Mikuni Idle Problem

[Nitrohorse]

Well, I finally started the engine on the MTD build tonight. I can't seem to get the idle lowered though. I checked the slide on the Mikuni and it's bottomed out as it should be. The idle screw is turned out as far as it would go without completely falling out of the carb. It's idliing so high that the TC is engaging.
Can the mixture clip adjustment on the slide cause a high idle situation?
I also used the rubber hose to make an angled intake and I'm also wondering if I'm drawing air in at one of the hose clamps....
I attached a photo of my set up. I have never worked on a Mikuni before and it's a learning curve for sure.
Any suggestion are appreciated.
Thanks,
Larry

 

[Kenny1]

The first thing that comes to mind is what kind of cable end do you have attached to the slide. If it is a barrel end it may be causing the slide not to drop down to the idle position.

 

[jmbmini]

Use some brake cleaner or cold based solvent that evaporates fast. Spray it lightly around the hose clamps to see if you have a air leak while it's running if the idle jumps higher you have a air leak. Fix and see where your idle is and then try to adjust the carb. I don't know much about the carb your using but I'm sure someone on here will help!

 

[~JM~]

Use some brake cleaner or cold based solvent that evaporates fast. Spray it lightly around the hose clamps to see if you have a air leak while it's running if the idle jumps higher you have a air leak. Fix and see where your idle is and then try to adjust the carb. I don't know much about the carb your using but I'm sure someone on here will help!

X2.

I'm thinking vacuum leak somewhere. Slide may not be fully seated while engine is running. Try lowering the needle to the lowest position.

How does the float level look?

Your pic looks pretty cool! When do we get to see the rest of the bike?

P.S. What kind of tire is that?

 

[Nitrohorse]

The first thing that comes to mind is what kind of cable end do you have attached to the slide. If it is a barrel end it may be causing the slide not to drop down to the idle position.

Kenny,
I did check the cable length and barrel lenght. In fact, I trimmed the barrel and sanded it to make sure it wasn not interferring with the slide position. I also placed the cable on the slide minus the spring and placed both into the carb. The slide was exactly at the bottom of the travel. This thing has me scratching my head.

 

[Nitrohorse]

Use some brake cleaner or cold based solvent that evaporates fast. Spray it lightly around the hose clamps to see if you have a air leak while it's running if the idle jumps higher you have a air leak. Fix and see where your idle is and then try to adjust the carb. I don't know much about the carb your using but I'm sure someone on here will help!

I have a feeling there's a leak somewhere as well. Tonight I'm going to fart around with it again. I will keep everyone posted as to what caused the problem.
Thanks.

 

[Nitrohorse]

X2.

I'm thinking vacuum leak somewhere. Slide may not be fully seated while engine is running. Try lowering the needle to the lowest position.

How does the float level look?

Your pic looks pretty cool! When do we get to see the rest of the bike?

P.S. What kind of tire is that?

JM,
I'm not convinced yet that the slide isn't the problem. I might have a small leak that's compounding the problem, but my money's on the slide being the culprit. I also want to adjust the mixture clip on the needle and see what that does. I haven't checked the float level yet but I will. I have to find the specs for the carb since I received nothing with the carb when I bought it from AGK. I have experience with Carters, Walbros, etc., but these slide valve carbs are new to this old fart.

The tire is a Chen Seng (Made in Japan-can you believe it..ha..ha) universal tire.
I have photos of the bike over in the Project forum under "Project: MTD".
Let me know what you think of it. I'm debating whether to put fenders on it.
I'm open to opinons on the fenders.
Larry

 

[G-REX]

Niro,start with clip in the middle position,tear carb apart,check slide and pin for burrs.sometimes I found everything ok,but when assembled it still hangs up.As for the float,if engine revs and then dies,could be lean(not enugh fuel).The best way I found to adjust floats is to have carb off,upsidedown wiuth bowl cover off.Have a fuel line on carb,blow air into carb hose and raise float until shutsoff.Make sure carb is sitting level,adjust float tab until it shuts off when float arms are parellel or level with carb body.This is normally a good starting point for me.Then go from there and adjust .Hope this helps.

 

[G-REX]

Sorry,forgot something,from your pic,your carb looks like it is leaning down,I woud level up the whole assembly,and brace it up.Good luck.

 

[bobco]

Larry, I can't see your picture here at work because of our firewall...but if it's the same carb I just put on a friends big bore Honda Mini Trail...I had the same problem of an idle condition way too high and it would run on like the throttle slide was stuck. It had nothing to do with the slide or the needle setting. Your idle is way too lean. On some of those Mikunis, there's an idle mixture screw under the manifold mounting flange that controls idle fueling. In my case, I just opened that screw another 1.5 turns from the factory setting to allow more fuel into the engine at idle. Now the bike idles perfectly! Look on yours to see if you have that mixture adjustment. It's not where you'd normally think it should be..... :wink:

 

[~JM~]

...On some of those Mikunis, there's an idle mixture screw under the manifold mounting flange that controls idle fueling....

