Just started playing with Innovate LM-2 on Mikuni 44 2.9L stroker

[inline6]

I got my new engine fired up last Sunday.  Instead of getting the LM2 set up right away, I was excited to get it started for the first time and check the usual basic stuff... for leaks and such.  After that part went ok, I wanted to play with it a bit just to see if I could get it idling alright.  I tried the few pilot jets I have in my inventory.  Started with 60's, went to 55's, then went to 52.5's.  With each, within a few minutes, my clothes and hair would stink...  (car is in the garage with the door completely open while doing this and I let it air out after these episodes - so I am fairly certain I won't die from it...   )  There is no smoke to speak of, but man is it running rich.  Anyway, the 52.5's are the smallest pilot jets I've got currently, so I have those in there and dialed the pilot screws in to about 1/4 to 1/2 turn out... and it still won't idle without throttle, but it doesn't die as fast as with the other sizes when I close the throttle plates completely.  

 

By this point, I am fairly certain that it is exceedingly rich, and I don't have any smaller jets to try, so I brought out the LM2 to start playing with it.  I figured I'd hook it up and get confirmation that I'm running stinky dog rich.  Tonight, I proceeded to read through the instructions, and the online manual.  And I learned a couple of things I wish I had known before now - clearly I should have looked at this stuff before firing up the engine...

 

First, it warns to never run the engine with the oxygen sensor installed in the exhaust pipe and not hooked up to the 12 volt power supply (that heats it up) or the 02 sensor will be damaged.  Oops.      Before the first start on Sunday, I plugged the 02 bung in the exhaust with... the oxygen sensor that cam with the LM2.     So much for that.  Who knows if I have damaged it?  I've started it about 5 times and run it for a collective 30 minutes perhaps - running exceedingly rich in each instance...  I guess, I'll just have to try to use it and see if it "works" at this point.  

 

Second thing is more minor, but it is pretty obvious it would be an issue... the manual warns of having absolutely no exhaust leaks or the readings will be inaccurate (leaner than should be).  The band clamps I am using on the exhaust joints are not quite sealing a 100% yet.  I have used band clamps in the past and have found that they have to be modified by hand to seal completely - they just don't seal 100% right out of the box.  So, that is next on my "to do" list before anything else.  

 

Then I have to remove the O2 sensor from the exhaust pipe and "calibrate" it in open air... Then, I can get down to trying to actually use the thing.  Judging by what I read through in the manual tonight, it looks like I have a lot of learning ahead of me.      

Edited February 10, 2013 by inline6

[RB26powered74zcar]

It shouldn't give bad readings if the leaks are at least 18" after after the sensor. I ran mine w/o power before too, and I got lucky it wasn't damaged. The main thing is don't use any thing on it to try and clean it (although I was told by Klaus, the inventor, to use a propane torch).

 

I had my current sensor running my LM-1 for over 5 years, and it still works perfect.  

Have fun with it. They are great tools...

[JMortensen]

Run your pilots 1 turn out. If you need more pilot, change the jet rather than adjusting the screws. There have been some pretty good threads on Mikuni tuning recently. Search and you'll find them. 

[madkaw]

Are you sure you have the floats dead nuts?

It would seem that you could get that big 2.9 to run fairly close with the 52.'s. I know it has a lot to do with cams , but I run 70's with my 2.5

No smoke and smells like a carbed motor in the garage-umm-yep. Not trying to a smart ass, but I think it is hard to judge anything that way. Not sure you will be able to idle a Mikuni fueled 2.9 in the garage without stinking a bit.

Like Jon said, turn the pilots out a turn and see what your LM2 says.

What's the condition of the carbs-especially the pilot screws?

Hopefully your gauge will be okay. I know for a fact that a blown HG kills the sensor. It will probably act erratic if it is bad. 

[madkaw]

I remember reading your other thread. I think you need to nail down your fuel pump/regulator issue first. As I have read many times on this site, the Mikuni's are very sensitive to fuel pressure.

