Topic: Fouling plugs

[kuyarico]

I have a 76 750 F in which I recently went through the process of jetting. When I got the bike, it had run rough due to some loose carb boots, dirty pods, and a general need of a full tuneup. It had been equipped with pod filters and a Kerker megaphone (with no baffle) by the PO and was running 122 jets. The bike had a pretty big flat spot between 3 - 5,000 rpms. I didn't really notice it until I rode a friend's 78 K model. It had much more throttle response and low end torque. I recently installed a Kerker 2 in' competition baffle, and new pods (which I have oiled), and 130 jets. I also recently rebuilt the carbs using a Keyster kit. The needle clip is in the middle position. I also lubricated the advance mechanism which wasn't moving very freely. I did a camchain adjustment, valve adjustment, and timing after the carbs were rebuilt. I also synched the carbs using a Morgan Carbtune. The bike ran very strong at this point, but would backfire a bit between 3500 rpms and 4100 rpms and on deceleration. Also, after about 70 miles of riding, the bike would start to lose some of it's mojo. Pulling the plugs revealed that the 1 and 4 plugs are getting fouled. 2 and 3 look nice and tan. My first inclination was that the timing on the 1 - 4 was off. The bike came equipped with a Dyna S. I had to adjust the 1 - 4 pickup slightly to get the advance timing correct.  I took another run but still ended up fouling plugs. So now, I'm thinking that I have a bad coil. Rather than test the old coils, I decided to upgrade to new 3 ohm dyna coils with 7mm copper core wires (which I had planned on doing anyway). I swapped them out. Threw in some new plugs, and still continued to foul the 1 - 4 plugs. At this point, I'm baffled. I rechecked my floats by draining each float bowls separately. The output from each bowl matched almost exactly. I had adjusted them to spec during the carb rebuild. The bike runs really strong with new plugs until they get fouled. It doesn't emit any kind of smoke. I do notice that the bike does surge and stumble very slightly in lower gears between 3500 rpm and 4200 rpm which is also where it backfires. While this does seem like a lean condition, the plugs tell a different story. I am almost at a loss here. My next step will be to buy a compression tester and check for compression. Other than that, does anyone have any ideas?

[mlinder]

Check to make sure the 1-4 coil is good.
Crappy spark could foul the plugs for sure.
Since 1 and 4 are on the same coil...
well.. it's a possibility.

[jdigga]

That would suck if your brand new coil is bad.

[kuyarico]

Check to make sure the 1-4 coil is good.
Crappy spark could foul the plugs for sure.
Since 1 and 4 are on the same coil...
well.. it's a possibility.

I just replaced the original coils with brand new Dyna 3 ohm coils. I'm going to swap them and retest for good measure. But it doesn't seem likely that the new coils are bad.

[mlinder]

Possibly not the coils, but perhaps the connections to the coils?
If something is grounding out, or there is a bad connection, the coil wont be able to get enough juice to store up for the spark?

[kuyarico]

I'll re-trace the connections to the coils. I too think that it has something to do with the coil. 

[eldar]

Well if it starts off good, why do you think it is the coil? Especially if it happens with 2 different coils?  I mean if I was having that issue, I would check timing and once that was dead on, then pull the plugs and lay them on the head and turn it over and watch the spark.

I have a dyna now and am very surprised at how white and clean my plugs are.  I kept the stock coils and gapped my plugs more and went back to the D8 plugs and they are still white even at the base of the insulator. You know what? I think it is running rich. Why do I think that? Well after even a couple minutes of running, no choke needed any more. At mid rpms, if I even roll on the gas too fast, not a snap, just a quick roll, I get a stumble and then it goes like hell since now it is opened up to the mains. Yanking the choke completely dogs it out if I try cut off some air to minimize the stumble. I know you all are probably still thinking that I am lean but what is one CLEAR indicator of lean running? Blued pipes. I have a slight yellowish look which is common on the 78 year but no blue.

My point is that with a dyna and still having tan plugs, I think you are running rich. You might not be at lower rpms but maybe in the mains. Before you rejet, why not just drop the needles? Try something simple first. Or try going back to the old jets and raising the needle?

I really do not think this is spark related even though it is on linked plugs but lay the plugs on the head and check it that way.

