Main jet changes

View previous topic View next topic Go down

Main jet changes

Post  Zoro on Mon Sep 02, 2013 6:03 am

Looking at the main/ pilot and needle postion charts it says I should be running a 168 main, I have the 175 in at present.

My question is would I be able to adjust the needle clip to a leaner position to negate having to change to the smaller main jet?

Zoro
XRR Jockey

Joined : 2011-07-08

Posts : 122
Location : Darwin, Australia
XR650R Year : 2004

Back to top Go down

Re: Main jet changes

Post  BuRP on Mon Sep 02, 2013 2:35 pm

You may want to try smaller wheels instead too?
Fwiw, a smaller headlight also won't work.....
A main jet is a main jet, nothing (like in zero!) will compensate for this.

Oh wait, the airfilter does, you could try and remove it, see if it runs better then.... not, don't do this, just get the bleeding jet BRP smile 
avatar
BuRP
XRR Monger

Joined : 2010-10-18

Posts : 1544
Location : Pretoria Souf Efrika
XR650R Year : 2007

Back to top Go down

Re: Main jet changes

Post  SkidMark on Tue Sep 03, 2013 12:24 am

Chart is a guide, albeit a very good one, what does a plug chop tell you?

SkidMark
avatar
SkidMark
XRR Freak

Joined : 2012-05-16

Posts : 320
Location : Liberia
XR650R Year : 2005

Back to top Go down

Re: Main jet changes

Post  Zoro on Tue Sep 03, 2013 3:47 am

I have not checked the plug and I guess its most likely what should have been done already, I just dont want to have to remove the tank (Safari) on the side of the road/ trail to get the plug out.

Originally the bike came with a 160 main, 65 pilot and already had the B53E needle however was on the 2nd clip position.

I was having a really hard time chasing an idle tune with it, hanging idle, stalling when idling and just generally all over the place.
Idle mixture screw would not change idle performance, my thinking was that the engine was being fed via the main jet.

The bike ran fine at speed just eratic/ non predictable idling performance, so pulled the carb and cleaned it out.
Changed jets to the base line 175/ 68S and kept the B53E but changed it to the 3rd clip (middle) position.
I now also have idle mixture tunability using the mixture screw.banana 
Float height was also checked

The bike still runs fine, maybe a tad more power (seat of the pants dyno).
The only downside to the jetting changes are that I'm getting increased decel and mid range "popping" from the pipe.

I then find the jetting chart on here and it recommends a 168 for my temperature, hence my question of whether or not I could mask the larger main jet using a needle clip position change (leaner).

Thinking my next course of action would be to go and buy two new plugs and a 168 main jet, change out the old one and go for a run and check it.
Install the 168 main, install 2nd new plug, go for a run and check mixture on plug again.

Use the best one of the two mains after plug checks.

Before finding the jetting chart on here I was originally just going to try a leaner clip change on the needle with the 175 to try and see what change that had with the increased popping.

FYI, I'm at sea level, temps here range between 30-40 degreesC and humidity is usually around 75% on average.

Zoro
XRR Jockey

Joined : 2011-07-08

Posts : 122
Location : Darwin, Australia
XR650R Year : 2004

Back to top Go down

Re: Main jet changes

Post  BuRP on Tue Sep 03, 2013 10:45 am

Firstly, a thumper will always burble and/or pop on the overrun, no 2 ways about it, and this is more noticeable when it's a big 'un. Smear some silicone on the various exhaust joints if this bothers you but better is to live with such.
Then, a "hanging" idle/low is more often than not caused by too-tight cables, so adjust some play here.
Also, if you dunno how to read a plug or do a plugchop then don't, and zero offense intended. A way better way is to do acceleration runs & measure time, the best time means the best main jet.
But, a bumseat dyno works well, and jets are cheap enough. Indeed this chart is a darn good one, don't stray too far off it - and 175 & 168 are quite far apart. Know that a too-rich main will more easily 'feel' right than a too-lean one and off you go, go play with jets.
The needle-clip affects only the 'mid', never the top. So, WO is the main only, and this is of course also the throttle position when doing the acceleration runs. (Edited: Analogue, the clip also will not affect the idling)
Lastly, again zero offense, you know how to measure the floatlevel - whilst rotating the carb? If you don't do this the level willbe wrong. Oh, add 1mm floatlevel (ie a 1mm lower fuel level) so as to prevent/minimize overflowing/leaking when lent over on the sidestand.
Pls tell us what you find?
avatar
BuRP
XRR Monger

Joined : 2010-10-18

Posts : 1544
Location : Pretoria Souf Efrika
XR650R Year : 2007

Back to top Go down

Re: Main jet changes

Post  Zoro on Tue Sep 03, 2013 11:51 pm

Good points Burp, I have done the float level by rotating the carb till the float just begins to push on the spring.

The plastic casting marks on the floats were parrallel with the carb base at this point. I think I may need to lower this level slightly.
I watched a video on youtube done by a local guy called Teknik (suspension guy in Aus), bit of an XRR fanatic.

Once I put the carb back in the bike I adjusted the cables and the throttle returns quite nicely.

I will purchase a 168 main and put that in with the adjusted float height and see how it goes.

The bike used to burble and pop previously I just notice now that it seems to do it more often after I changed to the 68S/175 combo.
The hanging idle is no where near as bad as what it used to be, I'm pretty happy with the way that is now.

One thing I have noticed is that if I attempt to lube the chain with the bike idling (leant over on the stand) I do get fuel coming out the overflow tube.

Anyone know the P/N for the 168 main?

