Hesitation when accelerating, Carb, Coil or Ignition - Finally Fixed

[ErikinSC]

Don't sweat the fuel screen being partially collapsed , it's just how they seat and no big deal . Just a quick idea - pull the distributor cap off and verify the timing advance parts aren't sticking , see if it will rotate against it's springs and return cleanly - if it sticks it would cause a lot of issues that mimic the carb .

Is the return line still in the engine bay near the charcoal canister ? There is a way to add a Jeep CJ filter to allow the use of a return line for the Weber . You haven't mentioned it - but is there any sort of pressure regulator in the fuel line to the carb ?

Sarge

Back in the shop. New OEM fuel filter installed. Fuel pump o/p is 4psi and holding. Only dropped to 3.5psi 5 mins after turning motor off. I have the CJ filter will install and route back to return - so that return port is not open. Checking the points next.

 

[ErikinSC]

The dist has a clean dust cap, rotor moves easily 3/16" back n forth, everything looks clean:

Hooking up CJ filter at carb, with vent back to fuel tank return.

 

[ErikinSC]

CJ vented filter installed.

Zip ties to secure vent line and then....

Time for a test drive.....

 

[ErikinSC]

Alright. Ran good, hasn't warmed up fully yet. Stopped to fuel up, and I DEFINETLY CREATED A VACUUM ON THE TANK. Swapped fuel tank caps to :

And continuing the test drive.....

 

[ErikinSC]

Drove fine, not sure that I warned the engine enough. DID NOT CREATE A VACUUM in the gas tank. 2nd test drive req'd. To confirm.

 

[Pin_Head]

Hesitation on acceleration is not a fuel delivery problem, it is a mixture problem. If it was bucking and spitting when the pedal is to the metal going up hill, then that would be a fuel delivery problem.

 

[Weber Sarge]

He's had other issues that indicate it's overrunning the carb at times - I still suspect it has dirt in it or the float valve is getting bad .
Speaking of which , when you had it apart , is the tip of the float valve solid brass or viton (rubber) tipped ?
Sarge

 

[ErikinSC]

If it was bucking and spitting when the pedal is to the metal going up hill, then that would be a fuel delivery problem.

@Pin_Head : It really wasn't 'bucking' - it was more like when I 'mashed the gas (as they say in the South)' it opened the butterfly valves, but no more fuel came out - so the engine acted like it wanted to rev, but there wasn't enough gas to make it rev.... clear as mud?

He's had other issues that indicate it's overrunning the carb at times - I still suspect it has dirt in it or the float valve is getting bad .
Speaking of which , when you had it apart , is the tip of the float valve solid brass or viton (rubber) tipped ?
Sarge

@Weber Sarge : I have not disassembled, inspected or cleaned the internals of the carb yet. I only checked the jets (the Secondary jet was partially obstructed) and serviced the fuel system to date. I'll go for a test drive shortly and see if the hesitation persists.

Thanks for your continuing assistance.

 

[Pin_Head]

A better description of what actually happens under what circumstances would help. I don't know what "acted like it wanted to rev" means.

Fuel delivery problems (gas tank, fuel pump, clogged inlet) don't just show up when you mash the throttle. They show up when there is a big fuel demand on the engine, like going up hill at high speed.

If it only happens when you mash the throttle, it is a mixture problem. The accelerator pump and the transition slot are not keeping up with fuel demand until you can pull more fuel from the main nozzles.

 

[ErikinSC]

Test drive today - with cleared secondary jet, vented (loose fitting) fuel cap, new OEM fuel filter, add'l vented fuel filter at carb inlet - and NO HESITATION ISSUES. Drove the interstate for 20+ mins with a little more than 1/2 tank of fuel. Normally this was enuf to cause the truck to hesitate when I tried to accelerate.

I really appreciate ALL OF Y'ALLS HELP!

@Pin_Head : Sorry that I havent been able to convey this any better. Let me try to re-explain / and summarize: The problem ONLY develops after I had driven for a short (10-20 mins of time) and usually only if I attained sustained highway speeds. I am on the coast in Charleston SC, so no hills, only an overpass or two. When I press the gas, it feels like the butterfly valves (is that the right terminology?) opens, and the carb gets more air - but it seems like there is no more fuel going into the carb -> and therefore the motor does not rev up, and actually seems to like it is being choked of fuel... is that a better expanation?

I talked to Glenn @lextechautomotive and with a hint from mud- I am going to check the check valve coming off of the Fuel Seperator.... maybe I have a block in the ilne there...? IDK, but I'm going to check that next....

 

[ErikinSC]

If it only happens when you mash the throttle, it is a mixture problem. The accelerator pump and the transition slot are not keeping up with fuel demand until you can pull more fuel from the main nozzles.

YES - it is more like that - My dad even told me I need to check the Accelerator Pump... does it seem likely that this mixture problem could be exaggerated by the wamed motor?

Uh-Oh, @Pin_Head : i just realized I had a typo above (Auto correct, actually so I just fixed it) It should have read :

@Pin_Head : It really wasn't 'bucking' ... not 'was' bucking...

