6 mpg... please help

[russgt]

I had an older 350 that was doing something simmilar a while back, bad mileage and wandering timming, ended up being the harmonic balancer was bad and was moving on its hub due to the rubber going bad. Might be wrong, but it could be something to check out.

[bitchin85]

How do I check the harmonic ballancer?

[68 TT]

Originally Posted by *****in85

Its got a stock 83 hei distributor. And what's the curve timing? Is that the timing at a higher rpm? I'm new at this but I know the timing at idle is 6 degrees. And with the weights and springs, where do I start? How do I know what ones to put where? Sorry if this all sounds dumb.I have never played with distributors yet

Does this distributor have a vacuum advance canister on it or not? An 83 HEI could be ESC where the computer tells the distributor what advance to run. I know in the cars it is but I don't know if the trucks were too in 83.

It could be a computer controlled distributor running with no computer to tell it what to do so you are not getting any advance at all while driving. This would really make a fuel economy and power difference.

[MTCK]

My 83 came with ESC from the factory. It was a 305 with a 4 barrel q-jet.

[68 TT]

Originally Posted by MTCK

My 83 came with ESC from the factory. It was a 305 with a 4 barrel q-jet.

Sounds like that is the problem then. No computer controls on an ESC distributor.

[bitchin85]

It only has a four pin ignotion module so I don't think its computer controlled and yes it has vacuum advance its hooked up to the passenger side port on a 1406 edelbrock

[68 TT]

Originally Posted by *****in85

It only has a four pin ignotion module so I don't think its computer controlled and yes it has vacuum advance its hooked up to the passenger side port on a 1406 edelbrock

Well so much for that idea.

Next thing to check is the air / fuel ratio. It could be really rich or lean.

[bitchin85]

I have been plkaying witrh the idle mix forever treying tro get it right.. What method do you use? Also I know the motor was rebuilt is it possible that it has the wrong timing tab or harmonic ballancer and its telling me the wrong time?

[68 TT]

Originally Posted by *****in85

I have been plkaying witrh the idle mix forever treying tro get it right.. What method do you use? Also I know the motor was rebuilt is it possible that it has the wrong timing tab or harmonic ballancer and its telling me the wrong time?

You are doing it right with the idle mixture screw setting. What max vacuum are you getting?

Not knowing if you have the wrong balancer / timing tab locations hurts diagnosis too. You need to find TDC on the engine and see where the timing mark on the balancer is at and where the timing tab is relative to that. A positive piston stop needs to be put into the spark plug hole and the engine rotated by hand until it stops in both directions and the average location of the timing mark on the balancer marked on the timing cover. This will show you where TDC is for sure timing mark wise.

You need to check the jetting next. The only accurate way to do this is with a wide band oxygen sensor or an engine analyzer. If you don't plan on tuning other vehicles yourself it will be less expensive to have a mechanic re-jet your carburetor than it will be to buy a wide band sensor setup.

[bitchin85]

I'm going to check the tdc out tonight and I'm not exactally sure on the vacuum but its on the high side of the average gap on my guage lol

[piecesparts]

Originally Posted by *****in85

Its got a stock 83 hei distributor. And what's the curve timing? Is that the timing at a higher rpm? I'm new at this but I know the timing at idle is 6 degrees. And with the weights and springs, where do I start? How do I know what ones to put where? Sorry if this all sounds dumb.I have never played with distributors yet

Go to your local O Reioly's or speed parts outlet and purchase set of weights and springs for your HEI distributor. The change of the weights inside the dizzy will make the distributor respond quicker to acceleration and allow the spark to advance quicker to make you follow the timing that you are going to be puttinginto the engine later. There will be a couple different spring sets with the weights and you can switch them around to find the most optimum tension for your truck. SMALL and SIMPLE thing to help out.

Now take time to set your initial timing on the dizzy. First and foremost, Make sure the vacuum hose is disconnected from the dizzy when you do the adjustments to the timing (did know if you were aware of this--if you do, OK) Now take the distributor and set the timing at 12 degrees BTDC and work from that point. This will make the engine pick up quicker on acceleration and make it respond where it is not sluggish. Play with the settings around this point for further gains or losses. Make sure that you do NOT pick a "Run-On condition" when you shut off the engine, or a "Detonation" --Loud spark knock on acceleration. You should be able to hear it relatively easy. If you have that, then you have advanced your timing to far and should retard the setting some.

