Jump to content
Sign in to follow this  
dvderlm

idle jet holders

Recommended Posts

dvderlm

I moved away from Momentum99 with 5% ethanol, but I think plain Tesco 95 unleaded has now gone ethanol too.

There's a new E5 sticker on the pumps and I've recently  been observing some leaning out about 2000rpm at very light load.

 

Initially I thought my vacuum tubes had gone porous again so replaced these with motorbike vac-tubing. Hesitation is still there.

 

At 2500 the main circuit activates and the pump jet will cover some of it but it was nicer. So I need to stretch the idle jet range a bit higher. 

 

It has been  using 43 idles in 7850.1 holders giving 14.9:1 idle and cruise at 15.3 to 16.4 (so economical for twin carbs thanks to manifold pressure mapped ignition advance).(yes I know it is colder).

I've previously tried 45 in .1 holders and that wass too rich. 

 

So today I tried 40 in .3 holders with mixture screw a fraction more open.

No, far too rich. Like 9.7:1 black smoke. 

So switched back to the 43 in .1 holders... and it went too rich in motion at cruise like 12.7:1 and chugging like 3 cylinders unless on the main circuit..

 

Adjusted mixture screws back to more closed and still wont go below 12.2 AT IDLE.

I think some crud has blocked a passage way. 

 

Oh and I lost a jet cover screw... sure hope that is not the blockage...

 

Share this post


Link to post
Share on other sites
dvderlm

Not looked at it yet, but ordered a replacement jet cover screw and some 44 idles.

And got some 38 idles to try in the .3 holders.

The GK Pierburg 2e3 has 38 idle for its 22mm primary choke.

 

Don't think the lost cover screw could fall inside the carb.

Not sure which passage would block to cause rich symptoms on idle circuit.

Perhaps starter circuit is leaking?

 

Must check the plugs for clues.

 

Edited by dvderlm

Share this post


Link to post
Share on other sites
dvderlm

Put some Startron 143 additive in the carb wells about 1ml per carb (and in the tank) 3 days ago. Just in case it's Ethanol crusting again.
It needs 30ml per 23 litres. https://www.starbrite.com/startron

 

#3 cylinder's spark plug was quite black n sooty. 1 and 2 were good clean just off-white. Could not be bothered looking at number 4 plug as the brake servo vacuum take-off is always a bit in the way.

3 was clearly fouled for far too rich.

I use Beru UX56 plugs which have 2 pairs of earth electrodes. I wonder if one of the lower (or higher) become more active at higher piston speeds with more swirl and squish?

Or just that main circuit is leaner than the fattened idle so would clean the plug until eased off the throttle?

 

Anyway - fitted 44 idles in the .1 holders. And the new cover-screw (after dropping it on the ground and finding it again).

 

Set number 3 idle mixture screw to 3 turns out approximately matching other cylinders. Would idle on the starter circuit, but not hold idle if I opened throttle gently. Push quickly for pump jet and it would die quickly too.

Went up to 3.5 turns out and opened 1 and 2 a bit and it idles fairly smooth at 13.8 to 14:1 and does not die if throttle opened gently or pedal stabbed.

 

Ran out of daylight.

Will need to get it up to operational temp and reset idle speed and mixture down a bit. Might even need some more idle bypass air.

Can't use flowmeter with the Dergo filters so differential vacuum manometer or 4x vac gauges.

Then see whether progression phase light throttle  is improved over 2000rpm.

 

If not try again starting with the 38 in .3 holders. 

Otherwise advance ignition map back to the Momentum99 settings.

 

Share this post


Link to post
Share on other sites
dvderlm

Nope 3.5 turns not enough with 44 in .1 holders. Would start from cold on starter circuit, but die as soon as touched gas pedal once a little warmed and starter pushed in. Could not pull away. Went to about 4.5 turns, reduced tickover rpm back to 900 ish and backed off mixtures for 14.6 idle fair vacuum and with 4 smooth regular pulses at tail pipe.

 

It'll need 4x vac gauges to get perfect balance I think. Can even go a bit richer then maybe use idle by-pass circuits to compensate back to reasonable when throttle fully closed. But so far just gently applying throttle feels smoother with no load.

 

Edited by dvderlm

Share this post


Link to post
Share on other sites
dvderlm

44 in .1 holders feels better in motion than 43. Amazing that 2.7% larger orifice can make such a difference. But I guess that matches 5% Ethanol stoich ratio of 14.3 rather than 14.7

 

AFR gauge showing 15s at cruise. As lean as 17 but still smooth in 5th gear 30mph lightest throttle touch down a slight incline, and okay at 2000rpm up, where it was hitting 17.6 or leaner. Slightly unbalanced, engine rock at idle below 1000rpm but no pops of leaning, no rich or lean racing.

 

So balance with idle bypass for best vacuum, then advance ignition degree by degree.

 

Edited by dvderlm

Share this post


Link to post
Share on other sites
dvderlm

Seeing some 18:1 at high vacuum, think it must be ignition advance.

Share this post


Link to post
Share on other sites
dvderlm

Rebalanced. Number 1 cylinder was a bit less vacuum than 2,3 and 4. Gave barrel 2 some idle bypass. Much better idle far smoother and no 18:1. Can reduce idle speed a bit but it then idles a little richer. Not yet sure why. Less air around throttle plate versus fuel via idle mixture hole screw?

 

For the middle and top end with ethanol upped max advance to 32 on the 5 static which gives 37 BTDC max. Not yet upped the "centrifugal" applied from 3500rpm.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. Terms of Use Privacy Policy Guidelines