Jetting

Hey Guys

I have my engine on a run stand and trying to dial in some good jetting. The motor has always run rich. The spark plugs get black pretty fast. Looking for some thoughts on jetting.

I my setup that I have been running since I built the 2276 motor with Panchito heads is as follows:

Dual 44 IDFs
Idle jet 60
Main 145
A/C 200
ET F11

Motor runs good with this set but very rich. No hesitations or flat spots A/F ratio ranges between 10 at idle and 12 to 13 on light throttle. I have not really check how the mains are running.

I tried going down to 57 Idle. I can get it to idle fine but the A/F ratio is down in the 11's (rich). When I slowly raise the engine speed it starts to go lean 15 to 16 and starts popping. I am staying in the idle circuit not going above 1800 RPM with light throttle.

I have good collection of main jets ranging from 145 to 160 and air correction jets from 200 to 175. I also have 55 idle jets.

I am not sure if the A/R ratio would be different with the engine under load vs running on a stand.

Any thought or recommendation would be welcome

Thanks

4/29/225:41 PM

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Original Post

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Gordon NicholsMassachusetts 1993 CMC Supporting Member

Any idea what size the main venturiis are?

4/30/224:37 AM

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Bobby D Supporting Member

Gordon the centuries are 36mm

4/30/226:15 AM

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Gordon NicholsMassachusetts 1993 CMC Supporting Member

Try dropping them down to 34s - Maybe even 32s, but on a 2276 I think the sweet spot will be 34s. The smaller venturiis cause a little more vacuum to increase the fuel flow through the transition ports to overcome stumbling. At least that's my experience.

That should allow you to run smaller idle jets and not have a dead spot in the transition.

If you jet it up on an engine stand you'll probably be re-jetting it when the engine goes in a car - it'll always act a little different under load.

4/30/227:35 AM

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Panhandle Bob'57 VS Supporting Member

Really, wait until it's in the car and under load. you will save frustration and time.

4/30/227:38 AM

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DannyP

Gordon, I think you're wrong here. The Panchitos flow all too well. I'll bet they don't flow quite as well as my heads(the valves and ports are small on the Panchitos: 40 x 35). My valves are 44 x 37.

34mm venturis on a 2276: too small. I'd go with 36, maybe even 38mm.

I had 36mm on a 2165 and they are the perfect size with 44 IDF carbs.

Before wasting everybody's time with any more of this:

You cannot get an engine to proper running temps on a stand.

And I'm only going to say this once:

You can't jet an engine running on a stand.

You can only jet an engine under load, either in a car or on a dyno. Period.

4/30/227:42 AM