Timing Issues

WTDWN

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Advocate I

Apr 3, 2022
2
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30
Abilene, TX, USA
First Name
David
Last Name
Kucharik
I will try and be as detailed as possible.
-I have a 78 Bronco, 351 gears 35 inch tires
--I swapped in a Ford 300 I6 and a T-18 Tranny/Tcase from a 1980-81 ish Bronco.
---It has a single barrel carb, stock intake/exhaust
---Here is the issues, I have great low end torque, slow to moderate acceleration. When I shift from 2nd to 3rd, all is good. When I shift from 3rd to 4th,( RPMs around 2200-2500) my RPMs will drop around 1000-1200, and it will take FOREVER to gain speed. If I am going up a hill it will drop to 45 MPH and creep forever untill it can gain momentum and speed up. Once my MECHANICAL advance kicks in around 1600-ish, then I can gain speed again.
-----Things I have tried
-I installed a vacuume guage, no matter if I connect it to carb vac or man vac, it DOES NOT MAKE A DIFFERENCE. This may or may not be an issue. It changes wheather I have vaccume at idle, but once I am driving, if I shift and get back on it, the vaccume goes to zero.....
-I have advanced my distributor to max advance (total advance) and it RUNS GREAT!!!!! However, once I shut the truck off it will not start. I have it set now where cold start and hot start are both pretty easy.
---I have put a new distributor on
---I have changed the mechanical springs-set my advance stops
---all back to stock distributor now
Nothing fixed it. is there a distributor I can get that will be tunable for cold/hot starts, but kick mech advance in at 1200? is the vac advance ports faulty?
I realize 351 gears were not stock for a I6, and 78 is a bit heavier, but still.......
 

Bronco V-8

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The 300 6 built in that era had issues with vacuum leaks at the throttle shaft. check for leaks at the shaft
 

paul rondelli

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May 21, 2020
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That 300 six cylinder and the stick shift should run FOREVER. I would think anything in the drive train causing that many problems ... would also make a ton of noise. I would try the vacuum test . Spray some WD40 or starting fluid around your lines .... if the idle increases you have a leak.

don't give up on that 300 ... unless she is leaking a quart of oil a week. I would replace the entire carb assembly next.

I'm leaning toward bad gas also.... or junk in the tank .. causing fuel delivery issues.

Drop the tank .... clean it out ... and install a in-line filter.

Have you tired a little fresh gas directly in the carb?
 
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WTDWN

Rank 0

Advocate I

Apr 3, 2022
2
0
30
Abilene, TX, USA
First Name
David
Last Name
Kucharik
This is an issue from day 1 of the swap. Tank is new, ive drove it like this for about 2 years. Carb was new as well. I am trying an MSD box with start /retard option to allow me to increase my advance and still start it easily.
-I used a dial back timing light and total timing was 48-52*. at 2900 RPMs. However, I am loosing all vac advance at that RPM. I am wondering if I can use a "T" and join the man vac and the carb vac and see if that will get me SOME advance in the curve. This may allow me to back off my initial timing a bit.
--Thoughts?

I forgot to add---- Shifting at around 2000-2200, engine just sounds like it NEEDS to shift. I advanced the distributor, and with a total advance of about 48-50* it runs better, and can shift around 2500 RPMs.
What is everyone here shifting at? When I ask that, I mean what is the RPM you feel its gonna explode at?? I have to shift that soon, but feel i need to tune it to be able to SOUND ok at 2800 RPM's and just shift. Theres Shifting, and theres RED LINE shifting.....
 
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paul rondelli

Rank V

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May 21, 2020
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515
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I over rev my 1996 Bronco with a 302 and a stick. The 302 ( which is about the same size as your 300 six) only starts making power at high RPMs. she doesn't have that same low end torque that the 300 has. If I were to shift at anything below 3,500rpms she wouldn't be able to get out of her own way. This is why everyone hates a 302 in a Bronco ... most are running auto transmissions that want to shift well under 3,500pms. The 302 is great in a mustang... pushing high rpms.. on a light weight ride. You really need to push a 302 a little harder to see any gains in a armored tank..... and then it will only be at or well above 3,500rpms.

i think you have a granny gear in the 4 speed stick that is made for low end pulling. My buddy had almost the same year Bronco and drive train. One day we hit some deep sugar sand on a trail in Florida ... he puts the Bronco in 4 low .. first gear (granny)... and steps out of the rig. She just slowly idles her way right through the middle of it. After that I was sold on a 300 with a stick and a granny gear.

most folks running the above set up .. don't even start out in first gear. They only use that for towing. It is a life saver when you have a heavy load behind you ... or you want to crawl your way though absolutely ANYTHING.

head on over here and introduce yourself ( if you haven't already). These guys are super cool and live and breath the Ford 300 six. The site is very active and the members extremely knowledgeable.


FordSix Performance Forum


I already own 2 OBS Broncos .... but always looking for a 1986.... with a 300 and stick. I relocating to Tenn next month ... and getting far away from my current HOA. They are the only reason I don't have a full stable of Broncos.
 
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Bronco V-8

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Its not a diesel, shift at 3200-3600 unless you in slow traffic.
I would set everything back to factory specs.
Vacuum will be zero at WOT ,but at part throttle cruise should be quite high.

Does that distributor have the dual port set up on it?