Help. Diagnosing problem carb? Plug?

[rabit1]

*Sorry for double post. But the previous post (same post) is somehow bad. I can't open/read it. I also don't know how to delete it. Could the moderator please delete my previous post. Sorry.* Anyway,

Hi,

First of all. I want to thank you to this forum members. You guys have been a lot of help. But I appreciate some more assistance.

Here's what I got: Gen 1 vmax with aftermarket exhaust. Everything else is stock.

I've been having problem with my cyl no 3. At first I thought it was electrical, but I wasn't really sure. I've replaced plug, move coils around and replaces HT and plug caps with new ones. But problem persists. (Don't know about TCI)

My cyl no 3 seems to heat up slower than other cylinders. Left exhaust is also weaker than right exhaust. I notice that the sound from left exhaust is very different from the right. The left one sounds and feels softer. (This is during idle, started from cold engine). Cyl#3 and exhaust seem normal if I rev the engine.

But the most noticeable problem is the plug on cyl no 3 is always black. See attached pics of how new plugs (ALWAYS) looks like after only 20 minutes ride.

I'm no expert mechanic, but I simply thought that looks like a too rich conditions. ( I could be totally wrong. Could it be valve/oil problem?, what do you think guys?)

So I tried to set the AF screw in on carb #3. But even after setting the screw all the way in to 1/2 turn out only, the plug still look the same. Also turning the screw actually doesn't seem to have an effect on the engine idle and the plug.

So after reading this forum, I decided to do the both the shotgun and pea shooter method, which I did. The pilot screw indeed looks dirty and the spring seems a bit rusted, but since I have no replacement part, I just clean em and did the shotgun then put them back in. ( I don't have the confidence and the skill to take the carb apart and clean it and I haven't find any mechanic in my area that knows vmax well.) And, yeah, I've also sync'ed the carbs.

But even after doing all that, the only improvement I notice is that the bike seems to run better/smoother and the cylinder no 3 heats up a little faster (but still a bit slower compared to others and left exhaust still feel softer). Turning the #3 AF screw still doesn't seem to have any effect (I could be wrong here again, as I don't really have the expertise).

The plug, however, still comes out black like the attached pictures after each test ride.

The bike, however, runs well especially on higher rpm. If I rev the engine around 1500-2000 rpm both exhaust sound the same and feel as strong.

So what do you think guys, any advice? Why is the plug always black?

Thank you,
Regards,

 

[1st Shirt Maxer]

So, I'll take a stab at this
First, you mention swapping the coils around, did you test the ohms on each coil to make sure they are within spec?
After that I would start probing the coil connector on your bad cylinder to make sure your getting good voltage supplied to the coil
If everything checks out then my suggestion is to check the plugs next. Maybe install a different plug into that cylinder to see if the problem persists
If you still have the same problem after that, I'm thinking it is a carb problem. Since you say you aren't comfortable digging into your carbs, I would send some messages to some of the senior members like One2dmax, PATMAX, fire medic and a few others and enlist their help as they are much more knowledgeable than me. Good luck.

 

[dannymax]

You might try a compression test just to make sure there isn't a big issue going on...which I doubt...but on the face of it I'd guess at a plugged or partially plugged pilot jet.

 

[rabit1]

Thank you.
I only check the coils resistance on both rear coils. Not the front. The primary resistance both are 3.6 volts. A little higher than what the manual says which is 2.7V +/- 10%. Here the temp are about 29-30 C.

The secondary are a little more than 13K ohm, which I think are within spec.

I did not check the voltage for the coil connector though. How to check for Voltage?

Since I already replaced the plug several times, Are you suggesting I replace it with different plug type? A hotter type?

Dannymax, I though so too at first, that's why I tried the shotgun. Would shotgun method always enough to fix plugged pilot jets? Or Do I still have to open up the carb?

I haven't find any that'll do compression check.

