Fixed - Popping through twin HPMX (IDF) Carbs

[T25Convert]

Hi,

When I rebuilt my engine (500 miles ago now!) I took a punt with some EMPI HPMX carbs, despite rather mixed reviews.

From day 1 they popped off idle (particularly no 2 and 4 but almost never 1 and 3), so I went through all the following:

1) Thought, ha, running lean and upped the idle jets (to 57's). Felt smug until I started it and it was still popping.

2) Two hydraulic tappets drained down, so had the whole lot out and replaced. Still popping.

3) Found split wire off hall sender plug - rewired. Still popping.

4) Foolishly I had tied my fuel lines to the water pipes - got very hot. Relocated. Still popping.

5) Balance, balanced and balanced carbs again. Still popping.

6) Cleaned idle circuits. Still popping.

7) Checked timing again. Still popping.

8 ) Read post on the Samba that said carb popping is always timing related or exceptionally lean.Bought shiny new timing light with advance features and checked advance at various RPM. All fine. Still popping.

As I watched the timing I noticed that the mark 'jumped' every now and again, accompanied by the pop. So popped the cap off the dizzy and found that the rotor arm and cap where both knackered, despite having only done about 500 miles. No 3 contact had a chunk missing and the carbon pick-up was badly worn. As a result, the end of the rotor arm was badly scarred. Put an old cap and arm on and the pop has gone.

So, moral of the story is popping in carbs may be timing related and some new parts are poo.

Hope this helps someone!

Cheers,

Alex

[what2do]

Helpful post, succinct and confirms that we often overlook the obvious. Well done you.