Ninja EX500 carbs on an XS650?

[Its been a long time]

OK, now I'm not so happy.

Here's what I've done this afternoon trying to improve the misfiring right side cylinder -

1 Swapped plug leads left to right after fitting two new spark plugs. (Then swapped them back, wasted spark ignition).
2 Tried pilot mixture screw adjustment between 1 and 3 turns out. (I started off at 2 turns out).
3 Double checked air leaks and replaced a suspect vacuum connection blank.
4 Swapped diaphragm and needles left to right.
5 Tried choke in several partial positions.

All revs from tickover to 3000, still same misfiring. I can actually feel a pulse as it misfires if I touch the carb top while the engine is running.

None of that made the slightest difference to how it runs.

I don't think I've got any alternative now other than remove the carb set again and go through the air/fuel passages on the right side carb. I have a sinking feeling here that right at the start when I extracted the seized mixture screw, there's something there that I haven't yet noticed?

Edited to add - the mixture screws on CVK34 are a pain to get to on the bike. So I've just ordered a pair of mixture screws with an extended shank that has a knurled grip at the end. Makes adjustment of the mixture screws so much easier. Should have bought them before now.

 

[gggGary]

cam chain tension and valves recently set? Compression test done.
carbs vacuum synced?
idle to 3000K would suggest a plugged pilot jet in that carb.
mix screw would only affect to maybe 1500 RPM.

 

[gggGary]

Fuel level in float bowl.
let it sit for a while at steady RPM with miss pull plugs that RH plug wet or dry?

 

[Its been a long time]

cam chain tension and valves recently set? Compression test done.
carbs vacuum synced?
idle to 3000K would suggest a plugged pilot jet in that carb.
mix screw would only affect to maybe 1500 RPM.

Cam chain tension - last week
Compression test - ~145lb both sides
Valves - set last week
Carbs vacuum synced - just broke my gauge set today, so not yet.
Idle to 3000 - I didn't rev it more than that!
Mix screw - agreed.

Agreed, likely issue with pilot circuit in right side carb. Will be looking closely at it again.

 

[Its been a long time]

Fuel level in float bowl.
let it sit for a while at steady RPM with miss pull plugs that RH plug wet or dry?

Fuel level - checked and found OK before installing carbs
Right side plug - clearly moist - when carb slide removed, slide damp and sooty from misfiring back through the carb. Left side no issue.

 

[troopthrowback]

Fuel level - checked and found OK before installing carbs
Right side plug - clearly moist - when carb slide removed, slide damp and sooty from misfiring back through the carb. Left side no issue.

If plug is moist on misfiring cylinder side your carb is not the issue. Its ignition!

 

[Its been a long time]

If plug is moist on misfiring cylinder side your carb is not the issue. Its ignition!

Thanks for the suggestion. It's a completely new Boyer Bransden ignition system, wasted spark. When I swap left to right HT leads, the right cylinder still runs badly.

 

[gggGary]

Rich misfire eliminates pilot valve. Might be crap on the float valve seat, open the float drain run some fuel into a clean container.

 

[Its been a long time]

Rich misfire eliminates pilot valve. Might be crap on the float valve seat, open the float drain run some fuel into a clean container.
View attachment 349395

Thanks for the advice, appreciated. It'll be tomorrow now. FWIW the fuel was fresh from the pump this morning and this is the first time fuel has been in these carbs since stripping them down and rejetting them. Clean temporary fuel tank was used today.

I was thinking along the lines of the adjustment to the mixture screw having no noticeable effect was pointing towards a partial blockage in one of the internal passages. Thanks again.

Edited to add - just noticed the comment about float valve assembly. Both carbs have new seats and float needle valves. They're rubber tipped in CVK carbs. Will take it apart and look closely at it as well as rechecking float height.

 

[Its been a long time]

For reference, CVK34 float height setting 17mm +/- 2mm. I set this to 17mm but will recheck.

 

[Its been a long time]

For reference, CVK34 cross section -

Port "E" has to be favourite for a good cleaning, and up through pilot jet B. See if I can squirt carb cleaner through to the mixture screw A.

 

[5twins]

For testing circuits, I use something mild like WD40, only resorting to the carb cleaner if they're plugged. And after using it, I "flush" the passageway clean with WD40 to remove any remnants of carb cleaner.

