Topic: One fouled spark plug - hole in exhaust?

[zabzob]

My #3 spark plug has fouled a couple of times now.

First time, I had a lot of backfiring. This went away after a while and instead I had poor idle and low power, indicating that I was running on 3 cylinders. Felt the header, and #3 was lukewarm at best. Attached a timing light to #3 to see if it was firing -- only intermittently. Pulled the plug and found that it was carbon fouled. Swapped plugs #4 and #3 and the problem moved, so it's clearly the plug itself. Replaced the plug and all was well for about 200 miles.

Yesterday, it started backfiring again, then went quiet. Header #3 not so hot. Haven't pulled the plug yet but I suspect it's the same thing.

Attached is a picture of a hole in the right side 4-2 muffler. As you can see, it's really big -- as big as the exhaust outlet itself. Could this be the cause of a carbon fouled plug? #4 isn't fouling... what's up with that? What other problems can this cause?

[dave500]

check the plug cap resistance.

[zabzob]

I can recheck that today, but I think it'll check out fine. All plug caps were replaced about 400 miles ago when I got the bike started up again after 17 years. All of the electrical connections have been gone over as well.

[camelman]

Might as well tell us what all you did after it sat that long, and how long you have been riding it since you started it up.  A whole slew of issues can arise from sitting that long.  The most likely culprit being dirty carbs.

Also, there are a few performance/handing items that you could likely do that will radically change how much you like riding your bike, and they won't cost much, and which we all will undoubtedly comment on.  For instance, fitting new steering head bearings will make such a large difference in how your bike rides that you'll be amazed you survived riding it without crashing before (assuming you haven't changed them yet).

Let us know what year/model you are on too.  Also, I'm glad you got it going... there's nothing like riding a motorcycle!

Camelman

[Tews19]

Might as well tell us what all you did after it sat that long, and how long you have been riding it since you started it up.  A whole slew of issues can arise from sitting that long.  The most likely culprit being dirty carbs.

Also, there are a few performance/handing items that you could likely do that will radically change how much you like riding your bike, and they won't cost much, and which we all will undoubtedly comment on.  For instance, fitting new steering head bearings will make such a large difference in how your bike rides that you'll be amazed you survived riding it without crashing before (assuming you haven't changed them yet).

Let us know what year/model you are on too.  Also, I'm glad you got it going... there's nothing like riding a motorcycle!

Camelman

Ok, now I have read a few threads of members changing out the steering head bearings. Hondaman has made mention of this as well.. Being new to bikes and now having a project 550f I want to resurrect, what brand should I look at for head steering bearings? I also need to replace the lower triple tree? I think that's what is it called. I know this as the right side is bent... Frame is not bent and I can post a pic to give a clearer pitcure as to what I am talking about.  I figure I can replace the bearings the same time I look into this... How drastic and what are the noticeable drive changes when replacing the bearings?? Sorry to sound elementary but still earning about these wonderful bikes.

[zabzob]

Hi Camelman,

Ah yes, once again I forgot to say the model of bike. I've updated my sig. 1975 CB750K5.

Since getting the bike, I have:
-Rebuilt the carbs. Lots of goo in there, cleaned the very well and made sure all the passages were open. I am willing to accept that I missed something though... I understand that 2-3 cleanings are often required to make them work perfectly. Floats were also set properly. Carbs were synced.
-Replaced wiring harness with new one from Parts N More.
-Cleaned all bullet connectors
-Replaced all blade connectors
-New AGM battery
-Rebuilt front brake caliper
-Rebuilt master cylinder
-New braided steel brake line
-New brake pads/shoes
-New sprockets
-New x-ring chain
-Tried to adjust the cam chain, but it still rattles
-New tires

The wheel/steering bearings and fork rebuild are definitely on the list for the winter, along with possibly powder coating the frame. While it's apart, I'll check the swingarm as well.

[w1sa]

Check the valve clearances are adequate, especially #3..........

[zabzob]

Ah, I knew I forgot to mention something. I set the valves before firing up the bike. After a couple hundred miles, I ran Seafoam through it to clear combustion chamber buildup. Ran it for a couple of days to burn off all I could, then let it sit for 24 hours before doing all the valves again. A couple had changed quite a bit.

Also, ignition timing was set with a timing light. I've got Boyer Bransden ignition.

Annnnd the fuse panel has been replaced with modern ATO/ATC type one.

[dave500]

i use boyer,did you set it as per the boyer instructions?dont set the light at the "f" mark,increase the revs watching the advance take place untill it stops advancing then adjust it to within those full advance marks.

[zabzob]

Ah, okay, I set it wrong then. I'll have to redo that as soon as I can get to my buddy's shop. Would having this set incorrectly make it idle rough?

[dave500]

it will end up some what retarded so yeah itll idle rough,get that sorted before anyone starts winding air screws.