So I hit the wall on my carb issues and brought the truck (early '91 S83P) to my mechanic. FTR, I trust him completely--smart guy, 35 years experience (including being a Toyota factory tech), but now he's a little confused: Symptoms were: deep bog right off idle, intake backfire, fouled plugs, running rich. So did these things : New: Vacuum lines Cap, rotor, wires, plugs Filters, fluids Rebuilt: Carb, including new needle & seat, new accelerator pump, float, gaskets Checked: Manifold vacuum (ok) Timing belt/marks (newish belt, has not skipped a tooth Adjusted Valves (.007/.010) Choke, mixture, idle After that, it ran a little better but still had a very nasty off idle bog, especially cold. Then... He started pushing the timing--and ended up maxing it out. No sh**, we're probably at 30 degrees before TDC right now. The weird thing, truck is running much better--but still bogs when cold. It starts right up, idles great, better power, and no pinging (guys, at 30+ degrees, shouldn't there be pinging?? I'm running regular farm gas here.) He thinks it's pointing to a vacuum issue. (I know a lot of the check valves are old and clogged, and who's to say some lines aren't misrouted? I'm going to open some beers and go through them one by one). Long question short...has anyone had to advance their timing to ridiculous extremes? And at the end of the day,what was the real cause? (Because 30 degrees advance seems like it's just covering up another problem which, with the cold bog, ain't really resolved anyway). Long post, sorry. Would love some help.
Is the vacuum retard line connected correctly? It is supposed to be on a ported vacuum source on the carburetor, and if it was going to the manifold, and always retarding, you might need to reconnect it.
Is the vacuum retard line connected correctly? It is supposed to be on a ported vacuum source on the carburetor, and if it was going to the manifold, and always retarding, you might need to reconnect it. It seems to be, and my mech even mentioned that there is good vacuum to the distributor and both mechanical and vacuum advance are working OK. But I think a visit to the vacuum diagram is in order, regardless. And when you say ported source, do you mean there should be an inline check or control valve on that line?
The carburetor has ports at various locations above the throttle blade, which lead out to the vacuum nipples on the outside. the retard is usually pretty close to the closed position of the throttle blade, and the advance is above it. So at closed throttle your getting the retard signal by itself. And as the throttle opens the advance signal comes in, and is stronger.
I get you now. Interesting, he pointed out the port & vac line at the top of the carb (the one on the horizontal stamped steel plate that I see on most all of our carbs) and said, "this one confused me, it just goes back to the manifold--doesn't seem to have a purpose." I'm thinking we may have some misrouted lines here, and in combination with some clearly clogged check valves, I think I have some vacuum work to do. Does anyone know if there is a better vac diagram than the one I've attached to this post?
JMM, the vacuum diagrams that you have posted here are the best i have seen. i too have carb problems and think they are related to misrouted lines and a bad ck valve somewhere. i've had no luck on this site checking all the old posts or with the various vendors. i've removed and re-built the carb 2x and i know it's not that but getting info on routing vacuum lines and ck valves seems to be non existant. all my vacuum lines have been replaced and i've checked all connections for leaks but still have low vacuum and ineffictive adjustments on the carb. VERY frustrating
So Flip, yesterday I checked and it seems like all my lines are routed OK, but the check valves are really badly gummed up. Most of them I can barely move any air through in the direction they are supposed to flow and can actually move a small amount of air through in the direction that's supposed to be blocked. I looked high and low, and direct replacements are not really available--but there are a few Audi, BMW and Mercedes ones that I think will fit (but at $20-$35 a pop, it seems foolish to buy 5 of them not even knowing if that's the problem). Not much luck on universal NAPA ones either, the inlets seem to be too large. Does anyone know: How freely vacuum should flow through these valves? If any of them should be delay valves vs. check valves? If anyone carries reasonable replacements? PS: Flip, what are your symptoms?
It seems to me, that the after market, $4, $5, dollar check valves, Dorman,(Advance Auto), (Summit Racing), would work, fine. Even if you have to reduce, size your vac lines,(adapt), to fit! I agree with you, $20-$35 a pop is crazy!!! At least that's what I would try! I know these thing's are, temp., and vac. sensitive, but it's only, a form of, pressurized air! NO? Any difference, when you remove the vac. lines? I haven't got this far yet, but I'm getting closer. It won't be long, and I'll probably join your frustration!!! Good luck! Limestone
I'll post here to let you know how I make out...i WILL find new check valves if it kills me, because if I later found out I was wrestling with the carb over a few 75 cent pieces of plastic, I know I'll die a little inside.
