How do I mellow it?

[DarkBuddha]

This is a big post, but I do it so seldomly these days... you'll have to forgive me.

Well, I just got back from a fun week of working on my Mach in sunny Tampa. Make that hot-as-all-hell Tampa. Anyway, I got a few things accomplished... the kind of stuff we should've done to begin with and caused lots of problems, but we're both cheap and stupid, so we suffered until we couldn't take it any longer. Here's the deal: The fuel system was complete trash. We'd never replaced the original tank and we didn't flush it, so basically we'd been clogging the entire fuel system with rust, scaling, and murky sludge for a couple years. We final replaced everything... new tank, new lines, new pump, new Holley 4160, new filter, new plugs, poured SeaFoam down the carb. Guess what, fired up and ran great, if a bit rough, which is my complaint now.

I've tuned the idle mixture screws (using a vaccuum guage), accelerator pump, idle speed (using a tach) set to 750rpm in drive. Still, it idles like it's got a bigger cam than it really does... a slight lope and "shake"... not misfiring, but just not smooth. It's completely smooth under accelleration. My concern is that I've screwed myself with the exhaust. Here are the relevant details:

- '70 302 rebuilt w/15K miles, reground cam, ran smooth as glass before sitting for 7 years.
- stock distributor w/ pertronix ignitor and coil, new accell 8mm wires, new Autolite plugs.
- new Weiand Stealth intake, new Holley 4160 carb, basic 14" air cleaner
- Hedmann shorty headers, 2.5" custom exhaust with X-pipe and Dynomax Turbo mufflers.
- engine pulls 19" of vaccuum at 750rpm, no locatable vacuum leaks.

Did I screw myself with the 2.5" exhaust? I know it's too big for the lowly 302 and probably killed a bit of torque, and I know it's probably hurting exhaust scavenging (too little backpressure for sure). But the car really breathes deep now and will wind past 6K with power (when it used to redline around 5K with the 2 barrel and single exhaust). My future plans include a nicely built 351W, so I figured I just do the exhaust now and not have to do it again in a couple years, thus the reason for the 2.5" pipes.

So, my question is: is there a way to smooth the idle a bit? Do I need to put some restriction on the exhaust? If so, any suggestions? Anyone got other ideas why it might be loping???

Any input much appreciated.

 

[iskwezm]

what are the specs on the cam???

 

[DarkBuddha]

what are the specs on the cam???

Funny you should ask... I was just looking through some old paper work and found the machine shop docs... it simply says "1970 Ford 302 - TRW stock replacement..... $38.00". No specs unfortunately. Heck, does TRW even make cams?

 

[mustangman70]

Hey man if your in tampa we should hang out, maybe do a little racing at sunshine

 

[302 coupe]

I don't think the exhaust system is causing your problems. It sounds like the fuel system should be ok also. I'd check the valvetrain and go over the ignition system.

 

[iskwezm]

Funny you should ask... I was just looking through some old paper work and found the machine shop docs... it simply says "1970 Ford 302 - TRW stock replacement..... $38.00". No specs unfortunately. Heck, does TRW even make cams?

yeah TRW makes cames,replacement mostly,but if the car been sitting for a while,why not change plugs(if you havent already). oops,looks like you have,maybe its just needs to be driven???

 

[mustangdave]

Did you install a new cap and rotor since it's been sitting so long?

 

[DarkBuddha]

Cap, rotor, plug wires, plugs, Pertronix, and the Pertronix coil are all new (or less than 6 months old) and have 0 miles on 'em.

Maybe it does need to be driven to "get the carbon out", but I'm still worried about the exhaust scavenging situation...

BTW...

Hey man if your in tampa we should hang out, maybe do a little racing at sunshine

Actually, I live in Seattle, attending graduate school, but the car is in Tampa. I'm actually hoping it will be "done enough" to ship to Seattle before August, so sadly, I'll have to take a pass on the racing. I used to take it out to Gandy in the early '90s with some success against 5.0s and Irocs.

 

[iskwezm]

Cap, rotor, plug wires, plugs, Pertronix, and the Pertronix coil are all new (or less than 6 months old) and have 0 miles on 'em.

Maybe it does need to be driven to "get the carbon out", but I'm still worried about the exhaust scavenging situation...

BTW...

Actually, I live in Seattle, attending graduate school, but the car is in Tampa. I'm actually hoping it will be "done enough" to ship to Seattle before August, so sadly, I'll have to take a pass on the racing. I used to take it out to Gandy in the early '90s with some success against 5.0s and Irocs.

your exhaust shouldnt be a worry,2 1/2 inch isnt anything too crazy

 

[thehueypilot]

I have found that when a carb cannot stay at the same idle speed (called hunting) you can offset the idle screws about one quarter to one half turn off each other. In other words if one side is 1.5 turns make the other side 1.25 or 1.75 turns. It has something to do with the tolerance of the idle screws and the holes they are screwed into causing the idle signal to be different from side to side. Just something else to check.

 

[DarkBuddha]

I have found that when a carb cannot stay at the same idle speed (called hunting) you can offset the idle screws about one quarter to one half turn off each other. In other words if one side is 1.5 turns make the other side 1.25 or 1.75 turns. It has something to do with the tolerance of the idle screws and the holes they are screwed into causing the idle signal to be different from side to side. Just something else to check.

