Help me diagnose this

[mcditalia]

My 66 went in to my shop a couple of months ago after i bent a pushrod and broke a spring. Luckily the shop said i didnt do any other damage. Symptoms when it happened started with a slight miss at hyway speed which got progressively worse. By the time i limped it home it was barely running.

Shop installed new valvetrain, pushrods, rockers and springs, reset the timing and adjusted the choke. I now have a problem where occasionaly, when im getting on the gas aggresively from a stand still, the motor just falls on its face, usually in third gear as im pulling past 3800. The car just winds down where sometimes it recovers and other times it stalls out after it scrubs off speed. The throttle doesnt respond at all when it acts up. If it does stall, it starts up again usually with no problem. Its kind of hard to replicate as it comes and goes.

I would like some ideas on where to isolate the problem. I dont know if its related to new valvetrain components, fuel system or ignition system. On a side note, the choke doesnt seem to work at all now ever since the shop i used tinkered with it.

 

[haganml]

My 66 went in to my shop a couple of months ago after i bent a pushrod and broke a spring. Luckily the shop said i didnt do any other damage. Symptoms when it happened started with a slight miss at hyway speed which got progressively worse. By the time i limped it home it was barely running.

Shop installed new valvetrain, pushrods, rockers and springs, reset the timing and adjusted the choke. I now have a problem where occasionaly, when im getting on the gas aggresively from a stand still, the motor just falls on its face, usually in third gear as im pulling past 3800. The car just winds down where sometimes it recovers and other times it stalls out after it scrubs off speed. The throttle doesnt respond at all when it acts up. If it does stall, it starts up again usually with no problem. Its kind of hard to replicate as it comes and goes.

I would like some ideas on where to isolate the problem. I dont know if its related to new valvetrain components, fuel system or ignition system. On a side note, the choke doesnt seem to work at all now ever since the shop i used tinkered with it.

Of the top of my head this sounds like a fuel issue, sporadic loss of power (no missing or skipping?). No response to the accelerator? Has the L79 (large Holly carburetor w/ engine heat used as heat source for choke) had the fuel filter replaced recently? Is the fuel pressure okay? On the original style fuel pump there is a pin in the pump that the lever pivots on, has this pin walked out of the pump body? A partially plugged fuel filter will not have an effect until the float bowl in the carburetor is emptied by engine demand ( hard acceleration until about 3rd gear ). The throttle response returns as the float bowl refills. After 60 to 90 seconds of low engine demand the fuel level returns and fuel is available for engine operation. The engine is running out of fuel at high demand and operates normally with reduced throttle openings. This only applies if the engine has remained unmodified and is running the original equipment. Electric fuel pumps and aftermarket carburetors aren't mentioned in your post. You said the choke has been adjusted and does not seem to be operating. Has the carburetor been removed? Replacing the rocker arms, push rods and valve springs can be done without removing the intake manifold and heads. Let me know how extensive the repairs were, intake removed or heads removed? Just the valve covers removed?

 

[mcditalia]

I replaced all my fuel filters within the last year. I have a fairly new replacement mechanical fuel pump and a universal replacement holley 4 barrel carb with electric choke set up. My choke doesnt seem to function properly, especially with warm starts, that is after letting the car sit for a while after running it and starting back up a half hour later. I have to keep the throttle depressed for a couple of minutes until motor goes back to operating temp, otherwise it stalls. Engine is essentially stock minus a higher lift cam that a po installed. Recent repairs only involved removing the valve covers and resetting the timing.

I was thinking of 2 things. Possible valve float at higher rpms or the secondaries not opening on occasion. I was going to check the function of the secondaries with a paper clip. Other than that i dont know where else to look. I emailed the shop i used over the weekend and am awaiting their response. If i can diagnose this without bringing it back ( hour plus away ) it would be a big help.

 

[haganml]

I replaced all my fuel filters within the last year. I have a fairly new replacement mechanical fuel pump and a universal replacement holley 4 barrel carb with electric choke set up. My choke doesnt seem to function properly, especially with warm starts, that is after letting the car sit for a while after running it and starting back up a half hour later. I have to keep the throttle depressed for a couple of minutes until motor goes back to operating temp, otherwise it stalls. Engine is essentially stock minus a higher lift cam that a po installed. Recent repairs only involved removing the valve covers and resetting the timing.

I was thinking of 2 things. Possible valve float at higher rpms or the secondaries not opening on occasion. I was going to check the function of the secondaries with a paper clip. Other than that i dont know where else to look. I emailed the shop i used over the weekend and am awaiting their response. If i can diagnose this without bringing it back ( hour plus away ) it would be a big help.

Filters could still be an issue, put them on the back burner. Check the choke with cold engine. Remove the air cleaner assembly. Without starting the engine, open the throttle to the wide open position. Quickly release the throttle. The choke plate should close over the primary opening (front two throttle bores). Look to the passenger side of the carburetor, you will find a black plastic disc with a metal retainer with three screws. Two wires should be attached. This disc is rotated clockwise to increase the amount of choke (loosen the three screws and rotate the disc, the throttle must be open to allow the choke plate to move). You must have battery voltage to the ignition side of the two wires with the Key On Engine Off (KOEO) and also a ground on the second wire. The small heater element in that plastic disc will warm up the spring and allow the choke plate to open. Your original choke used the actual engine heat to perform this function. If the ignition switch is left in the "on" position your electric choke will heat up and not function correctly. Engine compartment heat also affects this style of electric choke. From your description you have a "hot soak" start issue. You may need to advance the choke (turn slightly clockwise) for a hot soak start.

