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

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It seems contradictory that you are shooting for performance at 2000 rpm with main airs as big as you have them. I think IMHO that you are way too big on the main airs and it's throwing off your tuning.

Running that big of mains and then diluting the mix with that big of main airs seems self defeating.

Since you have had other issues(cam timing), maybe start back on the small side. Remember the smaller the main air jets the richer the main jet mix. How about something completely different like 155 mains and 180 main airs and see what that yeilds?

Once again I'm not sure you are going to get a street tune with that big of cam. I wouldn't even tune for WOT under 3000 rpm. That puts you right in the middle of the transition issue with triples and it also puts you in timing curve issues. I would tune for WOT and cruise and idle. Idle for easy starts, cruise to keep plugs clean, and WOT for WOT.

Staring at the Wide Band during driving could lead to insanity and a bad accident-lol

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Staring at the Wide Band during driving could lead to insanity and a bad accident-lol

 

with a different wideband and a different car almost had been there :ph34r:

 

as for the problem itself i have exactly the same. car is ripped apart for some months now so no tuning is possible but

before that if you go WOT below 2750rpm issue is going in the same direction. with the camed 3.1 and triple dcoe was running

140 mains 195 airs and 40 pumps...

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It seems contradictory that you are shooting for performance at 2000 rpm with main airs as big as you have them. I think IMHO that you are way too big on the main airs and it's throwing off your tuning.

 

I don't know if I buy the argument that these carbs can't be tuned to work across the entire engine range.  TonyD has repeatedly chimed in on many threads.  He is saying that it can be done - it is just harder.  From another perspective entirely, when folks go to the dyno, at the end of the day, they can typically take home some kind of chart that has a full RPM sweep with max torque and max hp.  I'd have to concede that with my engine combo, I wouldn't be able to do that.  I'd have to settle for a curve from like 4000 to 7700.  I don't think I'm ready do that yet.

 

Regarding too big on airs: per the Mikuni Service Manual, air correction jets affect "the flow of fuel mainly at medium and high-speed...".  Because my AFR is dropping to low 12s or high 11s right now at the highest RPM range for this engine (6900 - 7400, with redline supposed to be 7700 - I just haven't gone that high yet), and larger air correction jets lean out the mixture, then I should actually be going with bigger air correction jets, not smaller ones to try to raise AFR a bit at this engine speed range.

 

Running that big of mains and then diluting the mix with that big of main airs seems self defeating.

 

Hmmm... I don't know.  As long as I can put more fuel in with "bigger" main fuel jets and with "bigger" air correction jets (speaking relatively here) and still achieve a "power" target AFR, then I should be making more power vs. "smaller" main fuel jets and "smaller" air correction jets, right?.  Even if I do give up on tuning for full throttle at below 3000 RPM, I wouldn't go with smaller mains and airs at this point because my AFRs are not too rich at middle engine speeds.  I mean, I am currently seeing above 14s from 5700 to 6500... and above 13s from 5400 to 6700. That is too high for good power.

 

If I did go smaller, I'd experience lower total power output and probably an increase in fuel economy.  But, that is not really the goal.

  

How about something completely different like 155 mains and 180 main airs and see what that yields?

 

Actually, I already did this while at the dyno a couple of weekends ago - with the caveat that the cam timing was off, I know.  But, I changed the main and airs to be much smaller several times, trying to eliminate "rich" completely - trying to get to a "too lean" condition.  Basically, as I went down in size, a "hump of leaness" became more and more prevalent in the mid-range RPMs, and I still was not able to get rid of the 10s at snap open throttle and low RPMs.  You can see more detail about those runs on the dyno in this forum thread if you would like. 

 

Yes the cam was mis-timed, but I don't think that the general behavior vs. correctly timed would be completely different.  In other words, if correctly timed, I believe the overall trends I experienced would be the same... just different RPM points would be in play.

