CARBURETION for your 4AG

Technical How-To guides contributed by various technically proficient members from our community and voted popular by our members of the community at large.

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dr.occa
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CARBURETION for your 4AG

Post by dr.occa »

CARBED 4AGE GROCERY LIST ESSENTIALS

This is not an exhaustive grocery list but I'll do my best to mention the essentials.

1. Carb(s): dual side-draughts, dual down-draughts, single down draught 4 barrel/ 2 barrel, carb per cylinder (e.g. motorcycle carburetor(s))
2. Intake Manifold for mounting your carb(s) of choice to the 4AGE head
3. HVLP (high-volume low-pressure) Electric Fuel Pump:

Webers - no more than 4 lbs of delivery
Mikuni's no more than 3.5 lbs of delivery
recommendations: carter 4070 or holley's red low pressure electric fuel pump
I highly advise against a mechanical fuel pump

4. Adjustable Low Pressure FPR (fuel pressure regulator) and FP Gauge (liquid filled, low increment recommended)

---September 19, 2010---
When using the low pressure, non-bypass fpr from holley mount your gauge in one of the 3/8npt OUT ports (a 3/8" to 1/8" npt adapter can be used just for starters when "skinning that cat") for more consistent pressure reading.

---March 30, 2011--- I don't recommend this at all btw.
**For those wanting to run the GTS factory fuel pump, the Aeromotive 13301 return fuel pressure regulator would be ideal. It's adjustable from 3-65psi. Again, this is a RETURN STYLE fuel pressure regulator. (10/4/2012) - I cannot confirm that this will be a working and trouble free route but the parts for attempting this method is here mentioned for individual consideration.
---January 5, 2024---I must mention that several colleagues over the years have tried the afore mentioned method and have chased nothing but intermittent issues from day one. Doing away with the EFI fuel pump all together and going with a more appropriately sized fuel pump and matching regulator resolved those intermittent issues.

---December 14, 2011---
Please note also that nothing smaller than 3/8"(= 6AN fittings) FUEL line should be used for fuel delivery.

---February 29, 2012---
I have to re-iterate: go no smaller than 3/8" fuel line all the way from the tank -> fuel pump -> fpr -> carbs.

If you're going with a bypass fpr type maintain a 3/8" line for delivery and return. NO SMALLER.

**Also, do not attempt to use the Carter (P)4070 electric fuel pump with a bypass type regulator as the pump itself is already internally bypassed to maintain a no-higher-than 6-7psi amount of pressure in open flow. The carters should be coupled with a deadhead/dead-head type fpr. The inverse is also true.

5. Throttle Linkage
6. Appropriate means of plugging the fuel injector ports (e.g. freeze plugs, injector port plugs from Techno Toy Tuning
- i recommend using the fuel injector port on no.4 for your vacuum assisted brake booster if your manifold doesn't have an available vacuum port. you can also tap it and outfit it w/ a barbed brass fitting. you decide
7. Corrective Fuel & Air Jets or a vendor that you can easily obtain them from

IGNITION OPTIONS FOR CARBED 4AGE ENTHUSIASTS

1. Use the stock blue top 4AGE distributor locked out at the timing of your choosing.
2. Use the stock blue top 4AGE distributor w/ the MSD 6A/L w/ MSD p/n 8980/8981 timing curve "computer" - to use the stock tach you will need to use MSD's p/n 8920 tach/fuel adapter NOT the 8910EIS (fuel injected w/ 6AL) or 8910. the 8920 is for the magnetic pick-up leads that are used from the Blue Top Distributor. If using an aftermarket Tach then the 8920 is not necessary.


note* - The 8980 is a fixed timing curve. This means you would set your distributor timing at your intended idle timing. The 8980 will advance your timing and max out at 20 degrees full advance e.g. if your idle is set at 10 degrees just under 1k your full advance will be 30 at 3k.

note** - The 8981 is a "programmable" timing curve unit. It's still based on the same design of the 8980 BUT you get to dictate when timing advance starts and ends in your rpm range.


3. Use the 4K distributor from a Starlet. It will need to be adapted to mount up to the 4AGE head. You will also need the gear from a 4AGE distributor to replace the 4K's in order for it to spin off of the 4AGE exhaust cam.
4. IDS w/ Megasquirt and crank tooth wheel and sensor. Electromotive and other companies can provide you with good IDS setups.



MEGAJOLT LITE JR is yet another option which uses EDIS and your option of TPS or MAP. MEGAJOLT LITE JR does not allow for both simultaneously as of the posting of this thread. I've included this after taking a little bit of "heat" from an AEU86.ORG member about using the stock ECU for ignition which I personally advise against only because with the amount of work put into "rigging" it up you can easily go megajolt lite and have more programmable control. anyway, have at it. Hope this helps someone.

MSD PROGRAMMABLE 6AL II (p/n:6530) - This unit gives you the capabilities to program your timing curve via a laptop/desktop interface cable. It also has inputs that let you control external items via triggers or implement changes based on input from external sensors, etc. This is a more expensive option to the Megajolt Lite unit by Autosportlabs as I mentioned above.

