I've been noticing lately a loss of power after driving 15-20 minutes. The engine gets to temp, usually 200 degrees and I lose quite a bit of power. The car still drives fine but it definitely does not have the pep as it does from a cold start and the initial 15 minutes. Just looking for a starting point on what could cause this.


69 350 block bored .030 over
Stock Crank turned and polished
Speed Pro Forged pistons
supposed to be 10:1 compression according to builder. I did not confirm this
Unknown headers
2.5" exhaust with x pipe http://www.jegs.com/i/PYPES/958/SGA11SSV/10002/-1
Edelbrock 1405 600cfm carb
Edelbrock Performer 3711 intake
Erson TQ20 cam
Duration @ .050: 214/214
Lobe Center: 111
Stock #5 heads cleaned/new valves
DELCO HEI / Accel 8mm superstock wires
TH350 rebuit, shift kit #30228 installed
2400 stall Torque converter dynamic manufacturing
Factory 3.42 gears with 588 posi carrier

 

Did you use the original power wire for the points. Hei need constant 12 volts. The resistor wire drops to like 9 once hot.

 

Check: choke plate, then check the coil. Though usually when I've had coil issues it would just quit and car wouldn't start again until coil had cooled.

 

What air cleaner asm are you using for engine air intake? If the engine is taking in hot air from an open element air cleaner its reducing the A/F charge due to heat. The carb should have an insulator gasket under it to reduce the heat wicked off the intake. If the carbs getting exhaust gas crossover heat or excessive wicked intake manifold heat it will give the same effect especially if the heat stove system is stock and not working correctly. Ethanol gas isn't helping. Use non ethanol blended gas. As mentioned verify the coils (Ignition sys) isnt breaking down due to heat.

 

The choke plate is locked full open, my carb is a manual choke and I havent ran a cable to the dash yet to regulate it. The 12v source for the distributor is a 12-14 ga wire from the ACC terminal on the fuse panel. I can easily change this if not the proper way to have it wired. The air cleaner is an Edelbrock pro-flow 10 x 3" #1208 http://www.edelbrock.com/automotive/...c-proflo.shtml

The carb has a riser plate and gasket from the intake.

 

I have never had an issue with ehtanol blends. MY underhood temps get very very hot although the engine runs cool. I dont have any issues running wise. The only thing i see is you could use more carb and cam. That duration for the compression it "has" is not enough.

Too much cylinder pressure due to too much compression and not enough duration and a hot engine can lead to issues like you are having.

I have a 10 to 1 355 with #6 heads. im running a 233/241 duration. Although i had a smaller cam previous it ran fine it was a 227/232 duration cam.

 

When was the last time it was tuned up? Condition of your ignition parts and timing has a lot to do with your performance. When was the last time you changed your air and fuel filter. Have you checked your vacuum? There are a lot of things that can cause your issue.

 

The engine rebuild was complete 6/2015. I've only done 600-700 miles since. I timed it in the last few months. All components were new at the time of the build so only have about a year and less then 700 miles on them. I have not checked vac and will do that.

 

You might pull the plugs and see what they are telling you.

 

Ohm your plug wires when checking the plugs. I've seen a lot of tuning issues lately from running very high resistance plug wires (Napa brand for example) That simply don't play well when used with resistor spark plugs. You want 5000 Ohms or less per plug wire, and preferably 0 Ohm copper core spark plugs (non-resistor). Or run copper core wires with resistor plugs, but if both are resistive limit the plug wire resistance. Moroso Bluemax plug wires fall into the "good" category.

 

I have a very similar issue. For me, it's not filter related.

I started looking at the cooling system to try and bring the temp down, (i run right around 200 on the gauge), but I do notice the fuel in the inline filter gets very hot. Sometimes, if it idles in a parking lot on a hot day, you can actually see if start to boil in the filter. I think this is more so my problem.

I get vapor and not actual fuel in the bowls of the carb.

 

Vapor would just blow through the carbs. It won't force the needle and seat to close, so fuel levels would remain the same. Did you install dual exhaust and leave the fuel line right above the new exhaust pipes?

