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Discussion Starter #1
This is the oddest thing I have yet to have to figure out on a motorcycle. Yesterday, I was riding, and I noticed a slight miss at small throttle openings... the small miss got bigger, and by the time I got the thing home, it was only running on three cylinders. A "temperature check" of the exhaust header revealed that #3 was the one not pulling it's own weight; note that no smoke or other symptoms were present... just a miss. I pulled the plugs, and checked to see if there was fire present... #3 was fouled badly, #1 looked rich, but you can see from the pics that it was still firing; #3 was NOT firing.


all four


#1 close-up


#2 close-up

I cleaned up the plug, put it all back together, and it ran fine for about 20 miles. After a frustrating night, I went and got four new plugs this morning, thinking that it was simply a bum plug. I also removed the float bowls of the carbs, as well as the tops to see if something was amiss... nothing seemed to be. A resistance check of the coils showed them to be good, and all the wires and boots and insulators are less than a year old (I replaced most of this stuff back in January) and the connections were tight and still had dielectric grease in them with no signs of corrosion. I have had trouble before with crimped fuel-lines due to lack of space and poor design... so while I was in there anyway fooling around with spark-plugs, I went ahead and re-routed all the fuel-lines so that the tank can be lifted and set back in place without fear of collapsing or folding a fuel-line.

Everything seemed to be solved and sorted out, the bike ran fine, so I hop on the bike to go visit a friend of mine... and on the way there, after about 20 miles (how did you guess) it started missing again. By the time I arrived it was back to a 845.25cc engine again. After much fiddling around, I got it to idle on four cylinders, but on the way home (yup, 20 miles out) it was a three-cylinder again (maybe it wants to be a speed-triple?). ANYway, I'm about ready to pull my hair out at this point... I'm thinking of how much new coils are gonna cost (I always wanted a DYNA 2000 ignition system anyway) and I just couldn't leave bad enough alone, so I pulled the filters off the backs of the carbs (didn't do this earlier) and noticed that #4 carb moves up and down a *lot* easier, with less resistance than the other three carbs... weirder and weirder I think to myself. So, again, off come the tops of the carbs, and here's what was lurking inside #4 carb (I didn't actually pull the springs out and look at them earlier)


broken spring and schematic

A new spring (part #13417-42A00) will set me back a whopping $2.64 so I'm gonna replace all four. (hey, if one broke, the others are near their deathbeds too, right?) So, what I'm wondering now, is how the HECK the broken spring in #4 would cause me to foul plugs in cyl #3? I know that the pair of carbs (3 and 4) share vacuum, but I'm not convinced that fixing the spring is gonna be the end of my problems. Anyone got any input, suggestions, ideas?

I'm so frustrated, I can't stand it. I think I'm gonna go find something (else) to break.
 

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I would try replaceing your plugs and it looks like you need to lean out your 1 and 3 carbs.
 

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Since Suzuki's vacuum petcocks normally take their vacuum off the tit on #3's intake runner, I'd guess that your line is leaking and the thing is running too lean to run properly.

If it runs ok on 'PRI' (prime) then that has solved it. Replace the vacuum lines (and all the fuel lines while you're at it).
 

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Discussion Starter #4
Originally posted by bcjohn:
Since Suzuki's vacuum petcocks normally take their vacuum off the tit on #3's intake runner, I'd guess that your line is leaking and the thing is running too lean to run properly.

If it runs ok on 'PRI' (prime) then that has solved it. Replace the vacuum lines (and all the fuel lines while you're at it).
<font size="2" face="Verdana, Arial">Good idea... I forgot to tell ya... I moved the vacuum line for the petcock to the #2 cyl some time ago to give me more room to lift the tank without dis-connecting it... it's in good shape. ALL of the rubber parts in there are in good shape, most of it is 6 months old or less.

(edit) I forgot to mention... the o-rings underneath the carb tops are all new too... along with the emulsion tubes, etc, etc... this just all of a sudden happened; the thing was jetted *nearly* perfectly.

[ 06-15-2002, 08:51 AM: Message edited by: FastCat ]
 

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Discussion Starter #5


It's all better now. I re-did the coil wires while I was in there, and also noticed that the caps on the vacuum ports on top of the carbs were rather old... they got replaced too. Back in shape to ride!
...Still the *weirdest* problem I've ever seen...
 
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