New to Forum - 1986 720 Regular Cab

[Seaway]

New guy here.  Just picked up a 1986 720 with about 161,000 on the clock this weekend and I once I get into it, I am going to have a bunch of questions.  I have never worked on a Japanese vehicle before and never owned a car/truck with a carburetor.  I had a couple old Mercedes diesels, an old Mercedes 190e that I completely rebuilt, and I currently own a 1998 315hp Volvo wagon that I have modded a bunch, including an engine swap, suspension, tune, etc.  So while I don't know anything about these trucks, I know I can learn. I traded an old Volvo I got for $250 for the truck and then drove it about 90 miles to get home, all of it on the highway.  The truck is lowered and sits on 14" wheels with 205/75 -14 tires, so lots of sidewall.  It actually rides pretty well, and I like the height, though I may have to raise it back up if it makes hauling stuff problematic. The problems I have noticed so far are the following:

 

- The steering (manual, no power steering) has a pretty large dead spot in the center.  

- It idles at what seems to me to be really high at between 1200 -1300 rpms, but other than that, the engine seems pretty good.  Smooth and more power than I was expecting.

- There is a small leak/ooze from the drivers side of the valve cover gasket, but the oil level stayed the same on the ride home, so I am not that concerned.

- Every vacuum hose needs to be changed out - or should I delete all the emissions stuff?

- Headlights are extremely dim, I had a flashlight with me that cast more light.

- I am sure there will be a lot more once I get a chance to get further into it.

 

There are some minor electrical issues, wiring issues and rattles and clunks, but overall I am really happy with the truck.  Hopefully once I can get it to idle I can start to tackle a few of the other issues and get it up and running.

 

 

 

[Charlie69]

Welcome.

 

Great looking truck.  Idle is to hi.  Check the front steering and suspension parts for wear.  Replace parts as needed.  Get an alignment done and ask the alignment person to adjust the steer box play if needed.

[datzenmike]

 

 

- The steering (manual, no power steering) has a pretty large dead spot in the center.  

- It idles at what seems to me to be really high at between 1200 -1300 rpms, but other than that, the engine seems pretty good.  Smooth and more power than I was expecting.

- There is a small leak/ooze from the drivers side of the valve cover gasket, but the oil level stayed the same on the ride home, so I am not that concerned.

- Every vacuum hose needs to be changed out - or should I delete all the emissions stuff?

- Headlights are extremely dim, I had a flashlight with me that cast more light.

- I am sure there will be a lot more once I get a chance to get further into it.

 

There are some minor electrical issues, wiring issues and rattles and clunks, but overall I am really happy with the truck.  Hopefully once I can get it to idle I can start to tackle a few of the other issues and get it up and running.

 

 

Steering side to side looseness is an adding up of all the ball joint looseness, idler arm and gear box wear times the steering box ratio (about 20 to 1) So if all the wear added to 1/8", the steering wheel would move 20X that or 2 1/2". It adds up fast. Inspect and replace any worn steering ball joints. The idler arm is another place to look. The steering box has an adjustment bolt but if the wear is in the straight ahead position, and you tighten it up it might easily be way to tight at the far left and right and jam when turning.

 

Valve cover gaskets are affordable and easy enough to change.

 

Check hoses individually and replace cracked ones. Often removal add problems and it runs just fine when everything is working.

 

Dim headlights and fast idle.  These could easily be related.

If the alternator is not charging properly the choke heater will not work. If the choke heater is not working the choke will never shut off completely. If the choke is on, or part on, the fast idle circuit will be engaged. So fix the charge problem... fixes the fast idle problem. Maybe. Next time the engine has been run long enough to warm it up, remove the top of the air filter and look down. The choke plate should be vertical or fully open like this...

 

 

 

If it is partly closed or closed like this it then the electric choke heater is likely not working

 

.

[Seaway]

Wow, thanks for the quick responses!

 

I will check the alternator and make sure I am getting the proper output, thanks for the suggestion.

