Buck and Surging Problem Under Load

[BSB67]

Kind of hard to follow.

Exactly what problem(s) remain, and exactly when and how does it (they) occur?

 

[Road Grabber]

Sounds like it is leaning out due to not enough of a squirt of the accelerator pump. If you have an adjustment for more of a squirt try that. I had this problem on my carb a few years ago. Once adjusted correctly problem went away

I have been working with the pump nozzle. I went from .032 to .035 with an improvement so I will try .037

I will double check the pump adjustment as well. I was just watching the holley how-to tech video and plan to check the adjustment again. The carb came directly from a restoration vendor but it doesn't mean it doesn't need adjustment. I plan on checking the float level too.....

I'm gonna toy with purple secondary springs too for the hell of it later when I hopefully resolve this.

Thank you!

 

[Sam69sat]

I'm dealing with a similar issue. Traced it down to vacuum advance on the distributor. Once i unplugged the vacuum hose and plugged it, it ran great. When it's plugged in i get hesitation and bucking especially at light throttle.

 

[Road Grabber]

I will try that thanks. I took for another test drive and it’s still there. Just under load. Not at idle.
Does anyone know a good test processor checking intake manifold leak?

 

[RGAZ]

I will try that thanks. I took for another test drive and it’s still there. Just under load. Not at idle.
Does anyone know a good test processor checking intake manifold leak?

I have two processes I have used. One is messier than the other.

1. Engine running, lightly spray carb cleaner or a flammable spray on spots on the manifold that might be leaking. If engine rpm increases when hit with spray, that is your leak. It is messy and can damage paint, so be aware.
2. Using a propane torch with a tube end and valve, put a rubber hose on the tube end and turn on the gas, but do not ignite. With engine running, put tube end of gas where leak might be and listen for rpm increase. That is your leak. This is cleaner by far and can really pinpoint the leak. But some people are afraid of propane.

Go for carb gasket first.

Good luck,
Randy

 

[Road Grabber]

I have two processes I have used. One is messier than the other.

1. Engine running, lightly spray carb cleaner or a flammable spray on spots on the manifold that might be leaking. If engine rpm increases when hit with spray, that is your leak. It is messy and can damage paint, so be aware.
2. Using a propane torch with a tube end and valve, put a rubber hose on the tube end and turn on the gas, but do not ignite. With engine running, put tube end of gas where leak might be and listen for rpm increase. That is your leak. This is cleaner by far and can really pinpoint the leak. But some people are afraid of propane.

Go for carb gasket first.

Good luck,
Randy

Very interesting. Never heard of that one. I will see if my barn has the stuff I need. Would you use a vacuum gauge to notice this change or should I just notice this change in rpms if it were a vacuum leak by listening to the engine?

The engine doesn't pop anymore. It just has a dead spot during a sudden step on the peddle.

This morning it seemed like it was intermittent suggesting electrical again. Very frustrating. I did put the timing back to 2 degrees BTD and that seemed to help.

I'm almost ready to get one of "Petronix" type distributers and get rid of the points for good...
If someone knows someone who makes those types of setups I'd appreciate some advice if I was to buy a good one. Doesn't have to be a racing setup.


Some things I have done:
-I have replaced two vacuum plugs. One with a crack that plugged the manifold fitting. It did help..
-I have placed the timing to 2 degrees BTD. It was a bit advanced.
I have watched the distributor advance with a timing light working properly.
-Increased the accelerator pump nozzle from .032 to .035 with some improvement. I am waiting for a .037 nozzle to try when it arrives. I just don't want to be over compensating for a vacuum leak.
-I have sprayed carb cleaner on the manifold but there didn't seem to be a surge in rpms. I wasn't sure if the carb cleaner was being sucked up or just evaporating quickly from the heat but it did disappear very quickly.
-I will check for the plugged vacuum advance hose...Trying to keep up with suggestions...
-I will wire the choke plate open
-I will replace the points....again...
-I don't have a timing tape on the damper but I will get one because I would like to know total advance for intel..


I appreciate the feedback. Thank you

 

[RGAZ]

No gauge needed, the change in rpm should be obvious when the leak sucks in the "fuel" you are providing.

I think you are getting close to the root cause.

RGAZ

 

[Road Grabber]

I decided to pull the motor. I discovered in a compression check pressure anywhere from 125 psi to 150 psi. New battery - new starter so it cracked very well for a good test.

The car was assembled (over 20 years ago) and run during a time when there was zinc in the oil but must have had too many oil changes without the zinc because I wasn't aware of the change in oil ingredients. I think the cam has some wear. I plan to pull the valve covers first (leaks a bit anyway) and crank the engine to see any noticeable difference in lift at the rockers.