 

[Sweetwilliebrownjr]

The carbs have to be disassembled to clean the pilot jets. It's not all that difficult, but time consuming. The pilot jets are tiny and get restricted fairly easily. That's where I'd start.

 

[davesax36]

I vote pilot jets, too. What do the other plugs look like? Doing the carbs is only a pain in the butt. However, since you only want to do #3, you could just split the rack and do that one. It takes a while, but there are plenty of guys on here that could walk you through it and there's a how-to.

 

[rabit1]

Thanks...

I guess I'm going to have to learn to do just that (disassemble). I found naughtyG guide with lots of pics (thank u Dannymax). I'd just want to make sure and rule out that it's not electrical.

The other plugs looks OK, just looks a little bit on the white side. So I have turned the A/F a bit more out to 3 turns for the other carbs.

I thought doing the shotgun cleans up the pilot jet. So I'd assume that's not always enough?
Would another try at shotgun probably do any good?

The plug looks like that (all black) in just a few minutes ride. Is that enough time to make any plug diagnosis? In fact I'm not even sure that black is a rich condition or oil/valve problem? How to start a diagnose for valve problem?

Thank you again,
regards

 

[m-cman]

I may have missed it but did you test the spark on the plug in question? Remove it and leave it in the plug cap and ground it against the engine. Crank the engine and see if you get a good spark.

Also you might not be getting a good connection in the plug wires. Trim a small (1/8" or so) off the end of the wire going into the coil and re-attach. This is something everyone has to so at some time due to corrosion. I finally had to replace all my wires and plug caps. Was pretty cheap. Standard 7mm zero resistance copper wires (I bought 6 ft at $.50 a foot) and NGK SD05F plug caps (4 at $2.95 ea.).

 

[tugla]

there are guys here can help u if it is a carb rebuild issue. I'd start with danny or sean. but for sure sounds like they should be looked at. float settings sync etc. just the basics.

 

[rabit1]

Yeah. I'm going to check the spark again. I did check it before I replaced the wire and the caps.

The old wire+caps were bad and the spark was weak (yellow). But I havent checked it again with the new caps+wire. My mistake, I just assume spark is ok now after I replaced the wire and caps.

i did test the resistance on the new wire+cap, and I got 5K ohm. Is that OK?



Thank you

 

[MaxMidnight]

A black plug normally indicates a rich condition or excessive oil is getting into the cylinder

From what I can see from the picture the plug look sooty so suggests that #3 is running excessively rich.

I would have thought that a plugged pilot jet would lean the mixture and an ignition issue would cause a misfire or wet plug?

As it is only affecting one cylinder the air filter won't be the culprit.

I would start by checking the float height (access to a manual will be helpful) and that #3 choke mechanism isn't stuck on or allowing excess fuel to bleed into the system.
Failing that then you will need to dismantle the carb and check for wear.

 

[rabit1]

Thanks..

I manage to do the peashooter and shotgun, that was fairly easy. Now I'm reading and learning my way to open up and disassemble the carb. And to check float height. But reading about it, float height seems like a different beast... I'm a bit intimidated.. There's no easier way around this I guess.

If the carb is running excessively rich, what sort of problems we can expect to have in the long run? (other than MPG, as of right now with new plug, the bike feels and runs OK. Acceleration is good. The problem seems to be only with idling and the black plug). I haven't test it with a long ride though. Just a few quick test rides.

 

[tugla]

if you are in them anyways pull jet blck and make sure all is clean in there and the rubber plugs on top not old and cracked.....since you are in there

 

[2fear]

There is an easy way around YOU opening up your carbs, you ship them pain in the ass carbs off to one of our carb guys on this forum. It will cost you a little money but it will be done right and you will be back on the road with confidence. I'm here to tell you I have been inside mine a few times and it is time consuming, I finally shipped mine off to have Danny clean them and they came back perfect, kicked myself in the ass for not doing that in the first place. I'm a rider not a mechanic, I learned a lot but I wont open them again. Personally I would do the shot gun again first.

