LTZ 400 Bog at WOT

[New2Tri-Z]

I have an 05 LTZ 400. Its my wife's bike and back up bike for buddies so it does not get ridden every time. The last few times I took it out it has had some carb issues. Started with bad idle, I could adjust the idle and get it to idle but rpm seemed a little high. All in all it worked through out the day but didn't want to run great unless you were on it. Took it home, pulled the bowl and cleaned the jets. Fast forward a month later. Took it out riding again and seemed to idle a bit better but would really bog and sputter when you rolled on the throttle (anything above half throttle). SO I took it home and it sat another month or so.

Over the weekend I changed the oil & filter, replaced and oiled air filter with a new uni, new spark plug, drained old fuel and replaced and I tore the carb out. I took it all the way apart (air/fuel mixture screw also), cleaned every orifice and all jets everything had a visible clear passage. I ran carb cleaner through the passages of the carb and blew it out with air (120 psi max my little guy will do). Put it all back together and the idle is fixed, it starts and idles great. I can whop on the throttle in neutral and it seems to build up the RPM's just fine. But when I ride it, same issue, if I stab the throttle it just bogs out and wants to die. I assume it is either a float issue (bowl is running dry) or plugged main. I am thinking maybe I need to get a carb rebuild kit and go from there as it is over 10 years old now.

Just looking for some opinions or suggestions. I am wondering if maybe the timing is off, bad valve, or CDI/coil is going bad? Some suggestions of things I am not thinking might be helpful. Thank you in advance for your help.

[atc007]

We should never assume,and 120psi is not a lot more than a fart lol....But,,ASSUMING you did get the carb cleaned. It is Highly unlikely to have a plugged main jet or passage. I would see if you can swap a CDI with someone, ohm out the ignition system. Air leak? Intake boot looks ok?If you choke it,does it get better? That will rule out ignition and tell you fuel delivery. You said you drained the tank,,make sure the petcock is flowing perfect.? Gas cap venting good?

[New2Tri-Z]

I do agree not much more than a fart lol. I am sure it is cleaned well and is unlikely the main is clogged. Main is wide open and the nozzle sprays just fine. Intake boot looks good from both airbox and engine side, I will try the starting fluid trick when I get home just to rule out though. I have not pulled choke while it is bogging, but if I pull choke once its idling it dies instantly.

I don't have anyone to switch cdi's with but I do have an 06 LTR 450 (EFI), I wonder if the cdi is the same? Petcock seems to flow great. It only flows on prime unless the bike is running, but when I had tank off it seems to stream out of petcock just fine. I am really leaning towards CDI issue at this point. Thank you for your help Bill you always seem to chime in when I ask about these silly 4-wheelers?

[shortline10]

I get a lot of those machines threw my shop . The common problems with the z400 are valve lash , spark plug caps , they short out in the head and a very sensitive air fuel mix screw , don't go by factory specs , adjust it at idle for best throttle response . how's the choke plunger .... seating all the way ? the cables get pinched and the plungers don't completely close thus making the bike run like crap .

[atc007]

I'm just an old has been,but I assume the Z and R cdi's are vastly different,without a doubt. Shortline? lol.

[New2Tri-Z]

I get a lot of those machines threw my shop . The common problems with the z400 are valve lash , spark plug caps , they short out in the head and a very sensitive air fuel mix screw , don't go by factory specs , adjust it at idle for best throttle response . how's the choke plunger .... seating all the way ? the cables get pinched and the plungers don't completely close thus making the bike run like crap .

I have replaced the cable choke with a pull choke on the carb. I am pretty sure it is seating all the way as I looked at it when carb was out. I replaced the choke about 6 months ago and can't stand the cable operated ones. The only noticeable difference on the choke was the pull choke has a flat/blunt end, my stock choke has a needle/point at the end. But as for operation it looks to close off the circuit when pushed in and is fully opened when pulled out.

As for air/fuel mix screw, I just left it where I found it 2.5 turns out. I had the bike tuned years ago @ dealer when I bought a slip on Yoshimura silencer so I figured it was dialed in since it ran great for years. I just stuck with the same settings. When you say adjust at idle that must be fun to squeeze under carb and adjust? It seems to start and idle great with no issues. Like I said I can rev it in neutral and seems to rev to the moon with no sputter or bog. But when I ride it under load and stab it is when I get the sputter/bog. I just replaced the spark plug and did not notice any issue with the boot. It is definitely a long one so I will re-inspect it.

I have not adjusted the valves in the 5 years I have had it, so I am thinking this could easily be an issue. Is this a likely symptom for valves being out of tolerance? Thank you for your help.

[New2Tri-Z]

I'm just an old has been,but I assume the Z and R cdi's are vastly different,without a doubt. Shortline? lol.

Yes after a quick cross reference they are different in all aspects including $$$. Z's are far cheaper? :lol:

[atc007]

I stayed away from valve lash , they are usually hard to impossible to start when out of spec. But certainly warrants checking. Plug cap sounds very likely.

[New2Tri-Z]

I stayed away from valve lash , they are usually hard to impossible to start when out of spec. But certainly warrants checking. Plug cap sounds very likely.

I had an 86 ninja years ago that needed a valve job bad, so I would have to adjust the valves twice a year. I knew it was going out when it became very hard to start. I could kill a battery in no time.

I will look at the plug cap a little better tonight and see if I can see any issues.

Another questions that just came to mind. When I replaced the choke cable with a knob type I had to adjust the TPS slightly in order for the knob to have enough clearance to close all the way. Everything I have read about the Throttle Position Sensor is they are not necessary, some people even block them off. Could the position of the TPS be causing any issues? Its obviously adjustable as the mounting holes are almost slotted to allow for a few degree turn either direction. Just a thought

[shortline10]

Over time the packing in the performance pipe changes so when the air screw was adjusted then could be different now . A motion pro air fuel angle screw driver makes it simple to adjust carbs . A 1/4 turn can sometimes make a huge difference .

