Ford Racing 5.0 GT40x and quad 48IDA carb tuning

[Ron]

Hello Members.

I've been tuning my 302 in my 67 mustang for a while now and am wondering if anyone tuned this setup to save me some work.

I have a ford racing 302 with the gt40x heads and a swapped the cam for a comp camshaft (roller they recommended for use with the carbs xe270hr112). Static compression is 9.1:1.

My current carb setup is this:
- 48 ida with 33 chokes
- floats all set (carbs all setup)
- idles 120/70
- mains 145/f5/200
- 50 accelerator nozzles
- idle jets at 3/4 to 13/16 out
- fuel pressure 2.75psi

Here's what I go so far
- running smooth through transition but falls off above 4500rpm (it's actually pretty responsive and I can do 'almost' anything with the throttle)
- off idle and below 2000rpm if I nail it (in any gear) it falls flat
- steady cruise I get burbling in the pipes
- I get fuel splatter all over the back of the car if I do a hard run

The car runs real strong with the 37 chokes. But if I put them in I get a lot of stumbling between 1800-2800rpm.

I'd like to get the 37 chokes back in the car as the weber tuning manual indicates it should work. But:
- I'm already pretty large in the idle jets and holders
- I'm in an f5 tube (f11 minus the high holes) and unsure what to try

Thank you for the interest and assistance

 

[Rick]

Put 37 mm chokes in as you are currently strangling it with the 33's, thats why it noses over above 4500 RPM yet is very resposive in mid 3000 RPM. Try a 60 F10 idle fuel jet with a 100 or 110 holder. That will make the idle circuit leaner and help transition. The Bypass valve in the bottom of the float bowl needs to be a #50 or #55. Either the F5 tubes or possibly F16 tubes will most likely be the right ones. Be sure you have good fuel filters. 3/4 - 7/8 of a turn open on fuel mixture screw is correct. Check plug color.
Initial ignithion timing about 14-18 at 1000 RPM max 34-36.

Report back

 

[Ron]

Rick...thank you for the reply

It's back to car weather and am trying to sort the engine out

Still having problems. Here's what I have.

302; gt40x heads ; comp cam as described above
-4 weber 48 IDAs.
- 33 chokes
- 120/70 idles
- 215/F7/140 mains
- unknown idle bypass but think its a #50
- accelerator shooters .50
- timing is 18 base with 38 at 2200.
- fuel pressure 2.75psi

With the 33 chokes it transitions and runs really nice but the engine looses pull above 4500rpm.

When I put the 37 chokes in I get a stumble onto the mains in the 2700-3000rpm range.

Any suggestions or thoughts?

Thank you for the interests and replies

Ron


PS: I tried F2, F11, F16, F5 tubes. The F5 works with a small stumble hole at 2800-3000rpm; the f7 takes it away. The f11 has a huge stumble hole 2200-3000, f16 is a little better than the F2 if I recall but still has a hole. All of this is with the 33 chokes; with the 37 chokes the stumble to transition gets much bigger (add 400-600 rpm to any stumble with the 33 chokes)

The 110/60 idles and 120/65 setups make a stumble when transitioning to the mains with 33 chokes.

Plug color is coco-brown on idles. Blackish brown on mains (hot cut).

 

[Ron]

Pic attached

 

[Cliff Beer]

Ron, the smaller chokes improve the driveability simply because the smaller choke aids in good atomization of the fuel (faster flow past the choke, greater pressure drop, better atomization). The smaller chokes are really just masking the tuning issues so I would do as Rick suggests and go to the 37 chokes and tune from there. Once the major tuning issues are worked out then go back to the smaller chokes if you want a really driveable/friendly engine tune.

Have you read Pat Braden's "Weber Tuning"? It's an excellent book, and one I would know back to front if you're trying to dial in some downdraft webs. The book provides both the theoretical knowledge along with the practical knowledge. On the practical side there's some good coverage of IDA's/IDF's but all the other sections are pretty helpful as well since, for example, an IDA is really just a side draft turned on it's head in many respects.

Some would disagree with me but the IDA 48's are pretty big for a relatively standard 302. The gt40x heads are good heads but the valve sizing isn't overly large. I had the same FR302 crate engine with a stroke kit to 331 and the 48 IDA's were still a little large. 44IDF ran noticeably better.

The reason you get a stall when going to WOT is because the standard 302 isn't sucking a ton of air through the main bore (particularly below 2,000 rpm) and the accelerator pump dumps a ton of fuel into the pipe - the fuel doesn't atomize well and burns poorly/irregularly. If you want to stay with the 48's I'd lessen the accel pump flow.

One thing you might want to consider is installing an AFR meter and in-cab digital readout. These things aren't super precise but it'll give you some rough idea of the AFR as you cycle through the operating cycle. Best to put the pick up down stream of the collector so you're not just picking up one cylinder's reading.

I hope this helps.

[ame]http://www.amazon.com/Weber-Carburetors-HP-Books-774/dp/0895863774/ref=sr_1_4?ie=UTF8&qid=1401659674&sr=8-4&keywords=pat+braden[/ame]

 

[Rick]

140 main with 215 air corrector is too lean. Put the 37 chokes in and use a 55 or maybe 60 f10 idle jet with a 100 or 110 air corrector. Then a 145 or 150 main with close to a 190 air corrector. Keep an eye on your plugs. The Comp Camps recomended cams are pretty conservative. 37mm chokes restrict my 289 to 6700-6800 RPM.

 

[Mike Pass]

Without knowing what the air fuel ratio is at all throttle, rpm and load settings I think you are just guessing and hoping to stumble on the correct setup. The best way is to get the car on a rolling road with a good operator who knows webers and has a big box of jets, chokes etc and he can get a readout of exactly what is going on with the engine.
Failing that get one of the proprietary air fuel ratio meters. You will need to weld a boss into the exhaust for the sensor and two electrical connections and you will have a constant readout of air/fuel ratio as you drive along, accelerate etc. I got the AEM one off EBay. There are lots of them about. I think Holley do one also. When I did mine I found the idle air correctors on my Holley were way out.
Cheers
Mike

 

[Ron]

Thank You for the posts Guys. Will run some tests and get back to you all.

I know when I put the 100/110 idle holder in with 60/65 f10 fuel tips I get a huge gap getting on the mains. The 120/70 or 125/75 seems to make the gap onto the mains better or less noticable until the outdoor temperature rises about 75 degrees (which I think is a lean condition...correct me if my instinct is wrong).

I ordered some f6 and f47 e-tubes to try a deeper well on the e-tube (I may need to solder 3 of the 4 holes in it up at each level...basically leave one hole per level as I know the f5 and f11 are too lean...as I get a huge stumble on to the mains. The f2 and f16 do the same thing.). Right now I'm running the f7 and it runs about the best with it. I was hoping to find f49 e-tubes but no luck. I'm really thinking this is a etube issue...but I could be wrong.