So yeah, never got my IROC running right again after the heads and cam swap. This has me and a very reputable shop in my area completely stumped.
It's been months now since the swap because I just dont have the time to come back home from college and work on it as much as I did in the summer.

Symptoms were:
No idle
Missing
Shuddering
No power over 2000rpm

I've tried nearly everything and exhausted all my options, so I say screw it to EFI and am going carb'd.





What intake manifolds are you guys using for your carb swaps? Carbs? Also, were there any issues you guys faced when doing this swap? Anything I need to look out for? Thanks guys.

 

I've found that carbs are a lot easier to troubleshoot, especially when things get really messed up.
I like EFI, but one of the things about the SBC that I really appreciate is that carb swap parts are out there to save the day if something goes bad with the EFI system that is really hard to fix.
I had a rat chew up my harness on my TBI a few winters ago, and I couldn't fix it myself. A reputable electrical repair shop gave me an estimate of $60 - $1000 to repair it. They had no idea what it might have taken to do the job til they actually started getting their hands dirty.
A carb and a performer intake that I had lying around the garage took care of the problem. Along with the info from the TGO Tech section.

If you have a 700r4 be sure you connect the TV cable the right way.

 

Yes, look out for badly cast and machined Edelcrock intakes. That will put a screeching halt to your plans on some Saturday afternoon not to mention the frustration of putting the intake back on that fit after you pulled it all off.

Going with a mechanical distributor?

As for your car, sounds like a wiring problem to me... Either not grounded or a wire or three was damaged in the swap. Or maybe a vacuum leak.

 

Checked it all out and it seems okay. Vacuum is reading steady as well.

I was thinking of going with a Holley 750, and as for a distributor I havent decided yet. What would you suggest?

 

I'm using a Holley 750 VS that I've had for years and it's been tweaked on in every way shape and form imaginable to make it good for street with reasonable fuel efficiency and good top end too. It's got about $900-$1000 invested into it.
If I had it to do again, I'd go with a Q-jet that's been customized by a shop that knows what they're up to, like Brad Urban's Carb Shop, and I'd put that on top of a Spreadbore Performer RPM intake.
I'd go with Q-jet mainly because of fuel cost, but they have great drivability too, and great WOT performance.
And then an MSD vacuum advance distributor.

 

Depends on what you want to spend. Do the above and you'll have $1500+ invested... more than enough to fix your FI IMHO.

I went to the local store and picked up a run of the mill vac. advance distributor, an advance kit with springs and weights (Mr. Gasket?), pulled one of my old Carter AFB's off the shelf, ordered a Performer RPM (that wouldnt have fit any SBC in existence), Mallory FPR, and got to the point where the intake wouldnt fit and threw the idea out the window. I'm sure it would have ran just fine and probably would have easily surpassed the TPI in peak HP even with generic parts. Probably had less than $300 invested not including the carb. Find a dollar amount you want to throw at it, and go from there. I'd spend less on the distributor and more on the carb given the choice and a limitation.

 

Did you try another map senser yet?buddy of mine when hooking it back to TPI had the same problem.we went to the salvage yard got a few differnt map sensers went home put one on and ran good .and tryswitching some injectors too,you might not have them in the right ones,we had that problem too

 

I haven't yet tried that, but my thinking is this: "if it worked when I took it off, it should work when I put it back on." I mean, the injectors were all kept in order, along with pushrods and lifters in the same order. I mean literally, I pulled them off, put them 10' across the room on a bench and they sat there for a day before I put them back on. I just don't see it working out, but thank you.



Oh yeah, and my max I wanna spend right now is $500, since I just want this thing running for the time being and later on when I get some more cash I can get something a little nicer.


What's the deal with the Qjet? I hear good and bad things about it, and it supposedly gives you better mileage?

 

If you're on a budget, a rebuilt Carter from Summitt is pretty inexpensive, and they're easy to learn about. One of those with a chinese hurricane intake or whatever those are called + a scrapyard HEI with an recurve kit and adj vac advance should get the job done. Oh yeah a mallory AFPR.

Each different type of carb has it's good and bad points. If you know what you're doing, you can make any brand carb work well for you. Guys tend to get used to one brand of carb, then if they try another type they haven't paid their dues learning about it so they can't get it to work right and they think it's crap.

Holleys are good cause there's no end to the jets and different kits you can buy for them to tweak them to fit your application. Most racers use them and are familiar with them. Some guys don't like them cause they can be leakage prone with the bowl gasket below the fuel level. You have to be careful to get them clean when you assemble them or they will leak. And unless you buy a special bowl for them, you have to remove the bowl to change the main jets. You have to remove the carb from the engine to change the sec jets.

Edelbrock/Carter they say don't live up to their advertised flow #s. Also they are not true mech secondaries like the Holley double pumper. If you spend a lot of time with the secs open (racing) those mech secs of the Holleys with the sec accelerator pump is advantageous.
Edelbrock/Carters are the easiest to jet. You don't have to take the carb off the car, you just take the top off the carb. You can even re use the bowl gasket while you're going through the trial and error process of jetting, then put a fresh one on when you have it right.
They're a good carb to learn about jetting, and they work well for street, and you can get them dialed in to race if you follow the instructions.

