inline6 Posted March 28, 2015 Share Posted March 28, 2015 (edited) Well, I did my first ever attempt at tuning on the dyno today. Unfortunately I am baffled by the engine behavior I saw. First, some basics: All floats have been checked, checked again, and triple checked. The last method I used (Honsowetz book) was marking off .826" on a length of wire, removing one jet block per carb, and sticking the wire down the jet block hole. The fuel "jumps" to attach to the rod when it touches. The .826" measurement is from the fuel level to the jet block hole surface. My floats are set correctly within .020" of the specified measurement. Ignition is a Crane Hi 6S and is triggered by a Crane optical trigger in the distributor Distributor is a Nissan Euro unit with a functioning vacuum advance Timing verified to be no more than 34 degrees advance. Initial advance, if it matters is about 17 degrees at "idle speed". Fuel pressure is below 3.5 and above 3.0 psi. Initial jetting was determined by doing mainly half throttle pulls in 3rd and 4th on the street. I attempted full throttle pulls, but the LM-2 would show low 10's AFR when I "dumped" the thottle (even several seconds later). Initial jetting: Main 180 Air 240 Pilot 57.5 Pump 50 Choke 37 I didn't want to be at 10's for extended periods of time. Rather, I figured, I'd be able to find the right combination when I took it to the dyno. So... Listed below are the changes that I made in order to attempt to get the mixture somewhere close. I did all runs in 4th gear. The dyno operator told me that once I was in fourth, to snap it to full throttle and hold it to redline. From my prior experiences, I figured it the AFR would drop down to the low 10's and struggle to do anything... but what the hell. Once in fourth, I was around 2000 and went full throttle. The AFR dove to low to mid 10's. The engine struggled to build RPM. It felt like it was mis-firing ... Eventually, the AFR climbed up and out of the 10 zone... and the engine ran well for a short range of RPM... I'm guessing around 4000-6500 RPM, but RPMs were not increasing very rapidly above there, and I there were a few misfires, so I let out. Unfortunately, my LM-2 plot wasn't any good for this run. The dyno operator told me to make it less rich. Next, I went with: Main 170 Air 230 Pilot 57.5 Pump 50 Choke 37 Once in fourth, I was around 2200 and went full throttle. The AFR dove to low to mid 10's. The engine struggled to build RPM. It felt like it was mis-firing ... Eventually, the AFR climbed up and out of the 10 zone... and the engine ran well for a short range of RPM... I'm guessing around 4k-6k, but rpms were not increasing very rapidly above there. Unfortunately, my LM-2 plot wasn't any good for this run. Given essentially a repeat performance, I was told to make it less rich. Next, I went with this: Main 160 Air 210 Pilot 57.5 Pump 50 Choke 37 Once in fourth, I was around 2200 and went full throttle. The AFR dove to low to mid 10's. The engine struggled to build RPM. It felt like it was mis-firing ... The AFR climbed up and out of the 10 zone... not achieving a 12 AFR until 5150 RPM. The engine ran well for a short range of RPM... Looking at the plot from the LM-2, I'd say 4000-5500k RPM. RPMs were not increasing well above there, and the AFRs were going higher than before... into the 15s, so I let out. We were pretty confused as to why the changes weren't making a bigger difference. In an attempt to try to go too lean, I went with this next: Main 140 Air 210 Pilot 57.5 Pump 50 Choke 37 Once in fourth, I was around 2150 and went full throttle. The AFR dove to low to mid 10's (stayed there about 4 seconds). The engine struggled to build RPM. It felt like it was mis-firing ... The AFR climbed up and out of the 10 zone. As the AFR got into the 11 range, the engine ran better. Looking at the plot from the LM-2, I'd say 2500-5100 RPM, but rpms were slow to build, and the AFRs after 5k going higher than before... well into the 16s, so I let out. Additionally, I note the presense of a midrange bump in AFRs centered at about 2900 RPM (look at seconds 6-10 in the plot) If we were confused before, we were baffled now... as to why the changes hadn't elminated the dive in AFR to 10's when transitioning to full throttle. Because we had tried lowering the main and air jets many times and didn't see the kind of change that we expected, I started thinking that there must be a completely different problem... outside of the main and air jetting. Even though I knew the pumps only are a factor briefly in these running conditions, next I changed the pump nozzles from 50's to 35's to see what would happen. Main 140 Air 210 Pilot 