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Triple OER Carburetor Troubleshooting - Help

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Hello all from Australia,


 


Long time browser, first time poster here because I finally can't find the information I'm looking for!


 


First off, my name's Adam and I have a 1973 240z which is currently running a standard L28, N42 head/block combo, with brand new triple 45mm OER carburetors, and Trust headers to a twin 2" exhaust system.


 


I have just installed a new set of OER carbs I purchased from Japan and am having difficulties sorting out the idle/low speed cruise setting.


 


Bit of details into the setup,


 


45mm carbs


34mm venturis


#190 air correctors (not yet tested to see if these are the best)


#130 mains


#60 idles 


#40 pump nozzle


#1.8 needle valve


3.5psi fuel pressure from the mechanical fuel pump into Holley regulator


31mm fuel level using the OER level gauge.


 


Idle screws are setup so that the first progression hole is just 100% covered looking through the brass cap/inspection hole. Carbs are balanced the best I can using a unisyn.


 


I have a wide-band O2 sensor probe in the tail pipe. I am running 98 octane fuel. Timing is at 15 BTDC with no vacuum advance connected. Valve clearances have recently been adjusted.


 


Now, onto the problem I am having..


 


Driving with the #60 idles installed, 1 full turn of the mixture screw turned out, slow acceleration and cruise is very rich, 10.5 and 11.5 AFRs respectively.


 


I also have #50 idles on hand which I have installed to try and improve the current rich scenario and I cannot even get them to idle. With mixture screws out 1.5 full turns (recommended range is only 3/4 to 1 full turn), they cannot idle on their own, only when I blimp the throttle which I believe is activating the pump jets.


 


With the #50s installed, AFRs are off the scale in the lean area. They can't idle let alone drive.


 


My question is, is going down from a #60 to a #50 idle jet that big of a jump that the car can no longer idle on its own? Or is there something wrong with my idle screw setup? I would have thought that with the #50s installed, it would at least idle and drive albeit a tad lean..


 


OER offer a #55, but I would like to double check with the experts out there first before spending that money.


 


Any help would be appreciated. And please let me know if I am missing some information, I tried to be as detailed as possible.


 


 


Thanks,


Adam


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It's huge. At most a 55 would have been as far as I would have tried to go.

 

Your experience and WBO2 are confirming exactly what you think: 60 is too large, 50 is too small. Well, Goldilocks....order you some 55's!

 

NOW, that said...if you have gauges that can measure the hole in the 60 and 50 (probably not in thousandths of an inch like Rochesters...) you can extrapolate what size jet hole a 55 should have, soft solder your 60's closed and get a jet-drill to punch a 55 size hole to be absolutely sure what they will do....but it's a lot of work for the expense.

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1st off, set the timing at 32 degrees "all in".. That means rev the motor till the timing stops advancing. Somewhere around 2,800 or so depending on what distributor you are running. Until you do that you are accomplishing nothing. Webers or work-a-likes require correct timing. Once you set the timing then test. Don't worry about what initial timing the 32 degree gives you. It is what it is. Chances are you'll need to mark your balancer for the 32 degrees using a fabric tape measure since your factory marker doesn't go past 20. Easiest way to do this is mark the balancer in the opposite direction so 32 degrees hits at your zero mark on the factory marker.

Edited by steve260z

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I have got onto ordering a set of #55s and #57.5s from OER. I will throw them in when they get here.

 

As for timing, I have thought about giving that a crack. Have just been a bit lazy with measuring and marking out, and thought idle timing was enough. I will see how that goes.

 

I am running an electronic distributor from a 280zx.

 

 

Thanks

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The mix screws on O E R carbs are not the same as weber they are a fine thread so they need to be out about 2.5 turns to be the same as the weber 1-1.5 turns. I have 55 f9 with a ported head and a bit of a cam on a 2.8 and it is still a little rich. You probably need a 55 F8 for a little more air, that is what I will be going to after winter decides to leave. O E R brand jets are a little different than the weber equivalent as far as air hole size and how they sort them. I gave up on the OER idles because they are one piece unlike the weber set up that lets you replace the jet in the housing piece. PierceManifolds.com can help you out with the OER stuff they know what weber stuff fits and does not. They are great carbs and if you are familiar with webers then the learning curve is small.

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The mix screws on O E R carbs are not the same as weber they are a fine thread so they need to be out about 2.5 turns to be the same as the weber 1-1.5 turns. I have 55 f9 with a ported head and a bit of a cam on a 2.8 and it is still a little rich. You probably need a 55 F8 for a little more air, that is what I will be going to after winter decides to leave. O E R brand jets are a little different than the weber equivalent as far as air hole size and how they sort them. I gave up on the OER idles because they are one piece unlike the weber set up that lets you replace the jet in the housing piece. PierceManifolds.com can help you out with the OER stuff they know what weber stuff fits and does not. They are great carbs and if you are familiar with webers then the learning curve is small.