Hmmm... Good to know. Thanks.

 

[~JM~]

...The tire is a Chen Seng (Made in Japan-can you believe it..ha..ha) universal tire.
I have photos of the bike over in the Project forum under "Project: MTD".
Let me know what you think of it. I'm debating whether to put fenders on it.
I'm open to opinons on the fenders.
Larry

Yes, I believe it. After looking at tires for more than a month. I received a box with a couple of those same tires yesterday. I thought that red stripe looked familiar. Have you used this tire before & if so, how did it perform?

Fenders??? I'm thinking YES. In chrome or black. Either choice would allow you to use the base color to add some form of a GT type stripe down the length of each fender if you decided it needed it.

Nice work by the way. :thumbsup:

 

[Nitrohorse]

Larry, I can't see your picture here at work because of our firewall...but if it's the same carb I just put on a friends big bore Honda Mini Trail...I had the same problem of an idle condition way too high and it would run on like the throttle slide was stuck. It had nothing to do with the slide or the needle setting. Your idle is way too lean. On some of those Mikunis, there's an idle mixture screw under the manifold mounting flange that controls idle fueling. In my case, I just opened that screw another 1.5 turns from the factory setting to allow more fuel into the engine at idle. Now the bike idles perfectly! Look on yours to see if you have that mixture adjustment. It's not where you'd normally think it should be..... :wink:

I'll be damn, there's a mixture screw exactly where you said it would be.
There's an elongated casting off the bottom of the bowl that has the mixture screw.
I doubt I would have found it unless I removed the carb from the engine. I didn't get a chance to adjust it tonight, but I will try tomorrow and post my findings.
Thanks for your advice.
Larry

 

[Nitrohorse]

Yes, I believe it. After looking at tires for more than a month. I received a box with a couple of those same tires yesterday. I thought that red stripe looked familiar. Have you used this tire before & if so, how did it perform?

Fenders??? I'm thinking YES. In chrome or black. Either choice would allow you to use the base color to add some form of a GT type stripe down the length of each fender if you decided it needed it.

Nice work by the way. :thumbsup:

I have a set of chrome fenders for it and I'll mount them this week. I kind of like the look without them, but a little chrome always adds a bit to the bike.
I haven't used the tires yet, so the jury is still out on them. I do like that they're 4 ply and should hold up relatively well. I wanted a round shoulder tire since according to the gearing chart, the bike should be able to get up there in mph...not that I'm planning on going that fast with it.
Thanks for the compliment,
Larry

 

[bobco]

.....Thanks for your advice.
Larry

You're welcome! I know how frustrated I was and if I save you a few hours of scratching your head, I'm glad to help. Let us know the results... :smile:

 

[bobco]

There's an elongated casting off the bottom of the bowl that has the mixture screw.
I doubt I would have found it unless I removed the carb from the engine. Larry

Larry, that's not the mixture screw, it's the fuel bowl drain screw. The screw I'm referring to is on the 2-bolt mounting flange at the bottom of the flange. It is recessed slightly into the casting....look again...

 

[4strokr4life]

if your trying to make it sound like a low idling harley like me lol. .I have a elan with a 250 single and a mikuni carb ,the only way for my carb to run at low idle is if the filter is off try that but I don t recommend it ,its not so bad in the snowy winter.:hammer:

 

[Nitrohorse]

Larry, that's not the mixture screw, it's the fuel bowl drain screw. The screw I'm referring to is on the 2-bolt mounting flange at the bottom of the flange. It is recessed slightly into the casting....look again...

Bobco,
The mixture screw on my carb is located between the two float bowl screws
near the mounting flange. The factory had the screw set at one half turn out. I gave it another full turn and it's idling perfect.

I took the bike for a short shake down ride and it's great. The only problem is that I wanted the narrow drag bike seat and the engine vibration travels right up my butt.

I took it easy for a while till I believed that anything that was going to break or shake loose would have, and then cranked it up a bit. It's alot quicker than I imagined it would be. No wonder the guys on here own multiple minis..I forgot how much fun they are!

 

[jmbmini]

Well done guys! That's how these threads should be people helping other people figure out technical problems and sharing in the fun of the hobby. Not like I've seen and read on other threads in this forum recently! Nitrohorse super job on that mini. Now your hooked again it sounds. Enjoy!

 

[Nitrohorse]

Well done guys! That's how these threads should be people helping other people figure out technical problems and sharing in the fun of the hobby. Not like I've seen and read on other threads in this forum recently! Nitrohorse super job on that mini. Now your hooked again it sounds. Enjoy!

Thank you. These pissing matches on here are nothing new or unique to this forum. I belong to other groups and it's all the same. I try to avoid them.

This weekend I will completely finish the bike. I have the fenders to install and adjust the mixture on the carb and it's done.

I'm also planning for my next bike. That should make the wife roll her eyes...lol I'm definitely hooked.