Mikuni Tuning, Detonation
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Joined: May 2009
Posts: 70
Likes: 0
From: The South
Turning the air screw in on a Mikuni reduces air into the idle system, making it richer. Most of the pinging is coming in 4th gear, hard acceleration generally from 40-65mph. I can do it in 5th as well if I have enough room to get my speed up.
I think there's several things out of whack on this carb. The float bowl overflow tube has been occasionally dripping fuel. Would this indicate my float bowl is sticking up or is too high? It seems to measure the correct height according to the manual.
I also have learned that I'm probably tuning the idle system incorrectly. I'm setting the idle around 1k RPMs with the screw two turns out and then trying to get the bike to stumble. I believe I should be dropping the idle as low as possible with the screw two turns out and finding the stumble from there. I'll have to wait until the bike thaws out to try anything.
I think there's several things out of whack on this carb. The float bowl overflow tube has been occasionally dripping fuel. Would this indicate my float bowl is sticking up or is too high? It seems to measure the correct height according to the manual.
I also have learned that I'm probably tuning the idle system incorrectly. I'm setting the idle around 1k RPMs with the screw two turns out and then trying to get the bike to stumble. I believe I should be dropping the idle as low as possible with the screw two turns out and finding the stumble from there. I'll have to wait until the bike thaws out to try anything.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,081
Likes: 2,159
From: Ohio
You guys are correct on the mixture screw, been awhile since I touched mine. From tuning with a wego system I had low, cruise and wot set, reset my idle afr to 14.2 from 14 6 and rode it. The low speed afr also got richer, didn't see any changes In mid. I'll babble what I noticed with a wego when I get home
Last edited by 1997bagger; Jan 23, 2014 at 06:01 PM.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,081
Likes: 2,159
From: Ohio
If I remember Joe mentions the more aggressive needle with higher compression and detonation prone engine, check that accellerator nozzle jet and the rod adjustment. I have the 50 with the full rod travel and no issues with a Mikuni 45 and the aggressive needle.
Another thing to double check is the timing module set up right by the TDC method per instructions, if it is off a little could be out of range of adjustments and still be advanced or check the timing with a timing light to know for sure the timing is correct. You are in the roll on throttle problem area under load but shouldn't detonate when you get out of that area with those jets, the only other way to know for sure is a AFR gauge which takes the guesswork out of it.
Another thing to double check is the timing module set up right by the TDC method per instructions, if it is off a little could be out of range of adjustments and still be advanced or check the timing with a timing light to know for sure the timing is correct. You are in the roll on throttle problem area under load but shouldn't detonate when you get out of that area with those jets, the only other way to know for sure is a AFR gauge which takes the guesswork out of it.
3rd Gear
Joined: Oct 2012
Posts: 7
Likes: 0
From: Norway
On my 2000 Deuce I have the Mikuni HSR45. Maybe a larger Mikuni is the answer?
I bought the bike like this, sO i really dont know anything about carb sizes..
I also have 4 spark plugs and a Crane Cam TC88 along with it.
I bought the bike like this, sO i really dont know anything about carb sizes..
I also have 4 spark plugs and a Crane Cam TC88 along with it.
Tourer
Joined: Sep 2014
Posts: 420
Likes: 5
From: Kingsport, TN
If anything, the Mikuni 45 is TOO BIG for your motor unless it is 117ci or larger and/or has very aggressive cams and Stage 4+ headwork. For a stock through Stage 3 88/95/98ci motor, the Mikuni 42 is a better match.
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,116
Likes: 7,639
From: Poolville
do this.....
it definitely sounds like You're a little rich on you're slow circuit. If you were lean you would be pinging every where not just at higher rpm's. set your ignition curve to 3 and test drive. If that cures it then you are going to need to download dynatek software, get the patch cable and build your curve for your bike. Sounds more like to much timing too soon........to do that set switch 2 to off and switch 3 to on.. or a bad voes
Last edited by 98hotrodfatboy; Mar 6, 2015 at 11:45 AM.
Road Warrior
Joined: Dec 2007
Posts: 1,666
Likes: 3
From: Styxville
A leaking float valve or high float setting will make the bike run rich at idle as the excess fuel slops down the carb throat. Which then causes you to set the idle mixture wrong without knowing it.
But I would put my money on the VOES being the cause of your detonation.
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