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Old 04-21-2017, 05:17 AM
UngerMarkus's Avatar
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AMC 360 dies at wot

Hi guys!

I have a strange problem with my Wagoneer. Itīs powered by an AMC 360 with a brand new Street Demon carb and a HEI dizzy.

It starts and idles great. Also it performs well cruising around and under light acceleration. But as soon as you floor the pedal it cutīs out. No matter what speed.

No backfire. The engine just stutters. When you stay on the gas long enough, it dies.

Things I did so far:

Voltage on distributor is 12,6V regardless of RPM. (Transmission in Park)

I cleaned the carb (although itīs new). No improvement.
I installed an A/F-ratio monitor. It reads 12,5-13,5 at any load situation.

Vaccum gauge reads 18'' hg at idle. Reads very low when stutter occurs.
I checked for vacuum leaks with brake cleaner, but could not find any. All vaccuum lines seem to be ok.

I tightened the secondary air flap down. No improvement.

Any ideas?

Thanks

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Old 04-21-2017, 07:46 AM
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What's your initial timing?
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Old 04-21-2017, 08:16 AM
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Plugged fuel filter? Rubber or hard-line gas line? If older rubber, sometimes they will collapse, or deteriorate & constrict.
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Old 04-21-2017, 10:11 AM
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I had a similar but not as severe situation with my Pontiac. Chinese coil in cheap new HEI was the cause. Mine is coil-in-cap. If yours is and the coil says "Made in China" on top, I'd try another "known good" coil and pitch that one over the fence.
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Old 04-21-2017, 01:25 PM
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Are you using a vented gas cap or is there some other way for the fuel system not to pull a vacuum.

Is there any rubber fuel line in the system? Pump gas has ethanol in it, which will disintegrate rubber. I have heard of pieces forming a flap inside the line and blocking off the passage of fuel.
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Old 04-21-2017, 02:44 PM
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Quote:
Originally Posted by UngerMarkus View Post
AMC 360 with a brand new Street Demon carb
It starts and idles great. Also it performs well cruising around and under light acceleration. But as soon as you floor the pedal it cutīs out. No matter what speed.

No backfire. The engine just stutters. When you stay on the gas long enough, it dies.

Voltage on distributor is 12,6V regardless of RPM. (Transmission in Park)

I installed an A/F-ratio monitor. It reads 12,5-13,5 at any load situation.

Vacuum gauge reads 18'' hg at idle. Reads very low when stutter occurs.

I tightened the secondary air flap down. No improvement.
This is a stock, high vacuum engine? May need to tighten the secondaries air door down some more to prevent secondaries opening at too low an RPMs...

What happens if you rev up gently to about 3,500 RPMs in 2nd gear and then floor it?

Do you have a tach?

In other matters, what CFM is the carb.? Smaller ones really open the secondaries too soon because of high vacuum in the primaries...

Single or dual plane intake? Single planes usually require richer secondaries jetting... About #66 primary jets for a 360" size engine... secondary jetting depends on number of power valves, single/dual plane, etc...

Would like to see voltage around 13's at distributor with engine running... 14 at battery... mid 12's battery engine off... low 12's distributor with engine off... Did you replace a points distributor with an HEI and not bypass the ballast resistor?

A/F 12.5 - 13 at WOT... 15's while cruising steady speed...

About 12 degrees idle ignition timing (vac advance disconnect and hose plugged) and up to about 36 - 40 max advance at 2500 - 3500 RPMs...
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Old 04-21-2017, 07:04 PM
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Quote:
Originally Posted by BuzzLOL View Post
Single or dual plane intake? Single planes usually require richer secondaries jetting... About #66 primary jets for a 360" size engine... secondary jetting depends on number of power valves, single/dual plane, etc...
Forget the numbers I mentioned on jet sizes... Demon carb.s use a jet and rod arrangement like a Q-Jet carb., not a Holley...

Comparing the Street Demon with a Traditional Holley Carb
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