Hesitation

[Robbie693]

Hi all,

My plus 2 has developed an annoying hesitation problem on small throttle openings. Driving around town in traffic I get stutters when coming back on the throttle and when the engine is labouring (going up hills etc). Also sometimes there is a hiccough around 1800rpm on a constant throttle.

The engine pulls fine on wide throttle openings and picks up cleanly from idle when I rev it. The idle seems a bit rough - constant but seems to vibrate more than usual..

I had Paul Matty set the carbs up about a month ago and they also fitted a new 43D4 distributor. I don't think it was giving these problems when I got it back but has developed since. They fitted a new throttle cable which was very stiff so driving smoothly was tricky anyway until I lubricated it.

Checked the points gap - ok and the timing is set to 12deg static. (it's an S/130). Running on Shell Optimax with Millers VSP additive.

Paul suggests it may be sediment in the jets sucked up from the tank (it has run low on fuel on a couple of occasions), I'm going to be on holiday for a couple of weeks so would like some other suggestions to try if cleaning the jets doesn't work (no internet at home )

Any ideas please?

Cheers

Robbie

[steveww]

That sort of hesitation is usually down to the mixture leaning out. This sort of goes with the possibility of the progression jets being blocked.

Do you have a filter between tank and carbs? If so it would be worth having a look at it and see how mucky it is. Lots of muck in there would also back up the idea of obscured jets.

[Robbie693]

Thanks Steve,

No filter as far as I know.

I forgot to mention, I took the plugs out and 1 and 3 are chocolate brown in colour and 2 and 4 are black...

[65 Lotus]

Yah, it sure sounds like progression hole difficulty in some fashion. Unscrew the brass plugs and have a look using a flashlight (torch?). Also have a look at the idle jet blockage as suggested. Leaking idle jet threads could also be a culprit.

Does it still idle ok under no load?

[bill308]

What carbs are fitted?

Ensure the ignition timming (including advance mechanism) are working properly.

Check the float system and fuel pressure.

Assuming Webers or Dellortos are fitted, check the accelerator pump circuit. Look for a barrel not delivering enough (or different) fuel discharge. Also look for blockages in the idle circuit like small bits of fuel hose or rust.

Check balance. An SK meter, or better yet, a mecury based manometer system, measuring manifold vacuum, is best. If all this is ok, then start looking at the idle/transition circuit. Idle should be steady. Use a colortune or A/F sensor if possible. If idle mixture is too lean, it can affect the tansition circuit. If idle mixture is ok (should be at least marginal yellow with a color tune), increase the idle jet one size richer and see if this helps.

I hope this helps.

Bill

[steveww]

Thanks Steve,

No filter as far as I know.

I forgot to mention, I took the plugs out and 1 and 3 are chocolate brown in colour and 2 and 4 are black...

If you really don't have a fuel filter fitted I would fit one right away. To be sure if you have the original mechanical fuel pump the filter is in the glass bowl underneath pump.

[Robbie693]

Thanks for the replys,

It idles ok under no load and steady, just seems a bit lumpy with some vibration but nothing major.

Carbs are Dellortos

I should get a filter, the pump is the later replacement type without the glass bowl.

I would have thought the jets sizes are ok as it was fine a while ago, just started playing up in the last few weeks. Same for the advance mechanism as the distributor is brand new - will check this anyway.

As Paul Matty's have a lot of experience setting up carbs I was thinking the idle mixtures are ok also, but then why aren't the plugs all the same colour?

Cheers

Robbie