You have a mechanical fuel pump. If the engine is running out of fuel under heavy load, you can shut off the engine and check for fuel in the float bowls. Valve float is an issue that happens with a hydraulic lifter cam. If the redline on your tachometer 6,000 to 6,200 that is a L76 engine (mechanical flat tappet camshaft) speed limit. The replacement camshaft may be a hydraulic lifter camshaft. Until you know for sure limit your RPM to 5,000. Check your paperwork to see what exactly that camshaft is. If you have your valves adjusted periodically and can hear the lifters ticking slightly it may be a mechanical lifter cam. Hydraulic lifter cams are very quiet.

If the secondaries are vacuum operated (late model Holley) and do not open you would experience a lack of performance not a complete loss of power, the primaries will still supply air/fuel mixture to the engine. If your Holley has mechanical secondaries you could have a lean hesitation right as you open the throttle hard that would go away as the metering jets supplied fuel. Check that the acceleration pump is squirting fuel into the manifold.

 

[midyearroadster427]

either fuel delivery or your over revving the engine...valve float...

 

[mcditalia]

An update to the problem. I replaced all of the rubber fuel lines and both filters. The rear tank filter had the element loose in the casing. I cut it open and the out side part of the element had no ring at the end. Looked like it broke apart. With that being said i hooked everything back up and same problem at higher rpms.

First cold run i had no problems. After engine really warmed up/ hot, fuel cut off happens only in third gear at no more than 4,200 revs. 1 st and 2 nd same rpms no issue. When i shift to 3 rd get to 4,000-4,200 revs and it falls on its face, winds down from lack of power/ fuel, and most of the time it gets going again. Engine is not over revved.

I thought valve float also, but that would happen in any gear, not just 3 rd.

"If the secondaries are vacuum operated (late model Holley) and do not open you would experience a lack of performance not a complete loss of power, the primaries will still supply air/fuel mixture to the engine. " - didnt really think about it. That makes sense.

My shop thinks that there is a condition in my carb where the bowls aren't keeping up with the supply demand at high rpms and by the time im in 3 rd the lack of fuel cuts out the engine.

"If your Holley has mechanical secondaries you could have a lean hesitation right as you open the throttle hard that would go away as the metering jets supplied fuel. Check that the acceleration pump is squirting fuel into the manifold." - secondaries are vacuum operated. My condition is the opposite, that is fuel runs out after not at beginning of heavy throttle.

 

[Hib Halverson]

You're problem is not valve float.

Loss of power in the higher gears, ie: 3rd or 4th, starting at high-mid-range rpm points squarely at fuel starvation.

 

[mcditalia]

With filters and rubber fuel lines replaced i also checked the sending unit. Sock is good and there doesnt seem to be any obstructions in tank. Fuel pump was replaced about 7-8 years ago. Is it safe to assume that the carb is the culprit at this point?

On a side note, i noticedthat the hard fuel line right by the fuel pump has a small kink at the end where the rubber hose hooks up. Not sure if this would really amke a difference, but to be honest its been there since i bougth the car 10 years ago.

 

[Hib Halverson]

Have you tested fuel pressure and delivery volume?

Have you inspected the fuel pipes from the tank forward looking for sections where the line has been crushed?

 

[haganml]

On reading your posts I have to agree with Mr. Halverson. That RPM and with no loss of power in the first two gears suggest fuel starvation not valve float. The reservoir of fuel in the carburetor should be replenished by the fuel pump at higher RPM. You mentioned a "small kink" in the fuel line, the diameter of the line would have to reduced by half to restrict the flow enough to present your symptom.

A pressure and flow test are recommended. What follows is a brief explanation of the function of your mechanical fuel pump.

The mechanical fuel pump uses an eccentric on the camshaft to move the fuel pump actuating rod in and out transferring rotating movement to reciprocating movement. The push rod then moves a lever on the fuel pump flexing a diaphragm inside the pump, a series of one way valves allows the diaphragm to pull in fuel from the fuel tank and then push the fuel to the carburetor. The lever in the pump can have wear on the pivot pin or the lever itself reducing the efficiency of the pump. If the fuel pump push rod has been shortened by wear or the camshaft eccentric has worn to a degree that could be an issue also. The diaphragm can crack and leak, at that point you will have raw fuel leaking from the pump. The camshaft runs at half the engine speed and you need to rotate the engine over twice to get one complete revolution on the cam. You have a recently installed camshaft and this problem has appeared sometime after that replacement.

If the pressure and flow test recommends repair a new fuel pump is relatively inexpensive compared to a new camshaft and or carburetor. With the fuel pump removed the push rod could be easily checked for issues.

