Cylinders 3 & 4 not firing

[ben]

I've got a misfiring fazer at the moment. Using the old hand on headers trick, it looks like 3 & 4 are not firing.

Background... The bike was sitting for about 2 years, and it was a periodically misfiring before it went into storage. When recommisioning it, I removed the carbs and cleaned a lot of gunk out of the float bowls. I also removed and cleaned the jets. When I put it back together, I found that I've now completely lost cylinders 3 and four. The headers on those cylinders are stone cold. I'm guessing I've messed something up, but I can't for the life of me figure out what.

Sparks, caps, and coils are fine. No kinks in breather tubes. I've removed the carbs again and there was fuel in the float bowls (not sure how much though).


Any ideas?

[snoopysmutt]

Had similar probs with mine a few years ago, after standing over winter. By thoroughly draining all old fuel from carbs, fuel pump and tank and refiling  with fresh super E5. cured it. 

[darrsi]

Have you swapped plugs 3 & 4 over to 1 & 2 to rule them out?
Plugs can and do go bad from experience, especially if you already had issues before.
Snipping about 7mm off the ends of each HT lead then refitting the caps can help too, as over time the internal wires can sink into the plastic of the leads due to heat.


Are they original caps, or aftermarket ones?

[ben]

So a little update...

I re-installed the carbs after checking the jets on 3 & 4 to make sure they weren't clogs. All fine. Decided to change the sparks in 3 & 4 to see if that made any difference. It did! 3 & 4 are now firing!!! Success!

The really weird thing, is that cylinder 1 is now not firing  Changed the spark. Swapped the cap with the one from the now working 4. Even tried snipping the end of the HT lead. Nope! Still not working.


HOW?!

[ben]

Oh, and they're the original caps.

[unfazed]

The original caps can corrode internally and/or the carbon resistors can go high resistance and prevent a proper spark. Easiest option is to install a new set of NGK straight ones or clean the oem ones and replace the internal resistor.

[ben]

I've got some NGK straight caps. I'll change them tonight and see what happens. I have tried swapping the cap with one from a working cylinder and it made no difference, so I'm not too hopeful, but you never know.

[ben]

Ok, I replaced the caps with the straight NGK ones. For some reason that's fixed it. Despite previously swapping a cap from the non-working cylinder with a cap from a working one!

Anyway, thanks for the advice! It still has a intermittent misfire, but I'll make another post for that one if I can't find any existing ones.

Getting there slowly but surely 

[unfazed]

Is the misfire when starting up or when riding?

[ben]

When riding for a while at high RPM (say 10 mins @ 70mph) it starts to stutter, which will develop into a proper misfire if I carry on. If I then ride for a while at low RPM, the misfire goes away.

[unfazed]

Did you cut a piece (about 10mm) off the end of the leads before fitting the NGK Plug Caps. as they may be a bit loose when screwed into the caps., this is one cause of the issue.

Second cause is not getting enough fuel at high revs, check the breather to from the tank and the fuel line for kinking. Fuel line goes under the Frame cross rail not over it. Common enough issue after having the tank off .Third cause which is extremely rare, there are only 2 cases I know o and that was a faulty Regulator/Rectifer, over charging slightly, but enough to cause issues with the Ignitor creating the misfire.Since it is such a rare issue it might be worth replacing it with a  secondhand one and Boxeye one is different to the Foxeye one.The one on the Foxeye code is SH650C-11 whereas the one on the Boxeye is SH650C-12. If you do get one just be sure you get the right one.

[ben]

Quick update...

Yes, I did snip some of the HT leads before putting the new caps on. Checked the breathers and fuel line for kinking. All looks fine, but it's hard to tell when the tank is on. I also noticed the fuel filter was installed the wrong way round, so couldn't tell if it needed replacing, so I replaced it.

Still the issue persists. I've ordered a secondhand regulator/rectifier. It's cheap enough to give it a go. I'll post an update once I've fitted it.

[ben]

2nd hand regulator/rectifier fitted today. Still the issue persists 

I've got some new coils on the way, as the primary resistance is about half an ohm out on both. I don't expect they'll make much difference. The seconadary resistance is well in spec. Worth a try though.

Has anyone else got any ideas?

[BBROWN1664]

loosen the drain screws on cylinders 3&4 to see if you get any fuel out?

When you cleaned the carbs, did you blow through all the galleries with compressed air to get all the crap out? Did you replace the fuel filter?

Chances are, as i have had it before, dislodged crap has blocked the carbs completely from getting fuel or the jets are blocked again. If it starts firing on all 4 at higher (above 5k) revs then my money is on blocked jets. If it still wont run on all 4 then its blocked flue galleries.

All of the above assumes that the coils are correctly connected to the correct cylinders. #1&4 on the left coil, #2&3 on the right coil.

[ben]

Oh, I've managed to get 3 & 4 firing (new plug caps solved it). The problem is now a stutter/misfire at high RPM. I'll make a new post, as the original issue has been solved.

[BBROWN1664]

Could still be a blocked main jet

[basher]

I am having similar issues, had 2 headers cold, now after lots of messing around ive only 1 cold but it jumped around from 3 to 2. have spark on all plugs, i have a suspicion its the float valve seat but i would like to know if anyone has a link to a straight plug cap suitable for 98 model just so I can buy some and eliminate the issue 

[ben]

These are the ones that I got for my '99: (NGK SD05F) https://www.ebay.co.uk/itm/115379517846