L36 intake
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Joined: Sep 2006
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From: Modesto CA.
L36 intake
aluminum L36 intake for two years, 68-69? was there a problem with this low rise manifold? my engine runs good at first, then after a 30 min. run at 65-75 mph, exhaust is loud and seems down on power. water temp is 190 + or - 5 Deg.
thanks
thanks
Burning Brakes
Joined: Feb 2002
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From: Melbourne Australia
30 minutes seems a long time for problems to appear. I wonder if it is a fuel problem, maybe the tank is not vented properly causing a lean condition after a while? Maybe there is something wrong with the exhaust crossover or heatshield in the manifold causing the carburetor to get too hot? I had a problem once with the s-pipe from the fuel line to the mechanical fuel pump collapsing when hot enough and starving the fuel pump. These sorts of problems take quite some time running warm to appear.
Sorry I can't be more helpful. Others might chime in. Let us know what you find.
Joe
Sorry I can't be more helpful. Others might chime in. Let us know what you find.
Joe
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From: Modesto CA.
i'll check the tank ... i have a vented cap but maybe it's not enough... i'll look at it a little closer.. the fuel in california is a little strange.. blended, and it does flash off quick.
pluged the manifold off last week and two weeks ago i got a new S hose for 70 LS5 and made it work with a short piece off SS tubing... don't think 69's had a molded hose.. not sure about that...
been at this for a year and have 9000 miles on this fresh L36.. this is getting old!
it seems that i have changed everthing but the manifold so maybe it's time!
Thanks!
pluged the manifold off last week and two weeks ago i got a new S hose for 70 LS5 and made it work with a short piece off SS tubing... don't think 69's had a molded hose.. not sure about that...
been at this for a year and have 9000 miles on this fresh L36.. this is getting old!
it seems that i have changed everthing but the manifold so maybe it's time!
Thanks!
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No problems with the 68/69 L36 aluminum intakes unless you have a vacuum leak. Your problem sounds like fuel percolation or a carbeurator problem.
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From: Modesto CA.
vacuum leak?.. i have taken the intake off nine or ten times... trying different gaskets.. with sealer and without... checking the compression of the gasket.. this last time i used edelbrocks gasgacinch..... also new thick carb gasket.... maybe i'll set up a vacuum gauge and go for a drive...... vacuum at idel 16in. cam is close to the 435hp cam but hyd.
carb is a new edelbrock 1910... manifold is pluged at the carb mount and has the plates in, the intake gasket.... i'm lost... don't know what to try next
carb is a new edelbrock 1910... manifold is pluged at the carb mount and has the plates in, the intake gasket.... i'm lost... don't know what to try next
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If the exhaust sounds louder, perhaps you have an exhaust manifold with a loose bolt or a partially blown gasket that works better cold than hot. Also check the manifold to exhaust pipe gaskets and joints.
Melting Slicks
Joined: Mar 2005
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From: Austin TX
That intake as all Q-Jet intakes of 68 & 69 used a thin stainless heat shield between the carb and intake. If your crossover is still in play, and you don't have this heat barrier, the fuel in the carb will perculate causing lots of diagnostic fun. Believe it or not, the exhaust is routed directly to the primary side of the q-jet,..and it' hot.
Also, if you think you have a gasket with a block-off, I've seen many of the "blocks" blown out. You'll need special oval-port intake gaskets with the piece of tin in the middle. It's very hard to find,..I can probably dig up a part number if needed.
BTW,..there were some big Chevy Q-Jet recalls during this period,..turns out heating the pot-metal q-jets with exhaust heat, over and over isn't good. Later intakes were designed differently.
Good lucK!
Also, if you think you have a gasket with a block-off, I've seen many of the "blocks" blown out. You'll need special oval-port intake gaskets with the piece of tin in the middle. It's very hard to find,..I can probably dig up a part number if needed.
BTW,..there were some big Chevy Q-Jet recalls during this period,..turns out heating the pot-metal q-jets with exhaust heat, over and over isn't good. Later intakes were designed differently.
Good lucK!
Last edited by 73, Dark Blue 454; Jul 13, 2007 at 12:05 AM.
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From: Modesto CA.
THANKS TO ALL!
pluged the manifold cross over with 1/4 in. pipe plugs..
exhaust manifolds are mechined flat and no gasket... no leaks.. no bolts missing or loose... new donut ..
loud goes away when slow down and run at 40mph, or idle for a short while...
i think BigBlockk might be on to something.... edelbrock Q-jet is 850cfm it mght be lean at cruise and maybe check the fuel filter one more time?
Thanks for all the help and any more ideas!!!
pluged the manifold cross over with 1/4 in. pipe plugs..
exhaust manifolds are mechined flat and no gasket... no leaks.. no bolts missing or loose... new donut ..
loud goes away when slow down and run at 40mph, or idle for a short while...
i think BigBlockk might be on to something.... edelbrock Q-jet is 850cfm it mght be lean at cruise and maybe check the fuel filter one more time?
Thanks for all the help and any more ideas!!!
Thread Starter
Advanced
Joined: Sep 2006
Posts: 94
Likes: 0
From: Modesto CA.
That intake as all Q-Jet intakes of 68 & 69 used a thin stainless heat shield between the carb and intake. If your crossover is still in play, and you don't have this heat barrier, the fuel in the carb will perculate causing lots of diagnostic fun. Believe it or not, the exhaust is routed directly to the primary side of the q-jet,..and it' hot.
Also, if you think you have a gasket with a block-off, I've seen many of the "blocks" blown out. You'll need special oval-port intake gaskets with the piece of tin in the middle. It's very hard to find,..I can probably dig up a part number if needed.
BTW,..there were some big Chevy Q-Jet recalls during this period,..turns out heating the pot-metal q-jets with exhaust heat, over and over isn't good. Later intakes were designed differently.
Good lucK!
Also, if you think you have a gasket with a block-off, I've seen many of the "blocks" blown out. You'll need special oval-port intake gaskets with the piece of tin in the middle. It's very hard to find,..I can probably dig up a part number if needed.
BTW,..there were some big Chevy Q-Jet recalls during this period,..turns out heating the pot-metal q-jets with exhaust heat, over and over isn't good. Later intakes were designed differently.
Good lucK!