Been their. Heck your tryin, that's what we do! Yeah, I could see these vac check valves getting, tired, gummed up, dirty, or whatever! That's why I wouldn't even attempt used ones, not that your gonna! I would gamble on some inexpensive, fairly simple check valves! Remember, we can't screw up if were not trying! LOL! Limestone
my symptoms are that truck RACES when first started. like 4000 rpm's and no ammount of adjustment helps. when it warms up it will not respond to any adjustment and just stalls. it runs and drives fine down the road but when coming to a stop will either stall or over rev. mine is a 92 s83p with air cond. i've had the carb rebuilt 2x once by a professional shop and once by me. all vacuum lines have been replaced and i've gone thru all tutorials having to do with fuel shut off and operational adjustments. i figure something is not connected correctly or a vacuum pot is defective. i've been so frustrated i had to walk away from the truck for awhile. i've found ck valves on ebay under 5-1/8" polypropylene standard ck valves w/viton diaphragm for 10.00 might be worth a try? i question why the ones on my truck are color coded? seems like that would mean that they have different properties! someone out there MUST have the answers. flip
Summit Racing, URO Parts Check Valve (#116 800 0378) $4.99! Sounds like the ones I'm gonna order! Limestone
Flip, Recently, I think Jig's posted a color coded graph, describing these doggone vac. check valves! Very interesting! It was recent too! I'll try to find it if you haven't seen it! I'm wondering if you have a coolant line going to your carb. on your 91 s83? In many cases these get clogged and cause problems, based on temp's, and act like vac. problems! It is frustrating!!! Limestone
I'm sure you've checked, it almost sounds like a stuck throttle cable, linkage, or a bad cable! I've seen a lot of cables do dumb things! Disconnect the throttle cable, and start it! If you haven't already!
There should be free flow in the non delay direction. To the best of my knowledge: All of the little cylinders are delay valves. And, new replacements are rare. The only source I used to have was to go to the pick-a-part yard, and they are getting rare even there. Have you tried shooting carb cleaner through the inlet and outlet?
@Limestone, I just ordered these, will report on how they work: https://www.amazon.com/dp/B07JQ2L242/ref=cm_sw_r_cp_taa_0NbUEb75KGKSH @flip, I have a stupid question: after rebuilding the carb, was the choke adjusted while on the vehicle? My mechanic said it took him an "unusual" amount of time to get the choke right, and given that the choke pull off is vacuum activated I wonder if yours is not opening and closing right. (I am NOT a mechanic, just trying to put the pieces together). Might also check the choke springs, sometimes they break
Be careful with anything besides carb cleaner. Other solvents can dissolve the little rubber diaphragm. I’ve had luck by just using the little straw that comes with the carb cleaner, and alternating which end I shoot the carb cleaner into. As I alternated ends, there was progressively less discoloration, and eventually it came out clear.
thank's limestone for the vacuum pots info from jigs n fixtures. as to the carb it couldn't be any cleaner and the choke works like it should and the throttle cable is not bound up in any way. i've had two good experienced mechanics trouble shoot my problems with no joy! standard universal vacuum potts on e-bay in 1/8 side are 10.00 for 5. i'm going to go thru the vacuum system one more time when things warm up here before i give this truck a viking funeral! thank's for your ideas and help. flip
Reread the whole thing, and the problem might be the thermostatic vacuum valve. The vacuum retard, is connected to it, and if it isn’t closing when the engine warms up, you could have issues with the timing.
So as a follow up to this post, I found no issues with vac lines, increased the warm idle a little (my mechanic had it pretty low) and I have to say, the truck is running really, really well right now. I don't know how this massive timing advance fits into the minitruck scheme of things, but I don't want to borrow trouble.
The warm idle on my S110 is 950-rpm. I set the cold idle to 1250-rpm, because the manual doesn’t list one, and it makes sense based on experience. I tweaked the high idle a couple of times after that when the truck was being finicky when it got down to -25F. So it might be at 1350ish now.
