carb/mixture question

[neuroboy]

After throwing in the towel and having a shop install my new EMGOs and jets (the previous owner put on TORs), I took a trip to VT with a couple buddies. I'm noticing a couple annoying things about the fuel delivery

1. as opposed to intermittent pop that happened on deceleration/engine braking about 3000 rpms, the bike now sounds like a popcorn popper (or the quiet 4th of july) when I am engine braking.

2. i've noticed that if I quickly open the throttle all the way (90% or more) all at once the engine sputters and pops and I lose speed until until I roll back the throttle to about 60% where it kicks in and starts running strong again.

. . . I'm thinking both of these arise from a too-rich fuel mixture that the shop didn't address when they re-jetted the carbs. What y'all think?

I'm also wondering if I can just location the mixture screwed and back them off a quarter turn or if it's more involved than that.

 

[B06Tang]

To start off with, what are your mains and pilots that are in the bike right now? Do you still have the airbox or was it removed? Your mixture screws are not going to cure this problem alone if you have this much sputtering and you are going to have to re-jet your carbs

 

[neuroboy]

I just dropped a line to Bellacorse to get the jet sizes (they came with the EMGO kit I bought from them). Basically all that was done was an install of the EMGOs and a carb rejet using the ones that came with the kit. I'm thinking the shop probably did an incomplete job rejetting.

I'm guessing sputtering is happening because the engine is getting flooded when I floor it. This is not something that was happening before the rejet and is 100% reproducible.

 

[B06Tang]

You need to pull the mains and jets to see what sizes you have. The size numbers are stamped on the head of the screw. Any suggestion on my part right now would be a pure guess/shot in the dark. Do you still have the stock airbox in this bike? That will make a big difference as well

 

[bluesforchallah]

Matt brings up very good points. We need to know where you're at now i.e. jet size and if any other intake mods that may have been done before we can make any suggestions as to where you need to go.

 

[neuroboy]

yep. i didn't look at the size before they went in because they came in the kit with the pipes, so I figured they had that sussed out. I have an email into them and I'll report back when I get the answer.

The airbox is still on there.

 

[thearcticsea]

From what I remember the kits that come with any pipes out there are usually incomplete. I know when we ran my bike on the dyno and really spent a good day on it we ended up trimming springs and shimming needles before it got the actual best balance of power and delivery.

 

[beemerrich]

Not sure how WFO you are going when the bike bogs, but typically going full open on the throttle and then picking up when you back down the throttle a bit is indicative of lean main jets. In your case, it seems you need to roll back the throttle significantly for the bike to respond...so give us the main size to work with on this when you can. Honestly, its been years since I had the CVKs on the bike and can't recall if the diaphragm actuated slides act the same way as slide carbs...

The excessive popping on deceleration is certainly indication of lean jetting...this is generally addressed by richening the mixture screw.

Good luck,

--Rich

 

[neuroboy]

Heard back. . . I'm not quite sure why but it turns out they send me a couple of 140 mains. This means that if the shop didn't check them and just installed what I gave them then I possibly have two 140's in there. . . that would certainly explain the bogging at full throttle.

Either way, it's clear there wasn't due diligence on their part to be sure that the rejet was a good fit, so I'm going to get on the horn and make sure that they finish the job I paid for last week.

Bellacorse recommended 42 pilot, 140 main, and 2 1/2 turns out on the mixture screws.

edit: i don't need it to be perfect (shims to fine tune, etc) even though that's clearly ideal, but this popping and bogging thing is for the birds.

 

[thearcticsea]

Yeah you'll get it dialed in. No big deal man. Good luck.

 

[drlapo]

140 sounds too big
if you have just open mufflers
bigger pilots may be needed but I'm running EPCO mufflers with 125 mains, 40 pilots and 2 1/2 turns, 1 shim, opened slide vent hole, air box w/o snorkle and a UNI filter

 

[B06Tang]

That is way too rich for a bike with an airbox still intact. I am running 138s with 40 pilots right now with predators, gutted airbox and Dynojet needles with 1.5 turnouts. Also important to note is that I am fairly close to sea level where I am at right now. My suggestion is order the full range between 120s-130 and you will get it with leaving your pilots at 40. Keep in mind the name here is "TUNING" so there is no one magic number that proves everyone else wrong. I suggest that you drain your bowls, get a 8mm wrench with a screw driver and go to work. Order a set of 10 mains...I think they are only like $6 for the pair

 

[beemerrich]

With the airbox still on, main jets bigger than 130 are likely too big. With 42 pilots, you shouldn't have a shim under the needles...though I guess it would matter whether you are running the early 790 needles or thruxton needles.

Regards,

--Rich

PS - I have the jets pictured below that you can have if any are of value to you...they are all CV jets and I no longer have the stock carbs. PM me if any of them work for you.

 

[2Monkeys]

Those jets from Bella corse sound great for use with pod filters

 

[neuroboy]

beemerrich- Thruxton needles. . .


also, for the record, the mains that were pulled out were 110s (for TORs).

but yeah, so it looks like 130ish and 40ish for the mains and pilots (and between 1.5 to 2.5 turns out) is the way to go. Should I go on the smaller side for better ride vs. peak performance or the other way around?

is there anyone in the Boston area that has a mixture screw tool I could borrow for an afternoon?

 

[beemerrich]

It's better to work your way from rich to lean...its an aircooled bike and running too rich is fine until you dial it in.

Regards,

--Rich

 

[drlapo]

you can make a mixeture tool out of a .22 or.223 cartridge case
just flatten one side until it fits on the screw

go to Jenks.com for some advice