Needle jet not jet needle...



14 replies to this topic
  • Moto-Mike

Posted March 12, 2001 - 05:11 PM

#1

I've got a plug fouling machine and have checked out every electrical test given in the manual (except neutral switch) (see "fouled plug = foul mouth" on YZ400/426 board). Although it seems to be running pretty good right now the plugs still has a black and sooty appearance despite lean jetting. I am starting to wonder if the needle jet inside diameter could be too large. This would make a bike run rich due to the larger cross sectional area. Does anyone have any idea as to what the I.D. should be? Thanks!

------------------
2000 Yamaha WR400F
1988 Honda NT650 Hawk
1977 Suzuki RM250B
1974 Honda XR75K1

  • James_Dean

Posted March 12, 2001 - 08:44 PM

#2

2.90mm standard :)

  • Taffy

Posted March 12, 2001 - 11:20 PM

#3

try to put an airjet through every orifice in the carb.

go to the PA(J)S & go up to 1 1/2 turns out, this emulsifies the fuel better.

Taffy

  • James_Dean

Posted March 13, 2001 - 11:27 AM

#4

Mike,
Would you post your jetting so we can get an idea how lean it is?

  • Moto-Mike

Posted March 13, 2001 - 02:25 PM

#5

I am running a 175 main, DVP with clip in slot 1 (top position), 45 pilot and 1.5 turns out on the pilot air screw. I am also running "YZ" timing with air lid off, throttle stop trimmed and E-series with no discs. This combination produced a black sooty plug within minutes prior to the CDI and TPS ajustment.
I do need to mention that since my CDI replacement and TPS adjustment the bike is starting very good. My initial impressions were that the plug was still black and slightly carboned up...this after a short 15 minute ride. I am wondering if a cleaning out period is necessary to get a good plug reading (warmer temps and longer ride). I did measure the I.D. of my needle jet at 2.8 mm so that evidently is not the problem. At this point I probably need more time to determine the results of the CDI replacement and TPS adjustment.
Do you think the above listed settings are on the lean side? Thanks!

  • Moto-Mike

Posted March 13, 2001 - 02:25 PM

#6

I am running a 175 main, DVP with clip in slot 1 (top position), 45 pilot and 1.5 turns out on the pilot air screw. I am also running "YZ" timing with air lid off, throttle stop trimmed and E-series with no discs. This combination produced a black sooty plug within minutes prior to the CDI and TPS ajustment.
I do need to mention that since my CDI replacement and TPS adjustment the bike is starting very good. My initial impressions were that the plug was still black and slightly carboned up...this after a short 15 minute ride. I am wondering if a cleaning out period is necessary to get a good plug reading (warmer temps and longer ride). I did measure the I.D. of my needle jet at 2.8 mm so that evidently is not the problem. At this point I probably need more time to determine the results of the CDI replacement and TPS adjustment.
Do you think the above listed settings are on the lean side? Thanks!

  • James_Dean

Posted March 13, 2001 - 03:43 PM

#7

Mike,

Something looks very wrong with this. Normally clip #4-5 would be clean running. :)

Have you compared the needle with your stock DRS to see if the taper starts lower on the DVP (~3 - 4mm) and measured the diameter of the straight section, 2.735mm?

The height of the needle jet is important too. Wonder if the threaded needle jet is turned in completely.

Have you tried going to the stock #42 pilot jet? Is it possible the pilot is a #48-#50 instead?

You have described 1.5 turns on the pilot "air" screw, do you mean pilot screw? (edited) The screw on the bottom of the float bowl is the pilot screw. (edited) Turning it out will make the idle richer.

The pilot air jet is #75 stock, Taffy has suggested an aftermarket pilot air screw from Sudco to replace it. This adds some adjustability. As he said, the first thing is to make sure all the air passages are clear.

Have you attempted to adjust the accel pump screw under the black cover on the carb? Turning the screw in reduces pump flow and delays the start of the pump. Backing it out could cause too much fuel to enter. If you turn it all the way in and bottom the tension spring you will feel the free "delay" by pushing on the linkage with your fingers. There needs to be a little delay, about 1/2 to 1 turns.


James


(edited for clarity on what is the "pilot screw")

[This message has been edited by James Dean (edited 03-14-2001).]

