Hesitation when accelerating, Carb, Coil or Ignition - Finally Fixed (2 Viewers)

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ErikinSC

Been there, done that, got the T-shirt.
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My issue is FINALLY FIXED ! Once, I thought it was resolved, but only temporarily - read to the end! After I paid attention and did 100% of the steps necessary (and got an additional experienced evaulation), my problem was properly identified and I was able to correct it. Edit : I changed the title back also, as I wanted a future search user to understand how - what appeared to be a carb issue could be confused for an ignition issue or coil problem.

My '74 Southern Charm is (still) giving me a bit of a fit (occasionally which is the most frustrating part). This has been an on and off problem. After the motor warms (2F SN 882263-I think it is a mid '76 motor), traveling up to 12-15+ miles with some highway speed) - the truck will begin to run poorly when I try to accelerate - like it is starved for fuel (mechanical pump, good pressures). The timing is not off(non-use distributor with points) . Odd thing is - it does not do this every time I drive more than that, but most of the time.

If I pull over and stop, sitting on the shoulder, idling, I can manually throttle it up - not under load - and it throttles up fine (motor revs like you would expect) - but if it is under load (in gear) - at a stop sign, let the clutch out, try to get up to speed - anymore than 5-10% throttle and the motor will stop responding and it will not accelerate properly. From a stop, I can let it idle up to speed, shift into 2nd, let it idle up a bit more and give it just a bit of gas, shift into 3rd - and I can get down the road as a last resort. I just cant use the accelerator pedal or it acts like I am not giving it any gas.

Additionally, even once it starts to hesitate - I can cruise with minimal throttle at 40mph - 50mph, and you do not feel the hesitation - UNTIL YOU TRY TO HARD ACCELERATE. With a very light acceleration, it will slowly respond without the obvious hesitation.

I am running a Weber 38 from TPI (no sight glass, no fuel return line, electric choke - could this be coming into account after it warms up?). Fuel lines & filers recently replaced , plastic tank by the PO. It has a Mallory ignition coil which the PO installed (see pic). The inside of the dist cap is clean - no water / moisture. @lextechautomotive has tried to get it to run poorly, but it hasnt yet. Glenn recommended I replace the Mallory ignition with a stock coil & resistor(I have the resistor - but I haven't checked it). Additionally - it does not matter if it is 60F or 94F outside.

I've checked and it appears there are multiple coil PNs. Is there a difference between them? Is there a coild specification (Voltage, spark, Cap rating....?) Any other ideas that I could check / try to eliminate the coil / resistor / something else?
 

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Problems like these are a non-functioning accelerator pump in about 9 out of 10 cases in my experience. I know nothing about Weber carbs but if I were you, I'd remove the air cleaner, actuate the throttle (or have your assistant rapidly push the accelerator pedal) and look for a strong jet of fuel squirting down into the carb. If there isn't one, you've found your problem. I'm sure there are guys around here with Weber experience that can tell you how to repair or rebuild the accelerator pump, maybe just cleaning the jet with carb cleaner is enough.

Pete
 
Thanks Pete - I'll check that. If that were the case, do you suppose it would be a constant problem? Or could it to be an intermittent one?
 
Erik,

I know NOTHING about Weber carbs...

But, with my Aisin... I had the same problem - e.g. while driving along, fat, dumb and happy, I would reach a hill and 44 would stumble and try to die. If I pushed in the clutch and pumped the gas pedal, the engine would recover. As soon as I let the clutch out and tried to continue, the stumble and die.

When I called @FJ40Jim (from the side of I-15), he said, "It has to be either fuel starvation or bad coil. Since coils seldom fail, unless they dump their oil and you can't see any oil under your coil, my vote is fuel starvation". He suggested I recreate the problem and throw it into neutral, turn off the key and coast off the highway. Then check the sight-glass (which you don't have). He said, doing it in the listed order would 'leave everything exactly as it was when the problem occurred". He also said, "You can't recreate this without actually driving it under
load, it won't occur when it's sitting still because the secondary doesn't kick in and it's the secondary that demands the big gulp of fuel".

When I did that, it was obvious there was no fuel in my sight-glass... e.g. it was obvious the issue was fuel starvation.

Maybe doing what he suggested will help you diagnose the problem to fuel starvation... even without a sight-glass... I don't know...

Anyway, once I knew it was fuel starvation, I stared checking back upstream on the fuel feed line, from the carb and found that one of (I had two) my glass fuel filters (with replaceable filter elements) wasn't sealing properly (when screwed back together) and the fuel pump was sucking a ton of air, when the throttle demanded a lot of gas - e.g. under load.

So, your problem could be fuel starvation and the culprit could be a new fuel fuel filter (mine was brand new) - I would try a different fuel filter and see if it helps.

hth
 
Thanks Danny & Pete. I'll definetly check those also. Toyota doesnt seem to have a NOS coil available - so I'll have to rely on a used coil or a borrowed one. I'll keep checking the fuel issues while I look for a coil substitute.
 
Webers are simple - just pop the air cleaner top off and cycle the throttle arm a little - it should shoot fuel out of both nozzles above the throats with a fair bit of force , if not - the float level could be way off , check ball circuit has dirt holding the ball open , clogged nozzles ect .
Exactly what approximate position on the throttle does this occur ? It's important to diagnose from here ....? Slightly off-idle , or farther into it , like 1/3 throttle ? What if you slam your foot down , does it just bog and then slowly recover ?

There are some simple tests I can walk you through , but need more info on the above ...
Sarge
 
Your distributor advance/retard can contribute to this as well. Check to make sure it is functioning.
 
