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Old 07/13/18, 03:59 PM   #1
so cal
Joined: Jul 18
Posts: 3
Help with new crate 302 that wont idle

Have a rebuilt 302 (by a bronco company called "blank connection") with 400 miles on it. It wont idle. Its a 306 with a "RV" cam, holley truck avenger carb and flat lifters. You can see it on the "blank connection" company web site for build specs. They wont give me any information on the build because I bought the bronco from someone else. They wont even discuss the "standard" crate motor they offer. Go figure. Have had it to 5 shops. Vacuum steady, pertronix III dist and coil sent to factory for testing (ok), fuel pressure good, valve covers removed and rockers etc all good, TDC checked, timing at 10 degrees, firing order older 302: tried 351 order w/o success, holley was swapped out and no change, fuel fresh, plugs new NGK gapped at 35 (had autolites gapped at 45), air fuel ratio 13.9 to 1. Compression 170 on cyn 1 to 6, then 150 on cyn 7 and 8. Shop tells me that the original buyer probably did not break it in properly and rings or cam damaged. They recommend new motor vs removing and repairing mine as more cost effective. Anyone care to offer suggestion on troubleshooting what I havent thought of or comment on replace vs repair?
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Old 07/13/18, 04:18 PM   #2
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Maricopa, AZ
Joined: Jun 02
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Define won't idle. You state steady vacuum and the ability to set the base timing and it has 400 miles on it, which makes it sound like it is drivable.

As for replacing a 400 mile engine with no known mechanical flaws, sounds like they don't want to do any diagnostic work. The lack of knowing what cam is in it is a huge question. Often crate engines are built and sold on a HP number, often with a huge cam to make that number.

Sounds like you have the basics out of the way. I would be tempted to pull the engine and take it apart. Not so much of a rebuild but an investigation. Look over the parts, get numbers off of them, find out what pistons you have, what cam, etc.

"She's built like a steakhouse but she handles like a bistro"-Zapp Brannigan
“How hard can it be?”-Clarksonius 4th century BC.
Full throttle, it either solves the problem or ends the suspense.
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Old 07/13/18, 04:30 PM   #3
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Joined: May 18
Posts: 9

How does it run above idle?

“Sometimes I wonder whether the world is being run by smart people who are putting us on
or by imbeciles who really mean it.” - Someone
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Old 07/13/18, 08:22 PM   #4
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San Jose, CA
Joined: Nov 03
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Hey twood, welcome to classicbroncos! Sorry it's for such a crappy reason, but hopefully you can find help (or just solace) here.
And since I don't have an answer for you at the moment (still thinking), I'll just throw in an FYI that a rebuilt engine is not a "crate motor" just so we're on the same page.
Crate motor is all brand new stuff, including the block. A rebuilt engine is simply a rebuilt engine.

Ok, so that out of the way.... Did the company doing the diagnostics at least test for sure if the cam lobes were flat? Did they remove the valve covers and run it for a bit?
They're correct that this could be a cam issue of course. Not knowing if the new cam was properly broken in is a huge question mark with any new setup. But it's easy to test too, while the engine is running I would think. Messy, but doable.
Checking to see if all valves are being opened the same amount, even just visually, can go a long way to deciding which direction to take.
Even rocker arms get loose and pushrods bend and fall out.

But then, there's that steady vacuum thing you mentioned (good full explanation/description by the way!) which would normally indicate zero issues with the valvetrain.
But while that's not helping, it may still be very good news!

What is the vacuum reading by the way? Less than 15? Or is it between 17 and 21? The latter being fantastic vacuum for a cammed engine. Especially when it's an unknown generic "RV" cam and not a known part.
Crappy of the builder to keep information secret though. Once it's sold anyone can easily check there products and build quality. Wonder why they think nobody but the original purchaser has the need, or the right to know details.

I'm with Broncobowsher too, in saying hold off on all the new-motor talk until more things have been determined for sure. An engine can survive a wiped out cam and it would be a shame to waste all that nice new stuff.
The engine might not be happy by any stretch, but it can still survive and come back to play hard again.

When you were verifying the firing order, did you watch rocker arms, or at least put a finger over the different spark plug holes to verify the order 100%? This may be important, so keep that in mind if you did not.

