heavy85 Posted August 8, 2004 Share Posted August 8, 2004 Not from the exhaust but from the engine itself (well the exhause reeks too but that's not my question here). I have an L28 w/ tripple 44 Mikuni's in my 240 and it reeks of raw fuel around the carbs. There are no leaks and the carbs have all been rebuild but it still smells like raw fuel in the engine compartment. The smell seems to be coming from the carbs - all of them. I am only running stacks with no filters but I still would not expect this. Is this normal and any ideas how to stop it? I cant even park the stupid thing inside the garage because it stinks up the house. Thanks Cameron Quote Link to comment Share on other sites More sharing options...
Tekira Posted August 11, 2004 Share Posted August 11, 2004 Geeze mikunis are fun arent they! I have triple 40mm on mine and i noticed when i turned up the fuel pressure at my regulator the carbs smelled like gas. I turned down my pressure and no more gas smell except when i stab it! To much fuel pressure could be one of the things. Your pilot jets could be tuned to rich. Do you have a return line or are you running dead into carbs? Mikunis are very sensitive to fuel pressure, are you running a regulator before the carbs? Whats your fuel pump psi rating? The max pressure for my mikunis is about 4.5 psi give or take. Also does the engine produce a rich mixture (smoke) OR does just your carbs stink? Its easy to start guessing what the problem is. Check your fuel pressure with a low pressure guage, 1-10 psi, right before the carbs and tell me what that is. Check before you spend the $ this is very fixable and i know your pain. My girlfriend would let me park the z inside because it smelled like gas so bad! When i drove with the windos down it burned my eyes!!. Well check back with that fuel pressure Quote Link to comment Share on other sites More sharing options...
heavy85 Posted August 12, 2004 Author Share Posted August 12, 2004 I've got pump-regulator-pressure gauge-carbs-NO return line and the fuel pressure guage reads about 3 PSI at idle. This was all set-up by the previous owner I just rebuild the carbs and am trying to get it all working well. Same deal as you when I park it it just reeks of gas. There is a real strong exhaust smell which is another issue I think and may be partially attributed to some carbon build-up on the valves. The smell I am trying to fix here is a raw fuel smell coming from the carbs. I haven't yet tried to fix the exhaust smell and I know there is a lot of history I need to look up on that. Thanks Cameron Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 12, 2004 Share Posted August 12, 2004 Have you checked the float level? Quote Link to comment Share on other sites More sharing options...
heavy85 Posted August 13, 2004 Author Share Posted August 13, 2004 Yes, I set them up exactly per the Mikuni manual. Adjusted float level and accelerator pump travel to 12 mm and 7.5 mm respectively. Quote Link to comment Share on other sites More sharing options...
srgunz Posted August 13, 2004 Share Posted August 13, 2004 I also run just the air horns and my had been acting the same for quite awhile. In fact after I shut it off and let it sit I could actually see gas seepage on the air horns. This spring I installed a pressure guage. Its runs 3 psi. so I figured that was not the cause. My carbs have the grose-jet ball and seat instead of the regular needle and seat. What I did was pull the inlet hose off each carb and squirted carb cleaner down the fuel inlet to clean the ball and seat. That did it for mine, no more seepage. What I think happens to my Z is that it sits for 7 months then drive 5 months. During storage the gas in carbs evaporates and was leaving varnish on the seats causing them to leak. Good luck. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted August 26, 2004 Author Share Posted August 26, 2004 Hey Tekira - your host site cardomain installed adware (spyware) on my computer when I visited it. I just now got my computer back working halfway OK after reformatting my harddrive! Anyway, since I just rebuilt all the carbs I know they are not dirty. Fuel pressure is OK, the floats are set to Mikuni specs, what else could it be? Does it have to be in the floats - maybe the seats are bad? Thanks Cameron Quote Link to comment Share on other sites More sharing options...
zcarnut Posted August 26, 2004 Share Posted August 26, 2004 Sounds like the classic case of “fuel percolation” caused by heat soaking. After engine turn off cylinder head temperature will actually increase due to the lack of water circulation. Any fuel in the carb’s emulsion tubes expands and the fuel drips into the carb throat via the main jet. I had this problem with my triple Webers. The cure was to install a thick (0.125") plastic gasket as an insulator between the carbs and the aluminum intake manifold. Aluminum is a very good thermal conductor. Do you have such insulators on your Mikuni’s? Quote Link to comment Share on other sites More sharing options...