Thanks again @Weber Sarge and @shawnfj40 the throttle issue is anywhere from about 10% to any more. If I 'floor' it, it makes no difference. It does not hesitate any more or any less.

If I push the clutch in - and then press the accelerator, the motor will rev like normal.

It's raining this AM, will pull filters, air cleaner and start looking for obstructions this afternoon.
 
Just below the top cover on each side of the carb is a brass screw - one side has a smaller head than the other . Remove those screws carefully and do not lose the o-rings - they are a special size/type only found on Webers . Inside those screws are the idle jets - remove the jet from inside the screw and clean it with brake cleaner . Do not spray the o-rings in any way with solvent of any type . Make sure to clean the inside bore of the screws themselves and put them back together , noting the number size on those jets (we'll need this later) .

The smaller sized jet holder usually leaves it's o-ring inside the carb body - this is normal and it can be retrieved using a small hook or screwdriver . With the jets back in , give it a test run and see if there is any difference .

Sarge
 
Will do @Weber Sarge I also looked at the Weber page, and I need to finish reading about the accelerator pump. I'll check the jets first.
 
FWIW, yesterday with a cold engine - I removed the air cleaner, actuated the throttle and fuel sprayed in both bowls. The inboard bowl got more than the outboard bowl.
image.jpg
 
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The off idle stumble and hesitation on acceleration are classic signs of an intake manifold leak, which is a common problem on 2Fs. Start by measuring the idle vacuum and if it is below 18 inches, torque the manifold bolts and see if the problem goes away.
 
That's generally why Weber installs get such a bad rap - the adapter kits for the Cruisers are a joke . Vac leaks also result in false lean best idle settings which takes all the good points of the Weber away in a hurry .
Throttle response should be very crisp and powerful if everything is right , including the timing and ignition systems .
Sarge
 
Simple test to check the Weber adapter plate/manifold leak:
While idling, with air cleaner on, use aerosol brake cleaner (or something else highly flammable/combustible) to shoot short concentrated bursts of fluid around the carburetor base. I had fits with the Weber on my 22r pickup. If a vacuum leak exists where you spray, you will hear the engine rev as the fluid is sucked in and burned. Be careful to use concentrated, close range, small shots. Too much, or to far away will give a false positive through the air cleaner.
 
Didnt have an opportunity to :wrench: today, but I'll be able to tomorrrow - and with help. So I'm checking & cleanding the jets(get #s), checking the vacuum and looking for an intake leak. Got step one :wrench:

I did :steer: the truck today and filled up with ethanol free gas (best to have a good and clean slate). I've got to drive the -40 to work tomorrow where i can have a hand to check these things. I did not get up to highway speeds, but ran the truck for a few miles - to church, checked in on the parents, back to watch the kids BB tournament. The truck ran as per normal - throttle responded normal and properly; engine temp never got up into the mid range. Maybe the extended highway time lets the temp up and causes the intake to expand ? and maybe that is affecting performance.

Just below the top cover on each side of the carb is a brass screw - one side has a smaller head than the other . Remove those screws carefully and do not lose the o-rings - they are a special size/type only found on Webers . Inside those screws are the idle jets - remove the jet from inside the screw and clean it with brake cleaner . Do not spray the o-rings in any way with solvent of any type . Make sure to clean the inside bore of the screws themselves and put them back together , noting the number size on those jets (we'll need this later) .

The smaller sized jet holder usually leaves it's o-ring inside the carb body - this is normal and it can be retrieved using a small hook or screwdriver . With the jets back in , give it a test run and see if there is any difference .

Sarge

The clean and inspect will be my first step, and then I will check vacuum and for the leaks. Thanks again - will post up tomorrow by mid day. :beer:
 
I noticed you said the PO installed a new gas tank. Did he eliminate the 3 vent lines? If so, perhaps your tank gets vapor locked depending on how tight the gas cap gets tightened. Maybe take a run without a gas cap.
 
I noticed you said the PO installed a new gas tank. Did he eliminate the 3 vent lines? If so, perhaps your tank gets vapor locked depending on how tight the gas cap gets tightened. Maybe take a run without a gas cap.

Yes, I have a (TPI ?) plastic tank with the vents & evaporator device (under the fill tube sheet metal). I replaced the PO's fuel cap with a proper vented '74 cap (from SOR) also.... I don't have a return line from the mechanical pump or from the carb, so the return hose is doubled back on itself. The 'vent' from the gas tank terminates in the engine compartment on the drivers wheel well at the VSV (Vacuum Switching Valve?) - but I understand that it (the VSV) is not tied into anything else effectively. I've checked for excessive vacuum on the tank - and it has not normally been a problem - will recheck.
 
Pulled the jets, they are both "55" jets. The larger jet was partially blocked. Cleaned with brake cleaner & reassembling. Did not spray o-rings.

Checked the vacuum off intake manifold = 18"

Going on a test run
 
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Test ran good - but after 10 mins of highway speed, exited, and re-entered the highway - the hesitation continues on acceleration. Soft acceleration (10%)is livable, but any more (20-50%) throttle and she stumbles / hesitates.

Grabbing a new vacu gauge from HF (to retest) and a can of brake cleaner. Will check for intake leak next.
 
Have you pulled the fuel inlet fitting off the carb and checked the screen to see it has dirt in it ? That mesh is fairly small , so any dirt particles that get past it go to those idle jets first - that's why I suggested checking them . What are you running for a fuel filter ? It could be just an issue with the float height getting weird , or dirt down in the bowl .
Sarge
 

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