Ok guys I just put another motor in my 68 with a electronic Holly carb!!
It's starting right up and running real smooth even when I press the gas down easily, but soon as I rev it a little it backfires!!!
Any ideas???

Oh yeah I was wondering if this yellow wire not being hooked up properly could be causing this problem???
Where is the correct place for the yellow wire???
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sounds like it could be ignition to to me or a lean backfire from say a vacuum .
Did you hook a tach up? if you think the carb is wired wrong then take off wires. There is only a hot and ground on there. what do you know about the motor and how it ran befor switch.

 

I left the tac wire off the dis!! Most of the vaccum lines are plugged, the carb is grounded to itself but the hot (yellow wire) is not hooked up!!! Motor ran great before we pulled it and dropped it in, it's a 307 Out a 83 Cutlass I was trying to use to get my car around until the beast is ready!!!

 

The power valve in the carb is bad. You need to check your timing, but once it's backfired threw a Holley carb. Then the power valve is done. It will backfire all the time then.

 

So will I need to get the carb rebuilt? It's fairly new if that matters any!! And you say check the timing, how could it have jumped time and all I did was take it out and put it back in???? What's an easy way for a newcomer like myself to check it???

 

Just check to see if it is set right with a timing light. If timing is off it can cause it to backfire threw the carb.

No the carb doesn't need to be rebuilt just the power valve will need to be replaced.
All that has to be done to do that is take off the front fuel bowl. Then the metering block, between the jets is the power valve which is treads into the metering block.

 

Could it be you accidentally swapped a wire on the distributor? When I changed my spark plugs, I accidentally swapped two wires and when I started the car up, she ran beautifully. If I gave it gas, it'd backfire. And as soon as I put the car in gear, it ran horribly and backfired. But idling, sounded right. I traced the only two wires I thought I may have crossed, corrected it, and solved the problem. I'd double check that before taking apart the carb.

Wyze, where are you located? I sold my 83 Olds Custom Cruiser to a guy who wanted to pull the motor for a project. It had a strong running 307 Olds in it. We couldn't get it running due to a bad battery, but they just rolled the thing up onto a trailer and called it a day. This was a month or two ago. Sometime in Jan or Feb....or maybe even late December.

--Ryan

 

Yeah my buddy was pretty much just saying the samE thing!!!





St.Louis

 

Before replacing anything, check the accelerator pump cam and adjustment. You can change the cam and the squirter size to fix exactly this problem.

 

Sorry Joe but I don't know what that is!!!!!
Still very new to the game!!!

 

was this carb on the motor before swap? how old is gas in tank? Is it an hei if so do you have the 12 volts to it ? did you have intake off it ?

 

Here's a video on youtube about the accelerator pump should help you understand what it is and what it does.

http://www.youtube.com/watch?v=w3F3ssOb8lg

 

Thanks for the video link!!!
I'll have to check it out when I get on a desktop!!!!



Yes carb was on motor already...... New gas cause I ran out... Lol... Hei yes 12 volts yes........ No pulled motor out and dropped it in......
???????????????

 

would there be a computer on old (new) car that does not wsap to new one ?otherwise did you cut or short a wire to kill the coil that will spark a motor at idle but it take alot more to fire a motor in upper rpms or lugging it? Did you pull dist to swap motor to keep it from getting broke? does it pop once or twice then rev up slow or just pop and pop and pop.

 

Pops once out the carb!!!
I left the Dis in and damaged the cap, so I swapped it with another one I had!!!!

I just noticed my old cap only had 2 prongs where the dis lugs in, but the new cap has 3!!!!
Black (-) Red (12+) & Yellow (C-)

 

Not had any doings with an hei Do you think it might be the rotor might be wrong for that cap?

 

Ok I got a new cap and rotor, switch the vac advance around checked plugwires again!!!!
Crank up on the first turn runs smooth at idle but still backfires!!!
I drove it and it runs sluggess!!!!!

 

Vacume leak. BTDT.

Did you replace the carb base gasket? Many folks re-use them, i always toss it and start with a fresh one.

Easy way to tell if you have a vacume leak- buy a can of starting fluid (something that has Ether in it) take off your air cleaner- and lightly spray it around the base of the carb and the edges of the intake manifold while the engine is running (trying to shield it from getting sucked into the carb. If the RPMS pick up- you have a vacume leak.

Also- check the shoulders on the carb studs. If they are not all the same- then its possible to tighten down the nuts and feel like its tight, and have it not be (I had this problem and wrestled with it for MONTHS before figuring it out). Put washers under the nuts and it torqued down fine and no more leaks.

 

That's sounds like the next thing I'll try!!!
I would like to thank everyone for their help!!!!
We got the big Easter Sunday Carshow here in St.Louis tomorrow, hopefully someone might come over a be like look this is your problem!!!
Here she is, I just got the spoiler where I wanted and put her back up till tomorrow!!!

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were you playing with your plug wires?

recheck them if you were,sounds like one is crossed

 

I have to ask have you replaced the plug wires. You could have a bad one.

 

Their on correct, I've checked them numerous times!!!!




I haven't changed them yet but I've got another set that I'll swap them with if it doesn't keep raining!!!!