360 LA installing Promaxx Aluminum heads

TT5.9mag

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And after looking at all of them I still feel the same way. Little rich at idle and a little hot and I’d pull one degree. But I bet you could pull 100 plugs from various engines and 5% would look that good.
 

Hysteric

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Readout on the AFR is a hair leaner than last night.

If you didn't change any jetting and the 02 gauge indicated a change in AFR then what the 02 gauge is picking up is a change in the combustion or put another way a change in the burn

Go up a jet size and see what the plugs look like then.
 

74Scooter

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And after looking at all of them I still feel the same way. Little rich at idle and a little hot and I’d pull one degree. But I bet you could pull 100 plugs from various engines and 5% would look that good.

The cooler plugs are in it right now and they seem to run great. I'll get a couple out later and check heat range.
 

qkcuda

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Good read on carb tuning, thanks. I am using the same 625 Street Demon. My next purchase will be the tuning kit. I figured it was running rich, my plugs are brown.

IMG_20220731_211159556.jpg
 

74Scooter

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Good read on carb tuning, thanks. I am using the same 625 Street Demon. My next purchase will be the tuning kit. I figured it was running rich, my plugs are brown.

View attachment 1715964911

Get a set of spare gaskets too. I was able to reuse mine quite a few times but if one tears and you have no replacement your day is over.
 

Hysteric

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Not on pump gas. A brown plug will be dead rich.

I posted this before in another thread and bares repeating:

"A good mixture will leave tan on the strap and the porcelain nearly all the way down.

Here's a plug from some one who knows what he is doing. Notice there's no timing mark? When the mixture is good it wont leave one because the mixture is homogenous and leaves a consistent colouring of the plug way down onto the porcelain. Aim for light tan. Contrary to what is perpetuated on the internet unleaded fuels tan just like leaded fuels do if the plug is white it has nothing to with the fuel type and everything to do with the mixture quality at time of ignition."

-jpg-_nc_cat-103-ccb-1-3-_nc_sid-8bfeb9-_nc_ohc-ed-aex-wltaax__ondp-_nc_ht-scontent-fsyd11-2-jpg.jpg
 

qkcuda

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Get a set of spare gaskets too. I was able to reuse mine quite a few times but if one tears and you have no replacement your day is over.

Are the two bowl gaskets the same for the 625 and 750 carbs? I could only find one listing for each.
 

Rat Bastid

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I posted this before in another thread and bares repeating:

"A good mixture will leave tan on the strap and the porcelain nearly all the way down.

Here's a plug from some one who knows what he is doing. Notice there's no timing mark? When the mixture is good it wont leave one because the mixture is homogenous and leaves a consistent colouring of the plug way down onto the porcelain. Aim for light tan. Contrary to what is perpetuated on the internet unleaded fuels tan just like leaded fuels do if the plug is white it has nothing to with the fuel type and everything to do with the mixture quality at time of ignition."

View attachment 1715964982


Whatever dude. It’s easy to find out. He can add more fuel until the plugs are brown and watch the power drop and it will run like ****.

Once again you rely on what someone says or does rather than post what YOU do. Since I do it all the time, if you brought me a pump gas plug that looked like that and you tried to convince me you could tune I’d just laugh and show you the door.

I know you love to argue. Evidently it’s a thing for you. Someday, when you decide to test something for yourself you could post the results of that.

I stand by what I posted and if that doesn’t jive with your god it just makes you both wrong.
 

74Scooter

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Are the two bowl gaskets the same for the 625 and 750 carbs? I could only find one listing for each.

Looks like they have 2 calibration kits P/N 1921 & 1931. You will want 1921 as 1931 has jets and rods for a fatter than stock calibration.
Correct lean kit: Demon Carburetion 1921 Demon Carburetion Street Demon Calibration Kits | Summit Racing

For the throttle body gasket it looks like you will need P/N 1926 as 1914 call specifically for the 750.
Correct TB gasket: Demon Carburetion 1926 Demon Carburetion Carburetor Throttle Body Gaskets | Summit Racing

I could not locate a separate number for the 750 air horn gasket so I think that part is the same. I can confirm P/N 1925 worked fine on my 625.
Correct Air Horn gasket:Demon Carburetion 1925 Demon Carburetion Street Demon Air Horn Gaskets | Summit Racing

FYI they sell rebuild kits too: Demon Carburetion 1920 Demon Carburetion Carburetor Rebuild Kits | Summit Racing
 

qkcuda

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Thanks, the 1921 kit is the one I was looking at and the 1925/1926 gaskets were the ones I saw.
 

