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Need help troubleshooting engine........

rsd859

rsd859

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Springfield, MO
Got in my RR yesterday after not starting it for a week, she fired right up let her warm up for 10 minutes or so. Put in drive and she dies. I do this about 4 times. Something isnt right. While its idling Ill hit the throttle and there is hesitation. When I get off work today im going to check the timing, Fuel filter, maybe? We are working on a 400. 650 Holley Open to suggestions

Thanks, Rich
 
How did it run last time you had it out?
Check and make sure the accelerator pump is working OK.
Might have fouled out the spark plugs.
 
Ran good, I just changed the plugs and wires a couple of weeks ago. im gonna pull a plug or 2 and see what they look like. Ill post a pic tomorrow.
 
My experience with engines dying when being put into drive has almost always been because of a vacuum leak.
 
If you have the car stored near an open field or out in farm country the little mice love to chew the vacuum lines into. They after dining on the vacuum lines then have desert at your plug wires.

The quickest way to diagnois a problem is to always keep two tools in you tool box. One is a remote starter button with about 6 ft of wires. The second is a good vacuum gauge. This way you can start your car from under the hood and work the accellerator by hand. The vacuum tool once you learn to read one is invalluable in helping to locate problems.

However, the common sense part of locating your trouble is if the car was running fine when you last parked it and if that was recently then unles some one has tampered with it the problem is more than likely very minor.

If you have a remote starter you can check for a stuck float by looking ofr fuel spill over out of the breather tube.
You can also use a can of carburetor cleaner to spray around the carburetor and vacuum lines and if there is a vacuum leak the engine RPM will increase when the cab cleaner hits the leak.

With the lights out in your garage, the hood up and engine running you will be able to see any arcking plug wires.

The one thing you do not want to do is start making a bunch of adjustments to the timing and carburetor because if it ran right when you parked it those things are still in tune.

Check for all the wierd crap that could have happened while it was sitting before turning the distributor or adjustment screws on your carburetor.

Hope this helped
 
accel pump check is easy.look into carb while you move the throttle link from idle to full open when not running.look for a clean steady streem from the squirters(both sides).vac leak check is easy as well.while running slowly put you hand over the carb and see if it idles up(vac leak)if you choke it off it is normal.make sure your choke is tight and working as well.holley could have a power valve problem if all else fails.
 
I will check into the vacuum leaks, here is a pic of a plug out of #2 cyl 2013-01-12 20.19.09.jpg
 
Acc pump is working fine, havent had a chance to start it to check for vacuum leaks yet.
 
The accellerator pump has nothing to do with the idle circuit of a carburetor therefore messing with it is a waste of time. The function of the accellerator pump is to give the engine a big gulp of fuel when you initally mash down on the gas pedal. Without the pump the engine would stumble and maybe die.

But when the engine is just idling with out any pressure on the gas pedal the acc pump is not having any affect on the engine what so ever.

Think about it. when you were told to and how to check it to see if it was working you had to work the linkage inorder for it to be able to be checked out. Well when an engine is just idling the linkage is not being worked or operated; therefore the acc pump is not part of the system responsible fore the engine idling.

The idle circuit on the other hand is the part of the carburetor that is responsible for the idle. Therefore anything that can cause an effect on the idle circuit must be checked to amke sure they are all working properly.

Vacuum is a key player in that many cars depending on your type of carburetor need a vacuum supply to the vacuum advance in the distributor in order to advance the timing after the engine is started. If the vacuum is leaking and the vacuum canister is unable to advance the timing then the engien can die.

If the vacuum is leaking it also has a major effect on the idle circuit which can cause the engine to die.

If the choke pull off does not get enoguh vacuum in order to open the choke plate a proper amount then the engine will flood and die.

Proper amount of engine is one of the most critical parts of the tuning of an engine being in proper tune.

Did you notice how many things I mentioned that were tied to the engine vacuum? Well if you looked at it as individual problems then you missed the point.

A vacuum leak or low vacuum situation is going to effect every one of those things I mentioned at the same time.

Unless I am working on a race engine with an after market cam shsft I want to see between 18 and 21 inches of vacuum at idle. Any less and you need to start looking for why it`s low.

Leaky valves can cause low vacuum, burned pistions, loose valve guides, leaking head gaskets are some of the internal things that will cause low vacuum.


But it was my understanding that the engine in question was running fine before this problem reared it`s ugly head, which indicates that it must or should be something simple like a loos vacuum hose slipping off it`s nipple or a hose that`s been chewed by rodent.

Just don`t waste your time checking things that have nothing to do with the problem.
 
It's not gonna be something like timing. I wouldn't give timing a second guess. I put my money on something enthanol has messed up. I say look for rotten fuel lines or oozing gaskets in the carburetor. It'll be something that sitting up has helped along.
 
