New Mikuni issues on fresh motor MKIII

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mikegray660 said:
Coco said:
Choke is definitely off since I never use it anyway. I just blew out every passage with compressed air and nothing came out except a good stream of compressed air so no clogs. I can see daylight through all jets, needle jet is clear ect.

I'll put everything back together and go for a spin. If symptoms still persist, I'll retime again since I'm not sure what else to do.
Click to expand...

Coco
if you can start your bike cold and not use the choke on a mik something is a wrong... you should have to at least open it for initial start and then shut it off - i suspect you have a problem with the setting/jetting here - have you read victory library mikuni tuning guide? big help to get maximum benefit from these carbs

this is my 34mm set up as recommend

recommended by panic/victory libary

pilot 25
slide 3
needle 6DH3
main 260

runs good....
Click to expand...

I figured height had something to do with the jetting. I'm at over 1800 feet above sea level where I'm at. The pilot that was in my carb initially was a 40 and is now a 35. Slide is a 2.5 and main jet is a 230. Needle is 6DH3 with clip in middle position.
 
Coco said:
I figured height had something to do with the jetting. I'm at over 1800 feet above sea level where I'm at. The pilot that was in my carb initially was a 40 and is now a 35. Slide is a 2.5 and main jet is a 230. Needle is 6DH3 with clip in middle position.
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Your jetting is close, very close. I seriously doubt jetting is your problem here.

Perhaps something is clogged, because it still sounds like it's choked. I haven't read the entire thread, but is the float height set okay?
 
Holmeslice said:
Coco said:
I figured height had something to do with the jetting. I'm at over 1800 feet above sea level where I'm at. The pilot that was in my carb initially was a 40 and is now a 35. Slide is a 2.5 and main jet is a 230. Needle is 6DH3 with clip in middle position.
Click to expand...

Your jetting is close, very close. I seriously doubt jetting is your problem here.

Perhaps something is clogged, because it still sounds like it's choked. I haven't read the entire thread, but is the float height set okay?
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How do you check if float height is ok? I have it set how it came to me.

I did blow every pasage out with compressed air yesterday and nothing came out (that I could see anyway) except a real good blast of air so as far as I can tell things are clear.

I was told to also try to remove the pin and remove the needle seat ect but things looked really damn clean in there so I didn't remove that.

Before all of this, I never even changed an air jet before. Now I feel I can take apart a Mikuni blind folded. :D

Thanks for the advice so far guys. I'm going to put the carb on soon and go for a spin before it gets too hot out. It is way too hot up here today and I hate the heat.
 
Coco said:
MichaelB said:
I ran a 25 pilot on mine at sea level.
Started and idled perfect.
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I'm 1894 feet above sea level. I'm using a 35 now which leaned things out a bit.
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The pilot jet is a fuel flowing jet. 35 is richer than a 25.

Mikegray is right on with his info from Victory.
His settings sound similar to mine with a 3.0 slide.

A 2.5 slide has less air than a 3.0 so you really need a smaller pilot, less fuel.
I would start with a 25, I wouldn't be surprised to see it go smaller.

I chased a problem for the longest time on a Combat till I found it.
A HUGE Needle Jet was the culprit. 3 sizes to big. I found this problem with the help of Victory's Tuning manuel.
I doubt this is the problem, but it needs to be checked.



Where did you source the Carb?
 
I think your mikuni is set up perfectly now and it is not the problem.

The fact that it starts right away and idles well shows the pilot jet is not the issue.

You say the bogging thing happens at higher revs when shifting to second and third.

Does it bog or misfire when held steady at higher revs like holding it at say 4500 rpm?

How did it run before you put the mikuni and trispark on? Not the same issues?

Seems your mikuni and trispark are set up just fine, is it possible this is electrical related, intermittent bad ground somewhere that shows itself at higher rpm because that is when more vibration?
 
highdesert said:
I think your mikuni is set up perfectly now and it is not the problem.

The fact that it starts right away and idles well shows the pilot jet is not the issue.

You say the bogging thing happens at higher revs when shifting to second and third.

Does it bog or misfire when held steady at higher revs like holding it at say 4500 rpm?

How did it run before you put the mikuni and trispark on? Not the same issues?

Seems your mikuni and trispark are set up just fine, is it possible this is electrical related, intermittent bad ground somewhere that shows itself at higher rpm because that is when more vibration?
Click to expand...

The bike ran ok when I got. It came with a 36mm mikuni and a boyer. I tore it down soon after buying it. I've never made it to third since the problem started. The bike cant get enough speed up to need to hit 3rd. The engine sounds kind of rough and seems to lurch a bit so I let off the throttle and come home. I have not ridden it for longer than around the block since everything started happening. When one should shift from 1st to second is when the throuble starts so I go into second at slightly lower revs than normal sinvce the bodgging down or rough running occurs.

I'm going to put the carb back on right now and have a ride and report back.
 
Holmeslice said:
Just make sure that choke lever is UP.
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Yes it is up.

Bike idles nice and as expected with choke on too.

I just tried it again after blowing out that carb and still the bike breaks up and lags when under load at higher rpms. Good thing my tach just decided to quit working. :?

I'll look at the plugs and time it again after supper. I've been doing some yardwork as well so I'm hot and tired and pissed off.
 
If you have fuel fouled your plugs it may take a mile or so to clear out under load, but it will still idle due to the lower spark loading, not an uncommon problem with the mikuni, or try new plugs.
 
Coco

On a fresh restore I would check to see if crud in the gas tank is plugging up the filters on the fuel taps. Have a cold beer and when everything has cooled down pull the taps and inspect. Might have enough fuel flowing at idle but not enough when you give her the stick. Might be too easy but what the heck worth a try.

