Author Topic: Plug fouling  (Read 5541 times)

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Offline premiumjo

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Plug fouling
« on: October 06, 2014, 06:45:41 PM »
When i first got the bike going, it fouled the right side plug. I thought maybe it was the premix gas i was running while i got the oil pump sorted out. I cleaned the plug with brake cleaner, dried it and filled the tank with fresh gas and it ran like a champ. Just the right amount of smoke coming out of both sides and running pretty good. Today i took it out, it sparked right up and idled perfectly. Started up the street and it started backfiring on the right side smoking like a bitch, and then the right side stopped firing. Same thing, removed that plug, cleaned it off, put it back in and it ran fine. If this was a seal problem, wouldnt it do it all the time? The spark seems to be the same as it is on the left cylinder at least visually. Any ideas?
thanks
rd
Randy

Offline disc_valve

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Re: Plug fouling
« Reply #1 on: October 07, 2014, 06:22:52 AM »
Hi,

That sounds similar early symptoms to the ones I had on my 175v a while back. It would foul a new plug after 50 miles or so, run OK again for another 40-50 miles after cl;eaning the plug, then foul again. I tried swapping carbs and plug caps from side to side with no effect, and the problem turned out to be a weak ignition coil - even though the spark looked good when I tested it in the open air. Might be worth trying another coil to see if it works for you.

I assume, of course, that you've already checked over the connections to the coils and points, and have checked/set the ignition timing.

Graham


Offline BRT-GTR

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Re: Plug fouling
« Reply #2 on: October 07, 2014, 01:27:43 PM »
 RD,
        Just a few thoughts, it's obviously overloading on oil on the right pot. As Graham says could be coil breaking down under load, wrong points gap or ignition timing , all of which give poor combustion.
If those are OK and there's a big fat spark at the right time, a source of additional oil could be failure/leakage of the crank right oil seal. Might only suck in oil at higher revs. Not too difficult to replace , it sits in the disc valve cover.  Are you sure the oil pump is assembled, timed and set correctly (Good 'how to' article by Graham on the site). You don't tell us how far you went with it running 'like a champ' or whether you did anything to it afterwards. Let us know how you go on , Brian
« Last Edit: October 07, 2014, 01:34:23 PM by BRT-GTR »
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Offline premiumjo

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Re: Plug fouling
« Reply #3 on: October 08, 2014, 07:04:41 PM »
Thanks for the replies. I definately think something is going on with either the points or the coils. i started it today, it fired right up, and sat and idled fine. First the right plug fouled, then the left. after cleaning and drying the plugs off, i checked them. spark was good on the right, no spark on the left. Swapped the plugs, same thing. I am going to pull the points and check their condition first and see if i can resurrect the spark. Otherwise, drain the oil (oil tank under the gas tank is a pain in the ass) pull the tank, and check out the coils. I do have a spare set from a donor bike. I set timing last year with a dial indicator so i think that is prolly good.  i'll let ya know how i make out.
Thanks guys.
rd
Randy

Offline slawsonb

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Re: Plug fouling
« Reply #4 on: October 08, 2014, 09:00:25 PM »
Another thought (as if you need more), is that condenser performance can degrade as they heat up and cause issues like you are descibing. I suggest you give this baby a major tune up (plugs, points, condensers, timing,  and anything else you can think of, you know the drill). Good luck.
...bert

Offline premiumjo

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Re: Plug fouling
« Reply #5 on: October 08, 2014, 10:38:06 PM »
I think I will take your advice Bert. I pulled the points out and the set for the left cylinder was not even conducting with a test light. there was a lot of corrosion on them. I filed and used 1200 grit emery on em, but just couldn't quite get that last bit of pitting out of them. the condensers may be original for all I know. Anyway, it has decent spark now, but i'll want to check timing as I had the points removed. I forget the timing (I don't have a tool for the crank wheel slot method). Does 1.8mm BTDC sound about right?
Thanks for the input.
rd
Randy

Offline disc_valve

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Re: Plug fouling
« Reply #6 on: October 09, 2014, 06:30:20 AM »
Nope! 1.8 sounds a wee bit advanced. Should be 1.44mm

Graham

Offline BRT-GTR

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Re: Plug fouling
« Reply #7 on: October 09, 2014, 12:06:56 PM »
RD,
      While you've got the points off, check they are free to swing on their pivot posts. Take the spring - nut & bolt out if necessary, don't lose the 3 insulating washers. If they are a bit stiff, the corrosion you mention is the clue, this might explain the backfiring. I had something similar on a different bike when the points cam came loose, upsetting the timing.

We'll get that bike humming if it kills us ;D :D ;D,    Brian
« Last Edit: October 09, 2014, 02:11:23 PM by BRT-GTR »
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Offline slawsonb

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Re: Plug fouling
« Reply #8 on: October 09, 2014, 01:29:44 PM »
The good news is it has already hummed (more like crackled) a few bars!
...bert

Offline BRT-GTR

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Re: Plug fouling
« Reply #9 on: October 09, 2014, 02:32:51 PM »
Rd,
      I'm not totally familiar with the 175 engines but you may not need a special tool to use the crank slot timing method. Under left exhaust connection you should find a 6 or 8mm bolt in the front of the crankcase. Take it right out and find a suitable rod, pin, nail that will fit inside the threads. May have to round off end to find crank slot. Push lightly on pin and turn back wheel backwards, in a high gear, until pin drops into slot. Long arms help !! This is where the points should just start to open, job done.
Brian.
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Offline premiumjo

