Triple Mikuni thread

[Travel'n Man]

Well getting the same jets in all of them is a good first step. Can't imagine trying to get that thing in balance the way it is. Time to call Todd....

I have 62.5 pilots, 150 main and 200 airs 34mm chokes and idle screws at 1.5ish in my 44's on a 3.1 stroker

What is your AFR at idle, 35 and 60, and WOT?

Edited July 11, 2014 by Travel'n Man

[Travel'n Man]

Can't log, not set up for it. Have the gauge mounted on the steering column though, so my eye is on it as much as it's on the speedo and tach. Might take the car out into the country for a good rip tomorrow, and record the main cluster while doing so. Would be good to review.

Either way, looks like I need a higher number for my main air jets from the looks of it? Not sure what's up with the pilot's fluctuating in numbers like that.

When I bought this car 2 years ago, it ran very poorly. Suspected it sat longer than the previous owner indicated and I took it into a Z-specialist shop to have the carbs cleaned, rebuilt, and properly tuned. It ran me $1350 for this service - I'm questioning that investment now. I knew it was running rich, but couldn't tell just how excessive it was until I got the wideband installed.

Ah well, the rest of the car is doing well, so I am ready to sink some time into this area and learn all I can.

Ryan-

I use a good ole' piece of paper in the passengers seat. It will take a lot of different settings to find the best one for your AFR. I would start by leaning out your pilot since you are running a high AFR at idle. Only make one change at a time and log it on your chart. Then (depending on your results) move to your air jet - you may need a little more air...........log that, then move to your main fuel, which sounds like you will need to lean out (go to a smaller size). When you go to different jets only drop 1 size at a time. Don't go from a 65 to a 60, too big of a jump.

Over the past 2 months I have tried about a dozen setting recording all of them on a spreadsheet so I can keep up with the different combinations and the AFR results.

[Travel'n Man]

Pilot Jet => 0-2%% throttle - cruising - low end power - (higher number equals richer mix)

Main Jet => 25-100% throttle - Adds or removes fuel from the entire RPM range - (higher number equals richer mix) - top end power

Air jet => Larger the air jet the more air coming into the Mikuni = (higher number the leaner mix)

Pump Nozzle => Larger the Nozzle bore size the shorter duration of fuel into the system

Pilot Screw Setting => This is not an AIR adjustment - this is the adjustment for the amount of fuel/air mix going into the carb (Clockwise = LEANER / Counter Clockwiser = RICHER)

[Travel'n Man]

Here is an example of my worksheet - I can not figure out how to post a spreadsheet to this site:

As you see I was still a little phat on this setting with my Main Fuel/Main Air

Date 7-Jun-14

Main Air Jet (Higher number = Leaner Mix) 200

Main Fuel Jet (Higher number = Richer) = HIGH SPEED 145

Pilot Jet (Higher number = Richer) = LOW SPEED 65

Pilot Screw (Base Setting 1.5 turns out) 2.5

Venturi Large 32

Pump Nozzle 0.40

Bleed Pipe T

Jet Block 8

AFR @1,000 RPM Warm Idle => 13.5

AFR @ WOT @5000 RPM => 13.5

AFR @ 35 MPH - 3RD GEAR - even pull => 12.6

AFR @ 60 MPH - 4TH GEAR - even pull => 12.4

AFR @ 60 MPH - 5TH GEAR - even pull => 13

Spark Plug Type => BPR6ES-11

Syncrometer Balance => 4

Spark Plug Condition => GOOD - DRY

Notes

Starting => EASY

Exhaust Smoke => SLIGHT

Fuel/Exhaust Smell -> VERY SLIGHT

Backfire => SLIGHT - ON DECEL

Low Speed Power => GOOD

High Power Power => GOOD

Edited July 11, 2014 by Travel'n Man

[Travel'n Man]

Ryan -

zKars gave you his setting and both you have the same set up........unknowing about cam. You may want to start with his baseline setting (one he posts his ARF - or a pic of his plugs) in yours and start fresh. If you pull your plugs they are going to look very black due to the extreme fuel being dumped on them. You are loosing the 3.1 performance that your engine has to offer. Keep us posted on your results.

[zKars]

What is your AFR at idle' date=' 35 and 60, and WOT?[/quote']

AFR idle >13.5

AFR 35 >> 12

AFR 60 >> 13-14

AFR WOT >> 13ish

[zKars]

While we're at it, thought I'd share another Mikuni tuning observation.

