my truck still runs funny

[19mike69]

my question still has to do with the way it is running....it starts fine,idles fine and runs fine actually...but when you get out on the hiway say,and running like 55 and start putting the pedal to the floor it starts to cut out a little.....it only does it when it gets up high in the rpm's....is that maybe in the timing?...or cap or rotor?...i thought if cap or rotor it might act up all the time,i dunno though....i turned those 2 screws on the front of the carb like somebody told me to do(a half a turn counterclockwise) and i couldnt tell a difference when i drove it again.....what would make one miss and cut out a little at a higher rpm?....btw,this is a plain ole stock 350 that is just going to get me to work and back...i just want it to run right and start right....if you have any ideas please let me know....thanks again

[72CustomCamper]

19mike69
As you probably know, engines need three things to run:

1. Air/Fuel mixture
2. Compression
3. Spark

Sounds like your problem is with number 1.

If you had a cap or rotor issue (#3), the problem would be at all engine speeds and probably more noticeable at idle. Whole engine cutout due to ignition is usually linked to the coil or ignition control (HEI)

Those screws on the front of your carb are the Idle Mixture Screws and have basically no effect on how the engine runs above idle. Don't mess with those unless you have the proper tools to set them right (vacuum guage and/or an accurate tach).

High RPM cutout is often a problem with the air/fuel mixture. Especially if the cutout happens when you mash the throttle. Your engine is being starved of one or both.

Things to check:
1. Fuel filter - if clogged, you will most likely notice it at highway speeds. They are cheap.
2. Choke setting - Make sure your choke plate or "butterfly" is fully open when the engine is fully warmed up. If not, you may be momentarily flooding the engine (not enough air). Another cause of low air flow is a clogged air filter...
3. If you rule these out, you may have some internal carb or fuel pump issues.

Try these first, everything else just gets more expensive...!

[P455]

Replace your points and set your dwell. When points get worn out, the dwell goes out of adjustment causing exactly this symptom.

If you have HEI instead of points, disregard this.

[19mike69]

btw,yes it is HEI.....72,it is a new edelbrock 1406...i put on a brand new fuel filter...the breather i bought is 10" by 2" tall...the edelbrock people say that the carb is set up to run on a 14 by 3 breather that a smaller one will drastically reduce airflow,could that be it?...it runs absolutely great until you really punch it and the rpm's get way up there.....kind of pisses me off i bought a new carb and edelbrock intake and still have problems with it running right

[72CustomCamper]

Ah yes. The Edelbrock 1406. I had one on a 360 in a Jeep I once owned. Great carb, easy to adjust. For a 600 cfm carb like that, a 14x2 open air cleaner is more than enough. Think about it this way: What goes in has to come out and the cross sectional area of your exhaust system is about 9.8 square inches. A 14x2 has an intake area of 88 square inches. (Ample)

If you are not convinced, try a quick highway trip with the air cleaner removed (no dirt roads though). If it still cuts out, this will rule out the air cleaner issue.

Unless you live in the mountains somewhere high (high altitude jets), there is not much you can do with that carb. If the choke is adjusted properly then maybe your problem is with your spark supply...

One more thing, did the engine sit for any long periods of time? Greater than 3 or 4 months? The accelerator pump cup has a tendency to dry out and crack if not routinely soaked with fuel. That was the one problem I had with mine.

Sure liked that carb better than the Quadrajet I now run...

[19mike69]

no,its a brand new one i just put on about 2 weeks ago.....i have no idea where the timing is set since i dont have a timing light....but i dont guess that could be it huh?

[gmcstep]

hello, have you checked your fuel pump? maybe it isnt pumping fuel well enough to keep up at the higher rpm

[68 Suburban]

My 1406 needed to be tuned out of the box. I have a basically stock 350 engine. I went down two steps on the chart in your owners manual. It runs great. I don't know if this would be the cause of the hesitation you are experiencing, but just thought I would give you some input on how to get that carb working its best.

[Lippyp]

Just a thought, check to make sure your distributor is bolted down nice and tight.

This once happened to me on a Triumph Spitfire, the distributor hold down bolt became loose, the car would start and run fine until you gave it some welly at which point the dizzy would move and the timing go off, let off the throttle and the tension in the plug leads twisted it back into time and it would idle fine, would even run fine if you were gentle with the throttle. Just something to check.

[19mike69]

could any of this be happening if a rocker arm or two werent tightened down right?.....when i bought the truck it had a bad miss and the guy thought it was a burnt valve...but 2 of the rocker arm nuts had worked really loose to where the rocker arms werent doing anything....i bought 2 new nuts and adjusted them as best i could for the time being....if they were too tight,or too loose, would it make it act like i have been describing?

