madkaw Posted May 16, 2014 Author Share Posted May 16, 2014 (edited) I have ordered another length of fuel rail and I am going to re drill the rail to align with the port holes better. I'm going to shorten all the barb fittings and hope to get total length of rubber lines down to less then 2". I guess Jeff P manifold wasn't a bad idea after all. I just want to get rid of all the hoses across my pretty Mikunis. Hoping to have enough hose between the barb fittings to be able to pinch them shut for syncing. Yes I have read of the filter to modify the signal. MS actually has a set up for ITB speed density tuning. I need to do more reading Need to do more tuning too. Maybe next week I will make it to the dyno Edited May 16, 2014 by madkaw Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 17, 2014 Share Posted May 17, 2014 Pallnet made a nice vacuum log for my HKS ITB's... Quote Link to comment Share on other sites More sharing options...
z240 Posted June 16, 2014 Share Posted June 16, 2014 (edited) On the subject of vacuum logs, makes me wonder how many people know if their intake has shared passages between runners already? I have a Cannon triple manifold for my 44's that has a good 1/2 " hole running through ALL of the shared support casting between every runner, while another Mikuni manifold on the wall has nothing, even between adjacent pairs. It does however have six individual threaded and plugged bosses on top of each runner with a 1/4 or so internal cast hole running down to the ID of each runner just inside the carb mount flange to use as needed. Just a word of caution for those who now are rushing off to make a vacuum log... Edited June 16, 2014 by z240 Quote Link to comment Share on other sites More sharing options...
madkaw Posted June 16, 2014 Author Share Posted June 16, 2014 So you are saying there is an internal passage on every runner accessed how? Quote Link to comment Share on other sites More sharing options...
z240 Posted June 16, 2014 Share Posted June 16, 2014 (edited) Yes, an internal passage. All six runners are joined at the head end (no passage there, just joined), AND with a second roughly round casting just behind the carb flange between all runners. If you look into any runner from the carb end, you see a 1/2"-ish opening about 1" in from the carb flange on both sides of all runners (well, not the first and last...) that connect each adjacent pair. If you wanted to, you could weasel a single piece of wire in there and extend it through the entire manifold. I'll to post a picture to make it any more clear. While this is wonderful to get a nice all-plenum vacuum MAP signal for my 123 ignition dizzy or the brake booster, it does pose challenges for individual carb syncing. Edited June 16, 2014 by z240 Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 17, 2014 Share Posted June 17, 2014 Not on ALL manifolds. SOME have that feature. MANY do not. It makes it a PITA to get individual idle mix right with a balance tube. You need to isolate it when doing individual cylinder idle mix / balancing, and then reconnect when done. Quote Link to comment Share on other sites More sharing options...
madkaw Posted June 20, 2014 Author Share Posted June 20, 2014 Well it seems that my 'studder' during transition has turned into a random issue now along with an erratic idle. The two seem to be tied together, so when my idle gets erratic(way lean on the wideband), I get more lean during transition and cause the studder. So did I really do anything with my bleed pipes that was good? I don't know since the issue is back. Floats pop up in my mind as the culprit. Not sure what else would effect the idle and the transition. These carbs are too clean to have carbon build up on the pilot screws, but I will investigate. I'll pop the tops off tomorrow and start scrutinizing, Quote Link to comment Share on other sites More sharing options...
z240 Posted June 20, 2014 Share Posted June 20, 2014 Erratic = unreliable fuel pump/delivery/float level. Get a gauge on there and see if pressure goes wonky when the problems arise. Quote Link to comment Share on other sites More sharing options...
