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'82 720 won't idle, runs like crap


theboraxkid

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My truck failed California smog on Tuesday due to high idle,(it passed emissions and visual inspection, smog nazis suck) then it randomly died on the way home from the smog station. Turned out my choke snapped shut over a speed bump. I replaced the choke with a good used one, adjusted it properly (I think), replaced the fuel cutoff valve as well,(old one was missing the wire) and I made sure everything was hooked up right according to the parts carb I bought, which is an original Hitachi. The carb on my truck is also a Hitachi, but rebuilt at some point. The truck now starts, but simply will not hold idle and it sputters like crap whenever I hit the gas pedal. I really need to get this to idle, and below 700 rpm, or the smog Nazis will not let me pass. Help?

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Vacuum first, then re-check your carb.  I recently rebuilt my old Hitachi due to many issues.  When complete and having done everything to the book, the truck just was not happy.  Scrounged the money for a Weber, slapped it on, truck was a million times better.  I think having the Weber may screw you at smog again.  Look into a new or remanufactured Hitachi.  That might just do the trick.

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If no vacume leaks....dissconnect choke wire till u get to DEQ. Dump an ice cold bottle of water over bi-metallic spring housing/round choke. This should keep choke fooled enough so it doesn't die off idle. U can use dist(retard timing) to slow down idle speed. It will run like a dog but should get u thru the "BIG BROTHER" inspection. I recomend doing a weber conversion if you want good reliability with todays ethenol mixed fuels. Todays gas eats factory Hitachis. Set ignition timing @ 3deg....no more or it will detonate in high gear under a load.....less than 3 you will lose performance.  Make sure throttle butterflys are not closing off completely....adj idle with mixture screw not butterfly position. Tighten valve cover bolts 1/4 turn or more....can lose vac via pvc valve and cause erratic idle.

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Unexplained high idle can be....

 

Throttle cable too tight and won't let carb close fully.

Secondary barrel stuck just slightly open.

Idle speed screw not adjusted.♦

Choke on slightly or fast idle cam stuck

 

Check the choke is fully off when the engine has warmed up in (about) ten minutes. If the choke is even part on it will engage the fast idle cam. Check that the throttle lever is not closing on this plastic piece with the steps on it...

 

carbZ24fastidleadjustLg.jpg

 

carbZ24idlestepLg.jpg

 

If choke is fully open and the fast idle cam engaged it may just be stuck. Spray WD-40 all over this area and with the throttle held part open work all the linkages to loosen and lubricate it. It should normally fall back out of the way so the throttle can close fully.

 

 

Now listen near the carb while someone turns the ignition switch on off on off on off (don't start it) You, should hear a soft clicking sound. This is the idle cut solenoid opening and closing to let fuel in to the idle circuit. Without it, you will never get the idle below 1,000 RPMs. If you hear it click at least it is working.

 

 

Unscrew the idle mixture screw carefully, don't loose the spring around it. Count the turns so it can be put back close to the same spot. Now unscrew the idle cut solenoid carefully and spray WD-40 in the hole using the red straw. (these two are connected, so this should dislodge any dirt in the idle circuit) Put the solenoid back. Now spray the mixture screw hole well with WD-40 using the red straw that comes with it. Put mixture screw back.

 

 

Before adjusting the mixture screw the valve lash must be set or confirmed and timing at 3-5Degrees BTDC

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If no vacume leaks....dissconnect choke wire till u get to DEQ. Dump an ice cold bottle of water over bi-metallic spring housing/round choke. This should keep choke fooled enough so it doesn't die off idle. U can use dist(retard timing) to slow down idle speed. It will run like a dog but should get u thru the "BIG BROTHER" inspection. I recomend doing a weber conversion if you want good reliability with todays ethenol mixed fuels. Todays gas eats factory Hitachis. Set ignition timing @ 3deg....no more or it will detonate in high gear under a load.....less than 3 you will lose performance.  Make sure throttle butterflys are not closing off completely....adj idle with mixture screw not butterfly position. Tighten valve cover bolts 1/4 turn or more....can lose vac via pvc valve and cause erratic idle.

 

Retarding the timing to lower the idle is just... well it's, wrong. The engine will be less efficient and this will show up in the emissions.

 

A weber will never pass a smog visual inspection and never even get to the test, so you will have to put this carb back on next year. Might as well fix it now.