 

Hmm interesting.. I have an old SK-Racing manual here and they mention that it only needs to be unscrewed 3/4-1 full turn from full lean. I would have thought OER basically being the newer model carbs of SK-Racing, it would have been the same. But at the same time, depending on which Weber DCOE model you have, they also require 2.5 turns. Newer models required 2.5 and older models require 1.5 or vice versa.. So it might depend on the actual carbs?

 

I will try the #50s again with a the mixture screws out a little more and see if it makes a difference.

 

As for OER idle jets, I have noticed that they seem to have fixed air hole sizes, they only offer different sized fuel holes. From size #55 and up however, their increments are by 2.5, ie. #55, #57.5, #60, etc.

 

Thanks mate, you've given me something to think of and experiment with.

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As for OER idle jets, I have noticed that they seem to have fixed air hole sizes, they only offer different sized fuel holes. From size #55 and up however, their increments are by 2.5, ie. #55, #57.5, #60, etc.

 

That's why I went withy the weber set up, there is way more fine tuning that can be done. With all the different air sized available for each diameter fuel size.

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Okay, just another quick question.. With the #60s installed, my acceleration is now a tad lean in the high 13s range, causing hesitations and misses, but cruise is still rich at 11.5-12.

 

I am only suffering from the lean acceleration when take off is very slow, in the progression port area. Solution?

 

I think I might need a weber idle jet..

 

Thanks

Edited by adam.

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DEFINE "TURN"!!!

 

I have watched guys define a 'turn' as 180 degrees from seated. It's  not.

They mean 360 degrees from seated. In every case, when you dig into it...

 

I should have asked that question initially, I usually do. But the question was 'is a swap from 60 to 50 a big swap' and that answer is 'ohhellyes!' There's a reason they make 55 and 57.5's (splitting each by 1/4 of a size if you notice...)

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I have been mentioning 'full turns' which I think is pretty obvious as being 360 degrees, but I understand your frustration. My 'turns' are 360 degrees. 

 

And the main question of this thread was whether a #60 - #50 idle jet was big. I wasn't sure whether the AFRs reacted the same as say going from a #140 main jet to a #130.

 

I thought since the #60 was producing AFRs of 11/11.5 at cruise, maybe the #50s should run and produce 13/14 AFRs (and maybe the #55 and #57.5 would produce in between around 12 and 13). But my result was that they didn't run at all and I wasn't sure whether that was right.

 

I have ordered some #55s and #57.5s so we'll see what they produce when they're installed.

 

And I will get onto the timing first thing next time I go tinkering, Steve.

 

 

Thanks all.

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Yes, I figured we three were all on the same page.There's no frustration, you have it well in hand.

Your definition of 'full turn' is satisfied by some guys at 180 because the turn of their hand is completed.

It's the difference between us guys that read the manual and see the definition of 'turn' and other guys who don't!

I put it in to clarify to anybody who might be searching later on as it wasn't definitely quantified.

I can't tell you how many times I've watched guys 'turn' the screw 180 and say 'one' another 180 'two'.... Uh, No!

 

The idle jets have a huge effect because they have such a big range of varied conditions to cover. I've discussed in the past the balance between annular area around the idle needle and how this is calculated for idle mix, leaving the balance of jet flow open for the transition ports. By backing it out beyond the intended amount, you bias more flow from the jet to the idle therefore inevitably starving the transition ports. That's the purpose behind the 'turns out' as they know taper of the needle, they know axial displacement from the turn off seat, and they know the diameter of the hole for idle...therefore they know the amount of cross-sectional area that will be available to flow fuel compared to the idle jet size. 

 

On a jet change from 60 to 50, you may have to back out the needle so far, that the entire jet flow is going to satisfy idle and it dies if you crack the throttle. 
on the 60, it's a bit rich and you go off-idle and go slightly richer.
When you got the sizing right, it should stay very very stable around 13 plus or minus as you transition into main. The balance will be correct between the vacuum available to pull through the holes and the jet diameter available.

 

Hopefully explaining that makes sense on what is going on...

Edited by Tony D

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Yep, that makes perfect sense. So when I was running the #50s, they may have idled on their own, but only because I 'turned out' too much, using fuel intended for the progression holes on idle. Therefore when I got to rev the motor, it dies due to running lean.

 

Excellent. Thanks for explaining that.

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Yep, then people try to mask that lean by overinjecting an accel pump shot!

 

Somewhere in some manual they will tell you to disconnect the accelerator pump, then using the throttle lever SLOWLY increase engine speed from idle to 3,000 rpms and note your AFR's (in the old days it was listening for misfires and stumbles) 

It should be able to do that, smoothly without coughing or stumbling. Another way is to get on a long straight and level stretch of road and get up to a speed which equates to 1,000 rpms in fifth gear. Then slowly roll into the accelerator and let it sloooowly pull from 1,000 to as fast as you dare. If it does it without bucking and surging, you got it right!

The value of these tests is things happen slowly enough that you can take in when they are happening and have a vague idea on throttle position. 

Frankly, making a WOT run go well is EASY.