ELECTROMOTIVE - XDI - Another well known performance ignition system but using a "60-minus-2 tooth crank trigger wheel" for higher ignition definition ("...offering spark accuracy of ¼ degree of crankshaft rotation") and on the pricey side. Still a great waste-spark choice with a programmable timing curve. Read about it here.

4AG factory distributor + MAP harness & ecu - If you can get a hold of these then it should be self explanatory.

update:---June 2, 2023---
Microsquirt ECU v3 - A compact version of Megasquirt but without as many bells and whistles AND is capable of managing just ignition (you can easily go EFI later if you so choose). Though similar to the Megajolt Lite, Jr mentioned earlier the Microsquirt gives your more options for programmable ignition: factory distributor, CAS, EDIS/Waste Spark...etc...read more on it here.


LINKAGE OPTIONS FOR DUAL SIDEDRAUGHTS & YOUR 4AGE

If you're having a difficult time with deciding on a throttle linkage setup i'd like to make a suggestion using visuals:

I'm using the following setup w/ the stock SR5/GTS w/ cruise control throttle cable
smallport-4ag-miks.jpg
smallport-4ag-miks.jpg (57.66 KiB) Viewed 3788 times
- I then installed threaded spherical rod ends in the fuel rail mounting holes. - you may have to re-thread the mount holes depending on the spherical rod ends you source
rod-end.jpg
rod-end.jpg (2.43 KiB) Viewed 3788 times
- linkage rod through the sph. rod ends
linkage-lvr-kit-dcoe.jpg
linkage-lvr-kit-dcoe.jpg (30.87 KiB) Viewed 3788 times
- rod arm(s)
linkage-lvr-redline.jpg
linkage-lvr-redline.jpg (7.03 KiB) Viewed 3788 times
or
linkage-lvr-sw.jpg
linkage-lvr-sw.jpg (13 KiB) Viewed 3788 times
AND LAST BUT NOT LEAST:
shaft collars on each end to keep the linkage assembly in place
collar.jpg
collar.jpg (29.91 KiB) Viewed 3788 times
You may need these:
8mm-linkage-ball.jpg
8mm-linkage-ball.jpg (5.79 KiB) Viewed 3788 times
...as well as these type of linkage rods:
Lynx-linkage-lvr.jpg
Lynx-linkage-lvr.jpg (16.06 KiB) Viewed 3788 times
* image supplied by LYNX CORPORATION

Necessary components can be obtained from providers such as occamotif,
piercemanifolds.com, upgrade motoring and carbs unlimited - just to name a few.

* parts pictures are all borrowed from piercemanifolds.com unless noted otherwise



- added 3-19-2009
TOYCOOLROLLA - from Club4AG wrote:I don't have any ideas yet on jettings but I am not worried about it since we got lots of motorcycle mechs over here.

I am just choosing which to choose between the 2. =)
FCR jets are totally different from the dcoe/solex/delorto/mikuni phh side draught carbs.

for your perusal rhett: Keihin FCR carbs

click on the jet lists link on the left navi pane to see the FCR jets.

here's a quick look at Mikuni 40/44PHH side draught jets & jet block:
mikphh-jetbock.jpg
mikphh-jetbock.jpg (22.57 KiB) Viewed 3788 times
mikphh-vent-jets-accel-pump.jpg
mikphh-vent-jets-accel-pump.jpg (39.51 KiB) Viewed 3788 times
and weber DCOE jets:
mikphh-jets-emul.jpg
mikphh-jets-emul.jpg (19.3 KiB) Viewed 3788 times
1. Intake and discharge valve for accelerator circuit
2. Idle jet assembly
3. Main jet stack
4. Starter jet assembly
5. Accelerator pump jet
6. Idle jet
7. Air Correction jet
8. Emulsion tube
9. Main jet
10. Start jet (Cold start circuit)

(Weber DCOE info gratefully borrowed from "TerriAnn's TRIUMPH Web Pages"

For top notch carburetor servicing: Taka Sato at Kyushahouse

Regarding Motorcycle Carburetors - added 3-19-2009

mikuni sidedraught carbs are outfitted with chokes/inner venturis that range from 30mm to 41mm (30-36mm for the 40phh carbs and 34-41mm for 44phh models).

given the fact that the 40phh mikunis (found on toyotas from the factory) come with at most 30-32mm chokes stock while the 44phh miks show up with 32-34mm off the assembly line, unconventional carb candidates can be more easily considered.

so, for comparative purposes that should answer a good deal of concerns regarding bike carbs.


Runner Length Tuning - Intake Pulse Tuning - a.k.a. "further exercises in tuning pedantry" - 3-19-2009

Motorcycle throttlebodies and as well as the carbs are not as heavy or have as much girth as the sidedraughts so they're not all that cumbersome when at the end of the runners. so a support arm or brace isn't important BUT make certain the bike carbs are cupped via clamping hoses nearly surface to surface with the intake runners on the manifold.