[inline6]

I remember reading your other thread. I think you need to nail down your fuel pump/regulator issue first. As I have read many times on this site, the Mikuni's are very sensitive to fuel pressure.

 

Yep.  I addressed that before touching the pilot jets again.  Needle on the gauge which is on one of the regulator ports is bouncing between 2.8ish and 3.5ish now... hoping that the accurate reading is in the middle of that range.

 

Are you sure you have the floats dead nuts?

It would seem that you could get that big 2.9 to run fairly close with the 52.'s. I know it has a lot to do with cams , but I run 70's with my 2.5

No smoke and smells like a carbed motor in the garage-umm-yep. Not trying to a smart ass, but I think it is hard to judge anything that way. Not sure you will be able to idle a Mikuni fueled 2.9 in the garage without stinking a bit.

Like Jon said, turn the pilots out a turn and see what your LM2 says.

What's the condition of the carbs-especially the pilot screws?

Hopefully your gauge will be okay. I know for a fact that a blown HG kills the sensor. It will probably act erratic if it is bad. 

 

I am not sure I have the floats set 100% perfect.  The way I set them was to trim and sand a nail to the right length, then use that as a gauge for setting the float lever distance from the float cover.  I put the nail in position with needle nose pliers, seat the float assembly against it, and then blow (with my mouth) through the fuel inlet.  I consider it set correctly when no air gets by the needle and seat assembly.  This was done while the carbs were in hand many months ago - they were not on the car.  Two of the carbs are essentially new, and the third may be a touch older, but is visibly in the same excellent condition.  I totally rebuilt that one with a rebuild kit.  Everything is tight, sealed, nice.  If I confirm with the LM2 that it is still crazy rich, and the 45 pilots I have on order don't show marked improvement, I'll revisit the float levels.

 

Run your pilots 1 turn out. If you need more pilot, change the jet rather than adjusting the screws. There have been some pretty good threads on Mikuni tuning recently. Search and you'll find them. 

 

The only reason I turned the pilot screws in that far:  I only have 4 sets of pilot jets in my inventory - 52.5, 55, 57.5 and 60's.  Since, with the garage door open, my clothes and hair would reek after running it for 10 minutes with both the 60's and 55's, I hypothesized it is running absurdly rich.  Honsewetz says in the How to Hot Rod your Nissan book start at 1.5 turns out and that for each turn you have to go in, you need to go down one jet size and also the converse of this (I'm paraphrasing).  So, I put in the 52.5's - the smallest in my inventory.  then, I set the screws at 1.5 turns out and started it.  It still wouldn't idle but didn't die quite as fast as with the 60's or the 55's.  So, I turned in the pilot screws one turn, and tried again, hoping that I could at least discern some improvement - to give me some evidence I was on the right track.  There seemed to be slight improvement. I turned them in one more quarter... leaving them basically 1/4 turn out at this point.  That seemed to help a tiny bit more.  

 

Since I had no smaller jets to try and the screws essentially couldn't be turned in any more, I finally went and grabbed the LM2 off the storage shelf.  I wanted to test my hypothesis that it was indeed running really rich.  Then I got bogged down in reading the manual and the rest is detailed in my other post.  

 

I pulled the O2 sensor from the pipe tonight, and calibrated it per the instructions - in open air.  It reacts to exhaling on it, so hopefully that is a sign that it isn't damaged.  We'll see I guess.

 

Thanks very much for the input.  Between that and searching and reading the manual and some experimentation, I'm sure I'll have it running well soon.

Edited February 8, 2013 by inline6

[madkaw]

Might want to look at this thread I started over at Classic. I had many phone conversations with Todd at Wolfcreek in the process of working on my 40's. He was very specific about float settings-down to the mm.

Todd is very knowledgable, but doesn't like his time wasted. So if you plan on calling-better have a game plan and know your Mikuni parts.

