Triple Mikuni Help

[madkaw]

I guess there isn't many mikuni gurus here anymore. Anyhow, I took the #1 carb off again looking for possible air leaks. I looked over the plastic insolators for cracks, but found only some warpage of the insolators. You would think that being sandwiched between the intake and carb would flatten it out enough, but maybe not. The O-ring only sits about.3mm above the groove, not much room for error. I decided to take sandpaper to the insolators on a glass table and found a significant low spot on one of the insolators. I magic markered the all the insolators and sanded flat with wet sandpaper.  I can now run similiar mixture settings on all the carbs, so it must have helped.

Iv'e given up on #6 sputter issue for now. It doesn't effect much and doesn't foul plug, just makes that plug slightly darker. Last day of running hard I couldn't see a difference in any of the plugs. I can watch the AFR's bobble a bit rich----dam gauge, I'm obsessed.

Time to go to the dyno!  

Current settings

65 pilots 1.5 turns

200 main airs

145 mains

 

Afr WOT in 3rd is spot on-13.5, but 4th seems a bit rich 12.5 ish. I guess thats normal. I might need to drop to 140's for the dyno.

Third gear is all the fun with this car since I can get 100mph out of it, so i have mostly tuned WOT for it.

My AFR might be a bit skewed from #6 dribble, so I need(make mental note) to swap back wideband to from 3 cylinders.

[zbloke]

This may or may not help you but, I've had a couple of air leaks on my Mikunis, only found by listening around the offending areas with a piece of 5/16" rubber fuel pipe in my ear like a stethoscope

 

First one was the float chamber cover gasket, specifically in the area around the vertical tubes that take the cold start mixture down to the inlet manifold side of the throttle butterfly, new gasket cured that

 

Second one was between the face of the carb and the Misab plate insulator in between carb and manifold near the top of the flange, pulling the carb off and having a look there are drilling's, I believe for the idle/progression mixture, which are plugged with brass inserts, the inserts are slightly below the face of the carb and there where witness marks on the Misab plate rubber where it looked as though it wasn't sealing, and the cause of the air leak, I put a little Superglue gell over the brass insert let it go hard then sanded flat, fitted it all back up and retested and could only detect the tiniest hiss when listed to with my 5/16" fuel hose stethoscope

 

After spending some time setting up the gaps on the rubber bobbin and washer mountings that ensure the Misab plates are loaded equally and still having a tiny air leak I think the only way to totally seal the carb to manifold joint, for my application anyway, is to switch to gaskets and solid, phenolic?, spacers  

[madkaw]

So learned another lesson the hard way this week. Running my MAP sensor on the vacuum log was a good idea for a signal, but I guess running the PCV on the same log WITHOUT a oil separator of some kind was a bad idea. My engine started running wonky today and timing was way off. Long story short, blow by oil was gathering at my MAP sensor fitting and running down the vacuum hose right to my MS3X unit. When I pulled the line off there quite a bit of oil in the line and I believe ruined my MAP Daddy sensor.

I guess I will be making a catch can to run with my PCV, if I run the PCV again.

I also need to run the vacuum line for the PCV in the center of my vacuum line instead of one end. The 'controlled' vacuum leak of the pcv causes things to go lean at that end

[inline6]

I was instructed by David Weber of Malvern Racing never to run the plastic spacers with o-rings.  According to Dave, the carbs have to be "isolated" from vibrations to work properly.  He told me to run rubber isolators.  These use gaskets instead of o-rings.  No leakage issues are another benefit.

 

Here is a pic showing them between the carbs and the manifold:

 

Edited November 26, 2015 by inline6

[madkaw]

Been a while , but I guess that's a good thing. Car has really been running well . Went to the dyno and got lack luster results. Basically dyno numbers weren't much different than running SU's - about 150hp.

The few Z owners I know can't believe that it's only 150 the way the car performs.

Anyhow , I was considering larger chokes. I stated earlier in the thread that I had 34's, but they are just 32's. This Mikuni package was part of a complete street kit. This was meant to bolt on to a stock motor so 32's were plenty. I think those 32's are choking me up a bit and wanted to bigger. None available . So you guys that have machines out your 32 's to a bigger size - tell me about it.

I was considering 35mm since my ports are only about that big anyway. Don't know how thin that makes the venturis?

Is this something any machine shop could be trusted to do?

Also installing a .6mm HG to pump things up a bit.

[Leon]

Been a while , but I guess that's a good thing. Car has really been running well . Went to the dyno and got lack luster results. Basically dyno numbers weren't much different than running SU's - about 150hp.

