[Dave1]

Well chaps here was the old set up of my carb.
Main jet 120
Slide cut away 2.5
Pilot Jet 30
Needle Jet P0
Needle clip in the second lowest grove.

I have just changed the old main jet out for a 125. And tried to set the throttle. Got it ideling, was about to go out for a test ride and it stalled. When you open the throttle a certain amount the bikes stalls? So I thought to do a plug chop. And it is showing way to rich. The plug is black with soot.

So then I thought I'd try a 117.5 main jet. Again got the bike ideling. But again at a certain throttle opening it stalls? The plug is still showing soot. I will clean the plug tomorrow as its dark here, and go over the carb with a fine tooth comb. To see if I put anything back wrong. But I am fairly certain I didn't. I would appreciate any feedback.

Edit referencing you recomendations. My carb seems to have a right funny set up. I have a very rich pilot jet. A richer needle jet, according to online sources the slide cut away is on the lean side? For a 500. Should the 500 have the 3.0 slide cut away?

[Dave1]

Well I have continued to try and tune my carb this morning. I can now get it to idle. But the plug is still showing very rich. I have even put the colourtune on to check. And the colourtune confirms what the plug is saying that the idle(pilot jet) Is to rich.

Now I have not changed a thing to do with the pilot system. Other than try to adjust it for new idle? Any ideals chaps? Other than trying a smaller pilot jet?

I mean how can something be fine one moment? Then after you change the main jet and try set new idle speed, then the pilot system becomes to rich? Even though you have changed nothing in the pilot sytem? Apart from adjust the mixure screw as Toms and Mikuni instructions?

[Dave1]

Sorted the stalling issue. Needle jet wasn't seated properly.

A question please, all you carb experts out there. I can screw in my pilot air adjustment screw quite away in below 1 1/2 turns. Which to my brain says that should be leaning the mixture? Is that correct?

Because when I do a plug chop at idle, it is still showing rich? Which if the above is correct. Then I would think I'd need to go down to a 27.5 pilot.

[ace.cafe]

30 pilot is possibly too rich. Sea level conditions often fall between the 27.5 pilot ande 30 pilot, and it often comes down to your air filter or exhaust system to determine which one you need, so just try the 27.5 and see how it is.

[Dave1]

Thanks Tom, I am going to do a plug chop now in the other 3 jet ranges to see how they are performing.

Since I've started I might as well get this carb jetted in good and proper now.

[ace.cafe]

The air bleed screw lets air in.
So, screwing it in closes it down more, and lets less air in, so that makes the pilot circuit richer.

Find the highest idle speed with the air bleed screw (after engine is warm), and then set the final idle speed with the larger idle speed screw.

[High On Octane]

Dave1 - Something to keep in mind as well is that colder air temperatures will require richer settings in the carb than warmer air temps.  Basically, if the average afternoon temp is currently in the 40's and 50's it would likely require you to REjet and REtune the carb again when the air temps reach the 70's and 80's.  Not a big issue as you're trying to get the bike running correctly, but it is something to keep in mind as this could be directly related to your bike not running correctly now.  So, IF when it warms up again your bike starts running goofy, refer back to this page and return your jets to the original settings and go from there.

Scottie J

[Dave1]

The Saga continues. All the other posts today were with the 117.5 main jet. So I took it out for a test ride with the 117.5. It didn't pull right in the needle part of carb operation, and when I continued onto the main jet over 3/4 throttle. It pulled ok and not great and when you rolled the throttle off, I got a little power surge. So the 117.5 main is to small.

So back I come and think. I'll just swap out the 117.5 for the 125. Just out of curosity I picked up the 125 and 120 put it next to each other to compare the holes. To my surprise the hole in the 120 was bigger than the 125! To my shock, one of the previous owners must have reamed it out.

