Spark plug trouble.
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Road Captain
Joined: Dec 2008
Posts: 599
Likes: 1
From: Arkansas
Spark plug trouble.
A couple of months ago I fouled the plug in my front cylinder. Having twelve thousand miles on my bike, I thought it was time for new ones. I replaced them , and my bike ran like a rocket ship. Started better, ran better, everything was good. A couple of weeks later same thing. It started missing, running like crap. Checked the plugs, front plug out again. So this time I switched the plug wires to check the wires out. Got new plugs and a couple of weeks later, same thing. Front plug out again. So I know its not the plug wires. Checked the spark on both plugs, got fire. I checked the compression on both cylinders, front was 180 psi, back was 150 psi. It doesn't smoke, doesn't make any kind of strange rackett. It just blacks out the front plug. I cleaned the jets, checked the carb. All of thats good. All to no avail. Still running like crap. Does anyone know the correct compression? Anyone have any ideas?
Road Warrior
Joined: Jul 2006
Posts: 1,768
Likes: 4
From: eastern Pa
what year ?
what model ?
sounds like the petcock is bad (vac hose to carb) is sending more fuel than whats needed
this will cause a over rich mixture at the low end of RPM range
easy is to take hose off and put vac tester on petcock and see if any vac there
i forget off hand what it should read. 7-10 lb's
what model ?
sounds like the petcock is bad (vac hose to carb) is sending more fuel than whats needed
this will cause a over rich mixture at the low end of RPM range
easy is to take hose off and put vac tester on petcock and see if any vac there
i forget off hand what it should read. 7-10 lb's
Club Member
Joined: Feb 2007
Posts: 16,320
Likes: 306
From: Boynton Beach, FloriDuh
what year ?
what model ?
sounds like the petcock is bad (vac hose to carb) is sending more fuel than whats needed
this will cause a over rich mixture at the low end of RPM range
easy is to take hose off and put vac tester on petcock and see if any vac there
i forget off hand what it should read. 7-10 lb's
what model ?
sounds like the petcock is bad (vac hose to carb) is sending more fuel than whats needed
this will cause a over rich mixture at the low end of RPM range
easy is to take hose off and put vac tester on petcock and see if any vac there
i forget off hand what it should read. 7-10 lb's
Road Warrior
Joined: Nov 2008
Posts: 1,775
Likes: 6
From: Simpson County Kentucky
I'd like to know why there is 17% difference between the front and rear cylinders on the comp test. Was this a dry or wet test? Was the throttle wide open when the test was done? What does the plug that is fouling look like and please don't say like crap. What kind of spark plugs are being used? What's the gap on those plugs?
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Cruiser
Joined: Jan 2008
Posts: 213
Likes: 1
From: The Suncoast (FLA)
Compression is equal to 14.7 PSI (ambient) x compression ratio.
10:1 pistons shoud read about 147 PSI. For a reading of 180 you would need 12:1 pistons.
+1 what cHarley wrote
10:1 pistons shoud read about 147 PSI. For a reading of 180 you would need 12:1 pistons.
+1 what cHarley wrote
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Road Warrior
Joined: Jul 2006
Posts: 1,768
Likes: 4
From: eastern Pa
Sorry, but the petcock has nothing to do with excess fuel to the cylinders as it only controls the availability of fuel flow to the float bowl. The float and float needle meter fuel from the tank into the float bowl. Many people replace the vacuum controlled petcock with non controlled high flow unit (Pringle). Generally speaking, the only problem a petcock can cause is a lack of fuel.
already went thru this on my bike
sorry cHarley
Last edited by RATROD HOG; Dec 30, 2008 at 02:15 PM.
Club Member
Joined: Feb 2007
Posts: 16,320
Likes: 306
From: Boynton Beach, FloriDuh
I really don't mean to be rude, but you obviously have no clue how a carb works and misinformation is worse than no information.
Last edited by cHarley; Dec 30, 2008 at 02:58 PM.