[Desert1957]

I agree with everyone else about the timing issue , I have a similar combo in my 87. Even though its "TBI" I still have 273 gears with 31 X 10.50 X 15's but it still gets 15 on the highway.

my2 cents

1. Check the Balancer, If the outer hub has spun the timing could be ANYWHERE.

2. If OK , Set the initial timing around 10-12 BTC

3. Verify you are using the ported vacum port on your carb, not the manifold port. you need vacum to the Distributor while under load.

4. Check the vacum advance , if the diaphram goes bad it will KILL mileage.

5. If its a 4 pin module HEI distributor , make sure the weights under the rotor work and are not froze up.

6. Check for restricted exhaust, the old pancake style cat convertor's are famous for slow restriction problems.

7. Make sure your carb is not loading up , mid 80's trucks had a 4 port vacum valve that was noted for pulling a vacum on the bowl vent of the carb causing flooding.

Desert

[bitchin85]

I looked at my harmonic ballancer yesterday and noticed that my hole crank pully wabbles back and fourth while runningamam does that mean my ballancers bad or my pulley is bent? I also noticed a few of my plug wire insulators are real close to my headers. And at least two were arcing through the boot..

My vac advance is on trhe right port, the vac advance diaphram is only a few mpnths old, have to check if the weighjts are froze.. I think they're free.. No exhaust restriction.. Longtubes to duals to glass packs. No tailpipes. And explain more about the carb.. Because I can smell gas when I'm driving it

[russgt]

If you have 2 cylinders that are now missing, that is a very large problem. You will have to at least replace the melted ends and either dimple the tubes where they are melted or buy some high temp plug wire shields to keep them from melting in the future. As far as the balancer is concerned, check the rubber seal that is visible on the backside for cracking, I Can't remember exactly but something on the balancer should line up with the keyway on the crank, and if they no longer line up, its a sign that it has spun. Slight wabble may be ok, but alot of wabble could be a sign of a lot of crank bearing wear (crank is walking) or a tweaked crank snout?

[piecesparts]

I run an Accel shorty plug to give me clearance to my headers. I upgraded my wiring on the stroker engine to Taylor wires years ago and I have not had any burn issues with the plug insulators. I would also consider a set of MSD plug wires, because of two things. First, they are really heat resistant and second, the wires have a real low resistance to electron flow and they heolp to create horsepower. They are worth the cash for them. I agree, the arcing is killing your operational performance, as well as your gasmileage. There are basically two cylinders that are not working for you and just pumping fuel through them.

Also check that wabble or wobble on the crankshaft pulley--Is it the pulley or the whole balancer assembly. Possibly, you only have a bad install of the pulley (just a thought).


I remember that you first stated that you were running an Edelbrock 500 CFM carb, so there is possibly a lot of room to do some tuning on it. There are jets and needles that you can purchase to align it to your engine. I keep a full set around my shop so that I can do changes as I need to. I worked out a chart to let me calculate which direction to go with the different size orifices and needle sizes for making more fuel to the intake or less. If you are running rich, the place to start is the ignition and get your spark to the cylinders, then get the carb to align with that. Look at that timing for more performance.

I realize that all we have stated can run into bucks, but it does help.

NOW for one last thing---the short exhaust system is great for the strip or track, but it will also add to your engine running rich. The fact that there is very little or NO back pressure lets the cylinders sweep clean at a higher rate and that lets the unburned fuel out before it is consumed in the creation of power. Another thought to consider. If you are going to pay big bucks for the fuel---then use every ounce of it to get happiness.

[bitchin85]

Well I fixed the arcing problem.. For the most part and that helped a lot with the sluggish part. But still 6 mpg.. Would full flowmaster mufflers, instead of my glasspacks with no backpressure help anything? Any power gains? Mpg gains? Thanks.

[bitchin85]

O and its not a 500 edelbrock its a 600

[MTCK]

How cold is it there in Michigan? Do you have an electric or manual choke? I was running an open element air filter and couldn't get my truck warmed up enough to open the choke on the carb. A piece of cardboard in front of the radiator helped and I installed a heat riser off of my passenger size header to the stock air cleaner assembly with the temp switch inside it. I didn't check the mileage and only drove about 1/2 a tank but it was TERRIBLE with the choke partially closed all the time.

What you really need to do is systematically eliminate one problem at a time. Get a vacuum meter with some numbers on it. First tackle your timing issues and then go to the fuel system. How is your cap and rotor? Coil ok? Check the gap on your spark plugs? You can get a mechanical advance kit for about 15 bucks that will have new weights, bushings and a few sets of different springs. Also make sure your firing order is correct.

