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My car is a 1979 4-speed. 350 with Brodix IK200 heads, Lunati 268 cam, Performer RPM intake, Doug's headers and side pipes.
It's just a fun little hotrod. But I noticed the other day when doing a 1-2nd gear pull that in 1st gear it will pull up to 6,000 RPM (where I shift into second) but in second gear around 5,500 RPM it acts like it hits a rev limiter. What would be different about first and second gear? Maybe just the float bowls in the carb not able to fill up fast enough? Or maybe my tach is somehow messing up?
Can't remember what jet/rod combo I have in there currently (changed it so many times trying to get it right for my combo). But my wideband 02 reads right around 13:1 at WOT
It sounds to me like you have a plugging fuel filter. If you could see inside a fuel filter when you suddenly rev an engine real high large particles of sediment will get stirred up into a whirlwind and stick to the surface of the element; plugging it. When you back off the throttle those large particles will fall back down until the next time a high volume of fuel passes thru the filter.
It sounds to me like you have a plugging fuel filter. If you could see inside a fuel filter when you suddenly rev an engine real high large particles of sediment will get stirred up into a whirlwind and stick to the surface of the element; plugging it. When you back off the throttle those large particles will fall back down until the next time a high volume of fuel passes thru the filter.
Brand new fuel filter (well new 2 months or so ago).
It's extremely repeatable. 1st gear revs to 6000 easily, 2nd gear is revving freely and then just hits a wall at 5500 RPM. I need to test what happens if I just start in second gear and plant the throttle. If it will rev to 6000 in second in that situation, then I know it's a fuel issue (the float bowl not able to fill fast enough to keep up).
I also have an electric tach sitting somewhere in my garage. I'll try hooking that up too just to verify that my stock tach is reading accurately.
If you replaced the inlet fuel filter in the quadrajet you didn't by chance use one of those anti drain back filters did you? They have a small ball in the opening and restrict fuel flow greatly. I tried one and it always ran out of fuel at the top of second gear due to the poor design of the filter. You want to use one without the check ball. If that is not the problem is the filter in backwards?
If you replaced the inlet fuel filter in the quadrajet you didn't by chance use one of those anti drain back filters did you? They have a small ball in the opening and restrict fuel flow greatly. I tried one and it always ran out of fuel at the top of second gear due to the poor design of the filter. You want to use one without the check ball. If that is not the problem is the filter in backwards?
I vaguely remember researching that before I replaced that filter in the quadrajet, I can't imagine I would have researched it and bought the wrong one (I'm pretty meticulous before making purchases). But I'll check tonight, thanks for the tip!
I vaguely remember researching that before I replaced that filter in the quadrajet, I can't imagine I would have researched it and bought the wrong one (I'm pretty meticulous before making purchases). But I'll check tonight, thanks for the tip!
The one on the left is a normal filter and the one on the right is an anti drain back. That ball is a huge restriction and sometimes will jamb up completely. It is the one that was in my car and although it looks ok and is new it was causing the carb to run out of fuel under heavy acceleration.
Last edited by CanadaGrant; 10-04-2017 at 02:01 PM.
The one on the left is a normal filter and the one on the right is an anti drain back. That ball is a huge restriction and sometimes will jamb up completely.
If I accidentally used the anti-drain back one, I'm assuming I can just remove that piece of the filter?
Yes you can. The ball just lifts right out but you might need to make some sort of washer/seal or use an old one if you have it. Or you might just cut the ball and cage off and use the seal on it.
Last edited by CanadaGrant; 10-04-2017 at 02:13 PM.
My 79 does the same thing. Started right after I rebuilt my carb. Hubby said the metering rods were in the wrong holes or upside down or something so we switched them up from where they were.
Interesting! Run a q-Jet myself and thought that i exoerienced this on and off... not allways. Just changed my fuel pump, but could be a clogged fuel tank pick up sock also... my carb is ok, it was rebuild by Lars... i have read that a supporting low pressure (4psi) fuel pump right by the fuel tank in Addition to the original mechanical pump can help high rpm fuel starvation if this is the case. But a original fuel pump in good condition should be able to Support 6000rpm easy...
Brand new fuel filter (well new 2 months or so ago).
It's extremely repeatable. 1st gear revs to 6000 easily, 2nd gear is revving freely and then just hits a wall at 5500 RPM. I need to test what happens if I just start in second gear and plant the throttle. If it will rev to 6000 in second in that situation, then I know it's a fuel issue (the float bowl not able to fill fast enough to keep up).