57.5 Pump 35 Choke 37 Once in fourth, I was around 2000 and went full throttle. The AFR dove to low to mid 10's (stayed there about 4.5 seconds). The engine struggled to build RPM. It felt like it was mis-firing ... The AFR climbed up and out of the 10 zone. As the AFR got into the 11 range, the engine ran better. The midrange bump in AFRs is still there and in the same spot (2500-3200 RPM). With the 35 nozzles however, now a lean spike has been introduced when going to full throttle. Continuing with changing something other than main and air jetting, I began to think maybe there is a lack of air flow. Though the air filter and cold air tubing seemed adequate, I thought I would remove the air filter next and just see if it made any difference. Removed K&N air filter Once in fourth, I was around 1800 and went full throttle. The AFR dove to low to mid 10's (stayed there about 4 seconds). The engine struggled to build RPM. It felt like it was mis-firing ... As the AFR got into the 11 range, the engine ran better. Looking at the plot from the LM-2, I'd say 2500-5000 RPM, but rpms were slow to build again. Knowing that AFRs at the high end were going above 15, and seeing no substantial difference with the air filter off, I let out. The same behavior... including the lean spike by the 35 nozzles introduced when going to full throttle. Finally, just to use the remaining time, I did one last desperation attempt to go too lean. Next I ran: Main 130 Air 190 Pilot 57.5 Pump 35 Choke 37 Once in fourth, I was around 2000 and went full throttle. The AFR dove to mid to 10's (for about 2.5 seconds this time). The engine struggled to build RPM. It felt like it was mis-firing ... The AFR climbed rapidly and was hitting 15s before I even got to 3k RPM, so I let out. I'm not sure where to go from here. I'll be studying these plots, my previous tuning attempts, and think about how to proceed. Edited April 2, 2015 by inline6 Quote Link to comment Share on other sites More sharing options...
madkaw Posted March 28, 2015 Share Posted March 28, 2015 Review your engine specs again or put in your signature. Curious of your cam selection and build. Too lazy to search your build Quote Link to comment Share on other sites More sharing options...
gogriz91 Posted March 29, 2015 Share Posted March 29, 2015 Chet Wittel tuned my Mikunis on Thursday and troubleshot some interesting problems. If you know him give him a call, if you don't, PM me and I'll put you in touch with him to see if he has some idea of what might help. Quote Link to comment Share on other sites More sharing options...
inline6 Posted March 29, 2015 Author Share Posted March 29, 2015 Engine is basically a 3.0 stroker... only it is 88 mm bore instead of 89 which makes it a 2.933. Comp ratio is 11.15:1. Running on 93. Cam is big: IntakeSeat duration 320 degrees.050" duration 290 degreesValve lift with zero lash .565"Hot valve lash .015"Net valve lift .550"ExhaustSeat duration 315 degrees.050" duration 274.8 degreesValve lift with zero lash = .565"Hot lash = .015"Net valve lift =.550" Cam currently Advanced 3 degrees (101.5 ICL) Porting and polish done to both the head and intake. Quote Link to comment Share on other sites More sharing options...
madkaw Posted March 29, 2015 Share Posted March 29, 2015 Maybe should have tried a WOT starting at around 2500 or 3000rpm to see if that helped? I thought 180 mains were HUGE , but maybe not for your build. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 29, 2015 Share Posted March 29, 2015 (edited) Why did you change the air corrector at the same time? 140 Main 220 Air Corrector, less acceleration volume or duration... Main choke size should be near right for a power peak around 5,800-6,200. Try changing one variable at a time to affect the area it affects most. Once you are going in the correct direction, then follow with the second item to see the interrelationship between the two. Once you do it like that you will get a feel about what does what, when as later on you will need to go after targeted spots in the RPM/TPS range... If proper, you can go WOT at 1,000 and you will accelerate sloooowly, but your AFR will remain constant through transition, and any fuel shot by your Accel nozzles will definitely be cleared by the time the mains are in.... It will start "pulling" harder at around 3,000 ~ 3,500 and you should be able to hear the acceleration get quicker when your cam "comes on".... AFR's are pig rich, need to be around 11.8~12.5 and closer to 13.8:1 after torque peak. "Shift, Click-Drag, Control, Arrow Down, Down Down..." Edited March 29, 2015 by Tony D Quote Link to comment Share on other sites More sharing options...
