38mm Mikuni jetting on XR600

[Mick DMember]

I am thinking that the 230 main is to big. As I said earlier,I used a 220 and you could see a definate change in colour of the exhaust smoke and it smelt fuely.Is yours a 600 or 628cc?

I think Ballard’s settings are 10 pilot and a 200 main. I would go back to those settings and work from there.
Probably wouldn’t hurt to give Ballards a call and have a yarn to one of the crew there. I had troubles with mine running lean under load at about 1/2 -3/4 throttle. It would ping its head off,that is why I went to the bigger main (220) but ended up running the 210 from memory.

Here is some light reading that TB posted sometime back about jetting.

http://www.obtrailriders.com/index.php?option=com_kunena&Itemid=56&func=view&catid=8&id=1336

This will give you and idea what jet does what during the throttle range.

[GregMember]

The jets you fitted yesterday I thought sound about 5 sizes to big and I feel that’s why its bogging down. Go back to a 200 and work up in one size up increments (not jump 4 sizes in one go)

I told Mick last night the main was to big and why blame the main, use the chart here and some marks on your throttle to be sure because I would be pointing the finger at the needle height first but go back to the 200 mian you can always go up later

After thinking about it last night the pinging that Mick kept having dramas with would have been ignition based not fuel would have been a CDI advance problem (should have thought of that before)

1. IDLE: Set idle speed to correct r.p.m. by adjusting the IDLE SPEED SCREW. Turn The AIR SCREW to achieve the highest idle speed and best response. After this adjustment has been made adjust the IDLE SPEED again back to the correct r.p.m.

2. OFF IDLE to 1/4 THROTTLE: The SLOW JET and the AIR SCREW are most effective in this range. When you want a richer mixture use a larger SLOW JET or turn the AIR SCREW in. The opposite holds true for a leaner Mixture.

3. 1/4 to 3/4 THROTTLE: The JET NEEDLE is the most effective component in this range. Raising the needle by lowering the clip position at the top of the needle will richen the mixture. Lowering the needle will lean the mixture.

4. WIDE OPEN THROTTLE (W.O.T.): Changing the MAIN JET effects this range. Select the size which offers the best W.O.T. performance, then install one size larger MAIN JET for ideal engine durability.

NOTE: Not all Carbs have AIR SCREWS. Some have FUEL SCREWS, it is important to differentiate as to which one you have. This depends on the location of the screw on the carb. (looking at the center of the carb) If the screw is in between the cylinder and the carb body , it’s a FUEL SCREW, turn it OUT to get more fuel (richer) if the screw is in between the carb body and the air box, it’s an AIR SCREW, turn IN to richen it. As far as I know this rule of thumb is correct. Check with your dealer or manual if at all unsure. Note: most air/fuel screws should be set somewhere between 0.5 to 3.0 turns from seated, if it is outside this range you should look towards your slow jet.

As far as the jets go big is not always better

TB

[dougMember]

Thanks for your help Mick and TB the only jets i have are 190,230,250 so thats all i can play with for now and the pilot jet is 12.5 so i will go back to the 190 and change the clip position it is on 3 from the top now wish me luck

[Mick DMember]

Ballards have the jets,they are about $15 inc postage from memory.
Clip position certainly maybe something to fool with.

I would stick with the 12.5 pilot though

[Mick DMember]

I have another Mikuni flat slide in the shed,I will have a look to see what jets are in it this arvo if I think of it.

[dougMember]

well i put the 190 back in and started with the clip at the top and tried all clip positions still not working so i tried all of the jets and no change :angry:

a bit more on what is happening the bike will start 1or 2 kick always and idol good will run well even at WOT but if you ride it and start giving it a good bit of 1/2 to full throttle for no more than 30-40 seconds it will die like it just ran out of fuel and then stall but will start first kick so i dont think that it is the jetting :unsure:

what do you guys think it could be

[alanMember]

is it getting enough fuel check to see if enough fuel is coming through the fuel tap check the needle and seet also is the carby cleen maybe give it a blow out

[GregMember]

white rocket wrote:

Quote:

is it getting enough fuel check to see if enough fuel is coming through the fuel tap check the needle and seet also is the carby cleen maybe give it a blow out

That’s a real good point actually

TB

[dougMember]

fuel is flowing out the tap
gave it a good blow out before i put it on

could not get to needle and seet out the pin was to tight to get out was going to brake the support dont know how to get it out??????
going to try again tomorrow

[DeanMember]

madougxr wrote:

Quote:

fuel is flowing out the tap
gave it a good blow out before i put it on

could not get to needle and seet out the pin was to tight to get out was going to brake the support dont know how to get it out??????
going to try again tomorrow

is the pin a taper? not sure if it is or not :unsure: But I think rocket might be onto something there. With the carby removed you should be able to blow air thru the fuel line in the upright position. Continue apply pressure while slowly tilting the carby over, at about the 45 degree mark the seat should close and airflow will cease. keep persisting mate

Ollie

[dougMember]

I think that the pin dose have a taper on it still was very hard did not wont to brake anything

will try blowing air thru the fuel line aswell

[Mick DMember]

I just remembered I was gunna have a look at the Mikuni I have here in the shed. I went down to the shed and pulled the bowl off and had a look.
The main is 195 and the pilot is 12.5.It came off a bike that was a 630 with a full staintune system.

What pin are you trying to get out?

[DeanMember]

micknmeld wrote:

Quote:

What pin are you trying to get out?

The one that the floats pivot off

Ollie

[Mick DMember]

Ollie wrote:

Quote:

micknmeld wrote:

Quote:

What pin are you trying to get out?

The one that the floats pivot off

Ollie

OK,by the looks of things it isn’t tapered and should just slide out unless there is a bit of electolosis built up around it.I will have another look at the carby this arvo as it is still on my bench.

[Mick DMember]

Something else that sticks in my mind re the Mikuni is when I was endevouring to tune mine, I got Geoff Ballard on the phone and he basically said that the Mikuni is a race carby and you cant really have the best of both worlds,in order to have it running at its optimum at WOT the chances are you will have idle and low RPM issues.Whether that is 100% true is open for debate.

[Author]

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