fouled plugs

How many different things have you seen cause fouled plugs? Can something besides the carbs cause fouled plugs?

 

Sure. OIL fouled?

-a bad valve stem seal or seals;

-worn rings (extreme cases.)

Quite honestly, given the regularity with which valve stem seals seem to go bad on old British bikes, I'm surprised it isn't more of a common issue with the XJs.

 

Using NGK resistor plugs has resulted in lots of fouled plugs for me. If you have an R as the second letter in your plug code, get rid of it for your new plugs (Example DR8 ESL is resistor, D8 ESL is not/ BR7 ES bad, B7 ES good etc)

 

Using NGK resistor plugs has resulted in lots of fouled plugs for me on various bikes. If you have an R as the second letter in your plug code, get rid of it for your new plugs (Example DR8 ESL is resistor, D8 ESL is not/ BR7 ES bad, B7 ES good etc)

I think our bikes should not have resistor plugs anyway since they have a (much more reliable, but still fallible) resistor in the cap...

 

If you're using resistor plugs AND caps, it can cause a bad burn. Only use one of the other.

By bad burn, I mean it may be missing some power strokes and causing a buildup of gas on the plug. When it fires, it's rich and you see it as carbon fouling.

OR you're running too rich at idle.

 

If you're using resistor plugs AND caps, it can cause a bad burn. Only use one of the other.

By bad burn, I mean it may be missing some power strokes and causing a buildup of gas on the plug. When it fires, it's rich and you see it as carbon fouling.

OR you're running too rich at idle.

 

Wow this thread has an echo :? lol

EDIT-: huh, didn't do it that time...

 

sorry to revive a year old tread..
my 83 750 seca when I tried firing it very early this spring I believe I gas fouled the plugs in 1 and 2 due to the mix of bad gas and low battery, anyways,

I had forgotten about it and since it has been running good enough on fresh gas and a full battery. (its only been back on the road for a week).

yesterday I noticed that it has been doing a lot more stumbling on choke and warm idle since last year, when I had my brother soldering the wires on my aux light switch I pulled the plugs out and not surprisingly plugs 3/4 were the nice light brown, 1/2 were both carbon sooty.

gonna either switch out 1/2 or all 4 but after that long explanation my questions are these.
1. what are the plug gaps you would recommend for a 750.
2. I ride in cold to warm weather conditions usually , what heat range would be best for colder weather riding or does it not matter.
3. if I only replace 1/2 are there any negative effects of not using the same plug in each cyl, (just curious)

thanks

Krafty

 

I would replace all 4 plugs. After you ride it for a while, you'll have a good indication of your carb settings and know if you have to lean out 1/2.
There should be a label on the inside of one of the side panels that shows the recommended plug and gap. My 700 uses NGK BP8ES with a gap of .7-.8 mm (.027-.031 in.). I've always used the recommended plug and I've ridden in temps from 27F to 90+F with no problems.

 

Stock plugs. Stock heat range.

Clean the ones you have and adjust the pilot mixture on the two cylinders that are fouling. Those two are running rich; it's not the spark plugs.

 

@ k-moe, I've heard that once plugs are fouled then they should not be run in motorcycles due to weaker ignition systems or something like that.

also my bike has the BR 8ES not the BP8ES, that was from the old bike mechanic from my uncles shoplast year, should I not be running the resistor plugs in my bike? no sign of spark plug info inside the side covers, just battery info stickers.

since yesterday the plugs have not sooted up near as bad but it was still running rough on idle, this evening I drained all 4 fuel bowels then used the rubber tube to find float levels, 2,3,4 were at the same level as the heads of the float bowel screws, couldnt check one cause the drain tube did not work but I backed the screw all the way out to drain.

is that not way too low for fuel level?

 

If you have resistor plug caps you definately should not be running resistor plugs. If you are then that is the most likely reason those plugs are fouling.

Yes plugs can be cleaned and reused, though they are cheap enough that new ones are not a bad idea (I'm a cheap bastard and haven't bought a new sparkplug in ten years. My wood chipper still has the original 1964 sparkplug in it).

Fuel level should be 3mm below the float bowl gasket +/- 1mm when the carbs are level. A low fuel level won't cause plug fouling. What you'll get is fuel starvation during high-speed/ high RMP riding, and stalling during panic stops.

 

My XJ700 has two original resistor caps and two original non-resistor caps and the owner's manual specifies resistor plugs. I am running resistor plugs with no issues.

 

The XJ750 (the bike we are talking about) has resistor caps and non-resistor plugs. The XJ700 has a different TCI from the 750.

 

I thought it was odd to have both a resistor and non-resistor stock plug caps.

 

It is.
From Len's catalog:

XJ700 air-cooled models:

Pick-up coils:
120 ohms +/- 20% = 96 ohms to 144 ohms acceptable range


Ignition Coils:

Primary side (input from main wiring harness):
2.7 ohms +/- 10% = 2.43 ohms - 2.97 ohms acceptable range

Secondary side (spark plug wires, without their end caps):
12K ohms +/- 20% = 9,600 ohms - 14,400 ohms acceptable range


Spark plug caps:
1985 N/NC models: 5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range
1986 S/SC models: 10K +/- 20% = 8,000 to 12,000 ohms per cap acceptable range


Spark plugs:
1985 N/NC models: 0 ohms per plug
1986 S/SC models: 5K ohms per plug


So long as the total resistance of the plug and cap combination are the same as what is called for you can switch to resistor plugs, or non resistor plugs, or any combination thereof and still have good spark.

The resistors are there to supress radio frequency interference, which can cause the TCI to malfunction (weak spark, mis-timed spark), or even fail altogether.

 

with the good cleaning last night and the float bowel draining I was talking about the bike is running a lot stronger, ill give it about a week then pull the plugs again and see what they tell me.

 

Not sure I fully understand that, but the owner's manual for my 85 XJ700N calls for resistor plugs, which is what I am using. Oddly, the service manual I have calls for non-resistor plugs. Go figure!

 

was wondering if someone could help me.. I have an 82 XJ650

just bought the Dynatek DC1-1..3-ohm dual output and Dynatek copper core plug wire set..

using BPR7ES plugs on all four cylinders..

Is this the recommended setting (compare to factory settings)..in order to have correct resistance on the primary and secondary coils.

The dynatek wires are non-resistor caps..
Both the ignition coils (pri n sec) measure 14 K ohms..
and BPR7ES plugs..

should I change out the primary coils to non resistor plugs to have 5 ohms reading...Cylinder 4 plug is fouled up, while the rest are running consistent with each other...Thanks and lost

 

Hey heyalvin, did you sort it out yet?
I'm planning to upgrade to dynatek DC 1-1 as well.

 

85 Xj700 owner.
When I pulled my carbs apart and cleaned them. I reinstalled them with the pilot air jet and the main air jet at the top of the carb in side the top hat in reversed order. I figured main airjet bigger than pilot air jet I was wrong. Yes the bike would run just fine but I could not get 20 miles with out fouled plugs and I was going though gas like there was no tomarrow. The pilot air jet is clossest to the engine and is the bigger of the two under the top hat. I switched them and it fixed everything completly.