Another simple problem could be tire pressure. What are you running? I don't think you would see much gain from switching exhaust. Get the motor running right first before you throw more parts at it. Good luck and keep after it.

[bitchin85]

It has an ecel choke with an edelbrock triangle shaped foam element filter. And its coldhere. I know it has a 160degree thermostat init.. Could that be keeping it from getting hot enough? And the vac is about 21 pounds

[MTCK]

It has been a while since I have had an electric choke. Mine has a bi-metal spring that mounts to the intake and it deffinitely wasn't opening all the way. Try taking your air cleaner off after you drive around a bit and see if the choke is fully open. Is your motor warming up on your temp gauge? If the choke is opening I would just start working down the list above. My truck is optimized around 21" Hg of vacuum.

[bitchin85]

I have noticed that my choke opens most of the way but not all the way and my truck only runs about 170. I think tomorrow I'm going to throw a 195 thermostat in it and see if that helps. And the carb has about 3k miles on it so I don't think anythings worn out on it just yet

[russgt]

The carb probably isnt worn out, but the choke blade could be getting hung up on something and not opening fully. Was the edelbrock new or a reman?

[68 TT]

21" of vacuum is a decent number pretty close to stock so you should be doing much better on gas.

Mine pulls 13" due to a fairly large cam and even with 5.13 gears, no overdrive and hitting every stoplight red I still get about 8 mpg in the city and about 12 on the highway and I have the same carburetor and ignition you do on the same size engine.

Something odd is going on with your setup. We just need to figure out what it is.

[piecesparts]

Originally Posted by *****in85

I got a long bed 2wd with a 355 with 305 heads, edelbrock streetmaster intake, edelbrock 500 carb, basicaly stock cam, stock distributor, mallory coil, automatic th350. Its got a 2.73 rear end and 31x10.5s... I know its no honda but I drive a lot and I think I should be gettin a little better milage. Also its real sluggish. Anyone have an idea of what It could be? Thanks guys

All good ideas on how to upgrade, I agree on the finding ONE thing at a time and eliminate issues that way. The flow path given is the one that I would use to get this done. Start at the engine's basics and work your way out.

Your outside air temps and the choke setting could be a major part of the fuel consumption. However, you also have to look back at the combination that you are running. The TH350 tranny and 2.73 gears with a 31X10.5 tires could be making you work that truck harder than normal, on a daily basis. I figure somewhere in this discussion there has been some reference to what you are turning for RPMs to get this to roll down the road and what you have to do to accelerate. Taller tires and small gearing numbers for rear ends is not an ideal thing. The opposite of that is the fact that once you have it rolling and if you run too small of a tire diameter, then the RPMs are going to be to high to get decent mileage. So there must be a happy medium, you stated that the truck was a 2WD, so is there a reason for the larger dirt tires?

Once again, go for the engine basics, then look at the air intake---I live in Kansas and lately our temps have been really cold, but I do run open air cleaners. The chokes on my trucks tend to not open properly on a really cold day, but it is only now and then, so I live with it. Heck even my DD TBI tends to run cold choke conditions on a really cold day--so it is a normal thing. Changing to a 195 degree T/stat will help the engine heat up, but the cold air intake will not change, UNLESS you make a closed air cleaner setup. If it was me, I would put in a 180 degree Super/Stat and live with it for a year round temp control. This will make the heater work about right in the cab, if you want more engine bay heat then restrict some air across the radiator. I went to electric fans to get rid of the mechanical fan drag on my wengines--this also eliminated the pulling a lot cold air into the engine bay unecessarily. I also gained a MPG with the electric fan, by the way.

Exhaust improvements will help OVERALL, but for your immediate problem make the upgrades and see what happens there, first. The Flowmaster design will give a better sound and also in some cases better exhaust flow, but that is not a must right now. I still think your problem exists in the gearing and tire combo. I use your discussion about being sluggish as the reference---Timing/distributor components, Carb adjustments, Tires, and Gearing work against you in that area. EXAMPLE: My son's truck suffered when we traded trannys out and we had to change the rear end gears to get the mileage back. We went from a 3.08 gearing to a 3.73 gearing and gained back over 3 MPG---because we put the truck in it's power curve and not lugging the engine when it was doing work.

[nekkidhillbilly]

Originally Posted by *****in85

The plugs wires coil cap rotor are like a month old so that's all good. And an OD trans juat aint gonna happen for a while. I usually drive it normal or baby it but sometimes I lay into it.. How hard is it to swap out the gesars or do I have to find a new rear end

be cheaper honestly to find a 700r4 used you can get em for like 200 bucks all day long here