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jalexquijano

NGK BP6ES spark plug burn color OK?

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Just tuned both of my recently remanufactured by Ztherapy SU Carbs to 3 turns clockwise on my 1972 240z. I am getting this color of burn on the 6 spark plug wires (NGK BP6ES at .32mm gap). The car seems pulling okay. However if i get stucked in traffic, the plugs start to get black and the car rpms start to drop a Little bit more. I already made the following mods to the car and still cannot get a completely steady idle:

 

- Change pertronix coil and ignitor (3.0 ohms)

 

- Bypassed the ballast resistor

 

- Swapped the Far 311 Race cam to a 274F Schneider cam

 

-Changed rocker arms

 

-Retainer springs

 

-Lashpads

 

Am i still too rich and need to go down to 2.5 turns??

 

One of the mechanics says this non stable idle is due to a valve or couple of valves being damaged?? How come?? I did a compression test and the result was the following:

 

cylinder 6 --------------------- 175 psi

 

cylinder 5 --------------------- 180 psi

 

cylinder 4---------------------- 180 psi

 

cylinder 3 ---------------------- 185 psi

 

cylinder 2 ---------------------- 180 psi

 

cylinder 1 ---------------------- 180 psi

 

I do not want to keep on replacing parts that are not necessary. My aim is to bring the car to the steadiest idle and install an AC system.

 

Anyone????

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Edited by jalexquijano
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That plug doesn't look bad.  The ground strap is getting hot and burning off deposits like it should and the center ceramic looks clean even though it has some color.

 

Why don't you describe a typical situation where the idle starts to drop. "Stuck in traffic" doesn't have any detail.  Are you driving down the road just fine, then hit a stop light, and the idle drops immediately?  Or does it take 5 minutes of slow driving before the idle drops?  Does the engine temperature increase as the idle starts to change,or is it steady, and the idle changes just from sitting?

 

Tell a story about driving in to traffic and what happens, with lots of detail.  Don't tell what you've done to the engine, just what the engine does from your view, inside.

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Just tuned both of my recently remanufactured by Ztherapy SU Carbs to 3 turns clockwise on my 1972 240z. 

2.5 turns counterclockwise from the top.  Turn them towards the passenger's side until they're tight then back down towards the driver's fender 2.5 turns.  Put a scratch on one of the ears so you can keep up with your turns.

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I close them up clockwise until the nozzle is flush and then back it up 3 turns. After driving the car more tan 10 minutes, if i get stucked in traffic, the idle starts to drop and increase. It is not steady. the temperature changes to 3/4 of the gauge. If you speed up it lowers. It could also be a faulty temp gauge. Do i need to open the gap more?? ie .035mm??

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Are the carbs in tune with each other? To tune them you need one of these, if you don't have it already:

http://www.thezstore.com/page/TZS/PROD/classic07/60-9976

There's another similar tool, but I like this one better, it has numbers you can write down when you get the carbs tuned, so you can compare vacuum data at a certain RPM if you re-tune them. Also you need a copy of the FSM for the tuning procedure, if you don't have it. I suggest follow the FSM procedure exactly.  2.5 turns down is just the starting point before the tuning proceedure, and that varies according the elevation and temperature, see the graph in the FSM. There's also a tuning procedure you can download from Teglerizer. I like the one in the FSM better, to me it seems more clear and concise, but it's good to read both. The Teglerizer also explains the push-pin test, but maybe that test isn't extremely accurate. http://www.zcarz.us/TechnicalInformationPageCarburation.htm

 

Every time I check plugs, I clean them, unless they're perfectly clean.  Hit them with carb cleaner, use a small wire brush for about ten seconds, then another blast of carb cleaner, on each one. There are better ways to clean them, but that's fast. If there's oil on the threads, wipe it off. If any of the plugs are even slightly fouled, cleaning them always makes the car run and idle better, without doing anything else.

 

What happens to the idle after you drive at highway speeds for a half hour or more?

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 if i get stucked in traffic, the idle starts to drop and increase. It is not steady. the temperature changes to 3/4 of the gauge. If you speed up it lowers. 

This is a better clue.  You're saying that the idle speed fluctuates, like up-down-up-down-up-down.  That's different than just idle speed decreasing.

 

I'm not a carb expert, let alone Z carbs, but this sounds like a carb issue.

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High performance cams also do this but the 274 seems like a fairly mild grind.

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Check your nozzles underneath.......push 'em up by hand. Many times when I get an erratic idle, it's because the nozzle underneath the carb doesn't return after choking the carbs. If they are hanging up, you can hear them snap back up when you push em up. This also causes a rich mixture.

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Already checked and they are fine. I have a 274F Schneider cam and should not have any erratic idle issue. the rpm should remain steady at 950 RPM in traffic jams and stop lights. With this cam isnt this posible? I strive for perfect idle.

 

I bought myself the following vacuum gauge to verify for any leaks:

 

http://www.amazon.com/ATC-Vacuum-Fuel-Pump-Tester/dp/B00SHPLT50/ref=sr_1_90?ie=UTF8&qid=1432657183&sr=8-90&keywords=vacuum+gauge

 

Where and how exactly will i need to connect it to test for leaks?

