Author Topic: Motor swap has an oocasiomal pop  (Read 379 times)

Offline Cams Caddy

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  • Name: C Atkins
Motor swap has an oocasiomal pop
« on: October 08, 2017, 10:19:27 AM »
I put a 74 mill in my 71 eldorado ,seems sluggish with an occasional misfire pop when I floor it should timing be at 10, used carb to manifold gasket from the 71, could that be the issue! I know now I should have changed timing chain and gears , the car ran like new in the donor car but did pop and backfire  some gas spit out the carb, the donor 74 eldorado sticker says set at 6 degrees, others have suggested 10 tried both settings, just slow rev up and pops, tried different vac advance ports, no change,  and the 71 car had pertronics egnitiin, the donor car has hei, read a post that the old cars 12 vols supply may not be enough for the hei dist, ran a hot wire to coil, no change, all cylinders are above 110 psi compression, carb probs shouldn't make backfire?? Don't want to change timing chain and still have the same issue

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« Last Edit: October 15, 2017, 03:04:53 PM by Cams Caddy »

Offline 35-709

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  • Name: G. Newcombe
Re: Motor swap has an oocasiomal pop
« Reply #1 on: October 08, 2017, 10:45:51 AM »
How many miles on the '74 you put in?  Has it been rebuilt?  If not, did you at least replace the timing chain and cam gear (the 472/500/ 425 weak spot)?  What you are experiencing says to me the timing is off. 
« Last Edit: October 08, 2017, 10:56:57 AM by 35-709 »
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold
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Offline "Cadillac Kid" Greg Surfas 15364

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Re: Motor swap has an oocasiomal pop
« Reply #2 on: October 08, 2017, 10:58:51 AM »
What did the motor come out of? 
Greg Surfas
Cadillac Kid-Greg Surfas
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Offline TJ Hopland

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Re: Motor swap has an oocasiomal pop
« Reply #3 on: October 08, 2017, 04:09:36 PM »
There were some years there was an open exhaust port under the carb that required a special gasket.

Was the 74 an HEI?  That was the coil in cap electronic ignition.   Or still points?   

71 I think still had the speed controlled solenoid that cuts the vacuum advance.   73+ didn't have it.

74 would have EGR along with the proper port and tune on the carb to run it. 

Chokes were slightly different and gasket height effects the adjustment

How about smog pump?   Did they both have it?   If the dirverter valve isn't working so its always on it will pop sometimes pretty violently especially on deceleration. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
75 Eldo rusty but trusty
80 Eldo Diesel
And other assorted stuff I keep buying for some reason

Offline Cams Caddy

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  • Name: C Atkins
Re: Motor swap has an oocasiomal pop
« Reply #4 on: October 09, 2017, 12:36:06 PM »
The motor came out of 74 eldorado, has who and no smog pump

Offline Cams Caddy

  • Posts: 3
  • Name: C Atkins
Re: Motor swap has an oocasiomal pop
« Reply #5 on: October 09, 2017, 01:16:52 PM »
Has HEi , so would the timing be 10? And no smog pump, I did not changeting gears , all seemed tight, I no looking back for 50$ I should have but the car ran so good but it did pop in the donor car when I was trying a burnout, it seems to rev up slowly, not a big job to do the Cain and gears just want to eliminate weather it's carburatikn or timing

Offline "Cadillac Kid" Greg Surfas 15364

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Re: Motor swap has an oocasiomal pop
« Reply #6 on: October 09, 2017, 02:55:57 PM »
I like burn-outs.  It is a definite way to prove you know how to abuse cars.  They are especially good in an Eldo. Guaranteed CV joint or at least axle boot replacement after one.
That said, you have a bit of research to do. Is the HEI fully functional? Vacuum advance, mechanical advance and how many of the original emissions controls are still in th4 circuits and are they functioning?
Does the motor "rattle" when you try medium speed, third gear acceleration?
Essentially, determine what you have and how much of it is working.
Greg Surfas
Cadillac Kid-Greg Surfas
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Offline TJ Hopland

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Re: Motor swap has an oocasiomal pop
« Reply #7 on: October 09, 2017, 07:14:30 PM »
The early HEI's had a different design of the weight area that seemed to be really good at sticking.  Last one I had I could not even unstick it with a hammer in a vice.    The also do better with full 12v, not though a resistor wire which was how they did it in the early 70's.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
75 Eldo rusty but trusty
80 Eldo Diesel
And other assorted stuff I keep buying for some reason

Offline "Cadillac Kid" Greg Surfas 15364

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Re: Motor swap has an oocasiomal pop
« Reply #8 on: October 09, 2017, 07:23:42 PM »
I believe what TJ is saying is that if you have used the original ignition wire that fed the coil/distributor you are not getting 12 volts to the HEI.  That would tend to decrease the available power.
Greg Surfas
Cadillac Kid-Greg Surfas
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-