Stuttering while accelerating?

[BowlingSS]

I finally got back to the bike this week. Because of the fowling plugs on #1 and #2 and not #3 and #4 I decided to re-sync the carbs. When I hooked up my Motion Pro balancer it went nuts. Vacuum was extremely high on the left side. When I tried to balance it over the idle started to climb drastically. By the time I got the idle down it was too late. About half the fluid in the balancer had been sucked out. After doing some research on the web it turns out I probably had an air leak in the o-rings of the balancer. I took it apart and cleaned and re-seated the tubes and O-rings. I washed all the remaining fluid out. I had read in some forum somewhere that the fluid is glycol based and you could use auto antifreeze as a substitute instead of paying the rather pricey cost of the pretty blue replacement fluid from Motion Pro. I figured nothing to loose by trying it. So I refilled the balancer too the correct levels and it works great. Just like new. If anything the fluid seems a bit more stable. Less bounce in the readings. I re-balanced the carbs. Adjusted the idle mixture by ear and she is running good. Idle nice and smooth. But I still have the stutter @ 4500 rpm. Dam. Researching other possible causes. Maybe carb float level. Maybe main jet needle setting. I have never done a valve adjustment since I owned it. That's the next priority.

Thanks.My Motion Pro did the same thing. Where did you get the mercury to re-fill?
Thanks.
Bill

[Graman]

Hi Bill. As stated I drained all the pretty blue fluid out of the balancer. Pulled all the tubes out and cleaned all the o-rings and seats. Put just a small amount of light grease on the o-rings with your finger to help them seal. I followed the instructions on the Motion Pro website for re-filling to the proper level and just used regular auto antifreeze and it works like a charm. You can buy the secret blue fluid from Motion Pro or I believe you can get it on Amazon but it's expensive and why bother. Be aware I have read that you need more than just one bottle to refill it if the loss was significant. Liquid mercury would be the best but I don't believe you can legally buy it any more. Motion pro used to use it in there vac gauges years ago but had to stop for safety reasons and come up with their new secret formula. With a gallon of antifreeze you could probably refill it a million times. Even consider draining it if you don't plan on using it for a long while. When you turn your balance adjust screws do it a little bit at a time so if your idle starts to climb you can knock it back down before proceeding. If it climbs rapidly just yank the hoses off before it sucks the fluid to high.

Download the PDF @
http://www.motionpro.com/motorcycle/partno/08-0581/

[Graman]

runs great now, only tested about 20 miles,but I am happy with the way it runs. Needles are now at the groove one below the top,thus lowering the needles 2 positions from previous position, floats 25mm, pilot screws out 2 turns,have nice idle at 1050rpm,stutter is gone! pulls nicely to about 6,000rpm then pulls even harder to red line. good luck with yours G man.

bkham1972 is my hero. Thanks very much for this post. I finally after quite a while got around to pulling my carbs yesterday. After reading your post I decided to duplicate your settings and give it a try. I moved the needle valve clip up 2 positions and set the floats to 25mm. Wow! What a difference. It accelerates very quickly up past 6000 rpm and keeps going. I still did notice a small dead spot at about 6500 rpm in 4th & 5th gear but not that bad, I can live with it. For now. I rarely need to rev it that high with the type of riding I do anyway. I still have to balance the carbs again. I forgot to tighten one of my carb boot ring clamps on the engine side and didn't notice until I had everything back together. Had to effect the balancing of the carbs the first time. Probably go even better when that's done.
Thanks again bkham1972. I have been fighting this issue probably a year before I started this thread. You may have brought it to a close. Thanks to all for your contributions.

[motoman]

Havent read any of the previous rheteric, but your pilot jets side holes are still restricted my friend. Remove them and use a wooden toothpic and clean them. Keep all metal pins and reamers AWAY from them.....period. IF stock airbox, use stock jetting and spend a bit more time tuning.......idle mixture using lean drop method....re-sync all four......back thru and re-set idle mixtures same method and THEN sync the four together again(fan in front of motor to reduce heating)...........NOW go ride the durn thing.

