Carb advice for 620 w/ L20b

[banzai510(hainz)]

if your a daily driver a 32/36 is a simple cheap amd reliable carb.

a 38 38 is a a little big but since your in texas there is not alot of hills which I had proplems clutching it it can stall out but once rolling it take off say after 2500rpm. I would port port match the head and instake. and if a U67 head that wouldbe great as its a 1.375 size I believe.. also enlarge the throuts where the carb sits on and round out the edges will help.

Remeber if you have a Tall carb adapter which I like better youl need to run the 1.75 inch aircleaner as the taller one will hit the hood(L 20b)

 

To me used SUs are junk. if running good they great but I seen so many in the junk bins and sold for nothing. Mostly Kids dont know how to fix and adjust them. (including me)

Edited October 2, 2018 by banzai510(hainz)

[datzenmike]

What's your poison? 

 

Hitachi 340 (30mmX34mm), best over all mileage, performance, low emissions and drive ability

Hitachi SUs better performance and good drive ability once jetted properly

32/36 Weber, better performance than 340, less gas mileage when jetted and driven right but poorer drive ability. (has progressive throttle and has to be driven properly)

38/38 Weber, 6 or small v8 carburetor. Too big but has good top end power and poor low speed drive ability. Has synchronous throttle and opens fully on demand. Because of this, needs to be driven with light foot at mid and low speeds.use of this you have to step into it gradually. 

 

Drive ability...... Excellent cold starts and hot restarts in ALL weather and temperatures. Good mileage and easy start offs from a stop without hesitation and balkyness. Easy to drive in stop and go traffic. 

[damesta]

1 hour ago, banzai510(hainz) said:

if your a daily driver a 32/36 is a simple cheap amd reliable carb.

a 38 38 is a a little big but since your in texas there is not alot of hills which I had proplems clutching it it can stall out but once rolling it take off say after 2500rpm. I would port port match the head and instake. and if a U67 head that wouldbe great as its a 1.375 size I believe.. also enlarge the throuts where the carb sits on and round out the edges will help.

Remeber if you have a Tall carb adapter which I like better youl nee to run the 1.75 inch aircleaner as the taller one will hit the hood(L 20b)

 

To me used SUs are junk. if running good they great but I seen so many in the junk bins and sold for nothing. Mostly Kids dont know how to fix and adjust them. (including me)

 

This is an L20b w/ A87 head, if I go 38/38 it will be on the redline performance manifold made for the carb and kit includes their air filter. I agree with you on the used SU's...I have never had any luck with them, I love new or good fresh rebuilt SU's, they are great and easy to tune...but every time I have tried to set up used ones I'm just running in circles trying to fix multiple problems. I really make a point to try to start with brand new carbs whenever I can now, just too much bs trying to use old ones.

 

38 minutes ago, datzenmike said:

What's your poison? 

 

Hitachi 340 (30mmX34mm), best over all mileage, performance, low emissions and drive ability

Hitachi SUs better performance and good drive ability once jetted properly

32/36 Weber, better performance than 340, less gas mileage when jetted and driven right but poorer drive ability. (has progressive throttle and has to be driven properly)

38/38 Weber, 6 or small v8 carburetor. Too big but has good top end power and poor low speed drive ability. Has synchronous throttle and opens fully on demand. Because of this, needs to be driven with light foot at mid and low speeds.use of this you have to step into it gradually. 

 

Drive ability...... Excellent cold starts and hot restarts in ALL weather and temperatures. Good mileage and easy start offs from a stop without hesitation and balkyness. Easy to drive in stop and go traffic. 

 

The hitachi 340 may be a better option worth looking into at least, just to get this truck going and reliable without dealing with pros/cons of everything else right now. I just don't know which way to even go with webers anymore, everyone has different advice on them....half love them and say they are super easy to tune, half hate them and say they are difficult....half (including redline themselves) say the 32/36 is too small for 2000cc motor, other half say 32/36 is perfect size.....some people say drivability is shit with 38/38, other half say they have never had any drivability issues at all and drive them normally....so I really have no idea which way to go. 38/38 would seem to be the safest and most future upgrade proof carbs to invest in where I could adapt and tune them to any upgrades down the line....but I really have no idea any more.

 

How difficult is the hitachi 340 to tune properly, they look simple from my very limited knowledge on them. Is there somewhere to get a NOS 340 or high quality reman unit that you know of? I see these reman factory replacement carbs everywhere, ebay, oriellys, autozone, etc but none of them really have any details on the model. Are these all 340s?

[distributorguy]

You have the common 1 1/2" carbs.  Basically 36/36, which are properly sized for a 1.8 - 2L engine. 

They are the right size for the motor.  In fact the 1 3/4" version are the performance ones.  

 

Your choke tubes are worn out, and they are included in the rebuild kit.  They need a rebuild.  Period.  Call Jeff Palya at Paltech regarding the rebuild.  Its the easy way to go.  

[damesta]

1 hour ago, distributorguy said:

You have the common 1 1/2" carbs.  Basically 36/36, which are properly sized for a 1.8 - 2L engine. 

They are the right size for the motor.  In fact the 1 3/4" version are the performance ones.  

 

Your choke tubes are worn out, and they are included in the rebuild kit.  They need a rebuild.  Period.  Call Jeff Palya at Paltech regarding the rebuild.  Its the easy way to go.  

 

Alright, emailed Jeff. If he can get it done in a reasonable amount of time I'll just keep the su's.

[distributorguy]

I hate the argument of a carb being "too big."  It always comes from people who have never tried it, yet like to recite crap they read on the internet.

