Carburetor Fine Tuning, Trying to get my dual EMPI HPMX 44's as close to perfect as possible - Now running Spanish Weber 48 IDF's... |
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Carburetor Fine Tuning, Trying to get my dual EMPI HPMX 44's as close to perfect as possible - Now running Spanish Weber 48 IDF's... |
sgetsiv |
Jul 6 2014, 08:26 PM
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#1
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Former 914 Owner :( Group: Members Posts: 159 Joined: 20-June 08 From: Portland, OR Member No.: 9,192 Region Association: Pacific Northwest |
I've been working on my carbs for the past few weeks to try and get them to run as close to perfect as possible. Here are the details at this point:
2315 Raby built engine EMPI HPMX Dual 44's 52 idle jets 150 main jets 200 air correction jets 55 accelerator pump jets New CB Performance Rotary Fuel Pump - 3.5 psi - stock location No fuel pressure regulator - just a TEE fitting Stack electrical fuel pressure gauge 0-15 psi - reads 3.1 psi when cold, 2.4 psi once everything warms up and is running Wide band AFR gauge Fuel lines flushed and fuel filters cleaned Gas tank pulled and re-installed lines at base to be sure there are no kinks I rebuilt the carbs with the EMPI rebuild kits which includes all new gaskets, accelerator pump diaphragm, new mini fuel filter, new float needle valve assembly, new washers for the accelerator pump jets, new o-rings for the idle jets and idle mixture screws. Floats are set to factory specifications as well. I pulled the throttle plates and was extremely careful to be sure I put them back exactly the same way and that they do not hang up - their action is perfect and they cover the progression holes. This project started a few weeks ago after running into lean issues under load - turned out to be the fuel pump relay was going bad. There was a significant voltage drop across the relay and it finally ended up failing completely during testing. Once the engine is fully warmed up, my AFR is reading 12 to 13 at idle; adjusting the idle mixture screws can make a big difference in AFR readings without changing the idle significantly. I started out with the accelerator pump jets set to factory setting of 7mm of thread exposed. During my test drives today, I turned them in (richer) to about 10mm. Response is better but still not perfect. I'm getting AFR readings in the 12-14 range during "regular driving" on the highway. Going up hill under load at 60-70 mph in 4th gear (say around 3500-3800 rpm) and very slowly pushing on the throttle creates a lean condition. Once I step on it, the AFR drops down to 11-12 and then settles again in the 12-14 range. I would really appreciate some input on adjusting the accelerator pump and any other suggestions on how to get the most of these carbs. Are the accelerator pump jets (55) big enough? They can certainly be reamed out. I did measure the output and got around 0.3 ml fairly consistently for each jet. All 4 jets spray straight right into the center of the carb in an even stream. |
sgetsiv |
Jul 16 2014, 11:59 PM
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#2
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Former 914 Owner :( Group: Members Posts: 159 Joined: 20-June 08 From: Portland, OR Member No.: 9,192 Region Association: Pacific Northwest |
Just a quick update...
Idle jets are now 57's. Running mid 12's at idle on the AFR. I have the air bypass screws all set at exactly 1/2 turn out. All 4 barrels are pulling the same at idle and at 1400 rpm. The manifold bolts needed a bit more tightening as well. I have moved the accelerator pump screws in to about 10mm on both sides - just slightly richer than it was before. Response is nice and smooth. Flat highway cruising runs in the mid to high 12's on the AFR. Uphill highway cruising goes leaner but never gets above 15. Same RPM, just more load and more throttle. WOT at 2500-3000 rpm goes slightly lean - maybe 16-17 but just for 1/2 a second or so before dropping to 11ish once the accelerator pump jets kick in. It quickly settles in around 12.5 to 13. If I remember correctly, as I accelerate with WOT above 3000 rpm, the AFR readings are between 12 and 14. I can drive continuously at 4000-5000 rpm and am getting consistent 12-14 readings as well. I still think the transition from idle to mains is a bit heavy - I can probably move the accelerator pump screws in to 11 or 12mm to completely avoid the lean situation with sudden WOT. I was wondering if larger mains and larger AC's would allow the mains to come in sooner and help to eliminate that lean / hesitation condition? Or would that just make the mid range richer and the top end leaner? |
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