I also have an electric tach sitting somewhere in my garage. I'll try hooking that up too just to verify that my stock tach is reading accurately.
Anyone else have thoughts?
When you blast thru 1st gear it makes a lot of power up to say 5500 but it'll reach 6000 rpm because the wind resistance is low. Then when you blast thru 2nd gear it reaches the same 5500 rpm but because of increasing wind resistance it doesn't rev any higher. It's the lack of wind resistance that allows the higher revs in 1st gear. Then when you blast thru 3rd gear it'll probably top out at 4500 rpm because of the increasing wind resistance.
When you blast thru 1st gear it makes a lot of power up to say 5500 but it'll reach 6000 rpm because the wind resistance is low. Then when you blast thru 2nd gear it reaches the same 5500 rpm but because of increasing wind resistance it doesn't rev any higher. It's the lack of wind resistance that allows the higher revs in 1st gear. Then when you blast thru 3rd gear it'll probably top out at 4500 rpm because of the increasing wind resistance.
Prior to my carb rebuild my 79 would rev to 6000 in each gear. After it will go to 6000 in 1st and 5500 in 2 and 3rd.
Can't remember what jet/rod combo I have in there currently (changed it so many times trying to get it right for my combo). But my wideband 02 reads right around 13:1 at WOT
If its still reading 13:1 at 5,500 to 6,000 rpm then its not the carb/fuel.
Read like your tach is lying to you somewhat. If you cant find a dyno where you can do pulls in 2nd gear then you could play with the mechanical timing. Is your timing computer controlled or just the q-jet?
I think your problem is that the carb secondaries are not opening fully. You might get away with that in first gear [and still get it to wind up]; but it sounds like you are running out of fuel/air (at the correct mixture amount) in 2nd gear. It would probably die sooner in 3rd.
Remove air cleaner; manually hold open the secondary air valve (flap) and look down into secondaries; have someone else fully depress the accelerator pedal and you look to see if the secondary butterflies are completely vertical. If not, there's your problem.
And, NO, you cannot do the same thing by manually going to WOT at the carb.
I think your problem is that the carb secondaries are not opening fully. You might get away with that in first gear [and still get it to wind up]; but it sounds like you are running out of fuel/air (at the correct mixture amount) in 2nd gear. It would probably die sooner in 3rd.
Remove air cleaner; manually hold open the secondary air valve (flap) and look down into secondaries; have someone else fully depress the accelerator pedal and you look to see if the secondary butterflies are completely vertical. If not, there's your problem.
And, NO, you cannot do the same thing by manually going to WOT at the carb.
7T1 has a very good point. Most of these old cars have limited movement in the accelerator cable due to stretch and bending in the pedal linkage under the dash that prevents even close to full throttle. My new accelerator cable was 1/4 of an inch shorter than the old one which was preventing the secondaries from opening at all and linkage bending above the pedal is a very common problem.
Sounds like a fuel delivery problem. A mechanical fuel pump should deliver at least 1-1/2 pints in 30 seconds. I highly recommend sweat-soldering an 1/8" NPT "T" in the feed line so pressure can easily be checked even under full power by taping a pressure gauge to the windshield. If everything is working right the fuel pressure should remain constant all the way up to red line under full power.
Sounds like a fuel delivery problem. A mechanical fuel pump should deliver at least 1-1/2 pints in 30 seconds. I highly recommend sweat-soldering an 1/8" NPT "T" in the feed line so pressure can easily be checked even under full power by taping a pressure gauge to the windshield. If everything is working right the fuel pressure should remain constant all the way up to red line under full power.
Wow, that's the exact same fuel line setup that toobroketoretire uses on his engine. Same engine too! Actually, if you look real close it is the same engine... https://www.corvetteforum.com/forums...roblems-2.html
Post number 24.
Wow, that's the exact same fuel line setup that toobroketoretire uses on his engine. Same engine too! Actually, if you look real close it is the same engine... https://www.corvetteforum.com/forums...roblems-2.html
Post number 24.
Looks like he bought a can of orange spray paint since the earlier picture. Maybe he's not too broke, or too gone!
10-04-2017, 09:30 AM
Won't rev as high in second as it will in first
7T1 has a very good point. Most of these old cars have limited movement in the accelerator cable due to stretch and bending in the pedal linkage under the dash that prevents even close to full throttle. My new accelerator cable was 1/4 of an inch shorter than the old one which was preventing the secondaries from opening at all and linkage bending above the pedal is a very common problem.
