High Altitude In-line 250

[Anonymous]

I am going to college in Prescott, AZ (5045 feet above sea level). I used to live at sea level. I am trying to tune it up but cant seem to get it quite right. It is an In-line 250 with a stock motorcraft 1V. The only engine mod I have made is a 40 series flowmaster muffler. I have timed it out perfect but I have lost almost all the power. I tried adjusting the mixture but nothing really seems to help. I have heard rejetting is the way to go…any info would by great! Thanks…by the way I love this site…it is full of awesome info.

 

[Ronn]

What air breather do you have on that carb? Oh, my 250 runs much better at 12 degrees adavnce. try that and a K+N air filter with a MSD blaster coil and use a acetylene torch tip cleaner to open the jet a bit..or just put one that is no more than 10 sizes bigger until you find the sweet spot.

Just my suggestions.

I'm sure you will get lots of help here.

 

[Asa]

rejetting will help, you're going to need to lean it out because you're getting less air there (have you noticed that it's somewhat harder to breathe there as well?)
timing will also need to be played with a little bit

good luck with it

 

[CZLN6]

Howdy vandenwally:

First off, at that elevation you will need at least 14 degrees of initial advance.

What vehicle is this? What year? What Trans? Motorcraft, AKA Autolite only made the 1101 for the '69 Mustang 250. Is that what you have? The Motorcraft name came on several other manufactures carbs, but we will need to know what the actual carb is. And model number.

If it is a '69 Autolite 250, 1101 you will notice a roll pin on the side of the float bowl which limits the travel of the accelerator pump plunger. There are two holes, a bottom one marked "HI" for high elevation and "LO" for low elevation. Make sure the pin is in the lower, or "HI" hole to begin with.

Next you will have to ascertain what main jet you have in the carb now. To do this you will need to disassemble the carb. With an old carb it is best to have a rebuild kit handy. YOu will most likely destroy the gaskets on disassembly. Most likely this carb will either be an Autolite 1101 or a Carter RBS. Neither have new parts available so finding a smaller jet is a scrounge. Folks here are most helpful and sharing, so report back.

Also try a step hotter spark plug.

Adios, David

 

[Anonymous]

I looked at the carb and it is an RBS. I advanced the timing and it is running MUCH better. I am going to get some new plug wires for it for sure. I dont know if I am going to get new plugs for it though. I work at my flight schools maintenance hangar. We clean the spark plugs completely and then put them back in the planes. I am thinking about doing that to the ones in the mav. Let me know if you guys have any more suggestions for getting some more power out of it at the high altitude! Thanks again!!

 

[CZLN6]

Howdy back VW:

The RBS is a very simple and unique carb. It is similiar in function to the YF in that it uses manifold vacuum to operate a metering rod/jet system. It will be helpful to get as much manifold vacuum as possible, and at your elevation that will be hard. Best would be to tune the low speed air screw with a vacuum gauge for the highest reading.

To access the main jet, you will need to remove the carb as the jet is located above the float bowl. The bowl is attached with 4 screws that are accessed from the bottom- the need to remove the carb. The RBS uses a very small main jet and I do not know if it is the same as the YFs or other carter jets. I'd suggest that you buy a carb rebuild kit to read and study. As with all OEM one barrels the accelerator pump system on this carb is weak and needs to be replaced every few years.

The new plug wires may help some. In addition, try a slightly larger gap on your cleaned plugs. Try .038" if no miss, try .040". The Flowmaster muffler will help to lean out the A/F mix slightly too. And, as previously mentioned, make sure there is no air cleaner restrictions what-so-ever.

Adios, David

 

[Anonymous]

VW,
Strongly suggest you get one of David's Performance Handbook on the 6 cylinder engine you have. You can find it here.
http://falconperformance.sundog.net/
I have mine laminated and in a notebook.
It is the central part of my information for my 6's.
Very very useful information.
FWIW DaveP

 

[Anonymous]

thanks guys...i have a copy of that book on the way...by the way i got a new set of spark plug wires and an airfilter...it is running MUCH better...I think the accelerator pump on the carb is going out though...if you guys have any info on fixing that...it would be greatly appreciated...thanks again

 

[Anonymous]

The accelerator pump comes with a carb rebuild kit.

Check your vacuum advancer on the distributor (make sure it's not leaking). And, check the "spigot" on the side of the intake manifold where the hoses attach: they get old and work loose - need to be "snugged up" to stop leaks.

Also, if you have the charcoal vacuum canister under the hood, make sure the hoses to it are not split from age: a little leak here causes low mainfold vacuum, which reduces carb efficiency and spark advance, etc., etc....for $3 you can replace all these hoses, just in case.

 

[Anonymous]

Cool..thanks...how hard is it to do a re-build on this carb?? And about how much would it cost??