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My LUV had a number of problems that I knew about and was due to be smogged so I've non-opped it and have done a bunch of work. I'm amazed that the guy I bought it from got it smogged. I have found a bunch of things that should have cased it to fail. I've replaced all that I could find that might be a problem with getting it smogged.
But now the RPM still ranges up and down once the engine is warmed up and I cant figure out why.

The cat and muffler are brand new (old cat was shot and muffler was plugged up).
EGR valve is new and the EGR pipe has been replaced (old EGR had a leaking diaphram and the pipe was lose and would not seat).
I've isolated the carb from all the various vacuum lines and it still surges.
It's not likely the air injection smog junk because the surging is the same even with the pump belt removed (vacuum lines blocked and the injection manifold check valve is good).
New water pump, thermostat, coolant, hoses and radiator cap.
Brand new fuel pump (4lb max) and new filters.
New carb float and needle valve (float level is now correct, fuel was overflowing into the secondary before).
New carb accelerator pump piston, gasket and dust cover (old one was leaking).
New points, cap, rotor and spark plugs.
The choke and anti-dieseling valve both seem to work correctly.

My Luv has an auto trans and working AC (the surging happens with AC on and off).
The engine starts and sounds fine when cold but then when warmed up the rmp ranges up and down (prob more than 50 rmp not likely more than 150). The ranging is not random it is very cyclical. It does this at idle and when held at higher rpms, it does it in park, neutral or in gear, but might not when in gear and under load. It does it when the timing is advanced or retarded.
The ranging rmp does not brighten and dim the lights.

I'm suspecting ignition electrical, or distributor mechanical or valve adjustment, but I've little experience with these and at this point need some help...

Ideas and/or advice???

Thanks,
Tom

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79 Black Mikado longbed with AT & AC...

surging up and down at idle is text book vacuum leak. Something must open up a leak after it's warmed up.

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OK, I'm over it. Where's the beer?

The two vac lines that are temp controlled are the EGR and the air cleaner. If you are plugging and bypassing both and it still does it I'd say look at the carb base or the intake to head joint. Get some carb cleaner or WD-40 and spray around things looking for the leak. The RPMs should change when you spray over the leak.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

Thanks guys.
I'll do some leak testing today and post again afterwards.

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79 Black Mikado longbed with AT & AC...

I used carb cleaner and could not produce any changes in RPM. Then I modified a hand held propane torch so I could deliver the gas via a length of flexible hose with very specific placement. I went all around the carb, the intake, egr and it's pipe from the exhaust, the intake gasket, and the vacuum to the brake booster. I also checked around the air injection system. I cannot identify any leaks.

I'm still at a loss trying to solve this problem.

Any more suggestings?

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79 Black Mikado longbed with AT & AC...

I wish everyone put up this much info when asking q's

I'm probably incredibly wrong, but maybe, just maybe, the RPM change is from a differing load on an accessory... I'd try having the alternator/regulator tested (I'm not sure how this could be different warm/cold, but testing is cheap-free)...
Another possibility might be something to do with the cooling system... maybe the water pump requires different amounts of power when the thermostat is open/closed...

Good luck...

lol, if it was a computer controlled engine, I'd suggest testing the O2 sensor... but it's not... darn...
-ret

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1980 4X4 LUV daily driver, as stock as can be.

Thanks for the reply ret.

I tried to find a vacuum leak with the propane again today with negative results.
I thought about odd tension loads on the crank from the pullies. I removed the belt for the smog pump with no change. I didn't think it was the AC because the ranging doesn't change much when the AC turns on and off. I'll check the alternator.
I wonder if a slow flowing radiator could be the problem?
I'm learning more about the carb and will be checking it out some more. It seems to me the primary idle spits out lots of fuel and I dont know how to adjust that to see...

If it were computer controlled I read the error codes. Those have saved me some big bucks on service problems with other cars...

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79 Black Mikado longbed with AT & AC...

Check the dist. for wear in the shaft bushing( dose it wobble around) Check the vac.adv can and make sure it hold vac. if it has a small leak the timing will surge.This all sounds like it is time to put in an elec. dist.

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1978 pro street step/side 455Buick, 4sp,4.11s, 31/18.5s

Its the carb, Can't tell you why. But I had simular with mine. Would idle fine, then rev up at times and I could coast at 35 mph in gear. Would run at a gazillion RPM after warming up sometimes. Kind of embarrassing at a stop light. Or would just die and not idle. Depending the time of day. It would not run/idle on the way to work, than on the way home it would surge in RPM. Does it sound like it is missing a lot? One time it went away for a long time when I replaced the points, condensor, cap, rotor, plugs, plug wires. Then it came back. It was very frustrating, wanted to part the thing out, and I did the same replaced just about everything except the carb, because I did not have the money to invest in a new one yet. I would only guess it may be the choke mechanism or the selenoids on the stock carb?

