New Member with a new (to me) 720

[lostinthe202]

Hiya!

 

Yesterday I picked up an '86 720 King Cab 4x4. It's got some bed rust, but otherwise is in good cosmetic condition for the age. It's got a carb issue (why I got it cheap) and I was hoping to get some advice on where to start.

 

Basically, it starts on the first crank and runs great, but it won't idle bellow about 2500 rpm. The fella I bought it from is not mechanically inclined and all he could tell me is that the mechanic that did the state inspection (virginia) told him that the carb was "leaking internally"

 

I did a basic check (spray test) for vacuum leaks with no positive results and a basic visual inspection but nothing set off a bells. Is this carb generally thought of as reliable or should I scrap it and get a weber?

 

I don't have to worry about emissions so any tips on "de-smogging" would be greatly appreciated!!

 

If this is posted in the wrong place or the truck is considered too new to belong on this forum, could anyone recommend where I should look?

 

Thanks!!!

 

Will-

[freaky510]

welcome to Ratsun you will love to hate us :lol:we like pics lot and lots of pics

 

as for your carb junk it and get a weber you will be glad you did and post some pics:lol:

[Nissan_Boy85]

Ya beat me too it Freaky. We like pics! Junk the stock carb and pick yourself up a weber. It kinda acts as a de-smogger in itself.

[Phlebmaster]

Welcome to Ratsun! Ummmm....pics please :D

[Wharf Rat]

Welcome to Ratsun:fu: is the choke coming off and is there power to it? Linkage may be hanging up give it all a good spray with PB Blaster. And yes we need PICS want PICS must have PICS.

 

Thank you:)

[Skib]

 

this is my artists rendition of Wharf the last time someone didnt post pics.

true story.

[lostinthe202]

Haha, alright, alright here's your pics. Not much to look at yet, but here ya go,

 

 

 

So one edit, it's an '85 not and '86 if it makes any difference. I dug through the paperwork I received with the truck and discovered that the carb was replaced in 2006 so that would go against the "leaking" theory, unless the mechanic meant a vacuum leak and the owner misunderstood right? But then one way to take care of vacuum leaks is to rip all that stuff off with a weber which is probably what I'll do.

 

But I need to save up some pennies for that, so in the mean time any more ideas about what to look for on the carb will be appreciated. Wharf Rat, thanks for the tip on the choke, I'll check that out.

 

Also mentioned was that #1 and #2 cylinders had about 90psi due to "leaking valves". It doesn't say whether or not anything was fixed so I guess I'll be doing a compression check and see what's what. It did seem to be lacking a bit of power on the way home, but between the shot u-joint and the persnickity carb, who knows what's going on.

 

Thanks!

 

Will-

[datzenmike]

Is the choke fully off? If not off the fast idle cam will be engaged. If it is off the fast idle cam may be stuck. Here is the fast idle cam, note the bottom has steps to give less and less fast idle as the choke slowly opens as the motor warms up:http://i138.photobucket.com/albums/q251/datzenmike/720%20stuff/carbZ24idlestepLg.jpg[/img]"]

 

Here is the cam with the fast idle screw on one of the steps :http://i138.photobucket.com/albums/q251/datzenmike/720%20stuff/carbZ24fastidleadjustLg.jpg[/img]"]

 

With the choke held open and the throttle partially open, this plastic cam should be free to fall of it's own weight down out of the way. Use carb spray or WD-40 and spray this area and work all the linkages to loosen and clean all parts.

 

 

The secondary may be stuck slightly open. Had this happen to me. Very high idle could not figure it out. One day I reached around behind and lifted the rod connecting the secondary to the vacuum diaphragm that operates it. When I lifted it it revved up and when I let go it seated properly and the idle dropped to about 500RPM. I had to adjust the idle up because I had turned it down so far.

 

Funny thing is I later found a picture of the carb while rebuilding/adjusting and you can clearly see that the secondary isn't closed tight.

[lostinthe202]

Awesome descriptoin and pics DatzenMike, I'lll check that out tomorrow and report back.

 

Thanks!

 

Will-

[datzenmike]

Can you post a picture of the carb? Do you have an Oxygen sensor in the exhaust manifold? Two kinds of carbs were used including a feedback type used in California. Their use may have spread to DC.?? Good to know if it is, as it has it's own set of problems.

[ronnie93212]

if he was in need of a stock carburetor i have one ill let go for 50 bucks since he is a fellow ratsun :) it worked perfect for me.