Scooter
 
splatt said:
If you have fuel fouled your plugs it may take a mile or so to clear out under load, but it will still idle due to the lower spark loading, not an uncommon problem with the mikuni, or try new plugs.
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First thing I did after changing the air jet is new plugs. Symptoms occured as well.
 
Scooter62 said:
Coco

On a fresh restore I would check to see if crud in the gas tank is plugging up the filters on the fuel taps. Have a cold beer and when everything has cooled down pull the taps and inspect. Might have enough fuel flowing at idle but not enough when you give her the stick. Might be too easy but what the heck worth a try.

Scooter
Click to expand...

The alloy tank is brand new as are the petcocks. I've actually washed out the tank once since I had a small pinhole that needed welding. Tank was cleaned after that.

I'm pulling the ignition and magnet and will reinstall and retime. Maybe the magnet is loose on the end of the cam??? I honestly don't think it is a carb issue anymore and possibly ignition.
 
OK. Since putting in the new air jet and new plugs and retiming, I realized I had only checked ONE plug after the test ride last night which was the right one. I just pulled the left and noticed it is a nice light tan colour and the left is black.

I'm going to do another valve adjustment and see what is up on the right side and go from there before pissing around with the ignition.
 
You shouldn't be able to start it from cold without the choke engaged with a Mikuni. It needs the choke to bring it to life. I have an 850 with the same settings and cannot start it on a hot day without the choke. Still sounds like its the carb.

If it wasn't for that detail i would agree with electric.

But black plugs.... No choke needed to start... etc......
 
jsouthard said:
You shouldn't be able to start it from cold without the choke engaged with a Mikuni. It needs the choke to bring it to life. I have an 850 with the same settings and cannot start it on a hot day without the choke. Still sounds like its the carb.

If it wasn't for that detail i would agree with electric.

But black plugs.... No choke needed to start... etc......
Click to expand...

Add to that it runs the same with the choke on or off. Not right.

Coco, you keep mentioning air jet.
Mikuni's have an air jet and a pilot jet. Have you been fussing with both of these?
If so, what air jet are you running?
 
MichaelB said:
jsouthard said:
You shouldn't be able to start it from cold without the choke engaged with a Mikuni. It needs the choke to bring it to life. I have an 850 with the same settings and cannot start it on a hot day without the choke. Still sounds like its the carb.

If it wasn't for that detail i would agree with electric.

But black plugs.... No choke needed to start... etc......
Click to expand...

Add to that it runs the same with the choke on or off. Not right.

Coco, you keep mentioning air jet.
Mikuni's have an air jet and a pilot jet. Have you been fussing with both of these?
If so, what air jet are you running?
Click to expand...

The bike runs at much higher revs with the choke on. On initial start up the bike can run without the choke but just barely. Mentioning the bike runs without choke was referencing that the bike does not stall and die when no choke is on. It barely stays alive with no choke until warm.

I think I'm calling the pilot jet an air jet. I have a 35 in there down from a 40 that it came with.

I'm going to go through ignition and ,make sure that is or isn;t the culprit then I'll go onto something else. I am really starting to think it is not a carb issue.
 
Every time i hear about people and jetting these carbs, i realize how diverce they can be. For example, My 72 750 ran a 36vm with 40 pilot, #3 slide, 159 q2 needle jet, 6DH3 needle and, get this, 330 main. Don't know how or why but that's how it ran like a dream.

The fact that i run a Combat head (fresh), and 1 1/2" pipes may have something to do with it.

That being said, You should have a set of mains 3 or 4 in both directions, and a couple of needles, one for both lean and rich direction or at least the one that will benefit after experiment with clip positions.
I believe the #159 type Q2 needle jet is the one that work best for Nortons and should be tuned around it.

I now run a 34TM Flatside and transfered all jetting from the VM except for the main which I now run a 280. The single TM setup is completely comparable to twin 32 Amals from top to bottom in performance. The only real differance is the totally reliable and consistance Idle cold or hot. I rarely get nervous at stop signs worring if it is going to stall or cough up on giddy up.

I really think that every bike is a little differant and it depend on how well your bike breathes, Valve seat condition, compression, and maybe how clear your pipes are and anything in between. Mikuni has 1000's of combo's.

Sorry to be so lengthly (ALA HOBOT (he has gotten better and I have gotten worse :lol: )) but my setup can be concidered as a fair start. Maybe boost the main and drop the needle. This may seem counter productive.
 
pvisseriii has a good idea, I had a hell of a time with my new rebuild getting it just right. Same carb as you but Megacycle 560 NR cam. 2 into 1 ex. It started great, idled great but when the rpm got to about 2,800 it would start to crap out. But what was weird is that if I just opened it up it would just take off great, I just had a flat spot at about 1/4 to half throttle +- Screwed with everything I could think of. Someone told me to just try going to the top groove in the needle, leaner. Woke up the mid range and was able to go from there. But it gave me a starting point. Changed the needle jet and needle to lean out the mid range. But I still don't understand the plugs.
 
Coco said:
OK. Since putting in the new air jet and new plugs and retiming, I realized I had only checked ONE plug after the test ride last night which was the right one. I just pulled the left and noticed it is a nice light tan colour and the left is black.

I'm going to do another valve adjustment and see what is up on the right side and go from there before pissing around with the ignition.
Click to expand...

When you get a good colored plug and a black one with a single carb it sounds to me more like an ignition problem.
Hard to imagine a valve could be so badly adjusted to cause that kind of imbalance on the plugs.
Bad plug lead maybe.

Bob
 
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