‘83 720, Crank-no-start after tuning idle on Weber carb (newbie)

[Corapop]

Hi all. Newbie 720 owner, and newb when it comes to working on cars. I bought an 83 720 that has had the engine changed, a Weber carburetor swapped in, and a bunch of vacuum line changes/caps. In the past I’ve been good at following along with tutorials or YouTube videos to do moderate repairs on my cars, but following along ‘play-by-play’. So I think having this project truck that doesn’t look like it’s ‘supposed to’ under the hood will be a good opportunity for me to think more and understand how various systems work, and work together. 
 

so the issue: I have a crank-no-start. The truck was running great since I got her a few weeks ago, starting immediately upon turning the key. Over the last week, it’s either been idling very high, or very low. When it’s low I have to feed it gas at stop so it doesn’t stall out. In addition to that being obnoxious, I need to do emissions inspection where they need it to idle between 500-1300. So last night I adjusted the fast idle and mixture screws on the Weber carb to try and get the idle to 1000. Success, drove it around for fifteen minutes, went to bed. This morning, I get in to drive to DEQ test, and it’s crank-no-start. 
 

I read through various threads on this forum, and others, and watched some videos. Lots of people pointing to the fuel system, so I started there. The truck has a permanent jump to the fuel pump. I use a battery cutoff switch when I start and stop the car, otherwise it runs all the time. Today, however, I found an actual light switch under the glovebox that turns this off and on. Weird.

 

so I can hear the fuel pump. I went ahead and changed the fuel filter since it looked really old. I also replaced fuse #5. Still no starting. I wasn’t sure how to diagnose other problems with the pump, so I pulled the fuel line from the bottom of the carb, and let it fill a jar while I cranked. Seems like the pump is working. Put that line back. 
 

after purchasing a fire extinguisher 😅I tried spraying some starter fluid into the carb throat (3 second spray into one side, 1 second spray into the other, not really sure of the correct procedure here) then tried to start, still crank-no-start. Did I maybe not use enough fuel? Or does this tell me the problem isn’t fuel related?

 

call me crazy, but I really think it’s not coincidental that I effed with the carb and now it won’t start. Did I mess up the mixture so bad it won’t even start? I wouldn’t think the fast idle adjustment would affect the engine turning over, but maybe I’m misunderstanding how it works. Did I maybe shake some buildup loose or move/jam a linkage that would cause this to happen?

[Corapop]

I should also point out that the carb had no air filter or “cap” on it. When facing the engine bay, the left butterfly plate and tube are black/gunky while the right is much cleaner. When I push on the linkage for the plates, there is resistance like it’s sticking a little, before they open.

[datzenmike]

You can adjust the idle speed and mixture all you want. It should at least fire a few times while using the starter.

 

 

 You need fuel and spark.

 

1/ If not even trying to start check for spark. Pull an exhaust side (easier to get at) plug wire off and put an old spark plug in the end and lay it on a grounded surface. Have someone try to start the truck. Make sure it's grounded, like held against the exhaust manifold. Got spark?

 

2/ Look down the open carburetor and pump the throttle. If carburetor is full you should see strong squirts of fuel. Got gas?

 

 

3/ Does this Weber have a manual or an electric choke. If electric step on throttle it should close.

 

Try stepping on the gas several times. This will send in raw gas and richen the mixture for a start.

 

 

 

[Charlie69]

First you did not F the carb.  Weber carbs are very simple.  Great carb for you to learn on.

 

Second it sounds like you have no spark.  Check for spark the way Mike described and please post if you have spark or do not have spark.

[Corapop]

The choke butterfly plates open a tiny bit when the acceleration pedal is pushed all the way down and trying to start.

 

I pulled two different spark plug wires (one at a time), plugged in a spare spark plug, grounded on the engine, no spark whatsoever when cranking!

 

My lack of insight as to what to do next speaks to me never having had a spark problem before, and also not understanding how all the systems work. All these spark plug wires feed into the same canister though. Haynes manual said this is a distributor/coil assembly. I'll be reading up on that, now... Seem like the next step ?

