Someone please help - carb popping

[s10rodder]

OK I\'ve now tinkered with it myself for months, talked to tech people and tried two different mechanics and I can\'t get the damn thing fixed. I\'m getting a pop out of the carb off idle and in high gear at low rpm. Pretty much whenever I put my foot down with the engine below 2000 rpm it pops. It doesn\'t do it if I bring the rpms up gradually. It\'s also fouling plugs real quick (black carbon). The last guy that looked at it found a vacuum leak at the manifold and fixed that. It got a little better. It was also running real rich so he went a full 4 sizes smaller jets and it still seems to be running rich. He said he could fully back out the mixture screws and it wouldn\'t stall. The timings been gone over and gone over again so I don\'t think that\'s the problem. It\'s at 36 degrees total. The valves have been lashed and re-lashed, so it doesn\'t seem to be that either. Also, it doesn\'t always pop, sometimes it just has a bad hesitation, like a lean condition, but it\'s not running too lean. It actually got a little better when the last mechanic leaned it out. He\'s tried 3 different power valves and they don\'t seem to be making a difference.



Just so everyone knows, the motor runs great aside from the popping and the plug fouling. It\'s a 10.5:1 355 with AFR 195cc heads, a crane hyd flat-tappet (226,234 @ .050/.463,.488 lift) Victor jr. and a 750 vacuum secondary demon carb. Oh yeah, I tried a 650 holley doublepumper and that didn\'t seem to be any better - it still popped.



This is really getting to be a pain in the ass so if anyone can figure it out I will be forever indebted to you. I have faith in you guys. Thanks in advance...

[IceQueen]

sounds like your leaking gas from the carb some place which is making your idle rich and giving you blow back through the carb I had the same problem with my old carb after I replaced the carb with a rebuilt everythin worked perfectly. make sure your also using a gasket that seals all the va* ports on the bottoim there are some poor gaskets out there that dont cover all the ports burt this is more a q-jet problem. also if your as parinoid as me when you install your carb use form a gasket sealant on bothe sides of the gasket then torque things down snuggly dont over do it thow.

[lowrthnus10]

i\'m not very all knowing with carbs but dosen\'t it sound like a acelerator pump for the primarys. that was the problem with my friends truck it sounds like the same thing. don\'t go changing your pump with my advise just ponder and ask questions about the subject.

[Fergusonic]

From lack of knowledge....is a Victor Jr and Single or a Dual plane? If it is a Single Plane; that may be your prob.

[carguy1959]

Did you degree your cam when you installed it? It allmost sounds like your running the timing retarded. Are you sure you timing mark is in the right place? If your carb was too big it would bog and stall when you romp on it and then be hard to start (flooded). I had that problem before. I also had a bad cam lobe(exhaust) which caused it to back fire thru the carb, check to make sure that all of your rockers are moving correctly. Could also be a bad lifter. Just a couple of thoughs. Good luck...

[s10rodder]

victor jr. is a single plane, but it ran fine with that intake before. The problem started when I pulled the motor apart and replaced the cam, fuel pump, carb and heads. Before I was running a little bigger cam, stock heads, and a 650 holley dblpmpr. When I upgraded everything it started popping.



The carb isn\'t leaking anything, it\'s brand new, and all the unused vacuum lines are plugged. Besides, it had the same problem when I tried a different carb on it.



The cam wasn\'t degreed. I installed it straight up. The timing mark is in the right spot on the balancer - it\'s been checked. Could the cam itself be causing the problem? All the rockers seem to be moving properly. But I\'ve suspected the cam of causing another problem - low vac*. I\'m running a canister and my cam really isn\'t big enough to still be causing problems. From everyone I\'ve talked to I shouldn\'t even need a canister with the cam I\'ve got. But I\'ve only got like, 12 inches at idle, and the last guy who worked on the truck thought that I may just have a bad cam.



Keep the ideas coming. Thanks guys.

[Free85]

I\'ve got almost the identical problem, except comes and goes...I\'ve thought of everything you\'ve mentioned and the one that makes the most sense is a bad cam or cam bearings, (I\'ve also got bad oil pressure) with bad cam bearings the cam could be trying to walk around and changing the valve timing. although I think the plug wires may be causing it too. It will run for days without a problem and then just off idle it will pop every time I do more than ease into from a stop. then it will seem to fix itself. mine is a daily driver that sees 200 miles a week on average. sorry this is so long http://www.s10v8.com/images/smilies/icon_smile.gif

[bohn333]

have you ever changed the power valve in the carb..mine used to pop at idle but went to a weaker power valve and it solved it. IF everything is correct and you still have a pop, check the timing chain for play.



How heavy are your valve springs? If there too stiff this will cause it to pop when you get on it.

[s10rodder]

The last mechanic I had look at it tried 3 different power valves and none of them made a difference. Play in the timing chain wouldreally surprise me because the cam and timing set has less than 1000 miles on it. I\'m planning on checking out the cam as a last resort after I\'ve tried everything else I can. The valve springs are the ones that are supplied with the AFR heads. I\'ll check the specs on those and call crane to make sure my cam is OK with those springs. Good suggestions. Thanks alot. I\'ll let you all know what it was when I get it fixed.