 

The Z22 engine is calibrated to run with the proper mixture with the small vacuum leak made by the PCV valve. Valve cover loose or tight does not matter when the hose from the valve cover is open to the outside air in the air filter housing anyway.

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1. check all vac lines.

2. check all smog components.

3. check fuel pump/filter.

4. check/adjust timing.

5. check/adjust fuel air mixture.  helps to have a vacuum gauge and a friend to step on gas if it won't idle.

 

why do you need it to idle below 700rpm?  i believe the recommended speed is 850?

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Idle speed is supposed to be under 700 rpm, mine idles around 1400 if it idles at all. Can't mess with timing, smog check insists that it be at 3 degrees btdc. It doesn't seem to have any vacuum leaks,and I've made this carb as stock as I can. After messing with the carb a lot, I noticed it seems to shoot gas out straight up onto the choke butterfly. This carb is a reman from 2007. Is it just a fantastic piece of garbage?

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Idle speed is supposed to be under 700 rpm, mine idles around 1400 if it idles at all. Can't mess with timing, smog check insists that it be at 3 degrees btdc. It doesn't seem to have any vacuum leaks,and I've made this carb as stock as I can. After messing with the carb a lot, I noticed it seems to shoot gas out straight up onto the choke butterfly. This carb is a reman from 2007. Is it just a fantastic piece of garbage?

 

 

Check the plug wires. Every one, and be sure they go to the correct plugs. Don't assume they are right check them.

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Yes I know it is NOT normal procedure to use ignition timing to alter idle speed. Just a suggestion to help fool the darn goverment when at the testing site. Retarding the timing should not adversely affect emissions to the degree it fails test(CO/HC).....but temporarily may help reduce idle enough 2 pass test. Do they check the timing @ deq? If it wont idle below 1400.....10-1 it has a plugged up low speed jet. I have fought the same/similar problem B-4....more than once. O the joys of taking apart your carb @ 3am in the Wal-mart parking lot to unplug it....Bic lighter only light source. DON"T lose that spacer for the float...it keeps it centered and will flood if missing. Good luck. I think u could hide a weber under the factory air-cleaner if u were super sly!

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My Weber in Phoenix went right through the smog inspection.  I was surprised that it passed, but it passed with flying colors.  Just had to readjust it to run after the smog test.  Readjust means change the jets.

That's awesome for YOU.  That will NOT happen in California! 

 

On another note, I stay away from reman carbs.  I have had nothing but lousy experiences with them, REGARDLESS fro where I bought them.  My last Hitachi came from a reputable shop in Florida, of all places.  Truck ran GREAT!!!  Failed smog so miserably, they damn near took my truck away right there.  Turns out the shop as usual fucked up the rebuild and the carb was useless.  Fine at idle, but off the charts at speed.  In the end I rebuilt my old carb, glad I did NOT send it back as a core.  Passed smog by a mile!

 

What I learned is that this carb is often tuned too lean, causing poor running and higher smog.  I had to rich it a lot more than I thought advisable, but then quite suddenly the numbers dropped like a stone and it now passes with emission numbers close to a modern car.  The trick is to give the catalyst enough fuel to do it's job.  Truck uses a little more gas now, but KALIFORNIA is happy.

 

I have an old exhaust gas analyzer that I use to tune my truck.  It's not perfect, but it tells me enough.  I'll be happy to help anyone in LA with their 720 if I can.  You buy lunch.

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Yes I know it is NOT normal procedure to use ignition timing to alter idle speed. Just a suggestion to help fool the darn goverment when at the testing site. Retarding the timing should not adversely affect emissions to the degree it fails test(CO/HC).....but temporarily may help reduce idle enough 2 pass test. Do they check the timing @ deq? If it wont idle below 1400.....10-1 it has a plugged up low speed jet. I have fought the same/similar problem B-4....more than once. O the joys of taking apart your carb @ 3am in the Wal-mart parking lot to unplug it....Bic lighter only light source. DON"T lose that spacer for the float...it keeps it centered and will flood if missing. Good luck. I think u could hide a weber under the factory air-cleaner if u were super sly!

 

Are they really making you idle it down to 700 RPM? Usually 1000 or VERY close to it, say 950, will get you through a smog test. If you're idling at 1400, you're past the idle circuit and into the main circuit of the carb. You really should do what DatzenMike said and check the secondary valve on carb. I've had it stick on me a few times, and now if I get a high idle condition, it's the first thing I check. Just make sure the main throttle is closed, open it slightly, and give the secondary linkage a nudge.

