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Old 06/30/11, 09:05 AM   #1
Bhall75
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Won't start when hot.

I am out of ideas on why my 77 Bronco will not start when hot. Below is the story.

Before I rebuilt the engine completely, it was doing this. It has new pistons, heads, cam, crank, gaskets, intake, carb (rebuilt edlebrock 1406) etc... It will start up set at about 10-13 BTDC an run great. After it warms though it will start rough idle and won't restart if shut off. If you retard the timing to about 30 BTDC if will start when warm but not run well.

Replaced Parts:
Complete Distributor,cap,rotor,plugs,wires (all new).
Ignition Module (3 times)
Coil
Solenoid (2 times)

It will smoke a little out of one pipe after it warms. Not sure if the smoke is from prior build up in the pipes from old engine burning off. Also valves will chatter at high rpm's when hot. Could this be a problem with low compression in one of the cylinders? This is the original motor, not roller engine.

I feel I am missing something I am unaware of.

Any ideas are helpful.

Thanks,
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Old 06/30/11, 10:39 AM   #2
broncnaz
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I'd almost say it sounds like you develop a vacuum leak once the engine is warm and that is casuing the rough running and hard restart.
Are you sure your temp gauge is working correctly? how warm is the engine getting? Could also be vapor lock might try shielding the gas line to the carb and putting a thicker gasket or plastic spacer under the carb.
Hard to say why it smokes could be old residue in the exhuast or clould just be a cylinder or two that hasnt fully broken in. Sometimes it takes 5000 or more miles for everything to actually seat properly.

73 Ranger 2 1/2 lift 302 TFS heads NP435,PS,PDB, tierod over, 33x10.50x15 BFG M/T
71 Sport 63,000 miles all orginal except for cut fenders 302 3sp 4.11's D44/BBTrac lok rear
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Old 06/30/11, 11:08 AM   #3
Bhall75
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I would say it is at least getting to 180 degrees. Could it be a leak around the intake. I did take the intake and the heads off after they were torqued to check if I had the gaskets right. It was never started so I figured the gaskets were ok.
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Old 06/30/11, 11:36 AM   #4
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I had the same issue and considering the time of year, likely the same cause. Parked when hot, the carb would get heat soaked, resulting in fuel bowls percolating which flooded the motor. Condition is aggravated by tube headers radiating huge heat. My solution was to add a phenolic spacer under carb, adjust fuel bowel level a tad lower, and open hood when parked if a warm day. Given the chance, let engine idle down for a moment so coolant temp drops to lowest allowable level.

'75 w/modified Boss 351C, Centerforce clutch, NV3550, 3-inch lift, National springs, Douchtech shocks, Wilwood discs, Bronco Design body, 6-point cage, Runk push bar, door inserts, 33" BFG ATs, owned since '79. Also had '68 & and; '71
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Old 06/30/11, 11:55 AM   #5
Bhall75
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It does have tube headers. And it is parked on concrete. I will put spacer in and reduce bowl level and see if that helps.
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Old 06/30/11, 12:43 PM   #6
broncnaz
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While tube headers can put a lot of heat into the engine bay they also dont hold the heat when the engine is shut down like manifolds do. I really doubt its the headers many people with stock manifolds have the same issue. I'd try the spacer first without reducing the float level if the spacer doesnt fix it then try other stuff.

73 Ranger 2 1/2 lift 302 TFS heads NP435,PS,PDB, tierod over, 33x10.50x15 BFG M/T
71 Sport 63,000 miles all orginal except for cut fenders 302 3sp 4.11's D44/BBTrac lok rear
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Old 06/30/11, 01:37 PM   #7
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Quote:
Originally Posted by VT_Don View Post
I had the same issue and considering the time of year, likely the same cause. Parked when hot, the carb would get heat soaked, resulting in fuel bowls percolating which flooded the motor. Condition is aggravated by tube headers radiating huge heat. My solution was to add a phenolic spacer under carb, adjust fuel bowel level a tad lower, and open hood when parked if a warm day. Given the chance, let engine idle down for a moment so coolant temp drops to lowest allowable level.
Have to give credit when due. Nice to read a post of your's without the extra comments. Kudo's for you.

