2eighTZ4me Posted March 11, 2013 Share Posted March 11, 2013 Freshly rebuilt Mikuni 44 PHH's on a Canon long runner intake. Brand new isolators and rubber o-rings. Never had this problem before the rebuild. If I sit at a stoplight too long and take off, the car would stumble and lose power, but would eventually recover. The other day on the way home from work, I stopped at a buddy's place for 15min or so. When I got back to the car - I smelled gas rather heavily from the back of the car. When I left, I got about 500 yards up the road and it died. This time - completely. Pulled over and popped the hood - I could hear gurgling noises coming from my fuel lines. - Running a stock 280 EFI pump through and Aeromotive return-style regulator. - All AeroQuip braided lines routed along the backside of the motor along the firewall. - Nismo Comp header - large primary tubes. - I have a heat shield. Two actually. - Float levels are dead nuts across all 3 carbs - Regulator located after the carbs - Steady 3.5psi fuel pressure when cranking the car - Jetting is dead on. Car was tuned with a wideband on a dyno. I have a hard time believing that a system that returns fuel to the tank to cool (and on a 60 degree day) is boiling it. Yet it was. After about 10 minutes of trying to start it with no luck for the first 2-3 minutes. I tried it again after the gurgling noises stopped. Fired right up and drove it home. When I got home, however, the smell of gas was prevalent again, - some in the carbs, yet some while walking around the rear of the car - yet I saw nothing leaking. There was no hint of fuel smell in the cockpit - only exterior. I was thinking of wrapping the AeroQuip hose with a foil type heat barrier - but the stainless braid should knock down a good bit of heat in and of itself - especially where the hoses are routed. Haven't done any further testing, but thought I'd throw this out there to see if anyone had any ideas. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 11, 2013 Share Posted March 11, 2013 (edited) PERCOLATION! Make sure your timing is CORRECT and that the pulley isn't giving you odd wrong timing readings. In every case I've seen with Mikuni's percolating, the cooling bodies added to them stops the problem. Gurgling you hear is fuel boiling in the float bowls. The EFI gas we have is susceptible to this, when at atmospheric pressure. Running the return fuel through the cooling bodies stops this positively. The shielding and wrapping will help some, but cooling the carb body is what you need. Short of a 1 gallon ice-filled cool-can made from 20' of copper tubing and a Coleman Cooler (don't even ASK, man!) that's about the best solution you will find. Edited March 11, 2013 by Tony D Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted March 11, 2013 Author Share Posted March 11, 2013 My timing is a bit high. I've been meaning to back it down a little. I think I'm at 36 degrees all in and I'm still hearing some pinging in 4th on a hard pull. Thinking 32-34 would be about right. OK - pretty sure I have the cooling bodies. They're down on the bottom between the accelerator pump diaphragm and the carb body itself.. They have two hose barbs coming off each carb - one facing toward the front of the car - the other facing the rear. Is this what you speak of? I asked Todd at Wolfcreek what these were for and his response was 'it was a feature that Mikuni never ended up using'. Like a dumba$$ - I thought water went through them, so I plugged them off with some fuel resistant epoxy. So, it would be in my best interest to pull the carbs, remove the epoxy, and run the return fuel through these? I would have to assume this is post regulator? Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 12, 2013 Share Posted March 12, 2013 I'm suprised Todd said that. They were specifically addressed in technical literature and stocked as aftermarket parts in Northridge! Yes, your return line from the regulator should bypass the fuel through those bodies under the carbs, and back to the tank. It is a small orifice, if you have a monster pump you may have to 'sidestream' them. Only other think I could think of since it's after overhaul is you have a gasket leaking and running lean causing running hot. I found using the cooling bodies and running a 160F thermostat GREATLY reduced the temperatures under the hood and made the fuel much less prone to vaporize or boil in the float bowls. My webers would do this off the highway into city traffic...no remedy for that! Which is why I sold them and kept my mikunis! Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted March 12, 2013 Author Share Posted March 12, 2013 Tony - just running the stock 280 EFI pump. Nothing fancy or huge. Hmm....well - I guess the weather is going to be nice this weekend....just wish I hadn't mounted the regulator on the firewall in front of the wiper motor. That's going to be a heck of a run out to the carb bodies and then back to the tank. Thanks for the advice sir! Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 13, 2013 Share Posted March 13, 2013 (edited) Yes, then you should be OK that's what I had on mine! Of course, I also had an unwrapped turbo manifold and o heat shielding under them.... Blasting on the freeway at 9PSI non-inter cooled got the carb bodies 200+ F, then take an off ramp and sit in stop-n-go... It's amazing how cold N/A Carbies seem by comparison! LOL Edited March 13, 2013 by Tony D Quote Link to comment Share on other sites More sharing options...
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