So after the timing belt broke on our S83P Jumbo I replaced and recut the valves, new cap and rotor, t-stat, water pump and tensioner, full top end gasket kit etc... Did a compression test after reassembly and was between 125-135 in all 3 holes cold. Idles great. Set the timing to about 7 degrees per what I've read on the forum and seems to idle and respond to throttle blips well. Problem starts when I try to drive. Runs fine through the RPMs until I shift into 2nd, then the motor bogs down and won't run. Almost like the timing is way off or down a cylinder. If I give a lot of fuel it will barley stay running but cannot take any load from the transmission. I have no clue what this could be. Carb settings? I haven't touched it since I refreshed the valve train but don't see why that would matter. Anyone with advice or similar experience, I would appreciate the wisdom. Thanks!
Probable causes of lack of Power: Insufficient ignition advance, secondary butterfly on carburetor not opening, metering rods/power valve not functioning, restricted exhaust, starving for fuel I’m guessing accelator pump, or a stuck advance plate on the distributor.
Jigs, I did some more digging, new plugs are black. Guess is running too rich which is flooding it, timing not advancing makes sense to me. Does that help narrow it down, forgive my ignorance but what is the advance plate on the distributor? Fuel is not restricted, actually flooded when I first tried to start. What is the metering rod/power valve? I'm new to OHC engines and know very little about carburetors. Being from the states and under 35, I've grown up on pushrod EFI engines so this has been a learning process. Thx
Start with the vacuum lines and carb. The 83s didn’t have the constant velocity carb, so i don’t think you have a metering rod, but I think you do have a power valve. But with the carbs we have the vacuum lines are a big source of issues. So, start with the vacuum lines, and check out the carb for things that should move but don’t. There’s a guy on YouTube, who has an S83, that was running rich, and it turned out that the choke was stuck. Re, the breaker plate. There is a cam inside the distributor, and the ignition points ride on that cam. When the follower comes to the lobe on the cam, the points open, the field in the coil collapses, and sends a charge through the spark plug. The breaker points are connected to the breaker plate, and the vacuum advance diaphragm, and centrifugal advance weights move the breaker plate, which changes the position of the follower on the points, and varies the ignition timing, the carb has so much vacuum advance, and so much centrifugal advance for a total advance. Not sure how many degrees total advance these engines want. Guessing I’d say around 35-degrees.
So did some more digging over the weekend and it is defiantly a fuel delivery or fuel/air mixture issue. The spring that holds the choke closed was broken when I bought my truck and a manual choke cable was installed. This worked for the time I drove it prior to the timing belt breaking but now the choke cable and carb settings are not correct. What I need to know is if the choke flap should be wide open all the time once the truck is warm. I can get the truck to idle with the choke flap open but the RPM's are higher than I would like and if I adjust the idle screw to bring the RPM's down, the truck dies. If I retard the timing to bring the RPM's down the truck dies. I have the timing at between 7-9 degrees BTDC which I've been told is correct at about 1,000 RPM's. When I try to drive the truck once it's warm, it stutters and pops like it's not getting enough fuel but I wonder if this is choke issue not a fuel delivery issue? I know this is almost impossible to diagnose on the internet but any other advice is appreciated. Also, I did check the vacuum lines associated with the carb (checked them all actually) and the only issue I found was the one connected to the valve cover. It was split. THANKS!
does your distributor have two vacuum lines going to it ? if so, try switching them, One is for advancing and the other one retards the timing, If hooked up backwards, it will not run or accelerate well
The choke plate will be wide open when its warm. To put the auto choke operation simply 1.) cold not running choke flap is completely closed 2.) after start up vacuum is applied to the choke pull off and the choke valve is open 1/4 of the way 3.) during warm up choke is slowly opened and idle drops down 4.) when shutdown choke slowly closes if the engine is allowed to cool G&R imports has a handy trouble shooting page that will help you understand how the choke system works in greater detail. https://docs.wixstatic.com/ugd/d494d1_91ad485ec9aa4f7ab3e94d24a1e61870.pdf How old is the gas in it? Stupid question but we are all guilty of doing it before. If your choke system isn't functional I would just wire the choke plate open and trouble shoot your running issues. Did you clean the carb out while you had the head off the truck? Do you have a vacuum gauge? I am curious how much vacuum its pulling at idle.
