351c running poorly

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Joined
May 28, 2011
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Location
Phoenix
My Car
'73 mustang convt.
The symptoms are getting worse. Bad idle and really poor slow speed acceleration including uneven hesitation.

What I know: I went to check the timing and my timing light showed sporadic RPM on #1. When I put it into 'flashing light' mode the light was very inconsistent. I figured there was a problem with the light so I revved the engine and the rpm reading and light pattern became more consistent.

I moved the induction wire for the timing light to #3 and had the same results. (So I suspected the light had an issue)

At some point I moved it to a different wire and the timing light showed fairly consistent RPM and the light blinked as you would expect. I tried several other cyl with similar 'okay' results.

I swapped out the distributor cap and it didn't have any effect.

I also swap the #2 and #1 wires and the problem stayed with #1.

I had previously pulled the spark plugs and didn't see anything wrong with #1 and #3

#8 and #7 are firing fine. (They are on either side of #1 and #3 in the firing order).

#1 and #3 are on different intake planes.

Again, the problem got worse over time. That is it would drive funny after a 20 or so mile drive. Now it seems to happen much sooner. I don't have a choke so it always runs bad cold. In the morning I will check to see if I have the same 'timing light' symptoms when it is cold.

My next step is to replace #1 and #3 plugs.

Any input?

 
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I bet ignition problem.

Back in the day I had a buddy running the same dizzy and carb I had and we

could trade in and out parts for diagnosis... oh the good ol days.


Oh I just realized you are the 3 2 guy I envy!

I have had a couple Pontiac 6 pak setups in the past and

another thought is a worn accelerator pump in the center 2v

 
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It sounds like gas fouled plugs to me. Have you tried adjusting/re-calibrating the center carb (your sig line says ti-power)? What carbs do you have? You could try one heat range hotter plug in the two offending cylinders. Getting near even fuel distribution with a dual plane intake is difficult and running two different heat ranges of spark plugs is sometime all that can be done, practically, to mask the problem. Chuck

 
It sounds like gas fouled plugs to me. Have you tried adjusting/re-calibrating the center carb (your sig line says ti-power)? What carbs do you have? You could try one heat range hotter plug in the two offending cylinders. Getting near even fuel distribution with a dual plane intake is difficult and running two different heat ranges of spark plugs is sometime all that can be done, practically, to mask the problem. Chuck
I had pulled all the plugs and taken a look and non were visually fouled. Keep in mind also that 1 and 3 are on different intake planes.

The center carb is a 350cfm (2bbl flow measurement).

I like your idea of hotter plugs. I do have a lot of problems with plugs in this engine. I have fouled some before. The car also sits for more than a month at a time between starts and then when the weather gets nice I drive it more. It has had a pinging problem which I have resolved but I imagine that can be hard on spark plugs as well.

I forget which plugs I used this time. Normally it is Champion rv12yc. Do I go up or down to get a hotter plug? (I always get confused because it is backwards from what I think)

I am going to swap out 1 and 3 today and cross my fingers. I can deal with bad spark plugs...

 
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If the problem persist, swap the plug wires to see if the problem follows the wires. Take one of the wires that is of the correct length and replace the one on the cylinder with the issue. If it does a new wire set is in order. Inspect the inside of the distributor cap for carbon tracking.

 
If the problem persist, swap the plug wires to see if the problem follows the wires. Take one of the wires that is of the correct length and replace the one on the cylinder with the issue. If it does a new wire set is in order. Inspect the inside of the distributor cap for carbon tracking.
Thanks. I noted in the original (long) thread that I put on a new cap (I always have a spare). I also swapped #1 and #2 wires and the problem stayed with #1 with #2 not having the issue.

 
Is it idling off the center carb only? If so, has it gotten a little colder weather wise lately? You might need to change jets in that one and I'd Definitely put a choke on the center carb. If it's idling off all three you could try the above and a different distributor and coil as well. Coil first. Just replace/change one thing at a time till you figure it out. Have you compression tested it lately? Could be as simple/bad as low compression in a cylinder or two.... Another thing to check for is a leaky intake manifold sucking air, creates a lean condition.....take some starting fluid and spray it where the intake runners meet the head starting with the missing ones. If it smooths out, there you are. The only problem with this test is that it might be sucking from underneath the manifold....Come to think of it...I'd try this one first.....You might be able to fix it just by re-torqueing the manifold if lucky. I'd do that first just for general puposes. If any of the bolts are slacked off you could have sucked the gasket in toward the port till it no longer seals properly.

Grant

PS. Believe it or not when over carbureted you might actually have a lean condition because the "signal" to the jets is weaker and you actually have to put in bigger jets to get a good fuel/air ratio!

 
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It sounds like gas fouled plugs to me. Have you tried adjusting/re-calibrating the center carb (your sig line says ti-power)? What carbs do you have? You could try one heat range hotter plug in the two offending cylinders. Getting near even fuel distribution with a dual plane intake is difficult and running two different heat ranges of spark plugs is sometime all that can be done, practically, to mask the problem. Chuck
I had pulled all the plugs and taken a look and non were visually fouled. Keep in mind also that 1 and 3 are on different intake planes.

The center carb is a 350cfm (2bbl flow measurement).

I like your idea of hotter plugs. I do have a lot of problems with plugs in this engine. I have fouled some before. The car also sits for more than a month at a time between starts and then when the weather gets nice I drive it more. It has had a pinging problem which I have resolved but I imagine that can be hard on spark plugs as well.