The few Z owners I know can't believe that it's only 150 the way the car performs.

Anyhow , I was considering larger chokes. I stated earlier in the thread that I had 34's, but they are just 32's. This Mikuni package was part of a complete street kit. This was meant to bolt on to a stock motor so 32's were plenty. I think those 32's are choking me up a bit and wanted to bigger. None available . So you guys that have machines out your 32 's to a bigger size - tell me about it.

I was considering 35mm since my ports are only about that big anyway. Don't know how thin that makes the venturis?

Is this something any machine shop could be trusted to do?

Also installing a .6mm HG to pump things up a bit.

 

This was done on the same dyno? What else is different between now and then? Timing, AFR?

[madkaw]

Leon,

Same dyno, same operator. He said I was running lean though my Innovate showed around 13+.

He ran his sniffer at the tail pipe and said it might show lean, but than said I WAS lean.

WOT runs on the highway showed spot on. The car has never run stronger and better.

Since last dyno I reduced the chambers to 39cc but now run an ISKY 490/290 vs. 480/274 Schneider.

i am going to a different dyno next time because of location , so I will compare.

 

I was running 150 mains and 180 airs during dyno. First run I noticed my AFR peg lean deep into the run. Never happened on the road like that. Something to do with the slow ramp up in rpms? It seemed to take forever to get to 6500 on the dyno. Could he have had a setting wrong?

[Leon]

Leon,

Same dyno, same operator. He said I was running lean though my Innovate showed around 13+.

He ran his sniffer at the tail pipe and said it might show lean, but than said I WAS lean.

WOT runs on the highway showed spot on. The car has never run stronger and better.

Since last dyno I reduced the chambers to 39cc but now run an ISKY 490/290 vs. 480/274 Schneider.

i am going to a different dyno next time because of location , so I will compare.

 

I was running 150 mains and 180 airs during dyno. First run I noticed my AFR peg lean deep into the run. Never happened on the road like that. Something to do with the slow ramp up in rpms? It seemed to take forever to get to 6500 on the dyno. Could he have had a setting wrong?

 

Depends on the type of dyno. If you're going to a different one, make sure to change NOTHING until you get a baseline on that dyno. Dyno tuning can expose a lot of holes that you don't notice otherwise.

 

Can you post the data (HP/TQ/AFR)?

[madkaw]

The guy has never sent me the email with the sheet

[madkaw]

Wonder if my floats are just a tad on the lean side and the prolonged run on the dyno put them over too lean?

[Leon]

Remind him to send that email and post here.

[ryant67]

Good thread on enlarging venturis here:  http://forums.hybridz.org/topic/114865-change-venturi-size-or-stay-whith-what-i-have/

 

[madkaw]

Thanks Ryan, that opens up ideas a lot. Flapper wheel and a good mic- I have a good mic!!

[Chickenman]

Leon,

(Snip)

 

I was running 150 mains and 180 airs during dyno. First run I noticed my AFR peg lean deep into the run. Never happened on the road like that. Something to do with the slow ramp up in rpms? It seemed to take forever to get to 6500 on the dyno. Could he have had a setting wrong?

Lean running in top end gear pulls, but OK in 2nd and 3rd is usually an indication of inadequate fuel supply. Are you running a fuel pressure gauge that you can Monitor in real time?

 

Dyno pulls show this up more often than the street, because you usually can't do sustained high RPM pulls   in 4th and 5th gears on the street for obvious safety reason. A load Cell chassis Dyno where you can load the car up at a steady RPM is by far the best method of testing ( DynaPak is one such model )

 

If you are losing fuel pressure in Top Gear at high rpm , some of the things to look at are:

 

1: Correct float level of course. That is a given. Surprising how often this is out of spec though.

 

2: Adequate fuel pump to supply volume and pressure needed at sustained WOT in 4th gear.  Stock Nissan mechanical pump is NOT adequate to feed Triple DCOE's at sustained WOT.

 

3: Adequate fuel line size. Minimum AN 6 ( 3/8" ) from fuel tank to carburetors. AN 8 ( 1/2" ) is preferred. Return line to tank needs to be AN 6 as well. 

 

4: Non restrictive fuel filters. Again, minimum AN 6 and never EVER use those aftermarket " Glass or Plastic " inline filters. These are horribly restrictive. Stock fuel filters are too restrictive as well.

 

Bad Fuel filters:

 

 

A proper fuel filter is the Fram HPG-1 or similar.