[bkham1972]

stutter gone

graman, thanks for the compliment,really happy it runs better, when I installed the jet kits I did put in new pilot jets, one size up from stock,and you have read the results, mine does have a little ''bog'' in it from about 2500 to 3000 rpm, after it gets through that I don't think I could ask for a sweeter running bike,sometime when I have the carbs off I am going to raise the needles half a groove using shims, til then I have just been enjoying it.Also like you, I rarely rev past 6000. best wishes

[motoman]

Don't feel bad; the first time I really got on the throttle, I stuttered for about a week.

LOL.....I'm STILL stuttering.

[TopCatGr58]

Havent read any of the previous rheteric, but your pilot jets side holes are still restricted my friend. Remove them and use a wooden toothpic and clean them. Keep all metal pins and reamers AWAY from them.....period. IF stock airbox, use stock jetting and spend a bit more time tuning.......idle mixture using lean drop method....re-sync all four......back thru and re-set idle mixtures same method and THEN sync the four together again(fan in front of motor to reduce heating)...........NOW go ride the durn thing.

Hey Brant,

Actually, we have now learned that the side holes in the Yamaha Pilot Jets are a MOOT thing! The Chamber the pilot jets are IN is sealed....the end of the pilot jet is sealed against the carb body where it meets it in the tapered end, and the other end with the threads seals that end...and there are NO air passages to the Pilot jet tower around where the side holes are. The info we found came from when I metal bandsawed the carb bodies in half that Mack gifted me for this purpose.

Also, on MikesXS.net they have a message about the pilot jets, and that the newer ones do NOT have any side holes and that they are interchangeable with the older ones. This has also been confirmed by members who have ordered jets from Yamaha and have recieved NO SIDE HOLED pilots, installed them and they worked just fine!

The problem we have previously with the generic pilot jets we "ASSUMED" was due to the difference in the # of sideholes that the generics had vs. the Genuine Mikunis.....but this finding was a red herring....and it was the actual sizing that the Generic company used for the main metering hole that was different from the Genuine Mikuni's...and that they were larger which is what contributed to the excessive richness of them...not because they had less side holes!

Here's the photo of the pilot jet/main jet towers cut in half with the jets in place....and you can see there isn't any ports around where the side holes are in the carb body in the pilot jet tower.



T.C.

[motoman]

Hey Brant,

Actually, we have now learned that the side holes in the Yamaha Pilot Jets are a MOOT thing! The Chamber the pilot jets are IN is sealed....the end of the pilot jet is sealed against the carb body where it meets it in the tapered end, and the other end with the threads seals that end...and there are NO air passages to the Pilot jet tower around where the side holes are. The info we found came from when I metal bandsawed the carb bodies in half that Mack gifted me for this purpose.

Also, on MikesXS.net they have a message about the pilot jets, and that the newer ones do NOT have any side holes and that they are interchangeable with the older ones. This has also been confirmed by members who have ordered jets from Yamaha and have recieved NO SIDE HOLED pilots, installed them and they worked just fine!

The problem we have previously with the generic pilot jets we "ASSUMED" was due to the difference in the # of sideholes that the generics had vs. the Genuine Mikunis.....but this finding was a red herring....and it was the actual sizing that the Generic company used for the main metering hole that was different from the Genuine Mikuni's...and that they were larger which is what contributed to the excessive richness of them...not because they had less side holes!

Here's the photo of the pilot jet/main jet towers cut in half with the jets in place....and you can see there isn't any ports around where the side holes are in the carb body in the pilot jet tower.



T.C.

I believe Mikes XS bought as much as I would use 'any of their stuff. Some smart guy there tryin' to make brownie points to sell the generic stuff they wanna sell.........hey, way cheaper with a greater orofit margin got some ole' boy there 'brownie points'. 'Sorry, aint buyin' it. Those atomizing holes and number amount are for different engine applications for added smoothness.

