5.7 has spark question

[Mild 85]

I have a 1985 30' chris craft with twin 350s. when I bought boat I did a compression test, 127-140psi on all cyls. Drove boat to marina in Key Largo. Both were running fine. Three weeks later starboard engine fires right up. Port side turns over but wont run. Check the thunderbolt IV ignition with troubleshooting procedure I found online. It shows to be good. I swapped carbs to see if that was it nope. With spark tester I show spark at plug. When looking at spark at end of spark plug it is orange not white or blue. Also other things ive done. New cap, rotor, wires, and plugs gaped at .040. And they share fuel from same tank.

Any ideas?

 

[alldodge]

Howdy

When you pump the throttle do you see fuel squirt in the throat of the carb?

 

[Mild 85]

Yes sir

 

[Mild 85]

Could it be the sensor in the dist. I know it is basically a magnetic pickup, could it not be sending as strong a siginal as it should?

 

[alldodge]

You saying you have spark, just maybe not good spark. Since your getting spark I don't see it being a distributer issue. Check for spark by pulling the coil wire off and see if it comes steady, if it is steady I would go back to the fuel side.

Even a weak spark will set off gas unless your getting very little.

Just to double check here is the TB-4 troubleshooting guide. Is it the same as the one you have?

 

[grewvin1]

Swap your coil for a try.

 

[Mild 85]

yes, that is the one I used. I find it hard to believe that something mechanical happened. I've tried pouring a little gas in carb and small amounts of starting fluid but nothing

 

[alldodge]

Well your on the lower end on compression, that is IF your gauge is correct. You should have 150 psi =/- 10% on all cylinders. Even with low compression it should fire, but to get nothing with using either then I would be rechecking the spark. Also pull the cap back off and make sure the rotor tip isn't damaged

Also crank it to make sure the rotor is turning

 

[Mild 85]

I checked for rotation of rotor, good. Put new cap and rotor on as well. What a bad design btw. The rotor has to be destroyed to get it off.

 

[alldodge]

As I'm sure you know, an engine needs three things to run, fuel, air and spark at the correct time. Your telling us that you have all three but it will not even try to hit, your getting nothing. Now if your compression is a lot lower then what your gauge is showing then this could keep it from running, but starting fluid (either) and even a slight spark would cause something to happen.

I'm suggesting you need to go back to what you know is correct and recheck, something is not happening.

 

[Mild 85]

Only thing I have left is timing. What does it sound like when that happens? Never happened to me before. I don't have my timing light here.

 

[alldodge]

If the timing was off you would get a back fire out the carb or exhaust, or while cranking the motor would slow and almost stop and then crank some more. There should be some kind of hit, even the slightest and I would think timing, right now I don't think that's the issue

 

[Mild 85]

I try it again when I get to boat and let you know

 

[Mild 85]

How do I put video of attempted starting?

 

[alldodge]

How do I put video of attempted starting?

Upload to utube then link here using the icon that looks like a film strip.

 

[Mild 85]

It dosent sound like it jumped time. spark at plug is orange not white or blue. Can a bad coil cause this

 

[JustJason]

Are you grounding out a plug to check for spark, or are you using an adjustable gap spark tester, or timing light, to check for spark output?

 

[Mild 85]

Yes to grounding the plug. And yes to adjustable spark tester. I checked it from the coil with the adjustable tester. I tested at the plug with inline tester that lights up.

 

[JustJason]

If you are talking about one of those neon testers those are only good for lawnmowers. What you need is either a timing light or an adjustable gap spark tester where you can set the gap to 7/16ths of an inch. If the timing light doesn't flash, there is no spark. If it flashes, there is spark. If spark doesn't jump a 7/16'ths gap, and also be hot and blue in color, the spark is bad. If it jumps it, but it's orange/yellow, spark is bad. And you would want to start by checking voltages at the coil during cranking (should be 9V or better) disconnecting the tachometer, and if voltage is good, and disconnecting the tach makes no change, then replace the coil.

 

[Mild 85]

I have an adjustable gap tester. and the spark across was orange