How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask kalamykid Your Own Question
kalamykid
kalamykid, Shop Owner/ Tech
Category: Classic Car
Satisfied Customers: 3736
Experience:  I HAVE OWNED MY OWN SHOP FOR OVER THREE YEARS. I HAVE THE TOOLS AND SOFTWARE TO ANSWERE ALMOST ANY Q
5629372
Type Your Classic Car Question Here...
kalamykid is online now
A new question is answered every 9 seconds

I have a 1974 K 10 truck with a 350 chevy 4bbl carb and

Customer Question

I have a 1974 K 10 truck with a 350 chevy 4bbl carb and turbo 350 auto and when stepping on the gas hard the engine makes a thudding noise the noise is only heard under hard accelerating it only makes this noise under load not at idol or low speeds only at hard accelerating like passing a car or going up a hill sounds great at idol or revving it up in park
Submitted: 3 months ago.
Category: Classic Car
Expert:  kalamykid replied 3 months ago.

If you start the engine, sset the parking brake, put the transmission in drive and hold really hard on the brakes with your left foot and rev the engine up to about 2500 rpms then drop off of the gas pedal fast do you hear the same thud?

Customer: replied 3 months ago.
no
Expert:  kalamykid replied 3 months ago.

Does this only happen once when you hit the gas? Or does it keep doing it till you let off of the gas pedal?

Customer: replied 3 months ago.
keeps doing it until I let off the gas
Expert:  kalamykid replied 3 months ago.

Do you have it in 2wd or 4x4 when this happens?

Customer: replied 3 months ago.
2wd
Expert:  kalamykid replied 3 months ago.

Have you checked the u joints and transmission mount?

Customer: replied 3 months ago.
they are fine
Expert:  kalamykid replied 3 months ago.

Did you look to see if the fan was hitting the fan shroud?

Customer: replied 3 months ago.
it's not hitting shroud
Expert:  kalamykid replied 3 months ago.

From here I would pull the drive shaft out and manually check the u joints to see if they have any stiff spots. If they have any stiff or cluncky spots replace the u joints. The only other place you should be able to get a thud noise from would be a bad engine mount or trans mount.

Customer: replied 3 months ago.
the noise is coming from the area not transfercase or the u joints the noise is not just one thud it's thudding and when at high speed like on the freeway no noise until you put your foot in it to accelerate hard
Expert:  kalamykid replied 3 months ago.

What area do you think the noise is coming from, under the hood, around the transmission, or near the rear end?

Customer: replied 3 months ago.
under the hood its hard to pin down location because I can only get the when step on the gas hard
Expert:  kalamykid replied 3 months ago.

Do you think it could be a popping sound from the air cleaner?

Customer: replied 3 months ago.
no popping sound air cleaner
Expert:  kalamykid replied 3 months ago.

And it only makes this noise when you hit the gas hard in drive? will it make the same noise if you are backing up?

Customer: replied 3 months ago.
never tried going backwards
Expert:  kalamykid replied 3 months ago.

Can you try and see if you hear it gong backwards please? Just make sure you have plenty of room behind you. I do not want you to hurt yourself or your truck.

Customer: replied 3 months ago.
when I put it in reverse and stepped on the gas hard it started to shudder like it was going to stall
Expert:  kalamykid replied 3 months ago.

But no thuds correct?

Customer: replied 3 months ago.
no, butt I could not get it to very high rpm's it would almost start to stall as soon as stomped on the gas pedal
Expert:  kalamykid replied 3 months ago.

OK Here is what I think is going on. You are either running to low on fuel " running lean" or the timing is off. Do you have a timing light?

Customer: replied 3 months ago.
it does the same if full tank or low tank, I don't have a timing light
Expert:  kalamykid replied 3 months ago.

I do not mean the tank is low on fuel, but the engine is not getting enough through the carb.

Expert:  kalamykid replied 3 months ago.

If you take the air cleaner off, see if the secondary opens up when you hit full throttle. Also see if you hear any popping or if it sounds like a vacuum cleaner sucking in a lot of air?

Customer: replied 3 months ago.
it started to pop at half throttle and could not hear the distinctive sucking of air that 4bbl makes
Expert:  kalamykid replied 3 months ago.

The timing is off, either the vacuum advance is not working, the vacuum advance pod is not holding a vacuum, the base plate in the distributor is frozen, or the vacuum line has a leak. Or the timing chain has to much slack in it and the timing chain needs to be replaced. A timing light will help you find out if the timing chain is bad, but you will have to manually check the vacuum advance system.

Customer: replied 3 months ago.
Could the egr valve be bad also and is that why the secondary's are not working vacuum operated
Expert:  kalamykid replied 3 months ago.

Yes they are vacuum operated, and the egr can be part of your problem but not all of it. Take the cap of of the distributor and unplug the vacuum line from the vacuum advance pad, connect a clean hose to the pod and suck on the line and see if the vacuum pod pulls the base plate to turn the base plate. also see if the pod will hold a vacuum.