inline6 Posted March 29, 2015 Author Share Posted March 29, 2015 (edited) Why did you change the air corrector at the same time? 140 Main 220 Air Corrector, less acceleration volume or duration... Well... Only because I've never come across anyone running mains and air correctors that far apart, I guess. Recently, I came across some guidance that when you are just looking for a starting point, use air correctors that are about 30% higher than the mains. Since I appear to be not even close... I kinda was following that. 140 Main 220 Air Corrector, and move the pump stroke from middle hole to lowest hole... that is what you are suggesting I try? "Shift, Click-Drag, Control, Arrow Down, Down Down..." Electromotive TecGT and TWM throttle body setup with fuel rail, injectors, and even a custom harness for a z car is sitting in a box in my garage... But, I am trying to learn something about these Mikunis... After I struggle with them and live with what I am sure will be lots of compromise, I will switch and I will love fuel injection. Edited March 29, 2015 by inline6 Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 29, 2015 Share Posted March 29, 2015 You may as well just disconnect the accelerator pump. Your engine will (should) experience a lean stumble on tip-in, followed by the jets doing what they should. From there, try the jet you have with the larger corrector. That should give you a quantifiable different fuel curve than what you're now seeing, and from there get one part of your graph correct...then tweak the other variable until it's section of the chart comes in where you want it. Quote Link to comment Share on other sites More sharing options...
madkaw Posted March 29, 2015 Share Posted March 29, 2015 I wouldn't go bigger then 40's on the pumps for now. I think 2000 rpm struggle wouldn't be that out of line. How does the car accelerate starting above that? It seems your cam is waaayy to big to demand power at 2k. Isn't the power band about 4000- 7500 with that cam? Drowning the engine with fuel at 2000 with that cam may be partially fouling plugs and taking a while to burn it off. Quote Link to comment Share on other sites More sharing options...
madkaw Posted March 29, 2015 Share Posted March 29, 2015 I appreciate your endeavour to master the Mikunis. I also have FI in the wings and have megasquirt already wired in. Carbs can be a bitch Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 29, 2015 Share Posted March 29, 2015 I appreciate your endeavour to master the Mikunis. I also have FI in the wings and have megasquirt already wired in. Carbs can be a bitch No, now...c'mon! "Carbs are easy!" Says the guys on the Internet that pontificate and who have never walked this road! Anybody saying "carbs are easy" has never tuned them for total performance. It's always "it works" or "it runs fine" heck, they may even say it's run that way for XX Years "without any problems".... But as you see, it runs fine rich. They even may make a bit more torque on the bottom end...somewhàt. But compared to a proper crisp-clean & borderline lean response, it's just mushy performance that they find acceptable. It takes work, and experience comes through doing. The biggest bit of advice comes in only changing one jet or variable at a time and observing for yourself what it affects, and drawing your deductions on crossover and how the parts interact. Generally, I shy away from specific jet numbers... Learning the interaction becomes more valuable later on if something gets clogged! Quote Link to comment Share on other sites More sharing options...
inline6 Posted April 5, 2015 Author Share Posted April 5, 2015 (edited) Well... I found a big problem... Last Sunday, I decided to verify that the vacuum advance was working correctly. I disconnected it and ran the engine with a timing light, and was surprised to see very little movement. I decided to take apart, clean and lube the appropriate areas of the advance mechanisms in the distributor, as well as verify the vacuum advance was working. Afterwards, I was amazed to see that it did make a difference - I got a few more degrees of ignition advance from it. I reset the timing to only provide a max of ~ 34 degrees BTDC. After doing this, I took the car for a short drive. The engine was making a fair amount of noise... It had been since I took it to the dyno, and while I had been trying to say it was just my imagination, I decided it really wasn't. It really was making a lot of noise and it sounded like it was coming from the valve train. I checked the cam and rockers... everything looked great. I checked my valve lash, and found several to be .4 mm which is like 16 thou, so I tightened all of them up to .012". When I started the car, the noise seemed even louder, if that is possible. I ran it less than a minute. And, I shut it down in disgust. Not knowing what was messed up, I decided to do a leak down test. I got percentage loss for 1-6 of: 4,5,3,2,2,4. I then tried to see inside the spark plug holes to examine the bore walls. I saw a vertical mark or two, so I decided to buy a "borescope" and take a detailed look inside the bores. That cam on Thursday, and with it I was able to see quite a bit more. And what I did see looked like shiny have moons in the exhaust valve reliefs on the tops of about 3 of the pistons! That got me thinking... valves hitting pistons would cause LOTS of noise. And just before I took the car to the dyno, I had removed the Kameari cam chain tensioner to check into some unusual noise it seemed to be making. It turned out to that it just wasn't quite tight enough - there was nothing wrong with it. But, maybe I screwed up the cam timing when I took it off? A check of my cam timing was next. I was able to find the time to do that today... and sure enough, it was wrong. My timing chain had slipped one tooth on the crank sprocket when I was messing with it. That retarded the cam 18 degrees, (20 tooth sprocket - 360 degrees), however my adjustable cam gear is set advanced by 3 degrees. So, the net amount it was retarded was 15 degrees. And in that state, I went to the dyno last Saturday! Again using my Borescope, I ran the camera down the front cover of the engine. I was able to jiggle the chain to change it's position on the crank shaft and verify it with the camera. With the marked lower and upper timing chain links aligned properly with the lower sprocket and the cam gear, I started the engine. And the "clacking" - the noise was gone. Go figure, huh? I took the car for a brief spin tonight and MAAAAAN, what a difference. The power is soooo much better. And, I am not sure why, but the AFR's are much improved at lower RPM and heavy throttle inputs. I even tried what before would produce 10's, and could not! Next tuning session will be interesting. When I got back, I did another leak down test. This time the engine was warmer, and from 1 through 6, I got percentage losses of: 3,4,3,4,2,3. Now, I will get back to tuning. Hopefully, no problems crop up in the coming days or weeks related to the valves hitting the pistons. We shall see. Edited April 5, 2015 by inline6 Quote Link to comment Share on other sites More sharing options...