madkaw Posted June 20, 2014 Author Share Posted June 20, 2014 Well as I suspected my float levels were not same across all carbs. Not too bad off, but I definitely needed to correct the situation. This did NOT correct the erratic throttle. I resynced the carbs with my vacuum log lines pinched off. I noticed when un-pinching the lines my idle got higher(little bit is normal), but seemed also erratic too. Now here's what I'm trying to figure out. With the vacuum log connected I can go down the line and pinch each hose individually to look for vacuum leaks. Nothing happens until I pinch #1 cylinder hose, then the idle drops and seems more even? If I had a leak somewhere in that line, I would think pinching it would do nothing because you would still have vacuum pulling from either side of the hose-right? If the float was wonky, wouldn't it effect both 1&2? I can effect the idle by adjusting just #1 pilot screw in about 3/16 turn. I have not driven the car yet since adjusting floats-stay tuned Quote Link to comment Share on other sites More sharing options...
madkaw Posted June 23, 2014 Author Share Posted June 23, 2014 So I crossed valves off my list- though some were very tight. It made no difference in the way it ran. So I proceeded to pull plugs to do a compression test and 4&5 look black and 6 was headed that way. I had just idled the car for 5 minutes and AFR's didn't indicate that rich, but AFRs weren't steady either. No radical swings though . It seems that I have to turn the pilots out further then normal to get an idle down around 14AFR- at least more then I remember . Now I'm guessing between ignition and carb. 4&5 cylinders tell me it's not just one carb or really not likely carbs-3 looks great. I guess I will still do a compression test to see what it says. Not sure how to troubleshoot the ignition except to try the coils in test mode to see how the spark looks. Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 18, 2014 Author Share Posted July 18, 2014 Anyone explain to me how one half a carb will run rich? I about eliminated my MS as the problem. I ran the car with a dizzy and wires and 4,5 still look way rich. I would assume a bad float would effect both sides of the Mikuni-not just one side. What about fuel pressure? I noticed it was between 3.5 and 4 psi today-could that cause such an issue? I will back off the pressure to an even 3 tomorrow to see if that helps. I know there are many things that can cause a rich mixture, but it seems odd half a carb runs rich. Just trying to get an idea before I start ripping into these carbs again. Quote Link to comment Share on other sites More sharing options...
Leon Posted July 18, 2014 Share Posted July 18, 2014 Possibly an internal leak, such as the starter circuit? My knowledge is based on Webers, I haven't touched Mikunis but if they have similar starter circuit pistons I'd look there. Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 19, 2014 Author Share Posted July 19, 2014 (edited) The only other thing I haven't done to eliminate possibilities is swap carb positions around. I'm going to swap the middle carb with the front carb to see if the issue follows or stays. The starter circuit seems to be functioning normally, but not sure how to eliminate it unless I just tape over the holes after removing the 'lid' of the starter. The best I can tell they are very similiar Leon Edited July 19, 2014 by madkaw Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 26, 2014 Author Share Posted July 26, 2014 Can someone give me suggestions as to why one side of a Mikuni would pull more air then the other? I guess I will pull it off and measure throttle plates. Quote Link to comment Share on other sites More sharing options...
cnwayland Posted March 22, 2015 Share Posted March 22, 2015 Madkaw, I know this is a very old thread, but as I am just getting into the very initial beginning of tuning my 40s after my initial motor break-in today I wanted to post an answer your last question: Can someone give me suggestions as to why one side of a Mikuni would pull more air then the other? 1) Bent throttle plate 2) Twisted throttle shaft Did new emulsion tubes ever get produced? Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 22, 2015 Share Posted March 22, 2015 ^^^ Twisted throttle plate is VERY common. People back the idle speed screw all the way back, and the throttle plates snap shut and get stuck. Next WOT hammer-down you twist the shaft... Quote Link to comment Share on other sites More sharing options...