Customer: replied 3 months ago.
It's dark out now so I will get timing light tomorrow and check everything you said so far and I will get back with you tomorrow and thanks I was lost and I never would have checked for timing problems I will talk with you tomorrow thanks again
Expert:  kalamykid replied 3 months ago.

You are very welcome.

Customer: replied 3 months ago.
could a bad ignition coil be the problem the reason I ask is I hooked up the timing light and disconected the vacuum advance hose and plugged it and then checked the timing it was close between 6- 8 degrees BTDC but idol was fast so I tried to hook my dwell /rpm meter to coil red to neg on coil black to ground and could not get a reading I tried another dwell /rpm meter still no reading I even tried a tac I had still nothing
Expert:  kalamykid replied 3 months ago.

OK do you have the HEI distributor with the coil in the top of the cap?

Customer: replied 3 months ago.
no the coil is next to the distributor
Expert:  kalamykid replied 3 months ago.

You have to connect the tack lead for your meter or tac to the negative post of the coil.

Customer: replied 3 months ago.
correct thats what I did
Expert:  kalamykid replied 3 months ago.

Do you have a test light?

Customer: replied 3 months ago.
I don't think so
Expert:  kalamykid replied 3 months ago.

Do you have a side marker light and a piece of wire to make one with?

Customer: replied 3 months ago.
how do test the coil with light
Expert:  kalamykid replied 3 months ago.

Connect the test lead to a good positive power source and touch the tip of the test light to the negative post of the coil. Then have some one turn the engine over and see if the test light flashes. If the coil was bad it would not start, so you need to check for the pulse signal from the ignition module. unless you have a points distributor?????? Can you send me a pic of the distributor please?

Customer: replied 3 months ago.
it has points
Expert:  kalamykid replied 3 months ago.

Now we are in a whole new ball bark. When was the last time you replaced the points? Does the plate the points bolt down to have any play that would allow the plate to move up and down?

Customer: replied 3 months ago.
I will check and get back to you, I bought the truck last year it has not had anything done to it
Expert:  kalamykid replied 3 months ago.

If the plate is worn, and most likely it is, Then would you like to upgrade to a better set up that will be worry free and give you better gas mileage?

Customer: replied 3 months ago.
Im going get every thing and give it a tune up I will get back to you
Expert:  kalamykid replied 3 months ago.

Hold on

Expert:  kalamykid replied 3 months ago.

It will be better if you get a HEI distributor to put in this engine.

Expert:  kalamykid replied 3 months ago.

You can get a new distributor from oreily's for about $140.00 and it will come with everything you need except plugs and wires.

Expert:  kalamykid replied 3 months ago.

It is very easy to do this swap and you will have electronic ignition insteed of the old points. This will make start up faster, better throttle control, and you do not have to keep adjusting the points.

Customer: replied 3 months ago.
I all ready have some of parts Cap, rotor points and condenser I will get the HEI distributor next time
Expert:  kalamykid replied 3 months ago.

You need to check the base plate first, if it is worn out the points can not stay set, and the engine will never run correctly.

Customer: replied 3 months ago.
sorry for long delay Had wifes car brake down could not take chance of not being able to start truck had to be able to take wife to and from shop my problem not yours but here's what I learned so far the points base plate is tight no movement the point's are almost closed on high point cam timing is way off and it's idling at about 1100 rpms I tried to a just the point's to the correct gap of .016 for old point's gap and when I tried to start the truck it would not start so I adjusted the gap closer and it started right up I was trying to get it timed close before I put new point's and cap and rotor in so points to close idol to timing off if I put new point's in I'm afraid that I will not be able to start almost forgot I think the reason point's are so closed is the plastic on the point's arm wore down causing the point's to close whae should I do and I really want to thank you for all your help and bye the way my name is Gary
Expert:  kalamykid replied 3 months ago.

Good morning Gary. With the old points adjusted how does it drive?

Customer: replied 3 months ago.
all I did was close the point's back to where they were in the beginning
Expert:  kalamykid replied 3 months ago.

So if you bump the points open just a touch it will not start?

Customer: replied 3 months ago.
the point's are opening and closing but are very close together and when I tried to open them up to .016 it would not start
Expert:  kalamykid replied 3 months ago.

Will the plate the points are mounted to move side to side allowing the points to open and close? It does not matter how much of the plastic tip has worn off, you should still be able to adjust the points to spec and it still run.

Customer: replied 3 months ago.
the point's are able to open and close but with idol at 1100 rpms I'm thinking timing is so far off that when set to spec it won't start and I have not touched the distributor yet
Expert:  kalamykid replied 3 months ago.

If the points have to be set to close to closed then you end up with over lay when you hit the gas hard and the points are not opening to tell the coil to fire. The best advise I can give you to get the truck to run correctly will be to pull the points distributor out and put an electronic distributor in. The HEI distributor is quick and easy to put in and will make the engine run SOOOOO much better. All you have to do is remove the old coil. Change the connector on the hot wire for the old coil from an eyelet to a female blade connector, pull the old distributor out making sure to mark the location of the rotor button, slide the new HEI distributor in so the rotor button is pointing in the same location of the old one, put the cap back on and plug the power wire into the hei cap and start the engine and set the timing.

