running on 3 cyls?

[elbandtioCA]

can anybody tell me the symptoms of a bike that is running on 3 cylinders, or even two?  this is my first bike and i don't know too much about ignition systems, and i'm trying to trouble shoot a b4 that is running very poorly.  i just had the carbs totally rebuilt and it didn't do anything to improve the problem.  the mechanic also found that the pickup coil was bad, and put in a new one, but that still didn't help.  is a lack of throttle response, and really rough acceleration a sign that there is a problem with the spark getting to one or more cylinder?  will a bike even run with an intermittant spark in the first place?  i've also read about rectifier/regulator problems on teh b4s, but i'm not sure what the symptoms are for a bad R/R.  maybe if i new the symptoms of these things i could rule them out... thanks-

[Heyu]

When it's running can you touch each exhaust pipe with you're hand or a temp gun to see if all cylinders are firing?
 If all exhaust pipes feel about equal heat at idle what happens when you rev it up do all 4 pipes remain hot or does one cool down a bit?
 You just had the carbs rebuilt I would suggest that that wasn't done correctly you might want to take them apart and make sure it,s done right, it is easy to miss something when redoing carbs.

[CWO4GUNNER]

+1 and not only that but as a certified mechanic he should have been able to isolate the problem if not fix it, by determining through a compression check if the engine is basically sound, ignition timing check to determine spark to each cylinder, and if he rebuilt and cleaned the carbs fuel flow through all parts of the throttle circuit jets. These kind of paid for mechanic stories get my blood boiling so I better not  say more.

You just had the carbs rebuilt I would suggest that that wasn't done correctly you might want to take them apart and make sure it,s done right, it is easy to miss something when redoing carbs.

[Rocketjock]

If you have a needle pop out of its housing (carb) as I did, that will definately end the running of one cylinder.

[Russtang]

Welcome to the board!  So, to run, an engine needs proper air/fuel mixture, compression, and ignition.  My bike has run on three cylinders a couple of times since I've owned it. 

The first time the bike had the problem, I fixed it by cleaning/rebuilding/balancing the carbs.  The o-rings were past their prime and the idle air screws were all out of whack.  Turning them all to 3 turns out was the best setting for them.  Went back and forth between idle screw adjustments and balancing a few times but it was all worth it as the bike idled very nicely after that.

Were your carbs balanced after the rebuild?  All the ports on the top of the carbs plugged?  You can make a cheap manometer to balance the carbs using a length of tubing and some colored water.  I think I spent less than 5 bucks on the tubing.  You can find that tutorial here.

http://www.powerchutes.com/manometer.asp

Do you have an inline fuel filter between the tank and carbs (in addition to the tank filter)?  Doesn't take long for a tiny piece of crud to work its way from a rusty tank and into those clean carbs.

The second time I dropped a cylinder happened just a few weeks ago.  After crapping out on me at a stoplight, the bike wouldn't run at less than 3k rpm.  Touching the header pipes told me right away which cylinder was down a year and a half ago.  It didn't tell me anything this time, because at that rpm, the miss seemed to be intermittent, and all pipes got hot pretty quick.  I then checked spark at each cylinder with one of these.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=36258

It'll let the bike continue to run normally while telling you if that plug is getting a spark.  All cylinders were getting a spark, so I pulled the plugs.  All but cylinder 1 looked fine.  That plug was a little wet.  I then reinstalled the plugs and plug wires.  Fired it up and individually pulled each plug boot off its plug.  Only cylinder 1 showed no change.  All the other plug wire disconnects dropped the rpms dramatically and turned the bike into a twin.  So cylinder 1 was now my main suspect.

I didn't suspect compression (but didn't rule it out), because the bike was running fine one minute and just died on me the next.  Rings wear slower than that, and I would have probably heard a valve snapping!  ;)

Soooo, off came the carbs.  Verified the air screws were all at the same setting (they were all still 3 turns out).  Tore them all apart and cleaned them.  No obvious problem inside.  Reassembled and reinstalled, but the bike was still having problems.

I suspected that the cylinder 1 coil was flaky, so I re-crimped and soldered the primary connectors and measured the primary and secondary coil resistance while I was there.  All measurements came up good with my meter.  Refired, but the bike still ran on three.  I then swapped out the coil with a spare I had and it fired up and ran great!  Swapping around some spare plug wires and the bad coil proved that the problem was with the coil.