TimZ Posted April 5, 2015 Share Posted April 5, 2015 Sounds like you got lucky there! Regardless, Tony's advice on just changing one thing at a time is still the way to go. Quote Link to comment Share on other sites More sharing options...
Leon Posted April 5, 2015 Share Posted April 5, 2015 Holy cow, good catch. You got seriously lucky! I don't know how your valves didn't get bent, as your leak down numbers indicate that everything's okay. Quote Link to comment Share on other sites More sharing options...
madkaw Posted April 5, 2015 Share Posted April 5, 2015 That's a lot to be off with a big cam. I guess take the good with the bad here. I always wonder why more folks don't degree their cams since it has a big effect on performance. Quote Link to comment Share on other sites More sharing options...
BigC Posted May 13, 2015 Share Posted May 13, 2015 Like TonyD said. When tuning only change one thing at a time. Some of those lists you showed are main, air, pump, and pilot in one step! Wow you Will never tune doing that. When I switched from Webers to Mikunis I talked to Todd W. Sent him my engine, cam specs etc because my engine was more than the guy I got them from. I have a 2.9L, p+p E31 .510/300 cam and about 10.8 compression. 39mm choke 155 main 190air 60piot 50 pump middle hole 35 degrees total adv. Now haven't got to the dyno yet but I put in a wideband rather than just seat test and plug reading so far 14-15 idle, 13-13.5 light cruise and 11-12 WOT right to 7000. No stumble, no bog runs real nice. I also run Todd's stacks, short SK manifold and I'm at 1650 feet alt. Most of the 3.0L or bigger motors I've seen dyno sheets on with your cam specs run 39 or 41 chokes you might want to examine that. Quote Link to comment Share on other sites More sharing options...
inline6 Posted May 13, 2015 Author Share Posted May 13, 2015 Like TonyD said. When tuning only change one thing at a time. Some of those lists you showed are main, air, pump, and pilot in one step! Wow you Will never tune doing that. When I switched from Webers to Mikunis I talked to Todd W. Sent him my engine, cam specs etc because my engine was more than the guy I got them from. I have a 2.9L, p+p E31 .510/300 cam and about 10.8 compression. 39mm choke 155 main 190air 60piot 50 pump middle hole 35 degrees total adv. Now haven't got to the dyno yet but I put in a wideband rather than just seat test and plug reading so far 14-15 idle, 13-13.5 light cruise and 11-12 WOT right to 7000. No stumble, no bog runs real nice. I also run Todd's stacks, short SK manifold and I'm at 1650 feet alt. Most of the 3.0L or bigger motors I've seen dyno sheets on with your cam specs run 39 or 41 chokes you might want to examine that. Indeed, the 37 chokes could be too small. Regarding one change at at time... I have become learned. Separate threads occurred... here is the one that I am most current with. Since I already own a TWM and Electromotive fuel injection setup, spending money on new (or machining of some 34's I already have) chokes is not too likely. The TWM throttle bodies are 45's... with no chokes. Quote Link to comment Share on other sites More sharing options...
madkaw Posted May 13, 2015 Share Posted May 13, 2015 So he's running 155 mains with almost the same engine. It seems you have another issue or you have chased your tale to 190 mains. Not critizing, but your jetting has seemed way off for your build. 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.