Now I have a weber and eliminated all but the distributor advance and the pcv vacuum and the thing runs as close to perfect as you could from a 30 year old truck with 110,000 miles when you eliminate all the CA and federal emmisions BS. That probably don't help you in CA. But it is a night and day difference. Maybe you can keep all the emmisions stuff on with a weber?

Thank God I live in Montana. I noticed all the warning labels on cars when visiting CA a couple of years ago. Weird. I like the beach, good scenery.

I checked the vac advance when I did the points/rotor/cap and it dosen't leak. I have one of those hand pump vacuum deals with a gauge and it showed me the vac advance held vacuum and the distriutor springs were doing their job (I did find the EGR diaphram was waisted with theat tool).
I'll check the dizzy shaft for for wobbling, but wouldn't it be a problem when the engine is cold aswel as when warmed up?

Does anyone know if swapping to an electric dizzy will pass CA smog test?

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79 Black Mikado longbed with AT & AC...

CA smog rules are often way lame. I could put in a Weber, scrap much of the stock crap and then get better milage, more power and better results than stock for emissions tests but the state wont allow it... wtf?
My truck had many of the same problems as yours, many of which are corrected now but I expect it would fail the smog test because of the ranging idle.
Thanks for the responce.

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79 Black Mikado longbed with AT & AC...

Don't know what carb you have but whatever, I'd adjust the mixture screw[s]. Under the right conditions an engine can surge either from a lean mixture or a rich mixture. If it only does this after auto choke goes off that indicates you're lean.

One thing you can do is let it warm and remove air cleaner. Once it starts surging close off part of the carb throat with your hand or fingers to restrict air flow. If it smooths out as you choke it this way you're lean. Obviously be extra careful of moving parts grabbing you.

Some of these carbs have a welch plug or little cap over the mixture screw or else idle limiter caps. These have to be removed to find or adjust needle.

Sound to me like it's running lean....

Check vac. hose to EGR I don't know if these go to a TVS (thermal vac. switch) but it my have manifold vac. going to the egr instead of manifold vac. I quick check is ti unplug the egr and check running condition.There are other thing in these systems like vac. delays or restricters but not all egr systems use them ether

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1978 pro street step/side 455Buick, 4sp,4.11s, 31/18.5s

It's the stock POS carb. I've tried adusting the idle mix screw aswel as the other idle adjustments. I cannot get the mix screw to change the idle as much as has been my experience with adjusting other carbs. I have followed the various timing and tune-up directions in the manual which include turning the mix screw all the way clockwise (lean) then setting the idle, and backing the mix screw out a bit and so on.
The engine was running very rich when I started looking for its problems, I'm thinking it may still be rich. The primary dumps lots of gas down onto the shut butterfly valve when idling. I'm suspect that it is so much gas it collects on the valve and then all passes down at once thus increasing the RPM for a bit while more gas backs up again...
I cant figure out how to adjust this, could it be a jet that is too big, or is my needle valve messed up? I'm not getting enough info from the manual.

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79 Black Mikado longbed with AT & AC...

This has all been checked. New EGR valve and replaced EGR pipe, new TVS (old one leaked), new vacuum hoses and tested for vacuum leaks.

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79 Black Mikado longbed with AT & AC...

If you think is the carb then by all means check the float level.

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1978 pro street step/side 455Buick, 4sp,4.11s, 31/18.5s

Is it doing this in drive/reverse only, or in park/neutral also?

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OK, I'm over it. Where's the beer?

The float level is correct.

If I lower the float level will that decrease the volume of gas flowing into the primary while idling?

BTW, when I was replacing the float and needle valve, I swapped the stock fuel level gauge plate (the one with the puny glass porthole in a metal plate) for an all glass plate that makes seeing the float and level very easy. The all glass plate only cost a few bucks at a carb shop.

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79 Black Mikado longbed with AT & AC...

It ranges in drive&reverse and park&neutral. It also ranges if I throttle up and then hold at higher RPMs. I cannot tell if it does so while under load in gear...

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79 Black Mikado longbed with AT & AC...

The float level will effect idle quality in if to high you will have a rich condition and to low to lean.
I can't remember the exact architecture of the carb but i think there is a power valve in the bottom and in back of the float bowel and if it is loose or stuck open it would give you a rich condition at part throttle.

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1978 pro street step/side 455Buick, 4sp,4.11s, 31/18.5s