[ronnie93212]

just tryin to help out. With your replys doesnt seem like he needs one just trying to help :)

[lostinthe202]

Ronnie93212, thanks for the offer, but this carb is only two years old (and the pics show it, I could eat ceral out of this thing it's so clean) so It's probably either a vacuum leak I'm missing or some other external to the carb issue.

 

DatzunMike, here's the pics, hopefully they're useful angles. Yes it does have an O2 sensor on the exhaust manifold (looks fairly new itself, but if it's a generic one then "fairly new" doesn't mean much). I checked out the choke arm this morning and everything looks free moving, however I didn't have time before leaving for work to warm the truck up and make sure it was fulling closing so I'll check that out this evening when I get home.

 

Thanks again for the help!!

 

 

[Wharf Rat]

It's probly a adjustment. Datzen Mike will know for sure, but in the second pic there is a round cover with several screws, you can't see the center of it because of a ignition wire. If it's got a rubber plug, remove it to see a small adjustment screw there. If it is what I think (a antibackfire valve) you turn that screw counter clockwise just a little bit at a time and then rev engine up and release. You should hear a hissing coming from the carb throat for a few seconds and then stop, at that point it should drop to a normal idle. If you have already backed the regular idle screw off it may stall. Turn it in until it's normal idle speed. You can adjust that valve so there is little hiss time and the engine will slow to idle faster. I set them not to even function on my cars(back when I turned wrenchs for a living way back when:blink:) I like the rumble when backing down.

 

Hope this does the trick Peace WRAT

[lostinthe202]

Thanks for the tip Wharf Rat, put that on the list. But before I got messing with any adjustment screws, I think I should take care of this...

 

 

I had the air cleaner off today giving all the vacuum hoses a yank to see if I missed anything and bingo, this just slipped right off. Anybody know what it is? I assume this would be a dealer item and not a part store item? As you can see from those vacuum lines, they are not all in good shape. So I'm going to get a few feet of the stuff tomorrow and change everything before I go messing with any settings.

 

Thanks!

 

Will-

[Wharf Rat]

I'm not sure but I think it's probly dist. adavance related for smog control when engine is cold it won't allow it to advance. I'm sure if you bypass, it won't effect the running of the Ol' Rat:D It will like it:rolleyes:

[lostinthe202]

Hmm, alright. I just now realized that I should've taken pics of where the hoses went, ah well. I might just pop it off in the morning and take it to work and make another one. Or do as you suggest and just plug it up. Either way, faster then waiting for parts to come in from the dealer!

[Wharf Rat]

I see from your other thread that I was right about the broken peice for the vac advance have you tried the adjustment on the other yet it should be in the middle of that cover it's not round as I said but has philips screws around it. I'm curious now:)

[lostinthe202]

Naw not yet. I wanted to replace all the vacuum hoses before I adjusted anything. I've got the hose, now all I need is a spare moment to replace. I should get that tomorrow evening. I'll be sure to let you know.

 

Will-

[Wharf Rat]

Darn it the screws take reg or phil screw driver! The adjustment screw under the rubber cover thats in the center is a small regular normaly.

 

Good luck WRAT

[lostinthe202]

As soon as I get home I'll take a look and let you know if it's there...

[lostinthe202]

OK, looks like there's nothing wrong with your memory. Here ya go one adjustment screw,

 

[KELMO]

Will,

That vaccum part on your manifold is called a thermo vaccum(vacuum vaccum, I really don't know....or care how to spell it) valve. Part # is 14890-N8500 and runs about $25.00. I don't know if it is a dealer only item or or not.

Hope the info helps.

 

Oh yeah, Nice Truck

 

Kelmo

[datzenmike]

Well two things to check.

 

 

On the far right is an electric solenoid marked 'APDU40-1 3128' that pushes the throttle open slightly to raise the RPM. Trucks with air con have them. It's to prevent stalling when the compressor in engaged by raising the idle. Check the bottom of it, that this is not on or holding the throttle open.

 

 

 

The thing with the Philips screws is the BCCD Boost Controlled Deceleration Device. Briefly it senses very high manifold vacuum like suddenly letting off on the gas at highway speeds. This condition usually results in fuel but little air and causes high emissions. The BCCD adds extra air and fuel to promote better burning and is supposed to shut off then the manifold vacuum lowers. If badly adjusted it might stay on and cause a high idle. Turn the screw COUNTER CLOCKWISE 1/4 turn, rev motor to 3500 and suddenly release pedal see if idle is restored, if not try another 1/4 turn. Keep track of the number of turns in case this isn't it, so it can be returned to the original.

 

Try thesetwo things first... simple and easy things first. Do on a warmed up motor.