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Discussion Starter #1
Hi guys, i have a 347 SBF engine that's just exhausted me on ideas to solve it's issues.

This engine is in my 1971 Ford Bronco, which is a daily driver. I have a few issues that i can't seem to solve so i am now thinking maybe the camshaft is just a complete miss for my combo.

First major issue is dieseling, no matter the octane, plug heat range, timing it does it. (Yes i debured the pistons & chambers before assembly). Second is the A/F ratio is just plain stupid when i am cruzing along with no load. Bounces wildly between 13.8-15.5. Could the cam be giving me issues?

A little info on the engine,
9.8:1 CR,this was determined buy cc/ing everything so it's real.
Brodix ST5.0 heads with chambers smoothed.
Edelbrock F4B intake with 1" open spacer.
580 CFM holley.
1-3/4" mid length headers, 2.5 duals.

Camshaft XE268H-10

[email protected] .050
.509-.512 Lift 1.6 rockers
110 L/S installed straight up. Degreed it at assembly.

Any help or advise of things to try would be great.
Thanks Brandon.
 

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"580 CFM holley" Is this a mis-print?


Keith
 

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Cam doesn't look way off? Lift seems to be a little low, buddy has a stock 302 with a .517" roller, and I'd hope it would have a 750 cfm on it atleast...
 

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OK. What is the initial and total timng?

Do you know what PV is in the carb? I am thinking the cruise vacuum is close to the PV opening and it's pulsating. Try installing a PV with a higher rating and see if that helps the a/f at cruise.

I would have a minimum of a 650 on that engine.
 

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Discussion Starter #7 (Edited)
My timing marker was installed with the heads off and a indicator on the piston so it's dead on. Balancer is new also, so i don't think my timing mark has moved. Initial is 18 deg and total is at 34 now. Been as low as 24 and as high as 40 and everything in between with total timing. A/F acts the same but the engine just runs shity.

I have tried may different PV's and currently have a 8.5 in it now. 6.5 8.5 10.5 all act the same for the no load riding down the road situation.
I have tried a 3.5 PV knowing that is way off but i am at the point " try anything" to see a change.

This is why i am thinking the cam if F'ed up somewhere, or maybe just totaly wrong for the combo.
 

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the carb too small will not make it mess up like that... I know some friends of mine that ran a 390 holley on a dirt track for years and it did great. A carb prob could cause it but not because its too small.. Im thinking idle is too high or vacum leak or timeing problem or all of the above
 

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Discussion Starter #9
Thanks guys for your input! Not to sound like an ass but this isn't my first engine build so i have experiance diagnosing the tune up on a engine. I have tried timing, jet's, PV's, different carb it's just not happy. Sprayed everything possible looking for vac leaks and it's sealed tight. I can idle it at low as 700rpm all day. Pull the plugs and they are nice and clean so no oil or air from under the intake.

My friend has a 306 with a 650 carb so we switched just to see and my carb ran fine on his engine and his gave the same results as what i have on my engine.

I have tried everything possible to help but nothing does. This is why i think the cam may be crap. Never ever had any issue like this with any other build in my life!
 

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Not the cam or the carb size IMO, I only offered the different size carb for a reference, never said that was causing the issue.

Ok on the PV and timing.

What RPM are you cruising at when the A/F issue happens?

At what RPM does the advance start and what rpm is it all in by?

Keith
 

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Does this distributor have vacuum advance? If so, when it is acting up what are the advance numbers? Sounds like not enough timing when lean cruising to me.
 

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Discussion Starter #14
I have never checked the cranking compression, it is a vac advance Ford Duraspark distributor and it starts advancing @ 1800 rpm and done by 3200rpm. I drive between 2200-2600 rpm.

I have tried running it without the vac hooked up and everything is the same. The timing mark is rock solid with the light on the balancer. Like i said before i have had total timing @3200 rpm set at 24 - 40 advanced and everything in between and it doesn't help a thing.

Think i am just going to pull it all apart and have a look inside.

Thanks for all the help, Brandon.
 

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I have never checked the cranking compression, it is a vac advance Ford Duraspark distributor and it starts advancing @ 1800 rpm and done by 3200rpm. I drive between 2200-2600 rpm.

I have tried running it without the vac hooked up and everything is the same. The timing mark is rock solid with the light on the balancer. Like i said before i have had total timing @3200 rpm set at 24 - 40 advanced and everything in between and it doesn't help a thing.

Think i am just going to pull it all apart and have a look inside.

Thanks for all the help, Brandon.
If there is a problem with the cam cranking compression will be off.

If your using a durasapark where are you hooking up the vac line?
 

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Discussion Starter #16
If there is a problem with the cam cranking compression will be off.

If your using a durasapark where are you hooking up the vac line?


I will have to find my gage and check it before i pull it down just see whats going on.

My vac line is currently on a full vac port, if i put it on the timed port of the carb i could tell no change so i just left it where it's at.
 

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I will have to find my gage and check it before i pull it down just see whats going on.

My vac line is currently on a full vac port, if i put it on the timed port of the carb i could tell no change so i just left it where it's at.
If I remember right the vac advance adds timing so if you have it on manifold vac then as you increase the throttle the timing will retard.
 

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Discussion Starter #18
If I remember right the vac advance adds timing so if you have it on manifold vac then as you increase the throttle the timing will retard.

Maybe i got it all backwards on the distributor then. This is my first build using any type of a vacuume advance distributor so i guess i need to do some home work.

I thouhgt as vac left the manifold it advanced the timing. I hate the vac stuff, tempted to order a new mechanical dist this way i know what i have!!!!
 

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Maybe i got it all backwards on the distributor then. This is my first build using any type of a vacuume advance distributor so i guess i need to do some home work.

I thouhgt as vac left the manifold it advanced the timing. I hate the vac stuff, tempted to order a new mechanical dist this way i know what i have!!!!
It has been a while for me as well.LOL The easiest way too check ity is get a timing light and get a hand held vac pump and apply vac and watch timing.
 
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