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Rat-a-tat-Dat's '79 720 rebirthing of 'Helios'


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I'd considered putting on a Holley Sniper 2BBL EFI system on my build - self-learns and adjusts to suit your needs, but for me the cost was prohibitive. Mechanically it's relatively simple to convert to when you're doing a build, as you need a 3/8" fuel supply line plus a return line, and an electric fuel pump which you're probably already planning for anyway. 

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14 minutes ago, EDM620 said:

I'd considered putting on a Holley Sniper 2BBL EFI system on my build - self-learns and adjusts to suit your needs, but for me the cost was prohibitive. Mechanically it's relatively simple to convert to when you're doing a build, as you need a 3/8" fuel supply line plus a return line, and an electric fuel pump which you're probably already planning for anyway. 

I need a sponsor!

 

There are a couple guys here running that sniper unit with good results.. 

 

You still need to fabricate an adapter plate though to bolt it on , and I know one guy running it cant put his hood back on now, I'm not sure how close it is or how much clearance he needs, but height may be an issue, or atleast its something to watch out for ....

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Hail to you Crashtd420, that is indeed the cover of the Manual.

If I relate the specifics of my engine to you, perhaps you can then identify them in the manuals contents and post the pages. 

I know there are many combinations and different types of components that may be used but an educated deduction would be very helpful to start with.

 

1) 1980 L20B stock engine block

2) W58 peanut cylinder head, exhaust liners removed, port matched to intake and exhaust runners, stock cam, new valves and springs

3) Cannon regular length intake, port matched to head

4) Weber dual carburetor, 40 DCOE, 151 > 125 mains, F11 emulsion tubes, 180 air jets, need to confirm the Venturi diameter.

5) Tri-Y exhaust off an L18 ( round head to square exhaust opening ), 1 7/8"id pipe, stock muffler

6) Mechanical fuel pump, no return to tank line

7) Petronic dizzy, vac line plugged off.

😎5 speed manual tranny

 

Any graphs or charts are welcome too.

 

Many thanks Crashrtd420

 

 

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6 hours ago, Rat-a-tat-Dat said:

Hail to you Crashtd420, that is indeed the cover of the Manual.

If I relate the specifics of my engine to you, perhaps you can then identify them in the manuals contents and post the pages. 

I know there are many combinations and different types of components that may be used but an educated deduction would be very helpful to start with.

 

1) 1980 L20B stock engine block

2) W58 peanut cylinder head, exhaust liners removed, port matched to intake and exhaust runners, stock cam, new valves and springs

3) Cannon regular length intake, port matched to head

4) Weber dual carburetor, 40 DCOE, 151 > 125 mains, F11 emulsion tubes, 180 air jets, need to confirm the Venturi diameter.

5) Tri-Y exhaust off an L18 ( round head to square exhaust opening ), 1 7/8"id pipe, stock muffler

6) Mechanical fuel pump, no return to tank line

7) Petronic dizzy, vac line plugged off.

😎5 speed manual tranny

 

Any graphs or charts are welcome too.

 

Many thanks Crashrtd420

 

 

 

These are the bibles I keep on my side table....

20200718-064306.jpg

 

I'm not sure what your actually looking for? 

They show some engine combo examples but nothing specific to datsun....

There's close to 40 pages out of about 92 pages that could be relevant.... 

 

I am actually running a single 40dcoe with a lynx intake on my L16, I spent alot of time trying to understand how it works and what changes effect different running circuits .... I even played on a dyno watching what happens when I make certain changes....

 

Are you having problems with them running right? maybe I can point you in the right direction and post relevant pages to help....

 

Following this now so I'll get notified of posts, I'll try to respond in a timely manner.....

 

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My bad for not being more direct with the need to get the carbs running properly.

 

There seems to be an ongoing problem, fully developed now, with the idle ( very hard to setup and keep it steady ) plus the transition from idle until over 2K rpm.

 

I discovered an issue inside the front carb with the throttle plate sticking after the engine was at ambient operation temperature. Albeit this was only a partial discovery. 

 

The carburetors performance, over time, have slowly  become a disappointment. Lack of power, poor idle qualities, over fuelling ( smells of gas after engine shut down ) and of course the problem with the sticky throttle thing.

 

After reading the Weber set up guide and numerous other articles on said carbs, I figured the Webers needed a performance tune up. They are after all used and sat for who knows how long.

 

Soooo, I just need to know the correct jetting sequence for these carbs on a 2000cc engine with my specs in an earlier post.

 

I'm pulling both carbs off and disassemble for a rebuild, checking out why the one is sticking and then set them up with ( hopefully ) new jets while I'm at it.

 

Crossed fingers to correct what I'm experiencing and be able to enjoy the ride.

 

Thank you so very much for your help and experience on this matter.

 

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Ok....

Do you possibly have an air fuel ratio gauge?

