Nikki 2bbl help?

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pishta

pishta

I know I'm right....
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Common carb on early 80's 4 banger rice. Darn thing idles with the mix screw turned all the way in. Its an NOS carb with maybe 1000 miles on it, but no idle baseline settings can be found. the vacuum readings can be altered with the mix screw from a nasty 14 to a decent 20 inches vacuum but Im afraid the screw out to get the 20 is failing my low speed smog results They test at 15 and 25, 25 is fine, the 15 is about 10% over fail. The 20 is about 2-2.5 turns out. Will have to look at my old shaft leaking spare to see if the idle transfer holes are barely under the plates like a Holley. Also the distributor advance is hooked to ported vacuum, does that sound right? The only vacuum hose diagram shows the distributor vacuum going into the carb at butterfly level or slightly below, but when I put a gauge on it, I get nothing at idle until I blip the throttle, then I get some movement. One more thing: I got an inline vacuum metering device in the hose to the distributor and it has an arrow on it. Does arrow point toward the vacuum source or distributor? Its called a timed vacuum modulator, sort of a one way check valve with a slow leak. Supposed to help NOx by easing off the advance when you go off the gas, Im thinking the vacuum source must pull, then when it stops, the check valve holds the advance pod vacuum for 7-10 more seconds?
 
pishta said:
Common carb on early 80's 4 banger rice. Darn thing idles with the mix screw turned all the way in. Its an NOS carb with maybe 1000 miles on it, but no idle baseline settings can be found. the vacuum readings can be altered with the mix screw from a nasty 14 to a decent 20 inches vacuum but Im afraid the screw out to get the 20 is failing my low speed smog results They test at 15 and 25, 25 is fine, the 15 is about 10% over fail. The 20 is about 2-2.5 turns out. Will have to look at my old shaft leaking spare to see if the idle transfer holes are barely under the plates like a Holley.Yeah this looks like it could be a Tport sync issue;ie the butterfly is too far up the transfer port. Also the distributor advance is hooked to ported vacuum, does that sound right?To me it does. The only vacuum hose diagram shows the distributor vacuum going into the carb at butterfly level or slightly below,Hopefully above but when I put a gauge on it, I get nothing at idleCorrect until I blip he throttle,bring the rpm up to cruising rpm to see what it does then I get some movement. One more thing: I got an inline vacuum metering device in the hose to the distributor and it has an arrow on it. Does arrow point toward the vacuum source or distributor? Its called a timed vacuum modulator, sort of a one way check valve with a slow leak. Supposed to help NOx by easing off the advance when you go off the gas, Im thinking the vacuum source must pull, then when it stops, the check valve holds the advance pod vacuum for 7-10 more seconds? the BIG-Three all used similar devices at one time or another; sometimes one way sometimes the other. Do whatever it takes to get certified, then pitch it..
Click to expand...
 
Looks like the old carb did have ported vacuum, above blades. vacuum hole is about as big as this period. . Thanks for the support. Im thinking the transfer slot is out of whack with my fiddling trying to get the butter smooth idle. Should have dont that after it passed...first year- carb out of the box- it passed with flying colors. How much of the transfer slot should be exposed at idle, square like a Holley?
 
pishta said:
Looks like the old carb did have ported vacuum, above blades. vacuum hole is about as big as this period. . Thanks for the support. Im thinking the transfer slot is out of whack with my fiddling trying to get the butter smooth idle. Should have dont that after it passed...first year- carb out of the box- it passed with flying colors. How much of the transfer slot should be exposed at idle, square like a Holley?
Click to expand...
On the carbed 80's carbed four banger idle: It's a four cylinder,it's gonna have a slight twitch to it,when right.. It's carbureted,with a cat,it's gonna need to be slightly rough,to pass Cali tailpipe..(Used to be easy on four cylinders ,in the day..you are allowed 3 degrees retarded initial timing,for excessive h.c/C.o. readings....
You want the leaner side,on the vacuum gauge curve,...a couple of inches below peak,hurts nothing..If it idles slightly rough,touch that idle speed ,to 1000-1100...(should be close,to the allowable CARB/BAR Cali limits..) Raised idle speed,near stock ,slightly retarded timing,are your best friends...A freeway drive down the freeway,just before your smog appointment ,does wonders to light it off. Lazy ,non reacting cat? Hit it ,with a propane Benzomatic torch,wake that puppy ,up.(Still love the pictures,of the three angle valve job tool,with brake bits...)
 
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are they fuel adjusters or air bleed screws to correct idle.?
 
To be honest, i dont know. The adjuster has a limiting cap on the replacement carbs i see online. The screw sits behind fuel bowl but screws into base of carb at a diagonal. Its Strange that the thing idles with this turned all the way in so it may be an air bleed? Ill take that advice to the motor this weekend. Im waiting for my mightyvac to test a few vacuum lines. Just got a valve job and the head decked. He took off about .040 judging from the looks of the deep pits that are no longer there. maybe a little too much? They sell a .030 head shim for this motor because there is a fitted oil jet out the block that goes into the head. If you mill the head, the oil jet props the head up off the gasket. Found that out the hard way....it's the large screw by brass nipple
155963606_carburetor-repair-kit-kohler-cv18-cv22-cv25s-nikki-carb-.jpg
 
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wow Kit, that is some find! My shop manual looks just like that with a picture of a truck on the front. Thanks!
 
Have you encountered fig. 3-72? Seems they have sense of humor. :)

The Nikki carb are exotic, seems if everthing is working, they would run great.

Something sometimes overlooked, is proper closing of secondary bore butterfly. It can mess with primary idle control in bad way.
 
Yes, I did see that and knew what you were refering to before I looked it up again. Im going to play hooky from church and take the carb off to look at the idle transfer slot and maybe the bleeds, as well as the secondary now you mention it. It should not be altered from stock 'cept for the idle screw as it was NOS in the box when I bought it and ran great then. Id like to get a couple of those side draft "Bongo" carbs.....
 
Do the look at a light, thru the closed throttle plates. If they are loose or shifted slightly they can bind, not close fully. Many later emissions carbs rely on specific primary throttle stop, and do not use for idle speed adjustment.
 
Found an issue. Both primary and secondary main air bleeds were plugged. They were so plugged that when I looked at them, I thought they were blanks, no orifice was even seen until i stuck a strand of wire in there and poked it through. I then soaked both in carb cleaner and blew them out. So it was running rich and maybe thats why the idle screw didnt do squat. Its idling fine now. smooth as a 4 banger can I guess. I took the advice, opened and then leaned it out until it just dropped a few inches vacuum and left it. Ill update when it passes smog. AS this truck gets parked for weeks on end, I know now where to shoot the carb cleaners straw as you can barely see the bleeds when the carb is mounted. Thanks all!
 
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