66 half cab 203ci I6, Classic Inlines aluminum head and intake, DSII, Holley 390 cfm 4V, Isky cam, Keith Black flat top pistons, ARP studs, balanced, 9.7:1 compression
55 F100 build in progress
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Old 06/30/11, 01:46 PM   #8
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Explorer, yeah but just wait for the usual clowns with absolutely no FIRST HAND experience with this topic to add their two cents.

'75 w/modified Boss 351C, Centerforce clutch, NV3550, 3-inch lift, National springs, Douchtech shocks, Wilwood discs, Bronco Design body, 6-point cage, Runk push bar, door inserts, 33" BFG ATs, owned since '79. Also had '68 & and; '71
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Old 06/30/11, 05:55 PM   #9
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I betcha it that there vapor lock. I drive with a cooler full of borritos and when I park a throw a few next to the carb to cooler down some. Then when I leave the bar, i eat borritos on the way to work.
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Old 07/01/11, 04:13 AM   #10
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Vapor lock can not occur within the carburetor as its bowls are vented to atmosphere. Vapor lock happens within the fuel line between the pump and carb's needle valve. Both conditions benefit from increased airflow under the hood. As mentioned, use a proper shroud and fixed pitch fan typical of what short track, modifieds use. Flex fans are near useless.

Last edited by VT_Don; 07/01/11 at 04:49 AM..

'75 w/modified Boss 351C, Centerforce clutch, NV3550, 3-inch lift, National springs, Douchtech shocks, Wilwood discs, Bronco Design body, 6-point cage, Runk push bar, door inserts, 33" BFG ATs, owned since '79. Also had '68 & and; '71
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Old 07/01/11, 07:07 AM   #11
77BRONKOTN
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DId you change anything in the valvetrain. Sounds a bit like you could be chasing open valves with timing the dist.

Also, where do you have the vaccum advance hooked to. Any change in symptoms without using the vaccum at all.

After my engine change two weeks ago I overlooked something that drove me nuts. I reversed the firing order, then I fixed it but crossed two wires. Lazy, sleepy I dont know what happened as Ive built many motors etc.

Frank
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Old 07/01/11, 07:57 AM   #12
Bhall75
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Frank,

I had the heads shaved .008 and new exhaust valves put in. How can I check if I have valves staying open. The engine sounds great when at idle but around 1500rpms I get valve? or lifter? noise. Could it have something to do with the timing. I hit it with the light and set it at 13 last night and it sarted up fine after putting spacer under carb. I shut it off and it fired right back up when being hot but the chatter noise was still there at 1500 + rpms.

Thanks
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Old 07/01/11, 08:20 AM   #13
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Get a compression gauge. If you have a valve hanging open, you'll know definitively. I added cast, Cobra valve covers to a set of 351W heads and a compression skip was driving me nuts. Discovered one rocker arm was interfering with a rivet head on the cover baffle. If you have hydraulic lifters and a tapping noise, I'd be focusing on rocker arm interference.

'75 w/modified Boss 351C, Centerforce clutch, NV3550, 3-inch lift, National springs, Douchtech shocks, Wilwood discs, Bronco Design body, 6-point cage, Runk push bar, door inserts, 33" BFG ATs, owned since '79. Also had '68 & and; '71
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Old 07/01/11, 08:38 AM   #14
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Quote:
Originally Posted by VT_Don View Post
Vapor lock can not occur within the carburetor as its bowls are vented to atmosphere. Vapor lock happens within the fuel line between the pump and carb's needle valve. Both conditions benefit from increased airflow under the hood. As mentioned, use a proper shroud and fixed pitch fan typical of what short track, modifieds use. Flex fans are near useless.
Hey Don, where can you get the pitch fan you are speaking of? More specifically a page link to see what you are talking about

Bob-
1973 Bronco
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Old 07/01/11, 09:24 AM   #15
VT_Don
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Bob, the model I have has a blue hub, with heavy ridged aluminum blades. Had purchased it over the counter at a speed shop, but has no identifing markings. Could be a Derale product. Check out their ridged, race fans.
http://www.derale.com/
Believe they are SFI approved to 8000 RPM

'75 w/modified Boss 351C, Centerforce clutch, NV3550, 3-inch lift, National springs, Douchtech shocks, Wilwood discs, Bronco Design body, 6-point cage, Runk push bar, door inserts, 33" BFG ATs, owned since '79. Also had '68 & and; '71
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