In closing I remember a case (my fathers Hudson Hornet) that had the same issue. One of his children (which one I will never divulge) had taken blades of grass and put them in the gas tank. The blades of grass floated on the fuel and every thing was okay until it got below 1/4 tank then the blades of grass packed themselves into the unscreened fuel line choking off the fuel supply! He would pull over and the blades of grass would float up allowing the fuel to flow again. He could then drive off until the line plugged again. Quite the mystery until he blew out the fuel pump supply line with some air and got a handful of grass out of the other end. He eventually removed the tank to get all the grass out of it.

 

[haganml]

"An update to the problem. I replaced all of the rubber fuel lines and both filters. The rear tank filter had the element loose in the casing. I cut it open and the out side part of the element had no ring at the end. Looked like it broke apart. With that being said i hooked everything back up and same problem at higher rpms."

Rechecking the post I noticed this. If the ring did indeed break apart and the particles are not in the housing on the outflow side, they have to be in the fuel supply line. These could be obstructing the line near the fuel pump or inside the fuel pump itself during high flow conditions. This might be your "blades of grass" symptom.

 

[mcditalia]

Thanks all for the replies.

I havent been able to pressure test the fuel system yet, but its on my list to do. Problem remains.

Is there a way to fix the kink at the end of my hard fuel line? If i cut off the kink at the end then i would lose the "nipple" and not sure if this would promote a leak. I Thought i read that the hard fuel ines could only be replaced with the body separated from the frame. I guess i could use A temporary rubber line and see if the problem is there.

One last question: would a failing/maladjusted choke replicate these symptoms? I have an electric setup at the moment that was recently adjusted.

 

[haganml]

Thanks all for the replies.

I havent been able to pressure test the fuel system yet, but its on my list to do. Problem remains.

Is there a way to fix the kink at the end of my hard fuel line? If i cut off the kink at the end then i would lose the "nipple" and not sure if this would promote a leak. I Thought i read that the hard fuel ines could only be replaced with the body separated from the frame. I guess i could use A temporary rubber line and see if the problem is there.

One last question: would a failing/maladjusted choke replicate these symptoms? I have an electric setup at the moment that was recently adjusted.

The crimp ("nipple") on the end of the metal fuel line is to stop a flexible line from slipping off. If the small kink has been in your fuel line from the time you purchased you car you would have had this problem all along not just recently. For that kink to be the cause for your complaint the fuel line diameter would need to be bent almost closed. Modern fuel flex line and spring clamps are better at stopping the leaks than the old rubber lines and screw clamps used 47 years ago. You can cut the steel line, reform the crimp using a flaring tool or you can try a steel rod that fits inside the fuel line. Reduce the diameter of the steel rod to half by sanding or grinding to produce a short taper in the rod. Push the rod close to the deformation in the line and using pressure and movement (wiggle the line while pushing the rod into the dent) to reform the line. This all depends on if you are concerned about the originality of the car. Cut off the dent and use a section of line to test for that symptom is the fast and easy way to address that the kink is your problem. I honestly don't think that it is.

A improperly adjusted choke (too lean) would cause a hesitation on acceleration only while cold. You would need to hold the throttle open while cold to prevent the engine from stalling. Set too rich and you will get black smoke from the tailpipes. All of the symptoms from a choke will go away when the engine warms up. Your problem is under acceleration with a warm engine. Fuel delivery symptoms not choke symptoms.

 

[JohnZ]

Are you sure you have the correct (40083) fuel pump (see photo below) with the inlet and outlet 180* apart?

 

[mcditalia]

Are you sure you have the correct (40083) fuel pump (see photo below) with the inlet and outlet 180* apart?

Fuel pump was a replacement Style without the Ac logo with the inlet outlet sides 180 * apart. Looks a bit different on top but never had a problem. I bypassed hard line with rubber but haven't had time to test it out. I'm thinking at this point if problem persists with fuel lines taken out of the equation that by process of elimination it is either fuel pump or carb. I hope.

 

[haganml]

Fuel pump was a replacement Style without the Ac logo with the inlet outlet sides 180 * apart. Looks a bit different on top but never had a problem. I bypassed hard line with rubber but haven't had time to test it out. I'm thinking at this point if problem persists with fuel lines taken out of the equation that by process of elimination it is either fuel pump or carb. I hope.

Very well could be the fuel pump. They do wear out, or do not work as well as advertized. Good luck.

 

[mcditalia]

Wanted to relay that the cause of the problem ended up being the fuel pump. After I took out the old pump, the spring on the pump arm was broken. Not completely enough to make it fail, but enough that it wouldn't keep up with the high fuel demand. Just wanted to update in case someone else had similar issues.

 

[Tom Bryant]

I've had that happen in the past too. I'm glad it was an easy fix. There is still a lot of good fall cruising time left.

Enjoy,
Tom

 

[haganml]

Wanted to relay that the cause of the problem ended up being the fuel pump. After I took out the old pump, the spring on the pump arm was broken. Not completely enough to make it fail, but enough that it wouldn't keep up with the high fuel demand. Just wanted to update in case someone else had similar issues.

Excellent! Down the road burning gas and having fun! Can't get any better than that!