If you really wanna get these carbs right it's a worthwhile investment......

 

When I broke my engine in I did it on a dyno.... too many new parts, and the truck wasnt done yet.... barely a rolled with a running motor.... everthing was just a ball park guess to get the engine running and broken in.. as i was running it the engine felt like it needed more gas, well I was very surprised to see that it needed to be leaned out.... turned out my biggest enemy was too much fuel pressure.....

 

You said you have the mechanical pump so that should be good... a cheap low pressure fuel gauge wouldnt be a bad idea either.... just to make sure ...

I did I cheap inline one just before the carburetor....

 

With all that said, your main and air correctors seem to be in the right range..... 

The one good thing is the 151 dcoe are the newer version with 3 progressive holes vs older with only 2....

Do you have any idea what your idle jets are?

 

As far as the transition that works with the idle jet and the progressive holes....

I also found the emulsion tube can help by bringing in the main circuit sooner or later..... 

 

This has some good info in it....

http://240260280.com/Tech/Carbs/Weber/DCOE Theory Operation and Tuning.html

 

I'll put some more info together for you from the book.... 

Idle jets and the emulsion tubes are weird with the numbers and letters... 

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Have a look at your plugs too, are they telling you anything?

 

Also the vacuum balancing is a good idea... mine was brand new and it was slightly off between the 2 barrels...

You can have 2 carbs and 4 barrels so there is room for error there....

Edited by Crashtd420
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Air fuel ratio gauge will be purchased in the near future along with the carb rebuild kits.

 

The Venturi is 30 mm for both carbs, seems too small for engine (IDK)

 

Idle jets are 0.45 

 

Carbs are currently running without air horns/velocity stacks/trumpets on intake side (FYI)

 

I'll pull plugs and check colouring.

 

A lot of info here to digest...

 

Accelerator pump valve may be leaking,  gas smell symptom 

 

I got my work cut for me

 

Cheers,  crashtd420

 

 

 

 

 

 

 

 

 

 

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I think the 30mm is the choke which is what I comes with and the 45, probably f9 is the original idle jet too....

 

Depending on what your intended rpm range in I think the 30mm are good ... 

Bigger chokes are ment for higher rpms..

On my single I'm running 32mm chokes... oh and it's a done up L16 that I daily drive for reference...

 

The biggest key is starting at the idle and getting that right, with the weber each circuit sort of overlaps to the next.. 

 

I found the dead spot or transition was corrected by a different emulsion tube, it brought the fuel curve from the mains in sooner...

I think I have a chart that's shows them lean to rich.... they are not in order by f number.... 

 

Another thing I did that was recommended was to plug the drain back from the pump jet....

Basically the some of the fuel gets sent back to the bowl from the accelerator pump jet.... not sure why.... 

This helped when you go wot really quick.... 

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My calculation based on engine size is roughly 488cc per hole, which equates to an F2 emulsion tube. A logical place to start.

 

One main jet was a different size also on the rear carb, not too much out ~ 0.05", 120 vs 125's

 

Accelerator pump jet, on same carb as above, had a bad washer underneath its mating surface. Could be why it was leaking fuel.

 

Noted;  Most gasket surfaces between carb air filter housings and heat shield to carb mounting faces were discoloured, possible back fire residue? or heat transfer from exhaust manifold?

I fabricated a one piece heat shield for both carbs and yes, mounted it to the carbs outer intake bodies. Basically sandwiched it in between the air filter housings with gaskets on either side. Was this a bad idea? 

 

As I'm scripting this message, I have discovered my mistake with the heat shield. My brain, at the time, had focused on a singular piece of metal to which the outcome was satisfactory. However, my failure was in the mounting. It had been mounted onto the exhaust manifold to help hold it in place, thus directly transferring high thermal heat to the carbs. Oh, what a clever boy! This will definitely be corrected, pronto.

 

Live & learn.

 

Thanks again Crashtd420 for more info

 

 

 

 

 

 

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14 hours ago, Rat-a-tat-Dat said:

 

Carbs are currently running without air horns/velocity stacks/trumpets on intake side (FYI)

 

 

 

Was thinking about this comment,  

Are you running that short filter?

 

There are really low profile air horns

... top left...

20200719-075729.jpg

 

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As delinquency dictates, I've read several articles on the actuality and representation of the necessity for air horns and it is quite convoluted. Pro vs Con, there hadn't been any straightforward measure or evidence supporting benefits. Thus, my option not to include them was primarily an experiment. Plus, I had trouble locating the size and length required. More so, the options available, albeit the top mounted or the internal air horn fitment type. These were considerations but not on my priority list. Most of the articles are rendering parts sales and promoting business, hence the absence of really solid facts of conviction.

I'm not a naysayer, but with my set up the need of such short air horns mounted inside these short air filter housings makes me wonder if there would be a significant difference. However, a benefit I shall gladly accept once a noticeable change has been procured.

