Hesitation During acceleration

VaCat33

VaCat33

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Hi All

An unseasonable 70 degrees here today, so I took the Tiger for a cruise. Went about 20 miles with some traffic at the end. By the end of the cruise temp was in the 200-205 range, about normal for driving in traffic. When accelerating from the last few lights, the engine started hesitating, as if it were starved for fuel. When accelerating at cruising speed everything seemed fine. The hesitation only seemed to occur from a dead stop or slow speed. First problem like this…car has been running well all season. Switched out the fuel filter earlier in the year when I was getting some surging at higher speeds. That fixed that problem.

My first reaction is this is heat related and the fuel is cooking off prematurely, starving the carb at the critical moment (vapor lock like Duke had). I have considered a phenolic spacer in the past, but they do not come any smaller than ½” thick (at least as far as I could find) and that would cause clearance problems with the air cleaner retaining screw.

OBTW...I have a Holley 4160 4v, 465 cfm.

Do you think my diagnosis is correct? Remedies? Or is something else going on?

Thanks, Jim
 
I currently have the same problem in my Shelby--I was told that is my accelerator pump in the Holley--ugh. I was running AvGas this past summer and it sure smelled good, plus it started very easily--but these problems started after about 2 months. A friend was running the same fuel and had the very same problem in his Tiger----we believe it was the fuel ruining the accelerator pumps. He changed his and all is well, I am next.
 
And Again Etc

Find something to contaminate the modern fuel mixes. 4 oz. of Marvy Mystery Oil per 10 gal keeps the seals & other rubber parts pliable. Same amount of Kero or di-icer to slow down the burn on a knock/ping works well also. Of course when they up the corn content, it's all gonna get more interesting . . . . .
 
Yep.....accelerator pump.....maybe. The guy that does my carbs stated the kits for Ford and Holleys are coming with some crapola' parts. He orders some of the parts separately from the kits.

I don't do carbs so that is all I know.

How do you know it is the carburetor? When is the last time ya'all had your distributors restored and re-curved? I don't do those either.
 
Thanks...Sounds as if it is the accelerator pump. Weather is suppose to be nice again tomorrow. I'll take another drive to see if it occurs again.

It was just a gut feel that it was the carb...but for the record, the distributor was recurved in March 2010.

Based upon CAL44's comment, what is the best source for replacement part(s)?

Jim
 
I have heard others recommend Quick Fuel or Barry Grant in the past, but have no direct experience, or affiliation, with either.

Gene
 
Stabil

The perils of formulated gas. Marvel Mystery Oil, Sea Foam I would not call them snake oils but try Stabil on any fuel that you do not use in a short period of time say 60 days. I was in a Mobil yesterday and they too have added the "Contains Ethanol" used to be better fuel.

The use it or loose it applies to carburetors and everything except the Hollywood VW in the old Woody Allen movie Sleeper.
 
Okay…I took the Tiger out for another cruise today. Same route with almost identical results. Car ran great for 90% of the trip. I tested the acceleration from dead stop several times w/o a problem…until right at the end of the trip. While accelerating from the last few lights I had significant hesitation. At one point I thought I would stall.

Is the general consensus still the accelerator pump? Why do things work fine for over 30 minutes of driving and then all of a sudden the hesitation starts?

OBTW…ambient temp was a bit lower today so operating temp barely got over 200, which has never been a problem.

Thanks, Jim
 
In all likelihood you have a blown power valve (AKA "dumper" valve). Just one intake backfire can blow it. Holley carbs are notorious for this. I have seen it a hundred times!
The power valve is a vacuum operated mixture enrichment diaphragm valve. To test it, at idle turn your IDLE mixture screws all the way in, if your engine dies the power valve is not blown.
http://www.google.com/url?q=http://...kQFjAC&usg=AFQjCNHVR24alxw7bAIf1i3rdPbfubS9Ow
 
Holley put in a blowout protection check ball valve in their newer production models. If you do have a blown power valve, your carb can be easily retrofitted to add the protection for the future. HLY-125-500 kit for $13.95, plus handling, from Summit Racing.
 