[New2Tri-Z]

Over time the packing in the performance pipe changes so when the air screw was adjusted then could be different now . A motion pro air fuel angle screw driver makes it simple to adjust carbs . A 1/4 turn can sometimes make a huge difference .

That makes sense. I will mess with that and the spark plug before I get to the valves. Thank you for the help so far.

[Ryanq55]

My dad has a kawasaki 400 that are literally identically the same as the z's. His, as well, sits most of the time, gets borrowed from relatives, and is a back-up as is yours. Last time we took it out the throttle would cut in and out when stabbed, as well as under normal cruising speed. My suggestion, for what it's worth, is take that carb apart again and clean the pilot again. From my understanding the first 1/4 throttle is usually supplied by the pilot? I cleaned my dad's carb really well, blew it out with compressed air and it was still crap. Called my neighbor who runs a shop and he said clean the pilot out again. Use a wire brush and shove it all around in their, or what saves time and is fairly inexpensive, buy a new one. I did and it runs like brand new again...

[New2Tri-Z]

I am fairly confident it is not the carb. I have since bought a rebuild kit and am having the same issue. Stock main is a 130 and mine is a 145 for the pipe. Its the only jet I kept from the original set up. Replaced all other jets (even tiny pilot air jet under the slide). Realized my carb was missing the o-ring and washer on the pilot air screw shown in the parts fische (luckily rebuild kit had an o-ring, but no washer the correct diameter?). Set Pilot Air Screw at 2 1/4 turns out. Started and idled just fine but still sputters on the the blip of the throttle. Tried adjusting the pilot air screw while on the bike and nothing seemed to help the bog.

While testing the ignition system I cant seem to get a primary coil voltage in the test??? It says to remove the plug, re attach to spark plug wire and ground on cylinder. Then use multi meter (black probe on black wire and red probe on black/white wire) and measure voltage (min 130v) while cranking the engine over. I cant seem to get a reading at all???? SO the next step is to test the coil. The resistance on Primary side of coil is supposed to be between 0.1-1.0. My digital multi meter only does whole numbers on standard ohm setting and reading goes from 9 to 1 then sits at 0??? I assume this is because my meter cant measure 0.1 ohms (or less than 1.0), but I am not sure? I get awesome blue spark when grounding the plug on the cylinder. I can hold it about 6" away and still get the spark to jump to the head. Then I tested the secondary side, coil to plug wire. Red probe on plug terminal(black wire) and black probe to spark plug wire. Spec calls for 10-20k ohms. I am getting 16k, so well within spec. So assuming this is an accurate reading, coil is good so move to pick up coil and signal coil peak voltage and resistance. I have made it this far yet, but it is next. If these all test out fine then it says "faulty CDI; Open Circuit in wiring harness; or improper ignition coupler connection" I am still wondering if the readings on the coil are good as if they are not it says replace coil.

Now Shortline had mentioned the spark plug cap shorting out in the head, would any of the tests performed so far have concluded this to be the problem? Such as the coil resistance test? Because after visible inspection the cap looks fine and it does not appear cracked or damaged. I am still really puzzled with this thing???

Lastly I haven't checked the vales yet, but could they cause this type of symptom? Shortline Mentioned that they are a very common problem with the bike and mine have not been checked for a few years. I appreciate all the comments and I will keep at it rather than throw money at it or the dealer.

[oscarmayer]

that's a BIG jet for a pipe. we usually only jet up 1-2 sizes not several. you could be flooding it at WOT.
try droppign in a 134-135 jet and set the needle to center. make sure the mix screw is no more than 1+1/2 turns - 2+1/4 turns out.

[New2Tri-Z]

Thank you. This is what it was jetted by Dealer when I bought the bike. I bought it and it came with a new Yoshimura Slip on in the box. Installed it and took it to dealer for a proper jet. That was 5-6 years ago. Maybe the muffler packing is wearing down so in need of a re-jet? It ran great for years. You could be right about the flooding at WOT though, that almost seems likes what is going on. The needle only has 1 spot for the clip (no adjustment) according to the manual. I will try stepping down a jet though and seeing if I get any different response.

Not sure if you seen my comment about the washer and oring missing from the air mixture screw? As of now I only have the oring in there as I couldn't find a washer in the rebuild kit that fit in there. Could this be affecting the position of the screw? I would think the thickness of the washer and oring would affect the turn settings?

Thank you for the input.

[oscarmayer]

not sure that would cause this issue as mixture only affects mid throttle. at WOT it is only the jet involved. no other settings are used as the needle is completely out of the jet center and it's all jet, that is what lead me to believe you are running rich.

[New2Tri-Z]

Update*** I have since re-jetted the bike and dropped down to 135. This allowed me to turn the screw out to 1.5 and idle and start up are great. I think they threw the 145 in to be fat/safe and had to adjust the screw to compensate (it was at 2 3/4 turns out). Unfortunately I still have the bog at high RPM.

I had previously tested the coil with my test meter on the lowest setting 2000 ohms (it read 0 ohms). The manual says reading should be between 0.1-1.0 ohms on primary side of coil. I have since picked up another tester with a smaller ohm range setting. I tested using 20 ohm max setting and it is reading 3.0-2.3 ohms. According to manual I am out of spec so it says replace the coil. This is somewhat in line with what shortline10 was telling me about the plug cap shorting out. Just want to confirm my result that I need a new coil. Thanks for any input.

[oscarmayer]

Yep. Get a new one.