engine identify

i have a 1965 loadstar 1600. How do i tell what size engine it has. also i tuned up the engine points plugs etc, it cranks & runs great but when you let off the throttle truck backfires really bad, could the timing be causing this. she`s not pretty but gets it done. 16ft twin cylinder dump 4ft grain side boards. your help would be appreciated.

Is your exhaust tight? If there is a leak before the muffler that will often cause it to backfire.

6 or 8 cylinder?

How'd you buy tune up parts not knowing the engine.

well i`ll tell you how i did it. i opened up the hood looked in there saw it was a V8 engine 304 or 345 not sure. took spark plug out wrote down the #. then took off distributor cap took points & condenser out don`t forget rotor button went down to NAPA got replacements gaped plugs at .035 & points at .017 to try & better answer your question. i don`t mean to sound short with any of you i just came on this site to get some information. thank you

Here's a pic showing where SV8's are stamped with CID & SN.

(Click on pic to enlarge)

Tune up specs from an IH service manual.
Plug gap = .030
Point gap = .016
Dwell = 28-32
Idle speed range = 675-725
Firing order = 1-8-4-3-6-5-7-2
Timing = TDC
Set timing off #8 cylinder.

FYI,the factory spec plugs for a Loadstar;
RJ6 Champ
303 Autolite

Coil is a non resistor type,Loadstars have a resistor wire in the harness.

Didn't think of it at the time how you got the parts easily,you must have a Delco distributor.

thank you for that very helpful information, & it does have a Delco distributor.