 

[Weber Sarge]

I think the whole root of the issue is that carb needs to be cleaned badly . It's not that hard and if you have issues I can help.
Sarge

 

[skidplate]

After installing a "new" to me fuel tank in my '75, I would have similar problems. Found that small piece of debris had gotten around the fuel filter. I'd read here on MUD about the Oakie, Arkansas, etc. "carb rebuild", which is to remove aircleaner assembly, rev engine and cover the carb intake. The theory being that the vaccum created and the sudden covering of carb will cause any loose gunk in the carb to be sucked out. I kind of thought this was a bogus idea until I tried it. I now carry a plastic coffee can lid with a small hole dilled in the middle to use to cover the carb in my tool kit. Ive used it a few time with success. Won't hurt to try it. Hope you get it dialed in soon.

 

[ErikinSC]

Thanks guys, rig is parked until Sunday- have to travel for work. I will remove and clean the carb when I get back - from someplace warm and tropical.

 

[ErikinSC]

Intermittent issues such as you describe at that throttle plate position indicates , as Pin Head so correctly pointed out - idle jet issues with fuel flow . Here's the thing about Webers that folks don't understand and more insight to what Pin Head is talking about -

You can dial in almost every bit of the fuel/air curve in any Weber carb . This is accomplished through idle jets , main jets and air jets as well as the emulsion tubes . Mains/airs take care of the available fuel to those circuits . The emulsion tubes determine how that available air/fuel is delivered . Your 38DGAS probably has F55 tubes which is an all-around and pretty evenly distributed fuel curve that easily follows main air fuel jet sizing . There are a ton of different profile emulsion tubes , an F6 - for example , will deliver a fairly even air/fuel rate at mid and higher flows but be very aggressive at low end of the mains . Same goes with the idle jets - these judge the amount of fuel/air mix available for the transition circuit holes just above the throttle plates . These are the transition circuits and progress in size and placement as the air changes position and flow speed as the throttle plates are opened . Designs vary - Holley and Carter-based designs (licensed by Weber) use a slotted transition instead of holes .

To dial a Weber into an engine , and they all must be dialed in , you set the lean best idle per instructions as well as base idle speed at fully warmed engine temps . As the engine is loaded , if it stumbles just off-idle (right when you step on the gas) this means the transition circuit is leaning out too far . Either the carb needs a larger idle jet size or the circuit has dirt in it . In your case , since this is an intermittent problem - yours has dirt in the circuit . The holes above the throttle plate as well as the idle jets are quite small - so any dirt goes there first and plugs things up . Yours is still driveable since it runs on both barrels all the time , unlike a progressive 32/36DGV series . So , that tells me one side has dirt still , possibly in the jets but more likely in the circuit itself . It can build up over time and the only way to clean it properly is to remove the carb .

Once off , remove the idle jets and the top cover , carefully . There is a small 1/8" c-clip that holds the choke linkage arm to the choke plate - watch that thing as it usually hits you in the eye before disappearing into oblivion ...
With the top cover off and idle jets removed , open the throttle all the way while upside down . With a bright light you will see a set of holes just above the point where the throttle plate sits at idle position . Spray those hole hard with brake cleaner using the straw and finish by cleaning out the float bowl as well . You don't have to remove the main jets in the bowl or the air jets on the top of the main body but it can help to clear debris . Finish with compressed air - the more the better . If you screw anything up , I have some parts left here and with pics can fix it from here as well .

One note - NEVER , EVER ADJUST THE SCREW ON THE GEARS ON THE THROTTLE LINKAGE OF A 38DGAS - THEY HAVE TO BE TIMED VERY CORRECTLY !!!

I've had to reset so many of them I'm sick of it , it takes a dual dial indicator to get them right or that carb will not respond off-idle as it should . A 38DGAS should be really crisp and quickly respond to throttle input if it's right .

Ok , fingers hurt ...
Sarge

So, truck has seemed to be driving fine with the 2 idle jets cleaned, 2 new fuel filters installed (with the CJ filter vent routed back to the tank via the return line), and a vented cap on the fuel filler neck.... Then it started again. Drove for 35 minutes and then the truck started to act like it was starving for fuel during acceleration (hesitating on acceleration). Im going to pull a plug or two, check for lean vs rich, order a rebuild kit (in case I need parts), remove, dissasemble (as above) and clean the carb, and post pics as I go. Thought i had cleared the problem, but it's back.

 

[Solace in Solitude]

Are you finding crap in your fuel filter?

I think you said you had a new CCOT fuel tank... Is it possible that your hard fuel lines have sediment or something in them, that is breaking loose and finding it's way to your carb?

The hard fuel lines, along the frame rail are, I think, the lowest point in the fuel system.

Sorry if this has already been discussed.

Hth

 

[Pin_Head]

It sounds like there is some particulate junk rattling around in your float bowl. Take the top cover and peek inside.

 

[ErikinSC]

Danny @pngunme - I've not purged the hard lines, but i guess I should find a way to clear them - dont know how long a pipe cleaner they make, otherwise it'll be 80 psi air for the purge.

@Pin_Head - I'm sure that you willl be proven correct. I've pulled and cleaned the idle jets (twice) but I've not pulled the carb off or opened it yet.

With the motor warmed up, and the airfilter off, when I actuate the throttle by hand, I dont feel that the streams of gas being jetted into the carb are sufficient. Hopefully, once I have the carb disassembled - and post some pics - we'll get to the bottom of this. I appreciate everyones suggestions. I'm searching and looking at other Weber38 pics to make sure I understand what I'm doing and talking about.

 

[Pin_Head]

There are no idle jets on a stock Toyota carb; there is just the idle mixture screw. Not sure what you are talking about.

 

[ErikinSC]

@Pin_Head - I'm running a Weber 38.... the PO had installed it.