 

Good Fuel filter

 

5: What fuel pressure regulator are you running. From experiences with the experienced Turbo tuners on various racing forums ( Including the 510realm ) , there is one name to remember. Aeromotive. Accurate, reliable and non restrictive.  Even well known brands such as Holley and Mallory have proven to have many more issues than Aeromotive products. They cost more, but they are worth it. Don't rely on a Chinese clone either. Always run a return to tank Bypass system, even on carburated cars.

 

6: Correct float Needle and Seat size. Sometimes you need to increase the orifice size of the N&S. This is a last ditch effort though and usually only required on very high output motors.

 

All of the above areas of the fuel system must be checked and accessed accordingly. A weakness in any area can lead to a high rpm, Top gear lean out situation. Hope this helps.

Edited May 28, 2016 by Chickenman

[madkaw]

Once again the Chickenman speaks truth-

I screwed up because I had a fuel pressure gauge already under the hood and could have whipped it out for the run, but Nnoooooo, I didn't think to look at it to see if I was maintaining pressure correctly.

I think you confirmed my suspicions that the long run is running me lean. This car takes no time to rev out on the highway. That same day I did a pass and let off at 5800 because the speed was getting to high - but it pulled hard all the way there. That didn't seem to translate to the dyno.

If I was thinking I would have checked fuel pressure first, then I would have richened up my floats - it's so easy on these carbs. Only then would I have considered going bigger jets .

The operator said the AFR was kind of in a bad area - he rather see richer and or leaner, something he said about cylinder pressures.

 

The fact is I screwed up. After thinking about it I never even verified throttle plates opened 100%

 

Glass filters removed a while back- they are junk and gave me fits.

I'd love to have an areomotive FPR, but want to spend that money on one for my FI .

Wish I ran a return line , but dead head it is and stays, but need to verify pressure.

Pump is a high volume carter at 4 psi with a Holley regulator.

[Chickenman]

Hmmm... those Holley non-Bypass regulators are suspect. Lots of issues, especially when set up as a dead head. Not very accurate, slow to respond and when they limit pressure, they restrict the output flow which reduces volume. Monitor it on the the Dyno if you're testing again. Bypass style FP regulators do not restrict volume to carbs or injectors when they bleed off rail pressure. 

 

Electric fuel pumps should be mounted as close to fuel tank as possible and as low as possible. ( Stock 2080Z EFI position is fine )  Must be mounted as a pusher pump, not puller.

 

When you go FI you must run a pre-filter before the FI Hi pressure pump. Fram G3 is fine. New style pumps use Ceramic Turbine vanes and they can't handle minute dirt particles as well as the old Roller vane pumps ( Original Nissan Style ). However, the Turbine style pumps are are quieter, more efficient and will pump a lot more pressure and volume than the old style Nissan Roller pumps.

 

Carb or Fuel Injection, one other thing to check is the voltage drop to the electric fuel pump. A 1 volt drop can affect pump volume dramatically. Can reduce volume by up to 15%  A relay system should be used with a  40 amp Bosch continuous duty relay.   Run at least 12 gauge wire back to the fuel pump, with the main +12v  for the FP relay,  connected directly the battery terminal.  10 gauge is even better if you have a long run. Do not go through the factory fuse box. An  ATO inline fuse holder  with a 20 Amp should be wired in at the battery or use an Auxiliary fuse block. ( You'll probably want one of those when you go Fuel Injection )

 

CE Auto Electric Supply makes some nice auxiliary fuse blocks and other electrical goodies:

 

http://www.ceautoelectricsupply.com/fuseholders.html

 

.

Edited May 28, 2016 by Chickenman

[madkaw]

Fuel pump is done right. Separate relays , heavy gauge wire, pusher close to tank - high volume low pressure carter .

[Chickenman]

^ That's good. Just listing all the things I could think of...

[madkaw]

Take all the help I can get.

[ryant67]

Steve, I have noticed the same leaning out when in 4th on long pulls - usually at the strip when doing runs for fun.  It only happens when at WOT for extended time, something you never see on street driving.  On Chickenman's list, the only item on my car that doesn't meet his conditions in the Holley Regulator.    

What I find odd is that the Holley regulator to dead head at the carbs is a very common setup on these cars, and I have seen many race-oriented Z's running that exact setup.  Not sure why it would be an issue for some, but not for others.  Unless of course the stress of running a high flow pump to a dead head on a daily driver has weakened the pump over time and it's no longer putting out its advertised flow figures anymore, is that possible?

I agree that it's a better practice to run a bypass regulator after the carbs, but the stock return lines aren't large enough to carry the capacity and it's a decent amount of effort to plumb a larger one into the tank, unless there is some trick I am missing.