Popping front right cylinder when cold but dark spark plug

[RempageR1]

Hi,

When my max is cold, the front right cylinder backfires a couple of times when I drive off with the choke opened just a little. With the choke open full the popping is gone, so you would expect the cylinder runs lean. But here`s the funny bit:

The spark plugs of the other three cylinders have that healthy coffee color, but the one front right is a bit black. That would mean it would run a little rich...

Also, looking at the downpipes (that have been replaced last month), it seems the front right one is a little rich:

Front left:

Front right:

Some things checked:
-Compression is ok
-No leaks between manifolds or vboost linkage
-Carbs have been cleaned

Some other stuff:
- Pilot Air Jet No.2 is size 150 instead of the default 170
- It has factory needles set to the middle groove.
- Bike runs best with all pilot screws all the way in (strange), handled in other thread but I never really got to the bottom of it.
- Pilot screws look just fine.

So backfiring is lean, but the color of the spark plug is black... what to do?

Thank you!

 

[Cujo51]

Are you getting good spark ? I had same issue with left front plug getting wet , coughing , spitting and backfiring . I did the c.o.p conversion , removed the old coils and problem went away . Figure it was a bad coil ......after pissing a whole summer away thinking it was a carb issue !!!!!!
Just another avenue to look at bud !

 

[MaxMidnight]

Could it be a loose or damaged connecting joint on the exhaust?

As a separate issue, the top photo seems to show that the inner part of the header has started to crack around the weld.

This will be the mysterious rattle that will suddenly occur (been there, done that!)

 

[tugla]

both great points to look at first and then should get into the carbs for a cleaning or atleast shot gun and pea shooter. you got to let them warm up before riding, is the poping from the carb or exhaust?

 

[RempageR1]

Hi, thanks all for the replies!

@Cujo51, ATM the front right carb is in bits. If the problem persists i`ll move plugs, caps and coil around to see if the problem moves with it. The reason i`m not really looking in the ignition direction is: 1. It goes away when I use more choke. 2. It goes away after about one minute from cold. The last one however could still come from a coil/spark issue ofcourse.

@MaxMidnight, You`re absolutely right. Had that rattle too and it started to drive me nuts. In the end I replaced the front downpipes and the issue went away. It seems the inner tube starts to rotate a little when it gets warmer and was touching the outer tube. On one of the weld joints that was loose you could see it was rotating a little. After this, the rattle was gone but the backfiring still is there the fist minute. All other joints and stuff i`ve checked, no problems there anymore.

@Tugla,
Carb is as clean as when it came out of the factory now . Popping comes out of the carb (good point to mention). I do not drive away agressively, more like and old lady the first 500meters so that should be fine.

One other thing: The pilot screw issue is due to smaller PAJ2 jets making the stationary circuit more rich. This is also mentioned in the other threat. There, I got the feedback the other pilot circuit ports are blocked by the butterfly valve on stationary but this is not the case, it is always a little bit open as you open them with the stationary screw.

I`m thinking of getting the default jets and installing them so I can actually setup the pilot screws per cylinder. Also, i`ve ordered new rubber bushes between carbs and manifolds as they didn't look to fresh (although they didn't respond when I sprinkled water over them at stationary).

Still there is the contradiction: Black spark plug but backfiring from what seems to be running too lean. I`ll go ahead with the bushes and report back my findings.

Thanks all!

 

[94 V-Max Rider]

Hi, thanks all for the replies!

@Cujo51, ATM the front right carb is in bits. If the problem persists i`ll move plugs, caps and coil around to see if the problem moves with it. The reason i`m not really looking in the ignition direction is: 1. It goes away when I use more choke. 2. It goes away after about one minute from cold. The last one however could still come from a coil/spark issue ofcourse.

@MaxMidnight, You`re absolutely right. Had that rattle too and it started to drive me nuts. In the end I replaced the front downpipes and the issue went away. It seems the inner tube starts to rotate a little when it gets warmer and was touching the outer tube. On one of the weld joints that was loose you could see it was rotating a little. After this, the rattle was gone but the backfiring still is there the fist minute. All other joints and stuff i`ve checked, no problems there anymore.

