What does a vacuum leak act like?
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Joined: Feb 2009
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From: San Francisco CA
What does a vacuum leak act like?
I have serious hesitation at high RPMs... thought it was fuel, but it's got good fuel pressure and a new filter.
I can tool around the city no problem, but whenever I hit higher RPMs I lose power, it almost stalls out.
1977, L48, Auto all stock 56k miles.
I can tool around the city no problem, but whenever I hit higher RPMs I lose power, it almost stalls out.
1977, L48, Auto all stock 56k miles.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The two areas that can have symptoms like those you mentioned are: fuel and ignition. If the problem is fuel related, it will be something that causes the fuel supply to be limited so that there isn't enough fuel flow to support higher rpm operation. One of the diagnostic tests that you can use is to put the car in a lower gear and run up the rpms fairly slowly (not WOT) with a lesser throttle setting. If you can run cleanly at high rpms there...but not at WOT...then your problem is likely to be fuel limitation. Possible sources are plugged fuel filter, kinked rubber fuel line at pump or tank, float/needle valve problem in carb, 'sock' filter in fuel tank plugged/gummed up, weak fuel pump.
When you do the diagnostic test (above) and it shows that the car still jerks/shudders when you get to higher rpms, that would indicate an ignition problem. If you have a points system, faults could be bad condenser/points/cap/wires/plugs, bad/leaky coil, poor distributor ground, poor connections on power feed to coil/distributor. If you have an electronic ignition module or H.E.I. distributor system, the electronic module is likely the culprit.
Hope that helps.
When you do the diagnostic test (above) and it shows that the car still jerks/shudders when you get to higher rpms, that would indicate an ignition problem. If you have a points system, faults could be bad condenser/points/cap/wires/plugs, bad/leaky coil, poor distributor ground, poor connections on power feed to coil/distributor. If you have an electronic ignition module or H.E.I. distributor system, the electronic module is likely the culprit.
Hope that helps.
Last edited by 7T1vette; Mar 29, 2011 at 05:07 AM.
Thread Starter
Advanced
Joined: Feb 2009
Posts: 58
Likes: 0
From: San Francisco CA
The two areas that can have symptoms like those you mentioned are: fuel and ignition. If the problem is fuel related, it will be something that causes the fuel supply to be limited so that there isn't enough fuel flow to support higher rpm operation. One of the diagnostic tests that you can use is to put the car in a lower gear and run up the rpms fairly slowly (not WOT) with a lesser throttle setting. If you can run cleanly at high rpms there...but not at WOT...then your problem is likely to be fuel limitation. Possible sources are plugged fuel filter, kinked rubber fuel line at pump or tank, float/needle valve problem in carb, 'sock' filter in fuel tank plugged/gummed up, weak fuel pump.
When you do the diagnostic test (above) and it shows that the car still jerks/shudders when you get to higher rpms, that would indicate an ignition problem. If you have a points system, faults could be bad condenser/points/cap/wires/plugs, bad/leaky coil, poor distributor ground, poor connections on power feed to coil/distributor. If you have an electronic ignition module or H.E.I. distributor system, the electronic module is likely the culprit.
Hope that helps.
When you do the diagnostic test (above) and it shows that the car still jerks/shudders when you get to higher rpms, that would indicate an ignition problem. If you have a points system, faults could be bad condenser/points/cap/wires/plugs, bad/leaky coil, poor distributor ground, poor connections on power feed to coil/distributor. If you have an electronic ignition module or H.E.I. distributor system, the electronic module is likely the culprit.
Hope that helps.
You may have nailed it here... I had a mechanic just pull the tank down and put in new hoses they must not have tested it under serious power... I'll take it back and have them take a look. THANKS! (Again.)
Team Owner
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From: Crossville TN
The usual place for such kinking is at the hose at the inlet of the fuel pump. It has an "S" shape to it, but folks don't like to buy the molded hose. If a piece of straight hose is used there, it often kinks at the curves in the "S" segments.
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From: Where it's always hot as Hell-South Louisiana.
St. Jude Donor '07-'08-'09-'10-'11-'12-'13
They should spend the few extra $$ for the correct "S" curve lines (2) and be done with it. Ask me how I know.
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From: San Francisco CA
This is great you guys, THANK YOU, now I have something to go back to them with... the symptom perfectly matches a kinked hose, just enough gas to tool around at 20 mph, but as soon as I punch it it sputters and actually today it stalled, just like it was out of gas, once the gas pressure builds back up it starts again and I can cruise at 20 mph again.
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From: San Francisco CA
Is the fuel line inlet is at the bottom of the tank? Can I see it without removing the tank?
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From: Crossville TN
The "S" shaped line is at the inlet of the fuel pump (bottom-front/right on the engine). It connects the [steel] fuel feed line to the fuel pump. There is a rubber hose connection between the fuel tank and that same steel line at the right rear. It runs from the bottom of the tank at the [fuel gauge 'sender' location] to the line which runs along the top of the right-side frame box.
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Turns out there was something in my fuel tank... the mechanic filtered some gas and found fibers in the fuel, it almost looked like fiberglass insulation.
We had to pull out the tank and clean to fuel system. $600 later and everything is running better, but I think I need to rebuild the carb now... it's never been done so it's about time anyway.
Thanks for the advice... came down to a bad tank of gas.
Could anything have fallen into the tank after they pulled and replaced the tank the first time?
We had to pull out the tank and clean to fuel system. $600 later and everything is running better, but I think I need to rebuild the carb now... it's never been done so it's about time anyway.
Thanks for the advice... came down to a bad tank of gas.
Could anything have fallen into the tank after they pulled and replaced the tank the first time?
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From: Southeast, Tennessee
St. Jude Donor '09 thru '26
The two areas that can have symptoms like those you mentioned are: fuel and ignition. If the problem is fuel related, it will be something that causes the fuel supply to be limited so that there isn't enough fuel flow to support higher rpm operation. One of the diagnostic tests that you can use is to put the car in a lower gear and run up the rpms fairly slowly (not WOT) with a lesser throttle setting. If you can run cleanly at high rpms there...but not at WOT...then your problem is likely to be fuel limitation. Possible sources are plugged fuel filter, kinked rubber fuel line at pump or tank, float/needle valve problem in carb, 'sock' filter in fuel tank plugged/gummed up, weak fuel pump.
When you do the diagnostic test (above) and it shows that the car still jerks/shudders when you get to higher rpms, that would indicate an ignition problem. If you have a points system, faults could be bad condenser/points/cap/wires/plugs, bad/leaky coil, poor distributor ground, poor connections on power feed to coil/distributor. If you have an electronic ignition module or H.E.I. distributor system, the electronic module is likely the culprit.
Hope that helps.
When you do the diagnostic test (above) and it shows that the car still jerks/shudders when you get to higher rpms, that would indicate an ignition problem. If you have a points system, faults could be bad condenser/points/cap/wires/plugs, bad/leaky coil, poor distributor ground, poor connections on power feed to coil/distributor. If you have an electronic ignition module or H.E.I. distributor system, the electronic module is likely the culprit.
Hope that helps.
