Intermittent idle surging issues

R

RuleHard

Junior Member
1953 Ford with 8ba flat head and Holley 94 carb, stock distributor etc ..
Quick back story on what's been recently changed. Rebuilt carb, new fuel lines and filters, electric pump with regulator set to . 5 psi. Flushed rad and soldered up a hole in the rad. New oil, new spark plugs, new points, correctly set timing.
Car idled good and drive about 200 miles before this issue popped up at a stop light. It stopped about an hour later. I had some issues with my high idle sticking open a little on the choke so I thought maybe I set the idle with the high idle stuck open so I fixed the high idle sticking and re set my idle and that was it. I drive it 300 miles last weekend and it did it once at a stop light on a really steep hill and that it. Drove 20 miles to a cruise in and when we got to the cruise in it started doing it again and hasn't stopped now.
While driving you don't notice it at all. When you come to an idle it will idle normal for a few seconds and then starts surging to the point that you can nearly see the fan stop. It never dies though. Also while doing this you can hear the voltage regulator clicking. I assumed this was because it was nearly coming to a stop so the regulator was shutting of for a second.
This weekend I plan on checking the vacuum again even though it doesn't seem like a vacuum leak. Also going to swap out the points condenser and pull the bowl and see if there is anything in there.
 
Oh btw, this is my first post but I couldn't have put this car together without the search function on this site.
 
I set fuel pressure at 2.5 with good results You may have a vacuum leak These guys know far more than I do and you'll get it resolved.
 
For sure set the fuel pressure down to 2.5 lb. If that does not fix it, check the carb float level adjustment.
 
drolston said:
For sure set the fuel pressure down to 2.5 lb. If that does not fix it, check the carb float level adjustment.
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I did try to increase the fuel pressure and decrease it without any change. As far as the float level I set it to factory specs when I rebuilt the carb. Are you thinking it's too low or too high? I've never had a float position be an issue until higher throttle positions on other carbs.
 
If lowering the fuel pressure doesn't cure the problem, it's possible the power valve is ruptured, or leaking at the round gasket seal. These carbs were not designed for 5 PSI.
Also, make sure the bottom of the bowl is flat where it attaches to the base. There is maifold vacuum in that cavity and could be a vacuum leak, and also causing the power valve to open before it should.

Sal
 
RuleHard said:
I did try to increase the fuel pressure and decrease it without any change. As far as the float level I set it to factory specs when I rebuilt the carb. Are you thinking it's too low or too high? I've never had a float position be an issue until higher throttle positions on other carbs.
Click to expand...

First, you tried to increase and decrease the fuel pressure without any change. Do you mean that your attempts to adjust the fuel pressure and the fuel pressure stayed at 5 psi, or you adjusted pressure up and down and the surging did not change. In any case, be sure with a pressure gauge that your pressure is at or near 2.5; certainly not over 3.5.

Setting the float level on a 94 is a two part process: float top stop and float bottom stop. Being a bit off on either can cause problems. And if the float has leaked a little internally, or is a little overweight or dented, the mechanical stop adjustments will not actually give you the right fuel level in the bowl.

A low fuel level in the bowl generally will not cause surging at idle, unless it is way too low, in which case it would not run right at speed. If the float level is too high, that is near overflowing the bowl, it could cause surging due to flooding. Do you smell raw gas from the exhaust?

When you had trouble on a steep hill, was the car facing up hill or down hill?
 
drolston said:
First, you tried to increase and decrease the fuel pressure without any change. Do you mean that your attempts to adjust the fuel pressure and the fuel pressure stayed at 5 psi, or you adjusted pressure up and down and the surging did not change. In any case, be sure with a pressure gauge that your pressure is at or near 2.5; certainly not over 3.5.

Setting the float level on a 94 is a two part process: float top stop and float bottom stop. Being a bit off on either can cause problems. And if the float has leaked a little internally, or is a little overweight or dented, the mechanical stop adjustments will not actually give you the right fuel level in the bowl.

A low fuel level in the bowl generally will not cause surging at idle, unless it is way too low, in which case it would not run right at speed. If the float level is too high, that is near overflowing the bowl, it could cause surging due to flooding. Do you smell raw gas from the exhaust?

