timsz Posted December 10, 2014 Share Posted December 10, 2014 I have this fuel rail for my Mikunis. I want to run the fuel line along the firewall to the carbs. I want to run a return line to the tank. What is a good way ( good looking) to run the return line? Back along the fuel rail or under the carbs, etc. I can't seem to see any pics that show it. I've read where you run return fuel on cooling bodies on bottom of carbs. What does that mean? Any info? Drawing or pic would be awesome. Thank you very much. Quote Link to comment Share on other sites More sharing options...
TimZ Posted December 18, 2014 Share Posted December 18, 2014 001.JPG I have this fuel rail for my Mikunis. I want to run the fuel line along the firewall to the carbs. I want to run a return line to the tank. What is a good way ( good looking) to run the return line? Back along the fuel rail or under the carbs, etc. I can't seem to see any pics that show it. I've read where you run return fuel on cooling bodies on bottom of carbs. What does that mean? Any info? Drawing or pic would be awesome. Thank you very much. I don't think I'd be terribly keen on routing under the carbs (i.e., next to the exhaust manifold). Unless you are planning to use the cooling ports on the underside of the carbs I wouldn't want to introduce additional heat into the return fuel unnecessarily. Where is your fuel pressure regulator going to go? If you are going to do a pass-through fuel routing on your rail, the regulator will need to be between the rail and the tank. Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 21, 2014 Share Posted December 21, 2014 I might suggest center return and double feed from each end with a back pressure regulator dumping to cooling bodies that run through a fuel cooler on the way back to the tank. Quote Link to comment Share on other sites More sharing options...
timsz Posted December 22, 2014 Author Share Posted December 22, 2014 I don't understand what your saying Tony. Could you maybe draw a picture and post it? I don't know where the cooling ports are either. I'll put the regulator in the right spot. PHH carbs. Thank you very much. Quote Link to comment Share on other sites More sharing options...
TimZ Posted December 22, 2014 Share Posted December 22, 2014 I don't understand what your saying Tony. Could you maybe draw a picture and post it? I don't know where the cooling ports are either. I'll put the regulator in the right spot. PHH carbs. Thank you very much. Many 44PHH carbs (I don't if it's "many" or "most", but it's pretty common) come equipped with cooling bodies on the underside of the carb - they have two hose barbs and are meant to run the return fuel through in order to cool the carb body. Take look at part #85 in the exploded drawing below: ...do you have hose barbs like that on the underside of your carbs? .. Quote Link to comment Share on other sites More sharing options...
timsz Posted December 24, 2014 Author Share Posted December 24, 2014 Yes I have those hose barbs on the bottom of carbs. So the return fuel goes through them, then back to tank. How does it cool the fuel? Thank you very much. Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 24, 2014 Share Posted December 24, 2014 It DOESN'T! It cools the float bowl and carburetor body. Guys in SoCal have thanked me for turning them on the the anti-percolation benefits of these bodies. Yep, it's gonna make your fuel less dense as the tank temperature will rise. Keep the tank up and you have a VERY effective heat sink for pulling off the freeway at 120F and then sitting in Vegas Strip Traffic fighting for 45 minutes trying to get to your hotel! Quote Link to comment Share on other sites More sharing options...
TimZ Posted December 24, 2014 Share Posted December 24, 2014 It DOESN'T! It cools the float bowl and carburetor body. Guys in SoCal have thanked me for turning them on the the anti-percolation benefits of these bodies. Yep, it's gonna make your fuel less dense as the tank temperature will rise. Keep the tank up and you have a VERY effective heat sink for pulling off the freeway at 120F and then sitting in Vegas Strip Traffic fighting for 45 minutes trying to get to your hotel! Also, this was why Tony was suggesting putting a fuel cooler in the fuel return to cool it back down before returning to the tank. My recollection is that those hose barbs are kinda tiny, so if you do this, you should keep an eye on your fuel pressure. If they put too much restriction in the return line your fuel pressure could rise. Simple remedy is to run a second return line in parallel - don't go too big on the second return, though, so as not to divert too much fuel away from the cooling bodies. Quote Link to comment Share on other sites More sharing options...
Tony D Posted December 26, 2014 Share Posted December 26, 2014 From a standard fuel pump, there will be very little flow through the bodies. It's when you get off the gas that fuel surges through there and accomplishes the cooling. Quote Link to comment Share on other sites More sharing options...
timsz Posted December 27, 2014 Author Share Posted December 27, 2014 What is meant by back pressure regulator? Is it the same as pressure regulator? Thank you. Quote Link to comment Share on other sites More sharing options...
Kennymonster Posted January 21, 2015 Share Posted January 21, 2015 This may just be a question exclusive to Tony lol. My concern is, I thought the reservoirs on the bottom were independent of the float bowl / carb internals, and were more like an external cooling channels. However, when I uncapped the nozzles, and moved the throttle linkage, I saw fuel coming out. Not leaking, but it was being pumped out (per throttle motion, almost like the accelerator pump fuel was coming straight out of the nozzles). Without the throttle linkage motion, and with the float bowls full at 3.5psi, no fuel was coming out of the nozzles. The question I have is, if the reservoirs are not totally independent and does share some plumbing from the float bowl, and I run the return line through here, would this have an affect/become an issue on the float levels? Since there's no float needle or anything like that on the underside, my worry is the float bowl filling up from the reservoir side and flooding. Quote Link to comment Share on other sites More sharing options...
ryant67 Posted January 21, 2015 Share Posted January 21, 2015 (edited) Kenny,Tony might (and almost certainly will) know better, but I will throw my thoughts in here as well since I have spent quite a lot of time with these carbs over the past couple of years now. Fuel should not be getting into the cooling body of your Mikuni. What I suspect is happening here is that you have a damaged, or missing, gasket between the cooling body and the throttle pump assembly, and it is leaking fuel in. There are two lines that run through the cooling body:1] feeds the throttle pump a supply of fuel2] runs from the throttle pump to the pump jetsBoth lines are independent of the cooling reservoir. I attached a pic of the parts and circled the pump jet lines in yellow, and the inlets in red. I suspect the gasket around these parts isn't doing its job, and fuel is leaking in. If it's happening when you apply throttle, then it would very likely be the yellow circled ones. Edited January 21, 2015 by ryant67 Quote Link to comment Share on other sites More sharing options...
Kennymonster Posted January 21, 2015 Share Posted January 21, 2015 Ah that image is what I needed to see, I'll be taking mine off the car & apart shortly as well to confirm the condition of the gaskets, but what you're describing makes sense. Thanks Ryan. Looks like I'll have some gaskets on order from Todd soon. Quote Link to comment Share on other sites More sharing options...
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