74Scooter

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Thanks, the 1921 kit is the one I was looking at and the 1925/1926 gaskets were the ones I saw.

Quite glad you chimed in.. reminded me I burned through my spare carb gaskets. I'm off to Summit to pick up the replacements in a few minutes. :thumbsup:
 

74Scooter

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Driving around a bit more this morning, ran to Summit to pick up spare carb gaskets. Took the long way on surface streets and highway home. Think I'm about 95% there. She goes a bit lean coming off light throttle and just a hair at cruise/tip in sometimes. Backing into the parking spot at Summit she lean popped and died...lol. Think one step smaller metering rod will likely do the trick. I'm at 60-50 now.. I'm going to toss in 58-50.. it's that close. Headed out of state tomorra so that might need to wait till I get back.
 

Hysteric

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Backing into the parking spot at Summit she lean popped and died...lol. Think one step smaller metering rod will likely do the trick. I'm at 60-50 now.. I'm going to toss in 58-50.. it's that close. Headed out of state tomorra so that might need to wait till I get back.

I'll say it again. Go up a jet size and see what colour you get on your plugs.
 

74Scooter

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I'll say it again. Go up a jet size and see what colour you get on your plugs.

I started with a fatter 76 primary jet and the lil gal did not like it with any metering rod combination. She really likes the 74 jet, think a size smaller metering rod will do the trick.
 

Hysteric

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I started with a fatter 76 primary jet and the lil gal did not like it with any metering rod combination. She really likes the 74 jet, think a size smaller metering rod will do the trick.

Give it a go and get back to us with pics pls.
 

Hysteric

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Once again you rely on what someone says or does rather than post what YOU do.

RIP Shrinker. A man of true genius.

The Irony. Its Shrinker's work I quote.

He was a genius alright. He was also kind enough to share his knowledge a lot of which I saved and re-read regularly to get a better gasp on what happens inside the cylinder. I'll take Bruce's years of hard work and experimenting and figuring out how ICE's worked and learn off the best.

>>>>SHRINKER HAS PASSED<<<< - Don Terrill’s Speed-Talk

To quote Mattax:

"ken, I appreciate your letting us all know this bit of sad news.

In a way of course he will live in on -
In the snips large and small many us of clipped of his posts here, at MSV and Innovate forums.
In the way he taught (or certainly tried) to get us to think from a combustion point of view."

- Matt
 

74Scooter

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OK.. got the rod swap and escaped for a 20 minute ride mixed in town and highway.

Setup and results:

74 Primary jet
went from 60-50 rod to 58-50
Green spring
Idle about the same 13's and occasional 14.
A hair more rich on highway and around town.. more 13's fewer 14's. Fixed cruising & low speed tip in. Not as "smooth" by seat of pants.. might actually mean it's running better though.

60-50 rod was like a marble on a glass plate smooth on highway but went slightly too lean off cruise and in low throttle situations infrequently. If I had a long highway trip I might just toss it back in.

Not going to pull a plug right now as it's near 100 today and garage with hot car is... hot. :p

I'll get a plug pulled tonight after the sun goes down.
 

Rat Bastid

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The Irony. Its Shrinker's work I quote.

He was a genius alright. He was also kind enough to share his knowledge a lot of which I saved and re-read regularly to get a better gasp on what happens inside the cylinder. I'll take Bruce's years of hard work and experimenting and figuring out how ICE's worked and learn off the best.

>>>>SHRINKER HAS PASSED<<<< - Don Terrill’s Speed-Talk

To quote Mattax:

"ken, I appreciate your letting us all know this bit of sad news.

In a way of course he will live in on -
In the snips large and small many us of clipped of his posts here, at MSV and Innovate forums.
In the way he taught (or certainly tried) to get us to think from a combustion point of view."

- Matt

No ****. I’m familiar with Shrinkers writing. I also do my own research and testing.


Rather than pick what YOU want to quote, why not post a link to the whole quote?

Aping what someone says doesn’t make you smart.
 
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