My 1971 521

[Oilspot]

1 minute ago, Oilspot said:

or other way around. mark the drive shaft as well as the tire.  turn the drive shaft one full turn and see how many times the wheel turns

 

if the tire turns around about 3.88 times........  

walked away and started thinking.... is it two turns and count the tire rotation because of the differential!?!?! 

It's early, i haven't had enough coffee, and am not firing on all cylinders yet!

[datzenmike]

No.

 

If it's a 3.889 differential the drive shaft will need to be turned 3.889 times for two tire rotations. One drive shaft turn would be something like 1.944 tire turns.

[d.p]

Not the best picture but really the first time anyone but me has driven my truck for anything other than an alignment.  My dad used to take a new dishwasher to my brother's house today.  I almost shed a tear but I also learned how loud my truck is.  Sounds ridiculous on start up.  

 

[Crashtd420]

32 minutes ago, d.p said:

Not the best picture but really the first time anyone but me has driven my truck for anything other than an alignment.  My dad used to take a new dishwasher to my brother's house today.  I almost shed a tear but I also learned how loud my truck is.  Sounds ridiculous on start up.  

 

Your lucky you can still drive it down there... mines tucked away for a couple months now till the salt on the roads is gone....

 

Only person ever to drive mine was the tech for an inspection sticker...

No one I know is brave enough,  i have offered people but no takers and I'm too scared to teach my wife to drive a stick shift in it.... so broke my Chevy s10 then last time I tried...

Probably not her fault but she exploded the rear brake line panic braking...

 

[thisismatt]

1 hour ago, d.p said:

Not the best picture but really the first time anyone but me has driven my truck for anything other than an alignment.  My dad used to take a new dishwasher to my brother's house today.  I almost shed a tear but I also learned how loud my truck is.  Sounds ridiculous on start up.  

 

 

Must be nice...still having a dad.

 

I let my brother in law borrow mine a few times when his truck died.  I wasn't around so never saw it happen 😅

[d.p]

Yeah it was cool to see.  The guy never even rode in it and all of the sudden wanted to drive it.  Glad it didn’t shit the bed on him either cause that would have sucked.  

[d.p]

Oh and the weather has been decent down here. Cold in the 30s but no snow or anything so I can still drive it but don’t really.  
 

which leads me to next question do carbs need to be adjusted in colder temps? IE winter? I feel like it needs to be.  

[mainer311]

Technically yes, since cold air gets much more dense. Cold weather will make it run more lean.

[d.p]

49 minutes ago, mainer311 said:

Technically yes, since cold air gets much more dense. Cold weather will make it run more lean.

fuck I noticed that on my air fuel gauge and couldn’t figure out why.  I can’t do shit about it though cause I don’t have any other jets.  

[Stoffregen Motorsports]

You could run with the choke ever so slightly engaged. I have to do that with my old Farmall Cub tractor when it's cold out.

[d.p]

No choke my man. Dual Mikunis. 

[Crashtd420]

1 hour ago, Stoffregen Motorsports said:

You could run with the choke ever so slightly engaged. I have to do that with my old Farmall Cub tractor when it's cold out.

Is it possible to just turn the air/fuel screw up a little?

I know that's for mostly idle but it has some effect on the rest...

[datzenmike]

 Hair splitting. Set carb(s) for 60F and ideal a/f ratio. It will be only slightly lean below and slightly rich above this.  To be perfect you would have to calculate and change the jets daily and that's a perfect example of diminishing returns. Increasing effort for decreasing returns.

 

If perfect a/f ratio (stoichiometric) is 14.7 it is the top of a broad bell curve with 13.7 to 15.7 not really affecting mileage or performance very much. Yes it's lean on one side and it's rich on the other but not enough to matter much. It's just an imaginary perfect line.  

 

 If you want perfect connect an ATC system that uses warmed air from the exhaust mixed with ambient to maintain a constant temperature air to the carburetor(s)

 

 

[mainer311]

3 hours ago, Crashtd420 said:

Is it possible to just turn the air/fuel screw up a little?

I know that's for mostly idle but it has some effect on the rest...

The idle screw only controls the port behind the butterfly when it’s closed. He’d be better off going up an idle jet size if he had one.

[d.p]

19 hours ago, mainer311 said:

The idle screw only controls the port behind the butterfly when it’s closed. He’d be better off going up an idle jet size if he had one.

yeah which was my point. I don’t have any but would buy if knew what I needed to get.  Which ones are my idle jets and where can I buy?

 

[Stoffregen Motorsports]

The small jets on top are the idle jets.

 

I don't understand how increasing the size of the idle jets would solve the cold running issue. I would swap to a larger main jet. (it's the one on the bottom of the jet block. You can't see it in the pic.)

 

As Mike said, maintaining a warm air supply to the carb inlet would help.

[d.p]

5 hours ago, Stoffregen Motorsports said:

The small jets on top are the idle jets.

 

I don't understand how increasing the size of the idle jets would solve the cold running issue. I would swap to a larger main jet. (it's the one on the bottom of the jet block. You can't see it in the pic.)

 

As Mike said, maintaining a warm air supply to the carb inlet would help.

 Neither do I hence why I asked.  But see jets all the same or do I need Mikuni specific jets?

 

and I believe my main jets are 60. 
 

[d.p]

Its these at the bottom right? If so and they are 60 I should get 65s? Pic below is from when one backed out when I first out it all back together. 

 

[NC85ST]

Wow! That jet looks like the one in the Mikuni carb on the the Yamaha QT50 moped I have. Appears to be the same diameter.

[mainer311]

9 hours ago, Stoffregen Motorsports said:

The small jets on top are the idle jets.

 

I don't understand how increasing the size of the idle jets would solve the cold running issue. I would swap to a larger main jet. (it's the one on the bottom of the jet block. You can't see it in the pic.)

 

As Mike said, maintaining a warm air supply to the carb inlet would help.

Because the “idle” jets control the whole transition circuit until the main Venturi takes over. Most of your driving puttering around town is on the idle circuit.

[mainer311]

4 hours ago, d.p said:

Its these at the bottom right? If so and they are 60 I should get 65s? Pic below is from when one backed out when I first out it all back together. 

 

No. What that pic shows is (from top to bottom) an air corrector, an emulsion tube, and a main jet. Mikuni calls them different things, but that’s what they are.

 

In your picture further up, the small jets are the pilot (idle) jets. Since those are also 60’s, you could try 65’s.

Edited December 27, 2021 by mainer311

[Stoffregen Motorsports]

I would still try the main jet first. It controls the entire fuel curve.

 

Maybe a different emulsion tube/jet block?

[mainer311]

The air corrector controls when it takes over. Smaller air orifice, the quicker the vac from the Venturi starts pulling fuel from the well. None of this matters below 2500 rpm or so.

[d.p]

Ok so this is what I will need?  4 of them?

 

https://www.shop.upgrademotoring.com/Mikuni-Carburetor-Pilot-Jet-65-40-44PHH28-N101043-65-MIKN101043-65.htm?categoryId=-1

 

 

[Crashtd420]

Realisticlly how far off on your air/fuel are you?