Topic: Continual Plug Fouling - Where do I Start

[imamotohead]

Hello All,

I'm having trouble keeping my '75 750F from fouling spark plugs.  I just got it to the point that I can really ride it but I can't seem to fix this issue.  Tonight I rode the bike approximately 15 miles through stop and go traffic.  It was running great when it suddenly dropped a cylinder (#4) - plug fouled.  Last weekend I rode it approximately 10 miles and it was running great.  I was on surface streets but not too much traffic.  Got to my destination, shut the bike down, came back 20 minutes later, the bike started right up but cylinder #1 was not firing - plug fouled.  I find it confusing that one plug fouls out and the others don't seem to.  All the plugs are black but not wet. I know its rich but I'm not sure where to start working to fix it.  Tonight it fouled the plug while I was idling along in traffic but last week the plug fouled after I shut it down and then restarted a short time later.  Should I start by readjusting the idle screws or would something else be more appropriate.  Any suggestions will be greatly appreciated!

Thanks,

Scott

'75 CB 750F Cafe
'07 Aprilia Tuono - for sale
'99 Ducati ST2 

[scottly]

Your problem is most likely due to a problem with the #1 carburetor. The first thing I would check is the fuel level in the float bowl, using the "clear tube method".

[phil71]

something doesn't add up. Carb issues don't 'run great' and suddenly foul a plug.
 A condition rich enough to cause that would manifest itself as varying degrees of running #$%*ty before it gives up.
Not contradicting Scottly, he's  right, it's a great idea to check that first, especially since it's right on the end.

  If that comes up good, I'd start looking at spark..
 I've seen a bike or two that had charging issues cause similar stuff and were very hard to troubleshoot.
These ignition systems can be pretty power-hungry, and if you drop a leg of at the rectifier or something, the  bike still charges(ish) but you eventually get to an undervolt situation that makes spark weak, and that can look like a rich condition.

[dave500]

hows the air filter?if its old or unknown but looks clean it can still be choked,also check the resistance through the plug caps,,they unscrew from the lead,then probe them with a multimeter,,your looking for 5000 ohms,be sure your not lugging the engine,,these like to rev and burn hot and clean.

[nancy]

Check for fuel delivery to carbs from tank - are your fuel lines running downhill, no kinks? Do u have crud in your tank and consequently in your float bowls?

[dave500]

umm?that wont foul plugs nancy....

[ekpent]

Not much info to go on. Have you totally cleaned the carbs. How close to stock are you and what size jets are in there now.
  One common symptom so far is that the 1 and 4 plug foul and they do do work as a pair off the coil.Have you lost a 2 or 3 yet ? Are you putting in brand new correct plugs to replace which is best or trying to clean and reuse the old ones ?

[imamotohead]

Thanks for the replies.  The motor is stock as are the carbs.  Honestly don't know the jet sizes but I am assuming they are stock.  The bike was pretty ratty when I got it but completely stock  I had a local shop with a good reputation rebuild he carbs so they are clean (allegedly).  The tank is clean, and all the lines are new.  I am running the stock airbox and the filter is new.  I'll check the charging system.  The spark plugs are new (were before last night). The plug wires and caps are new as are the Dyna 5 ohm coils.  I am running a PAMCO ignition.  One dumb question - do the carbs have to be removed to rejet them?  Let the trouble shooting begin.

[ekpent]

Its easier to change jets when off but luckily you should have the snap bowls on the carbs so with some fiddling you can change them mounted. Hopefully when they rebuilt your carbs they reused the stock brass bits like jets etc. Some of the aftermarket can be problematic. May come a point when you may have to recheck their carb work if its not electrical.

[XLerate]

Apologies for length here, can't seem to avoid it...

Seems to me you'd first want to verify the correct plug # and heat range of plugs used.

Also brand. Please don't shoot, I know most bike guys LOVE NGK's! Me too, until recently. Very sorry to say that after being a great fan of NGK plugs, as was my neighbor, we both experienced serious and identical misery. For bikes I always considered NGK 'BEST!', end of discussion.

That was until I had a new correct NGK plug installed in an ATC110 work fine to start and run the bike, fresh rebuilt engine and carb tuned properly, then after hitting kill switch no restart. Checked plug, no good, no continuity. Installed second new correct NGK plug, identical scenario: start/run/fail. Installed 3rd new correct NGK plug: repeat. Correct plug was used in all.

2 plugs purchased from one store, 3rd from a different store so it couldn't have been a 'bad package of plugs'. Even installed a 4th new correct NGK requesting store pull from a different box than last purchase - same run/dead experience!

Changed back to my former favorite, Champion. No failure after multiple start/run/shutdown events, problem solved. During same time period my neighbor was working on his Honda CT90, uses same plug. He experienced exactly the same thing, identical. Brand new correct NGK plug installed, engine ran right one time, shut it down, followed by total failure of plug. He also installed 2nd NGK, and then a 3rd NGK, repeat - identical - start/run/fail.

