Playing with tune up

[Stangman]

Well I’ve been playing with the front carb on Friday I took the 5.5 power valve and exchanged it with a 6.5 and it had 70 and 71 jets in front so I put the 71 were the 70 was and a 72 were the 71 was and now at a steady speed on parkway it feels better less like it’s holding back. I actually think I need either air bleed change or PVCR a little bigger. After all this I adjusted mixture screws and it wasn’t to bad. But that’s not why I’m writing.

I’ve got the motor back with NGK iridium plugs and I wanted to put Autolite in there because I’m chasing an intermittent runs rough and I’ve been thinking it’s carburation.  So today I figured I would start from scratch and go over everything before I changed the plugs so I was letting it warm up and it started to run a rough. So I figured screw it let me pull plugs and of course the last one #8 is wet.  So I put the new plug in start it up and it’s still missing I check for spark and it has spark although it did seem to miss once or twice out of 10 times. So I pulled the brand new plug and it was wet. So I got my compression gauge and I pulled 6,7,an8 of course my compression gauge wasn’t working I think the Schroeder valve was bad so I went to the shop and got another and they were all between 170 and 175. So took an old plug put it in #8 and swapped #4 and #8 wires to see if the miss would follow it didn’t so I put the wires back the way they were. The wife called it was dinner time so I figured sausage and peppers would stop me from being aggravated.
So when I finished I went out and started it up and it seemed like it was running ok so I took it for a ride around the block and brought it back pulled #8 plug and it was clean.  It still has the original problem carb wise but not missing so I cleaned up and called it a night till I get more time to play with it.
Now being the way it was with the plug being wet then not I was thinking maybe I have a pickup starting to go bad. I did have a extended cranking no start even at the reunion so I guess it’s possible. I had put one in already like 3 years ago with the old motor and it can’t have more than 300 miles or so on it. So I guess I’m gonna try one. Of course it’s a MSD I think it’s really a ford pickup so maybe I can get one from the part store?? I have an 8594 ditributor.
Or is someone thinking something else I’m all ears.

[My427stang]

I think I'd likely look close at the plug wires to start, maybe you have some issues at the crimped end, however certainly could be a bad pickup but I just don't see a lot of pickups fail.  Ohm every wire and wiggle it around and look close at the cap side

Of course you are starting to find something with that dead cylinder, but also what size carb? LIST number even better  71/72  is pretty small jet for anything other than a 750, and even then to run a 72 in the rear of a 750 it would need a secondary PV, otherwise they are usually in the 76 ballpark.

[Stangman]

Hey Ross so I have 2 quick fuel 750s from Barry. Blair went through them but I think it ran good on dyno but not in my car.  Originally carbs came with 72/81 so that’s what I have in the front carb except he had a 5.5 PV and I put a 6.5 in which it came with. I haven’t taken the rear carb apart because my carbs are progressive so I was just trying to get it to drive around fine because when I stomp on it it runs great except for a little bog off the line which I really can’t duplicate on the street because it just spins the tires but at the reunion my 60 ft times were way off. I do know that the rear carb has the rear PV bolcked with the jets upped to make up for that. I guess it could be wires I was swapping them around maybe it was making connections and loosing it. I also thought about the cap and rotor so I changed them last week. I even bought one of those adjustable rotors which I haven’t used.

[6667fan]

What are the wires you are running Joe? If you are due for an upgrade that might help rule out the old set if problem disappears.

While the adjustable rotor might line up the spark under the cap better that probably is not responsible for one cylinder acting up. They would all be impacted if the spark jump was way off. Seeing as how you invested in that rotor I would try it at some point. It can be eye opening to see how much the spark has to stretch if it is in need of adjustment.

[My427stang]

Hey Ross so I have 2 quick fuel 750s from Barry. Blair went through them but I think it ran good on dyno but not in my car.  Originally carbs came with 72/81 so that’s what I have in the front carb except he had a 5.5 PV and I put a 6.5 in which it came with. I haven’t taken the rear carb apart because my carbs are progressive so I was just trying to get it to drive around fine because when I stomp on it it runs great except for a little bog off the line which I really can’t duplicate on the street because it just spins the tires but at the reunion my 60 ft times were way off. I do know that the rear carb has the rear PV bolcked with the jets upped to make up for that. I guess it could be wires I was swapping them around maybe it was making connections and loosing it. I also thought about the cap and rotor so I changed them last week. I even bought one of those adjustable rotors which I haven’t used.

