Spark Problems

cosmicblue · Post by **cosmicblue** » Wed Apr 14, 2004 7:35 pm

I have a 1975 Merc 440 SR. The sled runs but fouls a plug all the time. It has good comprssion, the flywheel key is ok, the carb has been cleaned and rebuilt. Whats the deal?

mercfrank · Post by **mercfrank** » Fri Apr 23, 2004 3:26 pm

What mix are you using my books show 50:1 normal service or 25:1 servere service & your plugs should be ACS43XLR but i'm using champion plugs N3C. I'm out in Colo. that plug seem to work out here in the high attiude. <blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by cosmicblue
 I have a 1975 Merc 440 SR. The sled runs but fouls a plug all the time. It has good comprssion, the flywheel key is ok, the carb has been cleaned and rebuilt. Whats the deal?
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SHewelt · Post by **SHewelt** » Sun May 09, 2004 8:45 pm

Another thing to watch is crank-seals. When they leak, you can really load-up the engine with gas. Often times I've missed it, thinking it was a carb/float problem, or weak spark. If the seals are old, save yourself some time & tail-chasing & replace them. It could be all that is wrong......Scott

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by mercfrank
 What mix are you using my books show 50:1 normal service or 25:1 servere service & your plugs should be ACS43XLR but i'm using champion plugs N3C. I'm out in Colo. that plug seem to work out here in the high attiude. <blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by cosmicblue
 I have a 1975 Merc 440 SR. The sled runs but fouls a plug all the time. It has good comprssion, the flywheel key is ok, the carb has been cleaned and rebuilt. Whats the deal?
<hr height="1" noshade id="quote"></blockquote id="quote">
<hr height="1" noshade id="quote"></blockquote id="quote">

cosmicblue · Post by **cosmicblue** » Thu Dec 23, 2004 10:49 pm

I have replaced a bad crank seal on the clutch side and still there is no change. It always fouls the same plug. Coils, wires, boots, plugs (NGK BR8ES), are all good. I buy new plugs it just runs for a bit and then the one plugs craps out. Reeds are good too. All out of ideas.

SledEd · Post by **SledEd** » Fri Jan 04, 2008 11:07 am

I realize this is an old post but I could really use come help. I have a 1974 Mercury 440 Max with this exact same problem. The #1 plug fowls and craps out. Always the same plug. I can’t get more then a couple, three miles and the plug fowls. When I put the plug out it’s not wet but black and won't spark. I’m using a 50:1 oil mix, compression is good, new wires, lots of spark when I put a new or cleaned plug back in, carb has just been cleaned and rebuild.

Don’t know what to do next, any help would be greatly appreciated.

250 twister · Post by **250 twister** » Sun Jan 06, 2008 2:14 pm

check the wiring for cracks breaks or weak wires from the stator to cdi. i had this problem on my 76 sno twister, it would start on first pull and run smoothly at idle, once it got to the mid range it would start to foul plugs buy dumping raw fuel out the exhaust and cause it to die. it was not a compression problem nor a jetting problem but simply rotted cracked corroded ignition wiring that could not deliver enough spark to the plugs to burn out all the fuel being brought in. i hope this helps, it only took my about 15 years to solve my problem.

Post by **Mercury** » Sun Jan 06, 2008 7:28 pm

What is the compression in PSI both sides?