PanzerAce Posted April 8, 2008 Share Posted April 8, 2008 Finally got around to taking pictures of the undersides of my carbs so I could see them easily, and what I found....concerned me, but I don't know how worried I should be. So, onto the questions: First picture: What is the tube directly in the middle that is un-capped, and how vital is it to have capped? I'm assuming it should be, so does anyone know where to get rubber caps that will fit over it? Second picture: Since all the other carb throats have something screwed into that threaded hole, and this one doesn't, I'm wondering wtf is supposed to go there. I have the Mikuni service manual, but I can't figure out which part it is Thanks for the help, I really want to get this engine running in top condition... EDIT: I *think* the stuff that should be in the threaded opening is N3-06 and N107/173.... Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted April 8, 2008 Share Posted April 8, 2008 1st picture is the hose fittings for running coolant (not engine coolant) through the carb bodies. This is not required and I have never hooked these up. You can hook them to the fuel return to keep the carb bodies cool. This will not effect the idle. 2nd picture is where the set screw, lock washer, and lock nut goes to hold the main chokes in. That choke is loose now and you probably have a *small* air leak through that carb. It is before the throttle so should not effect the idle at all. What is your idle problem? What idle jets do you have? How many turns out are your idle mixture screws? Take them and turn them in, counting the 1/2 turns, until they just seat. Do not over torque as you can break the tip off. Write down how much it takes to turn each screw in, and you now know how far to turn them out to at least get back to your starting point. You can then take each screw out and clean the tip, check for damage and spray some carb cleaner/compressed air in there. You might get better results posting in these types of question in fuel delivery. Sam Quote Link to comment Share on other sites More sharing options...
PanzerAce Posted April 8, 2008 Author Share Posted April 8, 2008 Ok, good to know about the coolant, since a bunch of those caps are cracking and the like. The idle problem is that when the engine has fully warmed up (ie: after a half hour drive), if I am at idle for more than about a minute, it starts to miss a beat here and there. The problem gets worse the longer the car is idling, to the point that it has actually stalled out completely on me twice. As for the idle jets/mix screws, no idea. I guess this weekend I'll get some canned air and carb cleaner and clean them up. Didn't even remember we had a fuel delivery section, I'll repost this over there. Thanks for the help. EDIT: Actually, re-reading your post and the service manual, Mikuni PHH carbs don't have chokes, and the starter system is on the top of the carb... Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted April 8, 2008 Share Posted April 8, 2008 By choke, I mean the constriction that provides the venturi effect. They are also known as the main venturis. They are changeable to tune for better low end or high end. The set screw holds it in place behind the auxiliary venturis. Your symptom sounds like your idle mix is on the lean side and when carbs get hot, vaporizing fuel makes it go leaner and leaner until you get a misfire. Let us know the idle jet size and how many turns out the idle screws are. Have you checked your float level? Also, are the 44mm or 40mm? What is their history? Quote Link to comment Share on other sites More sharing options...
PanzerAce Posted April 8, 2008 Author Share Posted April 8, 2008 I have no idea what the history on the carbs is like. I got the car in January, and they were on it for at least the past 7 years (as far back as the previous owner had kept records). They are 44mm. I have not check the float level, but if it runs fine at speed, wouldn't that not be an issue? And were would I find the size of the idle jets? (presumably on them, but I haven't pulled the carbs apart yet). Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted April 8, 2008 Share Posted April 8, 2008 The float level has more of an effect at idle than at speed. To get at the idle jets, remove the screw holding down the inspection cover. The idle jets are the smaller brass bits poking up to the outsides of the larger brass bits. They will have the size stamped on the top. I highly recommend joining the sidedraft central yahoo group and reading Keith's white paper on carb tuning. http://autos.groups.yahoo.com/group/sidedraft_central/files/Weber%20Tuning%20White%20Paper/ If you want to fix this problem, you will need to really understand how these carbs work. They are basically the same as Weber DCOE and Dellorto carbs, so almost everything in the sidedraft group applies. Quote Link to comment Share on other sites More sharing options...
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