When the tuning was "slightly too lean" like 15-16 idle, 15ish putsing around town and on cruise, 15-16 at WOT, the car never sounded so smooth, quiet, never idled better, it was a dream for my old kinda nasty cammed stroker. This was with 57.5 pilots, and 150 mains.

Trouble was, it wasn't just the noise and harnessness that was gone, so was the power. The WOT power was slightly hesitant and bucky, just like what you're told when its too lean. No strong pull, obvious faltering. Around town felt "ok" bit it lacked the punch it had before. But the smoothness and quieter exhaust note were intoxicating in some way. I guess I could use this baseline for days when we're cruising on long trips and there are no "fun" parts where you want power, just smoothness and fuel economy. Hardly convenient, and no dang good at all when do get a "look" from some hi-brow in a $50 bazzillion dollar hot rod ... or an actual curve appears on the road ahead. Dang carbs, why can't I hide some injectors in there somewhere....

So I'm back to 62.5 pilots and 160 mains (see edit above) with carefully tweaked idle screws to get the leanest idle I can stand. Its brasher again, noiser, rougher, but it runs like the perverbial violated primate.... WOT is a total hoot. Stomp it anytime from 2K and it just pulls. AFR''s are 12-13ish at WOT.

Another observation after careful inspection. The first transition hole is JUST covered by the blades when fully closed, at least on my carbs. Virtually ANY amount of opening exposes that first hole almost immediately. Pretty tough (dare I say impossible?) to get that supposed ideal position where NO transition holes are exposed, just running on ilde screw port fuel, but the blades open enough so that it can idle. Now my blades are hardly pristine and un-touched, my old Q types have seen many miles. They're clean, but the blades don't close all very evenly. A strong light shone from front to back with them in your hand shows a variable amount of light sneaking around tortured blades from barrel to barrel.

Still this idea that "no transition holes until you actually USE the gas pedal" is pretty darn hard to attain. This explains the option to plug up that first transition hole that I've read about. I don't have a throttle-on stumble, the accel pump takes care of that, but if the pilots are too lean, it starts to show up, as you have to open the screw too far and you steal all the idle fuel before it gets to come out the transition holes. What a crazy balancing act.... Maybe if I have a air bypass valve to the vacuum log to adjust idle. hmmm, more hoses, valves and tubes... It lets more air in, but its dry, so have to increase the pilots..... here we go again!

[240260280z]

Jim,

That last sentence seems like you(Jim) are an organic O2 sensor

How about this variation:

Maybe a straw from the tail pipe to a nostril and a motorized fuel height screw controlled by the choke lever (for adding fuel when you need it w/o the jet swap).

[Travel'n Man]

I'm happy at 13'ish........I was in the 11's and 12's but my plugs were black. I'm happy on the phat side without black plugs!

[RyanT67]

Well getting the same jets in all of them is a good first step. Can't imagine trying to get that thing in balance the way it is. Time to call Todd....

I have 62.5 pilots, 160 main and 200 airs 34mm chokes and idle screws at 1.5ish in my 44's on a 3.1 stroker

EDIT : Sorry, the original statement above said. 150 main was actually 160. 150 was an earlier iteration.

Thanks for sharing. I've no idea what I have for internals with my engine, purely the previous owners listing and an old barrett-jackson listing that state the car has a 3.0 stroker in it. Given all the other toys on the car, it's likely true. I should go ahead and at least see what cam I am running though.

I think I will head towards the jets you have posted though, shouldn't be too far off what I need. I am running a 34 choke already.

Here is an example of my worksheet - I can not figure out how to post a spreadsheet to this site:

As you see I was still a little phat on this setting with my Main Fuel/Main Air

Date 7-Jun-14

Main Air Jet (Higher number = Leaner Mix) 200

Main Fuel Jet (Higher number = Richer) = HIGH SPEED 145

Pilot Jet (Higher number = Richer) = LOW SPEED 65

Pilot Screw (Base Setting 1.5 turns out) 2.5

Venturi Large 32

Pump Nozzle 0.40

Bleed Pipe T

Jet Block 8

AFR @1' date='000 RPM Warm Idle => 13.5

AFR @ WOT @5000 RPM => 13.5

AFR @ 35 MPH - 3RD GEAR - even pull => 12.6

AFR @ 60 MPH - 4TH GEAR - even pull => 12.4

AFR @ 60 MPH - 5TH GEAR - even pull => 13

Spark Plug Type => BPR6ES-11

Syncrometer Balance => 4

Spark Plug Condition => GOOD - DRY

Notes

Starting => EASY

Exhaust Smoke => SLIGHT

Fuel/Exhaust Smell -> VERY SLIGHT

Backfire => SLIGHT - ON DECEL

Low Speed Power => GOOD

High Power Power => GOOD[/quote']

Very good idea!! Thanks for the template, ideal!

