ryant67 Posted March 26, 2015 Share Posted March 26, 2015 It does seem to do a great job of agitating grime off in those impossible to reach places. I've also read of people soaking parts in a can of carb dip with an orbital hand sander attached to the can - simulates what the ultrasonic cleaner does, but at nowhere near so high a frequency. Quote Link to comment Share on other sites More sharing options...
madkaw Posted March 30, 2015 Author Share Posted March 30, 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: 1) Bent throttle plate 2) Twisted throttle shaft Did new emulsion tubes ever get produced? Can someone describe a method to diagnose possible twisted shaft of bent plate? I looked at this closely and cannot detect a difference in bores with the naked eye. Would an issue bad enough to effect idle or airflow be detectable by just eyeballing or is there a method of measuring the opening in a round hole? The throttles operate smoothly and with plates closed completely they don't seem to stick, but I realize there is no vacuum . Quote Link to comment Share on other sites More sharing options...
Leon Posted March 30, 2015 Share Posted March 30, 2015 Can someone describe a method to diagnose possible twisted shaft of bent plate? I looked at this closely and cannot detect a difference in bores with the naked eye. Would an issue bad enough to effect idle or airflow be detectable by just eyeballing or is there a method of measuring the opening in a round hole? The throttles operate smoothly and with plates closed completely they don't seem to stick, but I realize there is no vacuum . How about a thin feeler gauge between closed butterfly and throttle bore? Quote Link to comment Share on other sites More sharing options...
madkaw Posted March 30, 2015 Author Share Posted March 30, 2015 Not sure how well a flat blade feeler gauge will work on a round bore. Maybe it would be precise enough. You have to measure the gap at a very specific point in the bore because the opening would be tapered to the pivot point. I thought maybe a drill bit or something round and small at the bottom of the bore maybe? Quote Link to comment Share on other sites More sharing options...
ryant67 Posted March 30, 2015 Share Posted March 30, 2015 Is the old light-inspection method not capable enough for this task? Just hold the carb up to sunlight or a good lamp, and look down the barrel with the butterflies closed. In a perfect world, no light should leak through around the butterflies - and if a tiny amount does, it should at least be equal on both side. Outside of the butterfly, the only other things that could be an issue are the little rubber seals around the throttle shaft on either side of the butterfly. They can get pretty brittle with age, and may not be sealing properly. Some pics of said rubber seal from my "practice" Mikuni... Quote Link to comment Share on other sites More sharing options...
madkaw Posted March 30, 2015 Author Share Posted March 30, 2015 Did that test which I thought would be conclusive enough, but asking if there were any other methods. Quote Link to comment Share on other sites More sharing options...
Leon Posted March 31, 2015 Share Posted March 31, 2015 Not sure how well a flat blade feeler gauge will work on a round bore. Maybe it would be precise enough. You have to measure the gap at a very specific point in the bore because the opening would be tapered to the pivot point. I thought maybe a drill bit or something round and small at the bottom of the bore maybe? I was thinking more along the lines of thin (~0.001") brass shim stock. Thin brass is pliable enough to work in a round bore. You can get creative and use thin pieces of paper, etc. This works well for setting butterflies as well: put shim stock around the butterfly and tighten screws. The flashlight method should work well as far as showing differences between bores. Quote Link to comment Share on other sites More sharing options...
cnwayland Posted April 2, 2015 Share Posted April 2, 2015 So jumping back in here, I got all of the accel pumps operating as they should. Beautiful streams of fuel out of all throats. But I still nearly drown the motor every time I apply over 15-20% throttle. I emailed back and forth with Todd@Wolf about the issue and I ended up reverting to my 40 pump nozzle and adjusting the cotter-pin to the last hole on the accel pump plunger. No major conclusive feedback. I was beginning to think tonight after putting the project away that I may have fouled my plugs, but my idle is solid and that wouldn't make sense at all. I think I have stop resisting the urge to get an AFR after all of this guessing which is just exhausting. Watanabe's are supposed to be here tomorrow so it's going to be a shame if I can only drive up to 2k RPM in all gears. Quote Link to comment Share on other sites More sharing options...
