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Discussion Starter · #1 ·
My 85' has a high performance 360. It has a holley 600 on it. For some reason, at sustained higher Rpm's, it back fires. Most days i can't go over 60mph (about 2500rpm) for very long before it starts back firing. Will a spacer help this? I'm not sure if the secondaries open up, but the fastest I've ever been able to go is 70mph. I have stock gears (3.21's I think) and 33 inch tires. I assume this is a carberator issue. is there sum way to test the secondaries?
 

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If it is a carb issue it's rich, what happens if you floor it from a dead stop until 70mph, be very very very very detailed
 

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Check your timing, I am willing to bet you are too far advanced.
 

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Discussion Starter · #4 ·
When I floor it normally, as in just smashing it to the floor, it hicups, back fires, and dies some times. I'll also say that when I'm not in gear and rev it, it goes up to 5000rpm no problem, no back firing and what not...if it's warmed up.
 

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I second a probable timing issue. either too much initial/total timing, or too much/too fast mechanical advance.

-SM
 

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Discussion Starter · #6 ·
How do I check/ change that, I have a timing gun some where, but have never done it.
 

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Seems that carb is out of adjustment , how does it idle, how is it's response, does it have problems when slowly getting into the throttle, on off the gas. This is more a VH ?
 

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Discussion Starter · #8 ·
IT idles rough, but taht may be cause it idles at 450-500rpms. Its response is fine when I slowly push the pedal down, IF I floor it, it usually hiccups/back fires, and dies some times. This is more of a VH? but I can't figure out how to move it...sorry
 
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Check your air gap in the distridutor too, Mine was doing the exact same thing. I replaced the carb, cap, rotor, wires, plugs and nothing seemed to help. It ran great, except under load. then it would "POP" thru the carb.Adjusted the gap & it's run great ever since.
 

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At the very least, you should get a Haynes manual for your truck. It covers the basics.
 

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The air gap is in the distributor, between the pick up and the reluctor. Look under distributor, it is in my Haynes manual.

1. remove distributor cap
2. align one reluctor tooth with the pickup coil tooth by rotating engine.
3. loosen pickup coil adjustment screw.
4. insert non magnetic (brass) feeler gauge (0.006") between teeth.
5. move pick up coil until light contact is made with feeler guage. NO force should be necessary to remove feeler.
6. using a 0.008 feeler guage, check the air gap. feeler guage should not fit between teeth (DO NOT FORCE).
7. replace cap.

If this doesn't fix your problem, you need to set your timing.
1. Disconnect vacuum advance line. If you have a vacuum guage, attach that to the vacuum port on the carburator. If not then disregard this part of the instructions.
2. Loosen the distributor hold down bolt and bracket enough to allow rotating of the distributor.
3. Start the engine. If you have the vacuum guage, move the distributor until peak vacuum is attained, then back the timing down slightly (clockwise). If you do not have a vacuum gauge, then listen to the engine. When peak rpm is attained, back the timing down slightly (clockwise).

Hope this helps.
 

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Discussion Starter · #15 ·
So, I checked my Airgap, it was fine. I went out and flogged on it and I npticed a few things. It seems to run fine into high rpm's, but if I floor it, it starts to backfire and hesitate. what's the deal?
 

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Disconnect and plug the vacuum advance pod, and go for a drive. If the problem improves/goes away, the vac advance is pulling in too soon, and when you floor it, the vac advance drops back to zero (retarding the timing greatly)

Additionally, make sure the vacuum advance is hooked up to ported vacuum, not manifold vacuum. Vacuum advance should only work at part-throttle conditions.

And for reference, what is your base timing set at? (remember to disconnect and plug the vac advance line to read initial timing---even though the vac advance should not be affecting your base timing. If it is, you found the problem)

-SM
 

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When the engine is off, and the and air filter. You should be able to look down the secondaries and watch fuel squirt into the venturies when you pull the throtle linkage to the wide open position. Do you see the fuel squirt when you try this? As for checking the secondaries, the only other way I know of is remove the carburator from the vehicle and take to a shop with a flow bench and have them test it! When was the last rebuild on that carb and or how old is it? Have you tried to run a carb cleaner through a tank of gas, and is your fuel filter been changed reciently?
 

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Discussion Starter · #18 ·
Ok, I was going to play with the timing today, only to find out that the gun has no connectors on the wires. So tommorow I'll go get connectors, a vacuum gauge and a bottle of carb cleaner. This Carb is just over a year old. I'll get back to you tommorow with more info. Thanks for the help so far.
 
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What do you mean by a high performance 360? Whats been done to it to make it high performance?

A 600 cfm might be enough for a stock 360 but if you're running headers or a bigger cam or modified heads, it may be too small. Give us the particulars of that motor.
 

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Discussion Starter · #20 ·
a new 360, bored .030, mopar w2 performance heads with big valves, kiethblack flat top racing pistons, steel racing crank, mopar performance purple cam, edlebrock intake and a holley 600. It's rated at just over 400hp with headers, but I'm to broke to buy the thorley's. How's that.
 
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