 

[Its been a long time]

For testing circuits, I use something mild like WD40, only resorting to the carb cleaner if they're plugged. And after using it, I "flush" the passageway clean with WD40 to remove any remnants of carb cleaner.

Thanks for the tip. I wouldn't have done that.

 

[Its been a long time]

Investigating poor running on the right cylinder. Carbs pulled off after draining float bowls to look for debris. Clean as it was yesterday morning out of the fuel pump.

As expected, the right side butterfly plate is sooty due to repeated blow back into the carb when misfiring. Right Side carb is on the left here.

With the float bowl removed, all as clean as it was when I put it together. Checked the float height and spot on 17mm. Picture isn't very good, poor lighting.

Used WD40 to squirt through the main jet and pilot jet air jet passages. Good squirt from all the right places. Pilot jet confirmed as 38. As new, no air or fuel hole issues.

Checked the three very small pilot mixture holes adjacent to the bottom rim of the butterfly plate were squirting. All fine. Checked port to the mixture screw flowing OK, it's fine. Spring, washer and O ring all correct on the mixture screw.

Finished off by blowing carb cleaner and canned air through the jets. Can't really say I found anything but it's done now.

Ready to reassemble. But the float bowl O ring seal came out misshapen. That's how they came out last time. It seems even short duration exposure to fuel is affecting them. Have to buy new ones.

 

[Signal]

I have found that the O ring will revert to normal size if left on the bench for a few days.

 

[Its been a long time]

I have found that the O ring will revert to normal size if left on the bench for a few days.

Thanks. I've had the O ring in hot water for about 20 minutes and it's just a bit deformed now. It might be reusable in a day or two then if I leave it. Meantime I have some in the mail.

 

[Its been a long time]

Float bowl O ring perfect shape again this morning. Leaving it overnight it regained original shape. Keep a spare just in case I need it.

 

[Grimly]

Float bowl O ring perfect shape again this morning. Leaving it overnight it regained original shape. Keep a spare just in case I need it.

That's how they seal. I first came across this when replacing fuel tank sender gaskets - you can't get them wet with fuel or they immediately swell and won't fit the recess. Leaving them for a day has them regaining shape.

 

[Its been a long time]

That's how they seal. I first came across this when replacing fuel tank sender gaskets - you can't get them wet with fuel or they immediately swell and won't fit the recess. Leaving them for a day has them regaining shape.

Thanks. The 20 minutes in hot water got it maybe 90% of the way back in shape. Leaving it overnight it was fine to reuse this morning.

Carbs are back on now. Made a top carb brace to fit between the carbs because I'm not going to use the standard back brace. The original front lower brace is pretty stout and still in place. So I think a top brace between the carbs is going to be more than adequate. It's far easier to fit and remove the carbs from the bike when that back cross brace is removed. And it's not going to be rubbing paint off the frame if it's not there.

Battery on charge ready for a start in the morning. Hopefully the misfiring right cylinder will be OK this time.

 

[Its been a long time]

Tried again this morning. I reinstalled the carbs. As a precaution rechecked inlet tappet clearance on the right cylinder. As expected, spot on. Rechecked static ignition timing again, still fine.

This morning the bike was far more difficult to start. At first I thought I had a failed ignition system, just no attempt fire. On Wednesday it started so quickly, I couldn't take my finger off the start button quick enough.

Eventually, got it started. Same as before the cleaning of the right side carb. Left side running OK. Right side misfiring very loudly back through the carburettor.

Revved the engine as far as 4000rpm or a bit more. I've never seen this before, the garage got full of exhaust smoke pouring out of the right side air filter. I was worried I might cause a fire, so shut the engine down.

So - cleaning the right side carb got me nowhere. If anything, it's running worse now than before. I'm now at a loss.

Set up is -

All new Boyer Bransden ignition system* with Denso plugs gapped at 30 thou.

ER5 CVK34 carbs with 38 pilot jet, 138 main jet, JJJ needle in middle slot, pilot mixture screws 2 turns out.

* static timing only, I can't get it running well enough to try a timing light. Swapping HT leads left/right makes no difference.

Thanks in advance regarding ideas what to try next? I'm out of ideas.