sudden drop in mpg after 5200 install

[Anonymous]

For a while I've wanted to convert away from my nos single barrel Autolite 1100 carb.

Last week I finally found the time to install the holley 5200 that Tom at Stovebolt sells. It installed easily enough, with the exception of the linkage. I have a '62 Ford Falcon with 200/6 from a 67 Mustang. On the throttle arm on the carb, I had to drill and mount another pivot knuckle more toward the center of the arm. In fact, right on the edge of it, about 1cm closer in than the stock position. This allows me to get 96% of the full throw of both barrels.

It runs super. After a week I checked my plugs and they are clear to mild toast color, and it idles fine except for the fact that I can't lower my idle under 650 before the idle speed screw disengages. But it's exactly where it needs to be in any event.

Last night I tested out the mileage on the highway in a controlled test: I drove out of Portland into the Columbia Gorge and drove exactly 100 miles at 65-70mph, and then returned for another 100 miles. I filled up and measured a disappointing 18mpg.

I used to get 20-24mpg.

I should also add that I have a C4 transmission and a Pertonix II setup with the accompanying flamethrower coil.
Timing is set to 14*.

The car runs super. Just thirsty.

Any thoughts on how I might get some of my mileage back?

 

[Bobscoupe]

Are you keeping your foot out of that second barrel?

 

[Anonymous]

At constant speed, there really isn't keeping my foot in or out of the accelerator. I'm not passing traffic. The whole experiment was to sample mpg at very constant speeds.

In town I keep my foot of the gas for sure, and I get about the same mileage.

 

[Bobscoupe]

Sorry, I guess I didn't read your post very well.

I got significantly better mileage from my H/W 5200, but my old one barrel Holley was in bad shape. I did have a tendency to punch it a lot more though and if I didn't drive right my mileage would be worse.

Check to ensure your choke plate is fully open. Lean the carb out as much as possible. There is a tuning page at the Weber web site that shows how to tune the Weber carb.

Bob

 

[Mustangaroo]

We saw 24-27 mpg with our 5200's when we were running them, have you checked the metering jets, you may have the larger jet in the primary side and the smaller one in the secondary side? Or they may both be the same size jets? Not much quality control on these rebuild carbs, they seam to just put any size jet where they want to? Hope this helps!

 

[Anonymous]

Several years ago I had put in larger fuel jets, however, I did not bother to upsize the air corrector jets. Last month I upsized the air corrector jets and the results are encouraging. I was averaging in the range of 18.5 mpg with mixed city, highway. My first tank was over 20.5 mpg in the same mix of driving. I am waiting to finish a second tank to confirm that it was not a fluke. I may then try to go another size larger on the air corrector and see if I can get consistantly in the 21+ mpg range.
Doug

 

[Anonymous]

when Chirs (Stang200) converted his...he told me that you have to ask for different jets to get proper settings...that Tom would reccomend one thing but to insist on other....let me see if I can find PM...


well, no PM but here is the link

http://fordsix.com/forum/viewtopic.php? ... eber+32+36

maybe you have wrong jets....just a thought

 

[XFlow_Fairlane]

hmmm with my straight off a pinto motor non rebuilt dirty as sin 5200 still got me 25mpg even at highway speeds.....but this was also with a T5

 

[LaGrasta]

My car is getting around 20mpg, depending on where my foot is.

MustangRoo, "We saw 24-27 mpg with our 5200's"
With my 300 mile/week commute, that mpg would be a God send. I'd really like to stick with my 1909 carb as I have all hard lines plumbed just for it. It runs great too. Now you have me thinking…

 

[Mustangaroo]

LaGrasta, our traffic is light compared to L.A. traffic. I don't remember who told me this but I was told that the Holly 5200 was as close to EFI without actual haveing EFI on your engine? That metering is very persice and the carb atomizes the fuel better than most other carbs! If you stay out of the secondary you can get great MPG with these carb.

Tuning is a Must
If you buy a kit for your specific engine, it will run fairly good out of the box, but should still be tuned to match your engine. If you obtain one second-hand, count on swapping jets, emulsions tube and other tuning parts to make your engine run right. Black smoke, smelly exhaust, jerky acceleration and poor fuel economy is what you get before you tune it. It may "feel powerful", but you can make it run even better with some patience and the right parts. You can get the tuning parts from Redline.

 

[LaGrasta]

Again, I say hmmm. Who knows, may be I'll go through thte trouble to swap.
BTW, I live in OC. It's far different than LA traffic. I live in South OC at that, even less traffic. I'm heading ot Visalia on the 23rd to visit a friend and his family. He's buildiung a 64 Nova with a six. Anything going on that week?

 

[Anonymous]

I'm not much of a carb tinkerer. I just left it alone because it runs so well. I do have a friend who is really into this stuff so I'll get some time with him and ask.

One thing I'll say though: Tom was very helpful with me and answered my questions, but when I mentioned the different jetting from the Stang200 post he became really agitated and told me that would be a total waste of time and just ruin my mileage.

I left it alone.

I would not mind losing a bit of performance if it meant getting better mileage. My impression from the different jetting on stang200's post is that it primarily a performance boost, not necessarily a mileage boost.

 

[Mustangaroo]

One thing I'll say though: Tom was very helpful with me and answered my questions, but when I mentioned the different jetting from the Stang200 post he became really agitated and told me that would be a total waste of time and just ruin my mileage.

That's funny because he said the same thing to me, even after he admitted that he didn't know which jets were being used in his rebuilt Holly 5200's! If they are rebuilt correctly he is probaly right but I haven't gotten one with the correct jets yet, and I have three he has shiped to me, over the past 3 years! I don't remember the online web site but someone has the instructions on how to tune these carbs posted online!

LaGrasta: Nothing going on but work on 6/23

 

[jamyers]

I say to re-jet it, there's a LOT to be gained. IIRC, there's info in that thread on a good source of jets via ebay.