I forget which plugs I used this time. Normally it is Champion rv12yc. Do I go up or down to get a hotter plug? (I always get confused because it is backwards from what I think)

I am going to swap out 1 and 3 today and cross my fingers. I can deal with bad spark plugs...
This may help. http://www.sparkplugs.com/learning-center/article/116/how-do-i-find-a-colder-or-hotter-plug

The stock plug, according to O'Reilly's, is a heat range 17 in Champion. The heat range required changes with modifications. Just a side note, I'd switch to Autolite or NGK. NGK heat ranges are opposite of most everyone else's. Let us know what you find. Chuck

 
I went with rv15yc4 in the two offending cyl. Fired it up for the first time (cold) and it seemed to be better. But once it warmed up it started misfiring again. Again, it was only cyl 1 and 3 that consistently didn't fire. Perhaps the others were not firing as well but no where near the consistency of 1 and 3.

I run a Mallory uni-light (small cap due to the tri-power). I noticed that the top of the control module had been cut into a little by the rotor assembly. Not a lot but enough to notice. The uni-light uses and led and pickup to determine when to fire. The rotor assembly has 8 notches cut out for each cyl. When the pickup 'sees' the LED it fires.

So I did two things. I cleaned the led and pickup with some distilled water and a q-tip. I also stuffed a small amount of paper into the where the shaft is inserted so that it wouldn't rub and sit so low.

Problem gone.

My only guess is the optics where dirty and the pickup was just barely picking up on the fire signal. Perhaps the rotor assembly was just a little too low and the 1 and 3 cyl slots blocked just enough light to make firing 'occasional'. I am going to drive it this week (mid 70's during the day, yeah!)

Next weekend I will swap out the other 6 plugs with the hotter champions and see what happens.

But it's running pretty sweet now.

 
I went with rv15yc4 in the two offending cyl. Fired it up for the first time (cold) and it seemed to be better. But once it warmed up it started misfiring again. Again, it was only cyl 1 and 3 that consistently didn't fire. Perhaps the others were not firing as well but no where near the consistency of 1 and 3.

I run a Mallory uni-light (small cap due to the tri-power). I noticed that the top of the control module had been cut into a little by the rotor assembly. Not a lot but enough to notice. The uni-light uses and led and pickup to determine when to fire. The rotor assembly has 8 notches cut out for each cyl. When the pickup 'sees' the LED it fires.

So I did two things. I cleaned the led and pickup with some distilled water and a q-tip. I also stuffed a small amount of paper into the where the shaft is inserted so that it wouldn't rub and sit so low.

Problem gone.

My only guess is the optics where dirty and the pickup was just barely picking up on the fire signal. Perhaps the rotor assembly was just a little too low and the 1 and 3 cyl slots blocked just enough light to make firing 'occasional'. I am going to drive it this week (mid 70's during the day, yeah!)

Next weekend I will swap out the other 6 plugs with the hotter champions and see what happens.

But it's running pretty sweet now.
Thanks for posting what you found. An interesting partial unilite failure. I'll try to remember that one. I feel like you've told the story before but, how did you come by the Tri-Power setup? Are the carbs from a Chrysler or 390/406 or what? Glad the problem is solved. Chuck

 
Yeah it's a weird one for sure. The uni-lite is a good setup when it works. I understand when it fails that's all there is and you have to replace the control module. I carry a spare.

I picked up the tri power manifold on ebay around 2000. It has the 4v sized openings and I had a 2v engine so I had to collect heads, headers, the smaller distributor and what not. I also needed to get some carbs. Unlike the standard Ford FE tripower the setup for the Cleveland has vacuum secondary's like the Mopar and Corvettes. There is no converting it because the carbs sit close enough together that you couldn't fit the metering block required for non-vacuum manual secondary's.

Like the corvette and mopar setups the center carb is the only one with an idle circuit. 350 center and 500 each outboard (measured 2bbl) so it isn't the same flow as a 1350 4bbl would be. I forget what the math is but its somewhere around an equivalent 900 cfm 4bbl. Way too much carb but you don't really notice it since the outboards don't open until you get on it.

 
Yeah it's a weird one for sure. The uni-lite is a good setup when it works. I understand when it fails that's all there is and you have to replace the control module. I carry a spare.

I picked up the tri power manifold on ebay around 2000. It has the 4v sized openings and I had a 2v engine so I had to collect heads, headers, the smaller distributor and what not. I also needed to get some carbs. Unlike the standard Ford FE tripower the setup for the Cleveland has vacuum secondary's like the Mopar and Corvettes. There is no converting it because the carbs sit close enough together that you couldn't fit the metering block required for non-vacuum manual secondary's.

Like the corvette and mopar setups the center carb is the only one with an idle circuit. 350 center and 500 each outboard (measured 2bbl) so it isn't the same flow as a 1350 4bbl would be. I forget what the math is but its somewhere around an equivalent 900 cfm 4bbl. Way too much carb but you don't really notice it since the outboards don't open until you get on it.
Glad you got it figured out.

Grant

 
BINGO Ign Problem Glad its Running Better!

\

I just installed a chevy type HEI for a 351c had to make a 1 inch

rubber spacer to raise the air filter to clear the huge HEI cap.

The point dizzy left me stranded when the condenser crapped out

at $50 the HEI is a steal but will not work with the stock air cleaner.

I put in Moroso cent adv spring and weight kit to get 23D adv in at 2500RPM

and this thing is a neck snapper now goodbye points! I dont use the vac

adv at all 31D all in is good enough no pinging on reg gas with 2v OC heads.

Thanks for the followup

 
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