Rookie question for you guys: Is it normal to lean out a lot when you let off the gas pedal, or drop a gear on deceleration? I drop down towards 16, sometimes as low as 17 when doing so, and get a pretty large amount of backfire. I built some det cans to listen in better on the engine, and don't seem to hear any detonation/ping though, thankfully.

As far as ordering jets, I think I need to build a solid base set of them for when I eventually take the car to the dyno to nail down the tuning and timing. So how about sets of:

Main fuel: 145(3), 150, 155, 160

Main air: 180, 190, 200

Pilot: 55 (3), 57.5, 60, 62.5

I'm sure Todd will keep me in the right on this. Don't mind spending the money, just want to get it done right and have some room to play - and being in Canada, it's a hassle to continually order and suffer shipping charges.

[zKars]

Ryant67, yes, it normal. Throttle blades snap shot, no air flow = no fuel, = high AFR. The back fire is something else, ie residual fuel in the system getting ignited by elevated temps in the exhaust. Definite sign of being too rich most of the time.

I used to get that engine braking down a hill. Sounds all racy and stuff, like I have a bad arse motor. Even got little flames some times. People point and stare, and I'm sure they are thinkin' "that guy is cool with that fast car"... That is what they were thinking wasn't it? Right?

Don't worry about spend too much on jets. I'll relieve you of your burden and re-line your pockets when you're done jetting.

[madkaw]

While we're at it, thought I'd share another Mikuni tuning observation.

When the tuning was "slightly too lean" like 15-16 idle, 15ish putsing around town and on cruise, 15-16 at WOT, the car never sounded so smooth, quiet, never idled better, it was a dream for my old kinda nasty cammed stroker. This was with 57.5 pilots, and 150 mains.

Trouble was, it wasn't just the noise and harnessness that was gone, so was the power. The WOT power was slightly hesitant and bucky, just like what you're told when its too lean. No strong pull, obvious faltering. Around town felt "ok" bit it lacked the punch it had before. But the smoothness and quieter exhaust note were intoxicating in some way. I guess I could use this baseline for days when we're cruising on long trips and there are no "fun" parts where you want power, just smoothness and fuel economy. Hardly convenient, and no dang good at all when do get a "look" from some hi-brow in a $50 bazzillion dollar hot rod ... or an actual curve appears on the road ahead. Dang carbs, why can't I hide some injectors in there somewhere....

So I'm back to 62.5 pilots and 160 mains (see edit above) with carefully tweaked idle screws to get the leanest idle I can stand. Its brasher again, noiser, rougher, but it runs like the perverbial violated primate.... WOT is a total hoot. Stomp it anytime from 2K and it just pulls. AFR''s are 12-13ish at WOT.

Another observation after careful inspection. The first transition hole is JUST covered by the blades when fully closed, at least on my carbs. Virtually ANY amount of opening exposes that first hole almost immediately. Pretty tough (dare I say impossible?) to get that supposed ideal position where NO transition holes are exposed, just running on ilde screw port fuel, but the blades open enough so that it can idle. Now my blades are hardly pristine and un-touched, my old Q types have seen many miles. They're clean, but the blades don't close all very evenly. A strong light shone from front to back with them in your hand shows a variable amount of light sneaking around tortured blades from barrel to barrel.

Still this idea that "no transition holes until you actually USE the gas pedal" is pretty darn hard to attain. This explains the option to plug up that first transition hole that I've read about. I don't have a throttle-on stumble, the accel pump takes care of that, but if the pilots are too lean, it starts to show up, as you have to open the screw too far and you steal all the idle fuel before it gets to come out the transition holes. What a crazy balancing act.... Maybe if I have a air bypass valve to the vacuum log to adjust idle. hmmm, more hoses, valves and tubes... It lets more air in, but its dry, so have to increase the pilots..... here we go again!

My observation has been the opposite. Engine purrs and sounds so much smoother with a rich mix. Exhaust sound is fuller if that makes sense.

I really don't think these carbs were designed for lean driving. Probably has much to do with the Tau layer. Love my Mikunis but ready to tune without my hands smelling like gas