 

http://www.classiczcars.com/forums/carburetor-systems-s30/45836-triple-mikuni-thread.html

[inline6]

I had some time today to work on it and made some good progress.  First I updated the firmware on the LM2.  The instructions weren't great.  Basically, what you need to do is go to the Innovate site and see what version of firmware is available - that latest, of course.  You download that file to your laptop.  Then you follow the instructions in the manual to get the LM2 into boot mode.  Then you fire up LM Programmer, which is the software for the LM2.  Then you click the button to "update firmware", select the file that you downloaded, and wait for it to update.  Do it in that order, and you'll have no issues.

 

Now, on to the tuning.  I fired the engine up and got it up to operating temp.  It still wouldn't idle without some throttle of course.  That is pretty much where we left off.  This time, I checked the fuel gauge with the engine running and it was showing something less than 3 lbs.  The needle wasn't bouncing as much... so I undid the lock nut, adjusted it up between 3 and 3.5 and tightened the lock nut.  

 

So, picking up where I left off... except now I could read the AFR and it was showing between 20 and 30 when I would let go of the throttle for brief instances.  Whenever the engine was about to die, I'd open the throttle a bit and keep it alive, and the AFR would drop down to around 13-15.  With this info, I started playing with the pilot screws again - backing them out to see what would happen with the AFR.  Interestingly, when I backed the screws out (they were at 1/4 turn out) the AFR dropped to the high teens.  So, I backed them out some more. Then I was around 16.  Then some more... 13. But it STILL wouldn't idle. 

 

It was at this point that I turned off the engine and pulled out the Mikuni manual, again.  I was thinking to myself "how could the AFR be that close to the right ratio, and the engine still won't idle?" and "you're supposed to be able to get it to idle without using throttle screws...".  Well, I happened to turn right the page in the manual with the instructions on setting the idle speed.  And what do you know?  It says right there "turn the throttle screws in until they touch the lever, then turn about one turn".     I thought, one turn on the throttle is about all I need to get this thing to idle.  And something else I had been thinking about clicked as well.  I was thinking that you were supposed to get it to idle with just the pilot screws, but if that was the case, there would be absolutely no need for the throttle screws.  Clearly they were there for a reason.  So, I screwed them in until they touched the lever, and then 1 full turn.  then I fired it up again and used the UNI SYN to check carb synchronization.  A few little adjustments to each throttle screw and the carbs were in sync and the engine was idling at 1000 RPM.  Then I went back to the pilot screws.  The AFR was close.  At this point, I stopped turning the screws 1/4 turns and went to literally 1/16 turns.  Doing this, I was able to get the AFR to around 14.4 to 15.0, with much of the time an indicated 14.6... 

 

Just a side note, there is a reason for the really fine pitch of the threads on the pilot screws.  1/2 turn on the screws was moving the AFR from around 16 down to 13.  So, keep that in mind.

 

So, here is a video - post changes...  I've got the idle set at 800-850 here:

 

Edited February 10, 2013 by inline6

[Tony D]

EFI idles via throttle bypass... Carbs need to be cracked off closed, or have a hole drilled in the throttle plate...

[inline6]

I decided to pull the covers off and double check the floats, to eliminate being unsure about that.  On thing I didn't pay much attention to last time was making sure that each float in the carb was set.  When I pulled them off and checked each one in each carb, I did find one where the floats were different levels - out maybe as much as 2 mm.  

 

So, now that I am confident the float levels are correct, next step will be to fire it up and adjust the pilot screws as necessary to fix any change in mixture the float adjustment caused.  Then, I think I will try to record some data.  

 

From just driving it around and watching the AFR, it runs ok at small throttle openings.  The more I open the throttle, the worse it seems to run.  For example, giving it full throttle in a taller gear, like third, at say, 45 MPH, the AFR quickly nose dives 14... 13... 12... 11... 10... 9 and at 9 the engine actually starts misfiring.  I don't have a lot of main fuel jets in my inventory, but my guess at this point is the 170's in there are too big.  Will need to see if the float adjustments changed any of that before I change anything else.

