TBI to carb problems
 

Just converted to carb from TBI and my car runs like complete ****... Here are some issues:

First the PCV valve. I don't have another vacuum port big enough for the pcv valve. Could I T off the big port on the carb and have my PCV valve and brake booster hooked up to it? Or better yet reduce it to the smaller port on the carb?

Second I have a crap load of pressure built up in my tank... I read something about the charcoal container having to do with it. Well The charcoal container isn't hooked up anymore. I actually took it out cause I didn't think I needed it. Did I mess up there? Also read something about a purge valve?

Third when I am driving and hit the brakes hard it shuts off. When I am at a stand still and hit the brakes hard it doesn't shut off. It may be low fuel but it says I have a 1/4 tank? What do you think?

And finally my car just runs like complete crap... I cannot figure out why... I have the sight plugs set to just where I can see it. Friend said to set idle mixture just keep turning it in till the car bogs down than 1/4 out.

Re: TBI to carb problems
 

There should be a vacuum port on the back of the carb for the brakes, and several on the front of the carb - the larger on the front being for the PCV. Check to see if there's another port on the back of the carb for the brakes - not having anything connected to it would make the car run bad.

Have you checked your vacuum with a guage? When tuning the car, you want the greatest amount of vacuum you can get. Sometimes you can change the timing a tad, adjust the idle up/down to compensate, and get a tad more vacuum that way. Im wondering here if there's not enough vacuum thus the hard braking kills the motor.

Make sure your timing with the vacuum port on the carb plugged that goes to the distributor - you want to set base timing with the distributor vacuum line unplugged.

Make sure all vacuum ports on carb and back of intake are plugged if not used.

Some more answers will help:

1) What carb?
2) What's timing set at?
3) Firing order correct?
4) Did you make sure you were at TDC on the COMPRESSION stroke when you stabbed the distributor?
5) What fuel pressure?

Re: TBI to carb problems
 

well i did this swap a while back. i have a tee on the back of the intake. i ran the a/c ducts and the brakes off of that one. then i took the big one on the carb and ran it to the pcv valve. then i ran the ported vacuum to the distributor. what all do you have hooked up to be out of ports. what all are you running to all the ports.

Re: TBI to carb problems
 

here is my swap info.
https://www.thirdgen.org/forums/carb...bi-update.html

Re: TBI to carb problems
 

Does anyone have any ideas on the pressure build up in the gas tank?

Edit:
A little bit of research found this:
https://www.thirdgen.org/forums/post...518-post4.html

Re: TBI to carb problems
 

Well, if you took out the canaster and blocked off the line the fumes have no place to go. You may need to get a diagram for a carbed car and re install it for that app as per the diagram. That could be the cause of your high tank pressure. You may even smell gas.
You didnt say what the carb is. I would need to know that in order to tell you how to adjust the idle mix screws. Holley,ect....
I would be happy to help.
Bill

Re: TBI to carb problems
 

Holley 650 DP (4777) only 2 corner idle mixture.

Re: TBI to carb problems
 

Ok.First make sure the timing is set to spec, this is a must. you will need a vacume gauge.This is done with the car in park. (1) to set the mixture, warm the engine up to normal, then shut it down and remove the vacume advance and plug it off on the carb. Find a manifold vacume port and attach the vac gauge.it has to be manifold. (2) turn the mix screws all the way in untill they lightly seat, then turn them out 1 and a half turns. Start the car, adjust the idle as needed to keep the car running if you need to. (3) turn the mix screw 1 at a time in or out THE SAME AMOUNT until you have the highest reading then do the other srew. and do it slow on both sides until you have the highest vacume reading you can get.
Now the vacume gauge may read steady or it may vary a little but not a lot,Thats ok,the goal is to get the highest reading you can get. It is important to turn both mix screws the same (ie. if you turn 1 screw a quarter turn you HAVE to turn the other screw the same amount,the same way in or out). When you get the highest reading you can, shut the car down hook up the vacume advance and the other vacume line as needed. Start the car then adjust the idle speed as needed. That should, acording to holley, set the mixture. as that is how they say to do it. I did and it runs great.
Bill

Re: TBI to carb problems
 

When I did mine I was running rich due to using the stock in-tank fuel pump. What was happening is that the pump was putting out 40+PSI or whatever the TBI PSI is. Carb onlt need 6-7PSI so it caused my engine to run VERY rich and crappy. Put a pressure regulator from holley on it. thats what i did and it fixed it right up.