If anyone else has a good way to check this I would be open to suggestions.

I plan on looking into roller lifters and rockers for the next cam if anyone has a suggest for that too. It's just a cruiser not a race car so I plan on some thing stock or maybe a bit more. Hemi grind spec?

I would be curious to hear if anyone else had cam lobe problems....I understand the engines can still run with hydraulic lifters pumping up to compensate.

Thanks again for the feedback and any responses for the above.

 

[Road Grabber]

Well I had enough and pulled the engine. I had a feeling I was chasing more than one issue and didn't like the way the #2 spark plug was looking The cylinder did have pressure.

Turns out the valve has a crack. Good thing I tore it down. Greasy clothes and constant grease cutting soap like the old days. The car is waiting for a freshen up.

I am thinking a slightly modified roller cam and lifters. I have a good set of closed chambered cast heads I want to put stainless valves in.

The rest of the engine looks fine. No ridge in the cylinder and clean. The only thing is I am used to starting off with a bare clean block and if I dip it I will have to tear everything down. Have to look into ways to get the block clean for repainting using an epoxy this time I think.

When I pulled the intake I noticed oil along the bottom of the gasket so I figure it was leaking.

I use an aluminum Chrysler dual plane. I put the 6 pack set of gaskets on and apparently they were too thick? I had to pry this manifold off but it must have still been leaking at the bottom.

Can someone tell if they use the paper along with the valley pan gasket to bolt down aluminum intakes?

Thanks for the responses. It's back to the drawing board for awhile and research.

 

[RGAZ]

This is very interesting. Can you shed some light on the valve crack? Intake or exhaust? Did it exist on the low compression cylinder? What about the other low reading? Gotta pic?

Let me walk the logic...... Car ran fine except for a flat spot when you accelerate quickly. Sound right? No other symptom? So you pulled it and found a cracked valve and "some" cylinders with low compression. So you surmise its the problem. Not sure I would stop there. What caused the crack? Did you see evidence of lean burn? Any mechanical issue (impact, bent, etc.)? Heat spotting from a bad seat? Detonation? You may have found the result not the cause. I would hate to have you rebuild and then right back to where you were.

From my past experience, a bad valve will run like crap in all phases of operation. But a lean burn will slowly damage or stress a valve, so I am back to you checking that carb and timing. Of course, after you get it back together.

Keep us informed.

RGAZ

 

[Road Grabber]

I pulled the engine because I noticed one cylinder was not firing consistently when I pulled the plug wire and no matter how much I tried to richen the mixture it wasn't enough. I removed the plug with less compression and noticed a strange white band across the plug. The others didn't have that strange white look like it wasn't firing. It wasn't clean. It was pure white. It showed signs of excessive heat. I figure this was a connection with an intake leak and that the cylinder intake port must have had a bigger leak. The engine had 150 psi in some and 125 in others. Too much difference.

The short block looks great except for some carbon build up on the pistons.

There could be a more than one issue. I still have to pull the cam and mic it. If the lobes are way off, I have a worn cam from not using zinc oil so I have been told. The engine was assembled over twenty years ago. I didn't discover this zinc issue until later...

The crack was the #2 exhaust valve. All the exhaust valves did look white. The plug where the valve crack was, had a spark plug that had a white band across the electrode. Not the other sparkplugs though. The pistons are not pitted or show signs of detonation but the intake gasket had an oil film along the bottom edge of the gasket suggesting there was an intake leak. I may have caused this by using too many gaskets installing the aluminum intake. I thought it was typical to use paper with the valley pan when using aluminum intakes. I used the 6 pack set of gaskets that has two thinner paper gaskets meant to use with the stock 6 pack aluminum intake. I use them already for my six pack and they work great. A lot of lining up but a much better seal so I did the same thing for the 383 with a Chrysler dual plane manifold. I really had to pry up the intake so I thought it did seal well. I noticed however the oil film along the bottom edge of the intake gaskets at the ports. I figure it might have been drawing up oil from the valley. The pistons did have carbon on top.

The engine always ran cool at 5 degrees BTD and never overheated.

I need a good way to check the intake fit before the new assembly in case the intake is warped. Put the intake on the heads and use a feeler gauge? Look for a gap at the bottom? I could use some advice here so this doesn't happen again.