Zoro
XRR Jockey

Joined : 2011-07-08

Posts : 122
Location : Darwin, Australia
XR650R Year : 2004

Back to top Go down

Re: Main jet changes

Post  BuRP on Wed Sep 04, 2013 10:11 pm

Of course, I did assume the cables are in good nick and properly lubed - they are?
Teknik knows suspensions, read about them & from them.
There's another thing with this bike idling-wise, and that is a leaking rubber manifold. Got a gas burner? Let it idle (vertical, on a stand) and blow gas (not a flame, duh) around the carb/manifold area. Rev's increase? New rubber!
Your dealer & you will know the part number. Find the std jet's part number and see how big it is - the jet's size being part of the number. Mod the number (ie jet size) you need and key that into the systen et voila, you'll have found the jet you need.
avatar
BuRP
XRR Monger

Joined : 2010-10-18

Posts : 1544
Location : Pretoria Souf Efrika
XR650R Year : 2007

Back to top Go down

Re: Main jet changes

Post  Zoro on Thu Sep 05, 2013 12:26 am

I'll check for the leaking intake manifold rubber with some WD-40 I have here.
I did find the clamp against the engine was a bit loose when re-installing the carb, tightened it but have not physically checked it whilst running.

175 main P/N is 99101-357-1750 #175, I'll just change all 175's to 168's then.

Will take a week for the jet to come in, standard wait time up here for anything.

I'll tweak the float height also, just drop it a touch when I get the jet.

I will report back once completed.


Zoro
XRR Jockey

Joined : 2011-07-08

Posts : 122
Location : Darwin, Australia
XR650R Year : 2004

Back to top Go down

Re: Main jet changes

Post  BuRP on Thu Sep 05, 2013 2:47 pm

WD-40 is a liquid hence not good enough. A liquid will temporarily seal a capillary, gas won't.
I'd have ordered a 170 too, no fortune and allows you instant comparison.
avatar
BuRP
XRR Monger

Joined : 2010-10-18

Posts : 1544
Location : Pretoria Souf Efrika
XR650R Year : 2007

Back to top Go down

Re: Main jet changes

Post  Zoro on Sat Sep 07, 2013 2:01 am

BuRP wrote:WD-40 is a liquid hence not good enough. A liquid will temporarily seal a capillary, gas won't.
I'd have ordered a 170 too, no fortune and allows you instant comparison.
Roger that BuRP, I'll chase up some gas. Hopefully I don't catch fire...Very Happy 

Zoro
XRR Jockey

Joined : 2011-07-08

Posts : 122
Location : Darwin, Australia
XR650R Year : 2004

Back to top Go down

Re: Main jet changes

Post  AURORA on Sun Sep 08, 2013 2:03 am

Zoro wrote:Looking at the main/ pilot and needle postion charts it says I should be running a 168 main, I have the 175 in at present.

My question is would I be able to adjust the needle clip to a leaner position to negate having to change to the smaller main jet?
No. You will only change the delivery schedule of when you will be running on the main.

Remember the chart is only a guide. You bike might need richer or leaner jets and or setting.


Last edited by AURORA on Sun Sep 08, 2013 2:21 am; edited 1 time in total
avatar
AURORA
XRR Freak

Joined : 2008-12-09

Posts : 689
Location : PHOENIX
XR650R Year : 2003

Back to top Go down

Re: Main jet changes

Post  AURORA on Sun Sep 08, 2013 2:11 am

Zoro wrote:

One thing I have noticed is that if I attempt to lube the chain with the bike idling (leant over on the stand) I do get fuel coming out the overflow tube.

Anyone know the P/N for the 168 main?
Your float valve is bad. They only last a few years. You will not be able to perform a proper jetting/tune with a bad float valve.

Float height while the carb is on the bike.

Try the old trick of hooking a clear tube to the bowl drain, opening the drain, and holding the tube end above the float bowl(with the bike level, BTW). You'll be able to see exactly where the fuel level is.

The float adjustment shouldn't be off unless someone made it that way. Usually overflows are caused by a stuck or worn float valve.
avatar
AURORA
XRR Freak

Joined : 2008-12-09

Posts : 689
Location : PHOENIX
XR650R Year : 2003

Back to top Go down

Re: Main jet changes

Post  Zoro on Tue Sep 10, 2013 2:04 am

AURORA wrote:
Zoro wrote:

One thing I have noticed is that if I attempt to lube the chain with the bike idling (leant over on the stand) I do get fuel coming out the overflow tube.

Anyone know the P/N for the 168 main?
Your float valve is bad. They only last a few years. You will not be able to perform a proper jetting/tune with a bad float valve.

Float height while the carb is on the bike.

Try the old trick of hooking a clear tube to the bowl drain, opening the drain, and holding the tube end above the float bowl(with the bike level, BTW). You'll be able to see exactly where the fuel level is.

The float adjustment shouldn't be off unless someone made it that way. Usually overflows are caused by a stuck or worn float valve.
Aurora, the carb only leaks when I tip the bike onto the side stand to get the rear of the ground, it does not drain constantly when leant over on the stand in the normal position.

I will also invest in a carb kit when I order the 168 main.

Does anyone know if the clear plastic washer (on the throttle linkage) comes with a carby kit?

Zoro
XRR Jockey

Joined : 2011-07-08

Posts : 122
Location : Darwin, Australia
XR650R Year : 2004

Back to top Go down

Re: Main jet changes

Post  Sponsored content


Sponsored content


Back to top Go down

View previous topic View next topic Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum