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PostPosted: Sun Sep 20, 2020 5:18 am 
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EFI Slant 6
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Location: Annapolis, Maryland
Car Model: 1974 Dart Swinger 225
Would a Carter BBS 6218S (for 1973 truck according to the eBay listing) plug and play in my 1974 Dart? What modifications or tuning adjustments would be required?

Why I'm asking: I have detonation at WOT in my newly rebuilt slant. (The whole rebuild thread is here.) I recently found out that the EGR vacuum amplifier doesn't send the signal for the EGR to open, so I've ordered a replacement amplifier. But I'm doubtful that will solve the detonation problem, and I'm running out of ideas.


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PostPosted: Sun Sep 20, 2020 8:37 am 
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Supercharged
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Location: Fircrest, WA
Car Model: 76 D100
Why do you think changing carburetors would solve a preignition/detonation problem?


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PostPosted: Sun Sep 20, 2020 9:11 am 
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Location: Annapolis, Maryland
Car Model: 1974 Dart Swinger 225
Reed wrote:
Why do you think changing carburetors would solve a preignition/detonation problem?


I'm open to other ideas, but I've already tried a lot of things. The spark plugs indicate running hot even after going down two heat ranges. People are suggesting the engine is running lean, but I've already installed a larger main jet in the carburetor and raised the float level according to the late-70's tech bulletin. Also, I know the 1945 was designed for lean combustion.


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PostPosted: Sun Sep 20, 2020 10:45 am 
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rich006 wrote:
Would a Carter BBS 6218S (for 1973 truck according to the eBay listing) plug and play in my 1974 Dart?


Pretty close. You'd need to pay attention to the throttle return spring; there's a built-in one on the 1945, with a light-duty external spring pulling on the throttle lever as a safety backup—you'd want to install dual inner/outer external springs where the single external spring is now. You'd need a different choke thermostat; use a № 1231 electric choke kit. The BBS will have a hookup for your PCV and your distributor advance, but no hookup for EGR.

Quote:
I have detonation at WOT in my newly rebuilt slant.


EGR is not active at WOT, so repairing the EGR system will not affect the car's behaviour at WOT (where did you find a new vacuum amplifier to order? Hope you didn't pay too much…).

Slant-6 engines built up like yours can generally be tuned easily to run well and not ping—even without EGR. That '73 truck BBS stands to make the engine run quite a bit better than the notoriously poor 1974 1945. If leanout at WOT in your 1945 is causing the ping, the new carb might well smash that bug along with others; you will likely have to go through your various sets of different-heat-range spark plugs again once you have a carburetor that's working for you instead of against you.

(But you should still make sure your exhaust system isn't restricted, too.)

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PostPosted: Sun Sep 20, 2020 12:23 pm 
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EFI Slant 6
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Location: Annapolis, Maryland
Car Model: 1974 Dart Swinger 225
SlantSixDan wrote:
EGR is not active at WOT, so repairing the EGR system will not affect the car's behaviour at WOT


That's why I'm asking about the BBS even though I'm trying to fix the EGR too.

SlantSixDan wrote:
where did you find a new vacuum amplifier to order? Hope you didn't pay too much…).


I found it on eBay, for $16 shipped. It's listed for 1975-76 Dodge/Plymouth, NOS part No. 4027110. It could be a different calibration than mine, but I figure it's worth trying. There's a very wide range of prices for similar parts.


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PostPosted: Sun Sep 20, 2020 12:45 pm 
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Sixteen bucks ain't bad for a brand-new vacuum amplifier. And if you don't wind up using it—for example, because better carburetor with no EGR vacuum provision—you can toss it in the glovebox in case a puck is needed for a sudden unexpected hockey game.

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PostPosted: Fri Sep 25, 2020 4:31 am 
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Wild guess your current amplifier might be hidden vacuum leak.


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PostPosted: Fri Sep 25, 2020 6:24 am 
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I am assuming that you have checked and properly setup initial and total timing in the distributor?

I found that the advance can on my dist. was not working - I was trying to compensate for it by using more initial advance which was wrong too.

Once in looked into it I put a re curve kit in the dist. Installed a proper / functioning advance can and now I have a good curve with less initial timing ... The slots also limit the max. mechanical advance as per the re curve kit's instructions as well.


Maybe just another thing to look at and check.

Greg

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PostPosted: Fri Sep 25, 2020 6:42 am 
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Also another thought.. If you think it's lean by reading plugs that's one thing.. but I may also suggest inventing in installing an o2 Sensor. That will give you more percise Data on if the the carb / Jetting or the Timing causing the Issues.


