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post #1 of (permalink) Old 04-09-2006, 10:28 AM Thread Starter
 
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Popping through carb

A little background. 83 F150 4wd 302 carb'd. Original motor threw a rod, but was running fine before. Found an 86 302 out of a Mustang. Swapped motors, used our intake and dizzy because it didn't have one.
Put #1 at TDC on Compression stroke (piston up, timing mark on 0) Correct? Started motor, found some minor vac leaks, and son broke ears off carb where you mount it, changed carb from my other truck that we just drove. Set timing at 9 degrees for now, idles like a new kitten. Firing order is 1-5-4-2-6-3-7-8 checked 3 times. Wires came off other engine and were good.
Now to the problem. Idles good, but when you give it a good kick of the throttle it pops through the carb, also when you let out the clutch and start to go it pops. Not a pop-pop-pop-pop, but a single pop everytime you give it gas. You can slowly give it gas by hand out of gear and it revs fine. Do I still have a vac leak or do you think the cap or wires messed up from the time it took to swap them between motors ( a week )or do I have the dizzy in wrong? I was assured the motor was good, they are reliable and I do believe them.
Sorry for the long post but I wanted to give all the info I could.
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post #2 of (permalink) Old 04-09-2006, 01:13 PM
 
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Re: Popping through carb

I would try playing with the timing some. I like to set mine by hooking up a vacuum guage to the intake and then set the timing to the highest vacuum you can get. Don't go past it but right where it's producing the max vacuum. Once you do that tune the carb adjustment screws a half turn at a time. Screw them all the way in (gently) and then start two whole turns out. Try leaning it innitially and see where the vacuum goes. Last adjust the idle. Your max voluum at idle may not be the same as what you want to hear. Go for your best compromise. I usually set mine between 800 and 1200 rpm depending. Right now I'm set at 1200 because I don't like to get out and fiddle with it when I hit high altitudes in my area. What kind of carb did you put on? Holleys do not like backfires and you may have to replace the (I forget the name of it right now but I think it's the enrichment valve which opperates off of vacuum) valve. If none of that works I'd be willing to bet you still have a vacuum leak. I know it's not recomended but I always use a gasket dressing on my intake gaskets just as a precaution agains leaks. NOT RTV (still use a little around the water pasages) but a regular gasket dressing that goes on with a brush. So far this has worked for me. I hope this helps you some.
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post #3 of (permalink) Old 04-09-2006, 02:18 PM Thread Starter
 
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Re: Popping through carb

Thanks Norm, It's a Motocraft carb, was running good on the other truck. We pulled wires one at a time and when the #2 is pulled it revs alot faster and higher before it pops it seems to be a 100 percent better but still pops. I'll put a vac gauge on it in a little while.
I think you are talking about the power valve, but like I said it was running good on the other truck no more than 30 mins. before. It is either a vac leak or something with the timing and dizzy maybe. I'll take ant suggestions right now. You helped me tune a carb about 6 years ago, so glad you answered. Think maybe a valve sticking? I thought about that but not on more than 1 cylinder?
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post #4 of (permalink) Old 04-10-2006, 07:30 AM Thread Starter
 
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Re: Popping through carb

Put vac gauge on it, can't get any higher than 15. Pulled plug wires off other truck along with the cap and still pops. Sprayed carb cleaner around and engine idles down when sprayed around back of carb? I thought it should idle up if it had vac leak? I am getting 2 new gaskets today carb to spacer and spacer to manifold and see if that does it. Last thing is to pull intake off again and see if we didn't seal it good. Sprayed all the mating surfaces around intake didn't change idle at all. Timing is set 9 degrees with a light.
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post #5 of (permalink) Old 04-10-2006, 10:11 AM
 
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Re: Popping through carb

Try swapping another distributor cap too. I'm not sure but if there's a small crack it can screw things up pretty bad. It don't hurt to try since I'm sure you've probably got a spare one laying around somewhere. New ones aren't too spendy either.
Yeah. the power valve is what I was thinking of. My old 2150 carb I had was leaking through the rail pretty bad telling me it had seen it's last. I love my 2100. I just bolted it on and it worked.
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post #6 of (permalink) Old 04-10-2006, 10:39 AM Thread Starter
 
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Re: Popping through carb

Can you tell I'm trying to avoid pulling the intake off and changing the gasket, my son put it on so it very well may be the leak is there, we just can't find it externally. I'll try another cap and see what happens.
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post #7 of (permalink) Old 04-12-2006, 12:36 PM Thread Starter
 
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Re: Popping through carb

O.K. got a suggestion from another forum I am on (bowing head in shame, sorry)I amusing the pre 95 firing order of 1-5-4-2-6-3-7-8 it was suggested that I use the 351W order which would be for the HO motor right. This sounds like a good fix and will try it tonight, I am not second guessing him, I am just confused on why it idles so good with 4 out of 8 cylinders not firing in the right order. I am confused and frustrated with this problem. A simple carb backfire can't be that hard, plus this is my 16 year olds truck we bought for him so I also have him over my shoulder being impatient. I've already threatened to sell him and the truck. LOL
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post #8 of (permalink) Old 04-15-2006, 03:31 PM
 
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Re: Popping through carb

How much for the kid? I've got yard work that needs doing. [img]/ubbthreads/images/graemlins/smile.gif[/img]

Don't feel bad about checking other sites. FSB aka fullsizebronco.com is where most the old members here left and went to. There's alot of info there but it starts to go downhill once you start doing things they consider extreme. Take everything you learn online with a grain of salt. Another thing I just thought of is to block off all your vacuum accessories and see if it still does it. If not then you can hook them back up one at a time until you figure out where the problem is. It's possible that you've got a leak in the brake booster or the vacuum silinoid thing on the tranny. After all's said and done though after all the grief it may just be a vacuum leak in the oil valley where you can't reach it to test it. I hope it's as simple as the firing order. post it up when you figure it out. [img]/ubbthreads/images/graemlins/smile.gif[/img]
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post #9 of (permalink) Old 04-17-2006, 07:08 AM Thread Starter
 
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Re: Popping through carb

Thanks Norm, We still have this pop when the throttle is rev'd. Like I said it idles good and you can rev it slowly. 1. Checked compression, 172 on the highest and 164 on the lowest cylinder.
2. Pulled off intake and changed gaskets, pulled off carb and changed gaskets.
3. Vac advance works and we have 36 degrees total advance.
4. Carb worked good on other truck ( drove truck and switched carb same day)
5. New wires, rotor, cap and plugs.
6. Plugged all vac lines except for the brake booster. Brakes seem to work fine, no constant hissing when you hold them.
7. Changed fuel pump and took off fuel filter.
8. Put linkage to accel. pump in every available spot.
9. Pulled hair out and cursed truck. Threatened to burn truck to the ground.
10. Shopped e-bay for large stick of dynamite.
11. Swapped firing order truck wouldn't even start.
I know I am forgetting something we did. It is only 1 big pop through carb when throttle is hit fast. Help !!!!!!!
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post #10 of (permalink) Old 04-18-2006, 07:08 AM Thread Starter
 
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Re: Popping through carb

Set timing at 4,6,8,10 degrees still pops. Changed firing order to 1-3-7-2-6-5-4-8 and it barely runs, so firing order is correct. Will check for timing chain slack today. Any way I can check the cam easily? One more thing, we took off the EGR spacer under the carb and replaced it with a phenolic spacer, could this be our whole problem? We even set timing for max vac. and it still does it. I am wondering about the EGR plate or spacer, whatever you call it.
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