4.3 backfire/ sputtering issue

[Ripcurl7278]

i have a 19 foot renken that had a 1988 4.3 with roller cams that spun a bearing. so I bought a reman 4.3 vortec long block from Michigan motors. ive got a new fuel pump and regulator since the vortec cant use the mechanical and also a new intake. im using my 2 bbl original carb that I have not messed with but ran flawless on the old motor. now when its bolted up to this motor the motor wont go above 1500 without sputtering/ backfiring and hesitation. idles absolutely perfect though. checked the timing several times 8 btdc and checked the firing order multiple times to make sure I didn't mess up. 165432. anyone have some advice to what it could be? thanks.

 

[Bondo]

Re: 4.3 backfire/ sputtering issue

im using my 2 bbl original carb that I have not messed with but

Ayuh,.... I'd start there,... it sounds like it's runnin' Lean...

 

[Ripcurl7278]

Re: 4.3 backfire/ sputtering issue

Pulled the plugs and they are black like its burning way too rich. Brand new plugs. Cleaned the carb and all the jets. It looked flawless. Could this be a symptom of a bad thunderbolt?

 

[dubs283]

Re: 4.3 backfire/ sputtering issue

Pulled the plugs and they are black like its burning way too rich. Brand new plugs. Cleaned the carb and all the jets. It looked flawless. Could this be a symptom of a bad thunderbolt?

when you installed the new long block did you install new ignition tune-up parts, fuel filters, etc...??

yes black sooty plugs is a result of running rich, did you replace carb parts or just clean??

have you checked the fuel pressure of the new pump??

 

[Ripcurl7278]

Re: 4.3 backfire/ sputtering issue

I put a new pump on that is 10 psi and pit a Regulator on and turned it from 1 to 7 and gave it a few minutes each time with no results. I took a art the carb and it is flawless and all the jets seemed to be cleaned out. It has a 2 bbl spacer but I also seen in another forum that I need a carb spacer in between manifold and carb? Doesn't sound like that would affect it to me. The thunderbolt and distributor were from the older motor but the plugs wires rotor and cap are new. Even switched the coil yesterday to knock that off the list. I was able to get it up to 5000 for a second yesterday but not again. It won't go above 1000 without sputtering and popping. Even checked the firing order with the plug wires over and over. Loosened the distributor and gave it gas and turned it to see if the popping would stop with no results. So its back on 8 btdc. I'm completely stumped.

 

[thumpar]

Re: 4.3 backfire/ sputtering issue

Do the plugs look good now? If they do check the valve lash. When I redid a 4.3 years ago I had it too tight and it did that.