@Tugla,
Carb is as clean as when it came out of the factory now . Popping comes out of the carb (good point to mention). I do not drive away agressively, more like and old lady the first 500meters so that should be fine.

One other thing: The pilot screw issue is due to smaller PAJ2 jets making the stationary circuit more rich. This is also mentioned in the other threat. There, I got the feedback the other pilot circuit ports are blocked by the butterfly valve on stationary but this is not the case, it is always a little bit open as you open them with the stationary screw.

I`m thinking of getting the default jets and installing them so I can actually setup the pilot screws per cylinder. Also, i`ve ordered new rubber bushes between carbs and manifolds as they didn't look to fresh (although they didn't respond when I sprinkled water over them at stationary).

Still there is the contradiction: Black spark plug but backfiring from what seems to be running too lean. I`ll go ahead with the bushes and report back my findings.

Thanks all!

Depending on the age and mileage, you may want to consider replacing the spark plug wires. I usually condemn them when I unscrew the leads from the coils and see green corrosion. A high resistance, low voltage condition would cause the the symptoms you're describing. I'd check that before delving into the carburetors. It's worth noting that unlike the old breaker point ignition systems, electronic ignition problems tend to clear up as engine speed increases.

 

[RempageR1]

Hi,

Just a small update. After replacing the rubber plugs under the jet cartridge and replacing the rubber bushes I ended up with the exact same, except for backfires when on high revs and throttle closed. After syncing carbs, the problem was almost gone.

This week I disassembled the carbs again to check there wasn't anything that got into the pilot jets from my last action, but there wasn't.

Some cool new things:
I`ve discovered that the smaller PAJ2`s are default on a 85 machine and the pilot screws themselves do not close the circuit completely when they are fully closed, the needle ends are a bit smaller than the hole they block. That way they are never actually completely closed....

Last thing I did was check all spark wires and found out the left front one was corroded , the other three were fine... One big coincidence that I had issues with front right and that cable was corroded (after 5K miles and two years or so, need to get out more).

Tomorrow I will to some testdriving, I`ll let you know how it went!

Thanks all!

 

[mattmullins]

Might wanna look down the carb when it's running a few gas coming out of the needle I had the same problem. My own ring on the needle and seat was bad Fixed it now I'm lean as heck

 

[RempageR1]

So this morning I took the bike to work and, everything was exactly as when starting this topic. Couple of backfires through carb (first 150 meters), after that no problem.

@Mattmullins, Could you elaborate? What should I be looking for?

Thank you.

 

[davesax36]

@Mattmullins, Could you elaborate? What should I be looking for?

Thank you.

+1. I think I've seen gas on the needles after shutdown, but never looked while it was running. More info, please...

 

[naughtyG]

I'm slightly stumped by one thing - you say you have the factory needles set to the middle groove, but I thought OEM needles only had 1 groove? You sure you haven't got stage 1 or 7 needles in there?

Black spark plug could mean rich, but it could also mean it's fouling cos it's not firing right all the time. I would defo replace the plug, wire and swap its coil if poss (a right PITA unless you're running COPs already..)
That would also explain the early on backfiring - if that cylinder is building up fuel/air and only firing when it wants! Shit resistance in the plug or HT leads maybe also alter as they warm up.

 

[maleko89]

G, Canadian Vmaxes have adjustable stock needles. Not sure on Euro.

 

[naughtyG]

G, Canadian Vmaxes have adjustable stock needles. Not sure on Euro.

Didn't know that! US ones don't... Thanks Mark

 

[RempageR1]

Hi,

Sorry for abandoning this thread. I never got this fixed so I kind of forgot about it and accepted it would backfire. However, since 1.5 month ago the whole CDI crapped out, I replaced it with a Ignitech unit and the problem is now gone . So this was a CDI related issue all the time... go figure that one out.

And for the needles, yes they are the 1st series canadian.

Thanks all for helping,
Rempage