When you had trouble on a steep hill, was the car facing up hill or down hill?
Click to expand...
Firstly to clear this up the fuel pressure is at .5 psi not 5 psi. Turning the pressure up to 2 and down to 0 had no effect on the surging.
I was facing up on the hill. Float was not saved in anyway when I tore the carb apart. I'm worried a out the quality of the material in the kit. The accel.pump has already started to fail so now I'm concerned it's something else in the kit such as the float needle.
 
flatjack9 said:
.5 is too low.
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I've read suggestions from . 5 to 2.5. I started on the low side and would add some if it needed it. I put 800 miles on the car with an issue with it being at .5 psi so I'm not saying your wrong but it's certainly working. The surging issue is only at idle and the car runs great other than that. Fuel pressure being low would certainly be a bigger issue at speed under load.
 
drolston said:
First, you tried to increase and decrease the fuel pressure without any change. Do you mean that your attempts to adjust the fuel pressure and the fuel pressure stayed at 5 psi, or you adjusted pressure up and down and the surging did not change. In any case, be sure with a pressure gauge that your pressure is at or near 2.5; certainly not over 3.5.

Setting the float level on a 94 is a two part process: float top stop and float bottom stop. Being a bit off on either can cause problems. And if the float has leaked a little internally, or is a little overweight or dented, the mechanical stop adjustments will not actually give you the right fuel level in the bowl.

A low fuel level in the bowl generally will not cause surging at idle, unless it is way too low, in which case it would not run right at speed. If the float level is too high, that is near overflowing the bowl, it could cause surging due to flooding. Do you smell raw gas from the exhaust?

When you had trouble on a steep hill, was the car facing up hill or down hill?
Click to expand...
I'll have to dig for some better info on setting the float level. The setting I used had only a high setting and not low.
 
If you want to get this solved in the best and fastest way, I would suggest you send your carburetor to a member here who goes by "Charlie ny". He has lots of experience with these and will rebuild it, test run it and return it in perfect shape. After you've been around for a while, you will certainly become aware of his reputation for quality work and fast turn around.

His service is simply the best.
 
tubman said:
If you want to get this solved in the best and fastest way, I would suggest you send your carburetor to a member here who goes by "Charlie ny". He has lots of experience with these and will rebuild it, test run it and return it in perfect shape. After you've been around for a while, you will certainly become aware of his reputation for quality work and fast turn around.

His service is simply the best.
Click to expand...

Sounds like a good guy and I'm sure he does great work but I've rebuilt a lot of carbs and this one is pretty simple compared to most. Other than the float level and throttle shaft seals there isn't much to mess up.ibe got a fair amount of equipment I've picked up over the years just for cleaning carbs so I like to use them.
 
I had a similar issue with a Holley 4 barrel. Wouldn't idle , but would run down the road just fine. Changed the inlet needle, problem solved. Easy thing to change' Try it.
 
flatjack9 said:
I had a similar issue with a Holley 4 barrel. Wouldn't idle , but would run down the road just fine. Changed the inlet needle, problem solved. Easy thing to change' Try it.
Click to expand...

By inlet needle you mean the needle valve that shut fuel off when the float rises? If so that's what I'm leaning towards. The in in there is brand new but as I said the accep pump has already failed so I wouldn't be surprised.
 
Yes that's what I mean. Also, when you put a new needle in I would up your pressure to 2.5 psi. I prefer the old steel tipped needles as opposed to the rubber tips for just this reason, especially if you are using ethanol gas.
 
Another thing to ponder is heat in the engine compartment.

I've had situations where I was boiling the gas in the fuel bowl and causing all sorts of issues. When going down the road a lot more air is circulating and more (cooler) fuel is coming into the carb.

You may be in a sort of "vapor lock" type of situation (partially).
 
One problem that plagues a lot of guys is the one where a question is asked, then the answers offered are discounted, because what could possibly go wrong with such a simple device.
 
Bored&Stroked said:
Another thing to ponder is heat in the engine compartment.

I've had situations where I was boiling the gas in the fuel bowl and causing all sorts of issues. When going down the road a lot more air is circulating and more (cooler) fuel is coming into the carb.

You may be in a sort of "vapor lock" type of situation (partially).
Click to expand...

I've seen a lot of guys running the insulated carb spacers but I'm not sure what the symptom of partially vapor locked bowl is. I've had carbs vapor lock on certain rides but this is an interesting thought with the cast iron intake and carb base.
 
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