Perplexed

Hi All

I would like to revisit this issue after taking car for a test drive yesterday. As is often the case with nagging problems, I was unable to recreate the hesitation experienced last week…the car ran fine. When I got home with engine temp at 200 I pulled off the air cleaner and with butterfly open I peered down into the carb while I goosed the throttle lever…gas shot in w/o delay. I then turned in the idle mix screw as recommended by Wag123…the engine began to die.

I did add Sta-Bil last fill up. The only other difference that I can think of is that I refilled tank with Shell Hi-test which is what I normally use…I had refilled with Hess Hi-test twice before the hesitation occurred.

So what say ye? Is accelerator pump or power valve still the prime suspects? Could it be something as simple as some gas it just did not like? I must admit I am hesitant to change anything right now.

Thanks, Jim
 
It appears that your accelerator pump is working and the power valve is good, so you can pretty much rule-out those problems.
It could have been bad/old gas or you could have gotten gas with too much alcohol in it (AKA "oxygenated fuel"). Alcohol contains it's own oxygen and burns leaner, this can cause a hesitation in an old carbureted engine when it gets hot. Also, keep in mind that today's gasoline spoils (like food) and will go bad in 3-4 months untreated and in 8-9 months treated. You can't treat old gas and make it good, you must treat gas when you purchase it. Gasoline looses volatility as it ages and eventually won't burn at all. This combined with the fact that most gas on the market today has at least SOME alcohol in it can cause the kind of problem that you are experiencing.
Also, since your problem is heat related, you could have a "lazy" fuel pump that isn't working well when it gets hot or even an ignition coil that is being affected by the heat (not common). You could also be experiencing fuel boiling in the carburetor which is more prevalent when oxygenated fuel is used. You can purchase a sandwich-type carb insulator that is under 1/4" thick, this will help.
 
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Phenolic spacer

Hi All

Just a quick update. I took the Tiger for a drive today...first time since installing a 1/4" phenolic spacer (fit in with a bit of room to spare.) I also made sure the rubber fuel line was routed out around the outside of the dizzy away from the manifold.

It was only about 60 degrees but I did get caught in some traffic which pushed the temp gauge up to 200-210, which is what I wanted so I could see if the hesitation occurred.

I am happy to report no hesitation when accelerating from dead stop. Hoping that continues through the summer.

Jim
 
Jim,

Glad it has worked out.. told you the spceer was a very cheap and effective fix.... On another note, (not stumble but temp realted) how long did it take stationary for the car take to get up to 210?

When was the last time the radiator was flushed.. the stock tiger system while not great if in correct running order does the job "ok" and a 60 degree day shouldnt be much of an issue for it.
 
Just Flushed

Michael

Took about a half hour to get up to that temp.

The rad was flushed just before this drive...but my bad...I did not notice that I needed some more coolant after I had run the engine after refilling the system. That surely contributed to temp. All topped off now.

Jim
 
Still stumbling

Hi All

Well that did not last long. Took my Tiger out this afternoon. It was a warm 85 degree day here. Once the engine got up near 200 degrees the hesitation and stumbling began...at speed and upon acceleration. At this point, I think I have looked at all the possible fuel related causes. About the only thing left fuel related might be the winter blend fuel (lower ignition point) still in the tank. I am still convinced this is heat related since all is fine for the first 20 minutes or so of cruising.

As a quick recap this is what I have done so far...

1. Tested power valve and acceleration pump as recommended in previous posts....OK
2. Made sure fuel line was well clear of the manifold and sources of heat.
3. Installed phenolic spacer
4. Stock fuel pump replaced one year ago
5. Fuel filter replaced a couple months ago

Is there anything I have missed barring pulling apart the carb.?

So could this be an ignition problem? I have a Pertronics ignition with a standard Ford coil. I believe the Pertronics, coil and new wires were installed in the spring of 2010. Distributor was recurved at that time also. Plugs were inspected less than 6 months ago.

