ok so I got great color plugs but stutter at 4000rpm?

I have been tweaking this thing and now I have good colors on the plugs. chocolaty brown. I seem to be having a stutter in the range of 3500-4500. Seems at only a particular position on the throttle. If I WOT it takes off and it doesn't do this. If I slowly allow the bike to climb in rpm it will seemingly stutter/bog. I assumed this was due to improper fuel adjustment. However now that my plugs look decent color what does this mean. I haven't found any air leaks so far.


Any Ideas???

It does idle incredibly well.

Another thing is if I slightly apply some choke (enrichment) the bike will idle really fast but under load it will perform like a champ. I do smell fuel

 

I dont know if this will help but my bike started getting a shudder around those rpms and i left it for a couple of weeks and then it wouldnt accelerate at all and then one of my coils fried. Thats my only idea hope it helps. Good luck

 

i think i would be checking fuel lines & filters.

 

I would think if fuel filter/ line were the issue then it would have symtoms further up the line.

It seems to stutter at 4000 and then takes off like a bat out of hell (seemingly when the big jet kicks in.

Im going to ride it to work today and really pay attention to all the details.


Thanks

Well i didn't send this post but now i am at work and I think the issue might be with my petcock.

But who knows. Anyone deal with anything like this?

 

i get the same thing.

I have replaced the fuel filter, no change.

i have a bunch of seafoam in it now trying to clean out any junk.

it only happens to me if i am trying to stay at a steady speed, like going 30 MPH. if i give it some more gas it's fine.

I'll let you know if the Seafoam does anyting after a week.

 

Ant Flat-spot you are having with break-down -- or, HOLDING 4,000 rpm would be:

1. Main Jet and Emulsion Tube + Diaphragm Needle Position

2. Ignition Components

I think I would look into the Carbs, first and make sure the Diaphragm Pistons aren't sticking and not lifting-out the Needle Jets well enough.

UNTIL you apply WOT Manifold Vacuum and they react to the maximum pressure in the Manifold and lift-up allowing the Mixture to be the Full Main FUEL Jet Flow.

 

Years ago the magazines would always suggest putting a .020 washer under the needles. That was done to fix the stumble. Easy thing about that change is that you do not have to pull the carbs to do it. Just unscrew the 4 screws holding the covers on then pull the slides. Easy to do and a cheap one. Let us know if it fixes it or not

Sean

 

The Seafoam seems to have done a ton of good.

i'm happy to report the flat spot is gone!

its only about 42 degrees here so i only rode about an hour but cold and warm there is not hesitation.

all i did was put about twice as much Seafoam in and ran it for 15 minutes then let it sit for a week. ran the tank dry and then filled her up with fresh gas.

you can get Seafoam at advance auto for around $10.

Good Luck!

 

I had the same problem with my Seca 650. I found that one of the needles had been pulled down in its nylon washer. If your carbs ever sat for a long period of time some one may have pushed the slide up when it was glued to the emulsion tube trying to break it free. This essentially adjusts the needle down in the tube making for a lean mixture until the slide is full up. Take a look at you needles were they exit the slide you are looking for a perfect line all the way around the needle. That is the shoulder of the needle that should be flush with the plastic washer that holds it in the slide from the top. You will need to replace the needle or try to puch it back up with out damaging it. I would also take a very good look at the emolsion tubes and make sure they are rely clean and all the side holes are compleatly clear. Good luck!