Qjets are a bitch to jet the primaries, you have to take a bunch of little parts off when you remove the top of the carb to get to the pri mains. And in addition to that, you have to take 2 of the mounting bolts out to remove the air horn, and amateurs tend to damage them trying to jet the primaries.
On the plus side, the secondaries could not have been designed to be simpler to jet. One little screw and 2 rods need to be switched. It takes about 2 minutes. Just don't drop that tiny screw down the air horn.
There are nearly infinite variables of jets and power piston rods and springs for jetting the primaries, and if you know what you're doing and have the patience, those tiny primaries can be jetted to atomize the fuel very well and give you better MPG than the others, especially in stop and go situations.

I'm not familiar with Demon carbs at all. I have too many of the other kind sitting around to justify going out and buying one.

If you do a carb swap, read the Bowtie overdrives TV made EZ. It tells you how to adjust your TV cable so you don't turn your 700r4 into junk.

Gud Luk

 

did you get your computer recalibrated?

does your cam have at least 112 LSA?

If you just took everything off and put it back on a crazy built new motor without calibrating the computer dont expect it to work

you can probably get everything you need to program cheaper than switching to a carb. but then you have to learn how to use it and that will take more time then the physical labor of switching to a carb. enjoy

 

your gonna have to programe that computer for sure.and run to a junk yard and get some map sensers.

 

Yeah guys, I got a chip adapter burnt at www.pcmforless.com, who I have heard nothing but good things about. They spec'd it to my cam, and pretty much anything involving the operation of the motor. That was one of the first things I did, @ 150$ too, Im not too happy about having to give up on it, but searching for this FI gremlin has me at my financial limit. Like I said, I have pretty much exhausted every option here.


Btw, thakns for the info Streetiron, I appreciate it.

I was looking at this from Holley http://www.jegs.com/webapp/wcs/store...10002_12893_-1
Is there anything that would be considered undesireable about that one? It seems cheap for a 750. That would be going on top of a performer RPM intake.

Also, where can that article be found on adjusting your TV cable for the 700r?

 

That carb would work ok out of the box. Edelbrock carbs are easier to work on, but if you don't plan on doing much custom jetting to lean it out for better economy or anything like that, the Holley will work. They're pretty well calibrated out of the box.

http://www.tvmadeez.com/article/index.html

Glad to be of help. It's good that you're wanting to do it right and asking questions before you buy.

 

With SD, you really have to be willing to invest some time in getting it to work properly. The idle problems are probably due to the changes in how much fueling the engine needs and Im sure the SA is all wrong as well. You'd really need to get a wide band and redo the fuel and spark tables. It takes a while to get the car tuned as the spark and fuel are coupled together with SD.

I got sick of it and went to MAF with my TBI and run a vac/mechanical advance type of timing curve. Essentially its like running a carb. Having a flow based system makes a head swap as easy as bolt on and drive away. If you dont have emissions, then going to carb and tuning with that would be easier. If you do have to pass emmisions, then it would probably be better to keep the FI and tune it.
----------
Those guys wont be able to help. Having a chip tuned like that is pure guesswork. You really need to tune it yourself with the car running during actual operating conditions.

 

My junkyard distributor and q-jet, along with edelbrock performer RPM spreadbore cost me a whopping $300 CA grand total. Figure $200 in USA dollars.
Nice thing is, if it works, you know you hit the problem, you can always go on to a different carb later if you want to. But that's a pretty cheap solution.

 

Well guys, after reading your responses, and reading "How to choose the right carb" on the main page, I think I have decided on a setup.

http://www.jegs.com/webapp/wcs/store...10002_12625_-1
Edelbrock 750 with electronic choke

http://www.jegs.com/webapp/wcs/store...14249_-1_11937
The 7101 model (although I'll probably snag one on ebay used and sandblast it clean for half the price)

http://www.jegs.com/webapp/wcs/store...26203_-1_10679
Jegs HEI distributor, figure I don't need anything special just yet.

http://www.jegs.com/webapp/wcs/store...10002_14185_-1
And the Mallory 3 Port regulator.


I decided to go with Edelbrock for the carb because of the ease of out of the box performance. I don't know much about carbs, and I am reading up on them currently, but I want to start with something simple that will get me decent power and fuel efficiency as well out of the box while still being easy to tweak. What do you guys think?

Oh yeah, happy Thanksgiving! Hope you guys are enjoying your turkeys!

Thanks for the help so far
_Clark

 

I approve.
Be sure you get the carb that's correct for your application.
One guy last year got an Edelbrock and he had all sorts of trouble. Finally after beating his head against the wall for about 2 wks trying to figure out the problem, he posted the part# of the carb he ordered ... because it was on sale.
It ended up he ordered a smog carb and tried to put it on a HP 350 and it was too lean. Then he got the jets to change it to the original specs of a HP Edelbrock carb and it worked perfect.
If you have a HP cam and intake and headers and all that, then get a HP carb.

