The V8 Owners Forum -

Hi Guys,

I've been watching the "Edelbrock 500 jets n stuff" thread and used the info there to change my step-up springs to great benefit on tickover.

However tickover cold(ish) runs 8-900rpm going up to 1000-1100rpm warm but when throttle is closed rpm only drops slowly and sometime 'hangs' around the 1500rpm mark!

Any clues?

Cheers,

Ian

One of the reasons that the revs can takes ages to drop is because the AFR at tickover is too lean. Having said that your description sounds like it's too bad to be just the AFR. What are the pilot screws set to?


Edit... I noticed that you are running one of the newer 650 carbs, bear in mind that the jets and rods that I've recommended in the other thread probably won't be right for your carb! (I'm sure that you knew that!)

What are the pilot screws set to?

God knows

I had it over to Slark Racing and on his rolling road and he set the pilot screws. I was on my way to the Pod the next weekend and we worked out the AFR @ WOT was spot on and then he just fiddled with the springs which seemed to cure some pinking on acceleration??

With the high lift and long duration cam I've got it's never going to run great at low speeds but I'm just a bit fed up of having to drop the revs by trying to stall it on the clutch. I'm fitting EFI this winter (well that's the plan) and I'd like to get the carb as well set up as possible just in case I have to retreat from the EFI due to terminal stupidity or something similar.

I've changed nothing but the step-up springs, going from silver down to blue which has certainly reduced the smell of unburnt fuel at tickover.

kev_the_mole wrote:

What are the pilot screws set to?

God knows

I had it over to Slark Racing and on his rolling road and he set the pilot screws. I was on my way to the Pod the next weekend and we worked out the AFR @ WOT was spot on and then he just fiddled with the springs which seemed to cure some pinking on acceleration??

With the high lift and long duration cam I've got it's never going to run great at low speeds but I'm just a bit fed up of having to drop the revs by trying to stall it on the clutch. I'm fitting EFI this winter (well that's the plan) and I'd like to get the carb as well set up as possible just in case I have to retreat from the EFI due to terminal stupidity or something similar.

I've changed nothing but the step-up springs, going from silver down to blue which has certainly reduced the smell of unburnt fuel at tickover.

Hi Kev,


Like I said it does sound a bit too bad to be just a lean AFR at tickover but you never know. You should make a note of how many turns out each screw is down to the last 1/8 of a turn. You could then have a go a setting them up as per the article that I wrote in the link below. My stuff is below the fuel pump gumph and its more about RV8 lumps than SBC lumps put the principles are the same!

If you cock the whole thing up you can just put the screws back to where they were before you started!

http://how-to-build-a-pilgrim-sumo.wiki ... ing-system

Regards,

Pete

Diamond geezer

Ian,

Just a thought, I had a similar problem on my Edelbrock 500 when the engine was fairly hot and found that the throttle wasn't completely closing to idle position.

Could have been heat expansion causing more friction on the throttle spindles.

When it's doing it check that the throttle is actually closed, it may just need a bit more tension on the return spring.

Kevin.

The return spring fitted to the carb is no way strong enough on its own, that's for sure!

I was thinking about this post on the train, do the revs eventually drop to the 800 RPM tickover or (whatever its set to) when the engine is hot do they always stay up high?

The reason that I ask is because the tickover really can only be set to 800 when the engine is hot. If you set it when the engine is cold the tickover is bound to go a few hundred RPM as the higher as the engine warm up. (That's why I run with the manual fast idle system connected but the choke plate removed) (sorry if I'm teaching you to suck eggs!)

The lean mixture 'clinging on to revs' thing shows in the form of the engine staying maybe 50-100 RPM too high when the throttle is closed for about 2-3 seconds before eventually settling down to the true tickover speed. BTW if the motor is rich, the revs fall below the tickover speed then climb back up after a couple of seconds.

Edit...Reading your first post again 1500 RPM is way too high for a mixture thing, I'm with Kevin on this one.....your throttle is sticking open!

Mind you, still worth checking out the mixture screws anyway.

Pete

Thanks for this guys

It'll go a bit quiet for a week as I'm off to Australia for the company (6-day round trip so it's not a holiday in any sense of the word) so I'll put your good advice when I get back and then start asking more dumb questions

Cheers,

Ian