Ron Mullins

Running so rich?

I have an 86 305 from a Firebird, bored 30 over, mild cam, Performer intake, Holey 600 carb, vac secondary, Accell dist, K&N 14" air filter. I have no idea what the timing is set at, but I used 8 gallons of gas in 2 days and never went a hundred miles. I have no leaks that I know of. The engine has about 40,000 miles after the rebuild. It ran rich from the get go. The varb has been rebuilt has new power valves, smaller jets, running at about 3.5 psi of fuel pressure.

Any Idea where to start?
My site is below, this engine is in an S-10. http://geocities.com/ws6_91

merf23

did you put an old style distibutor in? If you still have the computer controlled one you will have no advance resulting in poor performance and poor milage

jrr

I looked at the mods on your website. I hope that you aren't using the original ECM controlled distributor as a previous post had mentioned. Lack of mechanical and vacuum advance will kill fuel economy and power. Holleys are not known for fuel economy, either. You may have to go to leaner primary jets. Can't beat Q-Jets for gas mileage, though.

Since the original was a four cylinder, it probably had a 3.54 or 4.11:1 rear axle. THAT is going to cause your truck to guzzle gas! In such a lightweight vehicle, you could easily put in 2.75:1 rear gears and not really lose too much in the way of performance. Get a standard HEI, highway cruiser axle ratio, slightly leaner jets, and that should help you get decent gas mileage.

82camaro

How 'nice' do you drive it? Was this 8 gallons in a hundred miles on the highway at a constant speed? I can get about 18 in my 82 camaro with 3.73 and overdrive if I drive it nice. If I drive it hard, probably about 7 mpg. What tranny and gears do you have? You need to have the timing about perfect for max mpg--what is it set at? What do the plugs look like? Do you get a lot of black smoke out the tailpipe? How small of jets to do have in it now? What spring do you have in the secondaries?



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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

Ron Mullins

These are mostly highway miles to and from work, 65mph. About a 25 minute drive. I did put smaller jets in. I also put a power valve in but I put the stock size in thinking that the stock one just might have went bad and just needed a new one. Should I get a lower number power valve? I never have figured out what gear ratio I have. GM don't keep records back that far. I have the 700R4 tranny. Have no idea about the timing. Mot sure of the size of jets either. Stock spring in the seconary's. Sorry I don't know the numbers of things, I'm not a carb person. I have an Accell distributor, 41100 model, that has the four pin module on the side. They don't make this distributor anymore. I do get some black smoke from the tailpipes. It usually leaves 2 black spots on the ground wherever i start it up.

84FTA

The four-pin module is probably because it's for a computer controlled vechile. Take a timing light, check the base timing, then rev the engine and see if the timing moves. If it doesn't move then the distributor has no mechanical/vaccum advance and is half of your pour gas mileage. Your timing should be set anywhere from 6 - 12 BTDC depending on the engines, mods, and octane of gasoline. Don't mess with the jets and PVs just yet, on idle you shouldn't be getting black smoke unless you have a missfire in it. Secondary springs usually don't need much modification on a pretty much stock engine. Also if the gears are as large as they are the gasmile isn't all that bad....

So, what you should do
1. Find out about timing and advance
2. If those check out, pull and exam plugs for carbon build up. Clean and/or replace
3. If it's still very rich afterwards repost here aftering tearing your carb down and giving us jet sizes and the PV rating. Also bring along some idle and cruise vaccum readings if you can
4. Check the ratio of the rear end
5. Finally, 100 miles for 8 gallons is about 12.5 m/g. Not exactly great gas mileage but some of us here get around 8 mpg on 3.2x

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

84FTA

I'm also guessing you never looked into a switch for the TCC lock-up. This is especially deadly to gas-mileage on the freeway!

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

Jester

For running no timing advance or TC lockup, 12.5 sounds about right. Check on the advance situation as suggested, but I really wouldn't worry about the lockup. It doesn't make that big a diff.

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"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

Ron Mullins

Thanks all, I'll check the pv numbers and jet numbers. I do have the tc lockup, I got it from Howell. Unless its not working?? I can already tell you that the plugs are going to be black with carbon. They always are when I check/replace them. I did take off all the computer stuff off the engine when It was rebuilt. Jegs recommended that dist. I'll get the numbers as soon as I can.

Thanks again, Ron.

84FTA

While for the most part you can trust Jegs and Summit, they aren't always correct. An advertisment runs here every once and awhile to get a job at Summit. It reads

"....general automotive knowledge preferred."

I believe those were ads to run the computers/phones

I have to disagree though Jester. TCC's aren't given as much credit as they should be. My gas mileage doubled on the stock L69 with a T-5 swap, you can only blame so much mpg loss on slipping clutches.

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

[This message has been edited by 84FTA (edited December 10, 2000).]