 

I had it warmed up and idling (at about 1200 rpms) in my garage yesterday and the choke plate was definitely vertical.  I could see fuel dripping/spitting into the carb and when I goosed the throttle at the linkage on the side of the carb the fuel would atomize and the engine would rev.  Should it be atomized at idle, or should it be a drip/sputter of gas? I was able to manually manipulate the fast idle cam and the idle increased to between 1500-1600 rpms or about 300 faster than "normal" idle.  When I drove the truck (with the engine heated up to temp) it would run fine, but as soon as I slowed to stop, it would die and I would have to restart it.  Upon restarting it would again idle high and then the process would repeat.  

 

As far as the hoses are concerned, I am going to simply go through it and replace them all instead of ripping things out.  Once I get a bit more comfortable with what's what, I may delete the emissions stuff, but at this point it seems as though it will make diagnosing issues a bit more difficult.

[datzenmike]

If above proper idle speed it might suck gas from the primary but normally it doesn't. Try turning the idle speed screw down. If the adjustment caused the engine to not run below 1000RPM the idle cut solenoid may not be working. The idle cut allows gas into the idle circuit when the ignition is on and shuts off gas when the engine is turned off to prevent run on or dieseling. To see if electrically connected, without starting the engine, turn ignition on  off  on  off on  off. You should hear a soft clicking from the carburetor. 

[Seaway]

It does diesel a little at shut off, so maybe that is part of the problem.  I will give it a listen this evening when I get home to see if I can here anything when the key is turned.

[datzenmike]

That's from the fast idle. If the solenoid is faulty or the idle circuit plugged up, the previous owner may have just simply turned the idle up to get around it.

[Eagle_Adam]

Pics and a good description of the truck and it's problems!!

 

Good first post, welcome to Ratsun

[Seaway]

That's from the fast idle. If the solenoid is faulty or the idle circuit plugged up, the previous owner may have just simply turned the idle up to get around it.

So it sounds like I need to troubleshoot the solenoid and probably clean the carb and see where that gets me. Can I put a multi meter on the solenoid and see if it is functioning correctly and getting power?

 

 

Pics and a good description of the truck and it's problems!!

 

Good first post, welcome to Ratsun

 

Thanks, I am active on a couple other car forums as well as boat forums, so I know the drill... I wish I could be more specific about my problems with this truck, but I am still trying to figure out the names of the parts of the carburetor.  I just had to Google "idle circuit," for instance.  

 

After driving 90 or so miles on the highway, I burned about 4 gallons of fuel, so it seems to do okay in that respect.  The speedo is off I assume from the tire size, so I used a gps to determine my actual speed.  Other than that, it stayed at temperature and rode pretty well.  I am 6'4" tall and I was surprised by the amount of room in the cab.  

[Seaway]

Well, I got some of the vacuum lines replaced and took a closer look at the carb. The plug is still in the idle speed screw so it would seem that has not been adjusted. I replaced some vacuum lines and it slowed the idle down to about 1000 rpms. I think the stalling may be related to a vacuum leak at the brake booster. If I come out of gear and coast it is fine. If I brake it wants to stall.

[datzenmike]

There should be 12 v on the red wire to the solenoid with the key on.

 

 

Sorry all carbs from mid '82 have the idle set and sealed. You can drill a 1/8" hole and screw in a wood screw and pry it out but lets leave that for now.

 

 

Try this... pump brake several times. Apply brake and start engine. What should happen is the brake pedal should drop 1/2 to 1".

[Seaway]

Yep, the brake pedal drops I would guess a bit more than an inch,but not to the floor or anything.

[Seaway]

I picked up a bunch of bulk vacuum hoses and I am going to spend the evening replacing everything.  I have done some more reading and I am going to troubleshoot the electric choke as well, because I am not convinced it is working correctly.  With any luck, I will have this figured out before too long.  

 

The further I dig into the truck, the more I like it.  It has some pretty poorly repaired patches in the floor and the passenger wheel well, but, having had 3 old Mercedes in the past, I am not afraid of that.  The frame of the truck is rock solid and has been completely coated with POR-15 and looks to be in amazing condition.  The rest of the body has some surface rust, but no rot.  