Leon Posted April 2, 2015 Share Posted April 2, 2015 So jumping back in here, I got all of the accel pumps operating as they should. Beautiful streams of fuel out of all throats. But I still nearly drown the motor every time I apply over 15-20% throttle. I emailed back and forth with Todd@Wolf about the issue and I ended up reverting to my 40 pump nozzle and adjusting the cotter-pin to the last hole on the accel pump plunger. No major conclusive feedback. I was beginning to think tonight after putting the project away that I may have fouled my plugs, but my idle is solid and that wouldn't make sense at all. I think I have stop resisting the urge to get an AFR after all of this guessing which is just exhausting. Watanabe's are supposed to be here tomorrow so it's going to be a shame if I can only drive up to 2k RPM in all gears. Cam, at the very least check your plugs. I'd replace them if they're suspect as fouled plugs can cause a lot of heartache. The spark takes the path of least resistance. The more fuel-air mixture in the cylinder, the more resistance there is to the spark jumping and the more likely it is to short through carbon deposits. Wats are going to be sweet! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 2, 2015 Share Posted April 2, 2015 So jumping back in here, I got all of the accel pumps operating as they should. Beautiful streams of fuel out of all throats. But I still nearly drown the motor every time I apply over 15-20% throttle. I emailed back and forth with Todd@Wolf about the issue and I ended up reverting to my 40 pump nozzle and adjusting the cotter-pin to the last hole on the accel pump plunger. No major conclusive feedback. I was beginning to think tonight after putting the project away that I may have fouled my plugs, but my idle is solid and that wouldn't make sense at all. I think I have stop resisting the urge to get an AFR after all of this guessing which is just exhausting. Watanabe's are supposed to be here tomorrow so it's going to be a shame if I can only drive up to 2k RPM in all gears. My suggestion is to go bigger on the pilots. There are a lot of people who have had this same basic problem, and many of us tried bigger pump nozzles first. When I went bigger on the pump nozzles it made it worse. Bigger pilots made the stumble a lot better in my case and I was thinking of going down on the venturi size from 37 to 34. You're already smaller with a pretty similar build, so I would think that with any luck you can go bigger on the pilots, maybe even smaller on the pump nozzles and get things under control. Quote Link to comment Share on other sites More sharing options...
cnwayland Posted April 2, 2015 Share Posted April 2, 2015 (edited) Okay, so I tore down the #1 carburetor and found that the pump body had disintegrated, leaving the check ball floating in the bottom of the float chamber. When I ultra-sonic'd the ass'y, the brass bushings fell apart, so I had to JB weld the small brass peened fitting back in. I didn't however, JB weld the brass bushing seen below. More work! For anyone wondering what the internal pump body ass'y looks like (the small washer is part of the accelerator pump plunger/rod). However/unfortunately, I'm still pretty sure that this wasn't the cause of major hesitation (although it certainly wasn't helping at all. My suggestion is to go bigger on the pilots. There are a lot of people who have had this same basic problem, and many of us tried bigger pump nozzles first. When I went bigger on the pump nozzles it made it worse. Bigger pilots made the stumble a lot better in my case and I was thinking of going down on the venturi size from 37 to 34. You're already smaller with a pretty similar build, so I would think that with any luck you can go bigger on the pilots, maybe even smaller on the pump nozzles and get things under control. @JMortensen ~ Smaller than 40's on the pump nozzle? Pilots up from 57.5 to 60 ~ I believe the jetting parts list notates that they increase in increments of 5... not sure if that's .5 Cam, at the very least check your plugs. I'd replace them if they're suspect as fouled plugs can cause a lot of heartache. The spark takes the path of least resistance. The more fuel-air mixture in the cylinder, the more resistance there is to the spark jumping and the more likely it is to short through carbon deposits. Wats are going to be sweet! Cylinder 1 plug = wet... Regarding the Wats being sweet... They are. Trying to not worry about damaging my newly built motor with all of this rich-running carb-tuning. ~C Edited April 8, 2015 by cnwayland Quote Link to comment Share on other sites More sharing options...
madkaw Posted April 3, 2015 Author Share Posted April 3, 2015 I believe Jon was saying that in most cases 40 pump nozzles are plenty big enough for accelerating, but the pilot jets cam help a lot with hesitation. Go bigger on the pilots before messing with the pumps. If you read this thread you will read that I tried many options to cure transition issues. The changing of pump sizes and setting did nothing. Now if yours are not working then that's a different story. Quote Link to comment Share on other sites More sharing options...
