Engine stumbles/acts out of fuel ... ?

[CarnageZ28]

Picked up a 99 Blaster, internal engine mods unknown - if any at all.

Fatty & Silencer, K&N.

Rejetted to a 290 main. Needle in 3rd position. Stock pilot. 1.5 turns on air adjustment screw. The carb was cleaned out two days ago. And jetting changed from stock 230. My local shop had a 260 and a 290. I picked up both, threw the 290 in, and am trying to work out all the other little bugs so I can get the carb tuned right.

As it sits, the thing fires right up, idles perfect, revs ok in nuetral. Put it in gear and drive, it feels like it sputters, occasionally dashing into the powerband, hard. It's hit and miss, but it seems like I can get it to go full through the powerband sometimes in first and second, and then it losses power progressively as I work towards a 5th or 6th gear WOT Chop to read the plug. It will start to choke out (Like if you let the fuel off) and lose momentum. If I chop it then and there, the porcelan looks lean. If I kill it when it is pulling hard in first and second, it looks pretty close, a hair rich actually.

So here are my thoughts:

1 - The float height is way off because it was overflowing with fuel when I would turn the fuel line on, so I tweaked it a hair once I replaced the needle and seat.

2 - It has an inline fuel filter and I think that may be a restriction possibly? Has anyone had issues with this?

I'm open to suggestions but these are the two primary things I am going to look at once I get home today or tomorrow from work.

Thanks guys!

 

[cirame1]

well im pretty much having the same problem pretty similiar. Im running a 280 main jet with no airbox lid with a mikuni 28mm carb and fmf exhaust. It revs good in neutral and idles ok and wen i drive it sputters on low end and spirts up into high end and feels good but feels like its running rich. I checked my plug and its dirty and im trying to adjust my carb. Same though as 5th and 6th gear come up it feels like its losing power. someone made a suggestion about going up or down on the pilot jet so im gonna swap it out and see maybe go down on it.

 

[CarnageZ28]

Well, the pilot jet controlls idle to around 1/8th throttle. I mean, it meters fuel up top to some degree but it makes minimal effects, next to none at WOT. And my issues are coming from 1/4, maybe 1/3 throttle to WOT. This would indicate an issue with the needle jet being on too low of a clip (holding the jet higher in the carb, and hence richer, and the main jet primarily meters final fuel flow at WOT. My issue is that at WOT sometimes it feels strong, like in 1st and 2nd. Then it starts to fizzle out. Like it is leaning and losing power.

With you, if your in 5th and 6th gear, I imagine you are giving it more than 1/8 throttle so your NOT having pilot jet issues. If your quad is idling/your riding it from idle to 1/8ish throttle, are you fouling plugs? Do a plug test running the engine in this throttle range. It should have a nice tan look to the porcelin. If its black/sooty your too rich and need to go down on the pilot jet (or adjust air mixture) and if its whiteish looking, you are lean and need a larger pilot. Of all the bikes I have ever owned, I can never remember having to change a pilot jet for just an intake and exhaust. On my big bore 125 yes, and my ported YZ250, yes ... but just an intake and exhaust, NO. That only required bumps up (typically) for the main jet, and tweaking with the needle jet position a little.

I am ripping that stupid fuel filter off tonite. I dont trust it. And its not really needed... I think my issue is with the floats or the filter, NOT the main jet being too large. Ive rode grossly rich jetted bikes that still would pull to redline, and maybe even sputter some, but not like this. This is like someone shut the fuel line off.

If yours has a filter, try bypassing it. And if not, maybe ours have the float height set too low, so instead of having a full float bowl, its half full ... And when we are going WOT, it is so far out of adjustment that its not letting fuel in fast enough, so by the time we go through a cuople gears it is out of fuel in the bowl, leaning out, breaking up, and dying.

I may take it in 1st or 2nd gear, get it into the powerband, top end RPM's and run for a good 10-15 seconds to see if it starts to sputter/run out of fuel. Then we will at least have a better idea of what is going on. If its too small of a main jet, its not going to be sufficient at 8,000RPM's one minute, and then not meter enough fuel into the engine 10-15 secdonds later. I think we have some type of common fueling issue.

I wanted to get mainjets 260-290 so I could experiment but my shop was out of the 270 and 280's. And I am not buying them anywhere else because I get employee discount rates there lol ... think I have enough projects going on hahah ...

 

[cirame1]

yeah well my bike has a 28mm carb which obviously isnt much bigger and reeds and a reed spacer along with exhaust and no airbox lid. I def hear anout being wot and it sputtering not being the pilot but its actually pretty strong up top and it pulls just kinda had a rich feeling to it. my plug is black but not horribly black and wet. But the issues of sputtering are def. 1st gear and 2nd gear about 1/4 throttle at the most it feels like it wants to die and it jerks a bit. I am assuming its not a pilot b/c like u said its not typical to have to change one on this setup so im assuming mayb my air and fuel is off a bit. The trouble is im not good with tuning it and the carb has 1 screw on the choke side thats kinda big and gold and thats at 1 and a half turns out and theres 1 more screw on the opposite side near the opening of the carb thats a small flat head bolt alos gold... for tuning i would def. appreciate some help on which screw is what and how to maybe go a lil leaner on the mixture...

