Carb jetting question

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Mar 7, 2013 | 06:43 AM

Thread Starter

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From: Crystal Lake

Carb jetting question

My 54 is running bit lean. It was a California truck, and don't know if the altitude difference requires a change in carb jets. It's an OEM setup. Does anyone know what the best size jets that would work to correct this?

Any help is appreciated.

FP

Mar 7, 2013 | 08:42 AM

ALBUQ F-1

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From: NM

Illinois is about 600 ft ASL, no correction is needed until > 5,000 ft. What makes you think it's running lean?

Mar 7, 2013 | 10:16 AM

Lance Hogan

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From: Charelston, Illinois

I don't know what the stock jetting is for your truck, but you will need to find a jet one size larger to compensate for the ethanol enhanced fuel we get here in Illinois.

Just my 2 cents....

Mar 7, 2013 | 12:25 PM

truckeemtnfords

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From: Fallon,NV & Bainbridge OH

Just because you say a California truck it don't mean anything, I moved from the bay area, CA, at near sea level, to Truckee, CALIFORNIA at 6000' +/- . So jetting varies a lot in CA. If it was jetted for any elevation in CA you could be a little lean. Need more info.

Mar 7, 2013 | 12:59 PM

ALBUQ F-1

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From: NM

It's most likely a dirty carb if it is actually running lean. If it is just not performing well, it could also be bad vacuum advance, a failing fuel pump, a vacuum leak, etc.

Mar 7, 2013 | 01:13 PM

Thread Starter

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From: Crystal Lake

Good point Truck...., us flat landers tend to forget that. The truck was in San Clemente for the last 25 years.

Thanks Albuq, I'll,check that out.

Mar 7, 2013 | 01:37 PM

truckeemtnfords

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From: Fallon,NV & Bainbridge OH

That is pretty low elevation wise so if it was jetted right there it should be close for where you are at. But like Ross said if it sat at all it could have crap building up in passages. Take the carb apart blow some carb cleaner and air through it and try it again.

Mar 7, 2013 | 04:39 PM

ALBUQ F-1

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From: NM

What exactly are the symptoms? Have you checked the spark plugs? How is the color? Stock jets should be #51 or #52.

Mar 7, 2013 | 04:48 PM

#10

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From: Crystal Lake

The truck will backfire a bit, but if I pull up on the choke a little it's fine. Plugs have been replaced.

Thanks guys.

Mar 7, 2013 | 05:21 PM

#11

Jag Red 54

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From: Valley Center, CA

The backfire makes me think a timing issue, not fuel mix.
Step 1. Pull a plug and look for color of the previously white electrode.
Step 2. Adjust ignition timing appropriately.
Step 3. Check plug color again. If your carb, timing and plug heat range are correct, it should be a light tan or grey. The tip closest to the electrode may be colored differently than the porcelan deeper inside the plug body. The tip color shows you idle and the deep down indicates what's happening running down the road. Black means too cold 9may be too rich?). White or yellow indicates too hot, (maybe too lean?)

Good luck, Jag

Mar 7, 2013 | 06:31 PM

#12

oldmerc

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From: Edmonton,Alberta

Everything thats been said and a test with a vacuum gauge would not hurt

Mar 11, 2013 | 01:07 PM

#13

truckeemtnfords

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From: Fallon,NV & Bainbridge OH

A lean condition will also cause a mis-fire, which resembles a backfire. As stated a vacuum leak will cause a lean issue but sometimes it is as simple as a jet size issue. If it runs fine with the choke on a jet size increase may be in order.