  

Once again I'm not sure you are going to get a street tune with that big of cam. I wouldn't even tune for WOT under 3000 rpm. That puts you right in the middle of the transition issue with triples and it also puts you in timing curve issues. I would tune for WOT and cruise and idle. Idle for easy starts, cruise to keep plugs clean, and WOT for WOT.

 

You may be right, however, I'm not willing to give up just yet.   :)

Edited by inline6

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I was able to work on the tuning some more yesterday.  I started the day with:

 
Main 180
Air 250
Pilot 57.5
Pump 45 
Choke 37
 
Last change was going from 240 to 250 air correction to try to produce a leaner AFR above 6700 RPM. Here is what actually happened - the dotted line is the previous run with 240 airs - the solid line is the current run with 250 airs, both are in 3rd gear:
 
post-4218-0-54065200-1428854126_thumb.jpg
 
Interesting that the bigger air jet caused the range between 5300 and 6000 to lean out more while causing the range from 6000 up to get richer.  Isn't that the opposite of what you'd expect?
 
Because the AFRs were at or above 13 for all of the graphed RPM range except above 6600, I decided to try upping the mains another step to 185:
 
post-4218-0-92461600-1428854125_thumb.jpg
 
The dotted lines are the 180s from the previous run.  Only the mains were changed - again in 3rd gear.  The AFRs were made richer across the test RPM range.  
 
Here is a comparison of two 4th gear runs.  The runs differ only in that the prior run (dotted lines) had 180 mains.  This run has 185 mains:
 
post-4218-0-42258800-1428854125_thumb.jpg
 
Interestingly, when I went to full throttle on the 185 mains run, AFR didn't dive into the 10's as has typically been the case. I am more conscious of the problem, however, so it may just be that I am squeezing to full throttle over a couple of seconds instead of snapping to full throttle.
 
Since going with the bigger 250 airs richened the top end and leaned what has been consistently the leanest RPM area on many plots, I'm thinking the next step will be to lower the airs to something like 230.  My prediction is that my plot will flatten out - richer in the 5300 - 6000 range and leaner in the 6000 plus range. 
 
But first, I'm going to tighten up the manifold nuts.  I may have some slight leakage at the header, and I want to be sure that is not the case.  I'll do that and make a plot run. If nothing has changed, then I will change to the 230 airs and see what happens.
Edited by inline6

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Keep in mind Mikuni PHH were OEM fitments on probably a MILLION or more Toyota DOHC engines from 1967 into the 80's (with catalysts!!!)

 

If you can get Toyota drive ability and reliabilitynout of them in a 1980 Camry GT, you can do it on an L-Series.

 

It's not me just saying it, Toyota proved it! My 76 Celica GT would lug in fifth gear from off-idle to redline.

 

So would my Fairlady Z with the L20A and 40PHH's from a 2TG Toyota.

 

As would my blow-through 44PHH turbocharged 73 240Z....and that was no small feat.

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Keep in mind Mikuni PHH were OEM fitments on probably a MILLION or more Toyota DOHC engines from 1967 into the 80's (with catalysts!!!)

 

If you can get Toyota drive ability and reliabilitynout of them in a 1980 Camry GT, you can do it on an L-Series.

 

It's not me just saying it, Toyota proved it! My 76 Celica GT would lug in fifth gear from off-idle to redline.

 

So would my Fairlady Z with the L20A and 40PHH's from a 2TG Toyota.

 

As would my blow-through 44PHH turbocharged 73 240Z....and that was no small feat.

 

I'd like to think I can figure it out, but I am wondering if my cam and my intake as well as cylinder head porting haven't made that too tall of task for the limited action of swapping out jets.  I also could be experiencing some reversion...  

 

I'm going to try to get the AFR curve from 3500 RPM up to be "right" and then see where I am with full throttle dumps at 1200 RPM (that is as low as I go - it is my idle speed for this cam) up.  

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You really can't dump from idle.

This is one of the problems with Carburettors: they need velocity or vacuum to work.