Re: TBI to carb problems
 

Does ANYONE know if I can put a T in the big port on the back of my carb? One for my brake and one for my PCV valve?!?!?!

My car died today just randomly but than was able to start up again. Any reason why?

Re: TBI to carb problems
 

Is there a port on the back side of the manifold? It will be behind the carb itself on the maifold, it should be a screw in type. There may be a plug in its place if so you can get a screw in t and run them off of it. You can run off of the carb but it would be better to run of of the intake. Most intakes have a place for the fitting I am talking about.

Re: TBI to carb problems
 

http://img.photobucket.com/albums/v1...i/100_0415.jpg

brakes and a/c ducts.

Re: TBI to carb problems
 

I'm no expert on the Holley carbs and their vacuum ports - better let a Holley person chime in on this. Or maybe Holley has a diagram on their site showing recommended vacuum connections.

For the TDC - you mentioned the timing mark was at zero - but it will hit zero twice for every complete cycle - once for compression stroke, once for exhaust stroke - most of us take the #1 plug out, stick a finger in the hole, and while someone turns over the engine by hand, feel for the pressure.

There will be pressure forcing your finger out of the plug hole on the compression stroke, because the rising piston is compressing the air/fuel mix and BOTH valves are closed allowing the gas/air mix to get "compressed" - thus the compression stroke. There will be no pressure on your finger on the exhaust stroke because the exhaust valve is open and the rising piston is forcing the exhaust fumes out of the open exhaust valve.

Grab a timing light - pretty cheap anymore these days, and a necessity.

On the high tank pressure - I simply removed my gas evap canister altogether, and just attached a fuel line to the third hardline and ran it under the car, that way in the event that any fumes or gas were to leak out (haven't ever seen it in 2+ years now), they wouldn't leak out where there might be a hot surface or ignition source.

Re: TBI to carb problems
 

Thats the one he needs to see. Thanks. Now to the guy with the question. See were the lines are? From the looks of it this man has the PCV valve running off of the carb, that is also how I have mine.And were holley recomends running it via their diagrams. The port on the rear is were you would run the brake booster and were I supply vacume to the acc in the car. I am driving a 1982 berlanetta with a 350.
But this is a top shelf photo of what I was saying. So thanks to the man with very clean set up. A photo is worth a 1000 words.
Bill.

Re: TBI to carb problems
 

Problem with that concept is, that port I put a plug into because one of the fuel bowls are right on top of it. I maybe have 1 mm at that between the carb and the plug... I'll put pictures up here in a few minutes.

I know I need a timing light etc. I did time it at one point (borrowed friends but not available now) to 36 advance at 3300 RPMS (someone told me to do that) but it had really high idle so I adjusted it again.

What about the braking thing? Cause that is still happening and I don't think its a vacuum thing because I can hit the brakes as hard as I want at a stand still and I have no problems. and the fuel bowls are adjusted properly.

Just realized camera screen was broken so this was a blind shot:
Attachment 416373

Couldn't have done better if I tried lol.

Re: TBI to carb problems
 

check the vent tubes on top of the carb, see if they are wet again you may just need to reset the floats lower. you can also try Try putting without the breather on the car, a piece of tubing bridging the vents stacks. Cut a notch at the top of the tubing to give you a new vent location. I had the same problem, I had fuel sloshing out the vents into the carb under hard deceleration. causing a stall. If you havent done it yet you may want to rebuild the carb because in my case the floats were filled with fuel and you wont know until you go inside, so until I did the rebuild nothing was going to work because the fuel would never stop flowing into the carb .The floats only cost me 10 dollars each at O'Rellys. and the trick kit as it is called cost me 25 bucks (both in stock) It was after that,and they were in stock.After that it ran better than ever and only took 45 minutes to build and install.

Re: TBI to carb problems
 

And as far as the tubing goes, you can rum both the pcv and booster off of the carb at the base. the timing is run from the port just above were the idle screw is on the front of the carb on the passanger side. For some reason I cant get a photo of my set up loaded, that way I could point it out for what all I have been saying.

Re: TBI to carb problems
 

the secondary side of the carb doesn't have a vent tube. Could this be why? Also I just rebuilt the carb. not even 100 miles on it.

Re: TBI to carb problems
 

For the gas tank pressure just take off the purge valve and that will solve it. mine did the same thing.