I've got a 360FE or 390FE with a Holley 1850 carburetor, long tube headers into true duel exhaust. When I gun the pedal the engine falls flat and will die unless you let off. I've tried replacing both diaphragms and springs, changing the main jets and adjusting fuel mixtures on the carburetor. Everything I've tried hasn't worked so far.

The carburetor had a size 66 jet in it when I checked and because my spark plugs were black I tried the smallest jet size I had at 64. That made it worse. So today i tried a size 69 jet and its back to the same as the size 66 jet.

I'm still learning a lot about vehicles so if anyone here can help me out I would very much appreciate it.

 

I would check that your accelerator pump is working properly. You should see a squirt of fuel from the discharge nozzles when the throttle is moved.

 

A lot of variables that can cause this to occur. But as 0thPony said, 1st check would be the accel. pump. With a 600cfm like the 1850, you really shouldn't have much issues with the factory set of jets. I've ran them on a few 390s in the past when I was in Highschool just to help somewhat w/ MPG.

Also, has this been a constant occurance, or something recent? If recent, did you change anything with the motor? (Carb, distributor, etc...) I know you said your plugs were black, so have you set or checked your base timing? What gaps are you running on the plugs?

 

The carb should have 64 jets in it stock and a 6.5" power valve... although I find most of my engines like an 8.5" power valve for every day driveability. Make sure you renew the accelerator pump diaphragm as this sounds like the falling flat symptom you are describing - a dead pump.

Get a vacuum spring kit and start with the middle "silver" spring. Go up and down from there to find which one you like most. The "falling flat" symptom could also be a bad secondary spring which is actuating way too early - this kills performance and you need to be very touchy with the throttle or it will die due to the secondaries opening early and killing port velocity.

So, 64 to 66 mains with an 8.5" power valve and a standard "silver" spring in the pod.

- boingk

 

This is something more recent. It was there before I had headers and full duel exhaust put on but has gotten worse since then. I recently got a timing light so I will be checking that. But first I'm going to have to figure out where 0 is since I don't seem to have any timing marks or the rust just seems to be hiding them. I also have new plugs on the way.

I'll give the 8.5 power valve a try. I just need to find/order one in 8.5. I've got the secondary springs in hand so in the mean time I'll play with those.

Thank you guys for the help. I'll update with any progress.

 

Good luck! Let us know how it goes. I had a similar issue on a MC2100 that I run on my 84 Jeep CJ7. If you hammered on the throttle, it would bog down and die, due to fuel starvation, it however, was not a pump issue, but a blockage in one of my jets, and the following passage.


I would also pull your plugs and either replace them, or if not horrible you can clean them and recheck your gaps. I had a set that no amount of cleaning would bring them back to life due to the major rich-burning issue.

 

Does anyone know about where my ignition timing should be at? I haven't had a chance yet to work on my truck but hopefully tomorrow.

 

6° BTDC is stock spec.

Mine doesn't like anything beyond 10° BTDC ... it'll "sneeze".

 

 

Vapor lock? Its kicking myy *** this year.

 

White steam is coolant, black smoke is excess fuel, blue smoke is burning oil.

So if you're getting steam out of the tail pipe you may want to start looking for blown head gasket symptoms. Check the oil for coolant and the coolant for oil. Is one of your park plugs extra clean compared to the rest?

 

Sounds like it may be a mild oiling problem? Does the truck get used frequently or is it laid up a lot? How long have you had it and what was its history before that?

I ask because if it's been sitting a lot and hasn't been driven since then the rings may be a bit sticky and letting oil into the combustion chamber. Alternatively, there may be exhaust deposits that are burning off. These big old V8's take a while to warm up compared to modern engines and will need a while to overcome any issues caused by being laid up. You'll need to give her a good steady run (about half an hour should do it) to start to see a difference if the rings are sticky or there are exhaust deposits burning off.

If its driving fine I wouldn't change the jettings. The factory Holley settings are pretty much spot on for the vast majority of stock engines - I find a power valve is generally all that is needed for fine tuning.

The most serious thing that the fine white smoke may be is coolant... indicating a poorly sealed head gasket. Keep an eye on the coolant, if you see that you are using it (and its not leaking out) then you may need new head gaskets. People make this out to be the end of the world but its not too hard - buy a scraper blade and some new gaskets and you'll be fine.

Cheers - boingk

 

I haven't pulled all of the plugs. Unfortunately I ran out of time. I need to get a new and updated fuel transfer tube as my keeps leaking with all the times I've taken the bowl off and I like the newer style gaskets.

I really hope its not a head gasket issue. I haven't drove the truck much in the last few months because of the hesitation and weather. I also didn't notice any water on the dipstick when I pulled it or on the cap.

 

Built up carbon deposits from poorly burned fuel, can and will cause smoking, other than heavy black smoke... I've dealt with this several times on different builds. Currently dealing with it in my CJ7 due to carb issues I've since resolved. How long have you ran the motor since fixing the carb? Definitely replace all plugs, as I believe you said earlier they were completely black w/ carbon buildup. New Plugs, and running a for awhile should clear out any built up carbon in the combustion chambers, and exhaust.


If you have a cooling pressure gauge, you can check your cooling system for potential leaks like a head gasket, but if it wasn't doing it prior to your carb issues, then I doubt it's a head gasket issue.

 

I got my carburetor all back together and was still having some issues with it being harder to start and running a little rough. Took the truck for a test drive to warm it up and make some more adjustments but a couple of miles from my home the truck died. It acted like it ran out of fuel but a mechanic who has the truck now said that the floats were too high and it was really rich. The mechanic said that the carburetor will no longer hold any adjustments he makes. I was having the same problem.

I ended up buying a Holley street avenger 670 cfm for a good price and plan on trying that when it arrives. Thank you everyone for your help and advice. Unfortunately it looks like my carburetor was worn out.