Good to know, and I'll add it to my list. Unfortunately, mine isn't hunting at all. It's steady as a rock, just lopey... like it's got a Comp Cams 280/280 grind in it instead of the dead stock bumpstick.

 

[mustangman70]

Yah im at gandy EVERY sat night lol, the LEO's are getting real anal nowadays though, well next time your in town shoot me a PM

 

[D.Hearne]

TRW did make some performance grinds. You've may have one. What carb is it? You just said it's a 4160, that doesn't mean squat. Could be a 390 cfm or an 800 cfm. At least look at the list # on the choke horn and either look it up or post it here so one of us can translate that to see what size 4160 it is. I wouldn't worry about the exhaust, that's not the problem. Sure it's too big for it, but it's not going to make it idle funny. You could also possibly have two plugs wires crossed, like # 7 & 8, that would do what you describe, they fire consecutively and as such would do so without the usual back fire you'd get if it were another pair. I did just that last time I changed the wires on the 351W in my 95 E150 van, except it was 5 & 6.( yea I screw up too sometimes ) Idled rough but somewhat smoothed out when you gave it some pedal. Also (while wearing rubber gloves and not touching the vehicle anywhere else) pull one plug wire at a time while it's idling and find just what cylinder is missing ( if that's what it is)

 

[D.Hearne]

Two more possibilities: it could have a stuck valve or a bent pushrod from a stuck valve, if you can't find anything else wrong.

 

[WantaGT]

trust me the exhaust is fine. all the 5.0 guys run 2.5, it's not too big. focus elsewhere, where you may ask? I don't know LOL I'm no expert.

 

[10secgoal]

Two more possibilities: it could have a stuck valve or a bent pushrod from a stuck valve, if you can't find anything else wrong.

This could be one thought. Did your guage read steadily when testing it at idle ? The guage would be a bit jumpy if this were true. Also, maybe bump the initial up a little, and back down the idle speed a little, see if it clears any.

 

[DarkBuddha]

This could be one thought. Did your guage read steadily when testing it at idle ? The guage would be a bit jumpy if this were true. Also, maybe bump the initial up a little, and back down the idle speed a little, see if it clears any.

Yeah, vacuum at idle is a rock steady 19", no bouncing or real fluctuation at all. And we checked all the rockers and pushrods when we were having the fuel related issues and thought we had a wiped cam lobe or something. But they're all fine and operating perfectly. It doesn't mean the cam isn't worn a bit, but no loss of power, no backfiring, etc.

The carb is a brand new 600cfm Holley "shiny finish", part #80457S, straight from Summit Racing.

The timing is currently set at 12* BTDC and much more than that causes pinging.

I hadn't double checked the plug wire routing since I installed them last year, but I'll definitely check them. Though it's smooth as glass under accelleration, which makes me think that it isn't missing at higher speeds they way mis-routed plug wires would.

And that's the real annoying kicker here... it used to be smooth as glass way back before it sat so long. It ran so smooth it was hard to tell it was running at all, even idling at 600rpm in drive. And that was with points in the distributor, crappy 2 barrel carb/intake, and stock manifolds and single exhaust. It also used to pull down 22" of vacuum at 750rpm back then. I expected to lose a bit with the exhaust and intake upgrades though...

Heck, maybe I just need to put a crap load of miles on the car and see if it settles down on its own. I might look into some cheap temporary exhaust restrictors (i.e. potatos) to see if it helps at all though.

Keep the input coming though!

 

[TampaStang]

Yah im at gandy EVERY sat night lol, the LEO's are getting real anal nowadays though, well next time your in town shoot me a PM

You post on Tamparacing.com too? I post as tamparsx on there (old car)

Ever hit the meets over at Coastal Dyno?

 

[mustang70]

You said the new ignition parts have 0 miles on them. But if they've been sitting in Tampa they're still going to deteriorate. Especially the wires. Maybe you should pop the hood at night and see if there's a light show. Sometimes it'll be enough to cause it to lope at idle, but clear up at higher rpms. I've had that happen before.

 

[DarkBuddha]

You said the new ignition parts have 0 miles on them. But if they've been sitting in Tampa they're still going to deteriorate. Especially the wires. Maybe you should pop the hood at night and see if there's a light show. Sometimes it'll be enough to cause it to lope at idle, but clear up at higher rpms. I've had that happen before.

That is a really good idea actually... I've done this before and was completely shocked (pun intended) when I saw the freaking fireworks show under my hood. Heck, it was enough of a light show to easily read by. That is why I quit running cheapo 6mm stock wires. Engine heat + Florida heat kills stuff fast, expecially starters and batteries. I'll have to look into it.

You post on Tamparacing.com too? I post as tamparsx on there (old car)

Ever hit the meets over at Coastal Dyno?

I have posted on Tamparacing.com, but only to raz my brother who posts over there... he's got a 240SX with a JDM Silvia redtop conversion he did himself. It's totally ghetto-rigged, but he's done it super cheap and it's got plenty of bite. He's gonna do his front mount and crank up the boost a bit and should see mid-14s no problem. Not bad for a turbo 4 banger with a/c. We were at the Quaker Steak on 49th last Friday (my last night in Tampa).

As I mentioned, I'm back in Seattle now, so I'm trying to diagnose and solve this problem long distance with my father. Basically I tell him to try stuff and he does... There's plenty of other stuff to worry about in the meantime, so since it's running pretty well now, I'll just worry about this idle problem when it gets to Seattle.