 

It's these slow pulls at 25/50/75% throttle from 1,000 rpms that give you the reading on your transitional characteristics. On a track this fluidity and ability to actually USE any throttle position on the car (not just WOT or Idle) can pick up many seconds in decreased lap times.

That's really your last test to know it's all working well. The high load will reveal transitional leans on that AFR gauge and that will let you make incremental adjustments to the jetting or emlusion tubes to get exactly what you need. It's the closest most people can get to going to a dyno that holds load points and tuning for peak torque under those conditions.

Which, and this point I say: See TPS Dot, shift control, arrow up, up up or down down down and watch that dyno...then move on to the next mapping point! I'm SO over jets it's not funny! LOL

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Hahaha it's all part of the fun though, isn't it.. Building a car, you're in it for the journey, not the finished product.

 

And I have seen/read that method of tuning.

 

You first remove the air corrector, emulsion tube, and main jet assembly, block or remove the accelerator pump and drive with just the idles. Note the AFRs at cruise and adjust float levels to up to richen the mixture or down to lean it out. If you cannot achieve a good AFR with the range of float settings, either go up or down a jet size depending on which way you need to go.

 

It is only then that you reinstall the mains and check AFRs. Once they're done, you reinstall the accelerator pumps. And make sure cruise is still where they need to be.

 

Of course there's more to it than that but it's the basic guide to setting it up. This way, it allows you to focus on just the idle jets and you'll know for sure the mains haven't 'come in' yet.

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I have never heard of doing that. I don't even know if it would run...pulling the jet blocks out results in uncontrolled rich situation from a gaping hole.

 

Just put it in gear and roll on the accelerator without activating the pump to bugger up the mix.

 

You should be able to run the car with even and slow throttle puts without the accelerator pump.

 

After you get THAT right, you the start testing WOT applications at various speeds to determine best compromise for pump stroke across expected area of operation.

 

And it will be a compromise. There is no mechanism to tailor the accel shot on anything but rate of change and available stroke.

 

"Control-Shift Arrow Up Up Up!" LOL

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Running the car with jet stack out gives ya an excellent "view" of how often you're on the idles/progression holes.

One misconception is that people think the main jets come on at some certain rpm..Not So. The main jets come on at a certain butterfly position. You can be at 5,000 rpm and very partial throttle and be running nothing but idle jets. Hell, I got my car up to 60mph with the main jet stack sitting in the garage. 

 

Now, I wouldn't adjust the float levels for the idle jets. Yes, I assume it would have some impact but you need to focus the float level for the main jet. As you mentioned in an earlier post. 

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OK, noted Steve, regarding adjustment of floats for idle jet.

 

And you can definitely run the car without the mains installed.

 

There has been a delay in ordering and receiving of the new jets so no new information to be mentioned. It should hopefully be here by early next week.

 

I have access to a dyno at work again which will help dial everything in.

 

And I think my OER emulsion tube and jets should do for the moment! Will get too expensive otherwise

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Running the car with jet stack out gives ya an excellent "view" of how often you're on the idles/progression holes.

One misconception is that people think the main jets come on at some certain rpm..Not So. The main jets come on at a certain butterfly position. You can be at 5,000 rpm and very partial throttle and be running nothing but idle jets. Hell, I got my car up to 60mph with the main jet stack sitting in the garage.

 

Now, I wouldn't adjust the float levels for the idle jets. Yes, I assume it would have some impact but you need to focus the float level for the main jet. As you mentioned in an earlier post.

 

This is why you run the top gear test at progressively more throttle angle.

 

On Mikunis it's well known highway cruise is done on idle jets.

 

Mikuni specifically states at WOT you are tipping into the main transition at 3,000 RPMs as I recall (if their other parameters regarding sizing the carbs are followed.)

 

That pretty much is what I've used to explain to people why fiddling with a main jet for mixture adjustment below that point is basically fruitless. There isn't enough draw to top the mountain as it were...to get fuel flowing down into the boosters before that point.

Edited by Tony D

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Update:

I checked the timing and I don't know how you guys do it but it seems like the motor is reving too fast to tell what exactly the timing is at 3krpms.

I have received #55 and #57.5 idle jets, the #55s are still too lean to even accelerate, while the #57.5s have a cruise AFR of 12.5 and acceleration is in the 13s - 14/15 which cause stuttering (around 2.3-3krpms). Idle is about 13.

Any ideas what could cause this lean spot causing the stutter? I cannot get my head around it. I have tried checking timing and best I can do is 15 degrees at idle.

It seems like I can't get cruise any leaner without causing hesitation on acceleration.

 

I'm guessing it's that dreaded transition to the mains..

Edited by adam.

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I checked the timing and I don't know how you guys do it but it seems like the motor is reving too fast to tell what exactly the timing is at 3krpms.

 

 

If you are saying the timing mark is bouncing all over the place and you can't get a reading? That means two things. The dizzy is not holding a consistent timing or the timing light is not working correctly. The 2nd not being likely. Make sure the plug is gapped correctly, swap the ignition wire out with another from 2 through 6 and try again. And I just realized you have a 240..Are you still running points?

Edited by steve260z

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