v4 crossflow no spark

[pcrussell50]

i just rebuilt the carbs and re-sealed the gearbox of my "franken-crossflow", ('77 block, wiseco pistons, 140 carbs and bubbleback, on an '80 lower, mid, and tilt/trim). late this afternoon, just before i had to leave on a work trip, i decided to fire her up. not even the remotest stutter or fire. just fast
cranking the whole time. i put a spark tester on one random lead, port side upper, and got nothing, (i was running out of time, so i didn't do the others).

right now, I am assuming it was no-spark, instead of no fuel. i pumped the bulb till it was solid and right now, i'm assuming it filled the float bowls, but it was an old, suspect fuel line, so maybe pumping the bulb just filled up the line and fuel never made it to the carbs.

anyway, since i got no spark on the one cylinder i tested, i'm going with the reason for the no-start, being a no-spark condition.

i've never faced a no-spark situation on a v4 crossflow, so i'm asking you guys with more experience:

what you think is the most likely culprit?

I have the factory service manual, and i'll give the ignition section a read as soon as i get to my hotel room, but i still wanted to know from you guys who have been there before, what you think it is.

thanks,
peter

 

[Joe Reeves]

Re: v4 crossflow no spark

Spark must be tested with "all" park plugs removed. If no spark...........

Disconnect RED plug at engine. Re-Test spark by jumping solenoid. If you now have spark, the usual cause is a shorted ignition switch. To test switch...............

Re-connect the RED plug, disconnect the black/yellolw wire from the ignition switch. If you now have spark, replace the switch. If still no spark, the usual cause is a faulty powerpack.

 

[boobie]

Re: v4 crossflow no spark

Joe I don't want to start a pissing contest here, but how come you always say check spark with the plugs out? If you don't have spark with the plugs in, how is it going to start?? Remember the 1976 cross v's with the weak timer bases. Plugs in no spark, plugs out, spark. Just asking.

 

[Joe Reeves]

Re: v4 crossflow no spark

Boobie.... It requires that the engine turn over at least 300 rpm in order for the stator to energize the powerpack (keeping it simple). With the spark plugs installed, the compression has a tendency to lower the rpm and all four (4) cylinders will not fire properly for a spark test.

I've heard of the weak timer base thing but never really encountered one. Thought so a couple times but it was a weak starter that wouldn't crank fast enough.

The engine, when everything is as it should be, with all plugs installed, the spark that is actually obtained at cranking speed (as explained to me years ago by a factory rep) is erratic at best BUT within six (6) revolutions, at least one plug will fire which immediately increases the rpm to bring the ignition up to par.

I've had riggers at a large dealership I worked with, more than once they wouldn't be able to get a new engine started on a rig they just finished rigging and would explain to be that there was no spark. I'd yank the plugs... plenty of spark. Problem was always something like water in the fuel, flooded engine, someone pumped the oil primer bulb up too much (carb loaded with oil), etc.

Seems to me that the OMC manual mentions to remove the plugs but not sure... will check that tomorrow if I think of it.

 

[boobie]

Re: v4 crossflow no spark

Joe, I know about the 300 rpm and I still have a mechanical tach in my tool box to check rpm on the top of the flywheel nut. Let me know what you find in the manuals as I will look also. By the way, who was the OMC Rep that told you that? I've been through the the 1976 thing and lost some hair. LOL. Thanks for the reply.

 

[pcrussell50]

Re: v4 crossflow no spark

i hate to throw my own thread too far off topic, but how does over-squeezing the primer bulb oil down the cylinders?

-peter

 

[boobie]

Re: v4 crossflow no spark

Are you talking about the oil tank primer bulb or the fuel primer bulb??

 

[pcrussell50]

Re: v4 crossflow no spark

Are you talking about the oil tank primer bulb or the fuel primer bulb??

it's a '77... VRO did not start till later years

-Peter

 

[boobie]

Re: v4 crossflow no spark

Duh!!! I sit corrected. Thank You.