Edited by jalexquijano

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A vacuum gauge is useful, but a 240z only has a few vacuum hoses and other places that could leak vacuum, so it's easy to check. Maybe you have a  vacuum leak.  I had a big vac leak in the PCV hose on my truck and it was sort of like you describe but worse.

 

Bad hoses always leak on the side you can't see, otherwise you'd see it and fix it. There's the brake booster hose, the hose to the  transmission modulator if you have automatic trans, the PCV hose, and the little tube from the carb to the vac advance on distributor, and the connections for all the vac hoses. Old hoses leak at the clamps. Also could leak around intake manifold connections. If you have the smog stuff on the balance tube, maybe it could leak if it was shot, I don't know. If the smog was taken off, and the holes weren't plugged with the right thread (BSPT) it might leak a little, not enough to cause much problem, though.  If the PCV valve was clogged with gunk and stuck open, there's a vacuum leak. PCV's are cheap.

 

I posted a thread couple weeks ago about a vacuum gauge, you can see how I set it up under the dash by the steering wheel. You can also put the gauge right on the balance tube if there's a vacancy. Just need a BSPT/NPT adapter and some elbows, etc., from the hardware store. The instructions for the gauge  say to cut a vac hose and install a tee (kit probably includes wrong size tee), but I don't like that idea, especially if it's the brake booster. Not PCV hose, either, since the valve would mess up the readings.

Edited by Stanley

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Do both of the idle mixture knobs need to be set up equally? ie 3 turns clockwise on the front carb and 3 turns clockwise on the rear carb or could i set 3 turns clockwise on the front and 3.5 on the rear carb striving to get a brownish tan color burn in all 6 spark plugs?

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You can have different turns on the jets due to mechanical differences, wear and user error.

Getting all plugs to the same colour is a good goal.

Also lifting the piston in the back carb with your finger and idling on the front 3 cylinders then doing the same and running on the rear 3 cylinders is a good balance check. We call it the equally shitty test.

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Also lifting the piston in the back carb with your finger and idling on the front 3 cylinders then doing the same and running on the rear 3 cylinders is a good balance check. We call it the equally shitty test.

I spit coffee on my screen when I read that.  :D

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First of all, both of these carbs were fully remanufactured from scratch by Bruce Palmer at Ztherapy so they do not have any type of wear. I did this piston lifting test on the rear carb, if i lift it too much, the engine shuts down. If i do the same in the front carb, the engine slows down but does not shut off. I drove the car last night at 3 turns clockwise each of the idle mixture knobs with Brand new bp6es spark plugs at .35 mm gap. The car lacked power as it tend to stumble when accelerating under 3,000 RPM. I closed the gap to .31 mm each and richen the mixture of the rear carb to 3.5 turns and it has more power.

 

Any clues of what could be wrong? as background of my car it has a Shneider 274F cam with  crank and rods from a L26, special oversized 84mm flat top black coated pistons from D.L. Potter Engineering with E88 Head. Recent rebuilt 5 speed transmission from 280Z with new Center Force 1 clutch with stainless steel clutch hose.

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I did this piston lifting test on the rear carb, if i lift it too much, the engine shuts down.

This means you need more fuel to the front carb. give the front carb 1/2 turn more fuel and retry.

If i do the same in the front carb, the engine slows down but does not shut off.

This carb has enough fuel. You may have to reduce.

Be sure to balance air after each adjustment using unisyn or flow gauge. The engine should be able to run on 3 cylinders when fuel and air is balanced.

Repeat the test at 3000rpm then balance air then adjust fuel so that the rpms drop the same amount when you finger a carb.

Edited by Blue

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Thanks Blue.

 

Will i need to get a Timing light gun to adjust the time also as follows:

 

12 BTDC at 950 RPM IDLE

 

36 BTDC at 2,800 RPM

 

I really appreciate your assistance on this.

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Glad to help. I am now in Fiji.... one day I will be back in Panama!

 

I hope so!! Mechanics here in Panama only know how to change parts and not diagnose anything. I will need your technical advice to complete my Project.

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Tuning the SU's is not that bad. The various methods all work if you do it right. If you download the FSM, or Blue's method, or the one from the other link,  print it out so it's sitting on the fender while you do it first time. Need the uni-sen or synchrometer. It's almost fun. Just setting both at 2 1/2 turns down only works if the engine's perfectly stock, float bowl settings are perfect, your temperature and altitude are happen to be correct for that setting, and you're lucky. Even if 2 1/2 turns is correct for both carbs, you still need to balance them.

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Well i finally managed to tune both front and rear carbs at a Little less than 3 and a half turns. I am using Automatic Transmission Fluid as damper oil. However, i am getting a hesitation and stumbling if i drive the car at slow speed between 1st and 2nd gear or if the car passes through a bumpy Street at slow speed. Could i have the ignition time wrong? I read that if the time is not set properly with a timing light you could present this problem.

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Since I put the SM needles in, I think I'm going to give blue method a go. Picking up a used wideband next week! I was going to switch back to stock needles, but the new motor is going in, in about a month anyhow so I might as wel keep them for the time being.

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