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Re: Plug fouling
« Reply #10 on: October 12, 2014, 09:29:34 PM »
after sanding the points smooth and polishing and gapping and retiming, it started and idled great for a couple minutes and fouled the right plug. Pulled them, dried them, and same thing. Cleaned them again, and started it. this time it ran good. Took it around the neighborhood a couple times (no license plate yet), no issue. let it sit in the driveway and idle for about 10 min. - idled great and didnt load up. took it back on the street. no issue.
Started it about an hour later and it went back to fouling the plug, (this time the left cylinder) This thing is kiling me! If it were carburetion, i think it would do it alll the time. Coils maybe?
Grahm, The bridgestone tech manual calls for 21° BTDC which is indicated as 1.8mm?? are you sure about the 1.44
When it's not running crappy, it runs great.
Randy

Offline disc_valve

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Re: Plug fouling
« Reply #11 on: October 13, 2014, 06:27:00 AM »
Hi, again,

You've got me thinking now. I downloaded the Technical handbook on this site, and yes, it does state 1.8 / 21 degrees. I was working from memory with the 1.44, but I'm sure that's what I use (equivalent to 19 degrees). I'll have to go out to the workshop and check my 175 timing to see what it is, but whatever it's set to, it 's running sweet as a nut.

The ultimate confirmation, of course, will come from setting the timing point using the timing pin hole on the front left of the crankcase, and measure the piston position with a dial guage.

Sorry for the confusion!

Graham

Offline premiumjo

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Re: Plug fouling
« Reply #12 on: October 13, 2014, 07:12:05 PM »
No problem!
Yeah, I was going to check that while I had the dial gauge in, but was too lazy to remove the exhaust to get at the hole................. I have pretty weak compression on the left side, seems like that could be it, but then sometimes I get it running right and it runs great which makes me think it's an ignition thing. Frustration......................... :'(
Randy

Offline disc_valve

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Re: Plug fouling
« Reply #13 on: October 14, 2014, 06:30:55 AM »
Hi, Folks,

I've checked a bit further and I now realise where my Ignition timing figure came from. Tho BS90 had the same timing figure of 21 degrees as the 175. There is a Rockford Service letter (BSG-0019) on BS90 igniton timing, which recommends setting the timing 2 degrees retarded from standard to give higher rpm and incresased performance. That makes the optimum BS90 timing as 19 degrees btdc (1.45mm).

I tried that figure on my 175 Dual Twin years ago and it seemed to run fine, so I've stuck with 1.45 ever since. In fact, that is still within the factory tolerance of +1 / -2 degrees from standard, so there's no real problem.

I guess 1.8mm is also OK to use - maybe I'll try setting mine back to standard one day and see if there is any difference.

Graham
« Last Edit: October 15, 2014, 07:13:07 AM by disc_valve »

Offline premiumjo

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Re: Plug fouling
« Reply #14 on: October 14, 2014, 08:45:52 PM »
Hmmm. At this point i'm game to try anything. I did notice that with the point gap set at .014, the adjustments for both sets of points are almost bottomed out to achieve 1.8 BTDC. Maybe i will try a degree less and see what that does.
Thanks!
rd
Randy

Offline disc_valve

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Re: Plug fouling
« Reply #15 on: October 15, 2014, 06:42:47 AM »
Well, the 175 ignition timing puzzle gets curiouser and curiouser (as Alice would say). I had a look at my own original Bridgestone 175 Technical handbook, and the timing is given as 21 degrees in the Specifications section. But.....  in the main Ignition Timing section (13.3), the figure is explicitly stated as 1.44 mm (i.e. 19 degrees), and the table of degrees against piston position goes from 17 degrees to 20 degrees, with 19 degrees highlighted as the nominal figure (and there is no reference to using the Timing pin). This is different to the same manual in the downloads sectiion of this site.

Also... the early Owners Handbook for the 175 Dual Twin shows 21 degrees, but the later combined Owners Handbook for the 175 Dual Twin and 175 Hurricane Scrambler state 19 degrees.

Last evening I went out to the garage with Dial Guage and Timing Pin and found that the notch in the crankshaft is set for 1.44mm on my engine, which all suggests that Bridgestone updated the timing figure to 19 degrees part way through the run and 1.44mm / 19 defrees is the correct figure to use - at least for the later models.

The road bike crankshafts were all the same, but there were three different sets of crankcases produced to match variations in the generator drive, so it is likely that the very early 175s had the timing pin hole in a different position to set a 21 degrees timing position. This is further confirmed by the wording in the early Technical handbook downloaded from this site.

The moral of this tale is that I have learnt something new about Bridgestones today - I'm glad you raised the question!


Graham
« Last Edit: October 15, 2014, 06:55:12 AM by disc_valve »

Offline premiumjo

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Re: Plug fouling
« Reply #16 on: October 17, 2014, 11:20:29 PM »
Graham, thanks for checking that out!
Ok, now I will have to pull the pipe on mine and check the notch on the crank to the dial gauge. I hope it is 1.44mm. at least that would give  me something to try. I pulled the seat tonight and checked the coil resistances - Primary 4.7  both sides - secondary 9800  and 9500. All within the specified ranges in the manual...................
Randy

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Re: Plug fouling
« Reply #17 on: October 18, 2014, 05:00:48 PM »
Strange. I took my left pipe off so I could get at the hole, made a little brass insert with a plunger in the center (so I knew I was dead nuts center in the hole), stuck the dial gauge in and zeroed it, and got exactly .072" BTDC (1.82mm) when the plunger engaged. So apparently my bike is different. As far as I know, its a 1967 model 16K19410. When I got it, it had scrambler pipes on and HS badges, so maybe there is a difference between the Dual Twin and the Scramber? ???
Might try the retarded setting just for giggles.
rd
Randy

 


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