Triple Mikuni thread

[madkaw]

It's my understanding that the accel pump sizing effects how quickly the fuel dumps more than overall amount. So even being careful you might be overloading things. The 40's might spread the squirt over a larger are of time thus making it easier for the engine to digest.

When you "blip' the throttle several times does the engine respond quickly every time or does it start to bog a bit with fuel?

[zKars]

Glad you're making progress.

Wish we had a simple way to measure flow, not pressure.

Running pressure is irrelavant, all it has to do is keep the bowl full, which is a flow determined variable. The car would run perfectly at 0.25 psi if the pump could flow enough to keep the bowls full at all times. The 4 psi is just a ceiling that shouldn't be exceeded as the float valves can't keep back any more.

Remember its all big system. The fuel lines, the return lines, the fuel filter and the flow valves in the carbs are resistors, the pump is a voltage source. The flowrate (current) is determined by the resistance in the circuit at the applied pressure. Unfortunately the pump pressure can vary depending on the supply and return circuit. Complicated.

There are an infinite number of pumps and plumbing arrangments that will let the car run just fine. Thats why you find so many people with a huge variety of systems who's car's run just fine. The problems occur at the extremes. Long term high flow rates (can the pump really keep the bowls full?), extended life (is the pump always deadheading most of the fuel, and getting hot?) etc etc etc....

[Kennymonster]

It's my understanding that the accel pump sizing effects how quickly the fuel dumps more than overall amount. So even being careful you might be overloading things. The 40's might spread the squirt over a larger are of time thus making it easier for the engine to digest.

When you "blip' the throttle several times does the engine respond quickly every time or does it start to bog a bit with fuel?

 

Response is very crisp with current setup, I've only observed mid range rich condition at dyno setup where I was just dumping the pedal to WOT, which probably is contributed a bit from the cam profile as well.

 

Overall I'm happy with the setup, but then you occasionally see 'those other' l28 dyno charts with a perfectly flat afr which makes you want to tinkle more, it's a disease I swear.

[madkaw]

I know EXCATLY what you mean Kenny. Always trying to extract that last bit of ponies. I should have been satisfied a log time ago, but I would go in and tinker, but that time is almost over. After this next dyno the Mikunis are going on to someone else(highest bidder!) I'm going FI and not looking back.

 

Jim, not sure who you were addressing. My fuel supply issuewas all a fuel filter issue. My new Carter high volume 4psi pump has been great.

[madkaw]

My latest version of my triple Mikunis include a new location for the pcv and adding a oil catch can. I also moved my MAP sensor all the way back to the brake booster hose, which seems to work well enough. What really

turned out cool was the luckiness to be able repurpose some old braided

hoses I had laying around. I needed formed hoses for all the weird angles

The pcv valve was moved for several reasons. The biggest being that the

oil and crap being pulled from the crankcase was condensing inside my

vacuum log and filling my MAP sensor vacuum hose that was at the low

point. I also wanted to center the vacuum leak created by the pcv to

the center instead of being off to one side. The pcv seemed to want to

make the first carb run leaner.

Speaking of the PCV, I have learned a little about them lately. Mostly

that they are not created equal. Might seem like a no brainer, but I

thought most of the differences were because of packaging reasons.

So I was running who knows what kind of PCV, but it wasn't Datsun

approved. What I had going on was a PCV that was allowing considerable bypass at idle. So I had a sizable air leak right at idle, vs. the stock

PCV that closes off at idle. This could equate to almost a 1/2 turn or

more of mixture at idle . Is this a bad thing? Jury is still out.

I have more investigating, but I think the car idled better, started

easier and ran cleaner at idle with the wrong PCV. Someone want to

explain the science behind that for me:)

Good thing is that despite some richness on the 5&6 at idle or pilot

circuit, carbs run good and plugs are a beautiful tan!

[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.

[siteunseen]

So is the EFI conversion off the table? I was anxious to see how that turned out.

[madkaw]

EFI is still in the works and getting closer . Intake, fuel rail, injectors , TB , all acquired . Just a few last efforts on the Mikunis before I sell them off. It's been a fun ride but it's about time to move on. 

[madkaw]

Enjoying this spectacular fall weather and an engine that is running really well. My Mikunis have been really good to me and parting will be really tough. It's really a cool feeling when you open the hood for someone and they say - DAM! 

The fall weather means one last jet change for me . Time to increase the mains a size . Might go back to the dyno ( a different one) for one last pull. Still don't buy the last results . 

Ready to move on to FI , but don't want to take my car down for a minute. I've been driving it to work( 50 miles) lately just to drive it.  But I will never be able to move on unless I say good bye to these. Might need to take another video too. 

Wish I had the money to make them wall art, but rather share them with another Z . Hopefully see them on a car in a show someday with that funky airbox !!

[siteunseen]

How about a new video?  Chirping into 4th?

I have an old compressed air boat horn I crack with the windows down when I'm shifting.  No chirp just a "whooooop".  Freaks out dogs and kids!

[Galaxybj]

Has anyone used the Mikuni 44 PHH Cooling Body Option?  Any thoughts of if they are necessary/useful?

[RyanT67]

I've never seen them used, but I'm also dubious of the benefits.  A decent heat shield keeps most of the heat off of the carb bodies, and the cooling bodies would only be effective if you were running a return line, which most triple carb folks don't bother with.  

Edited January 3, 2017 by RyanT67
Autocorrect...