I suspect that even though the coil resistance measured fine on my handheld fluke meter, it would fail a high voltage resistance (Hi-Pot) test.  Which implies the primary and secondary transformer wires inside the coil assy are shorting out to each other when powered up.

So, hope this helps a little with the troubleshooting.  Good luck and let us know how it turns out!

Russ

[interfuse]

What Russ said. Once you figure out what cylinder is down check the sparkplug wire and boot to make sure everything is connected. When the wires get old they seperate easy from the boot. Cracked wires can lead to sparking off things like your frame... which can be painful if you touch the spark. Don't ask how I know...

It could also be carb related. I had to clean my carbs a couple of times before I got the pilots completely clean.

Worn needle jets can make the bike run like crap in the low end... another thing you should have them check if they're tearing apart your carbs again.

[elbandtioCA]

hey guys, thanks for the advice.  between this and what gsxr400racer has suggested to check out with the carbs i'm hoping to solve this problem when i get a chance to get my hands dirty.  i have already identified which cylinder is getting fouled, but it isn't clear weather it is a carb issue or an ignition problem.  i'm going to get one of those ignition test devices, but will that tell me if my coil has an intermitant problem, like the one russ describes?  if the standard continuity test doesn't catch the bad coil, then how will i find out if it really is bad?  i don't have a spare coil lying around to test out... 

also, once i clean the plugs the bike runs fine and idles at low rpms, but only for a short while.  after a little bit it starts running poorly and missing--which suggests the plug is getting fouled.  but would a bad coil have this symptom--i.e. starting out ok and then fouling?  the mechanic was starting to wonder if it was a carb problem after all, and if it was fouling because it was running too rich at the mid rpm.  but i don't want to pay to have him open up the carbs again so i'll get to learn about all this stuff soon!

[PitterB4]

Couple tips....

I know you've already figured out which cyl is the problem but I always keep a spray bottle of water in the garage.  Spraying a little water on the headers is a quick (and painless!) way to figure out if you have a cool one.

To see if the coil itself is the problem, swap them.  If the misfire follows the one you suspect to be bad, you've found the problem.

I'm too lazy to go look but if I haven't suggested this to you over in the 400 forum...  check the connectors on the wires going into the coils (from the harness).  Those spade connectors suck and can spread out and make intermitent or worse contact. 

Good luck!

[PitterB4]

And Interfuse is right, THE most likely problem is the old, brittle plug wires where they attach to the boot.  Especially if someone has been in there mucking around with them, it's likely that one of them pulled loose. 

[elbandtioCA]

i've now got two posts running (the other on carbs in the 250/400 forum) but i thought i'd update this thread because you wanted to know if i solved the problem.  not quite yet but i'm confident i found the problem.  the carbs were missing the pilot jet plugs that gsxr400racer told me to look for.  there also might be signs of wear in the needle jets.  so i'm thinking that the fouled plug/s are a result of these two things, rather than an ignition coil or bad cable. 

i just paid the mechanic to rebuild the carbs and he did so without checking/replacing the needle jets or noticing that it was missing these rubber plugs.  is it standard to do a carb rebuild without checking these parts? 

[Red01]

I could see missing the plugs... it's something commonly missed on the B4. Most folks expect the pilots to be open.

[gsxr400 racer]

An experienced mechanic would have caught it there where many bike that used plugs on the carbs gs started it out some Honda's commonly over looked if they are snug or fall out when you turn the carbs over you need new ones.

[elbandtioCA]

that's what i figured about the plugs.  but the bigger question for me is about the needle jets.  since they seem to be a common problem that leads to running too rich, from my novice point of view, it would seem like they should be checked/replaced if the carb is opened up.

[gsxr400 racer]

Again those unless your experienced and know first hand about that stuff or  looking for some causes of richness while dyno tuning, you would probably never replace the emulsion tubes.

On another note if your mechanic replaced the floats with OEM Suzuki floats then they came with new float needles.

[albertinhouston]

Couple tips....

.  Spraying a little water on the headers is a quick (and painless!) way to figure out if you have a cool one.

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+1 more to the point of which one is NOT HOT!!!!!!!!!