Our Bonneville Engine idled at 2,200 rpm son the big predator carb (hey, it's just a big SU, right?) that was as low as it would go.

We swapped to Weber 45 DCOE's and the idle was able to be dropped to 1,700.

This was the exact same engine, just changed induction...

We went to an Electramotive TEC2 and TWM 45 ITB's and we idled at 950! And could turn it down to where the cranking signal was intermittent...it would bang-bang-bang along at 450 RPMS with a triple plate clutch and flywheel that weighed 15# total. I'm convinced even though it made peak power over 8,000 RPM's, we could have put a stock weight flywheel and run that cam on the street with the EMotive/TWM's.

 

The Quoted Procedure of getting it into top gear and making pulls smoothly from 1,000 rpms represents a reasonable driving demand: being in traffic and not wanting to take the car out of top gear.

 

This also assumes the engine idles somewhere around 750 rpms. So 1,000 represents just off-idle by about 33%.

 

The translates roughly into 1,600 in your case with a 1,200 rpm idle. That is a reasonable expectation.

 

On the B-Ville car we could move the car around at 2,500 on the Webers, but more like 3,000 on the Predator.

 

Sometimes I assume too much and think people will make these interpolations. Reason I say it was because the process of writing the Toyota example reminded me of my dunderheaded old USAF Supervisor who had 2TG Toyotas and was convinced he needed to replace his entire brake system because there just wasn't sufficient braking. Long story short was "Wait, is this the car you put the TRD 304/308 Degree Cams into? The one that won't idle below 1,700?" He was convinced the car should work like stock with hella cams in it, and thought idling up to 1,700 was wrong. He had brakes driving down the road, just not at "idle"!

 

Same thing here, I'd say don't expect much below 1,600 at all, you don't put your car into gear and idle it down the road. This is an off-idle test, and off idle is 1,600-1,750 rpms. You just won't work well below that due to carbs needing vacuum to properly atomism the fuel. Up the engine speed and your atomization improves.

 

In Japan they have all sorts of bolt-on TPS and Stand-Off Injector Mounts to strip the venturis out of those PHH's and make them ITB's for better drivability and more power everywhere..."Ctrl-Shift Arrow up up up, or down down down"!

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In Japan they have all sorts of bolt-on TPS and Stand-Off Injector Mounts to strip the venturis out of those PHH's and make them ITB's for better drivability and more power everywhere..

 

You wouldn't have a link to some of the above would you? 

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Sometimes I assume too much and think people will make these interpolations. Reason I say it was because the process of writing the Toyota example reminded me of my dunderheaded old USAF Supervisor who had 2TG Toyotas and was convinced he needed to replace his entire brake system because there just wasn't sufficient braking. Long story short was "Wait, is this the car you put the TRD 304/308 Degree Cams into? The one that won't idle below 1,700?" He was convinced the car should work like stock with hella cams in it, and thought idling up to 1,700 was wrong. He had brakes driving down the road, just not at "idle"!

 

Same thing here, I'd say don't expect much below 1,600 at all, you don't put your car into gear and idle it down the road. This is an off-idle test, and off idle is 1,600-1,750 rpms. You just won't work well below that due to carbs needing vacuum to properly atomism the fuel. Up the engine speed and your atomization improves.

 

I started out thinking I could tune these carbs for "acceptable" AFR with full throttle application in 4th gear from 1200-7700 RPM... even with this big cam.  Right now, I can't use full throttle at below 4000 RPM in 4th without a dive of the AFR to mid 10s along with experiencing what I perceive to be engine misfire.  The taller the gear, the more prevalent this issue is.  If I am in first, it isn't a problem.  My understanding is that I am a still a long way from what I can yet achieve with these carbs (and my specific engine) from a tuning standpoint.  But, yeah, I am starting to realize that I won't be able to achieve the original goal until I switch to the Tec GT and the TWM fuel injection.  

