecu with a second throttle body parallel to the one hooked up to the actual throttle. He uses this to maintain the correct a/f ratio.

You should take a watch through, at least take a peak around 14:30. He shows a/f ratio
 

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sooo,, what's the difference between a normal carb at part throttle and a lawn mower carb at full throttle????

seems to me what he has is half of a quadrajet.
 

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However it’s pretty impressive what he does to get it to run so well for such a restricted carb. He basically makes his own ecu with a second throttle body parallel to the one hooked up to the actual throttle. He uses this to maintain the correct a/f ratio.
This is what impresses me the most. What us common folk are capable of doing these days. It's insane like imagine what the cost would be for something like this 40 years ago.

sooo,, what's the difference between a normal carb at part throttle and a lawn mower carb at full throttle????

seems to me what he has is half of a quadrajet.
This is what I can't get through my Mellon. The differences between this and a regular carb economy wise.
 

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Well, imagine you have a throttle stop so that you cant open the throttle more than 1/2. That's what running the lawnmower carb is essentially doing .
 

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It does change the dynamics of the situation of the vacuum on the manifold side at WOT compared to what a mower would see as he goes through in the lengthy white board section of the video (I skipped through some of that) so it would have a different AFR than a more appropriately sized carb... it's all about balance

There were a couple hints about like 40mpg or whatever which might be doable since it isn't getting any air so it isn't going to use much fuel, there's not much excess power there...

I thought it was going to be janky at first when he said it was dialed and it's a rusty garbage can and whatnot but watching through it it seemed well thought through and mainly just to see if he could since people were saying he couldn't, heck, that's kinda why my '90 exists...
 

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ok, Devil's advocate mode ON

how about EFI at partial throttle?
one could think a PCM can handle the parameters.

is there a difference between a mower carb at WOT 100 cfm and an EFI at partial allowing 100 cfm in?
same load, same rpm, results in same vacuum.
the mower carb will have maximum air velocity giving the best fuel atomization. jet size will determine AF ratio.
in addition the sizeable increase in plenum volume helps.

the efi has higher fuel pressure so it has excellent atomization at any flow rate.
O2 sensors will tell the PCM what AF is best,,,,according to the fuel mapping, after considering rpm and vacuum.

But wait, there's more!

there is nothing new about small carbs.

many years ago,,like 40+ or so, one of the car magazines had an article discussing/mentioning Taxi carbs.
they stated we'd be surprised at the mileage they obtained with factory equipped small carbs.
it was also noted that those taxis had severly limited power as speeds increased. not a big deal in city traffic.
 

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I’m surprised it was even drivable.
 

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remember how small the one barrels were that came on the older cars? they looked like lawn mower carbs
 

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I don’t remember the single barrels being that small. It is possible I’m thinking of a two barrel though.
 

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