I ran straight C12 in my 686, a little more compression that you. I had trouble getting the floats and needle valves to work with the thin race gas. As part of an ongoing R&D effort, I drilled out the needle valve seat to allow the stock carb to flow more fuel and trimmed the float stop to allow it to open further. Both of those mods helped but it was not consistant, now folks are using the stock Grizzly needle valve/seat and switching to a dual feed setup. 190/195 Mikuni needles on the 3rd clip with 27.5 pilots ~1.5 turns out gave the best performance in mine. 195/200 at sea level if you don't have heat coatings in the combustion chamber. Keep an eye on your plug porcelain, you'll probably need to run one or two colder than stock. If you don't feel like messing with your carbs, send them to Craycraft Racing for upgrade. There are other builders that can upgrade the stock carbs to work with a bigger motor, I've been completely satisfied with Craycraft. If you give up on the stockers (and you will), I wouldn't go less than 39mm FCRs to replace them. I had 35mm FCRs and didn't think they had the top end of modified stock carbs. The bottom end was much better and they worked great with race gas but they wouldn't scream:-)

 

Wow, this is getting like NASA stuff. I need simplicity. I'd think thier is enuff 686's out there where they'd have this down to a science but, i guess i'm wrong! This is getting to be a joke. I didn't realize i'd need to hire on a pit crew. LOL

 

Capt,

One thing keeps grabbing my attention when reading your symptoms...

If I understand you correctly - You have had it at a point where it ran pretty
good, but seemed rich, and was blurping and sputtering like it was over rich..right ?

That right there screeeams float level too high. The reason I say this is because I
had a few experiences with it.

Right after my 686 build, I was running VPRed straight. Before the build, my floats ran
a tad higher than recommended using Regular 87 pump gas. After the build, using the VP Red,
I checked the floats, and the different specific gravity of the VP made the float level on the low
side. ( Just different fuel, level went from 1/8 inch above the mating line, to 1/8 below the line. A
1/4 swing in float level). All my uphill blurping and hesitations from before went away with the
lower float level.

Now recently, I made another fuel switch ( cheaper), and am running Citgo 110 - which is almost identical
motor rating as the VP Red, but with "this" fuel, my floats are now way high again, and if I went up a
trail at even 20 degrees slope, or wheelie it, or climb a hill - it loaded up and sputtered like no tomorrow, and
barely would make it up hills...

Basically Im suggesting to do Sixsixt's method of checking your floats. With the carbs on, it only takes like 2 minutes
to check. You may have already , but I didnt see anywhere that you posted what your float level was. Im betting
its too high, and this makes it overload with too much fuel (rich) and run like crap.

Let us know. Dont get frustrated..... I dont think your problems are because your far off on jetting... your motor should still run
ok mostly, even with jetting thats miles off. The problems your having are not jetting based Im guessing... its float
based, or some other carb problem. Mine runs great with 170/175 DJ mains and DJ needles. I can guarantee that you
can put in mains bigger or smaller by several sizes each way, and barely notice a difference, if at all. Sure you have to get
it fine tuned in the end, to keep your engine safe, but for testing purposes, if your a little lean or rich, it isnt gonna cause the
problems your describing.

Give us a measurement of your float level - and we will go from there. Im positive we can get you fixed up and running good.
If your any higher on the float level, than a couple mm above the split line of the carbs, then your toooo high.

 

Uh eddie.......how do u figure we are 45 ft below?....i always thought we were more like 20..

 

So, different fuel makes the floats run at different levels? How/Why? Density of the liquid?

This is nuts! So if i buy 110 from one place it will make my floats off from 108 or, even 103 at another?

I ran Cam2 110. I never thought to try a different fuel? Weird..

By looking at what your running i'm starting to think even at the richest setting i tried it may still be lean.

I was under the impression that the thicker (more humid) air would make me need to lean it from Arizona's climate. But, now the more i think of it I may have to richen up - do to the air is more dense and, will not flow as clean. Or, maybe i have 110 Octane on the Brain?

 

To answer you about different fuels running at different levels in the bowls.... Absolutely ! And
yes you had it right.... each fuel has a different specific gravity - so you can be too high with one
fuel, fill up with a different fuel, and be totally different on float level. All you gotta do is know
what fuel your gonna be running, and measure the floats with that fuel. Cant hurt nothing to
double check it. Let us know what you find... good luck.

 

Well,, I got pissed and, sent the hole bike not just the motor this time back to the builder. So it is in Route now. All I know is i hope it gets sorted out or, it gets stolen on the way so i get get something else. LOL

I saw for Trinity's 686 build they recommend 180-185 mains, needle on the 5th clip and, 2 and, 2 3/4 out on the air screws (all Mikuni Parts).

I'm really thinking i was lean "all around" for my area the way it came. And, 110 octane was probably too much for 11:1 compression. Can running to high of octane create a lean condition?


Oh, and, Raptor AZ - to answer your question (i must have missed it) = no i didn't try running it w/ the Race Core instead of the quiet core for 2 reasons 1) I have to use the quiet core to get in the places i ride so i wanted it tuned for the Quiet Core 2) with all the testing i was doing and, i live in the burbs, the noise level needed to be down or, the testing would have stopped real soon do to Tickets!

The thing is now I'm prolly gonna run the Race Core at every chance, when i was at the dunes this past weekend no one had a Quiet Core and, they were getting on the Dunes so why should i be crippled. I will bring the QC w/ just in case but from now on it is Race Core for me w/ Spark Arrestor Screen!

 

In reading your posts and all the replys, I really thing the biggest problem was your 110 octane fuel. The higher the octane the later the detonation. If you had a 12:1 you would need it.

I have a Trinity 686 with the 11:1 J.E. piston and Web Cam., Pingry aluminum air box wide open K & N filter with outerware. Trinity also did the Pro Port job with the larger center intake valve.

When you have head work done, in many cases, your compression actually goes down. I am probably somewhere in the high 10's on compression. My bike HATES race fuel!! It runs like total crap.

I live in Ohio at 850' elevation and I know what humidity is and have also changed jets enough to do it in my sleep. I think I did a few times [img]i/expressions/face-icon-small-blush.gif[/img][img]i/expressions/face-icon-small-shocked.gif[/img]!!

I wish you still had your bike, I think this would have helped.

1) Run 92-93 Octane Premium
2) Main Jet (182.5 left) 2-1/2 turns out on the fuel screws
3) Main Jet (187.5 Right) 3 turns out on the fuel screws
4) Mikuni Jets & Needles
5) Both Clips in the 4th. position.

.........I know you would be real close!!

SixSixT knows his stuff, and others out here too. I know what you going through.

It would be so bad if you didn't have to dissasemble half the bike to get to the jets!

GregV

 

Darn Greg, where were you a few days ago?! How did you come up with those settings? Are you pretty sure it is "spot on"?

Thanks for all your help guys! I get the feeling i'll need it again when it gets back.. I just need to make sure everything is right!

 

Well, your running a pretty close set up to what I have, our elevation is close...........and a lot of trial and error!!

In my oppinion, the race gas has probably been your biggest problem. When beeffing up you motor it kinda natural to think that you need race gas! That's not always the case. The higher the octane, the later the detonation.

I have kept a notebook on the mods and set-up changes. It's had a lot of entries. ha ha At one point I was running the same airbox setup as you too. She is running strong now!! I am even running Mikuni Needles with the clip on the right carb in the 4th notch and the left in the 3rd. notch.

There are a lot of combinations, the settings that I gave you above may not be perfect.....but you will be close.