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Coming back today and reading what I posted I went "WOW!" -- curious how that number off-idle (33%) coincides with the original Bosch-Licensed EFI "WOT Switch closing point!"

 

What happens when you do a slow-roll-on to the throttle compared with a WOT Mash?

What happens when you disconnect the Pump Plungers and try the same thing with both Mash and Slow-Roll-On?

 

When you tune EFI, in similar manner, you disable all enrichments to get the base WOT curve, once that is dialed in...you start working on transients. 

 

Jetting for WOT takes 45 minutes on a Dyno. It can be 3-4 more hours to get transients and partial throttle dialed in. . . 

 

Come to think of it, you are running an appropriate rear end ratio, right? Not the 3.36? More like 3.9 or 4.11? N/A Carbbed engines need to twist to work well.

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What happens when you do a slow-roll-on to the throttle compared with a WOT Mash?

 

That makes a huge difference.  If I squeeze the throttle, AFR on the screen of the LM-2 doesn't go as low, and the engine doesn't misfire.  I have to squeeze slower in higher gears vs. lower (4th vs. 3rd specifically - I haven't even tried full throttle in the .745 overdrive in 5th anytime recently).  I have to squeeze slower at lower RPMs vs. higher.  Anything over around 4500 RPM right now, even in fourth, and I can snap the throttle open and I am ok, meaning I don't get the low to mid 10s and perceived misfire - the AFR still drops into the low 11's initially though.

 

What happens when you disconnect the Pump Plungers and try the same thing with both Mash and Slow-Roll-On?

 

Haven't done that yet.  I can put it on the agenda for this weekend.  Bummer is I have to travel about 6 miles through stop and go to get to my "test area" on the interstate.  I could schedule another dyno session.  

 

Come to think of it, you are running an appropriate rear end ratio, right? Not the 3.36? More like 3.9 or 4.11? N/A Carbbed engines need to twist to work well.

 

I've got an R200 4.11 in the car. 

 

Here is another plot from when I had the best set up in the car thus far.  Because the tune was improved with the change I made for this run, I decided to snap open the throttle at lower RPM in third than I had been doing - to test that issue.  I eased off until I was around 4k instead of 5k, and quickly went WOT.

 

post-4218-0-73023700-1429157460_thumb.jpg

Edited by inline6

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I managed to get a few runs in despite the rain showers.  One goal for today was to check to see if tightening down the intake manifold and header nuts changed anything.  I saw essentially no change due to that.  Next, I discovered that the front carb was being held to the manifold by only the top two nuts.  It took me forever scrounging around my boxes of Nissan hardware to find a couple of 8 X 1.0 mm nuts for the carb isolator studs - what an uncommon size!  I also changed out the pumps to 50's because I have seen that anything less causes a spike on full open throttle for the tuning runs I have been doing.  Here is a comparison of 45's to 50's:

 

post-4218-0-05523300-1429408820_thumb.jpg

 

The brief "jump" to lean at WOT, is essentially gone with the 50's.

 

This is a run in both 3rd and 4th:

 

post-4218-0-24403200-1429408819_thumb.jpg

 

It's not exactly easy to see, but the AFR curve is actually very consistent - just compare the same RPM in 3rd vs. 4th.  As you can see with the stat markers I have, it doesn't matter what gear, the curve is essentially the same.  I've logged a large number or 3rd and 4th gear pulls now, and I have overlayed them and compared the differences.  

 

Right now I have this combination in the car:

 

Main 185
Air 250
Pilot 57.5
Pump 50
Choke 37
 

By looking at 3rd in this chart, all I am dealing with is revealed.  Even with many main fuel and air correction jet combinations, the shape of this curve generally does not change.  

