1978 Trans Am Problems

9769 Views 11 Replies 8 Participants Last post by jimfulco, Jun 16, 2009

86_cookiemonster

Discussion Starter · Jun 10, 2009

I have a 1978 Trans-am with the Pontiac 400 engine in it. It is the 220 horse version, the one with the 350 heads. I have several serious problems with it. The first and by far the worst is the car has started hesitating really bad when I step on the accelerator. It will surge a little then eventually start to slowly accelerate. My dad was telling me that it might be the distributor. Any ideas what could be causing the problem.

The second problem is that the carb keeps clogging. I changed the fuel filter twice now and these little chunks of gunk, that kinda look like rat turds, keep forming inside it and clogging the primary metering jets. Any idea where these particles could be coming from?

This car was given to me by my grand-father, and is kind of a family herlom, when it isn't running right it is really depressing not only for me but for my family. So any help would be greatly appriciated.

Thank you

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babygene41042

· #2 · Jun 10, 2009

If the car has been sitting for awhile you might need to rebuild your carb. Does it have a quadrajet? Does it pop through the carb if you stomp on it from a dead stop? If so it could be your accelerator pump. Did it sit with old gas for a long time? You might have to drop your gas tank and clean it and remove the filter that's on the end of the pickup. Check your timing and advance it to about 12 to 15 degrees. Todays fuel is garbage and burns real slow so you might feel a big difference with more timing.

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hotrod389

· #3 · Jun 10, 2009

Your Tank Needs To Be Pulled And Cleaned.

For 50-60 Bucks Speedwaymotors.com Has A Tank Treatment Kit.
It Comes With A Acid Cleaner, A Etcher, And A Sealer.

After You Clean And Seal The Tank, You Should Replace All Rubber Lines In The Fuel System, And Using Air To Clean Out All The Steel Lines.

If You Got A Bit Of Coin, And You Want To Do It Right, Replace Your Fuel Pump And Carb. (some People Say "why Replace Fuel Pump?"... Its Only 14 Bucks, THEN YOUR WHOLE FUEL SYSTEM IS NEW) Your Carb Should Be Rebuilt By Someone That Knows Q-jets. Or Get A After market Carb.

I Would Also Recam The Engine. Its A Bit Of Work, But When Your Doing Burnouts By The End Of The Day... You Wont Complain

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86_cookiemonster

Discussion Starter · #4 · Jun 10, 2009

h0trod389 said:
Your Tank Needs To Be Pulled And Cleaned.

For 50-60 Bucks Speedwaymotors.com Has A Tank Treatment Kit.
It Comes With A Acid Cleaner, A Etcher, And A Sealer.

After You Clean And Seal The Tank, You Should Replace All Rubber Lines In The Fuel System, And Using Air To Clean Out All The Steel Lines.

If You Got A Bit Of Coin, And You Want To Do It Right, Replace Your Fuel Pump And Carb. (some People Say "why Replace Fuel Pump?"... Its Only 14 Bucks, THEN YOUR WHOLE FUEL SYSTEM IS NEW) Your Carb Should Be Rebuilt By Someone That Knows Q-jets. Or Get A After market Carb.

I Would Also Recam The Engine. Its A Bit Of Work, But When Your Doing Burnouts By The End Of The Day... You Wont Complain

I had a bit of coin, then i started driving the car

.

I already replaced the fuel pump, and rebuilt the carb. (My dad helped me, I am pretty sure he could rebuild one of these carbs in his sleep.) So the gas tank i was fearing it might be coming from there. My only question is how could the clumps be getting through the second filter?

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cobalt327

· #5 · Jun 11, 2009

86_cookiemonster said:
how could the clumps be getting through the second filter?

They're not.

There are several places that will allow crap to fall directly into the fuel bowl area of a Q-Jet carb, including the 2'ndary rod holes and that big-A vent.

There's a good chance the junk is coming from the filter assemble somewhere- and if there's been a rat under the hood- it might really be rat turds!

Take a good, long look at the air filter assembly for any small leaks where crud can get past the air filter (you ARE running a filter, right?) from inside the filter housing (including the carb/air cleaner base joint- it needs to have a paper gasket to seal the air filter base to the carb).

Has the car- since you've been driving it- ever run right? If so, what has been changed AFA the timing or carb settings?

