SEM recon and jetting

B

Badvoc

Joined Apr 2004

118 Posts | 0+

West Sussex, England

Discussion Starter
• Mar 20, 2011

• #1

Hi
Last February I had the jetting set up at HMRacing because it just seemed to be off all of a sudden, after years of running smooth. Well, all was fine, then, a few months ago the SEM stator packed in so I sent it to sparks to mend.
Now the jetting seems wrong again,
On the first run with the recon sem it would idle fast, so I adjusted the idle (just turned the idle screw down) its ok for pottering around but open her up and she picks up speed then chokes.
Now, I’m useless at this jetting lark, is this a sign of rich or lean.
If the sem was on the way out last Feb could this cause the jetting to seem off all of a sudden?
B

 

S

sparks

Joined Sep 2006

989 Posts | 23+

Hayle Cornwall

• Mar 21, 2011

• #2

Hi Badvoc,

Yes this could be quiet possible, I've seen this many times over the years but mainly on 2 strokes. What happens is when the output voltage from the stator starts to drop off you get a smaller spark duration this causes some of the fuel to be unburnt leading to what seems like a rich condition, leaning off the jetting will cure this for a short period of time till it happens again, also you will feel a drop off in power. Once the stator has been restored to it's full output you will find the jetting has to be redone because of the engine is now running to lean.
Can you post up your current jetting spec, Taffy might be the one to comment on that if it is a Dellorto.

Regards

Sparks.

 

B

Badvoc

Joined Apr 2004

118 Posts | 0+

West Sussex, England

Discussion Starter
• Mar 21, 2011

• #3

Hi sparks, yes the bike defiantly has more power.
I played with the jetting and went from a 155 main to a 170 and it’s a lot better, could go to a 168 I think.
The needle clip is in position 6 so that’s as rich as it’ll go (this was the first thing they changed at HM), I think I’ll try changing it to position 3.
The pilot jets a 42 and the fuel screw is 1.5 turns out. Air Screw is 1/4 out.
She starts and idles fine.
oh its an FCR sidedraft carb not a FCR-MX.

 

S

sparks

Joined Sep 2006

989 Posts | 23+

Hayle Cornwall

• Mar 22, 2011

• #4

Hi Bladvoc,

It would seem you are running the PAS on the rich side for a 42 PJ, try backing it out to between 1/2 and 3/4 of a turn.
Can you tell us what the needle code is?.
You will also find that atmospheric and temperature conditions will also have a big bearing on your jetting settings.

Regards

Sparks.

 

Taffy

Joined Nov 2001

17K Posts | 774+

Ely, England

• Mar 22, 2011

• #5

the 1/4 turn on the PAS and the 42PJ don't correlate at all Badvoc?

also, your Tickover shot up when you fitted the new SEM proving that the bike is 'happier' now whether that is just sparks Stator or you also helped with a 'lucky' move of the ignition timing I'm not sure?

there are 7 clip positions and unless we know your needle code we can't help but getting the PAS right would be a good start.

regards

Taffy

 

F

frank46

Joined Mar 2011

5 Posts | 0+

• Mar 27, 2011

• #6

happy runnin ! i like when a bike does that..gets faster the more efficient it becomes..you know yur doin good.
those old gs suzuki cam chain adjusters spring to mind..ya think ha ! thats better! an turn down the tickover.....

 

B

Badvoc

Joined Apr 2004

118 Posts | 0+

West Sussex, England

Discussion Starter
• Mar 31, 2011

• #7

Having checked the Air Screw it was 1/2 turn out.
The revs where high because the throttle snagged one of the wires from the stator and not letting it return to the idle stop Doh!
The setup at the moment is:
Needle Clip 6, Main Jet 168, Pilot Screw 1.5 out, Pilot Jet 42, Pilot Air Screw 3/4 out, Air Jet 200 Needle OCEM-R
She starts lovely, I tried to set the main jet first, the only way I know how to do this is put it second a open her up, now she starts to pull really well then sort of Bwooooooor, at about half way up the revs, Iv tried changing the main jet and gone from a 155 to a 175 and the same thing happens every time?
Could it be timming?
So I don’t know where to go from here.
Its now Thursday night and Im supposed to be racing on Saturday

 

B

Badvoc

Joined Apr 2004

118 Posts | 0+

West Sussex, England

Discussion Starter
• Mar 31, 2011

• #8

will one of those gunson colourtune things you can get in halfords be any help?

 

B

Badvoc

Joined Apr 2004

118 Posts | 0+

West Sussex, England

Discussion Starter
• Apr 1, 2011

• #9

bump

 

Taffy

Joined Nov 2001

17K Posts | 774+

Ely, England

• Apr 1, 2011

• #10

to me you should be on clip 1?

but I don't run anything like your jetting so....

regards

Taffy

 

B

Badvoc

Joined Apr 2004

118 Posts | 0+

West Sussex, England

Discussion Starter
• Apr 1, 2011

• #11

the pilot screw seems to have NO effect on the tick over at all, close it all the way in and she still ticks over, open it out to 2.5 turns and its like Iv not done anything, so what does the pilot screw regulate air or fuel?

 

Taffy

Joined Nov 2001

17K Posts | 774+

Ely, England

• Apr 1, 2011

• #12

the two after they have mixed. basically, if that is happening it means that your bike is getting its fuel elsewhere. you run an R straight and a 42PJ so the R straight is letting it all through.

this is a good example of why you shouldn't run a DVR let alone yours Badvoc. with your needle so high the R may as well be a P or a Q.

regards

Taffy

 

B

Badvoc

Joined Apr 2004

118 Posts | 0+

West Sussex, England

Discussion Starter
• Apr 1, 2011

• #13

well been messing with it most of today and now I need to leave for Lydd, it seems to like hard accelleration upto 3/4 throttle so I'll be doing some short shifting and just pin it everywhere haha.

Taffy, I might be after one of your jet kits to try and sort it for the next round.