19 replies to this topic

[Dusky]

Check the timing and set the contact breaker points gap.

 

If the car is standard it could be a worn needle, but then it will be overfuelling.

[dklawson]

Do you have a tachometer fitted?  If so, what is it doing when the engine stumbles?  Does its needle bounce wildly or slowly sink as you open the throttle?

 

Describe the way the car feels as you have trouble accelerating.  Is it a straining like it has lost power or does the car reach a speed where it cannot go any faster?  When the car is struggling, does it buck and jerk?

 

How long has the car been sitting?  The brown stuff you found in the float bowl are often corrosion byproducts mixed with fuel varnish.  When you find heavy buildup of that it can indicate a need to replace any/all fuel filters fitted.  You can confirm the fuel delivery by disconnecting the supply hose at the carb and aiming it into a catch jar.  Have a friend turn the engine on the starter motor as you watch the fuel flow out of the hose.  A mechanical pump will move fuel in a steady series of pulses.  Electric pumps can deliver either faster pulses or a seemingly continuous stream.

[Revan239]

Timing and points were set the evening previous to this happening dusky appreciate it though!, it's a pain to describe its like I say as if the mixture isn't strong enough when I go out and start it she works first time and will sit ticking over just below 1000 rpm as if all is well but if I think about going near the accelerator it starts to struggle almost, we've definitely narrowed all probable causes down to the carb tonight. Whenever I put my foot down to rev it it starts to hunt like an old tractor, and if I try to power through it she just dies on me, we even tried putting extra petrol down the elbow joint at the back of the carb which should of made it rev it's guts out but it sickened it and it died again, the carb is coming off tomorrow again to be probed by my grandad. I'm contemplating on trying my neighbours 1.5" hs4 on my engine to see if it makes a difference( then at least we can know for sure that it is my carb at fault) and no tachometer fitted, it was a pain in the a**. There is only one fuel filter inline just before the float chamber it's getting replaced anyway and the car has only been sitting for a fortnight not long and we tried the catch jar trick tonight plenty of fuel getting there, the area of fault seems to be between from when the fuel leaves the bottom of the float bowl and when it enters through the manifold so maybe the needle? The only thing that has changed about the carb was that a new wax stat jet was put on in march (we actually needed the rubber seal for the bottom of the float bowl) so that's everything so far, thanks a lot guys!

[dklawson]

Before completely tearing the carb apart, revisit the waxstat jet and the float valve.

 

Start the engine and rev it until the problem surfaces.  While the engine is struggling, turn the key off and release the clutch to stall the engine.  Now remove the 3 screws holding the float bowl lid in place.  Lift the lid off and look at the level of fuel in the bowl.  If the float and valve are working correctly the bowl should be between 1/2 and 2/3 full.  If the level is below 1/2 take a look at float valve blockage and float level settings.

 

Since the waxstat is relatively new, make sure the rubber seal connecting the tube to the float bowl is properly seated.  The seal could be partially blocking the plastic tube.

 

Do all waxstat carbs have spring loaded needles?  If the needle is the fixed type, make sure the jet is centered.

 

If you have not checked this yet, make sure that with the dashpot filler removed from the top of the carb... you can lift the carb piston and drop it.  The piston should be very easy to lift without binding and it should drop to the bridge of the carb landing with a definite "click".   Before refitting the dashpot filler knob to the top of the carb make sure the metal tube in the middle of the carb is full of oil.  People will suggest different types and weights.  The original oil from SU would be straight 20W.

[Revan239]

Okay I'll check those things and get back to you !