There may not be enough room in the engine bay for say 14" length runner (that's from the opening of the stack to valve head) for a 1587cc with peak torque rpm at ~6000rpm. There's a means of calculating optimum runner length regarding pulse tuning. check out Wallace Racing's Runner/Torque Calculator(s).
Last edited by dr.occa on Thu Mar 19, 2009 4:59 pm, edited 5 times in total.

Dorikun
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Post by Dorikun »

Hey Occa, can you pm me for help(looking to source one) on an EDIS system/setup? I want to install one if possible next time, I'm trying to have a surprize up my sleeve to share with you guys next time I see ya's. I'm running that lightweight pulley of course, not sure if that's going to be a problem or if I have to go with a new one? BTW, do you still have those Oval shaped filters or extra funnels/horns lying around?
____________
Thanks again,
Dorikun

dr.occa
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Post by dr.occa »

Dorikun wrote:Hey Occa, can you pm me for help(looking to source one) on an EDIS system/setup? I want to install one if possible next time, I'm trying to have a surprize up my sleeve to share with you guys next time I see ya's. I'm running that lightweight pulley of course, not sure if that's going to be a problem or if I have to go with a new one? BTW, do you still have those Oval shaped filters or extra funnels/horns lying around?
sorry, no filters or velocity stacks to spare my friend.

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Post by Dorikun »

'Doh! I forgot about the everything is Top Secret Initial D information tax >.> <.<
____________
Thanks again,
Dorikun

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pecx
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Post by pecx »

nice write up

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Post by dr.occa »

pecx wrote:nice write up
thanks pec.

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Post by rywats »

I guess I will ask you questions on here rather than club4ag.

A friend of mine has some Keihin FCR 41mm carbs for sale. Do you have any experience with these ones and what can you tell about them.
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dr.occa
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Post by dr.occa »

rywats wrote:I guess I will ask you questions on here rather than club4ag.

A friend of mine has some Keihin FCR 41mm carbs for sale. Do you have any experience with these ones and what can you tell about them.
FCRs, in fact flat slide motorcycle carbs are quite nifty. jets should be really easy to be had. the problem that arises is they are a little more involved when re-jetting. also, intake manifold mounting are not common nor cheap unless you have one custom made. the custom route will at least give you control over runner length. the longer the more low to mid end torque emphasis. the closer the carb is to the head the further up top it places your power band. velocity stacks, i'm not sure if standard dcoe/ida trumpets will fit. those may be had through a cycle shop and could be pricey or the same.

i've got a set of 80s cycle carbs i plan to use on another build but plan on building my own intake.

wish i had more info for you on the flatsliders. mikunis and webers are just a little more researched and affordable in the 4AG realm ryan.

kevlarcorolla may be a good point of reference being that he's using bike carbs and in a turbo'd application. they just aren't the FCR's but somewhat similar.

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Post by rywats »

A friend of mine does fab work so he said he could make me a manifold. Then I could choose the length of the runners. He would be able to make me trumpet also.

What would you suggest for runner length?

It will be used for autocross and drifting of course.
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Post by rywats »

Here are some pictures of the carbs.

Image

Image

Image

Do these generally go for more money?
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Post by CBR_TOY »

man those are pretty!!! but FI for the win!
JDM AE86/AE92


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Post by hvguy »

CBR_TOY wrote:man those are pretty!!! but FI for the win!
I spoke to a guy at mayday and he said he couldnt get the performance out of his FI setup with MS versus his mikunis. :?
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Post by dr.occa »

ry, consider 4" length runners but probably no longer. the purpose behind the longer runners is for better atomization of the air and fuel mixture as well as generating low/mid end torque. manipulating the torque band can also be affected via the trumpet lengths. power band is also affected: longer trumpets locates the power band towards the lower to mid end and as the stacks get shorter the power band starts moving to the upper rpm range.

also, what may affect your final decision on runner lengths is the longest stacks you would ever plan on using. the longer your runners, the less room you'll have for longer stacks. i think you get the idea.

since the FCRs have a slight angle to them, it may squeeze you a little more wiggle room but a strut tower bar may again limit your options.

if anything just keep in mind longer runners are intended to create/maintain/improve low end torque which would greatly benefit the 4AGEs.

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Post by rywats »

Ok I am beginning to understand.

Would you suggest these carbs then. He is asking 400 bucks for them, and I have never seen them for sale before so I am not sure on the price. They have very low hours on them.
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Post by dr.occa »

rywats wrote:Ok I am beginning to understand.

Would you suggest these carbs then. He is asking 400 bucks for them, and I have never seen them for sale before so I am not sure on the price. They have very low hours on them.
if they are in as good a shape as they look, that is one serious deal. even if it's just to hang to, they're worth picking up at that price.

though i would initially recommend weber dcoe's or mikuni PHH carbs for familiarizing yourself with tuning carburetors. then trying your hand at the flat sliders.

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