[Corapop]

I replaced the ignition coil fuse, in case it was that simple. Nope. I've been going through the Haynes manual 5-2 Ignition Testing. Primary and secondary resistance across ignition coils within spec (1.1, 10.38k). I inspected the distributor cap and rotor. No major corrosion. Before I disassemble the distributor to test the IC module, is there another likely cause I'm missing, or does this seem like a reasonable path...

[datzenmike]

4 hours ago, Corapop said:

 

 

 

I pulled two different spark plug wires (one at a time), plugged in a spare spark plug, grounded on the engine, no spark whatsoever when cranking!

 

 

 

 

So right there you don't have any spark. That alone will cause it to not start.

 

Goes your gas gauge work???? Back up lights work? Turn signals work? If these are not working then the fusible link is not functioning.

 

 

If the above ARE working ...

Do you have a test lamp? They are under $5.

 

 

Clip the alligator to ground and touch the coil positive terminals. with ignition on)  Bet there is nothing.

 

 

[Charlie69]

Check the wiring ends for corrosion or broken wire.  Read up on carbon tracking on distributor caps.  Also there are 2 spring loaded contacts on the inside top of the distributor cap, be sure both move in and out easily and are in good shape.  When I buy rotors and distributor caps I buy the as a set.  They cost a little more this way but you are sure the cap and rotor and compatible with each other.

 

Edited September 28, 2021 by Charlie69

[Corapop]

8 minutes ago, datzenmike said:

 

So right there you don't have any spark. That alone will cause it to not start.

 

Goes your gas gauge work???? Back up lights work? Turn signals work? If these are not working then the fusible link is not functioning.

 

 

If the above ARE working ...

Do you have a test lamp? They are under $5.

 

 

Clip the alligator to ground and touch the coil positive terminals. Bet there is nothing.

 

 

I don't have a gas gauge,  the only gauges functioning are aftermarket tach and water temp gauges.

The turn signals don't work. The backup lights don't either, but I never confirmed that backup lights did in the first place.  But the signals definitely worked before this. (seemed like the aftermarket tach was tied into the turn signal circuit, because the needle tapped along with the signal).

 

I did run a wire from the coil positive, grounded a plug wire and plug onto the engine block, then tapped the wire on the engine block. Apparently if there was power I should see spark at the wire and some at the plug? but I couldn't figure out which coil was for which plugs, so I didn't wind up deducing anything from that.

 

I'll get a test lamp. And read up on the fusible link, if there's no power at the coil.

[Corapop]

Just realized I no longer hear the fuel pump when the battery disconnect key is turned. I've never not heard it...

[datzenmike]

 

30 minutes ago, Corapop said:

I don't have a gas gauge,  the only gauges functioning are aftermarket tach and water temp gauges.

The turn signals don't work. The backup lights don't either, but I never confirmed that backup lights did in the first place.  But the signals definitely worked before this. (seemed like the aftermarket tach was tied into the turn signal circuit, because the needle tapped along with the signal).

 

I did run a wire from the coil positive, grounded a plug wire and plug onto the engine block, then tapped the wire on the engine block. Apparently if there was power I should see spark at the wire and some at the plug? but I couldn't figure out which coil was for which plugs, so I didn't wind up deducing anything from that.

 

I'll get a test lamp. And read up on the fusible link, if there's no power at the coil.

 

This does not help. Go and look.

 

 

Does your temp and gas gauges work?

Does your back up lights work?

Do the turn signals work?

All these and the fuel pump are powered from the same fusible link. Are they working or not???? If not you can go directly to the fusible link and fix that.

[Corapop]

10 minutes ago, datzenmike said:

 

 

This does not help. Go and look.

 

 

Does your temp and gas gauges work?

Does your back up lights work?

Do the turn signals work?

All these and the fuel pump are powered from the same fusible link. Are they working or not???? If not you can go directly to the fusible link and fix that.

 

I don't have a gas gauge. Turn signals don't work. Backup lights don't work.

 

I looked near the battery positive post for the fusible link,  and it looks like all that may have been rewired.

 

 

[datzenmike]

 

Better post a picture of the wires connected to the positive battery terminal. Good news is someone messed with the wires. Bound to be something a previous owner did. And have a test lamp handy

 

 

 

[Corapop]

Thanks for the help.

 

I'll get some pictures in the light tomorrow, and pick up that test lamp. I bought the truck for 500$ from a coworker. While I dont want to be constantly asking him questions about it, when I get up against a wall I can reach out to him about stuff he modified. 