On a 620, I've run the DGV, DCOEs, 1 1/2" SUs, 1 3/4" SUs, and 2" SUs.  

The best drivability on a stock compression engine was the 1 3/4", which is similar in size to running dual 45DCOEs in terms of effective cross section of the throttle plates when wide open.  

Drivability is great on almost ALL carbs, once they are tuned.  Some are easier to tune than others.  SUs win that battle.  Weber DCOEs lose as the most difficult to tune of all carbs, although persistence can result in an exceptional running vehicle at ALL rpms.  Our race truck idles smoothly at 500 rpms with 14:1 compression and launches like a rocket with dual 50DCOEs - when tuned properly.  WIth a stock motor the 1 1/2" SUs were great, but it ran out of steam earlier in the rpm band (carbs too small).  The bigger the carbs, the higher you can rev.  Most people don't have the guts to go past 7k.  We go past 10k.  ?

[banzai510(hainz)]

Be honest I like the 38/38 and be perfect for a cammed L20 with a lowerr gear ratio like a 521 pickup. jetted down a little and be a perfect simple daily driver carb.  To me its cheap and ez to maintain even for a  novice machanic.

Edited October 2, 2018 by banzai510(hainz)

[Ron1200]

Just sharing my experience with SUs... I liked them alot for my daily driver, once I got them working right on the L20b. It took a long time to figure out that the air box that came on the truck - L16 at the time - was causing the SUs to run extremely rich (my wife could smell gas when she followed me in her car).

 

There were two things that I have not seen mentioned that may be useful to you... 

From my 10/12/16 post

I reached Steven at Z-Therapy and found out a couple of things:

1. The air box fitted to the 620 when I purchased it blocked the vents and made the SUs run rich.

2. The jet nozzle can easily be removed (via one screw) out the bottom of the carb and cleaned with a wire brush to fix the sticking choke. (I used a rifle bore brush).

[10/9/18 note: I can't remember what size bore brush - maybe .22 or 9mm]

 

From 2nd 10/12/16 post

I got the SUs balanced and adjusted, not perfect, but close for a SU newbie... And all I can say is WOW!.  This truck drives sooooo much better.  Smooth acceleration from idle to redline and better MPG to boot.  I can see people here like them.  Woot!  :thumbup:

 

Took me a while but I finally got the linkage figured out.  I could not find adjustment info specific to these carbs... maybe it's obvious to some, but it wasn't for me.  Screws circled in red are the high speed balance screws, the screws circled in blue are the typical idle adjustment screws.

Edited October 10, 2018 by Ron1200

[wayno]

I only have one of the screws circled in red, it is for balancing the carbs so they both move at exactly the same time when the throttle is pushed.

[damesta]

6 hours ago, Ron1200 said:

Just sharing my experience with SUs... I liked them alot for my daily driver, once I got them working right on the L20b. It took a long time to figure out that the air box that came on the truck - L16 at the time - was causing the SUs to run extremely rich (my wife could smell gas when she followed me in her car).

 

There were two things that I have not seen mentioned that may be useful to you... 

From my 10/12/16 post

I reached Steven at Z-Therapy and found out a couple of things:

1. The air box fitted to the 620 when I purchased it blocked the vents and made the SUs run rich.

2. The jet nozzle can easily be removed (via one screw) out the bottom of the carb and cleaned with a wire brush to fix the sticking choke. (I used a rifle bore brush).

[10/9/18 note: I can't remember what size bore brush - maybe .22 or 9mm]

 

From 2nd 10/12/16 post

I got the SUs balanced and adjusted, not perfect, but close for a SU newbie... And all I can say is WOW!.  This truck drives sooooo much better.  Smooth acceleration from idle to redline and better MPG to boot.  I can see people here like them.  Woot!  :thumbup:

 

Took me a while but I finally got the linkage figured out.  I could not find adjustment info specific to these carbs... maybe it's obvious to some, but it wasn't for me.  Screws circled in red are the high speed balance screws, the screws circled in blue are the typical idle adjustment screws.

 

I've never used an airbox so thats not a problem I've ever had and all the syncing/balancing linkage stuff I had already learned from the last few 240z's I've buily with su's....I never knew you could remove and clean the jet nozzle though, that's interesting, never heard anyone mention that before.

[datzenmike]

 

If bigger were better we would all have four barrels but it's obvious that going larger and larger has a limit.

 

Everyone drives differently and some drivers are willing to give up some advantages of a stock carb and put up with minor to major drive-ability issues and quirks running a too large carb to get a performance increase.

 

Not everyone can tune their carb(s) 'properly' or want to. They expect a larger carb to have no down side. There is always compromise.

 

 

Generally, don't over carb your engine. Or go ahead but don't throw your old carb away.

 

 

 

[damesta]

59 minutes ago, datzenmike said:

 

If bigger were better we would all have four barrels but it's obvious that going larger and larger has a limit.

 

Everyone drives differently and some drivers are willing to give up some advantages of a stock carb and put up with minor to major drive-ability issues and quirks running a too large carb to get a performance increase.

 

Not everyone can tune their carb(s) 'properly' or want to. They expect a larger carb to have no down side. There is always compromise.

 

 

Generally, don't over carb your engine. Or go ahead but don't throw your old carb away.

 

 

 

Exactly why I didn't end u going with 38/38. I'm playing with a weber 32/36 right now just because it was so cheap. If I decide I like it I'll keep it, if not the su's are getting rebuilt and going back on.