The carb has a fresh rebuild on it, so friday when Im able to get some more work done, I WILL get a vacuum reading and let you guys know what it is. All my vac lines appear to be in good condition. Where at in MO are you KY509?
 
Ok now that you have confirmed the vacuum lines are all good (no leaks) The nect thing to check is the power valve in the carburetor; that is unless you have removed it and plugged the hole. On a holley behind the front float bowl in the plate that holds the jets at the bottom is a part called the power valve. This power valve is critical in helping to control the engine at idle. What it does is when the idle trys to drop off it will allow more fuel to enter the idle circuit which keeps the engine from dying. The power valve is sentisitive to back fires through the carburetor. Most powere valves will blow after it has experienced 2 to 3 carburetor back fires. They can stand only so many beofre the little diaphrams give out, then they stop working. Again the power valve is also dependent on good engine vacuum. Also each power valve is set for a spicific engine vacuum and the size of your power valve is probably stamped in really small digits on the side of the valve.

What determings the size is the amount of vacuum your engine pulls and the size of your am shaft can really make a huge difference in the size you need. Cam shafts with a lot of over lap can cause low engine vacuum so you will need a power valve that opens at a low vacuum signal.

It has been a long time since I worked on a holly carb but I bet if you go to the Holly web site they will have plenty of information on how to check the power valve and the different sizes they sell.

But, you are in some what of a delima unless you know what your vacuum was before you had this problem.

If you have an after market camshaft you should have already checked your inches of vacuum and logged it into your records.

If you are running a factory can shaft you can probably safely say that your engine is pulling at least 16 to 18 inches of vacuum in a well used condition. If the engine is new with fresh rings and valve job it could be higher up to 20 to 21 inches. I forget the spread of how many inches of vacuum each power valve covers but again check with holley for the appropriate info and make a judgment call based on what you know about your engine.

PS There is one other thing to check.
You need to check your choke plate. Some of the holley choke plates need to run at about a 1/8 inch opening to the air horn untill the engine starts to warm up. Then as the engine warms the choke plate will gradually start to open at a rate equal to the engine temperature. With all that said, if your linkages to your choke plate are gummed up, bent, out of adjustment to where the plate opening is too wide then the engine will not idle properly when it is stone cold.

Keep in mind, a cold emgine needs a lot of raw fuel in order to keep running on initial startup. Anything preventing this needed additional fuel is going to keep the engine from idling properly.

So before pulling the carbureor apart to check the power valve take a look at your choke assembly. Get your self a shop manual and get the settings for the plate opening, and the rate of choke pull off.

The choke pull off, The choke pull off is a little vacuum canister generally bolted or rivited to one corner of the carburetor. it has a linkage that attaches to the choke linkages and a vacuum line that runs between it and the carburetor.

If the choke pull off is not working at all then you choke plate may be staying closed at start up which is flooding the engine and causing it to immediately die.
If the choke pull off is out of adjustment and opening the plate too far then the engine is running too lean at start up and again it will die or run poorly.

Please note; if you noticed every thing I just told you relies on engine vacuum. I know you said everything is good with the vacuum lines but trust me with out proper vacuum nothing works correctly in your tune up.

If you have low vacuum
The power valve fails
The choke pull off fails
The choke plate fails.
The distribuitor vacuum advance fails

If all five of these things are going to be effected due to low vacuum, and they will, then you can see how low vacuum could cause a problems.


About 13 miles East of Ft Leonarwood just off I-44

Or 125 miles west of St Louis
 
Last edited:
There are some inaccuracies in the above post. The main one is that the Holley power valve has a function at idle. It doesn't. The only time it will affect the idle quality is if it is blown or its opening rate is below the vacuum produced at idle. In both cases, the engine will run rich. What the OP said in his original post is that the engine idles fine. His problem is when he comes off idle the engine stalls. Not enough information was provided to determine if this happened just when cold or all the time. Therefore, determining the fix is difficult. Tearing apart things without accurately diagnosing the problem is just wasting time and money. OP, please provide more information.
 
Yes, on a warmed up engine it will die when put into gear. What else do you need to know? Im working on her today and will be getting vac readings and searching for vac leaks.
 
fuel

Something I would check is the fuel quality,alcohol doesn't like the old cars.
 
Alright, Im pulling 10 inches of vac, the needle was bouncing like crazy too. No vac leaks, Took her for a spin, she didnt die when put into gear but when you give it some gas she wants too, pumped the pedal and she took right off.

Also when I was crusin about 30 I hit the gas again and it hesitated then took off, but it only did it once during my test drive, I tried it a few times, so its not consistant.
 
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