At one point I had considered too fabricate an adaptation of an air horn. I got inspired by what DatsunMike had done on his build.

"Appropriate measures emancipate inadequate gains".

As always, thanks. I really do appreciate the help.

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I had SU's without air horns and drove it like that for years.Then i added them.There was a difference,it ran better with them.The same thing with the Mikuni's i run now.I'd use them even if you have to run shorter ones.

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OMG, what a challenge. I don't know about you fellas down south but up here in Canukville, Weber carb emulsion tubes are worth as much as gold. A set of four is north of a hundy, without shipping. Ouch!

Another century note for air horns.

Time to be creative!

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2 hours ago, Rat-a-tat-Dat said:

OMG, what a challenge. I don't know about you fellas down south but up here in Canukville, Weber carb emulsion tubes are worth as much as gold. A set of four is north of a hundy, without shipping. Ouch!

Another century note for air horns.

Time to be creative!

Ya they are not as cheap as jets....

One reason they dont get changed as often... 

 

I think I paid around 15-20 per for mine, luckily only need 2... I just realized your up in Canada,  so with the exchange rate I could see that for 4 tubes.. 

 

Also watch out for the knockoff stuff... 

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  • 3 weeks later...

Immersed myself into the depths of understanding the intricate details and internal operations of all the components that make these carbs perform well.

Knowing basic tuning of these carbs was not helping but only hindering the outcome. Step by step measures unravelled a plethora of inconsistencies and under compensated values.

I can divulge several details, at this prominence, which entail an early diagnosis but not limiting rectification by assumption.

Hard choices demand specific characterizations and involves a total, if not complete, understanding on how everything is related, balanced and controlled. 

I'm no expert by any means but I do like to understand how things work. Decisions get easier with knowledge and knowledge is the key to success.

 

Known issues were:

1) poor mounting location of the heat shield for the carbs

2) used carbs installed on a completely different application

3) rough idling

4) over fuelling ( gassy smell )

5) performs better at higher rpm's 

6) newbe trying to do the impossible

 

Newer finds and results:

1) not all main jets were same size

2) emulsion tubes are underrated for cylinder size

3) Venturi size require a larger opening

4) float level gap inconsistent

5) open float (full drop) over rated value

6) idle speed screw value critical 

7) mixture screw settings are very important

8 ) idle air bleed screw adjustment requires a synchrometer, if needed

9) spark plug colour indicates issues

10) timing degree mark vs actual

11) total advance at 3000rpm?

12) check throttle plates for restrictions and trueness

13) soft mount, attached between carb and intake, clearances are critical

 

As I dive deeper, I'll keep record of any other asymmetrical encounters and remedies.

Parts order list is near completion.

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I think your on the right path to head down the rabbit hole....

This is probably the reason people just learn to drive their weber as is.... tuning takes a bit of effort and understanding...

 

Only advice I can say is dont change too much at once.... I'd start with balancing everything then start making the changes.... 

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If your looking at buying a fair amount of tuning parts for your Weber's,  you might want to consider sourcing out of the UK.

 

https://www.burtonpower.com/catalogsearch/result/?q=ram+pipes

 

https://www.burtonpower.com/catalogsearch/result/?q=weber+jets

 

https://www.burtonpower.com/catalogsearch/result/?q=weber+emulsion+tubes

Edited by docbainey
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On 8/7/2020 at 6:54 AM, Crashtd420 said:

Only advice I can say is dont change too much at once.... I'd start with balancing everything then start making the changes.... 

Real good advise, it's advantageous be methodical and deliberate one step at at time

 

On 8/7/2020 at 10:03 AM, docbainey said:

If your looking at buying a fair amount of tuning parts for your Weber's,  you might want to consider sourcing out of the UK.

Those sites were very helpful and enlightening, thanks

Considering exchange and shipping rates need to be included, I may have a meagre margin to work with but when the supply is insufficient, alternative action is imperative

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  • 1 month later...

Well, my mini vaca from Helios was not on account of neglect but of frustration and disappointment, all because of a Weber specialist from Redline. We were exchanging carburation information between us and I thought our progress was going well... I'll edit this novel and turn it into a short story. After several weeks of on again off again tag, I wasn't sure if he had gone on vacation or what but a lack of responding on his part was irritating and so unprofessional, it left me haggard and it exhausted my enthusiasm to calibrate the carbs. 

I had hope and anticipation in completing this task without subjecting myself to needless and expensive trial and error costs but alas, thanks to good old what's his name, it seems my trepidation of having profound and logical advise gets tossed into the abortion bin, again. So much for the professional approach.

 

Oh, and thanks for letting me hang for weeks on end without responding to any of my emails, JERK!

 

Biting the preverbal bullet and ordering emulsion tubes, previously perused info from Crashtd720 via Weber Tuning Manual 

 

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