Plugs came from different stores, different boxes purchased at obviously different times. Very popular plug so lots of them go through the parts store's inventory, meaning different mfg. runs of product.

He also changed to Champion at my suggestion - no further problems at all. Also experienced similar problems with other NGK's #'s in the last 12-18 months. There's a problem in their mfg. process. Don't know if NGK mfgr's in house or out-sources some to foreign, but suspect the latter. I'd guess a materials problem which would explain numerous failures even of different #'s and mfg. runs.

Problem shows as zero continuity between plug connection on one end and electrode on the other.

As FYI: following some serious problems at Champion a few years ago, with a vendor giving them materials that were far below contract's specification, Champion's reputation was destroyed. They finally discovered the junk materials as the cause. At the same time they instituted a company wide change and now have the most intense, rigorous and effective ongoing Product Quality Control monitoring of any spark plug manufacturer. Continuous random sampling and intense testing is performed on every plug model they mfgr. to guarantee the highest possible quality and performance.

NGK's Quality Control sampling and testing is virtually non-existent.

[ekpent]

Mercy that sure sounds extreme !!   http://www.ngk-sparkplugs.jp/english/techinfo/fake/

[XLerate]

Mercy that sure sounds extreme !!   http://www.ngk-sparkplugs.jp/english/techinfo/fake/

Interesting. Doubt that it applies in the cases I mentioned because the plugs were either purchased from NAPA or Western Auto - Carquest brick & mortar stores. All 3 have enough horsepower in the aftermarket sales and of course have long standing direct purchase agreements with NGK. Can't imagine how fakes could slip in to fill their product line? Internet sales, maybe. NAPA, Western Auto Carquest store fronts, I doubt it.

I was real disappointed because I had trusted and depended upon NGK for years, only plug I used in countless bikes.

[bollingball]

Thanks for the replies.  The motor is stock as are the carbs.  Honestly don't know the jet sizes but I am assuming they are stock.  The bike was pretty ratty when I got it but completely stock I had a local shop with a good reputation rebuild he carbs so they are clean (allegedly).  The tank is clean, and all the lines are new.  I am running the stock airbox and the filter is new.  I'll check the charging system.  The spark plugs are new (were before last night). The plug wires and caps are new as are the Dyna 5 ohm coils.  I am running a PAMCO ignition.  One dumb question - do the carbs have to be removed to rejet them?  Let the trouble shooting begin.

Did you take the entire bike to the shop or just the carbs? What work exactly did you do? Have you ask the shop what they think? I am a little suspect of the low speed circuit and would want to take a look at the slow jets. That is the bad thing about a shop you paid them and still don't know what your carbs look like inside or how they are setup float height fuel level jet size. Who and how were they synced? You will need to know all of this sooner or later. I do agree with all the other post too. If you start from the beginning and do a 3k tuneup you will usually find your problem.
Ken

[nancy]

umm?that wont foul plugs nancy....

Whoops too true...smack on face...

[HondaMan]

Thanks for the replies.  The motor is stock as are the carbs.  Honestly don't know the jet sizes but I am assuming they are stock.  The bike was pretty ratty when I got it but completely stock  I had a local shop with a good reputation rebuild he carbs so they are clean (allegedly).  The tank is clean, and all the lines are new.  I am running the stock airbox and the filter is new.  I'll check the charging system.  The spark plugs are new (were before last night). The plug wires and caps are new as are the Dyna 5 ohm coils.  I am running a PAMCO ignition.  One dumb question - do the carbs have to be removed to rejet them?  Let the trouble shooting begin.

Things to look at, in order:
1. Make sure the hose clamps on the carb hoses between the head and carbs are tight. Loose ones will cause adjacent cylinders to run rich because of the type of system we have, here. Also, if REAL loose, the idle circuit runs rich (my book explains why, kinda lengthy for here...).
2. Make sure the air screws are set between 7/8 and 1-1/8 turn out, no more. In is leaner. Bottom them gently: if they were once before bottomed too hard, they should be set more toward 7/8 turn as the seat will be spread open a little (they are very soft seats).
3. Make sure the ignition timing is correct. If it is advanced at idle, the plugs will foul (see#1 for the reasons why, same physics in the carb throats). Make sure the timing is right on "F" (and "LF" for 2-3) at idle, and full advance should happen about 2500 RPM.
4. Use correct plugs: the D8EA are too cold for today's gasolines unless you're blazing down the hiway at 75 MPH. So, if you are trying to use those, run regular grade instead, which will heat things up a little more. A better plug is the ND brand X24ES-U series, which has an extended, hotter tip.
5. Measure the sparkplug cap resistance: the caps must be within 800 ohms of each other on any one coil, or the lower-resistance one will foul plug(s) quickly. Use the NGK brand 5K (5000) ohm caps as today's replacements, available at most bike shops. Take your old ones with you for the trade, as they come in many shapes and resistances.