 

A quick look at the regs online show you can be 100 RPM within the idle speed, so if the book calls for 850, 950 will work; timing can be within 3 degrees. What a racket.. There's still smog testing where I live, but it's not as ridiculous as that. 

 

If you failed on HC, retarding the timing will help, FWIW. However, the timing is so low on that thing to begin with, it appears there is practically no wiggle room. If you have the owner's manual for your truck and can PROVE that the idle speed is 850, show it to them. I've been this route with my state; they were telling me my truck had an airpump according to their book, so I took out the owner's manual and proved their book was WRONG. That was fun :D

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Intake and exhaust coil wires do not matter as both coils fire together anyway.  FWIW the intake coil is the one connected to the outermost rotor. At TDC it will be at the 9:00 position.

 

720timing002Large.jpg

 

 

 

The Z22/Z24 intake coil will/should have a Brown wire to the + coil terminal.

 

 

 

It should idle down below 700 so why not make it so?

 

Is the fast idle cam out of the way???

 

Is the choke full open when warm????

 

 

What I failed to ask is...

 

If you try to lower the idle does the engine stall OR is there no adjustment... it just idles at 1,400.

 

If lowering the idle speed screw causes it the stall, then there appears to be no fuel to the idle circuit. It won't run on only the primary barrel that low. See my post on idle cut and mixture screw removal and blowing the circuit out with WD-40, compressed air is even better.

 

If the idle speed screw is all the way down and throttle closed against the stop and still idling high then it's getting fuel and air from somewhere else. Secondary could be stuck open a hair, I've had this. Another thing is a BCDD that is adjusted too sensitive and does not shut off. 

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The coil wires matter on my 86 Mike you mix them up and it runs like shit.  Mine is CA emissions.  Mike if they fire at the same time why have an intake and an exhaust coils.  The Z24 with the eight plug head could run off 1 coil firing all 8 plugs in your theory.

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You can't fire two plugs with one coil. The exception is the wasted spark set up using one coil for every two cylinders, but one plug is always well into the exhaust stroke and the spark will jump the gap. This would never work on twin plugs on a compression stroke. One electrode would always be slightly closer and the spark always finds the easiest path to ground.  How would you wire it up?

 

 

If your '86 only ran like shit with the coils swapped then one wasn't working and there would be a difference moving the spark from one side of the combustion chamber to the other. A twin plug head running on single plugs will be timed for twin plugs and will act retarded.

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just out of curiosity... how many volts is your alternator putting out?

 

i just recently replaced my alternator cause when it started putting out 16-18 volts my idle speed got faster.  first it was around 1500 then as it got worse even as high as 3000rpm.  everything's back to normal after i replaced it with the o'reilly special.  hope this one lasts.

 

also, my truck doesn't seem to mind which coils i use to fire the plugs.

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also, my truck doesn't seem to mind which coils i use to fire the plugs.

 

 

...and it shouldn't really.

 

Dual plugs need way less advance because the time it takes to burn the fuel is much shorter with two ignition sources. In order to get the maximum power transferred to the piston, timing is around 3-5 degrees BTDC and maximum cylinder pressure is around 15-17 degrees ATDC. Any later, and the mounting pressure is chasing a rapidly accelerating piston down the cylinder and is wasted. If one coil fails (fuse or wiring) the burn time will be longer and maximum pressure is much too late to do much good.

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You can't fire two plugs with one coil. The exception is the wasted spark set up using one coil for every two cylinders, but one plug is always well into the exhaust stroke and the spark will jump the gap. This would never work on twin plugs on a compression stroke. One electrode would always be slightly closer and the spark always finds the easiest path to ground.  How would you wire it up?

 

 

If your '86 only ran like shit with the coils swapped then one wasn't working and there would be a difference moving the spark from one side of the combustion chamber to the other. A twin plug head running on single plugs will be timed for twin plugs and will act retarded.

That is a good point about the coil being bad, as I remember correctly I changed coils after I noticed this behavior.  I will have to try swapping coils again.

 

Mike I have to compliment you for sticking with this member and trying to help him with this annoying problem.

 

I do not buy rebuilt carbs from a mass re-builder.  I did twice years ago and had nothing but problems.  I rebuild my own or buy new.

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The re-builder is min wage -don't much care-get it done cheap.

 

Dirt/sediment is the most likely problem followed by out of adjustment or incorrectly installed. Third most problem with carbs is that it wasn't the carb but something else.

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