 

[rabit1]

Thanks Chuck, Yes... that would be an option. ..
But I'm going to try to do this myself first...

What would happen if I keep running in rich condition for a longer time?

Regards,

 

[tugla]

give dannymax a msg....

 

[MaxMidnight]

Thanks Chuck, Yes... that would be an option. ..
But I'm going to try to do this myself first...

What would happen if I keep running in rich condition for a longer time?

Regards,

It depends on how rich it is - initially the plug may foul so you end up on three cylinders = poor running and performance, difficult starting, poor idle and higher fuel consumption.
If there is too much fuel and this isn't being burnt then you could end up with bore wash (the fuel removing the lubricating oil) which will lead to excessive wear and possibly seizure = big $$$!

The black plug is your motors way of telling you it ain't happy and should be fixed a.s.a.p.
Ignoring the problem will, in the long run, cause you more hassle than taking the time to fix it now.

 

[rabit1]

Hi guys,

Here's an update on what I did on cyl/carb#3 , so far:
- Did the shotgun again. Looks clean and not plugged
- Check the spark: is good
- Check wet float level (clear hose trick): 17 mm below the line. (good?)

Here's what I got. Basically problem persists. Same:
- Black #3 plug (even after just a few minutes ride).
- Softer left exhaust on idle. Higher rpm seems OK. Bike rides fine too.
- #3 cyl heats up slower compared to other.
- The #3 A/F screw doesn't seem to have any effect. Turning it in or out doesn't change idle. Neither 0 turn nor 5 turns has any effects on idle.

Considering all that. What do you think I should do now?
Do I still to check float by opening it up?
How do I make sure the black plug is not oil problem? Any sure way to test/differentiate it with rich condition?

Thanks guys, really appreciate all the help from you and this forum. Thank you
Regards,

 

[MaxMidnight]

Lets start with your last question - a fuel blackened plug will have a dry sooty look and if rubbed will have a powdery appearance.

Oil blackened has a more, er, oily appearance and the residue will leave skid marks when a finger is rubbed over it.

If it was oil and the plug fouls that quickly then I would have thought that you would see a significant of smoke out of the RH exhaust.

The test would preferably be a cylinder leakage test of if not available a compression test.

Moving on, if the idle screw still doesn't have any effect then that would suggest that there is still a blockage somewhere in the system. If the Shotgun doesn't do the trick then ultrasonic cleaning should be considered.

Did you check the float height with a header tank or using the fuel pump to fill the bowl. The advantage with the former is that you can maintain a head of fuel going into the float chamber and should be able to see if the float needle is leaking by looking down the venture with the throttle slide pulled back.

Have you checked that the choke mechanism is shutting off?

Given what you have done then now is probably the time the carbs need to come off the bike for a full strip and inspection.

That said am alternative would be to beg, borrow, steal or buy another carb and substitute for #3.
Might save a lot of faffing around n the long term?

 

[rabit1]

Thank you Steve,

The plug does have a dry sooty look, but if I use my finger to rub it, it certainly leaves skid marks on my finger. It doesn't seem to have an oily appearance, but I didn't use it for a long time, just a 10-20 minutes ride.. Maybe not enough time to make it really look oily?

If I take the plug out after running the bike, the plug does look black and a little wet and I can smell gas. But if I leave it out after a while, it looks dry (evaporates?). Which is why when I took the picture it looks dry. But definitely leaves black marks on my finger if I rub it. I'll take a picture next time with a black mark on my finger.

I tested the float level by using the clear tube method. And it is 17mm below the line. I didn't open the chamber. http://www.vmaxforum.net/showthread.php?t=17274

O ya I forgot to tell you guys, there's a little bit of smoke coming out on the left exhaust, not much, but only on the first few seconds when I start the bike, then the smoke is gone. No smoke on the right exhaust.

And yes I did check the choke mechanism, looks OK.
The task today I guess will be doing the compression test. I'll report back the result here.

How much would a carb replacement will cost me?

Thanks again,
Regards,