tauh Posted January 22, 2011 Share Posted January 22, 2011 I have triple mikuni 44's ready to go on my 240Z. They have the external float adjustment. I rebuilt them but have some questions about setup. On the bottom of the carbs are some plates that fit under the accelerator pump. One of these plates has 2 vacuum fittings (I think) on each carb. I can not find these fittings anywhere in the books or printouts that I have. Anyone know what they are for? The starter discs on mine are attached to a spring that holds them all the way to the left (looking from the carbs toward the intake). In reading, it seems that all the way to the left is full choke and that under normal driving (after warmup) the discs should be all the way to the right. Why would you spring something where the normal position puts pressure on the spring? Does not make sense to me or am I mistaken about the disc position. If this is covered somewhere else, please direct me to the right place. Thanks Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted January 22, 2011 Share Posted January 22, 2011 The fittings under the carb are for running a coolant (not the engine coolant) through. some have plumbed the fuel return through them to keep the carb bodies cool. I never used them when I was running Mikunis. All the way to the left is closed, i.e. inopperative. These are not chokes, but a separate circuit for starting. I found that I never needed them, just pumped the throttle to use the accel pump when cold. Sam Quote Link to comment Share on other sites More sharing options...
tauh Posted January 22, 2011 Author Share Posted January 22, 2011 Thanks for the reply. That answers my questions. Now to just install and adjust. Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 23, 2011 Share Posted January 23, 2011 They indeed are for using fuel cooling of the bottom of the bodies. It helps quite a bit with fuel percolation on hotter days. The Mikuini setup states they are fuel coolers, not coolant lines. You use fuel as the coolant. The tank is your sink for heat. Quote Link to comment Share on other sites More sharing options...
luvemfast Posted January 25, 2011 Share Posted January 25, 2011 So we run the fuel return line through these fittings? Why did you not use them Sam? Would I be best to utelise them? Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 25, 2011 Share Posted January 25, 2011 That is their design function. It keeps the fuel in the Accelerator pump below it from percolating out and making a TERRIBLE lean flat spot on quick throttle application. Heat boils the fuel in the accel pump and it discharges up therough the pump nozzles, leaving them dry when the time comes to quickly hit the throttle and inject the accel squirt. Running a volatile light solvent (gas) over the top of the accel pump (and under the float bowl) sucks out heat from both areas and keeps the bowls and accel pump full of liquid gasoline. These are an OEM part for some JDM cars with hot non-crossflow engine compartments! Quote Link to comment Share on other sites More sharing options...
tauh Posted April 1, 2011 Author Share Posted April 1, 2011 Tony, Thanks for the additional information. That answers my next question. I have the "Terrible flat spot" on quick acceleration. I will try your idea. Pat Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 1, 2011 Share Posted April 1, 2011 glad to see someone using the 'search feature' gets some use from my miscellaneous ramblings... Quote Link to comment Share on other sites More sharing options...
chicago240z Posted April 1, 2011 Share Posted April 1, 2011 Glad this was answered, I also have those and was told to cap them off because they may leak fuel? but now knowing the feature I believe I will use them as they were intended, Thanks Tony again Im thinking to use some type of heat insulator on the fuel lines would help also along with the heat shield, do thicker heat shields work better or have the opposite effect due to time to cool thicker metal? here is what is being discussed Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 3, 2011 Share Posted April 3, 2011 Heat shield should be a low-transmission materal. Ideal metal would be Stainless. Really best is a ceramic/carbon aerospace composite sandwich. NO radiant heat is transmitted. Putting asbestos blanket under the heat shield seems to help more than metal alone. I have used Aluminum, with asbestos cloth underneath...I'd use stainless if I had some on hand. Quote Link to comment Share on other sites More sharing options...
tauh Posted April 3, 2011 Author Share Posted April 3, 2011 OK. I hooked up the fuel coolers to the return line and installed a heat shield but I still have the issue. It will rev through the entire range slowly. It has a HUGE bog at just off idle on a quick punch and will not recover until I let off the gas. Any ideas? Pat Quote Link to comment Share on other sites More sharing options...
zbloke Posted April 3, 2011 Share Posted April 3, 2011 I'd be tempted to say the accel pump jets where too small, but having read other posts on here from ppl using Mikunis and having the same issue as yourself, its more than likely the pilot jets which are too small. You could really do with having the AFR monitored while your engine is bogging to tell you whats happening fuel wise and base your next move on the results of that test. Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 4, 2011 Share Posted April 4, 2011 Does it spit when it happens? What is your curb idle set at? What is your idle set to, and are you using vacuum advance on the 1st carb through the damper pot? Mikuinis like 900 for curb idle, and usually idle jets in the 55-62 range with initial timing bumped up accordingly. A recurved distributor is not necessary, but it helps. Having the idle too low, timing retarded, & heavy flywheel, will all exacerbate the 'bog' of insufficient accel pump. And if it doesn't come off bog when you keep it floored likely there are venturi size and vacuum leak issues as well. They may stumble, but even 44phh's on an L20A will start revving and once they hit 1500-2000 will take off like ZOOM! If they don't you have other basic mechanical issues that need to be addressed before monkeying any more with the carbs. The cooling bodies and heat shield only help with a percolation issue which may or may not have these same symptoms. Quote Link to comment Share on other sites More sharing options...
tauh Posted April 5, 2011 Author Share Posted April 5, 2011 Thanks for the helpful advice. I have some idea of what it might be. Now to the garage! Quote Link to comment Share on other sites More sharing options...
Badler Posted July 12, 2014 Share Posted July 12, 2014 (edited) Sorry to resurrect a thread from the dead, but Wow!! so THAT is what those are! I didn't know, so I plugged them up... so let me get this straight. ALL I need to do is run my fuel line past the last banjo bolt, then loop it down, go in one hole, out the other repeat twice more and get back to the fuel return line? is it really so simple? And it will really improve my 44 PHH performance without any drawbacks? This seems too good to be true!! (so please tell me if it is ) Edited July 12, 2014 by Badler Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 13, 2014 Share Posted July 13, 2014 If your carbs are percolating. What exactly have you read into this thread as a " performance improvement " other than eliminating percolation of the fuel? Quote Link to comment Share on other sites More sharing options...
Badler Posted July 13, 2014 Share Posted July 13, 2014 I read getting rid of the flat spot on quick acceleration as an improvement and there really isn't a drawback to running the return line through there, is there? If it can't hurt, and might help, then do it, right? Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 14, 2014 Share Posted July 14, 2014 The flat spot on quick acceleration caused by percolation will be cured by using them... If you have incorrectly sized idle jets, pump squirters, pump check balls that are stuck, wrong pump stroke.... It won't help anything but keeping the carbs cooler. Quote Link to comment Share on other sites More sharing options...
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