Squeaks, Gas is about 2 months old but I always put stabilizer in it because it can sit around. I'll try going straight from a fresh can just to see... always a good idea. Thank you for the info on the choke, I think part of the problem is that when I setup the manual choke cable right after I got the truck, I didn't realize that it's always been held about 3/4 open. It's never been opened all of the way. I leaning more and more to the side that the carb is just gummed up, seals are leaking, valves stuck etc... Or it just needs to be setup by someone who know what they are doing which I'll never find near me. I've never messed with the carb other than the high and low idle screws. I set the timing to about 8 degrees BTDC after the new head and timing belt and the idle was screaming. Used the screw to adjust it down to about 1000RPM and set the timing there again. It will sit and idle absolutely perfectly. It will pull through 1st gear great. As soon as I go to shift to second, it falls flat on its face and bogs down and starts to sputter. If I keep it running, after 30-45 seconds, it will be ok again but that cycle just repeats itself. I don't have a vacuum gauge but I can get one. Is there a specific vacuum line that I should test it on? Thanks!
Any port that's after the throttle blade will work to read manifold vacuum. Just about every sub system on these trucks is ran using manifold vacuum, that's why it looks like such a mess under the engine cover. You can get a cheap gauge from the freight harbor (your going to need it to setup the pilot scew after you get it running better anyway). It ought to be pulling between 15-20 in Hg at idle in my experience with these motors. If it is much less than this you have a vacuum leak. A can of starter fluid or carb cleaner is a good way to try and find a leak, just keep it away from the hot exhaust system. Vacuum leak symptoms seem to mostly effect idle performance and tend to smooth out when the butterfly begins to open and the more abundant intake air can bring in more fuel to offset the lean condition. This is only with a small leak though, if you have a really bad leak like a carb or intake manifold gasket it very much can cause a hard lean condition in every situation. So pretty much if the vacuum gauge is showing a good reading at idle your probably going to be taking the carb back off to clean it out. If you capable enough to get the head off and setup a new timing belt you ought to be able to handle cleaning out a carb pretty easy. Another thing I would check before digging into the carb would be pulling the fuel line that supplies the carb and crank the motor over a couple times with the starter to see if a good amount of fuel is getting pumped to the carb.
Squeaks/TTC, Thank you both for the advice. My biggest concern trying to pull the carb are all of the vacuum lines on top of and around it. I'm just going to mark them with colored tape, take lots of pictures and videos and give it a shot. It was pulling just under 15 in at what I believe is about 1,000 RPM so if there is a leak, its very minor. I'm guessing the issue is somewhere with the carb. Have either of you cleaned/rebuilt a carb for a mini truck before? I've been told getting carb re-build kits is very difficult because they are so many carb variations. I'm wondering if it might be easier to just buy an aftermarket carb? I did check the fuel pump as well, getting lots of fuel. I'll let you guys know what I find as I continue to investigate.
NAPA, and other parts stores sell sets of numbered/lettered plugs and caps. You pull the line off, put a plug in it, and the corresponding cap on the nipple it came off of. They are a real time saver.
great tips in this thread & im using it to try & get my carb closer to decent. im the opposite of the OP in this thread. mine is running great! but idling for crap. uneven, dies & so on.
SDK, it would be better to post your own thread regarding your running issue so we can help diagnose your issues separately. Steve, most of the mini truck parts suppliers carry carb kits for these trucks and should get able to find one that will work for your truck. I would give rebuilding your carb a shot, the price of the oem rebuilt carbs can get pretty expensive over almost $600. There are some manual choke carb options available for a lot less but I don't have any experience with them, I would be interested to see how they work.
