What carb?

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Bugman

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Hi Folks - new boy here!
I have been following the forum for a couple years and now need some of your wisdom. I have a MK1A with an original 260 CID, 5 speed Tremec and Petronix vacuum dizzy. I believe it has the cams from a 289. Car runs smoothly but I have poor gas mileage when cruising (mid-teens). I was hoping the 5 speed would give me mid-20s. I suspect the 600CFM 1850 Holley (recently rebuilt) is really too large – plugs are black and sooty. I also suspect that this is made worse by the fact that I live at 3500 ft above sea level. I am thinking of going for a smaller carb - to either a 1848 or a 8007. Any thoughts on these options or recommendations, of what to do or not do, would be gratefully received. Note, I use the car for long distance cruising. Thanks Bugman
 
How about the 500 cfm Holley 2-barrel carb? Probably has enough performance for the 260 and offers decent gas mileage. No personal experience with this carb, but have heard good things from other Tiger owners.
 
What intake manifold do you have? Do you have exhaust headers? They play an important role in breathing ability and thus carb selection.

At highway speeds in 5th gear, you should be running only on the primaries. In a 4 barrel carb they will be probably be smaller than a reasonably similar two barrel. (I think 2 and 4 barrel carbs may be rated differently when it comes to CFM, not sure.) Anyway a smaller 2 barrel equivalent mode should be actually helping with gas mileage.

Sounds like you are running rich, so you might want to experiment with smaller main jets before spending a lot of money on a new carb. But the 465 cfm model is said to be a good one for a stock 260 if you are upgrading to a 4 barrel. Remember that it is designed to work with stock exhausts and utilizes a hot air driven choke. No direct experience though.

Despite all that, hottigr's straight two barrel suggestion certainly has merit if highway cruising is the main use of the car. Back in the 60's I had a larger Holley 2 barrel on my otherwise stock engine. Do not recall the model. But I was getting about 20mpg on the highway driving back and forth between Texas and California, running at about 3000 rpm. Could almost make it across New Mexico on a tank of gas. Of course the gas was also better back then...

Gene
 
First thoughts

Black and sooty means the primary jets are too large for your altitude. Just lower the jet size to lean it out some.

Also for highway cruising you are driving a 2 barrel carb. Only the primaries are actually open and only a little. When accelerating the power enrichment will kick in and the secondaries (may) open up.

If you are cruising with the secondaries open you are going real damn fast! Slow down.

One telltale that it is too rich is running ok when cold. If it idles and drives ok cold? it is too rich.

Rick
 
Im with Gene on getting the carb jetted properly first.. you would expect that it would lean it up a fair bit.. i run a 650 on a 340hp 302 and i had to lean it up when I got it.

I also second Gene on the 465, much better size for a 260, and assume you are running stock heads so not like you are really exploring upper RPM.. a friend bought a new Edelbrock 465 from Summit late last year... quite cheap and a good carb.
 
Thanks for all the suggestions. Apart from an Edelbrock F4b inlet, the headers and exhausts are stock. I have jetted down from the standard 66s to 64s (as per Holley recommendations for altitude driving) I could try lower but a reply from Holley, direct, did not recommend this?? Bugman
 
Bugman said:
Thanks for all the suggestions. Apart from an Edelbrock F4b inlet, the headers and exhausts are stock. I have jetted down from the standard 66s to 64s (as per Holley recommendations for altitude driving) I could try lower but a reply from Holley, direct, did not recommend this?? Bugman
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Bugman,

people often stay on the rich side to avoid the risk of burning valves, from your situation it sounds like you are running quite rich and should move down some.. the carb is quite large for the motor you are running.

Out of interest.. when you change the oil does it have a fuel smell?
 
Bugman said:
I could try lower but a reply from Holley, direct, did not recommend this?? Bugman
Click to expand...

Welcome Bugman,

No one can tune a carb through email or the phone, Holley does not have a clue about a 260 and their response proves it. Keep reducing the primary jets till you start getting a lean miss, then go up one jet size. Your not going to hurt that 260.

