OMC 165 (GM L6 250 cid) backfiring on test...

[DukesFin]

Okay, I've got everything installed and took her to the lake yesterday to "test fire" the new long block. <br /><br />I got oil pressure up by cranking with no spark plugs in her. Put spark plugs in, connected wires, (double checked the wires vs. firing order), and started cranking, hoping for an easy start.<br /><br />All I could get her to do was backfire occasionally. White smoke from spark arrestor upon backfire.<br /><br />Do you think this is:<br /><br />A: Timing Issue?<br />B: Valve Adjustment Issue?<br />C: Water in Fuel Issue?<br /><br />D: All or some of the above?<br /><br />Any other info needed for help? Let me know...

 

[coalbucket]

Re: OMC 165 (GM L6 250 cid) backfiring on test...

Sounds like a timing issue. Almost sounds like it is 180* out of time.<br /><br />It could be a valve adjustment issue but the valve/valves would have to be way over adjusted.

 

[ziggy]

Re: OMC 165 (GM L6 250 cid) backfiring on test...

i agree with timeing for a start(no pun inteneded). was the dist. rotor pointing to #1 after it was installed? can ya see a timeing mark with yer timing light? did you adj. dwell, then timeing? <br />ya might think about the valve adj. too. this is how you said you were gonna adj. the valves. <br /><br />"I was not feeling too confident about the whole "valve lash adjustment", so I called the techies that built my longblock and they told me to forget what the manual said. Instead, start with No 1 cyl at TDC and adjust the valves for it. Rotate the crankshaft to No 2's TDC and adjust those valves. Keep doing that through No 6 and it's done. Much more simple, but same good results."<br /><br />to me, there would seem be the chance that you weren't on the compression stroke with both valves closed when adj. this way. <br /><br />if yer wondering about water in the fuel. ya could always run a remote fuel tank with some fresh fuel. <br /><br />three things have to happen for it to run. fuel, air, spark. start running some checks to see what ain't right. <br /><br />hang is there. bet she'll run great when yer done with her. your real close to success it seems. cool.....

 

[DukesFin]

Re: OMC 165 (GM L6 250 cid) backfiring on test...

Well, if I was off by 180 degrees, I assume I need to re-adjust my valves too, huh? (Or are there 2 compression strokes per cyl. per 360 degrees of rotation?

 

[ziggy]

Re: OMC 165 (GM L6 250 cid) backfiring on test...

i think ya can be a little off on the dist. make sure that the rotor points to #1 on a compression stroke, timing mark would be lined up and at 0, rotor pointing to #1 sparkplug. i think yer mateing a gear, not a slot. the slot would be the oil pump. <br />4 stoke engine:<br />stroke 1: intake, 180*<br />stroke 2: compressin to tdc. 360*<br />stroke 3: power stoke 540*<br />stroke 4: exhust stoke 720*<br />it takes 2 complete revolutions of the crank to complete all 4 strokes.

 

[Alumarine]

Re: OMC 165 (GM L6 250 cid) backfiring on test...

Distributor orientation has no impact on valve adjustment.<br /><br />If the the valves were adjusted correctly they will still be ok.