cnwayland Posted March 26, 2015 Share Posted March 26, 2015 (edited) I'm going to update this post with the current problem I have/had that I'm trying to go about resolving, because I haven't found specific information that relates to it anywhere. I'm copying an e-mail that I sent to Todd @ Wolf Creek, and will add his answers, plus how I am moving forward ~ I was having an extremely difficult time just getting the motor to idle, but I had just completed 20 minutes of new motor break-in. I'd just rebuilt a 1981 280ZX motor I pulled from Pick-n-Pull Richmond. "Todd, Left message this afternoon. Thought I'd email as I'm not always available via phone. This way I can include some images. After trying to get my car to run over the past few days I pulled the 40s off yet again. Rough running without the starter circuit engaged, and then coughing from the carbs off the starter circuit. Couldn't actually get it to idle at all. I few things seemed to be needing changes. 1) When I pulled the carbs off, carb #2 was sending great streams of fuel from the pump when actuating the throttle. The other two, nada. Nothing. I pulled the first carb off and checked the pump body. No rattling present. The other carb the small brass ball actually popped out. I am guessing this is not ideal. They should be able to spray while off the car so long as there is fuel in the float chamber, correct? I think I need two replacements unless you can advise a way to fix what I've got. I wondered if my diaphragms had gone bad also..? The one that sprays makes a nice "squish" sound as the fuel gets primed and sprayed out of the throat. The other two sound dead. 1. Yes, the pump body MUST rattle. That is the check ball and is the only moving part that makes the pump body work. If it doesn't rattle, it doesn't pump. YOU MUST MAKE IT WORK as it is one of the few items no longer available. Squirt carb clean in all holes, bang it on the bench, you won't hurt it. That brass ball goes back into the hole shown in the pix and then gets peened into position. It blocks off that end of the hole so fuel goes the other way. Must be put back and secured. Pump diaphragms may be bad, may as well replace while doing all the other work. 2) Most of my mixture screws look like the following: I thought these tips looks healthy enough, but can you confirm please. 2. Yes, those pilot screws are "screwed" it's not the length that matters, it's the profile of the taper and it should NOT be stepped like that. They are abused and no good. 3) I found the o-ring style insulators I'd gotten from you and think they need to go on. The insulators that came with the Harada intake I'm running look to be potential blocking the brass fittings on the carb body just above the butterflies. They might have not be sealing so great, causing a small leak, leading to my conditions. 3. Yes, probably so, get them on there. Finally, 4) Neither the second or third carb has a vacuum advance pipe. Are these then just openly leaking?? Like a PO just pulled the pipe out? What to do? Is it okay to just devise a way to plug it up. 4. Yes, that is correct. Even though the "hole" appears to be there, it isn't actually drilled thru to the bore, it is only cast into the body to hold the brass pipe but it isn't installed. It is fine and correct, no need for plugging. " Here's where the car is at: L28 E88 head, 280 valves, Rebello mild cam, compression around 10.4:1 Current jetting: 57.5 pilot 190 main air 140 main jet 130 starter 32 venturi Floats set at 12mm Fuel pressure set at 3 PSI ~ Holley Blue Pump & Regulator, running stock hardline return from the FPR (I couldn't get pressure below 14PSI until I connected it). Carbs are deadened. Edited March 26, 2015 by cnwayland Quote Link to comment Share on other sites More sharing options...
cnwayland Posted March 26, 2015 Share Posted March 26, 2015 My additional question to everyone here is: do you have any additional techniques to really free the check ball loose in the pump body? I've been after the two that were seized with carburetor cleaner and a large mallet and have freed them slightly, but in comparison to the one that works well they still 'rattle' less. Quote Link to comment Share on other sites More sharing options...
ryant67 Posted March 26, 2015 Share Posted March 26, 2015 ^^I just cleaned up a really crusty set of 44's I got off ebay. 'Simple Green' degreaser and water, 50/50 mix, in an ultrasonic cleaner. Set the cleaner to go for about 20 minutes or so, with the heater function on. It was pretty remarkable just how much crap came off (and out) of those carb bodies. Might be worth a shot, and it's a handy tool to have for cleaning all sorts of metal items - I got mine for about $70 at Harbor Freight. Pic of one of the carbs that hadn't been cleaned, and one that I had just finished up with. Quote Link to comment Share on other sites More sharing options...
cnwayland Posted March 26, 2015 Share Posted March 26, 2015 ^^ Bought one of those when I originally bought my triples. I returned the ultrasonic cleaner after having better luck with Pine Sol. Maybe it is worth another go now with just the pump bodies. Quote Link to comment Share on other sites More sharing options...
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