Where to get Thicker Mikuni Check Valves

[JKMike]

Hey yaw,

Does anyone know where I can order the extra thick Mikuni Check Valves?

 

[DylanS]

I’m assuming you’re dribbling fuel, have you moved to gp800 kidney blocks?
I’ve had luck with cutting my own out of some blue plastic sheet that I believe @cubaden sent me

 

[JKMike]

I’m assuming you’re dribbling fuel, have you moved to gp800 kidney blocks?
I’ve had luck with cutting my own out of some blue plastic sheet that I believe @cubaden sent me

Yea It was dribbling a bit last season or at least it seemed like it would sometimes. I tore down the carbs and gave everything the once over and i didn't find any issues. I did find that one of the carbs had two check valves stacked while the other only had one.

 

[JKMike]

What the deal with the gp800 kidney blocks? I haven't heard anything about them before.

 

[DylanS]

What the deal with the gp800 kidney blocks? I haven't heard anything about them before.

The hole where your check valve sits is offset thru the side of the block instead of directly overtop of the valve. I’ve always had great results running them, in-fact I don’t even bother running any other block.
The real trick is to be running at the proper fuel pressure but even then I’ve had some leakers and the gp800 blocks pretty much sort it right out. They aren’t cheap new but
You can find them used on eBay sometimes.

 

[Pro-pulsion]

Double up on the check valves and test. If it's still dribbling add one more. You can max out at 3 but more than likely the dribbling is because your popoff is too low and the engine vibration is bouncing the needle valve off the seat.

 

[JKMike]

The hole where your check valve sits is offset thru the side of the block instead of directly overtop of the valve. I’ve always had great results running them, in-fact I don’t even bother running any other block.
The real trick is to be running at the proper fuel pressure but even then I’ve had some leakers and the gp800 blocks pretty much sort it right out. They aren’t cheap new but
You can find them used on eBay sometimes.

Interesting, I'll give them a shot. I mean what isn't expensive in this sport! haha

The carbs were set up for me by Phill Clemons who had a hand in developing my motor so I would think they should be pretty close to where they should be.

 

[DylanS]

Interesting, I'll give them a shot. I mean what isn't expensive in this sport! haha

The carbs were set up for me by Phill Clemons who had a hand in developing my motor so I would think they should be pretty close to where they should be.

Yeah, sometimes you can’t quite get what you want with a higher pop off pressure.
If he has them close I’d try doubling up on the valves as mentioned above but sometimes that just won’t cut it.
Fuel pressure, valves, kidney blocks is generally my approach when dealing with big cc motors with lower pop off pressures.
Just keep in mind altering fuel pressure affects jetting.
Not sure what your setup is but I’d just throw valves and blocks at it first to minimize retuning.
I’m assuming you also did a pop off test and your stuff is in working order?

 

[JKMike]

Yeah, sometimes you can’t quite get what you want with a higher pop off pressure.
If he has them close I’d try doubling up on the valves as mentioned above but sometimes that just won’t cut it.
Fuel pressure, valves, kidney blocks is generally my approach when dealing with big cc motors with lower pop off pressures.
Just keep in mind altering fuel pressure affects jetting.
Not sure what your setup is but I’d just throw valves and blocks at it firsr to minimize retuning.

Ill have to rig up a fuel pressure gauge and check that as well. Mostly out of curiosity. I'm reading through this thread again right now: https://www.x-h2o.com/threads/importance-of-the-correct-return-jet-sizing.176798/

Yea that's what i was thinking as well, extra valve and those blocks. I would rather not risk having to retune my setup as that's not something I fully trust myself to do, at least not without having an ECU and sensors I can data log off of.

 

[DylanS]

Tuning really is an art especially with stupid horsepower setups.
Change blocks and double up on factory valves.
I promise what you’re seeing dribble at idle is nothing compared to the fuel that’s blasting out after you let off the throttle on a hard pull.

 

[Sparkplug]

You can make your own gp800 kidney block. Jb weld the hole and Re drill it like the gp800 passage. It's super easy to do.

I had a yamaha 1100 that dribbled fuel at 70psi pop off. And nothing fixed it until I modified the kidney block

 

[Sparkplug]

You can make your own gp800 kidney block. Jb weld the hole and Re drill it like the gp800 passage. It's super easy to do.

I had a yamaha 1200 that dribbled fuel at 70psi pop off. And nothing fixed it until I modified the kidney block

Oops. I was trying to modify my post to say 1200. It was the earl non pv triple 1200 known for dribbling issues

 

[AlexC651]

You can make your own gp800 kidney block. Jb weld the hole and Re drill it like the gp800 passage. It's super easy to do.

I had a yamaha 1100 that dribbled fuel at 70psi pop off. And nothing fixed it until I modified the kidney block

Did that really work for you?