High fuel consumption - Stock 1500

D

Dobbs

Daily Driver
Hi All,

I recently been getting very bad fuel economy.
Car is stock 1500, 34DATR carb with points ignition.

Some history first . . .
This car always seemed to run rich.
Recently I replaced the intake/exhaust manifold gasket due to a vacuum leak and new carb base gaskets. Also installed new points, condensor & Bosch WR7DC+ plugs (Yttrium electrodes).
It did run will after this however running when cold was sluggish so I checked and reset with the choke settings - still no improvement in cold running.
Car does seem to run smooth when warmed up but seems to take a long time to get to this point (10mins?) in warmish climate.
Ignition timing is set to 5 deg. BTDC as per specs - note only have mechanical advance on dizzy.

Before I replaced things, fuel economy seemed ok.

So, whats happened? What should I check or test?

Any comments welcome.

Dobbs.
 
!

Lot's of things could be wrong, but check these things.

Carb base gaskets backwards or incorrect, could block an air passage to an idle jet.

New points may not have right dwell angle.

New capacitor may be weak or bad.

Distributor may not be advancing correctly.

Sounds like you may still have an intake leak.

Also there could be, stopped up exhaust, or leaky internal carb gaskets. Are your spark plugs black or sooty? That's a rich mixture indicator. Check for weak spark too, yellow spark is bad.

There are more things to check as well. Is your thermostat bad? Maybe time for a new one. It goes on and on, but check those things first.
 
Fuel consumption

Fuel consumption is nearly always a carb issue vs. ignition (unless you have tuned the carb to make up for incorrectly adjusted timing). I would check the jetting and float level (particularly the needle valve).

I used to get bad fuel consumption as well, but then learned to drive under 5000 RPM.:wink2:

Cheers,
Dom.
 
Dobbs... not to be a stickler here... but...

I think ya need to put some numbers against this problem.

OK and GOOD and BAD are hard to measure. So just what are the numbers?

Mileage numbers... and then some kinda performance numbers.

I THINK you are more concerned with MILEAGE at this point... and maybe the performance numbers will tag along.

Get a baseline number to start with... and if you have a 5 gallon can of gas and a means to accurately measure topping off the tank a gallon or so at a time, you won't need to take months and tankfuls to determine if there is an improvement.

Lots of suggestions here but some seem MORE likely than others and some are kinda contradictory.

You do not mention if the carb has been recently cleaned and overhauled. That could be a major factor. Also, timing with regards to the mechanical and/or vacuum advances working properly. I think I would go to these two areas first.

Then do ONE thing at a time and get some new mileage numbers. Change, better, worse, or none. Then move on to the next thing.

We're here for help and more details... sounds like an interesting thing to do... love to be a part of it!
 
Fair point . . .

regards putting numbers against the fuel economy and fuel consumption.

I'll try figure out what I getting at the moment so watch this space.
Roughly in the last week or so, I've gone through about half a tank having done my usual journey and covered about 90mls.
What should I expect to get, I know a lot of factors involved but any rough ideas.

Thanks for all suggestions so far, I'll hopefully get round to checking some of these over the next few days. Unfortunately, this is my daily driver so I can't muck around with it too much during the week.
 
Pulled the plugs . . .

Had driven car home last night and just left it til this morning and then removed plugs (see photos) - somethings not right for sure. Will be checking it out today if the kids and wife let me :)

Hopefully photos upload OK on ImageShack - first time I've done this.
plugsrunningrichphoto1.jpg

plugsrunningrichphoto2.jpg

plugsrunningrichphoto3.jpg


I've also saved them in . . .
http://cid-86673d9c2d08c8d3.office.live.com/browse.aspx/Fiat X19 Stuff?uc=3
 
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Rich and lean

Meaning, you've got both conditions by the looks of things. The outer plugs look sooty, indicating a rich mixture or incomplete burn, while the inner plugs look like they're running lean.

I would hazard a guess that you have a vacuum leak at the carb base or the manifold gasket. Use some unlit propane or carb cleaner spray and check around for leaks.

I could easily imagine a vacuum leak causing poor running, so richening the mix up a bit to compensate.

I see you note that you only have mechanical advance on the distributor, so make sure the vacuum port on the carb etc. is capped.
 
2 and 3 lean, 1 and 4 rich?

The two middle cylinders are seeing a mixture way leaner than the outer two. Look for a vacuum leak at the manifold gasket, at the center. Something is giving those two cylinders way more air than the outer two are getting.
 
OK... it's LEANER, not necessarily LEAN...

