Missing at low rpm's

[davemccorkle]

Finally finished breaking in my new 2.7 RS configured engine. I do however have an annoyance and was wondering if you had any thoughts. When i start accelerating in 1st i always have a little missing until the rpm's get up. Once I am moving it runs like a dream. The other issue that i noticed is that every time i shut off the engine, like for gas or something and then start up again, it misses big time for about 15 seconds. This obviously seems to be a fuel issue but would love suggestions.

Thanks

[Walter_Middie]

What kind of fuel system are you using? Carbs? MFI? CIS? Motronic? Other?

[davemccorkle]

Carbs

[66DC]

Pretty typical of a hot start, from my understanding. Valve adjustment may improve the hesitation.

[davemccorkle]

It is like extra fuel needs to burn off before it can run correctly. It does happen ever time I stop and restart the engine that is hot.

[davemccorkle]

2.7 RS configuration, webers carbs, holley fuel pump running about 4lbs pressure

[davemccorkle]

No one has ever had this issue? I am guess it could be a jetting issue but I do not know what the sizes are yet without taking them out. That is my next step

[davemccorkle]

nothing at all? hmmmmm

[stlrj]

It is quite possible you may never get this resolved due to the new reformulated gasoline that was never designed to be fed into carburetors. High RVP's and high volatility of gas to meet smog may be the culprit.



Cheers,

Joe

[davemccorkle]

never thought of that. sometimes it is the simple things

[1QuickS]

Check accelerator pumps for equal output and check for blockage in all idle jets, one may be plugged but you haven't noticed the missing cylinder. If you have a check valve bleeding in your accelerator circuit then you won't get a full shot of gas to enrich during acceleration.

Sounds like heat soak of the fuel at your fuel stops causing some percolation. If your fuel bowls have crud in them or if they had pitting from previous corrosion then these will provide points for fuel to boil earlier than when the bowls are clean or smooth like when new.

Careful idle setup is vital: float levels set while engine idling, idle air balance (STE flow meter works very well) and idle mixture (I use a Colortune tool for idle mixture setting.)

Fuel pressure should be 3.5 psi, this is per Weber and OEM Porsche spec although 4.0 is probably OK.

2.7RS jetting is typically something like:

• 34mm venturis
• F3 emulsions
• 145 mains
• 180 air correctors
• 60 idles

I assume your Webers are IDA, IDAP, IDS; not IDT, IDTP or IDTP1. The former have a richer progression than the latter.

[davemccorkle]

Thanks a million! I will report back what i find.

[davemccorkle]

I finally dug into the carbs and discovered that they are setup for a 2.0 not my 2.7 so I ordered all new jets, and emulsion tubes. I hope this takes care of the issue. I already had 34mm venturis