Weak spark

[gldavison]

I am having trouble getting my engine to fire. I have fuel (now) and spark but the spark seems very weak. I have 8-11 v going into the coil but at the plug I have a spark that is weak in my estimation. I did switch out coils but found same thing to happening.
Any suggestions?

Thank you!
Greg

 

[Don S]

Re: Weak spark

What are you working on ??????????

Make, model, year, etc.

 

[gldavison]

Re: Weak spark

Sorry- this is a '76 Merc 888 302 Ford v8

 

[Haut Medoc]

Re: Weak spark

How old are the ignition wires?......
The cap & rotor are in good condition?​

 

[wire2]

Re: Weak spark

Pull the center HV lead from the distributor and hold it near the block while someone turns key to start. Is the spark still weak? If so, look at the points.
Is there a peak on 1 side, crater on other? Change them and condenser, set gap to .018", try again.

8-11v is normal while running, the + lead is through a resistor to limit current and keep coil from overheating. It will be a full 12v when cranking.

 

[gldavison]

Re: Weak spark

Thanks for the advice. Points and condesor are new. The cap and rotor seems good, I cleaned up the contacts when changing the points. Gap is OK.
The plug wires I did not change as they appear to be in very good condition. I spose I could change the rotor/cap and wires to see if this helps.
The spark off the coil does seem weak as well.
Can a coil produce spark but just not strong enough one if it goes bad? I thought since I had a spark the coil was good. Perhaps this is the bugger, although I did put a new one on and the spark looked the same so I returned it...... Thanks for your thoughts.

Greg

 

[wire2]

Re: Weak spark

If you can grab another coil from somewhere, try it.

You can test the wires with an Ohmmeter, should be ~1000Ω per inch. If way more, replace them.

What color is the spark, red or blue?

 

[gldavison]

Re: Weak spark

The spark is blue.

Thanks,
Greg

 

[wire2]

Re: Weak spark

Blue spark is good.
If the coil wire can produce ?" long spark or more, I think you're ok.
Are you viewing the "weak" spark in daylight?

 

[gldavison]

Re: Weak spark

yes I am working on it in the daylight. For awhile I did not think I had spark till I was working on it towards dusk and it showed up.
Just if my spark is OK than why won't she fire? I have gas to carb. This boat has been sitting for 10 years without use, fyi.

Thanks
Greg

 

[wire2]

Re: Weak spark

Does gas spray into carb if you open the throttle from idle position?

Try pouring a couple tablespoons of gas into carb & hit start.

 

[Daddy5295]

Re: Weak spark

Try wire's suggestion and see if that makes it start. If it sat for ten yrs there's probably varnish in the carburetor, clogging off fuel from getting into the intake. Then time to take it off and give a good cleaning and rebuild.

 

[gldavison]

Re: Weak spark

Hi Guys-
Thanks for the help and patience thus far. I have given everything a good going over but still no fire.

I rebuilt the carb and cleaned it thoroughly to getting to this point. I do have fuel in the carb chamber, at least it is wet when I check.

I pulled the coil wire at the distributor as suggested and inserted a screwdriver and went to ground. I was getting spark but it looked more white than blue or red as asked earlier. I then pulled a plug and checked the spark at the plug and it also seemed to be a whiteish color.

I am really sorry to keep bugging you guys with my problems. I am very grateful however that you are hanging in there with me and feeding me advice, thank for that.

What's next?

Greg

 

[gldavison]

Re: Weak spark

[QUOTE=wire2;1464572]If you can grab another coil from somewhere, try it.

You can test the wires with an Ohmmeter, should be ~1000Ω per inch. If way more, replace them.

What color is the spark, red or blue?[/QUOTE]

I tried this and I simply got the red light to flash on my meter with no digital reading of ohms each time the cylinder fired.

The coil was @ 1888 ohms.

Thanks.
Greg

 

[gldavison]

Re: Weak spark

Please don't give up on me. I need you guys.
Thanks
Greg

 

[wire2]

Re: Weak spark

"I tried this and I simply got the red light to flash on my meter with no digital reading of ohms each time the cylinder fired.

The coil was @ 1888 ohms.

Thanks.
Greg[/QUOTE]"


No, not like that. Motor OFF!

Remove 1 wire at a time, place the Ohmmeter leads on each end. Set the scale to R x 10K

Never put any electrical energy into a circuit when you're reading resistance.

I'm surprised you didn't get a shock or damage the meter.
Since you're still posting, you must be ok.

 

[gldavison]

Re: Weak spark

Oops, thanks for the advice. I did also try to test the wires only and did not get any reading. This was done the correct way.

Could the trim limit switch be cutting out the engine preventing it from starting? I found that my switch is bad. I will try to bypass the switch and reconnect wires to see.

I am about at my wits end with this thing.

Thanks again,

Greg

 

[thrasher]

Re: Weak spark

Have you checked compression? Everyone seems to be talking like it's an electrical problem, but if the engine stood for 10 years, there could be sticking valves. That would mean no compression and no starting.. My apologies if I missed something.

Gary

 

[gldavison]

Re: Weak spark

Gary,

Thanks for taking this road. A co worker suggested this too. My thinking was that if one hole was out that the rest would still fire and simply produce a miss. Am I wrong in this thinking? Thanks again for your help in my dilema.

Greg

 

[thrasher]

Re: Weak spark

Hi Greg,

If it was just one cylinder, the engine would probably start, my concern would be that it's more than one cylinder. Its very common for the valve stem to rust when the engine stops with the valves in the open position, then the valve can't return back onto the valve seat because the rust interferes with the valve guide and you loose compression on that cylinder. If you can get a compression tester (they are quite cheap) it would be a quick and easy way to check the compression, then you can rule out this problem, or know that you have a head's off job to fix the valves.
An engine requires 3 things to work, compression, spark and fuel. I think your previous tests prove that you have a spark (If it's weak it will limit max performance, but shouldn't stop the engine from starting), so we need to look at the other 2!! You say you rebuilt the carb (So I am assuming you did that correctly), so that only leaves compression..

Gary