[TopCatGr58]

Hey Brant,

Well, here's the larger wider view of that same 78-79 carb body so you can see the other half....and there are NO air ports around the portion of the pilot jet tower at the same position of the pilot jet bleed holes. In the half on the left...at the top end of the pilot jet tower I have placed a piece of blue wire insulation that I used to mark the AIR paths....but it's AFTER the metering hole/tapered end of the pilot jet. The Pilot jet is completely SEALED within the Pilot Jet TOWER....the threads seal that end, and the tapered end is pressed/sealed up against the other end of the tower and carb body. ONLY after that point is where the Pilot Air Jet tunnel meets with the Pilot Jet fuel stream further up in the carb body.



Here's the 78-79 carbs sliced across the body at the Pilot Jet.


The right half of the carb body shows the diagonal tunnel that the pilot jet fuel takes up from the pilot jet tower....then meets with the port from the Pilot AIR JET where the diagonal tunnel ends, and then it goes straight up to the pilot jet tunnel where it ends up under the Pilot Jet Screw!

The diagonal tunnel on the left side of the right half stops at the carb body surface where it's capped off after machining.

SO....hopefully you can now see that the AIR gets into the Pilot Jet circuit up into the carb body, and NOT AT the pilot Jet or via those side holes! I don't doubt that perhaps other earlier model and styles of carbs utilized air supply venting that DID enter the carb AT the pilot jet and the side holes were then a necessary part of the metering and atomizing process of the A/F mixture...but not in OUR carbs.

Yes, the actual jet Metering orifice is still critical in properly feeding the right amount of fuel for the pilot circuit and so it's size is critical thus the need for Genuine Mikuni jets...but the jet side holes in OUR carbs are MOOT.

T.C.

PS, here's the 80-81 bodies also sliced thru the Pilot Jet tower.

[motoman]

Somehow knew there'd be a comeback from ya T.C.

[motoman]

It sounds like we have almost identical problems. What did you adjust your float height too? I am curious about the jet sizes you used. I have never heard of using different size jets for the carbs. Not that it isn't a good idea but what made you use different jets in 1 and 4 than in 2 and 3?

Main jet sizes and float levels ARE two different scenarios, but creaate the same scenario............hows that T.C.?. Oh, and you'd have had to have gotten up yesterday to follow my knowledge and cerifications.

[TopCatGr58]

Hey Brant,

In NO way was I trying to compare or compete with your knowledge and experience and expertise. Just thought that I/We were talking about the PILOT jets and their side holes....not the Main Jets or the Main Jet Nozzles/emulsion tubes....where YES those side holes are totally necessary and definitively problematic when they are clogged. And wasn't putting the side holes info to throw in your face, just more to help inform the others that read these threads about the NEW information that we discovered when we cut the carb bodies apart and were better able to explore and examine the pilot circuit.

T.C.

[motoman]

graman, just being lazy, not wanting to r&i the carbs any more than needed.after I put the mac 4into2 set on mine crapped out about 3600rpm.got a jet kit from sigma, put in 140.5 on1&4 cyl 142.5 on 2&3, put 45 pilots in &raised the needles 1 notch, now it craps out about 4300, it will stutter to about 6000 then smooth out, but it does not pull as hard as it used too. not sure if rich or lean, plugs look ok to me. I will post the results of my next try, but I am sure it is in the carbs. tks, bkh

Too rich with nothing more than pipe change.........and staying with 4into 2.

[motoman]

Hey Brant,

In NO way was I trying to compare or compete with your knowledge and experience and expertise. Just thought that I/We were talking about the PILOT jets and their side holes....not the Main Jets or the Main Jet Nozzles/emulsion tubes....where YES those side holes are totally necessary and definitively problematic when they are clogged. And wasn't putting the side holes info to throw in your face, just more to help inform the others that read these threads about the NEW information that we discovered when we cut the carb bodies apart and were better able to explore and examine the pilot circuit.

T.C.

May wanna relook and follow the discoveries.