 

Dual exhaust was installed before I bought the car. The fuel lines comes up through the frame in the OEM spot and into the fuel pump. Over the intake(now in rubber lines) into an in-line filter, then into the ebrock carb.

Do people typically re-reroute the fuel lines when changing to duals?

 

In my '68. the fuel line ran along the floor pan (or was that the brake line?) right above the exhaust pipes. Old age. Might have been the brake lines. Sorry.

The only reason your fuel would boil is if it was introduced to high temps. You may just be seeing fuel flow normally through the filter. With all the cleaners in it, it can bubble a little. Even then, it shouldn't boil while driving. This is a common blame, rarely the case. You could be sucking air through leaks in the lines, but percolation is rare, unless the fuel line is too close to the exhaust heat.

 

Check the timing, plugs, fuel filter, vacuum lines said. Make sure your carb is set where it needs to be, a lot of problems with the Edelbrock carbs. I would personally go QJet or Street Demon in it's place. I also would have went with the 7111 RPM intake. Good luck.

 

Identical to how mine is routed.

 

Does your fuel ever boil in the inline carb?

I'm temped here to replace the fuel pump just for shi*s and haha's because I'm not sure what else could be happening.

 

..... or if it was under vacuum.

If your filter is before the pump, you are creating even lower pressure after the filter than if it wasn't there at all. This brings it even closer to "boiling" even without heating it.

Conversely, if your filter is plumbed between the pump and carb, the fuel passing through it is under pressure and much less likely to "boil."

 

It could come down to a distributor phasing issue that would develop heat in the coil, decreasing coil output. Close inspection of your cap and rotor terminals is in order. If they appear to be lined up when firing, burn marks will be centered. If not, the black marks will be offset to the edges of the terminals, stressing the coil with a larger gap in the distributor than you would see at the spark plugs.
When you raised compression did you install the appropriate cooler spark plugs?
Have you had it on a scope or a dyno to see what your fuel mixture is after all the changes? This could also identify a vacuum leak that may otherwise not be easy to find - like at the bottom of an intake port sucking from the valley.

 

So if it's boiling after the pump and before the carb, then the underhood temps are too hot. I could post a picture, but how can I get the filter away from the heat of the intake? It's gotta go that way.

Conversely, I could heat insulation wrap the fuel lines to try and keep them cooler. But that seems excessive. I'll have to let it run in the driveway before it gets too cold here, and really watch the fuel. If it's really boiling, or if like the other member said, if possibly it's air going into the filter. I'll even try and get a video.

 

It never bubbles, it almost looks like a boil due to flow and vibration though.

 

I've had the problem of fuel getting hot several times on my 403. First I had rubber line with a inline filter and the filter would get a little to close to the t stat housing and boil the gas. I went to a hard line, the line still came right out almost against the t stat housing, so I used a shorter Chevrolet fuel inlet and I wrapped my line in heat wrap. From what I've seen this is a common problem with Olds due to fuel line routing.

 

I'm not sure fuel temp is my issue. If you look at the pic you can see the primary line go into my fuel pump and the secondary come out and to the inline filter on top of the passenger side valve cover. The valve cover never gets hot to the point that I can't keep my hand on it so I don't know if being that close to it would affect anything.

 

I had the same set up as you with no issues. My current set up in my 72 is all AN- fittings and raided lines but still ran the same way.

FWIW my underhood temps are right down ridiculous . To the point that after a long drive like 80 miles or so you cant touch the manifold or valve covers ., My point being my car still runs fine and no loss of power. The diffrence between my car running at temp Like makeing a pass at the drag strip after driving there 60 miles or me letting is sit and cool down is 1 tenth of a second.

What i have done to try to help keep heat from the carb is i run a heat sheild and the correct gaskets to try to keep heat away.

Now the only thing my underhood temps have killed is I constantly keep warping dist. caps and i run into some serious arching issues. heat kills the ignition modules in the HEI heat creates resistance. Just fwiw.

 

I see what your saying. Your fuel temp should be fine like that I was thinking front inlet like a quadrajet.

 

Copper, hunt down the brown Accel distributor cap and rotor if you're not running an MSD distributor. They have brass terminals and are thicker, far less prone to warp.