Does it start easily? Does it have a clean, non-smoky exhaust?

Does the engine miss, or is it "smooth, but slow"?

Hate to ask, but you're sure it's a Pontiac and not an Olds 403, right? IIRC, if it has a Pontiac, the shaker will say "T/A 6.6". If it's an Olds, it'll say "6.6 Litre". The Olds will have 10 bolts for each valve cover and the oil fill tube comes out above the water pump.

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hotrod389

· #6 · Jun 11, 2009

86_cookiemonster said:
(My dad helped me, I am pretty sure he could rebuild one of these carbs in his sleep.) QUOTE]

q-junk rebuilding is an art, im sure your pops has rebuilt thousands of carbs.... but there touchy.. and youll never get it right.. get pissed off and end up spendin the 250 on a new edelbrock anyways....
been there done that!

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1957plymouthhemi

· #7 · Jun 11, 2009

The first thing (and cheapest) I would do is replace all the rubber fuel lines in the system, what you describe sounds to me like the hose is coming apart from the inside, which is something I've seen in the past on old original hose and some of the cheaper new stuff, especially if you're running fuel that has any ethenol in it.

I would recommend using fuel injection hose as a replacement as it seems to hold up better. Make sure you do the line that comes out of the tank also. If the problem remains then look at the tank.

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cobalt327

· #8 · Jun 11, 2009

h0trod389 said:
q-junk rebuilding is an art *snip* but there touchy.. and youll never get it right.. get pissed off and end up spendin the 250 on a new edelbrock anyways....
been there done that!

I LOVE IT!!!

As long as this is the general mentality, I will keep on getting Q-Jet cores given to me, for nada.

IMO, the Q-Jet is one of the all-time BEST carbs ever used by the OEM, and I would not take 3 EDDY's for one good Q-Jet.

In fact, I have a perfectly good Edelbrock sitting 10 ft. from me as I type this. Needs nothing. 20 ft. away is a Q-Jet w/problems that (if I can get a part I need) I will use instead.

But that's just me.

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86_cookiemonster

Discussion Starter · #9 · Jun 13, 2009

h0trod389 said:
86_cookiemonster said:

(My dad helped me, I am pretty sure he could rebuild one of these carbs in his sleep.) QUOTE]

q-junk rebuilding is an art, im sure your pops has rebuilt thousands of carbs.... but there touchy.. and youll never get it right.. get pissed off and end up spendin the 250 on a new edelbrock anyways....
been there done that!

Click to expand...

We have tuned Q-jets hundreds of times and have not had any problems. Actually up until recently i had this one tuned in perfectly.

Plus it is an all original car, so putting on an edlebrock carb would just ruin it.

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ericnova72

· #10 · Jun 13, 2009

Along with the fuel system stuff mentioned, check the HEI distributor. I have several times seen the mechanical advance be sticky or seized up tight simply from age and had to remove and dis-assemble and relube the entire distributor. The symptoms were the same sluggishness you describe, on a similar year Z28 and others using mid 70's HEI's.

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matt69olds

· #11 · Jun 15, 2009

If you have junk in the float bowl of the carb that looks like rat turds I bet the charcoal canistor has started to come apart. Its the round canistor in the front of the engine bay. I have no idea where you could find a replacement but thats probably your problem. Good luck!

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jimfulco

· #12 · Jun 16, 2009

cobalt327 said:
I LOVE IT!!!

As long as this is the general mentality, I will keep on getting Q-Jet cores given to me, for nada.

IMO, the Q-Jet is one of the all-time BEST carbs ever used by the OEM, and I would not take 3 EDDY's for one good Q-Jet.

In fact, I have a perfectly good Edelbrock sitting 10 ft. from me as I type this. Needs nothing. 20 ft. away is a Q-Jet w/problems that (if I can get a part I need) I will use instead.

But that's just me.

Not just you, me too. The only thing better than a good old Q-jet is a well-functioning EFI setup.

And like Eric said, check the HEI. Pull the cap and rotor. If it looks like somebody sprayed a coating of rust on the parts under the rotor, that's likely to be your problem. Excessive resistance in the secondary ignition circuit can cause high voltage to jump to ground through the rotor, and that causes the rusty coating, along with wear and binding of the advance weight pivot points. Some came with plastic pivot point bushings that deteriorate with age & heat, and those should be replaced if that's the case.

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