Customer: replied 3 months ago.
here's what I wanted to try with the engine running- slowly open point gap and adjust the idol down and turn the distributor and slowly get all close to spec and then put new points in
Expert:  kalamykid replied 3 months ago.

If you are going to put new points in, do all the adjustments after you have the new points in. You will have to readjust everything when you replace them, so why not do it just once?

Customer: replied 3 months ago.
if I do that should I start with the point gap close to what it is now so hopefully it will start, I really want to adjust with it running especially since idol is all most double what it should be my thought is when I bought the truck instead replacing point's the idol was turned up so it idle smoother for the dumb buyer to think everything was good to go, the points were probably going bad and only got worst since I had it
Expert:  kalamykid replied 3 months ago.

Do you have the distributor cap off now?

Customer: replied 3 months ago.
not yet had to put everything back on to pick up wife and I will get a HEI distributor once I make sure nothing else is wrong and truck is running
Expert:  kalamykid replied 3 months ago.

I need you to do a few things for me so we can find the root of your problem. I need you to stay with me for just a few minutes and not run off and doing things with out testing to see what is really going on.

I need you to take the cap off of the distributor and pull up on the rotor button. I need to know how far up you can pull on the rotor button? I also need to know if the plate will float side to side letting the points open and close? There is something really wrong in the distributor and unless we find what is really wrong we can not get it to run correctly.

Expert:  kalamykid replied 3 months ago.

I am telling you now the distributor is your

problem. With the points set correctly it will not start and run. This can only be one of two things, the plate is worn out, or the bearings in the shaft of the distributor are worn out and the shaft moves up and down or side to side.

Customer: replied 3 months ago.
rotor cap moves less 1/4 inch and the plate the point's attached to does not move in any direction
Expert:  kalamykid replied 3 months ago.

Does the rotor button move side to side?

Customer: replied 3 months ago.
no
Expert:  kalamykid replied 3 months ago.

The rotor button should move less the 1/32 of an inch up and down. Try this for me please. Rotate the engine so the plastic on the points is in the center of the high point of the distributor shaft so the points are fully open. Then see if you can pull the rotor button towards the points and see if the gap of the points is larger? Then try to push the rotor button away from the poits and see if the gap closes?

Expert:  kalamykid replied 3 months ago.

Then pull up on the rotor button and do the same test with the rotor button pulled up as far as it will go. NOTE pulling on the rotor button will move the shaft in the distributor but may only be ever so slight so using a feeler gauge will help see what is really going on.

Customer: replied 3 months ago.
no movement with rotor cap in up or down position
Expert:  kalamykid replied 3 months ago.

If the shaft has no movement, then the base plate has to be floating around. Can you grab the points and pull and push the points towards and away from the shaft and see if the points open and close the gap?

Customer: replied 3 months ago.
no movement at all
Expert:  kalamykid replied 3 months ago.

Then you should be able to set the air gap of the points correctly and the engine run.

Expert:  kalamykid replied 3 months ago.

Replace the points and set them correctly and see if it will start and run.

Customer: replied 3 months ago.
I will give it a try thanks
Expert:  kalamykid replied 3 months ago.

Let me know how it runs with the new points.

Customer: replied 3 months ago.
sorry it took so long, when I took old point's out one side look like some one drilled crater hole in it and I was completly backwards on what I said about the points being to closed they were to open when I was checking points with the rotor cap on, between the round rotor cap and coil being in the way and blind I wasn't getting feller gauge in the right position and I guess I wasn't getting on the high point of the cam either, so I put the new point's and condencer in set the gap to "019 spec started it up now the only thing I could not do was check the dwell my meter was not working but I went ahead and timed it dropied the idol to 600 rpms and got timing to right around 8 degrees after this was done I reved the engine it was still popping through carb but it seemed to be at much higher rpm then before
Expert:  kalamykid replied 3 months ago.

That's good to hear. At least we know now that it's all in the ignition not anything else. If you put an HEI distributor in it will completely cure all of your problems. The points are not opening and closing like they should. With an HEI distributor you'll get more precise ignition timing and the sparkle get to the plugs quicker and more efficiently. Let me know what your reaction you want to go in. I'm willing to bet the points are still your problem.

Customer: replied 3 months ago.
I'm going to borrow a buddies dwell meter and check the dwell and check the timing again. I'm not trying to be a dick head, could anything else be wrong like egr valve fuel pump or carb or anything I realy do aperciate all you have done
Expert:  kalamykid replied 3 months ago.

With the changes in the way it runs just by changing the points, I do not believe there is any thing more wrong with it. I am not trying to beat a dead horse with the hei but I know it will make you very happy with the way the truck will run. You have to get the timing problem fix and all the rest will fall in line.

Related Classic Car Questions