The two center cylinders are running LEANER... all are FAT or RICH relatively. They should have a nice even brownish-gray color. All these are BLACK!

In order to prove vacuum leaks... use a can of WD40 or an UNLIT propane torch... and spray around the intake manifold and all the vacuum hoses as the engine idles. If it speeds up, there is your leak.

I suspect your carb though... you have NOT spoken yet to its condition or if its been recently properly overhauled!

As for mileage... looking at this, I would doubt you are getting better than 20 or 22 mpg. Properly tuned, a 34 would probably get about 24 - 26 around town and about 28 - 30 on the road, maybe 32. FI cars get up to about 36 I believe.
 
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FI mileage

I have never gotten better than 28 mpg with my 83 X19. Air fuel ratio is spot on ( per the smog testing) My driving is 70% at 75 mph and the rest is city. I am suspect of claims north of 30mpg.
Bob
 
28 was pretty normal with my FI '87 in Germany. Anything more than that just wasn't much fun. :eek: Probably had the "best of both worlds" in the 24 to 26 mpg range...
 
Ya know... me too. But I betcha...

I got those BIG numbers from the guys that use IMPERIAL gallons.

I've never had an FI car or driven one long enough to know for myself.

BUT... I have achieved over 30 on the road with the 32 in my 1500 to Visalia and back... UP the Grapevine and DOWN again twice... HA!
 
Same; only times I get close to 30 is on drives greater than 100 miles each way and keep it under 75. With the latest exhaust and around town, milage is really low; I would estimate 23-24 at best. But it sure sounds nice and is a lot of fun :)
 
Fingers crossed . . .

Pulled the carb and started to clean it.
Mmm, that base doesn't look right . . . guess that would be a vacuum leak alright :wink2: . . .
carbbasebefore1.jpg

carbbasebefore2.jpg

carbbasebefore3.jpg


So, resurfaced the base flange - started with a sheet of 100 grit sandpaper taped down to a thick sheet of glass for an hour or more, finished off with wet 600 grit for another hour or more, doing figure of 8 patterns (Steve C's technique I believe) . . .
carbbaseafter1.jpg

carbbaseafter2.jpg

carbbaseafter3.jpg


So far so good - sounded better and ran smooth on choke whereas before it struggled. Haven't driven it yet though so fingers crossed.

Lesson learned - the hard way :dunce:.

Thanks for all the comments gents.
 
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Wow, that looks(ed) bad. And you sanded it out? Good on 'ya! Hope that was it.
BTW my '81 FI gets 29mpg, about 70% highway at 75ish.
 
Well... that's gotta help! Geez!

But obviously the carb has NOT been disassembled and properly BOILED out with acid.

I suspect... especially with the OUTER condition, that there MAY be some internal issues OTHER than the usual crud in passages and in the metering rods and emulsion tubes.

It would appear that you do learn the hard way... Just trying to save you lots of headaches here...
 
!

WOW! It looks like somone WAAAY over tightened the mounting bolts on that carb. Be sure to check the butterfly valves inside the barrels (venturi, throat) to make sure BOTH are closing properly. It looks like they don't close the same, and you have a LEAN condition on two cylinders at idle, then rich the rest of the time.

It can be hard to tune a PERFECT carb, let alone one as jacked-up as yours. I'd say to look for a replacement.
 
+1

Better replace that carb as there could easily be a lot of hidden ills in this mangled carb. It is also a reminder of how much force is applied when nuts & bolts are torqued.

The carb studs are M8 size, torque the nuts to 18 foot/pounds and something like 4,000 to 5,000 pounds of clamp force is generated. There are 4 of these M8 nuts making a total of something like 20,000 pounds of clamp force on the base of that carb...

No wonder why over tightening warped the base of that carb... Over tightening is the number one cause of fastener failure and problems in general.

eflexter said:
WOW! It looks like somone WAAAY over tightened the mounting bolts on that carb. Be sure to check the butterfly valves inside the barrels (venturi, throat) to make sure BOTH are closing properly. It looks like they don't close the same, and you have a LEAN condition on two cylinders at idle, then rich the rest of the time.

It can be hard to tune a PERFECT carb, let alone one as jacked-up as yours. I'd say to look for a replacement.
Click to expand...
 
Wow, that would be the most distorted carb base I have ever seen...that has to be 100thou /2.5mm gap at the widest point in the before pictures!!

Good work to get it back to flat again, that was certainly ONE of your problems... and it would have been impossible to tune the way it was.

My guess would be your going to need to back off the idle mixture screw a few turns...as all the air will be getting into the engine from where it's supposed to, not from the warped base..

SteveC
 
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