[madkaw]

170's are big.

What accelerator pumps are you running?

What's your ignition timing set at?

It will be hard to dial in those carbs doing hard tip-ins at lower rpms.

Dial in your mains above 3500rpm - don't do a hard WOT until you are above 3500.

 

Hard tip-ins on my motor at low rpms show rich AFR's also, but above 3500 they are perfect.

 

[inline6]

170's are big. What accelerator pumps are you running? What's your ignition timing set at? It will be hard to dial in those carbs doing hard tip-ins at lower rpms. Dial in your mains above 3500rpm - don't do a hard WOT until you are above 3500. Hard tip-ins on my motor at low rpms show rich AFR's also, but above 3500 they are perfect.

 

Thanks for the advice.  The pump jets are 45's.  I have an OEM, european distributor (single points instead of dual and possibly a difference advance curve than US spec - and of course, I have replace the points with the optical pickup for the Crane HI-6 ignition) and I have the initial ignition setting at 17* BTDC.  On my last motor, total advance was about 36* and it was all in at something less than 3k rpm - haven't checked that with this motor, but it should be identical.

 

I am confused by the "Setting of Carburetor Main System with Running Test Alone" section in my Mikuni manual.  It says "After warming up the engine, bring the engine revolutions up to the maximum rpm through rapid acceleration from around 1,000 rpm."  I can't tell if that description is just of just blipping the throttle when the car is stationary, or while driving under load.  I can discern nothing really when blipping the throttle heavily.  The throttle response is good and the engine revs instantly and high.  I don't want to rev it past 6k yet, as the engine only have about 100 miles on it.  Thus, the reason I did a road test and was watching the AFR under various instances.  

 

I guess I don't need to make sense of what the manual says since I have the LM2.  My plan is to change the main jets lower and then go see what the AFR is with the throttle open more than 20% (to get out of the pilot circuit) and at some RPM that should be sufficiently high as to require operation of the Main circuit.  Recording several pulls from 40 to 80 in 3rd gear with half-plus throttle application should do it.  

[madkaw]

I suggested hard tip ins above 3500 to be above the pilot circuit, so you can read AFRS on the main circuit.

What main air jets are you running? Too small of main airs might be bringing the mains in too early.

[inline6]

I suggested hard tip ins above 3500 to be above the pilot circuit, so you can read AFRS on the main circuit. What main air jets are you running? Too small of main airs might be bringing the mains in too early.

 

I currently have 210 air correction jets installed.  So, 170 main, 210 air, 55 pilot, and 45 pump.  

 

Today, I drove the car on the interstate some.  I did a couple of downshifts to 4th to bring the revs up above 3500, let it stabilize, then squeezed deep into the throttle - not fast and not full throttle.  I typically held it there for about 4 or 5 seconds at a time.  At the beginning of that 4 or 5 seconds, the AFR would drop down into the 10's and then as rpms would build, AFR would climb with also.  In the back half or last part of the 4 or 5 seconds the car would start pulling hard and I could see the AFR was around high 12's, low 13's.   

 

The above is really quite different than from a few nights ago, and nothing really has changed with jetting.  I think the float adjustments caused a noticeable difference.

 

I've got the pilot screws turned out 1 and 3/4 turns exactly right now.  I'm thinking about going one size larger on the pilots because the Honsowetz book says to shoot for 1.5 turns.  I've got 55's in there right now.  Driving around with low throttle applications, here is what I am seeing, generally, in the following three situations:

 

• steady state on flat surface - generally seeing high 14's low to mid 15's
• climbing a slight hill where a small amount of throttle is needed - generally seeing 16's and briefly into the low 17's... no hesitation when this is happening.
• down hill with no throttle at all - generally much like at idle in the 14's and down into the 13's some if I remember correctly

[madkaw]

Doesn't sound like you are far off. My measly 2.4 runs about the same AFR's at steady cruise and leans a bit just like yours during slight elevations(slight loading). My car seems to like this pilot arrangement for cruise  and you'll probably see some decent MPG running those AFR's. I'd leave the pilots alone-this isn't giving you rich AFR's-that's for sure.