[kuyarico]

I didn't get a chance to look this tonight, but the reason I thought that it may be due to weak spark was because the 2 - 3 plugs looked decent. I do admit that 130 mains are pretty big, but it pulls very nicely in the higher rpms. It's at the lower rpms where it surges and pops a bit. I'll lay a plug on the head to check the spark tomorrow. Does anyone know what gaps to run with a dyna coil? I'm still running at the stock setting.

[eldar]

With the stock I think I went to .035 or something like that. With the dynas you could probably do .05.

Well the upper might be ok but you spend the most time in the middle with both the idle and mains. So maybe drop the needles some to lean out the middle range.

[CB750F2]

G/Day. I suggest that you check the exhaust header bolts for tightness. Pat from Australia.

[Somemonkey]

So whatever happened with this? Did this ever get resolved? I'm having the same issue with my 2 and 3 plugs and wondered where I should start.

[kuyarico]

So whatever happened with this? Did this ever get resolved? I'm having the same issue with my 2 and 3 plugs and wondered where I should start.

I finally got things resolved. I think that it was a combination of things. #1. Weak battery, which I did not suspect because everything my idiot lights and headlights were somewhat bright. I suspect that I'm still losing voltage at my cruddy fuse box. #2. I'm bad at math. When I rebuilt my carbs, I adjusted my floats I had incorrectly converted mm to inches. It turns out that I was running 31mm instead of the factory spec of 26. #3. Timing on the 1 - 4 cyls were off. #4. I yanked the header off this bike for the first time and discovered that the exhaust seals were non-existent. So I replaced those. Everything finally came together after I had replaced the battery and performed a carb sync.

sabotage, Have you performed all of the regular maintenance things. Cam chain adjustment, valve adjustment, points gap and timing, and carb sync. What is your current setup? Are you running pods or a standard airbox? Is your battery in good order? If you suspect that it is the coil, try switching them. If that doesn't work, I'd re-verify your regular maintenance items. Check for vacuum leaks on the carb boots. Check your floats. etc. Post more of your symptoms and details about your setup. I'm sure one of the old timers will chime in 

[Somemonkey]

Actually, I haven't done anything other than adjusting the air screws in the carbs and replacing the plugs.
I have a 76 CB550 which is currently running with the original airbox and, as far as I know, hasn't had any special mods. The battery is new has a good charge. This is the most recent issue I've had

The other day I took it out with brand new plugs and it died on me after about five minutes. (of course it died at a busy intersection)  I had to push the bike up on the sidewalk while people were giving me dirty looks. She started again after a few minutes and I was able to get her home but when I checked the plugs again, 1 and 4 were good but 2 and 3 were covered with soot.
 
From reading through your posts, I think I have the problem narrowed down to the following:
Bad exhaust gaskets - which I don't remember seeing when I took the pipes off a few weeks ago.
Bad timing on cylinders 2 & 3
Carbs in need of cleaning
Bad ignition coils

I'd like to start with the timing. That means I have to find a timing light at Pep Boys or NAPA. I'll do some research today to find out the cost of such a thing. After that I'm going to check the spark on 2 and 3 to see if the coils are bad. If they're ok, I'll then take out the carbs and start cleaning them. I don't know how much the exhaust gaskets would have to do with all this but from what I've read, they are not to be discounted as part of the problem.

If you or anyone else has some input for me, that would be greatly appreciated.

76 Honda CB550

[eldar]

I got a cheapo timing light from harbor freight for about 12 bucks. Has worked flawlessly. Dont spend a lot cause some salesman says you need too.

[kuyarico]

I think that the best thing for you would be to do a full tuneup. You will learn a lot about this bike in the process. Check the FAQs. I like to do the cam chain first, then the valve clearances. And then the points gap and timing. Messing with your carbs should be the last thing you do. Your issue may very well be solved with a good tune up. If is doesn't, then you can rule out those issues. Next step would be to clean the carbs thoroughly and sync them. Check for vacuum leaks on the boots. If you don't have a Carb sync tool like a Morgan Carbtune, then perform a bench sync(see FAQs). Keep us posted.

[Somemonkey]

I'll take your advice and give the bike a tune up first. I should be able to work on it this weekend, so I'll post an update Saturday or Sunday. Thanks for the tips!

[TwoTired]

How old is your air filter?

It is addressed as part of a tune up.

[Somemonkey]

How old is your air filter?

It is addressed as part of a tune up.

I don't think the air filter is all that old. It's the foam kind and I rinsed it out a couple weeks ago. Seems fine.