468 bbc diesels bad - Chevelle Tech
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post #1 of 24 (permalink) Old Mar 22nd, 20, 4:46 PM Thread Starter
 
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468 bbc diesels bad

I have a new 468 bbc, brodix race rite heads
9.7-1 compression and a bootlegger roller cam,
585 lift .232/244 ,edebrock rpm intake,770 quick fuel, fuel/air 12.5 ,base timing 16° 36°full advance. No matter what I've tried I cant get it to stop desieling and spitting fuel back when the key is turned off, tried selinoid stop, drilled holes in throttle blades,vacum advance to full vacum,not enough to to keep it pulled back, 6inches of vacum,as of now all blades are completely closed with 5/32 holes in all 4 blades..very frustrating
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post #2 of 24 (permalink) Old Mar 22nd, 20, 4:53 PM
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re: 468 bbc diesels bad

All 4 blades have holes, as mild as that combo is you should not need 4 holes and 2 holes may not be needed.

The deal is you can't shut off all the air with the holes there and then think about the PCV or other vacuum sources feeding the carb some air.

If no holes in throttle plates your solenoid would slam the throttle plates all the way shut and it would die.
Well unless your secondary side is opened too much and there is Idle feed in the secondaries.

You may be out of luck until you fill the holes.
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post #3 of 24 (permalink) Old Mar 22nd, 20, 5:46 PM Thread Starter
 
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Couldn't get it to idle with 2 holes,even before the hole got drilled and all closed it would still run off the selinoid was the qst thing I tried ,and the cam doesn't like to idle below 800 rpms and to accomplish that the throttle blades are way open, main and secondary. But I have new blades on way ,probably start from scratch again
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post #4 of 24 (permalink) Old Mar 22nd, 20, 8:54 PM
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Re: 468 bbc diesels bad

Did you verify your damper is zero @ TDC. It should have more vac. than that.

Jim

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post #5 of 24 (permalink) Old Mar 22nd, 20, 10:06 PM
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jeff
 
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Re: 468 bbc diesels bad

^^^^^ What 77 cruiser said 468 with that little cam and 6" of vacuum is perplexing.

But you only mentioned Brodix Race rites.. not what RR you have.
If you stuck a large runner one on there that would explain the low vacuum reading.

Cam timing may be off also.
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post #6 of 24 (permalink) Old Mar 23rd, 20, 6:12 AM
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Bob
 
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Re: 468 bbc diesels bad

holes in the throttle blade contribute to run on obviously, the o2 reading reading is not reliable at low rpm with your cam, is the carb 4 corner idle? do you have multispark ignition? a cranking compression test will indicate whether the tuning tactics are worth the effort
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post #7 of 24 (permalink) Old Mar 23rd, 20, 8:23 AM
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Re: 468 bbc diesels bad

jeeze, ever though to notice the idle speed? Can it be turned down with the idle speed screw in the drivers side of the baseplate?

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post #8 of 24 (permalink) Old Mar 23rd, 20, 9:24 AM Thread Starter
 
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The heads are the race rite 270 runners, even before the holes got drilled it still desiels like a pig, I have a new Holley 81053 I believe thats the number ,its a 850 vacum secondary and no change and that carb didnt feel right, the 770 in my 77 blazer with a 4speed would break the tires loose at 30mph and the 850 was a pig. I'm going to try a bigger power valve , I have a 3.5 now going to move up to a 65, been doing alot of reading on power valves and they dont change idle are flood when there open at idle,I had this same problem with another 454 i have, but for the life of me I cant remember what I did to get the vacum up.
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post #9 of 24 (permalink) Old Mar 23rd, 20, 9:31 AM Thread Starter
 
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And before the holes were drilled the only way it would idle is if main and secondary blades were open well past the transition slots, again i was defeating the purpose of those, the 850 had a bad hesitation when getting after it. The engine has maybe 30 miles on it. Professional built bottom end, all forged, balanced. I installed the top end and I guess you can say I know what I'm doing. With the lanuti roller lifters i set preload at half a turn,custom pushrods from crane. The ignition it a davis United ignition. HEI
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post #10 of 24 (permalink) Old Mar 23rd, 20, 10:07 AM
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Re: 468 bbc diesels bad

Was the cam degreed? Have you checked the damper to make sure the timing marks are correct? Any vacuum leaks?

Jim

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421 Profilers ported by Eric Weingartner, Straub HR 3200 conv. from Jake 200-4r w/ 3.73's
Machine work by Torvinen's machine
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67 Imp.SS for the wife 275 hp 327-TH350
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post #11 of 24 (permalink) Old Mar 23rd, 20, 10:14 AM
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jeff
 
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Re: 468 bbc diesels bad

I have to ask.
When you had the solenoid stop hooked up I assume with key on it had voltage and key off the voltage went away.

I have seen a bad diode in an alternator keep voltage flowing through the system.

I assume you unscrewed the throttle plate idle screw all the way when you installed the throttle solenoid.

There is just no way it should diesel if all air is shut off..Unless you have a very weak throttle spring and the venturi vacuum
is pulling the throttle blades open.

No vacuum leaks around the intake gasket or carb base??

I had one SBC 11.9 compression Iron heads and [email protected] .050 cam turn the key off and it was like you never turned the key off.
First time it happened I got out and popped the hood and pulled the HEI power wire off.
It kept on running like you pulled nothing off.

Idle solenoid fixed it..I removed the idle screw completely.
It was a carter AFB 750..They always ran better than my stock Holleys. Especially on the big end.
Later I began modifying the Holleys with thinned throttle shafts small screws in throttle plates and a lot of porting and epoxy work.
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post #12 of 24 (permalink) Old Mar 23rd, 20, 10:23 AM Thread Starter
 
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Yes it was hooked to the fuse box, this is a new alternator, the motor does seem to drag on after the key is turned off, that sudden stop dont happen ,its like the engine turns off slowly. Perhaps I should pull lead wire to the hei and see what happens.
And for the other comment ,no the cam ain't degreed, never degreed a cam for my use,maybe if I had a all out race engine I would,that's another subject i read into alot , for my application straight up seems legit.
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post #13 of 24 (permalink) Old Mar 23rd, 20, 10:43 AM Thread Starter
 
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And the issue I had with the selniod was i had to have the blades open alot for a decent ilde,that created a bad dead spot in my carb
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post #14 of 24 (permalink) Old Mar 23rd, 20, 11:18 AM
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Re: 468 bbc diesels bad

cranking compression test results might reveal the cam is retarded thus the low rpm lack of power or some problem with an individual cylinder, I would do that before changing a bunch of things
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post #15 of 24 (permalink) Old Mar 23rd, 20, 11:26 AM
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Re: 468 bbc diesels bad

Have you tried more initial timing.. I would bump it to 22 and then 24 initial and reset the idle stop screw.
See if it dies then.
It may just not like the 16 initial.

I know my cars all like 18 or more Yea the total will be way up there unless you have a stop built in.

Not worried about the total at this point just they dying part of it and the idle part.
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