FYI - I have a 454 HP 347 in my Tiger with a Holley 650 Ultra HP racing carb. I am running 64 primary jets and run ~13:1 AFR while cruising which is a little rich. That is in the winter, for the summer I run 63 jets. For your application, I would start with 58's and move down.

Better yet, install a wide band O2 sensor and gauge ($240) and know exactly what is going on.

http://youtu.be/86erf8z_cKY
 
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I have a setup close to what you have, a basically stock 260 (except for a mild hydraulic Edelbrock Performer cam and Pertronix igniter). Stock bore & pistons, stock tranny, stock axle, stock air cleaner, and stock exhaust system.
I went with a 500 cfm Edelbrock Performer 4bbl (Carter AFB) with manual choke on a Edelbrock Performer intake manifold (NOT a Performer RPM). BTW, when you are going for gas mileage, the intake manifold is just as important as the carburetor (if not MORE important)! The F4B is not really a good economy intake manifold. Admittedly the 500 cfm carb is even a bit too much for this engine setup, but since the secondaries only open as much as demand dictates, it works just fine. The key to it's economical operation is the 250 cfm primaries, which are smaller than the factory stock 2bbl.
Out of the box the carb was jetted a bit too rich so I had to jet it down a couple of sizes as well as a notch leaner on the metering rods. Changing the jetting and metering on a Carter AFB type carb is a much easier procedure than on a Holley and the AFB holds it's "tune" better so it is not as "fussy". I also have the ignition advanced a bit further than the factory setting and I'm using Shell Rotella T6 5W-40 synthetic oil as well as synthetic gear lubes in the tranny and axle. The car starts easy cold or hot, runs great, and the last time that I checked I was getting over 22 mpg on the highway running about 70. I'm happy with it. With this same setup and a 5-speed overdrive reducing the engine RPMs you should be able to get up into the mid the 20 mpg range you are trying to get to.
 
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wag123 said:
I have a setup close to what you have, a basically stock 260 (except for a mild hydraulic Edelbrock Performer cam and Pertronix igniter). Stock bore, stock trans, stock axle, stock air cleaner, and stock exhaust system.
I went with a 500 cfm Edelbrock Performer 4bbl with manual choke on a Edelbrock Performer intake manifold (NOT a Performer RPM). BTW, when you are going for gas mileage, the intake manifold is just as important as the carburetor (if not MORE important)!
Out of the box the carb was jetted a bit too rich so I had to jet it down a couple of sizes. I have the ignition advanced a bit further than the factory setting and I'm using Shell Rotella T6 5W-40 synthetic oil. The car starts easy cold or hot, runs great, and the last time that I checked I was getting over 22 mpg on the highway running about 70. I'm happy with it. With this same setup and a 5-speed overdrive you should be able to get up into the mid the 20 mpg range you are trying to get to.
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I agree about the 500 c.f.m. Edelbrock... I've had it on a couple of SBF's and found it was one of the least 'finicky' carbs I've ever owned and worked great!! Mine was the electric choke model and still have it on the shelf...

Jim
B382000446
 
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Carbs

When my MKIA had a 260 in it I put a stock Ford 4 BBL manifold on it with a 600 Holley and it was definitely overcarbureted. I bought a brand new 1848 (465 cfm) and was much happier. It had a 500 Holley 2 BBL on it when I bought it, which was Ok, but I was glad to have the little more punch from the 4 BBL when I put my foot in it...
 
The final carb I had on my 260 was a Autolite 4100 (1.08) that flowed 480 CFM. The engine ran like a dream and I got over 20 MPG. This was on a Weiand X-CELerator 7515 Intake intake that is now on my 347.

600 CFM is WAY too big for the 260 and even if you jet it way down, it will not run well.
 
follow up

Great replies guys.Thanks
@Michael King - Ok, yes I have noted a slight fuel smell on the dipstick (oh dear, is this another issue?)

@Duke Mk1A and @TigerBlue and @cadreamn67 - All very interesting. Using smaller jets was my thought as well (but I do not claim any expertise here) but given the reply direct from Holley and the fact that a finger-wagging-know-it-all at my local shop refused to sell me some 58s for my 1850 (600CFM) a couple of months ago (and said I should check the power valve - which is OK), I was having my doubts about this. I did not have the courage of my convictions to follow through. This would certainly be a simpler and cheaper fix and I will try it.

