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Intermittent miss?

Baz

Yoda
Offline
Clocked about 250 miles yesterday, 5 or 6 times the motor sounded like it was running on 3, full gas pedal will hold a speed, but couldn't accelerate.
If I slowed down and dipped the clutch or change down, it would go away, only to come back several miles later.
My dizzy is rebuilt, carbs are rebuilt and everything else in top notch condition, which led me to believe my fuel pump may be too weak?
Any thoughts on this?
My fuel pump is the same that's been on the car for several years and it had this symptom last year during a long run, which I dismissed as being carbs or diz. I don't know what fuel pump is on it, but all I can see is that it is made in New Zealand.
Not a big deal for driving around town or whatever, just on a long constant (about 60mph) trip.
TIA!
 
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Sounds like a a weak pump or clogged filter/pick up tube.
 
OP
Baz

Baz

Yoda
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I don't have a filter, so I'll try a new pump.
Any recommendations?
If it's a clogged pick up, do I have to pull the tank for that?
 
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Get a filter! Actually two. One before the pump and one before the carbs.

If the new pump doesn't work then you can try gently blowing back into the tank to loosen junk around the pickup tube. However, if that is the problem, then a tank cleaning may be in order.

Every one has their own electric pump preferences so I'll not enter into that debate. However, it is important that the pressure is LOW. Less than 3 psi ... I think.
 

tosoutherncars

Jedi Knight
Offline
Which carbs?

For a low-pressure pump, I went with the Carter 'green' (similar to the early cars' SU pumps in that it's a rotary vane pump.) Others use the Facet (cube) pumps or cheaper knockoff versions, which have the reputation of being loud but reliable.
 

healeyboz

Jedi Knight
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Baz,
I am having a similar issue and currently trying to figure out the problem. I am running a pretty hot motor and am wondering about a few issues. It happened again yesterday and was worse than it has been in the past. I wonder if octane could be a factor??? I noticed yesterday that the fuel gauge was at 1/4 of a tank and wonder if that is a symptom? I limped to the gas station and put premium in the tank. It would only take 5 gallons.... However, before I started the car the fuel pump sounded like it didn't have any fuel in it for a second. I don't know the cause, but with it being intermittent, tests are in order.

I look forward to hearing your results!
 

regularman

Yoda
Offline
I am still having a problem with my weber on a long hard pull or trying to run 70 on the interstate it acts like it is runnng out of gas. Back off on the gas a bit and it catches up and runs fine. It works fine when it is cold. I am starting to think vapor lock. That is where the gas gets too hot in the lines or the float bowl and starts to boil into a gas. The trick and test for that used to be aluminum clothes pins on the fuel line right before the carb, but I have not seen any of those in a long time.
 
OP
Baz

Baz

Yoda
Offline
I'm running stock SU's.
I tried switching octanes yesterday Barry, had less ping with lower octane, but it still had the symptom as described.
I figure if I'm going to do this, I'll do it properly and replace the tank, sender, fuel pump etc and maybe add a little more pressure to the fuel pump.
One thing I thought it sounded like, is the float bowls emptying faster than the pump can replenish, which is why when I back off the gas, similar to Kim, it's fine.
Thinking of vapor lock, has anyone re-routed fuel lines so they're not in the tunnel? I do get some tunnel heat.
 

tosoutherncars

Jedi Knight
Offline
I can't see it being vapour lock at speed... normally that shows itself at low speed and after shutting down while hot, when the gas has a chance to sit and boil from the heat kicked off by the exhaust / header. Much more likely to be a fuel delivery problem of some sort, I think. Do you have excessive hot-start issues?
 

healeyboz

Jedi Knight
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I am experiencing the same symptoms. Vapor lock has been thought as a possibility. I have routed my lines underneath the car and in front of the header.
 

texas_bugeye

Jedi Knight
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healeyboz said:
Baz,
I am having a similar issue and currently trying to figure out the problem. I am running a pretty hot motor and am wondering about a few issues. It happened again yesterday and was worse than it has been in the past. I wonder if octane could be a factor??? I noticed yesterday that the fuel gauge was at 1/4 of a tank and wonder if that is a symptom? I limped to the gas station and put premium in the tank. It would only take 5 gallons.... However, before I started the car the fuel pump sounded like it didn't have any fuel in it for a second. I don't know the cause, but with it being intermittent, tests are in order.

I look forward to hearing your results!
If you are experenceing this problem at about the same consistant tank level it could be the same issue I had in that the pickup tube solder joint in the tank is cracked. Allowing air to be picked up by the pump and pulling dry. If you have a soliniod type pump it will get loud. then quite down when the cr moves and fuel sloshes over the crack allowing for a seal.
 

healeyboz

Jedi Knight
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This is a new tank that I got off of ebay. Do you have the same type? I am wondering if the lack of a baffle is the issue?
 
OP
Baz

Baz

Yoda
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texas_bugeye said:
If you are experenceing this problem at about the same consistant tank level
Hmmm, now that you mention it, about 3/4 of a tank full.
What about you Barry?
 

regularman

Yoda
Offline
Oh wait, guys, one more thing just hit me. Sounds crazy but I remember this on another car with an electric pump. Flow problem can also be related to no fuel vent and all the replacement tanks are now not vented. I think I will go check that my gas cap vent is now working right now while I await parts for my midget. No air in= no fuel out ,or limited air in=limited fuel out. Electric pumps don't have the absolute force from vaccum that way mechanical ones do. One guy had a 36 plymouth with a 20 gallon tank. he drives along and hears a strange pop every once in a while. Keeps on driving. Stops after a long drive to get gas and the tank will only hold 9 gallons. The pump had sucked the tank in because the vent was blocked :lol:
 

Dave Russell

Yoda - R.I.P
Gold
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Baz said:
I'm running stock SU's.
I tried switching octanes yesterday Barry, had less ping with lower octane, but it still had the symptom as described.
Hi Guys,
Be very careful about running lean under power, even just for tests. Lean burn can cause detonation & at higher rpm detonation can happen without hearing pinging. Heard or unheard, detonation can cause serious damage to the engine. At the very minimum, I would do frequent plug readings, cut the engine clean after a fast run, & check for signs of overheated plugs.

Just a caution --
D
 

healeyboz

Jedi Knight
Offline
I wonder?????? I think that I will drive her until it does it again and check the fuel gauge level. I will also pull the cap and drive with her a bit, careful of the level not to spill out the top, and see if that takes care of it. Anyone have a source for a vented fuel cap? Might just try that for starters. The vapor lock is a possibility, might have to wrap the headers as well. I felt the fuel line when it happened yesterday and they were quite warm. Hmmm?
 

jlaird

Great Pumpkin
Country flag
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A peice of alum foil, a rubber band and a small hole.
 

texas_bugeye

Jedi Knight
Offline
So if you were to fillup just as it starts weretalking 2.5 gallons bingo!same problem.. Tank was purchased from VC. To test if it the same problem, with about 3/4 of a tank of gas maybe alittle less Jack up the rear of the car till the rear wheels just come off the ground The problem will clear up. The fuel will submerege the the bulk head fitting exting the tank. now breing the car back on the floor and allow to run long enough to go thru 1 - 2 float refill cycles and it will start starving.If this is the case let me know I have the cure.
 
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