 

Your dealing with a fresh engine that you can't hammer on -which makes it tough to dial things in.

Also, cam and  acc pumps has a lot to do with this.  45's shoot a ton of fuel in there, you might consider smaller like 40's.

Haven't read your whole build, but a large cam won't want to burn all that fuel down at the lower rpms. 

[madkaw]

Good thread

 

http://forums.hybridz.org/topic/106649-triple-mikuni-help/?hl=triple mikuni help

[Tony D]

Two things:

Your AFR if not pump squirted should remain stable on the main circuit as RPMs rise, if its leaning out it MAY be your fuel pump is not keeping up. WATCH YOUR FUEL PRESSURE! Even my 70RWHP car was experiencing Fuel feed issues! After fixing the regulator and return setup to backpressure regulation, I picked up HP and my AFR's stayed steady under sustained main jet load.

 

One thing I usually point out to most people are that the mains in our 300HP L28 Bonneville car were 135's.

 

You are probably one or two jet sizes large...but make sure you have unchanging fuel pressure at higher RPM's, if it's dropping then so is your effective float level and your jets may need to be even smaller than indicated by this latest test.

 

This is really where a dyno to hold a load point becomes handy!

[inline6]

Good thread

 

http://forums.hybridz.org/topic/106649-triple-mikuni-help/?hl=triple mikuni help

 

Thanks.  I read the whole thing.  Definitely some things to keep in mind in there like it's ok to run lean (leaner than 14.7) at idle and cruise...  if having stumbling during pilot to main transition, go with the largest pilot possible and get the pilot screws dialed in to less than 1.5 turns...  big cams require less pilot.

 

 

Two things:

Your AFR if not pump squirted should remain stable on the main circuit as RPMs rise, if its leaning out it MAY be your fuel pump is not keeping up. WATCH YOUR FUEL PRESSURE! Even my 70RWHP car was experiencing Fuel feed issues! After fixing the regulator and return setup to backpressure regulation, I picked up HP and my AFR's stayed steady under sustained main jet load.

 

One thing I usually point out to most people are that the mains in our 300HP L28 Bonneville car were 135's.

 

You are probably one or two jet sizes large...but make sure you have unchanging fuel pressure at higher RPM's, if it's dropping then so is your effective float level and your jets may need to be even smaller than indicated by this latest test.

 

This is really where a dyno to hold a load point becomes handy!

 

Hmmm.  My fuel pressure gauge is on the regulator in the engine compartment.  I'll have to wait until I can get it on a chassis dyno before I can check that properly.

 

I've got a full set of 6, 155 main fuel jets.  I'll give them a shot.  Unfortunately my full set of 160's actually measure out to be the same as my 165's --- they are all 170's!  I learned from Tom Howen (driver and engine builder for Malvern Racing) a long time ago that Mikuni jets are often totally different sizes than the number on them - seems to be especially the case with the main fuel jets in my experience.  

[Tony D]

Rated according to actual flow, not wire diameter hole drilling like Rochesters!

 

It's why "jet drills" so commonly used on Holley & Rochester stuff, with somewhat repeatable results can be maddening with Webers & the like. I think there is an admonition in the manual against "drilling he jets" due to the "ream-test-stamp based on flow" procedure.

[madkaw]

The problem with those AFR gauges is that you wind up fixated on them all the time.

When I had too big of pumps and mains in there the engine sounded like it was drowning under WOT accel. It stumbled a bit-but not from fuel startvation.

Reading your build again--- a lot of nice work by the way----your cam is pretty damn big, which will probably make tuning harder. Your AFR's might always look rich around transition with that motor, but is it blowing black smoke, what does your plugs look like.

Wait till you get that motor broke in and you can drive it HARD, then see where your at. For now itt sounds like you have cruise mode set-up fairly close.