heavy85 Posted August 27, 2004 Author Share Posted August 27, 2004 I have very thick - maybe 10mm - spacers (insulators) but I do not have a heat shield between the headers and the carbs. I've been thinking about adding one but haven't yet figure out a good place to attach one to. I do know they get hot though because you can't even hold onto the carb linkage! Cameron Quote Link to comment Share on other sites More sharing options...
zcarnut Posted August 27, 2004 Share Posted August 27, 2004 Too bad. A heat shield for the Webers is easy to make as it can be flat and there are threaded bolt holes in the bottom of each carb to secure it. Cameron, are you running your fuel return line through the fittings on the _bottom_ of each carb? I assume that Mikuni put them there so the fuel in the return line would remove some heat from the fuel in the bowl. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted August 27, 2004 Author Share Posted August 27, 2004 Is that what those barbed fittings on the bottom are for? There is one on either side of the bottom of the carbs but the only thing they would cool is the back side of the accel pump diaphram if memory serves. Also, I dont have a return line but am thinking it would be a good idea to add one. Wouldn't that require a different pressure regulator - one that's a relief valve instead of a reducing valve? BTW - Anyone out there have details or pictures on their heat shield for Mikuni's? Thanks Cameron Quote Link to comment Share on other sites More sharing options...
zcarnut Posted August 28, 2004 Share Posted August 28, 2004 The fittings on the bottom go to a small chamber that is in between the float bowls and the accelerator pump supply chamber. So, you would be removing some heat from the fuel in the float bowls. If you have a return line you do not need a pressure regulator. Simply adjust the pressure by placing a restriction in the return line. I used a plug with a .050" hole on my Webers. Start out with a small hole and gradually increase the diameter to obtain the desired pressure. This is the same method that Nissan used to set the fuel pressure on the stock SU's. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted June 30, 2005 Author Share Posted June 30, 2005 Well I now have 100 miles on the complete rebuild (finally - woohoo), but I still have the stupid raw fuel smell from the carbs. To review: floats are set per Mikuni manual, fuel pressure 3 PSI, I have insulators between carb and manifolds, and I have now installed a heat shield - I can now grab onto the carbs and they are only warm to the touch! Any other ideas as this is really driving me nuts and making it hard to park inside. As soon as I figure this out I can really start enjoying it. Are these carbs able to not smell like raw fuel? Thanks Cameron Quote Link to comment Share on other sites More sharing options...
ezzzzzzz Posted June 30, 2005 Share Posted June 30, 2005 I'm not familiar with Mikunis but suspect that the cold start circuit is possibly leaking. This would also affect idle richness which no amount of tuning would compensate for. Fuel would drip into the venturi area and vaporize causing this gashouse affect. Webers are notorious for this problem so I've heard many times.. Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 30, 2005 Share Posted June 30, 2005 If you have the fittings on the bottom of hte carburettor USE THEM! They are for the fuel return to pass through ,and are there to prevent PERCOLATION. They are referred to in Mikuini Literature as "Cooling Bodies" and are optional equipment. They were used in MANY OEM applications of the Mikuini PHH (Celica DOHC's for example) to prevent what you are smelling: raw fuel (AKA: Evaporative Emissions!) The carburettors WILL give off FAR MORE SMELL if you don't have an air box or good air cleaner assmelby on them. So will SU's for that matter! But heat boiling the fuel will be GREATLY reduced by using the return line (they were designed to use a return line....) and letting the return flow cool the bottom of the bodies. This solved the stumbling and precolation that was happening in my friends 3.2 some years back---he had to retrofit them to his car, and was glad he did. Also, if it's hot and you have a deadheaded system, the regulator will not bleed back pressure to the supply side, it invariably restricts the flow to control fuel pressure, so once shut off, the fuel rail will heatsoak, the pressure WILL rise, and the fuel in the rail will sink the floats and dump into the fuel bowl of the carburettor. A proper fuel system with a return line or return line regulator will help with fuel pressur control, but I think your problem is those three things in concert: No Air Box to contain vapors, percolation of the fuel in thebowl, and sinking floats after shutdown adding "more fuel to the fire" all together... Getting an airbox, heat shield, and running the cooling bodies will reduce many of the ill effects you are experiencing now. My Mikuinis on a blowthrough turbo setup never smelled like raw fuel. But when N/A with the ITG air Cleaner ther ewas a faint smell just like the SU's give when run without an aircleaner box. These older cars are captive emissions nightmares. After a hot run, you can have your eyes water from the fumes given off by the fuel system! BTW, have you checked you gas tank vent hoses for integrity lately? Smelling gas in the cabin may not be your carbs! Quote Link to comment Share on other sites More sharing options...