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  • Mathew

Posted March 13, 2001 - 09:19 PM

#8

Moto-Mike - Have you tried a "7" heat range plug? I have been using that for the last year or so on my '98 and just checked my plug - nice and clean. Lots of trouble with black and fouling before. Also - my experience with my 98 is that proper warming before any major throttle application is required to prevent fouling (read do not blip the throttle until fully warmed, no matter how tempting it is just let it idle). It seems like once you "soak" the plug by blipping the throttle it is very hard to ever get it to clean off again, leaving the bike with wierd symptoms until you replace the plug. Maybe the 2000's are different with the accel pump but mine is very sensitive when cold.

Mathew

  • Taffy

Posted March 14, 2001 - 01:52 AM

#9

WE HAVE GOT TO GET THESE NAMES RIGHT!!!!!

if we don't nobody is going to understand a thing we say. the pilot screw isn't the pilot fuel screw because it controls a mixture of air & fuel.

it's the pilot screw & it hangs underneath the carb.

moto-mike does "slot 1" mean the last clip on the needle right near the end?

are you thrashing the bike enough?

seriously!

don't just start it up. ride the knackers off it!

turn the pilot screw in to either zero or 1/2 turn out & then go up on your needle clip to third from the very top. eventually you should go to clip 4 like JD says.

Taffy

  • Moto-Mike

Posted March 14, 2001 - 09:23 AM

#10

Probably before I spend to much time on the carb I need to ride some to determine if the CDI and TPS adjustments cured my fouling problem. It's a snowy muddy mess here right now so that might not be for another couple of weeks.
I feel if it is in the jetting it probably would not be in the pilot circuit. I've seen my headpipe glow with the jetting listed above after sitting and idling in my garage at night! The main jet does not seem that out of line (same as what the YZ400's came with if my memory serves me). And the midrange (needle and clip) does indeed seem lean compared to others. I started in the 3rd slot and it would foul very quickly and finally arrived at the #1 (top groove) position. Oh and yes James Dean I did check the needle per your recommendations on an earlier post and it did check OK. It is 2 clips leaner then the "DRS". A hotter plug as mentioned above sounds like a good idea to see if it will clean the plug up.
Anyway this is probably not worth pursuing until I determine if my bike still fouls the plug after the above mentioned ignition changes. Thanks for the advice so far... :)

  • James_Dean

Posted March 14, 2001 - 11:43 AM

#11

This has to be the position of where the needle sits in relationship to the needle jet. If the nozzle is not threaded in fully or if the needle is not held down in the slide you would have the resulting condition you describe.

Did you remove the needle jet to measure it? Could it be unseated?

Is the needle being held down by the brass washer & spring?

An EVQ needle should work very well in your bike using nearly the middle clip(#4 or #5). It won't work for others because it's too lean.

James

[This message has been edited by James Dean (edited 03-14-2001).]

  • Tree_Crippler

Posted March 14, 2001 - 05:57 PM

#12

Could this be from using an exhaust with no discs or end cap that is designed to work on back pressure?

  • James_Dean

Posted March 14, 2001 - 10:28 PM

#13

Tree Crippler,

No, not in this case, the exhaust is not making this much of a change.

  • Moto-Mike

Posted March 15, 2001 - 09:16 AM

#14

The idea of the needle "floating" would definitely cause a rich condition. In the next day or so I will pull the carb out of the boot and see if there is any play between the needle and slide. I also called up the exploded view of the carb and noticed that there are 3 parts called out - adjusting screw, spring and a collar. When I take my needle out there is only 1 piece which consists of a threaded cap with a spring...is the "collar" integrated into this piece or am I missing a piece?
As far as taking the needle jet out it was coming out when I removed the mainjet, still threaded to the main jet. I did not have to remove the bowl I went thru the drain hole so getting a good look at the seating area was nearly impossible. It seemed to thread in fine though.

  • James_Dean

Posted March 15, 2001 - 11:38 AM

#15

If you are missing the collar or if it is below the needle clip this would explain your problem. The collar goes on the spring and is a snug fit. It will normally stay with the (locking) "adjusting screw" and spring when they are removed.

collar (#17) P/N 5JG-14264-00




 
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