Duffster

Just out of curiosity...
which port on your carburator do you have the vacuum advance connected to?
I had EXACTLY the same situation with the carbon spots from the tail-pipes and when I switched the vacuum connection...problem solved. Not sure of the mileage I'm getting, but close to 10-12
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<marquee type="slide"> </marquee>

Ron Mullins

Sorry but there is no vacuum advance. My dist. is mechanical. Don't know if I mentioned that before. The only vac line on the carb that is hooked up is the one from the secondary's that connects on top of the choke and loops down and reconnects to underneath the choke. The jets are in the low 60's, 60-61, maybe 59.

Bort62

Ding ding ding! WE have a Winner. thats the computer Controleld Dist you have, and as I understand it, if You are Not Running the computer controleld Qjet with all the Fixin's , then Your getting No Advance, Wich Is going to make your Milage and performance Bite..

Im experianceing the Same problem on My Car Right Now, I Just cant seem to Find where I put that extra Vaccum advance distributor, Lol




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60 Ranchero - Project ( Money Hole )
85 Z28 LG4 - Daily Driver
**Mods**
MSD Superconductors
14" Open Element
KYB all around

five7kid

iTrader: (14)

You just answered about 1/2 of your problem. I've seen as much as 30% improvement going from mechanical-only to mechanical/vacuum advance. That was on an engine that wasn't even close to being built for mileage, in the '57 (2 tons being pushed through the air) w/3.55's and 14" tires.

With the improved advance at cruise, your vacuum will go up, which will close down your power valve and lean back your mixture closer to where it belongs. You may still have to fiddle with the jetting (that's the other half), but until you get the ignition doing the right thing, you're not going to get other things to work right.

For what it's worth, I took a road trip of 700+ miles in the Camaro back in late September, averaged over 26 mpg round trip. The TCC lockup doesn't work. Someday it will (need new convertor), but it doesn't seem to be hurting my mileage much.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

88'camaro305TBI

iTrader: (2)

Hey Duffster, How did you get that pic into your sig??? Mine doesn't show up. Sorry Ron Mullins, can't really help you.

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Mods:Hooker Aerochamber 3" exhaust, gutted kitty,
March 2 piece underdrive pullies, smog pump gone,
14x4 K&N, 3.42 gears,
Eibach springs with KYB's all around.
Appearance: Harwood cowl hood, Z-28 wing, painted black(7/20/00)-original color was light blue
*All these mods were made this year
Stock Options:120,000 miles on motor, 5spd, TBI, 305, T-tops
Run a best of 16.7 @85mph before gears

merf23

The mechanical advance only dist is good for racing, but the vacuum advance allows the engine to run properly at leaner mixtures. Regarding your jets....if you go too low, the vacuum will drop and the PV will open causing poor performance and milage. Id put some 68's in, a 6.5 PV and the standard vac sec spring, along with a mechanical/vacuum dist and see what happens. An old style HEI works well; make sure the vacuum canister is functioning. By doing this i bet youll get at least 15mpg and then you can fine tune from there. I am not specifically familiar with your accel dist but you may be able to stick a vacuum canister on it.

Ron Mullins

So what kindof dis. do you recommend? Any vacuum advance dist.?

84FTA

Get a distrib made for GM cars from 75 to 80ish with a vaccum canister. 68's are too heavy for a 305, hard to even run those as secondary jets without being rich. Most 305 guys here run 60 - 64's in the front and 62 - 66's in the rear. I had mine on 62's in the front and 64's in the back and ran really good. If you go too lean your idle will drop as mentioned, however, in order to go lean enough to open the PV, the PV would enrichen the mixture just about enough to offset the extreme lean condtion in the primary circuit.

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

Ron Mullins

So the power valves when open let more fuel in? Sorry, not much of a carb person.

[This message has been edited by Ron Mullins (edited December 18, 2000).]

five7kid

iTrader: (14)

Jets affecting the idle? If they do, then you've got something really messed up. The jets don't affect idle mixture (unless the throttle blades are open so far that you're getting the main circuits into the picture).

Ron, yes, the power valve lets more fuel in. The concept is that when manifold vacuum drops, the engine is under load and therefore a richer mixture is required. With inadequate cruise vacuum, the valve will be open sooner and more than it should.

Whatever distributor you get, it should have an adjustable vacuum advance. Such canisters are available for factory distributors such as old points type (which should be converted to electronic) and HEI. Many aftermarket distributors come with them. To optimize it, work the mechanical advance first: something like 34 degrees total advance all in at 2000 rpm, 8 degrees initial advance at idle (both without vacuum hooked up). Then, adjust the vacuum for maximum advance without pinging. Then you can work on your jetting.

I wouldn't be surprised that your current distributor was recommended because they thought you were running the car out of which the engine originally came.

84FTA

I just re-read my post and I think I meant RPMS ("revs" as the little homo's call them)not idle.



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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration

billyde

Just a note, my computer controlled GM distributor from 84 lg4 z28 has a "7" pin module.