Carburetor Fine Tuning, Trying to get my dual EMPI HPMX 44's as close to perfect as possible - Now running Spanish Weber 48 IDF's... Options

[rhodyguy]

excellent. (IMG:style_emoticons/default/cheer.gif)

[rgalla9146]

Great thread
What AFR equipment are you using ?
Two Ox sensors ?

[sgetsiv]

I'm running the wideband AEM AFR - got it on Ebay for just under two clams.
http://www.aemelectronics.com/?q=products/...-uego-afr-gauge

Just one sensor in the headers after the pipes come together, well before the muffler.

[72hardtop]

You want to actually see how well you have the jetting? Remove you main jet stacks (all of it) and drive around on the idle jets only for a couple days. This will absolutely tell you when and where the idle jets fall on their face. Once that's done go a larger size or two on the mains and start adjusting the mains down.

Don't be surprised if you find you need a 47.5 idle at or near sea level.

Are you using an LM-2?

[sgetsiv]

Once that's done go a larger size or two on the mains and start adjusting the mains down.

? Did you mean go a size or two larger on the AC's?

I do have 50 idle jets handy so I can test those out sometime soon.

[72hardtop]

Once that's done go a larger size or two on the mains and start adjusting the mains down.

? Did you mean go a size or two larger on the AC's?

I do have 50 idle jets handy so I can test those out sometime soon.

Mains...larger on the mains. Then work down on them. As for your air correctors start with 190 - 200. Always start with the idles when jetting. When done with them go to the mains. Be sure and remove the main jet stacks and drive around with them removed...you'll be surprised how far you can get on the idles. Since you have 44's stay with the 52 idles for now. When ever you make a change only make (1) at a time then drive it.

[sgetsiv]

On a hunch that the transition circuits were likely plugged up I decided to replace the EMPI's with a pair of Spanish Weber IDF's. After discussion with CB and a very strong recommendation by them to go with 48's instead of 44's, I went ahead and ordered a pair of 48's.

First impression, WOW! What have I been missing!! My Raby 2316 loves the 48's. Top end is much stronger and it really feels like the low end is better as well. Transition is good, drivability is not an issue.

I started out with the factory jetting - 55 idles, 150 mains, 180 air corrections. It was rich in the main circuit, like 10-12 on my wide band AFR. I switched the AC's to 200's and then switched the idles to 57's. Very, very nice, but a touch lean on decel and in transition. I kept it this way for a week and waited for 60 idles to arrive.

Put in the 60 idles yesterday - way too rich. Amazing that such a small change could make such a difference. The transition was close to perfect but it was just way too rich throughout the entire RPM range. We are talking AFR's of 11-12 under load.

Back to the 57 idles today. With the 57's, the AFR reads 13-14 under load.

I also added a second light spring on the linkage (running the McMark linkage) and I can get the engine to idle smoothly as low as 500 rpm's. With a really low idle, the engine didn't coast very well on downhills - a bit of back firing. At a 700-720 idle, and an extra quarter turn open from fastest idle on the idle mixture screws, the engine coasts without any back firing.

I might try the 180 AC's again next. Not sure they will have any effect at all on the transition or coasting...

I think it's time to buy a jet gauge and measure everything. I'm shocked that going from a 57 to a 60 idle would make such a difference. Gotta measure and verify.

[72hardtop]

On a hunch that the transition circuits were likely plugged up I decided to replace the EMPI's with a pair of Spanish Weber IDF's. After discussion with CB and a very strong recommendation by them to go with 48's instead of 44's, I went ahead and ordered a pair of 48's.

First impression, WOW! What have I been missing!! My Raby 2316 loves the 48's. Top end is much stronger and it really feels like the low end is better as well. Transition is good, drivability is not an issue.

I started out with the factory jetting - 55 idles, 150 mains, 180 air corrections. It was rich in the main circuit, like 10-12 on my wide band AFR. I switched the AC's to 200's and then switched the idles to 57's. Very, very nice, but a touch lean on decel and in transition. I kept it this way for a week and waited for 60 idles to arrive.

Put in the 60 idles yesterday - way too rich. Amazing that such a small change could make such a difference. The transition was close to perfect but it was just way too rich throughout the entire RPM range. We are talking AFR's of 11-12 under load.

Back to the 57 idles today. With the 57's, the AFR reads 13-14 under load.

I also added a second light spring on the linkage (running the McMark linkage) and I can get the engine to idle smoothly as low as 500 rpm's. With a really low idle, the engine didn't coast very well on downhills - a bit of back firing. At a 700-720 idle, and an extra quarter turn open from fastest idle on the idle mixture screws, the engine coasts without any back firing.

I might try the 180 AC's again next. Not sure they will have any effect at all on the transition or coasting...

I think it's time to buy a jet gauge and measure everything. I'm shocked that going from a 57 to a 60 idle would make such a difference. Gotta measure and verify.

Put in a 190 for your air correctors. As for being lean during no load or transition don't worry about that. Normal. What is important is WOT and steady pedal state. Don't let it hang at 14.7...Danger zone!

Under load shoot for 12.5 - 13.2 or so.