[Jackal2k9]

mike got a few things for ya. Readjust the valves. taht can cause it if they are too loose not likely if too tight unless to much too tight that they wore a lobe off the cam.. which would cause a rough idle. Also your carb may need to be jetted up in the front or back. Some times tou end up with jets so small you have to run all secondaries all the time just to get anything at all and at high rpms theres nothin left. Also HEI distributors have a module in them... generally when they go out its all or nothin but occasionally i have seen some cause lack of high rpms power. moisture in the distributor can cause a similar problem. Also if the vacuum advance is not functioning properly and not advancing the carb enough or advancing it too much at higher rpms that could cause it. To check make sure the Vac. adv. is on the small left side port on the front of that carb. That should be partial vacuum. You can mke sure the port isnt blcoked with a vacuum guage hook it up rev the motor if it(vacuum level) goes up its fine. If it doesnt then your carb base is mounted wrong and/or something is blocking the hole. If its advancing too much it may b on full vacuum. Also the vac. adv. diaphragm at the distributor could be out, not very likely but possible.

to adjust valves:
one valvle at a time with engin running at lowest possible rpms loosen until it brings to tick. then VERY slowly tighten down until tick goes away, then turn half of a turn. Oil will be shooitng at you. Two ways to prevent this. Custom cut out(or drill) the tops of a set of valve covers OR buy the hard to find rocker clips that block oiling holes from pushrods. email me fo questions on taht stuff sorry about all the words.... Jackal@satx.rr.com

[cdowns]

along with checking the fuel pump you should check the fuel pickup in the gas tank theres a screen in there that gets gunked up

[cdowns]

along with checking the fuel pump you should check the fuel pickup in the gas tank theres a screen in there that gets gunked up

[19mike69]

Jakal....when i put the carb on i put the vac adv on the right port of the carb because when i put it on the left it wouldnt hardley run.....but it DOES go on the left?....

['72 Shorty]

I'm thinking your timing is retarded a little to far if it won't run with ported vac advance. It should run fine with that line disconnected and plugged, at least at idle. (ported vac is the higher of the 2 right side looking at the front of the carb)

[spinning wheels]

I'm with cdowns. My truck did the same thing. When I finally replaced the gas tank sending unit. Wow, the stock one was so plugged up and full of rust. My truck sat in the previous owner's back yard for six years, before I traded him for a F*#@d ranger with a dead motor. This was after installing a new Edelbrock 1406. Also, check your plug wires. I burned a hole in one plug wire cause it got too close to the exhaust manifold. Finally found that problem by looking under the hood at night. Then I could see the plug wire grounding itself on the manifold. Good luck on finding your gremlin.

[19mike69]

72shorty....so the right one should be plugged and my vac adv line hooked to the left?....i check into all these things you guys have told me this weekend,thanks for all the help

[krazy_texan]

when i first bought my truck i had the same problem it was partially the gasoline that i was putting in it and my timing was way off it was suposed to be at 8 over tdc but it was 6under

['72 Shorty]

Originally posted by 19mike69
72shorty....so the right one should be plugged and my vac adv line hooked to the left?....i check into all these things you guys have told me this weekend,thanks for all the help

That's the way mine has always run the best. I've tried both. I'd invest in a timing light, or find a friend that has one. I'm still not sure it isn't fuel, but without knowing where your timing is, it's hard to say.

Remember, when you set your timing, disconnect and plug the vaccum advance line.

[gangforward]

I ran into this same behavior with a couple of rides - my truck did the same thing until I fixed the Ground straps on the engine. I didn't have a good negative ground on the engine. (It's those knitted cables that attach to your firewall.) Once I replaced those and had a good solid ground, the truck no longer missed at higher rpm's and loads.

The other issue I had was a plugged connector coming out of the fuel tank. The pump was working, but the hole was so small the engine couldn't get enough fuel at higher RPM's and loads.

Good Luck!

[19mike69]

well,i switched the vac adv line from the right side to the left side of the carb and plugged the right side and that seemed to take care of the missing at high rpm's....of course now it has a miss it seems at idle....when you sit there and put it in drive and hold the brake and give it a little gas the almost break the rear tires loose,it seems to have a slight miss....like a dut-dut-dut....i have no idea if my timing is right so i need to get a timing light and check it...it has new plugs and wires but the cap and rotor are the ones that were on the dist when i bought it used....guess i need to pull my head out and replace those too...lol