 

Once I get the engine running well I am going to begin to tackle the electrical problems.  Namely the turn signal stalk - it has to be held in order to make the signals work, and the dim headlights.  One of the Mercedes I had suffered from this and the fix was new pig tails at the headlights and new, clean grounds.  I would love to get away from the sealed beams, but I am not sure how far down the rabbit hole I want to get with with the lighting. 

 

Most of the exhaust is in really good shape with the exception of one slip joint that was clamped poorly and has resulted in the pipe being kinked.  There may be enough room to weld it in place, or I may simply use a wide band clamp and avoid the frustration of removing the exhaust to weld it.

 

At any rate, I am excited to get to work!

[Lockleaf]

A common issue is on the contacts on the headlight stalk as well. They get grungy on these 720s. Sometimes a little cleaning on them is all it takes.

[Seaway]

I will take it apart before I order a new one, I am having trouble figuring out the correct part anyway, so I need to look at what is there first.  

[Seaway]

Got about 85% of the vacuum lines replaced and then the truck wouldn't start. It was not getting fuel. After locating the fuel pump relay I gave it a jiggle and it started right up. Idle is still at 1200 or so, but it is not nearly as lumpy as it was. I would live to get the idle down a bit but I am happy with the progress. It makes it much easier to drive when it doesn’t stall every time I stop.

[datzenmike]

Yep, the brake pedal drops I would guess a bit more than an inch,but not to the floor or anything.

 

This at least is normal.

[Seaway]

What is the normal idle speed for these engines? 7-800 rpms?

[Charlie69]

Probably late but the vacuum diagram is placed on the engine side of the hood.

[Seaway]

I am pretty sure the hood is not original.  In any case, it doesn't have anything affixed to it.  

 

I am going to have a bit more time to try to dive into it tonight, so I am going to see what I can do to bring the idle to somewhere a bit closer to "normal."  The truck drives pretty well once it is moving, seems to have plenty of pickup and sounds pretty good.  I did take a look at the suspension and ball joints, etc, and all of that is going to get replaced after I get it running well.  At that point I will have to decide if I want to leave it lowered or raise it back up to stock height.  Form vs Function?  My other car is lowered as well, so I am at least used to it...

[Seaway]

Quick update:  Still having some idle problems that seem to be vacuum leak or fuel pressure related.  I an getting some surging at idle that I would love to get rid of.  The engine sounds great now and the aftermarket tach that is hooked up seems to think it is now idling at about 1000 rpms.  I sounds slower to me, but I am not 100% sure.  Also, it seems to run more smoothly before it gets to temperature. Once at temperature it stumbles a bit, dropping 200 or so rpm and then picking back up at every stumble.

 

Thus far I have done the following:

 

New vacuum hoses (more on hose is on the way so I can get the rest of it replaced tonight).

New spark plugs (new wires, distributor cap and rotor on the way).

New air filter

New O2 sensor is also on the way.

 

Basically it will be a full tune up with all new vacuum lines.  

 

It does seem that my electric choke is working as it is supposed to from what I have read.  Set it with the pedal, and then watch it slowly open as the engine heats up.

 

Is there a way to test the fuel pressure regulator?  

[Lockleaf]

FPR is nothing more than a restrictor orifice in the fuel return line. Not likely to fail in any way

[Seaway]

FPR is nothing more than a restrictor orifice in the fuel return line. Not likely to fail in any way

Okay thanks.

 

Any advice on the kind of high lumpy idle?  

[datzenmike]

The orifice in the return line is not a FPR. The fuel pump has a built in regulator. If the return line was open the fuel would just pump back into the tank. By placing a restriction in it, pressure will build on the carb side and be able to push into the carb. The orifice is about the size of a large pin.   

[Lockleaf]

Have you done the good old fashioned carb cleaner/starter fluid check for vacuum leaks?   With the engine running, spray the intake manifold where it meets the head, and where the carb mounts to the manifold.  If the idle changes when you spray, and you can repeatedly cause the change, there is a leak in that location.