WOT causing stutters

[nukacola]

I usually don't ride wide open, but did the other day. It kinda bogged down on me in gear. It will do it in any gear but not all the time, just sometimes. I wanted to test, so I stopped and put in neutral and opened throttle WOT. It cut the engine off.

I'd say now that I've been trying it out at WOT it's happening maybe half the time where it starts to bog down and lose throttle response in any gear. But the other half the time it's fine.

I have a brand new carb installed less than a month ago and no mods other than a K&N filter. I doubt it needs a bigger jet or something. Does it need a spark plug change or something? I ride it regularly but just recently noticed this problem.

I always use premium fuel from the gas station btw...

 

[nukacola]

well it's not the fuel cap hose at least. I have had that shortie thing on there a while and no pressure buildup in the tank causing problems down into the carb...i don't have enough light to check plug now.

Also in neutral at least it will rev up to WOT if i do it slower, as in not pressing the throttle button all the way in really quick. The really quick full rev is what causes it to die. It will start right back though. Also this is when warmed up. I don't like to open it up too high when the engine is still cold.

 

[nukacola]

I'm kinda wondering if it's the accelerator pump. Do these carbs have this and can you replace it?

 

[Kreep]

Not an expert by any means but I doubt it's an accelerator pump problem. I just had an accelerator pump problem and what happens is the accelerator pump gets stuck because the spring is to weak or broken and won't return so my idle just kept getting higher and higher until it wouldn't return from wot. Sounds like a fuel or air issue. Thats why putting the stronger pen spring and valve cap in fixes the pump and response. When you say new carb what kind? Brand new? What's your air fuel screw adjusted at? Could be a spark issue how old is the plug? What's it look like?

 

[geeessfore]

I had same problem. Had to drop my main to a 150 it was running to rich

 

[nukacola]

Just pulled the plug. What ya think?

 

[03yamwarrior]

How olds the plug? Looks really rich. Sand it down and put it in again so we can see on a single run

 

[nukacola]

I'll have to post back tomorrow, will be dark out soon.

That plug has been in there since I got the bike like 5 months or so ago. Judging by the 18 mm nut's condition it looks like it's been on and off several times.

BTW the carb is brand new from Zoom Zoom Parts from ebay. It's not a stock Mikuni, but it's a stock replacement. I did not make any adjustments to the pilot screw when we put it on.

 

[nukacola]

New before:

after:

I know the lighting is a little different but to me it looks a tiny bit darker after running for about 15 minutes driving around using wide open a few times. It still bogs. And it still will die during a quick full throttle at idle.


Can I just turn the pilot screw a bit to lean it out a little? It seems it's def running rich. I dunno what to do...


Oh yeah, does the gapping change anything really? My Clymer manual says to gap it at 0.6-0.7mm. To me it looks like it's slightly over 1mm.

 

[nukacola]

There were a few dead leaves in the air box that I just saw. Maybe they were getting caught in the air filter intake? I took them out but now too tired to put the plug back in. Maybe they were blocking air intake causing a rich condition.

Don't knoww! I'll check tomorrow when I get a chance. Also I can smell fuel on the plug if that makes any difference.

 

[nukacola]

Leaves are out, plug back in, still doing it. :/

 

[BigCassell]

I'm having almost the same problem. Everyone is telling me the jets in my carb aren't set right. Don't know if that helps any

 

[03yamwarrior]

What's the plug look like after sanded up

 

[nukacola]

It's the picture above that shows a before and after. I did the best I could with sanding it. And it was a little darker after.

 

[nukacola]

Big Cassell, you might need rejetting with the mods you have.

 

[nukacola]

got a new plug, actually 4, just in case. Put one in gapped to correct size. Still the same.

Have a friend coming over tomorrow to look at it.

 

[nukacola]

ok so he can't make it out today...another guy said my fuel filter is built for fuel injection motors and I need to get one that is built for gravity fed top down applicaitons. Maybe I'll go to the tractor supply store and see if they have one for that. Supposedly the FI filters get clogged in 4 wheelers?