Need your help w tuning Mikuni 45mm carb please

[mleach72]

Take the air cleaner off and post a picture of the front of the carb. The sizes are easily identified by the the size of the ac mounting spigot.

 

[mleach72]

Could you show me how to check that? Do i have to take the carb apart? Here is what it look like. I have not have to use choke when i start the bike.View attachment 124756View attachment 124757View attachment 124758

It appears that you have the mikuni choke cable on your carb, so it's likely you have the correct choke plunger. If you want to check to make sure, unscrew the choke cable from the carb. Here's a picture to compare. Also, make sure you have a little free play in the cable or the plunger won't seal completely. There's an adjuster on the mikuni cable to give you some free play.

 

[john sachs]

Or could mine be 43 instead of 45?

Mikuni NEVER made a 43 mm Flat slide. 42, 45, and 48 only. All of them are great carbs. Their intake manifolds, are a different story.
John

 

[johnle712]

Take the air cleaner off and post a picture of the front of the carb. The sizes are easily identified by the the size of the ac mounting spigot.

 

[johnle712]

I got a new 27.5 pilot yet and a 177.5 main jet. I will install them tonite. Looking at the old 25 pilot yet, i notice it was clog at the tip.

 

[mleach72]

I got a new 27.5 pilot yet and a 177.5 main jet. I will install them tonite. Looking at the old 25 pilot yet, i notice it was clog at the tip.

Remove the air cleaner backing plate and take a picture. It's hard to tell, but it kinda looks like a 42mm. That would make sense. A 172.5 main jet would probably be about right in a 42 on a 117.

 

[mleach72]

I got a new 27.5 pilot yet and a 177.5 main jet. I will install them tonite. Looking at the old 25 pilot yet, i notice it was clog at the tip.

Also, I noticed you have a huge gap in the accelerator pump. It shouldn't be near that big. That might be some of your problem. Turn the screw out until there is no gap. Then turn the screw in 3 full turns. If you are getting a carb sneeze during blips of the throttle, turn the screw out 1/4 turn at a time until the sneeze disappears.

 

[johnle712]

Remove the air cleaner backing plate and take a picture. It's hard to tell, but it kinda looks like a 42mm. That would make sense. A 172.5 main jet would probably be about right in a 42 on a 117.

 

[johnle712]

Also, I noticed you have a huge gap in the accelerator pump. It shouldn't be near that big. That might be some of your problem. Turn the screw out until there is no gap. Then turn the screw in 3 full turns. If you are getting a carb sneeze during blips of the throttle, turn the screw out 1/4 turn at a time until the sneeze disappears.

Could you tell me where is the accelerator pump?

 

[johnle712]

Mikuni NEVER made a 43 mm Flat slide. 42, 45, and 48 only. All of them are great carbs. Their intake manifolds, are a different story.
John

Sorry

 

[johnle712]

Also, I noticed you have a huge gap in the accelerator pump. It shouldn't be near that big. That might be some of your problem. Turn the screw out until there is no gap. Then turn the screw in 3 full turns. If you are getting a carb sneeze during blips of the throttle, turn the screw out 1/4 turn at a time until the sneeze disappears.

Is this accelerator pump?

 

[mleach72]

View attachment 124781View attachment 124782

That is definitely a 45mm. I would try some bigger jets than that 172.5 and see how they feel. Every bike is different, but that seems unusually small for a 117. I run a 182.5 in my bike and I'm pretty sure it's correct. If anything, I may need to move up to a 185.

 

[mleach72]

Is this accelerator pump? View attachment 124783

Yes. I see in your other picture that the rod is up where it is supposed to be. The rod isn't moving freely in the rubber boot. Give the rod a squirt of WD40 and work the throttle several times. The rod should come right back up when you release the throttle. Also check that the fuel squirt is hitting the needle when you open the throttle.

 

[johnle712]

That is definitely a 45mm. I would try some bigger jets than that 172.5 and see how they feel. Every bike is different, but that seems unusually small for a 117. I run a 182.5 in my bike and I'm pretty sure it's correct. If anything, I may need to move up to a 185.

I got a 27.5 pilot jet and 177.5 main jet in. Start the bike. Sound better no spitting/cutting like before but then it suddenly die. I try again and same thing happens at idle. I have not have a chance to ride it yet but engine sound better than before.
This morning after reading your comment about the rod. So i check it out. It is free moving but it is not moving up and down. Also i notice there is no fuel squirt inside the carb when i turn the throttle. ?????

 

[mleach72]

I got a 27.5 pilot jet and 177.5 main jet in. Start the bike. Sound better no spitting/cutting like before but then it suddenly die. I try again and same thing happens at idle. I have not have a chance to ride it yet but engine sound better than before.
This morning after reading your comment about the rod. So i check it out. It is free moving but it is not moving up and down. Also i notice there is no fuel squirt inside the carb when i turn the throttle. ?????

It sounds like your accelerator pump plunger is stuck. That happens sometimes. Remove the bowl. The plunger is in the corner of the bowl. Tap on it and move it around. It should pop up. Sometimes when you have the bowl off, you accidentally push the plunger all the way down and it gets stuck. It's happened to me a few times.
As far as the engine shutting off, did you adjust the idle mixture screw for the new pilot jet? Is the idle speed set high enough? The idle speed adjuster is the cable hanging off the left side of the carb.

 

[mleach72]

I got a 27.5 pilot jet and 177.5 main jet in. Start the bike. Sound better no spitting/cutting like before but then it suddenly die. I try again and same thing happens at idle. I have not have a chance to ride it yet but engine sound better than before.
This morning after reading your comment about the rod. So i check it out. It is free moving but it is not moving up and down. Also i notice there is no fuel squirt inside the carb when i turn the throttle. ?????

I know these are going to sound like stupid questions, but it happens to all of us at some point. Are you sure you have gas in the tank? Is the petcock on?

 

[johnle712]

I know these are going to sound like stupid questions, but it happens to all of us at some point. Are you sure you have gas in the tank? Is the petcock on?

hehehe. Yes. There is fresh gas in the tank and full. I have installed an inline fuel filter so i know for sure gas makes it to the bowl.

 

[john sachs]

Here's a pic of a 42 mm Mikuni, on my 98 Buell. Won 8 dyno shoot outs, although it's irrelevent.
Look at the pic of the nylon linkage pivot that operates the acc pump. Also where I have it adjusted to the pump rod. Also, it looks like your nylon pivot may be broken (could just be a bad picture) ????
John

 

[johnle712]

It sounds like your accelerator pump plunger is stuck. That happens sometimes. Remove the bowl. The plunger is in the corner of the bowl. Tap on it and move it around. It should pop up. Sometimes when you have the bowl off, you accidentally push the plunger all the way down and it gets stuck. It's happened to me a few times.
As far as the engine shutting off, did you adjust the idle mixture screw for the new pilot jet? Is the idle speed set high enough? The idle speed adjuster is the cable hanging off the left side of the carb.
[/QUOTE

Here's a pic of a 42 mm Mikuni, on my 98 Buell. Won 8 dyno shoot outs, although it's irrelevent.
Look at the pic of the nylon linkage pivot that operates the acc pump. Also where I have it adjusted to the pump rod. Also, it looks like your nylon pivot may be broken (could just be a bad picture) ????
John

wow.. cool. And ill llook into that.

 

[johnle712]

I have two question:
1 - first picture - is there a gasket go between the carb and that mount? There isnt one when i take off.

2 - second picture: should there be a cover on the upper nozzel/nipple at the back right side of the carb ?