cnwayland Posted April 3, 2015 Share Posted April 3, 2015 (edited) After going back into my bag of Mikuni leftovers.. I found the old pilots. 55's. Trying to buy 60's, 62.5's, and 65's (up from 57.5's) ~ At this rate I'll just buy a few more 40s for parts... Edited April 8, 2015 by cnwayland Quote Link to comment Share on other sites More sharing options...
madkaw Posted April 3, 2015 Author Share Posted April 3, 2015 I have a complete set myself:) Quote Link to comment Share on other sites More sharing options...
cnwayland Posted April 3, 2015 Share Posted April 3, 2015 I have a complete set myself:) If only you were in Cali! Quote Link to comment Share on other sites More sharing options...
cnwayland Posted April 10, 2015 Share Posted April 10, 2015 (edited) An update: I found a vacuum leak. Small, but detectible with brake cleaner from the spark-plug side of the motor. The culprit was the aforementioned o-ring insulators. On my Harada intake, the o-ring slips just BARELY outside the intake mounting surface, creating a small leak which I am presume at WOT would cause serious difficulties. It just never ceases to amaze me how quickly I turn to the most complex issues when the solution is stupid-simple (i.e. thinking my 5-speed transmission was crap when I had the 4-speed shift lever installed... ). In the process of removing the carburetors yet again I replaced my Taylor plug wires with the blue NGKs I used to run. They just seemed to be something funky about the Taylor wires and she feels more steady after swapping them out. As tuning continues I've come across a few questions/statements I'd like to ask/pose to you folks: 1) Recurving distributors: the 280zx distributor swap was probably the first major upgrade I performed on my motor. Even at 16 degrees I get light pinging under WOT. I backed it down to around 14 but apparently with my compression and cam I'm supposed to be up around 18 degrees. To me, this sounds like a curve issue, yes? What distributors have been successful with your Mikuni setups? 2) After discussing with Dave Rebello the fact that my venturis are significantly undersized for my motor (32s), I'm curious if I could potentially run an open throated (without large venturi) 40's. I've heard of people with race motors doing this and wanted to know if anyone has direct experience doing so. Leon, you'd mentioned that they'd be easier to tune with undersized venturis. What is the reasoning behind that? I've found a local who says he has "bundles and tons" of Mikuni PHH jets. I'm hoping to pick them up this evening to have on hand for a serious tuning session. Edited April 11, 2015 by cnwayland Quote Link to comment Share on other sites More sharing options...
Leon Posted April 11, 2015 Share Posted April 11, 2015 Smaller venturis give a stronger vacuum signal. The mains will kick on sooner and thus help with throttle transition/hesitation issues. With the right jetting, you should be able to make bigger venturis (36-38mm) work just fine though. Quote Link to comment Share on other sites More sharing options...
cnwayland Posted April 27, 2015 Share Posted April 27, 2015 (edited) Was at Rebello Friday. Here's my quick update and download of what I learned. But upping the pilot jet size (I'd gotten up to 80) I was masking the issue I was having with what were essentially under-active accelerator pumps. I had 40 pump nozzles all the way across and the 80 pilot jet was pouring fuel through the motor, so on my 1 1/2 hour drive down to Antioch I literally watched the gas gauge fall. Rebello used a lathe to open the 32 venturis up to 35, bent a retaining spring inside the 280ZX distributor to manually recurve/allow less advance, twisted one of the throttle shafts that was causing the Mikunis to go out-of-sync, and then went back to a 65 PILOT (mostly for fuel mileage on the way home - this being on the leanest side of tuning), 150 main jet and retained the 190 main air. All in all, I think the most useful part of the day was getting to test-drive a few jet settings with Dave (who is just as nice as can be and a wealth of great insight) who in just a few words was able to summarize what was happening. I also have a great kinesthetic reference for what in-sync carbs feels like, versus going just off of the syncrometer. Highly recommend Rebello to anyone, anywhere. Edited April 27, 2015 by cnwayland Quote Link to comment Share on other sites More sharing options...
madkaw Posted April 27, 2015 Author Share Posted April 27, 2015 To keep things correct - you ended up with 65 pilots, not 65 pump Jets. Interesting to know you can turn down the venturies like that- good info. Quote Link to comment Share on other sites More sharing options...
cnwayland Posted April 27, 2015 Share Posted April 27, 2015 @madkaw, thanks. Corrected that info. Also, forgot to mention moving from the 2nd to 3rd mark on the cam sprocket. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.