Carb Problems - Pontiac GTO Forum
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post #1 of 10 (permalink) Old 12-31-2012, 01:19 PM Thread Starter
 
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Carb Problems

I am having trouble with my car when i put it to full throttle. I have a Edelbrock 650 carb on my gto and as long as its in Park or Neutral i can open it up and have no problems, but when i get on the highway and put the hammer down it tries to die out on me. Is there anyone out there that might have any idea of what the problem may be.
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post #2 of 10 (permalink) Old 12-31-2012, 03:21 PM
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You're starving for fuel. Could be delivery, could be carb. For a GTO, a 650 is marginal....the stock Q-jet is 750cfm for the 400 and 800 cfm for the 455. You can check fuel pump pressure and volume, and if ok, it's the carb. If not, it's the pump or a restriction in the lines.
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post #3 of 10 (permalink) Old 12-31-2012, 03:32 PM Thread Starter
 
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ok i'll check all of those ..one question how can i check the fuel pump to see if im getting good enough pressure.....i have a filter on the inlet line before the line goes into the carb, could that be part of the problem.
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post #4 of 10 (permalink) Old 01-01-2013, 03:07 AM
 
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carb

Just recently went through this with our '66 Lemans convertible with a Carter 625 cfm competition carb. Yes, it would be extra nice to have a period correct intake and carb. such as a Qjet or Holley, but don't forget that Carter was also listed as an option in the '66 chassis shop manual. Carter= Edelbrock in this day and age. Don't know what year Goat you got, but I ran that 625 on the old 326. Now it is on a '71 455. VERY small carb. for that engine; didn't ever think that would run the 455, but lo and behold... she run damn good now... Had a terrible time with it, checked everything under the sun: timing, dist., wiring, carb. rebuild-(three times) etc... turned out to be a cheesy Chinese crafted brass vacuum block at the back of carb.(attached to power brakes and modulator) that had a casting flaw and was sucking just enough air to make it run slightly higher rpms at idle and do all sorts of crazy things. One day it'd run great, next day terrible. Problem didn't show up with any amount of carb. cleaner spray. Had to disassemble that vacuum block and THOROUGHLY visually inspect it. Check basics first... VACUUM LEAKS, carb. gasket, ignition timing, fuel filter, vacuum port configuration, fuel pump pressure, float level, compression check, etc... You'll get to the bottom of it with a little persistence. You can rent a fuel pump pressure tester at most any auto parts store. Maybe someday I'll have a real intake and carb. on mine, but for now, this'll do.
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post #5 of 10 (permalink) Old 01-01-2013, 10:15 AM
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When you say "it tries to die out", what exactly does it do? Does it stumble, and sputter? Does it behave like someone just turned off the key briefly? What?

Most of all, you need a systematic approach. Check for and eliminate one thing at a time - you'll eventually find it. Engines behave quite differently under load in actual driving conditions than they do in neutral with no load on them, so the fact that it seems ok sitting in your driveway really tells you very little. Start with the easy things first. If any/all of the fuel filters aren't new, replace them. Check your ignition timing, both at idle and at 2500 rpm if possible (doing that requires a timing light that can read "total" advance). Carefully check for any vacuum leaks anywhere around the carb, fittings, hoses, and intake manifold.

with GeeTee that the carb you have is a little small for the engine, but that shouldn't make it stumble or act like it's going to die as long as it's set up properly.

The only reliable way to check fuel pressure is to use a good fuel pressure gauge. It needs to be installed in the line close to the carb inlet, and if you want to see what's happening under driving conditions, temporarily mounted OUTSIDE THE CAR so you can see it while driving. Don't "cheap out" and put the gauge inside the car with you - one problem with a fuel line leak and you'll be spraying gasoline all over the inside of the car and maybe all over yourself - not something you want to take a chance with.

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post #6 of 10 (permalink) Old 01-01-2013, 08:30 PM
 
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I had the same issue with the 800cfm e-brock on my 455. I chased the problem all over the car. New fuel pump and line, new coil for the dizzy, new wires and plugs, new jets and rods. While everything helped a little my real issue was that the needle and seats that allow the fuel to fill the floats were caked with grime and the fuel couldnt get into the carb fast enough to keep the car going while in drive. In park and the 455 would rev and was very responsive to the throttle. these cars need very little fuel in park to keep running. In closing after 300 bucks in new parts were I should have started was by opening up the carb and running through it with my air compressor and two cans of carb cleaner.

65 LeMans, 455,TH400, Edelbrock preformer Intake&Carb, K&N Filter, Custom Headers & Dual Exhaust W/ H pipe, 15in ralley wheels...... More to come.
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post #7 of 10 (permalink) Old 01-02-2013, 12:09 AM
 
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carb

You bet! It appears the needles and seats in these E-brock's and newer style Carters are very touchy. But the major problems seem to be in the accelerator pump delivery passages. Make certain that you're getting a good solid spray of fuel out of the discharge nozzles. Like I said, I disassembled the carburetor 3 times and checked float levels (and tweaking them), cleaned it, blew it out, scrutinized all settings, and STILL had problems. Was just about ready to give up and buy a Qjet, but found that vacuum leak at the final hour. Don't overlook the obvious, even though it may not seem all that obvious.
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post #8 of 10 (permalink) Old 01-08-2013, 04:42 PM Thread Starter
 
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Thanks everyone for your input ....im going to try to go through everything and see if i can get this thing figured out.
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post #9 of 10 (permalink) Old 01-09-2013, 11:15 AM
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Fuel pressure gauges are available at the parts store. Not super cheap. The volume test is in the manual, usually. It's a cranking test and a fire hazard, so be careful. It involves disconnecting the fuel line and cranking the engine over with the ign disabled...if you fill up a quart jar with fuel in about 20 seconds you're okay. Usually NOT the problem. Check your pressure, your lines (especially the rubber line back by the tank!!) etc. Any cracking of the rubber, replace the lines.
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post #10 of 10 (permalink) Old 01-09-2013, 07:10 PM
 
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Your carburetor is certainly on the small side for your application, but I tend to go with Bear on this one... by properly setting up your initial timing and your advance mechanism(s) you should be able to eliminate much of your drivability issues.

There's an old saying that goes "90% of carburetor problems are actually ignition timing." Been there, done that.

When the only tool in your toolbox is a hammer, you tend to see every problem as a nail.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Technical and Electrical Wiring

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