Mikuni 40mm how to securely attach to '92 EVO?
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Stage IV
Joined: Nov 2025
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Mikuni 40mm how to securely attach to '92 EVO?
I had a shop replace the stock carburetor with a mikuni 40 back in early '90s and ran fine until recently. Took it to another shop...there are not many that work on evo's anymore...and they said I had an intake manifold leak and they replaced something(s) and it ran fine for a short period, but then the interface between the carb and the intake keeps leaking.
In my original install, the carb was firmly held in place solid like a rock, regardless of whether the air cleaner was attached and pushing the carb into the manifold. Now I only have a compression fit that requires the air cleaner to hold it all together....not reliably.
What is missing from the initial installation? Do I need some kind of hose clamp or something? Thank you!
In my original install, the carb was firmly held in place solid like a rock, regardless of whether the air cleaner was attached and pushing the carb into the manifold. Now I only have a compression fit that requires the air cleaner to hold it all together....not reliably.
What is missing from the initial installation? Do I need some kind of hose clamp or something? Thank you!
Seasoned HDF Member
Joined: Mar 2010
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From: Poolville
No on the house clamp...
The seal between the carb and intake is called a compliance fitting and all it does is seal between the carb and the intake.. It is not designed to support the cam alone.. You should have a carb mounting plate that will secure the carb the way it's supposed to be..
Also I'm not familiar with a Mikuni 40, there are the HSR 42,45 and 48 though..
The seal between the carb and intake is called a compliance fitting and all it does is seal between the carb and the intake.. It is not designed to support the cam alone.. You should have a carb mounting plate that will secure the carb the way it's supposed to be..
Also I'm not familiar with a Mikuni 40, there are the HSR 42,45 and 48 though..
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From: Beyond Fucital
Depending on your intake manifold design there are either 2 bolts that secure it to the carb
or 3 bolts that hold it to a cross bracket that screw to the breather holes.
What manifold are you running?
or 3 bolts that hold it to a cross bracket that screw to the breather holes.
What manifold are you running?
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Stage IV
Joined: Nov 2025
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It is a Mikuni TM40, ancestor of the hsr42
stock intake manifold
Everywhere I look online I see this compliance fit O ring but no evidence of any kind of mounting plate. What was holding my carburetor on so tightly previously? I could have ridden the bike with no air cleaner no problem.
stock intake manifold
Everywhere I look online I see this compliance fit O ring but no evidence of any kind of mounting plate. What was holding my carburetor on so tightly previously? I could have ridden the bike with no air cleaner no problem.
Last edited by TommyHB; Nov 17, 2025 at 06:13 PM.
HDF Community Team
Joined: Dec 2005
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From: NC USA
It is a Mikuni TM40, ancestor of the hsr42
stock intake manifold
Everywhere I look online I see this compliance fit O ring but no evidence of any kind of mounting plate. What was holding my carburetor on so tightly previously? I could have ridden the bike with no air cleaner no problem.
stock intake manifold
Everywhere I look online I see this compliance fit O ring but no evidence of any kind of mounting plate. What was holding my carburetor on so tightly previously? I could have ridden the bike with no air cleaner no problem.
Here is a MIkuni catalog from Parts Giant. Hopefully it will help with the 40.
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Stage IV
Joined: Nov 2025
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I have those brackets in place. My issue is that the carb now just falls out of the intake manifold without the air cleaner keeping it in place, whereas for the 30 years before my recent repair, the carb was very firmly held in place without the air cleaner. Is there some kind of glue that should be used on that rubber gasket/ o-ring that goes between the intake manifold and the carb?
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Seasoned HDF Member
Joined: Aug 2008
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there might be an manifold to carb adapter that has a bead to grip&seal to the carb body and that adapter bolts to the stock manifold the adapter has a band clamp the secures it and yep will not fall out. over time, the boot will either become soft from fuel contact or dry rot and you will have issues.
https://shop.mikuni.com/wp-content/u...3-04042025.pdf
run through this
https://shop.mikuni.com/wp-content/u...3-04042025.pdf
run through this
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HDF Community Team
Joined: Dec 2005
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From: NC USA
Thanks, I forgot the link in post 5.
Tommy, the manifold seal does not use sealant. If you're using the Mikuni air cleaner, either the rubber is soft and out of shape, and/or the brackets are not where they should be.
Look thru the catalog bustert linked and you will find all kinds of options.
Tommy, the manifold seal does not use sealant. If you're using the Mikuni air cleaner, either the rubber is soft and out of shape, and/or the brackets are not where they should be.
Look thru the catalog bustert linked and you will find all kinds of options.
Seasoned HDF Member
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From: South Carolina
Not sure if a TM 40 is the same, but...
The kit that was sold by Mikuni USA was a Mikuni HS40 flat slide carb.
It was supported by a rubber adapter at the intake side, and by the air filter on the front side, the air filter was supported by mounting bolts, brackets and spacers to the cylinder head.
The mounting arrangement was a real hokey setup.
I ran one for about 15 years on my `89 Softail, the engine performed great, but the throttle return spring was way too strong even at the low setting.
It also stuck out too far for my liking and I finally gave in and found some OEM CV carb stuff.
The kit that was sold by Mikuni USA was a Mikuni HS40 flat slide carb.
It was supported by a rubber adapter at the intake side, and by the air filter on the front side, the air filter was supported by mounting bolts, brackets and spacers to the cylinder head.
The mounting arrangement was a real hokey setup.
I ran one for about 15 years on my `89 Softail, the engine performed great, but the throttle return spring was way too strong even at the low setting.
It also stuck out too far for my liking and I finally gave in and found some OEM CV carb stuff.
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