PanzerAce Posted July 1, 2009 Share Posted July 1, 2009 Thread revival time, but it's on topic. Now that the weather has hit 100+ ambients, I'm starting to have the same fuel smell with my triple 44s. Is there a good off the shelf heat shield for a triple mikuni setup? Preferably one that attaches b/w the air horns and the carbs, rather than the carbs and the intake? (like so: http://www.zccjdm.com/catalog.php/azcarbum/ct/pd1276448/JDM__L6_CUSTOM_TRIPLE_CARB_HEAT_SHIELD_ but IIRC, someone on here had some bad experiences with that specific company). As for the cooling bodies on the bottom of the carbs, is there a pressure limit on them, or can I just re-route my fuel return line into the carbs and then back to the tank? (and presumably the carbs are designed to be run inline with each other?). Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 1, 2009 Share Posted July 1, 2009 The cooling bodies are designed to work as a fuel return routing path. Any pressure you put there is minimal, but it's at least 1/8" thick mazak alloy and a gasket, so they should be good to about 60 psi (my blowthrough was running 25psi on the feed, and somewhere near that lift-throttle on the return line until I got my surge tank swirl pot orifice straightened out) The cooling bodies are run in series, usually with the back carb first. So flow from a feed rail from the pump would go Feed Carb 1, Feed Carb 2, Feed Carb 3, then to Cooling Body 3, Cooling Body 2, Cooling Body 1, Return Line to Tank. This puts the coolest fuel in the hottest carburettor first. If you run a cool can it helps. I had one made that was a 1 gallong thermos, and it would run 2 hours before the ice was totally melted and hot to the touch (water)...but MAN did it keep the carbs cool. One other thing, theorists and such aside... The COOLER you get the underhood temperatures, the better. I'm willing to give up the THEORETICAL loss of efficiency by running a 160F thermostat in the car, as opposed to a 190. The temperature coming off the radiator and blasting through the engine bay is at LEAST 30 F cooler under the hot day scenario using the 160 as opposed to 'standard' thermostat. Keep it around, you can use it in the Winter. But for the summer, it's a 160 in there, baby! I wonder what would happen if you hooked up a can of Radio Shack "Freez-It" or some R134 to those cooling bodies... Man, before the drag race, a quick hoze to freese up the mazak and precool the bottom of the carburettors... And almost to the DAY 4 years ago today...my last post on this subject in this very thread! I'm haunted, I'm sure! I digress... Quote Link to comment Share on other sites More sharing options...
heavy85 Posted July 3, 2009 Author Share Posted July 3, 2009 Mine are long gone but the heat shield under the cabs helps with a lot of things but not the smell. I ended up having to park outside with the hood open for a couple hours, once cool put plastic bags over the carbs, then push the car into the garage. Even then the smell wasn't too bad but it was still there. I never finished the bowl cooling deal so cant say how that works. Cameron Quote Link to comment Share on other sites More sharing options...
PanzerAce Posted July 3, 2009 Share Posted July 3, 2009 Mine are long gone but the heat shield under the cabs helps with a lot of things but not the smell. I ended up having to park outside with the hood open for a couple hours, once cool put plastic bags over the carbs, then push the car into the garage. Even then the smell wasn't too bad but it was still there. I never finished the bowl cooling deal so cant say how that works. Cameron Damn, that's way worse than my issue. Only happens to me for at most 5 minutes after a hard drive in hot weather. Quote Link to comment Share on other sites More sharing options...
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