So in with the 125. I thought simple job, nope wrong again! When you revved the engine the bike stalled again! I knew this time that it was not the needle jet not sitting correctly. So I raised the needle to the middle positon. Back together, hey presto it now doesn't stall. The air screw is 1 1/2 turns out. So I take it for a test ride and it stutters a bit under 1/4 throttle. I came back after the test ride turned up the large air screw. Sorted the cutting out. And it doesn't stutter any more, and is pulling well through the complete throttle range. I am still not happy with the idle, so I will have another go with that tomorrow.

One weird thing is the plug is still showing black soot, rich? Could a pilot jet really influence the plug chop that much? Even after a complete throttle range test/test ride? 

[High On Octane]

I would raise the needle one more position and see how it responds.  To me it sounds like you are lean in the idle circuit {needle jet, possibly the needle itself(the cause of the hesitation and misfires)} and still rich in the main circuit {main jet(lack of power and black carbon on the plug)}.  I would recommend getting a CORRECT 120 main that hasn't been drilled out and try that and maybe a P1 or P2 for the needle jet.  You're getting close, if these jet changes don't get it to where you want, then you will need to look into getting a slide with a bigger cut-away.

Scottie J

[ROVERMAN]

Dave 1, regardless of the outcome to your issues let me say that you may not ever get it perfect. With my 03' i finally settled for a strong running bike off idle because no matter what i tried jet wise i could never get a consistent idle. I became the master of on the fly idle adjustments and finally came to an agreement with the bike to leave it alone and enjoy.
 The next step for you, assuming the only issue is the carb, would be a nice shiny new flatslide. Wish you luck, all the best.
Roverman & the GREen B.

[Dave1]

Thanks Rover man, thing is this bike before today used to idle like a charm, people had commented on that, and it used to pull well up until the 60 mph area. The original problem which this thread was originally about was hunting up in the rev range around the 60 mph mark. That according to my last test ride earlier is now sorted. All I'm trying to do now, is get the bike running leaner not a sooted plug. And to idle like it once did. Thanks with the help of Scotty J and Ace. I'm sure I will get there.

Yes I have been looking at the Mikuni TM32 Flatside. If my VM28 messes up anytime soon after being sorted this time. It will be getting replaced with a flat side carb!

On my last RE before this one. I put on a Monobloc because I got annoyed with always stripped and resetting the damn Mikarb. The Monobloc did give a performance increase but didn't idle as well!

Scotty J I have just ordered Main Jet 120, needle Jet P2, Needle Jet standard, Pilot jet 27.5. With this lot I should get this sorted! I already own the Needle jet P0 if thats what you ment by P1? Or do you mean the standard needle jet?

[High On Octane]

No, I meant a P2.  Brain fart.   

Scottie J

[Dave1]

Hi guys, had to go out today. So only had a small chance to work on my bike. But it was productive.

I fitted the 27.5 pilot jet which seems to be running better. Idling better and the plug no long soot's up black, and that's at 1.5 turns out. It still sometimes isn't 100%. So I may just to sooth my mind. Chuck the 30 pilot back in the carb and turn the mixture screw 3 turns out.

I wasn't quite happy with the 1/4 to 3/4 rev range. I still feel this could be better. So I raised the needle to 2nd position from the bottom. Tomorrow I'm going to put it in the bottom groove to see how it runs. If it still doesn't run how I want it to, I will fit the P2 needle jet, and lower the needle to the top position the leanest.

I feel at the moment that the 125 main jet seems to be doing very well. When ever I take it to 3/4 throttle plus it pull well, and when you roll off the throttle there is no power surge. So I don't think going smaller is a good plan. I may in the future try a 127.5 just to see.

So do you guys think I'm logically thinking along the right lines now with all this adjustment?

[ace.cafe]

I think at this point you need to do some plug chops and 1/4 and 1/2 and 3/4 and show us the pictures.

[Dave1]

Ah thats an issue, because my kill button doesn't work. My bike has the Eureka electronic ignition fitted. If I could make the kill button work, that would be helpful.