carb needle shim, backfire, sluggish

[warp1]

After going to the dyno this morning and finding out I was a little lean in the mid-range...realized I needed to shim the needles. Followed the how-to on here...got the radio shack washer pack, mic'ed at .019. Added 2 washers between the nylon and the retainer clip, making sure to push the nylon piece back up tight to the clip and re-installed. (total of .038)

Now have hesitation and backfire between 3000-5500, and seems to run normal when v-boost kicks in. I tore them all apart and no missing orings, loose needles, or anything obvious to me.

My bike is a 98, k&N air filter, marks 4 into 2, and 1 sized down on the stock main jet. A/F is 2.5 turns out each carb.

Possible I shimmed too far or sound more like a diaphram leak? Ran perfectly before I shimmed it...just noticed the pipes were starting to blue so was worried about lean condition...that's why the dyno.

As always, any help appreciated.

 

[KosRider]

After going to the dyno this morning and finding out I was a little lean in the mid-range...realized I needed to shim the needles. Followed the how-to on here...got the radio shack washer pack, mic'ed at .019. Added 2 washers between the nylon and the retainer clip, making sure to push the nylon piece back up tight to the clip and re-installed. (total of .038).

Hey Warp1, I think your problem might be that the nylon piece isn't in the correct spot in the slide. The tiny locating pin on the bottom of the nylon piece MUST be in the correct hole / spot in the slide or the needles will be too high and off center. I normally add the nylon piece to the slide, rotate it so it drops into the correct spot, then carefully slide the needle & shims thru it.

Also, you might want to try just one shim first. More than one shim you need to correct the screw cap that holds everything in the slide, so it doesn't bind the needle.

 

[maleko89]

Those washer are too thick and it made it worse by using two of them. It doesn't take much and wouldn't go any more than .024".

 

[dannymax]

I slide the plastic spacer back on the needle, drop it in the hole, install spring and screw the large plastic screw down only enough to put pressure on the needle....then spin the needle and it will pop back in when the hole & pin line up.

 

[KosRider]

Hey Dann-o, I'll have to try your method. Probably simpler than what I'm doing ! :worthy:

 

[06VMAXIMUS]

I still think that nasty little tit could be snipped off. I see no reason for it, and it makes a person second guess himself when assembling.

 

[midmoraider]

Crap. I've been tightening the hell out of the retaining nut on top of the needles. So, how snug should it actually be?

 

[maleko89]

Doesn't take very much at all. I'd say barely snug.

 

[midmoraider]

What will be the effects of it being too tight? Not trying to hijack this thread.

 

[maleko89]

The big effect would be to shear the head off the top of the screw. I've had that happen when trying to loosen it on customer carbs. Over tightening it won't affect the running the of the bike at all.

 

[warp1]

Thanks guys...I double checked the retaining part of the nylon immediately after the problem and all the needles are tight. I'll try removing a washer tomorrow and let you know how it goes...

I just saw a bunch of posts on here with Marks 4 into 2...and they seemed to be using 2 for .038, so I used that as a starting point.

 

[naughtyG]

post your dyno sheet.. how did your A/F ratio look?

 

[dannymax]

Hey Dann-o, I'll have to try your method. Probably simpler than what I'm doing ! :worthy:

It works well using a pair of hemostats to hold the top of the needle when dropping it in....I'm sure most everybody has a pair of them hanging around....
probly a lot even have black tips.....:ummm: :rofl_200::rofl_200::rofl_200:

I still think that nasty little tit could be snipped off. I see no reason for it, and it makes a person second guess himself when assembling.

Yamaha must have had a reason for that but I can't for the life of me figure out what it is, and yeah Bob, I've done that "did I drop that little tit in the hole?" thing a time or two also!

 

[warp1]

No dyno sheet...he said A/F was getting up to 17 and didn't want to go any further. He recommended lifting the needles. Have it rescheduled for this coming Tuesday.

 

[naughtyG]

wow 17? That's way out I think, supposed to be around 13, right?

 

[06VMAXIMUS]

If the needles are tight, then they will bind the slide and not allow it to operate correctly. You can check them by using your finger and seeing if they lightly push open, then slide home freely with no assistance.

 

[Maxine]

B,
Everything went together perfectly, and I just dont see the addition of the shims as causing the popping at a steady rpm. I think its a out of spec float, coincidental...yes, but thats how it presents itself to me. Ive seen these bikes develop this issue suddenly(right out of the blue with no issues previously) Usually after a hard acceleration.
R

 

[Redbone]

It works well using a pair of hemostats to hold the top of the needle when dropping it in....I'm sure most everybody has a pair of them hanging around....
probly a lot even have black tips.....:ummm: :rofl_200::rofl_200::rofl_200:
I think the black tips are "stickier" so it holds better!:biglaugh::eusa_dance::rofl_200:


Yamaha must have had a reason for that but I can't for the life of me figure out what it is, and yeah Bob, I've done that "did I drop that little tit in the hole?" thing a time or two also!

The infamous 'ol tit - n - hole dilemma, all I say is be careful, you could shear a head off while screwing!:rofl_200::rofl_200:

 

[dannymax]

The infamous 'ol tit - n - hole dilemma, all I say is be careful, you could shear a head off while screwing!:rofl_200::rofl_200:

Oh JEEZ!! I hate when that happens!! :rofl_200::rofl_200:

 

[warp1]

Thanks for all the help. Took 1 of the 2 shims and put her back together. I did feel one slide sticking/rougher compared to the other 3 so cleaned will a dallop of WD40. Runs like a raped ape now. Wish I knew if it was the excess shim or if the slide was sticky.

Side note...getting the tit/detent seated is the easiest part of the whole thing to me. Only one place for it to go and always try spinning the needle once the nylon screw it tight.

I'll find out at the dyno Tuesday if 1 shim at .019 was enough...carb work is getting old . Just saw that many on here had .038 shim in their signature line, especially with Mark's 4:2 exhaust...so thought 2 would be perfect....oh well.