@Bullpit and @hotigr. Thanks for this info. If the smaller jets (the cheaper fix) does not work I will definitely look into your recommendations.

@wag123 - lots of good stuff here for me to think about, especially if the simpler fix is no good - cheers

Finally just to explain, my main concern is that on long distance drives with poor gas mileage, I spend to much time with one eye on the gas gauge, especially when driving on the back roads.
 
Duke Mk1a said:
The final carb I had on my 260 was a Autolite 4100 (1.08) that flowed 480 CFM. The engine ran like a dream and I got over 20 MPG. This was on a Weiand X-CELerator 7515 Intake intake that is now on my 347.

600 CFM is WAY too big for the 260 and even if you jet it way down, it will not run well.
Click to expand...
Duke, were you ever able to get rid of the 4100's signature hesitation problem?
 
wag123 said:
Duke, were you ever able to get rid of the 4100's signature hesitation problem?
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Yes...It ran fantastic and had much more power that the Holley 600 CFM I had on it.

4100 have to have the boosters matched with the carb. It is hard to find a carb that has not been messed around with and I have a book that details which carb had what booster and jets. That was a big help.
 
Bugman said:
Great replies guys.Thanks
@Michael King - Ok, yes I have noted a slight fuel smell on the dipstick (oh dear, is this another issue?)
Click to expand...

Fuel smell in the oil means that it is running very rich and fuel is getting down into the sump. This thins the oil and means the beariungs are not as well lubricated and also its washing your bores and can lead to glazing them.

Basically fuel smell in the oil is a the sign of a very rich running car... so If i was you oi would not be concerned about leaning the jetting up.
 
follow up

@michael-king - OK thanks for the explanation - clearly I need a significant transplant to something smaller
 
I am suprised nobody has mentioned checking the power valve for leakage yet. The 1850 Vac. Sec. Holley (600cfm) you are running uses a power valve located in the primary metering block. If the power valve fails it will run very rich no matter what jets you choose. Although the newer Holleys have "power valve blow out protection" they do still fail from age, poor quality from the get go (I have had a few that were bad right out of the package and dammit that makes me mad because the store will not believe that), and even a backfire. The failure rate is not linear so your results may vary. I have one Holley that has had the same power valve for over ten years now with no issues, of course it will fail now that I said this but still.
Anyway, while a 600cfm carb is a bit large for a basically stock 260 you must remember it is a vacuum secondary carb. If it is tuned correctly the carb will only supply what the engine asks for. If the carb is tuned poorly it will supply what it can regardless of engine needs. A 600cfm vac. sec. Holley will work on the 260 if you tune it properly. Keep in mind that to PROPERLY tune a carb you must first verify your timing curve is correct for your particular engine. Until you get the timing curve correct you are wasting your time messing with the carb. The Autolite 4100 model carb is a perfect carb for the 260, and most small displacement engines for that matter. They have only a couple gaskets so leakage is almost non-existant. They can get very good economy when tuned correctly. They come in a few different cfm sizes
(1.08, 1.12, 1.19 cast into the side of the float bowl) with the 1.08 being the most common and the one you would use. They can be found on MANY Ford products regardless of engine size (the stock 428 in my 1966, 7-LITRE Galaxie uses an Autolite 4100 with 1.08 bores) and they are fairly easy to rebuild if nothing is broken. Just look for worn out throttle shafts and main bodies to find a good rebuilder. There is some dispute over the actual CFM rating of these carbs but the 1.08 carb is in the 465 CFM area with the largest CFM rating being just under 600. Even if you have a carb shop do all the work on an Autolite 4100 (provided it needs no major surgery) the total cost of purchase and rebuild will be far less than purchasing a brand new carb. Plus, the 4100 looks right at home atop a small block and the choke stove hookup can be easily converted to a cable operation that works well and looks correct too. No matter what you do I suggest you begin with checking the tune of your timing and then check the carb for proper operation and tune it to your needs. If, after you have done that and things still do not run right (they should) then move on to finding a different carb. Good luck.
 
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