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Wheel bearing - Ram 2500 4X4

From : radiohead

Q: check to see how much play your timing chain has in it. turn the crank by hand in the direction of rotation till the timing mark is on 0. if you go past the mark do not back up go all the way around again. take the dist cap off and watch the rotor while you or a helper gently start to turn the crank backwards. turn till you just see the rotor start to move then look at the timing mark and note down how many degrees it has turned. anything more than about 10 degrees and you need to replace the chain and gears. alot of play in the chain can cause backfiring but it usually does it on accel. denny ive scanned the 26000 + messages since sometime in 2002 and havent found a problem such as mine described or solutions suggested. so here goes vehicle description 1974 dodge b300 1-ton maxivan. 318 automatic no factory air. engine had a good rebuild at 91000 current odo reading 179000 southern california vehicle all its life as far as i know. im the second owner. everything sounds good - no clatters or knocks anywhere carter bbd 2-bbl carburetor dual exhaust no crossover pipe vapor cannister and pcv are the only emission controls i know of this truck ever having. no evidence of anything being removed. ive owned it for 19 years. it used to run great. the problem ive been experiencing an increasing occurence of backfire through the carburetor. the weird thing is that it doesnt do it on acceleration or deceleration just at cruise speed. it doesnt matter what the cruise speed is - if i go 50 it starts to splut and backfire at 50. if i cruise at 75 same thing. if i could keep a constant acceration going it runs great. going up a grade i couldnt expect better performance. the carburetor is a holley-rebuilt. its not a holley carb - just rebuilt by them. cost nearly $200.00. in doing some investigating i found a gasket missing from under the step-up piston cover plate. made me wonder what else wasnt done right. i checked the float level and it was 1/8 low 1/4 is spec. i reset it and things seemed to be a bit better but it didnt cure the backfire at cruise speed. ive put on new plugs cap rotor ignition module coil plug wires. timing is dead on at factory spec of 0. vacuum advance is working properly advance weights are free and recently lubricated. when i put in new plugs champion n11y as per oem spec all the old plugs were white and had some blistering evidence of perhaps advanced timing and/or lean mixture. all the intake manifold bolts are tight. im starting to see some whitening of the metal of the choke stove well in the intake manifold. when i put a vacuum gauge on it i get a little fluctuation 3-6 in. at idle. other vacuum tests seem to check out fine. compression check shows one cylinder at about 90 others at between 130-150. im about ready to give up. can anybody point me in the right direction what other tests can i do does this sound like a carburetor or intake problem the questions keep coming - any advice or suggestions are welcome. thanks greatly. t maki riverside ca .