 

[cirame1]

and wheres the fuel filter is in in or near the petcock? or wat eva thats called

 

[CarnageZ28]

Well, the pilot jet controlls idle to around 1/8th throttle. I mean, it meters fuel up top to some degree but it makes minimal effects, next to none at WOT. And my issues are coming from 1/4, maybe 1/3 throttle to WOT. This would indicate an issue with the needle jet being on too low of a clip (holding the jet higher in the carb, and hence richer, and the main jet primarily meters final fuel flow at WOT. My issue is that at WOT sometimes it feels strong, like in 1st and 2nd. Then it starts to fizzle out. Like it is leaning and losing power.

With you, if your in 5th and 6th gear, I imagine you are giving it more than 1/8 throttle so your NOT having pilot jet issues. If your quad is idling/your riding it from idle to 1/8ish throttle, are you fouling plugs? Do a plug test running the engine in this throttle range. It should have a nice tan look to the porcelin. If its black/sooty your too rich and need to go down on the pilot jet (or adjust air mixture) and if its whiteish looking, you are lean and need a larger pilot. Of all the bikes I have ever owned, I can never remember having to change a pilot jet for just an intake and exhaust. On my big bore 125 yes, and my ported YZ250, yes ... but just an intake and exhaust, NO. That only required bumps up (typically) for the main jet, and tweaking with the needle jet position a little.

I am ripping that stupid fuel filter off tonite. I dont trust it. And its not really needed... I think my issue is with the floats or the filter, NOT the main jet being too large. Ive rode grossly rich jetted bikes that still would pull to redline, and maybe even sputter some, but not like this. This is like someone shut the fuel line off.

If yours has a filter, try bypassing it. And if not, maybe ours have the float height set too low, so instead of having a full float bowl, its half full ... And when we are going WOT, it is so far out of adjustment that its not letting fuel in fast enough, so by the time we go through a cuople gears it is out of fuel in the bowl, leaning out, breaking up, and dying.

I may take it in 1st or 2nd gear, get it into the powerband, top end RPM's and run for a good 10-15 seconds to see if it starts to sputter/run out of fuel. Then we will at least have a better idea of what is going on. If its too small of a main jet, its not going to be sufficient at 8,000RPM's one minute, and then not meter enough fuel into the engine 10-15 secdonds later. I think we have some type of common fueling issue.

I wanted to get mainjets 260-290 so I could experiment but my shop was out of the 270 and 280's. And I am not buying them anywhere else because I get employee discount rates there lol ... think I have enough projects going on hahah ...

 

[cirame1]

bump..

 

[CarnageZ28]

Blaster Fixed!!!

Combonation of a few things.

1 - Drained existing fuel, and mixed up some 32:1 Super M with premium (So I can run the same as my YZ250 and 250 Quadracer) for it. Imrpoved throttle response slightly, still dying out from 1/4-WOT. Idled slightly better.

2 - Removed Fuel Filter - Restricted flow - ALOT. Now runs and will pull strong 1st-6th, but is too rich on plug readings.

3 - Removed Airbox lid - WOW ... Big difference in noise and now doing a WOT plug chop comes out just about perfect with a nice golden tan, not rich, not lean. Just right.

So all in all, I have it together and running pretty good. From 1/8, maybe 1/4 throttle, it starts to run a little rich from there to around 7/8 throttle. I am dabbling with the idea of dropping the needle jet one clip to see how it responds/how plugs look.

My big question however now, what is the stock setting for the air-screw? I have it at 1.5 turns out. Mixture could be leaned out slightly at idle.

 

[quam]

cirame, are you sure the a-m carb is set up for 2stroke? i believe 2 stroke carbs need a different size slide than 4 stroke.....
carnage, the pilot screw will prob be at a different setting from the factory on each bike.....they never really set these things up to any kinda standard. plus you'll need your screw tuned to the atmospheric pressure at your altitude.....

 

[cirame1]

yea its for a 2 stroke but its bogging in all gears at all throttle positions so today im taking my pilot out and im gonna take my 280 main jet out and try a 270 and a 260 with a new plug and see how it goes... ill let you know what size my pilot jet is and maybe adjust it.... its running really good for wat it is but it stutters and skips a bit and boggs down low noticeably so i hope i can fix it. we will see wat happnes today my 400 ex shock also came in so ill have some fun putting that in to.

 

[CC&Fabb]

carnageZ28 You said that your balster was still running a little rich? I have the same exhaust set up (FMF Fatty and Powercore 2) plus a K&N w/out the air box lid and I am running a 250 main and stock Pilot. I live at about 2500 feet and my blaster runs perfect. Maybe you might try going down a few jet sizes.

 

[AZblaster]

Go a ? here about the Blaster 06'. I got this problem of the blaster jerking with drive like if the engine is going to stall but then it takes off again...wondering what was wrong? Thanks

 

[Triple_B]

Thread Dig !

 

[blasterkiidirl]

well im pretty much having the same problem pretty similiar. Im running a 280 main jet with no airbox lid with a mikuni 28mm carb and fmf exhaust. It revs good in neutral and idles ok and wen i drive it sputters on low end and spirts up into high end and feels good but feels like its running rich. I checked my plug and its dirty and im trying to adjust my carb. Same though as 5th and 6th gear come up it feels like its losing power. someone made a suggestion about going up or down on the pilot jet so im gonna swap it out and see maybe go down on it.

im kinda having the same problem wit my blasty and like u i have a fmf sst and I find the power band a bit finakey the low end is fine to as it hits the mid revs its a bit dead but its top end is fine :-/ :-/

 

[blasterdemon7]

Clean carb and air filter. Plug chop to check jetting. Compression and leak down test.