surging on overrun

[andy198712]

Got a 2110 with oval ported 40x35 heads and 9.3:1 compression with a 86b cam.

currently running a 34 pict3 with stock end casting (no match ported)

160 main jet and about a 60 idle.

i can't get it to idle with the throttle plate set as is (although just changed the ignition map so maybe will try again)

but i have the idle adjuster on the side wound out very far and the fast idle screw opening the throttle plate a bit (bad i know) and i get a nice stock ish idle.

This is all just till i got FI and to run it in, but i just replaced the stinger with quiet pack and i'm finding on over run i'm getting a sort of surging at about 2-2.3krpm and below which is very annoying! bit like a jerking
also a little bucking at times at low rpm too.

Now i know this is askin a lot from this carb and the mis match of inlet port to end casting, but is there a way i can tune this out a little more, WOT it feels strong i've dropped back to 26 advance at full throttle as it sounded like i was getting some pinging (not on premium fuel yet but will try that next)

Any ideas?
open the idle jet up some more?

Cheers

Andy

PS ignition is via megasquirt

[Clonebug]

Try bumping idle advance to 12-14 degrees and see if you can get the throttle plate closed again.
That way you can adjust the idle mixture.

With the throttle plate open you are running on the progression circuit which is not good for tuning.

[andy198712]

Try bumping idle advance to 12-14 degrees and see if you can get the throttle plate closed again.
That way you can adjust the idle mixture.

With the throttle plate open you are running on the progression circuit which is not good for tuning.

i forget what i've got it on at the moment, is it a case that more advance will increase my idle speed?

i use the row under my idle speed to bump up the advance to hold my idle (instead of using a choke) if that makes sense....

i agree i need to get that throttle plate closed though!
cheers buddy

[Clonebug]

Increasing idle advance will raise idle speed.
If you need to you can set cranking advance lower and increase just the idle portion.
On my FI I was at 12-14 advance also.
Not sure where I am at now since I haven't hooked up the computer in quite some time.
That's the nice thing about these ECU's.... You can try any timing you want and change it back if you don't get the results you were hoping for.

[andy198712]

indeed!

i'm at 13 already between 1000 and 1500rpm which bumps to 17 at 900 rpm to hold the idle but can try bumping that up. tbh i haven't checked actual timing yet since making my new trigger setup so need to check that over.

today i rebuilt the carb again, got the throttle plate set correct now, but the idle speed screw doesn't really effect it, i had it out as far as i can, till it was loose and although it kinda sped up it wasn't enough.... is that too small idle jet?

i put my hand over the carb and it died quickly and spray checked for leaks and nothing...


cheers bud

[Clonebug]

Edited my post so it actually makes sense.....

I forgot what carb you are running.
Although they all have their quirks....
When I ran the 34 pict it idled very nice with the crank fired ignition.

Edit

I see it in the first post now.......

It could be the cam duration causing some of it..... But I would check your intake boots carefully and the rest for any vacuum leaks.

[andy198712]

Edited my post so it actually makes sense.....

I forgot what carb you are running.
Although they all have their quirks....
When I ran the 34 pict it idled very nice with the crank fired ignition.

Edit

I see it in the first post now.......

It could be the cam duration causing some of it..... But I would check your intake boots carefully and the rest for any vacuum leaks.

new rubber boots, but i think a lot has to do wit the lady cam for a single carb! just think it can't give me enough air for what i need maybe.... TBH its only short term hopefully get FI up and running next month!

i learnt that lesson from you

[Clonebug]

Edited my post so it actually makes sense.....

I forgot what carb you are running.
Although they all have their quirks....
When I ran the 34 pict it idled very nice with the crank fired ignition.

Edit

I see it in the first post now.......

It could be the cam duration causing some of it..... But I would check your intake boots carefully and the rest for any vacuum leaks.

new rubber boots, but i think a lot has to do wit the lady cam for a single carb! just think it can't give me enough air for what i need maybe.... TBH its only short term hopefully get FI up and running next month!

i learnt that lesson from you

It just took me a lot longer to change.......It must be the Friesian in me.

[andy198712]

i keep thinking i can tweak the carb more and more... and then i remind me self to spend that time going FI!

[andy198712]

So I fitted my plx afr in prep for EFI and it's saying lean at idle, as in LEAN when cold and about 15:1 or worse when warm but that was only on a short drive, the slight throttle say 2000rpm cruise is about 12:1 , wot is high 12's to 13.2 I think...
Higher rpm cruise is ok I think....
Odd thing is idle is so lean but slight throttle is rich....
I'm thinking plug the throttle plate hole to suck more fuel through at idle and then I can close out the throttle plate as it should be....
Or make the idle jet bigger but it's already about .63mm

Makes sense in my head to cover that hole.


Makes more sense to go efi lol but I got a to wait till pay day and I like to tinker!
Even tempted to connect up the auto choke! Cold it needs about 2krpm to pull away without dying. And doesn't like to idles for a while...