The engine never had the proper carb on it so I was never able to really get into it. It always had a problem restarting the engine after reaching temp and when you stopped for gas for instance and tried to restart the engine I always had what seemed to be percolation. A hard start. You had to pump and floor it to get it going again if it didn't start right away. This drivability problem, I thought, was various carbs that weren't correct. I had a Holley with the correct list number restored and thought this would be the fix. It did run better except for the flat spot. The only way I could get it somewhat better is to add a bigger accelerator pump but it was just compensating for a bigger problem. The engine has had a surging problem for some time so I guess there was an intake leak and eventually burnt the valve because all the valves look white.

Either way I couldn't stand looking at a motor that leaked oil no matter what valve cover gaskets I used. I am going to investigate better sealants to use when I button it up again. Same thing with the trans. It needed new seals and leaked so two days later the motor is out and I am trying to get this resolved with better components and sealants. If that means a roller set up than I will put one in. My engine builder says he won't assemble flat tappet engines any more...

I will send some pictures. Sorry it's long winded but I hope it provides some background info. Thanks for keeping in touch and trying to help. Every thought is appreciated.

 

[440 Charger]

This is good advice. Did you have to adjust the idle a lot when you put the new carb on? I would expect the idle to be crappy or high if a big vaccum leak, but use the "carb cleaner mist" technique to see if there is a vacuum issue.

My question was: Do you still have the stock ignition installed (points)? If so check them AND the timing advance. Maybe you have a bad dashpot on the dist and not getting appropriate advance under load. On second thought...did you connect the vacuum advance to the correct port on the carb? Maybe a leak on the dashpot.

RGAZ

Spray some carb cleaner around se it the rpms change.

 

[Road Grabber]

The motor is out. I have inspected and removed the heads, cam and oil pan (just so I can seal it again with better sealant). The timing gear and chain was still in excellent shape.

The cam is fine. Not excessive lobe wear and mics out the same for all intake and exhaust.

I did notice that some valves were sinking in the pockets. I plan to switch heads and do a valve job with stainless valves UNLESS I can use aluminum heads like the 440 source heads. It's not a race car. I want to keep the magnum cam specs and original look. My understanding so far is that the engine needs a higher compression to use the aluminum heads. I know the Edelbrock RPM heads are nice but they are more money and the cam doesn't need the breathing. I plan to use cast iron close chambered heads to up it a bit and use roller rockers. I never did like the stamped factory rockers. Something to fit under the stock valve covers.

Nothing set in stone yet. If anyone has any thoughts I welcome the feedback. If you use a slightly modified cam that works I'd love to hear about it.

 

[Darter6]

440 Source heads are closed chamber.

 

[440 Charger]

Sticking to cast iron 906.

 

[beanhead]

Just to throw this out there....toughest thing if your looking to upgrade is parts availability, aluminum heads in particular. Edelbrock, 440Source/Stealth, Trick Flow....even the Speedmasters are unobtanium right now and the "estimated ship dates" seem to just keep getting pushed back. So if you don't want your car down for that long it might be worth considering fixing what you have for the time being.

 

[Road Grabber]

Sticking to cast iron 906.

Any particular reason?

 

[RGAZ]

Any particular reason?

Yeah, please elaborate. I have old 906 heads and am deciding if I want to rebuild them or just go with Aluminum aftermarket. Cost seems to lean towards AL.

I am all ears...
RGAZ

 

[Road Grabber]

I am all ears too. The research I have performed on our forums is that the aluminum heads don't have the heat cross over for the stock choke operation.
I am leaning towards keeping the cast iron heads because I intend to keep the stock choke. It's a cruiser car.

I am looking into the cost of buying new stainless valves (I was going to purchase them anyway) & increase the exhaust valve size to match the aftermarket heads. I am dropping off the engine today and should know the cost. The builder will shed some light on this build too. I will certainly listen to their experience/feedback and share later.

On a side note:
I have a 6 pack 440 engine with the stock 10.5 compression pistons. My 440 has a detonation problem with the 10.5 pistons with cast iron closed chamber heads. I plan to use the 440 refreshed cast close chambered heads for the stock 383 to liven it up and purchase the aluminum heads for the 440 street machine with the detonation problem hoping the aluminum heads will cure the detonation I experience now with the high compression 10.5 engine. The 440 with the close chambered heads is too much for pump gas. It was fine when I built it 30 years ago but not now. I want to pull up to any high test non alcohol premium gas station and filler up without problems. If I can get them, I was planning to use Trickflow heads for the 440.

Again - any feedback is welcome......

 

[Johnpat]

Put a little wd40 spray down the accelerator pump shaft.
Sometimes the seal in the pump dries up and won't
hold a good seal. Try to see if flat spot goes away.
I used to try this year's ago to check seal.