 

That's the last set I warped the brown cap.

 

Not sure where you're located, but if it's cooler out this week(it is in mass), take the car for a ride and see if the problem is still there, or if it takes longer for the problem to occur.

I drove my car to work today(30 minutes, mixed highway and 40mph backroads) and I noticed I got less than a mile from work where I started to fell my car "acting up". It was also only about 60* here this morning. Mine, is definitely temperature related. I may try to heat wrap my lines like you guys did.

 

Unbelievable. That must be an enormous amount of heat. Enough to cause significant drivability issues, destroyed engine gaskets, boiling fuel, etc...
Or a mis-diagnosis. It takes 400+ degrees for an extended time to warp that cap, if it was the Accel. Could be an out of phase scenario.

 

When I bench tested it I could see the park between the body and cap. My under hood temps are not nearly that hot but they get toasty. The spark was going every which way but the wires. Everything was tested. Got a new cap and rotor and problem fixed. Quality is in the crapper. Went back to an msd Cap since my last one lasted me 4 years. Just my experience. I could have gotten the one cappy cap. Who knows.

 

After 80 miles? My valve covers get hot enough in 20 minutes to not be able to keep my hand on them.

You guys can really run your cars 10 miles, pull over and put your hand on the valve cover? My temp gauge hovers 195/215 depending, and my valve covers are too hot to touch all the time.

 

My temps never go over 190 ish 200 in realllllly hot weather maye 210 on the way back from the track after beating the crap out of it all day . I went to the track about 3 weeks ago and it was about low 70's and the car never got over 175 on the drive to the track. I hit 190 on the drive back but by then it was in the low 80's and the engine was heat soaked etc etc. pretty much a 60 mile drive at about 3500 rpms with a few stops here or there ( country roads).

Thats 60 miles each way.

 

Maybe cross firing on your bunched together plug wires?

 

cross firing would happen even when cold . I have never ran across that issue personally.

 

Copper, it takes a LOT of resistance in the HT wires to cause the spark to attempt to jump to ground instead of the nearest cap terminals. Or high resistance aluminum terminals. Or a failed rotor that's pushing voltage elsewhere. You've made a good choice with the red cap and rotor (China's finest), although brown or blue should work too. Black is embedded with carbon to color it - bad idea except for the vintage stuff that was phenolic with black paint.

I've seen this in a lot of Delco distributors when a phasing problem is present. When advanced, the rotor lands half way between 2 cap terminals and you fire to anywhere that'll take it. If you inspect the distributor with the rotor off, there is a dimple drilled in the gear adjacent to the roll pin. With that dimple facing toward you, holding the distributor vertical, the square locator hole for the rotor should be on the left side of the distributor.

 

Cman,

We're actually running the same carb, and where we're having simliar issues, It'd start somewhere with the carb.

Do you have a phenolic spacer between the car and manifold? a 3/4" one would be a good place to start.

Secondly could it be something with the electric choke? For the first few minutes the choke is partially activated, is something changing after that point?

 

Crazy thing is i ran that carb out the box no tuning with no issues. My car went 13.3's with my old 355.

 

I know. I still think thats a miracle. Mines a stock motor and I couldn't get it to run out of the box. I had hesitations, stumbles, bogs, etc.

 

I have never, ever seen a new carb that had the correct float levels. Not once. The new Edelbrock I recently installed had an adjustable secondary air door and it was WAY out of spec. The secondary linkages were junk and needed to be modified to work at all. The needles and jets were otherwise perfect for a 350. Accelerator pump had to be moved to the largest squirt.

The last 3 1406s before that had the wrong needles and jets for a 350, no adjustable secondaries to worry about. Again, floats all way out of spec.

 

I installed mine and went on my way. Granted ! I buy factory reconditioned carbs because of all the issues. So the rebuilt carbs get more attention vs assembly line.


One of my old engines went on my dad's 77 pontiac and my old 1405 carb. It ran great in my car but needed tuning on the pontiac. It had more restrictive exhaust , more weight , less gear etc etc. All i did was changed the pump shot and curved the dist. And for a land yacht with 3.08's that baby moves and it's just a 350 with 9 to 1 compression and a towing cam.