 

I have low 14's at steady state cruise 3100 RPM in 5th.  I have low 13's at steady state 4600 RPM in 3rd.  I can snap open the throttle at 4600 RPM in third without a lean spike.  The AFR drops very briefly to low 12's, then climbs.  It crosses over to the 13's around 5200 RPM.  5800 RPM is often the peak in lean AFR around and is about 14.4.  Then AFR turns downward again.  I don't see below 13 until about 6500 RPM.  AFR keeps marching downward linearly from there until about 7000 RPM - where it hits low 11's.  It does pretty much level off right at 11... I have rarely been going much above 7200 for now.  

 
Since low 12's for WOT through the power band of this cam is the goal, my next move will be to throw some 190 main jets in.  250 airs are as big as I own at the moment, but it looks like I'm going to need to buy something bigger.    
 
300 airs is the largest size - I am at 250 now.  Perhaps I need to start thinking about some larger outer venturis to reduce the "pull" on the aux venturi.
Edited by inline6

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Spent the time to adjust the accelerator pump lever throws to the Mikuni manual spec. - 7.5 mm.  They were about 4 to 5 mm prior to doing so.  I went out after that change and got new baseline curves.  That is the solid line in the plot below.  Interestingly, my lean spike at WOT is back now.  

 

What I had in the carbs for the baseline:

 

Main 185
Air 250
Pilot 57.5
Pump 50 

Choke 37

 

Also in the plot are the dotted lines which is the change to 190 mains after recording new baselines (no other changes):

 

post-4218-0-84274600-1429583975_thumb.jpg

 

No matter what jets I throw at this thing, I can't get that hump in the middle hammered down.   Stepping up the size of the mains is making the curve richer for the entire RPM test range.  While the bump in the middle shrinks, the AFR at the ends - just after WOT and full throttle above 7000, also descends.  

 

Combo in the car is now:

 
Main 190
Air 250
Pilot 57.5
Pump 50 

Choke 37

 

I am pretty far outside any other jet combo for Mikuni 44's than I have seen for any other 6 cyl. Z engine.  Seems like I have something weird going on... wish I could identify it.  Need to start thinking outside the box.  Maybe I should revisit my cold air intake system... or maybe I have some weird fuel pressure fluctuations as RPMs change...

Edited by inline6

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Your study is interesting!

You should plot the AFR vs. Rpm. It would be easier to compare data.

 

I just rediscovered this suggestion from you last night while reading back through this thread - it helps to have all of this info in one place to see where I have been and to hopefully inform where to go next.  I am playing with AFR vs. RPM.  Will see if I can get some plots together.  

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I've been trying to lean out the top end as of late.  But, I have found that even substantial size increases has little to no effect in AFR at the high RPM range.  For example, here is an AFR vs. RPM plot of the following jet combinations - the dotted line is the run with a 250 air jet:

 

Main 190
Air 250
Pilot 57.5
Pump 50 
Choke 37
 
vs.
 
Air 270

 

post-4218-0-56100900-1430671482_thumb.jpg

 

I bought the 270's this past week and tested them this weekend.  It seems no matter how high I go, I can't change the AFR at the high end.  

 

Here is another plot.  This one shows a comparison of a much earlier run when I had 180 Mains and 220 Airs (dotted line), and everything else is the same vs. the latest 190 Mains 270 Airs that are in the car now.

 

post-4218-0-29421000-1430671483_thumb.jpg

 

This is the problem... I can't get the upper range to lean out.  What could be the problem?  Are the carbs somehow not getting enough air?

Edited by inline6

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Decided I would try 195 Mains to see what the change in AFR would look like.  Obviously, I'd like to lower that hump in the AFR in the 5400-6400 territory if at all possible.  So, I figured I see what the 195s would do.  

 

post-4218-0-05033000-1431219624_thumb.jpg

 

It was a pretty substantial change.  And, as expected, AFR got richer where I didn't need it to also.  I haven't had any luck getting airs to lean out the top in, so I am hesitant to order something bigger than 270's - I don't think it will make a difference.  

 

So, now the question is, which of those two plots is better?  Should I stick with the 195's, or go back to the 190's.

 

Edited by inline6

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