The carb recommended for the RPM intake is the 1407 and the one you're getting has leaner primary jetting, but the elect choke is a good thing. You might notice a lean stumble at mid throttle, but you'll be able to clear that up with a simple jetting change.

There's an H.P. book called Carter Carburetors that has good info on how to do custom jetting on those, and other adjustments.

As I mentioned Edelbrock/Carters are easy to work on. You can work on it without removing it from the engine, or even draining the float bowls.
I'm pretty sure you'll be stoked.

 

Yeah the 1407 and 1411 have the same secondary jets, but the performance one has .113 jets and the economy one has .110 jets. The main reason I wanted the 1407 was to have the electronic choke, because it's just convenient. But do you really think I should sacrifice the manual choke for the performance match, or should I get the electronic choke, and the bigger jets and tune it as needed?

 

Keep the electric choke.
It may work fine out of the box. But even if it doesn't you can play around with it to make it right.
Learning how to do jetting changes on your carb is a good thing anyhow. And Carters er... Edelbrocks are super easy to work with on that.

Do you have a hi flow lower intake that you're going to be getting rid of?

 

Sorry no it's just the stock one, but I do have a plenum that's been hogged out. That's the best I could do for you. If you are looking for someone with a TPI setup, gimme a shout.

 

well i had a problem like this before, but apparently the bolts on the runners werent in there the right way and it was causing a massive vac leak. after i fixed that it ran fine.

 

I've learned a few things about different carbs over the years. I never wasted much time messing with Quadrajets. You CAN make them work well, but you really have to know what you're doing with them. Not too many people mess with them so it's hard to find someone who really knows what they're doing with a Rochester. What I've learned with Holleys is that the double pumper/mechanical secondary styles (4150 series) work great with a manual trans. I've been running a Holley 650DP in my 4 speed 69 Camaro for years and I love it. Cars with an automatic trans seem to work a lot better with the vacuum secondaries, like the Holley 3310/4160 series. My brother bought an Edelbrock 750 for his 327/TH350 Camaro, and it bogged horribly. He also tried a Holley 650DP with the same problem. He ended up running the best with a Holley 600 vacuum secondary carb. Unless you have a pretty stout 350, you're usually better off with the 600 model. We finally put the Edelbrock 750 on my dad's Corvette with a 350/TH400. It still bogged pretty bad no matter what we tried until I went online and found a chart with the correct metering rod/jet combos for different situations. I finally got it running great after paying close attention to that chart. Judging by your engine combo, you'll probably be okay running a 750VS, but you may have to do some tuning to get it to work ideally. If you go with the Edelbrock, just make sure to buy the tuning kit they offer for each model, which has all the different metering rods, jets, and step-up springs for the power piston. Good luck!

 

If Pat Hall says his brother had some difficulty with an Edelbrock 750, then maybe you should do some research before buying. It would be too bad if it ended up not working.
It sounds like they did get it figured out though.
I've used Carters... Same concept basically. But I did a lot of jetting on them.
It's my belief that all carbs ought to be custom jetted. And Edelbrock/Carters are vastly simpler to do work on than a Holley. A power valve change in a Holley means 1 1/2 hours of downtime for me (on a good day) plus a fresh set of gaskets. But with an Edelbrock, power pistons can be done in 15 min if you're good.
Still... I have a Holley, and a Carter, and a Qjet and I like all of them.

On one hand, it comes down to whether you want to use the carb out of the box or not.
Out of the box, a Holley VS 750 won't be perfect, but like Pat says, it will definitely work.

Also if you have a stall converter, it can make the difference between whether a carb will bog or not.
A carb that bogs with a stock converter sometimes won't with a hi stall converter.

I have never run a carb out of the box for more than a few days. And I sometimes assume that other guys are like me and want to fine tune their carbs. If you want to drive it out of the box, Holley might be better.
Also electric chokes sometimes need to be tinkered with before they're right.
If you don't want to tinker with it, you should probably get a manual choke Holley VS750.

 

As far as ease of tuning goes, it is important for me since I am a student and don't have the time to get a carb that will eat up hours out of my weekend when the weather changes, and have to buy a new set of gaskets whenever I have to work on it. I get home on Friday and I work for two days and live off of 75$ a week, which I also have to pay bills with. Like I said, the Edelbrock 750vs is so cheap too, that if in a year or two I am dissatisfied with it's performance, I can probably get half what I paid for it on ebay and invest in a holley or the like. By then I will know enough to go more advanced.

And yeah, I know adjusting the electronic choke can be a pita at times. Buddy of mine had a rough time getting his right on his Demon, but it's something that I can learn.

I'll definately pick up the tuning kit that Edelbrock offers as well Pat, would be a great idea to fine tune it, especially with the weather changing up soon.


I can't thank you guys enough for your help!
_Clark