Yet another thought... if you suspect it's the carb then try running a tank of 93 octane. if it pings less or not at all on 93 it's the timing in my opinion.

Greg

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PostPosted: Fri Sep 25, 2020 7:02 am 
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Location: Annapolis, Maryland
Car Model: 1974 Dart Swinger 225
Greg Ondayko wrote:
Also another thought.. If you think it's lean by reading plugs that's one thing.. but I may also suggest inventing in installing an o2 Sensor. That will give you more percise Data on if the the carb / Jetting or the Timing causing the Issues.


Yet another thought... if you suspect it's the carb then try running a tank of 93 octane. if it pings less or not at all on 93 it's the timing in my opinion.

Greg


Thanks for the ideas. In my rebuild thread (linked above) I have some measurements of the timing. I have measured it at various RPM and vacuum settings and it doesn't seem way out of line. Also, initial timing is set at 0 per the fender decal. Finally, I had this same WOT ping before I rebuilt the engine, and 93 octane did not help then. That's not to say I shouldn't try it again...

The O2 sensor: how would I install that and use it? Searching didn't turn up much that is helpful to a noob like me. I've also been recommended to use an AFR sensor but that's another one where I wouldn't know where to start.


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PostPosted: Fri Sep 25, 2020 7:07 am 
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afr and O2 are the same thing.

THis may be helpful:

https://www.youtube.com/watch?v=lyv0wh3fsLM

Greg

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PostPosted: Fri Sep 25, 2020 7:36 am 
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You mention you've gone down two heat ranges on those plugs. Did you cut the crush washers off the plugs? The plugs will run hot if the crush washers are left on.
What plugs are you running? Don't use projected electrode plugs in a high compression build. (Over 10:1) anything less is generally happy with them.

Where do you have the vacuum advance can plugged in? Should be ported vacuum.

Carbon or other buildup in the combustion chamber can lead to hot spots.

Do you have oil burn? If your getting engine oil in any volume into the combustion chamber, it's going to run hot and make deposits.

CJ

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PostPosted: Fri Sep 25, 2020 8:37 am 
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EFI Slant 6
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Joined: Mon Sep 23, 2013 6:52 pm
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Location: Annapolis, Maryland
Car Model: 1974 Dart Swinger 225
Ceej wrote:
You mention you've gone down two heat ranges on those plugs. Did you cut the crush washers off the plugs? The plugs will run hot if the crush washers are left on.
What plugs are you running? Don't use projected electrode plugs in a high compression build. (Over 10:1) anything less is generally happy with them.

I've got 3 ranges of NGK plugs, all with washers removed. They all have different length electrodes, but the ones installed now are not too long. Anyway, my compression is 8.9:1 static so that shouldn't be an issue.
Quote:
Where do you have the vacuum advance can plugged in? Should be ported vacuum.

The port is in the throttle body, right beside the PCV port. The connection is intended to go to the OSAC valve but I have it going direct to the distributor.
Quote:
Carbon or other buildup in the combustion chamber can lead to hot spots.

The engine only has 300 miles on it since being rebuilt. When I had ping at WOT before rebuilding, I suspected carbon deposits but I can rule that out now.


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PostPosted: Fri Sep 25, 2020 12:29 pm 
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Location: Vermont
Car Model: Slant Six M37
rich006 wrote:
When I had ping at WOT before rebuilding, I suspected carbon deposits but I can rule that out now.


I remember the plugs looking shiny white from your previous post. I don't know if it is good advice, but I personally would try a different carb if I had one, and or work to get the plugs have a tan color on them. I remember you richened up the Holley something like 4 jet numbers, and while that helped the look of the plugs it did not get them anywhere near a rich looking signature... When you are successful in getting the plugs to look tan to light brown, that ping ought to go away...


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PostPosted: Fri Sep 25, 2020 11:42 pm 
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Car Model: 2023 Eichman Digger?
The replacement amplifier may help at partial throttle, but not at WOT. I think your right there. I take it the distributor is in stock trim?

I have a 74 Valiant. The distributor had far too much advance, both mechanically and vacuum once work had taken place to get the engine breathing. Curve and all in mechanical can cause this. My Distributor had a 13R. Even the 9R became an issue at a certain point.

I Had the opportunity to work with Duster Idiot to get the distributor to play nice once a little work was done. The thing detonated like mad at moderate to WOT. That was going from the noodle pipe to a single 2-1/4" down pipe and a Holley 390 at a bare 8:1. Volumetric efficiency changes even a little bit, and the stock curve isn't right. At 8:1, I think the car was actually slower with the four barrel. :lol:

Hope you find the issue.

CJ

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