tuning stock carbs/best after market carb

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evan_calgary
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Re: tuning stock carbs/best after market carb

#16 Post by evan_calgary » Sat Mar 04, 2017 4:27 pm

check what MK says first as it is super simple but you are describing poor compression almost perfectly. Colder weather impacting and cold bike that starts fine when warm is compression. You should be able to feel it in the kicker lever. Run a compression check if you like to confirm without a tear down. No point messing with carbs when the issue is your motor...the stock carbs are perfectly fine units.

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Questo vecchio rz
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Re: tuning stock carbs/best after market carb

#17 Post by Questo vecchio rz » Sat Mar 04, 2017 4:49 pm

MK wrote:Im my world poor cold starting is usually a result from jerks throwing all the parts in one box and then swap left/right float bowl on reassembly.
By this mod you successfully disabled the cold start enrichment as the choke jet is only in the right float bowl.
You have stock Mikuni 26mm carbs..as I mentioned and MK as well, this is a common issue W floatbowl location.

I'm sticking on point here as you requested carb info, however its a good practice for a comp & leakdown test. Kits can be found on E-Bay for $50.00 or less. http://m.ebay.com/itm/172516978619?_mwBanner=1" onclick="window.open(this.href);return false;
Y

"Generally" poor running issues often more times than not, are carb related. Clean them, set them..dont forget your bowls location and your floats MUST be set correctly.

Before you start reinventing the wheel by re engineering your entire carburation system or manufacturer, rebuild them, do a easy comp and leakdown test...if it runs good theres no point in altering anything else.

Again assuming your bike is a US spec that is stock w airbox. Aftermarket exhuast Pipes generally wont affect your jetting on a stock bike, you can run stock jetting w no issues.

If you dont have a airbox and your running indavidual filters buy a "Toomey perfect jet kit or Dyno Jet kit", either works very well. Set it & forget it for a streetbike
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TN-592
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Re: tuning stock carbs/best after market carb

#18 Post by TN-592 » Sat Mar 04, 2017 9:32 pm

Thank you guys for nice replys :smt002
Now I have notice,when it don t want to start I just take one spark plug out and wipe it with towel put it back again and it starts with no problem,but I have to keep it in high rpm when the rpm drops it wants to shut down then when it gets hot it works with no problem.After I tune my flow level again to 21mm,open air screw to 4 turns and now it runs little better,but it looks like it is still getting to much fuel from some where,or oil,I make my own premix 2 percentage and use CHAINSAW two stroke oil maybe that s a problem!?Tomorrow I will try with different oil and make a video.

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wolfman
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Re: tuning stock carbs/best after market carb

#19 Post by wolfman » Sun Mar 05, 2017 12:23 am

Now that sounds like you have the float bowls reversed.
As for oil use what you have on hand but get some good synthetic motul or the like.
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RuZty
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Re: tuning stock carbs/best after market carb

#20 Post by RuZty » Sun Mar 05, 2017 6:49 am

Have you rejetted for premix or still on stock jetting? I assume you are not running the oil pump as well.

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Re: tuning stock carbs/best after market carb

#21 Post by MK » Sun Mar 05, 2017 7:33 am

Sorry to shatter your diagnosis, but the symptoms are too lean, not too rich.
I remember a RG500 guy I met at the race track in Poznan. He suffered similar issues with fouled plugs all the time, especially when opening the throttle at low rpm.
I rode the bike and advised to use bigger idle jets. Afterwards no fouled plugs and no bogging when opening the throttle fast.
The explanation is easy: The mixture is too lean due to insufficient fuel flow from the idle circuit thus the plug doesn't get to temperature. If you open the throttle, you supply much more fuel through other circuits like the main jet and needle jet. This is virtually flooding your plug and that's it ...

My advice for you:
Air screw 4 turns is plain lean. Re-adjust to 1.25.
Get your carbs off and check the float bowls. There's a bore in the bowl. At the end of this, there needs to be a small brass jet in the right side carb. If it's missing use the other carb's float bowl (as it'll likely be there).
If it still does not pick up throttle in low rpms when cold, try a number more on the idle jet, or screw in the air screw to some 0.5 - 1.0 turns.
Bye
Martin

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Re: tuning stock carbs/best after market carb

#22 Post by RuZty » Sun Mar 05, 2017 11:41 pm

MK wrote:Sorry to shatter your diagnosis, but the symptoms are too lean, not too rich.
Right, and adding oil to the fuel without jetting up will make it leaner, which may or may not be a problem depending on where the initial jetting was.

TN-592
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Re: tuning stock carbs/best after market carb

#23 Post by TN-592 » Sun Mar 19, 2017 9:03 am

I have meassured the compresion and the riding is 8.1bar in both cylinders,is this enought?

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Re: tuning stock carbs/best after market carb

#24 Post by TN-592 » Mon Mar 20, 2017 7:45 pm

I am not sure but I think I have solve the problem,I was running to rich so the plugs where getting black,the same problem I had with my ktm bike.Now bike is starting from the third kick,the odd this is that bike was not showing any symptons or to rich mixture the power was great,no 4 stroking or anything like that.Now the bike is not so aggressive like before but at least I can start it.

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Re: tuning stock carbs/best after market carb

#25 Post by hondaror » Thu May 18, 2017 12:46 am

Sounds like you were so rich you were going leaner.
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