[datzenmike]

Might be best to not know. Fusible links can blow, though rarely. Owners often see it as just a burned wire and replace them themselves. Need I say more?

[Corapop]

 

https://postimg.cc/64vVR90n

 

Closer up

https://postimg.cc/47rVXDgd

 

Right now all I can tell is that one end of the positive cable goes to the alternator and one goes to the battery cutoff switch in the cab then back to the battery.

 

Once the rain lets up a little I can  start tracing some more of it, and move the battery to see if I'm missing anything. But I definitely don't see any of the "connectors" (2 white, 1 black) that show up on images of the fusible link, connected to the battery positive.

 

Does the fusible link show up on any circuit schematics? In my Haynes manual there's only two sentences about it.

[Charlie69]

The metal piece in the middle looks like the piece that goes on the positive battery cable clamp screw.  The fusible link wires connected to it.  I would get a longer battery cable bolt and put that mess back on the battery terminal where it belongs.  By doing this it will eliminate the cable the come off the battery terminal lessening the mess.  Never safe to have a bolt with a bunch of positive cable and wires hanging around looking for a way to short out.  Start by cleaning up that mess and when you take it a part clean al terminals.  If you just have to have that setup at least use this instead of the bolt.

 

Positive Insulated Battery Power Junction Post Block

 

 

Edited September 29, 2021 by Charlie69

[datzenmike]

 If it comes from the battery to a cut off switch then goes back to the battery what exactly is it doing??????

[Corapop]

Thanks for the clean up recommendation Charlie. This mess was inside of a big rubber tube, not ideal, but a little isolated.

 

Datzenmike, it goes from the battery terminal, to the cutoff switch, Then back to the 'mess' pictured here.

 

Also I fixed the problem. I'm not sure why or how, but replacing the blown "LH Headlamp" fuse fixed the "no-start". The previous owner wired in new head lights, so I'll have to figure out what's going on there. The fuel pump has gotten disconnected from the fusible link when I was investigating that area, which is why I could no longer hear it about midway through my investigation.

 

I bought a 12V test lamp and a continuity tester, and started to establish what's going on with where the fusible link should be. It seems some of it has been replaced by in-line fuses. I found the fusible link on the Haynes wiring diagram, and am starting to compare it to what's going on in my truck. Not sure that they're the same,  but so far seems close. I'd like to get the battery terminal connections /fusible link back to the original setup.

 

This is just the beginning with this truck,  I'm sure. Every time I open it up I find more cut wires, dangling relays, and entire hoses and components loose inside. That's why it wasn't immediately obvious that I'd disconnected the fuel pump. You haven't seen the last of me. 😋

[Charlie69]

On all my trucks I am getting rid of the fusible links and replacing with fuses.  The fusible links have left me stranded in the past and do not want the hassle of trying to find them in a junk yard.

[captain720]

Hey Charlie that's a great idea! I could just out them on fuses on my fender fuse block

[Corapop]

When I started the truck back up and ran it for a while, I’m getting white smoke out the tailpipe. It definitely wasn’t happening before. Is it possibly a symptom of me messing with mixture screw and fast idle on the carb? I also slipped while turning the mixture screw and poked the red RTV “gasket” at the base which was greasy and loose and just kind of slid out from under the carb a little. I was reading that a leak here may cause some white smoke?

 

Regardless if that’s causing it, I ordered the rebuild kit and an air filter kit, since there’s no filter on the carb, and the whole thing is kind of filthy and sticky.

[datzenmike]

As the weather gets cooler and damper it's normal to see the exhaust as a white vapor. Often goes away when engine id warmed up. That said, a blowing or blown head gasket will boil coolant and send it out the exhaust. If it is, then the engine will need the radiator topped up every day or so. If not doing this then probably ok.

 

A gasket leak will let in more air leaning out the idle mixture and causing a poor idle. Doesn't affect running much just idle.  

[captain720]

Did you get a Redline kit like the one I used in this video? Redline is the only way to go.

 

If you have a catalytic converter they convert exhaust to water and make white smoke in the colder air

 

 

[Charlie69]

I buy all my Webers and parts from Pierce Manifolds

 

Been doing business with them since the 70s.