To me it seems like a miss that comes and goes, with no other indicators, and valves adjusted correctly, etc, two sets of plugs, almost has to be a wire. The cap end can be tricky sometimes and I have seen them break where you fold them over.  Not often but can happen

As far as the carbs, the 6.5 would bring fuel in earlier, but I'd probably see if you can find something with the plug first, then tune later.  As far as tuning the carbs, I generally like to start with basics, get them to a known good setup, usually as delivered, make sure accelerator pumps are working immediately and adjusted correctly, make sure both primary and secondary idle are correct and float levels are correct, and then start making one change at a time.

My gut says the dyno liked a little less fuel, and one jet size isn't going to fight you either way, my guess is intermittent spark on one or many.  There is an old saying that most carb problems are ignition problems, can't say it IS the case, but seems like it here

[fe468stroker]

I have the exact same carbs that you do.  Also have the dreaded intermittent miss especially when engine first starts.  Running a Mallory Unilite with new wires, plugs and pickup.  I have experimented with jet and PV sizes with no real difference.  But the engine runs like a raped ape when fully warmed up (195* thermostat).  If you figure it out I would be all ears.  Good luck.

[Stangman]

I will probably get a new set of wires of course i will be checking at least #8. They are 9 years old but like alot of you guys that dont mean much.
Maybe 1500 miles and 100 passes. Ross thats what i meant about starting from scratch. Going through the floats and everything. I was really throwing it out there if sombody thought it was something weird like a pickup even though having one bad cylinder is not a common problem for a pickup. I did twice have a cranking no start but i will start with ohming wires and doing a wiggle test.

[Drew Pojedinec]

Having the secondary carb with no power valve is kinda meh.
The linkage isn’t THAT progressive. Anyone with a little gear is cruising on both carbs.

[My427stang]

I missed that..the short 4160 style carbs won't have secondary PVs, but I wouldn't run the second carb without a primary PV unless maybe drag only, but still odd for me in that application unless somehow you were fighting it coming uncovered at launch or something. 

That being said, I'd still want to chase the ignition first   After that, I have found carbs really like being normal...

[BattlestarGalactic]

Having the secondary carb with no power valve is kinda meh.
The linkage isn’t THAT progressive. Anyone with a little gear is cruising on both carbs.

I know that I have my truck set up just so it can get up to 35-40 mph on one carb.  You can just feel the resistance in the throttle as it wants to start on the other carb.  Being a stick shift surely makes it more possible then an automatic (especially if it has any stall in it).

[Stangman]

so thats sort of what it feels like when im driving on parkway its telling me hey give me more gas call it resistance or I need to change i believe the inside bleeds and make them smaller which would make that curcuit richer right drew. If I go from 1/4 throttle to1/2 throttle or more it takes off. I believe that i am on the progressive portion of throttle i can fell the extra resistance of the next carb.
I geuss a air fuel meter would tell the tale but i would like to avoid that. The car is a street car so i dont mind throwing a power valve in the back.

[BattlestarGalactic]

Ya, thinking about it, it seems like the 2nd carb is just into the transition slot and leans out a touch, thus it noses over until you get past it.

I think mine is a bit like that at times.  Not sure you can fix it for all driving conditions?  This is where my buddy rides my case about Fitech!  Ah, no, not in the budget.

[Drew Pojedinec]

Changing hsab does waaaay more than just make it richer. Do not alter unless you want to go down the wormhole of chasing the tune.  (It’s a lot of fun, but kinda beyond the scope here).

Typically a lean spot between idle and mains can be closed by either richening mixture screws, or raising float level.
Often a combo of both is the magic bullet.
The higher the float level, the less pressure differential required to lift fuel.

[Stangman]

thanks Drew i will try this weekend. I havent had a chance all week and my dads birthday is sunday so its gonna be tough.

[BattlestarGalactic]

And it makes me wonder if a 1:1 linkage would be better overall?  Even street driving.  Would fuel economy really tank that bad or would it be negligible??

I have the 1:1 linkage off the wagon since I changed intakes.  Wonder if I put it on my truck and see how it does.  Not that mileage is a consideration on a truck with 428, 2x4s, 4 spd and 4.56 gears.