And what about the carburetor? Will it idle (even too high) at some point if you just keep turning the adjusting screw farther and farther? At what point does it run without you pushing on the throttle?

Did you check for vacuum leaks while it's running? And what about the PCV valve? Is it connected correctly?
Ignition timing, pcv valve, evaporative emissions stuff connected (if applicable)? Anything else modified you know of?

Got any pics of the engine compartment you can post up for us to see? Aside from the act that we love to see pics of all our Broncos here, we might also be able to see something amiss that others might have missed.
Not sure how familiar you are with Early Broncos in general, but not so much a pic might help. As it often does.

Good luck! Oh, and what year is your Bronco? Not sure if I asked that already.


'71 Wagon, 3.5" WH, F150 disc brakes and steering, 4.11 33x11.50 Thornbirds, Kayline soft top, Hanson bumpers. "Built, not bought"

'68 LUBR, 2.5 + 1 WH, 31x10.50, 4.56, Explorer and 4R70w by EFI Guy, WH disc brakes, Hanson front bumper, Warn winch. "Bought, not built"
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Old 07/15/18, 09:20 AM   #5
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Long Island, NY
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Hi, been thinking about the idle and I keep coming up with a couple of things. Besides young guys mostly don't know or want to know about carbs, I would triple check the basic stuff. First, check and make sure the high idle cam on the choke side is completely off. Next remove and plug any vacuum hoses from the carb and intake manifold to eliminate these as a source of a vacuum leak. Next remove the carb and all the gaskets and spacers and make sure they are all right side up and lined up properly. Make sure the holes in the gaskets are not hanging up the throttle plates. There should be no sealer used. I've re- used carb gaskets before that should not be a problem, unless a gasket or spacer is ruined or cracked. Just snug down the carb nuts, medium snug. No muscle power. If you take the carb off you can verify the throttle plates are completely closed, and in the transfer slot area in the venturis. Good luck
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Old 07/15/18, 09:52 AM   #6
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Maricopa, AZ
Joined: Jun 02
Posts: 28,186
I'm still waiting for what "won't idle" means to the original poster.

"She's built like a steakhouse but she handles like a bistro"-Zapp Brannigan
“How hard can it be?”-Clarksonius 4th century BC.
Full throttle, it either solves the problem or ends the suspense.
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Old 07/15/18, 12:00 PM   #7
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Posts: 5,261
What does won't idle mean? Stalls? Rough? What is the vacuum?

My dad sold his 1968 GTO because it was too "loud". I keep reminding him of that error..

How does it run off idle? 400 miles it moves then? How, scalded ape fast, barely, middle of road fast?

What is the name of the engine shop? Not finding a blank connection in google, do you have a link?

73 Explorer , 347stroker, NV4500 D20, Quadrajet spreadbore with manual altitude compensation, 4.1 ARB, Moser CTM Currie, 78 FSB disks, 76 Tbird calipers. 3.5 WH suspension lift, 2" Body lift for NV clearance.

Build here:
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Old 07/15/18, 02:23 PM   #8
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Stockton, CA
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I'm guessing Bronco Connection

'When my Bronco is finished' is only a hypothetical statement.
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Old 07/16/18, 08:09 PM   #9
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El Monte CA
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So your off on a bad foot. Someone sells you a used Bronco that the engine is running poorly and you start out bad mouthing the company you have no personal dealings with. Then you post that 5 shops can't fix or find what the actual problem is. Slaming the first company isn't fair. You bought a problem its your problem not theirs. Take it up with the seller.

With such low miles pull the engine out and do a full tear down of the engine. Suspect everything. Unless the bores are scored parts to repair should not be too expensive. 7/8 are a problem, focus on there, starting at the pistons and work your way up from there. 2 or 3 days labor if you use someone that knows what they are doing. My guess a grand should do it. Then you have to take it some place to be properly tuned with someone who knows what the hell they are doing.

1974, stock 302, C4, BFG KM2 33x12.5x15, 8in rim, detroit rear, trutrac front 4.11 gearing, Warflairs,2.5" lift, chevy disc conversion, Hydraboost, owned since Christmas Eve 1977
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