"Surging"

adamjack

Member
This is an odd one ,but I will describe what my car is doing

When I pull away ,it feels like the car is hesitant ,but once it is up to speed it is fine ,but below 30 it seems intermittent,almost like the power is coming on and off ,it feels like it is something to do with the propshaft .

If I rev the engine at standstill it will not misfire ,so I don't think it is an ignition/fuelling issue


Thanks

Adam
 
Revving the engine at a standstill won't put the same load on as driving the car. What engine? What makes you think it's the propshaft at fault?
 
Revving the engine at a standstill won't put the same load on as driving the car. What engine? What makes you think it's the propshaft at fault?
Hi Harvey

It is a 1972 3500 converted to 5spd manual ,it feels like the issue is coming from the rear ,not the front of the car ,it is difficult to explain ,I had the UV joints replaced a few years ago ,so I am wondering if it is a balance issue with the propshaft .
 
Balance issues, including misalignment of the sliding joint, would cause a vibration rather than causing the car to "surge" in the way that I would define surging. I'd definitely check the alignment arrows on the prop though, because if you didn't do the conversion yourself, most people would align the yokes rather than the arrows, and that is incorrect.
 
Sounds like a restriction in the fuel system to me. Like it's going lean and bogging down.

I had this problem with 'Hazel' (Ser 1 V8) many years ago & also a few months ago. It was simply a dirty fuel filter each time & the problem disappeared when I renewed it :)

The difficulty is to find a genuine filter as the aftermarket ones don't seem to fit / seal very well (that's my experience, anyway...) :(
 
Oh the Weber 500, I still have nightmares about mine. The way I sorted my fueling issues with it was to remove it from the car, and fit fuel injection :oops:

Anyhoo, if it's fine after the initial accelration, then it could be the metering rods aren't lifting quickly enough. Check your springs are the same both sides, and maybe try different ones to see if it improves it. A stronger spring will allow the rod to lift quicker under acceleration/pulling away from rest.

Alternatively, it could be the accelerator pump. Have you tuned this bit, as too little from this pump will cause hesitation. It may also cause hesitation if it's too much as well, just to make life interesting :)

What pressure is your regulator set at?

Before all of that, do what Phil says and check filters, etc.
 
I recently fitted a four barrel to my engine and was concerned about fuel delivery being adequate. I managed to find some figures on a powerboat site giving fuel consumption for a 5 litre V8 at WOT being roughly 16 galls per hour. So I disconnected the fuel pipe at the carb and timed how long it took to pump a gallon into a jug - 3 minutes which is 20 gallons per hour. This is using a Facet cube pump ( a higher flow rate one )
So the point is, it is not so much fuel pressure, it is flow rate, or volume that needs checking as well once you move away from a stock set up. With an electric pump it is easy to check and if you take the pipe off at the carb it will show up blocked filters, kinked pipes etc along the way.

Of course some carbs are sensitive to fuel pressure, and changing the pressure will change the fuel height in the float bowls. So after the pressure is set then checking the flow will confirm if there is adequate supply.
 
Good point Mark, which also reminds me that the float height on the weber is very important. Make sure it's exactly 7/16" as this does apparently make quite a difference.
 
I am fairly certain that derby police are using this 'manufactured' tyre to promote awareness of sidewall bulges. It's not real :)
 
I did a job for a mate of mine back in the day, a mini with a strange regular thump from the rear of the car. It was a bulge on the inside of the OSR tyre big enough to hit the radius arm each time it went past...
 
It turns out it isn't a tyre and doesn't seem to be related to fuelling issues ,it feels more like a propshaft balance problem .
 
Hi, In that case it could be a U/J partially seizing, so drop one end of each of the three shafts and move the joint around and feel for any stiffness. Do the propshaft first because the units each end don't move around much relative to each other and the joints can freeze.

Colin
 
Hi, In that case it could be a U/J partially seizing, so drop one end of each of the three shafts and move the joint around and feel for any stiffness. Do the propshaft first because the units each end don't move around much relative to each other and the joints can freeze.

Colin
I will give this a try ,as the car hasn't had much use over the last few months maybe one UJ is sticking ,they have all been replaced in the last five years or so ,so they are not worn .
 
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