85 k10, took off catalytic converter now backfiring

[gbnbrb123]

Okay, so I am a little new to the exhaust world but figured I had some knowledge of the subject matter. I removed most of my exhaust because of corrosion and rust and literally falling to pieces. The k10 is stock with a 305, the only pipes left on the vehicle is the y pipe. After taking the catalytic converter off the truck has started backfiring and barely starting at times, while previously it was running fine, at least I thought so. I went ahead and replaced the spark plugs due to how bad it was running and fuel filter, but no change, time for them anyway. I also had put in a new gas tank prior to everything along with a new fuel pump and everything seemed to be running fine at that time. My plan was to run straight pipes with maybe a magnaflow muffler with exit behind front door but was curious if that would make any difference in how it was running due to backpressure. My other option is to put a generic 2.5" catalytic converter with piping run to a muffler. Curious as to what you guys think are the best options and why the truck is running so rough.
Thanks, Nick

[Malo83]

When i bought my 83 Silverado new with the 305 i had a true dual exhaust made for the truck, ran great! kept the original single exhaust and would install it on the truck when i had to do a smog test, this went on for years until i got tired of swapping out exhaust pipes, now run a single 3" exhaust coming off the Y pipe thru a 3" High Flow Magnaflow cat and 3" Flowmaster muffler dumped in front of the axle.
Never had any problems running a dual exhaust on the truck.

[gbnbrb123]

But why would that make the truck run rough? Once it warms up runs good, I will be spraying some carb cleaner on the choke to see if that helps.

[johnwaynejeep]

It sounds like a timing issue or a valve overlap issue. The exhaust system and cat may have provided enough backpressure and exhaust burn to hide this issue.

Do you have a factory camshaft? If you have an oversized camshaft with a larger overlap, the lower backpressure could be causing some of the intake charge to be sucked out your exhaust valve and ignite causing backfiring.

A new exhaust may hide the issue but hiding is not always the best bet. Get a timing light and post up your timing at idle and 2000 rpm.

[gbnbrb123]

Johnwaynejeep, I suspected that may have been the problem but will have to check with a timing light, unfortunately I don't have one at the moment. I inherited the truck roughly 4-5 years ago and have been constantly fixing and restoring stuff. Pretty much redid the whole frame and etc, so don't know a whole lot about carburetors and timing, but i have been constantly watching videos and learning along the way. Thanks and will keep you guys posted.

[gbnbrb123]

The camshaft is factory I believe. I purchased a rebuilt quadrajet, replaced vacuum lines, and some other stuff, but nothing on the motor itself.

[Dead Parrot]

Backfiring thru the carb or exhaust? If exhaust, it is likely the old leaky pipes were muffling the backfire or covering it with leak noise.

Possible the converter mostly plugged up years ago and a PO adjusted things attempting to get it to run better.

Might check the plugs to make sure you don't have one or two cylinders running way rich or lean.

If it still has one, make sure the exhaust riser valve isn't stuck closed.

[gbnbrb123]

What is a PO, sorry?

[Desert_Eagle02]

Originally Posted by gbnbrb123

What is a PO, sorry?

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