This is starting to frustrate me.:(:mad:

Thanks, Jim
 
Ignition problem?

Several years ago I had a mid range miss most noticeable on acceleration. Drove me to have a pro dial in the carb and adjust the mech advance curve of the new Accel distributor. This was frustrating because it was spoiling my enjoyment of the up HP 260 engine I had built up and recently installed in place of the stock 2V 260. Lots of things were new to the car? What was wrong. Turned out it was the new Accel dual point distributor.

The thing that worked right was replacing the sexy new distributor with a worn out old Ford standard distributor. The miss was gone! The reason was hard to find but the internal ground wire which connects the moving plate with the points to stationary ground did not complete the circuit. Manufactured with the crimp holding only the insulation .. not the wire inside.

My conclusion was that at idle - low rpm the mechanical advance was at the low stops and provided a good ground. Same above a 3,000 rpm or so when the advance was firmly maxed out. In between there was that damn miss and most noticeable with moderate acceleration. I was ecstatic with the engine pulling hard & smooth to 5,000 rpm but the miss drove me crazy until I figured it out.

Rick
 
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Hi Jim,

Like Rick, I am thinking it is ignition as well.

Are the cap and rotor in good shape?

After it starts missing, can you stop the car physically with the motor running and have it miss under throttle reasonably open (say 2500 rpm)? If so you could have someone check for a consistent spark. Or if it has to be a one man operation, temporarily tighten down the idle screw to keep the rpm's up and check for consistent spark yourself.

Or, you could just temporarily remove the Pertronix replace it with points and condensor, set the gap and see if that makes a difference. I personally would look closely at the Pertronix and the coil. Mine went bad on me about two years ago. I vaguely recall reading somewhere that Pertronix had a bad batch of product around that time. Since you are still running a stock coil, it should be compatible with the points set up. You still have the ballast resistor in the circuit with the stock coil right?

If it is the Pertronix, I recommend you upgrade it with a more recent version II or III and add the matching coil for that unit. I know you show your car a lot and want to keep everything as stock looking as possible, so you may not want to change the stock coil. But performance wise it would be better to get the matching Pertronix coil and functionally eliminate the ballast resistor. (It can be kept for appearance purposes, just shorted out internally.) Of course, the coil could also be going bad and the engine heat causing it to act up.

Just some ideas.

Gene
 
Starting with the Coil

Thanks guys.

First to answer some questions.

Yes I have the ballast resistor in play.

My coil is a stock ford coil which was obtained from National Parts Depot. See link.

http://shop.autocraftinvestments.com/products/12029_1A-141831-2871.html

The coil terminals are marked BATT & DIST and that is the way they are presently hooked up. My concern is that since Tigers are Negative Ground and Fords are (I am guessing here) positive, are the terminals reversed. I have read that the engine will still run if terminals are reversed but the spark to the plugs is reduced by almost 50%.

So my question is...should the BATT terminal on my current coil be hooked to the Battery/Resistor...and the the DIST terminal to the Distributor OR the exact opposite.

OR an I thinking too much.

Jim

PS. I saw the pencil test you can do to determine correct polarity but right now I am just trying to noodle this out.
 
Totally Perplexed...Again

Just came back from a cruise. I followed the same exact route as yesterday. Drove about 20 miles in 30 minutes...no traffic. Air temperature was down to 72 from the 85+ degrees it was yesterdy. Accordingly, my car ran in the 190-200 range today...while yesterday it was in the 200-210 (My gauge actually is about -5 degrees off.)

Today it ran absolutely flawlessly. Not a bit of hesitation in any rpm band.

The only variable was a fresh tank of gas (same brand). I asked in the station about summer blend...but the attendant thought they were still pumping the winter mixture.

The only thing I get from this is that there is a point on the thermometer somewhere when heat begins to affect something...ignition, fuel, whatever.

Any more thoughts?

Jim
 
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