Other Check your throttle plate screws! PSA

[Aquaholic]

I've been asked to post up a public service announcement. Do yourself a favor , and take a minute to check your carb throttle plate screws. They should be tight obviously, but more importantly, the footing of the screw should be peened, so that screws cannot backout and go through your motor.

Note: This is a fresh rebuild on a Dasa 1200. Rebuilt crank and new top end. Less than 1 hour of runtime.

 

[E350]

Are those Oval Head screws or Pan Head screws?
How about a profile photo of the screw?

 

[Aquaholic]

Uffff! Ouchhh!

Mikunis always come with the Butterfly Screws peened.

Don't Novis? Or were New Throttle Kits recently installed?

What a bummer....

Thanks for the Tip.

Are those Oval Head screws or Pan Head screws?
How about a profile photo of the screw?

OEM carbs from Mikuni have black screws that are long enough, so that they protrude out the opposing side of the throttle shaft. This allows for proper peening or staking of threads, so that the screw(s) cannot backout , nor be removed without grinding the footing of the screw off.

These screws are not available from Mikuni. They don't want the liability of people replacing throttle shafts or butterflies and then improperly addressing the screws upon reassembly.

However, these screws are available if you know where to look.

The manufacturer of this set of carbs, as well as some other aftermarket carb manufacturers, are choosing to not use OEM style Mikuni screws. Instead, they are using the same screw that is used to hold the popoff spring lever to the carb body. It is a shorter, countersunk style screw. And, it's readily available. It sits flush with the opposing side of the throttle shaft. The only downside of using this style of screw, is that it is trickier to peen or stake the foot of the screw.


The screws on my set of carbs were definetly not peened , nor staked. The manufacturer may have used a locking agent at the time of assembly, but I saw no evidence of that, on the other 3 screws. If that's all that they are using, to secure those screws though...it's a very risky gamble.

 

[Wetbuffalo]

What is the preferred tool to use to peen them?

 

[E350]

@Aquaholic thank you so much for the photo and the description of the screws. Yes, those are Oval head screws which seem to be appropriately counter sunk for the throttle plate. Your photo and discussion regarding peening is priceless and should save all of us some future grief.

How you would peen the screws to the shaft when the shaft is already in the carb throat is hard to imagine without an appropriate support/anvil supporting the shaft on the other side. How can it be done without bending the shaft?

 

[Aquaholic]

@Aquaholic thank you so much for the photo and the description of the screws. Yes, those are Oval head screws which seem to be appropriately counter sunk for the throttle plate. Your photo and discussion regarding peening is priceless and should save all of us some future grief.

How you would peen the screws to the shaft when the shaft is already in the carb throat is hard to imagine without an appropriate support/anvil supporting the shaft on the other side. How can it be done without bending the shaft?

You're welcome, man. This game we play is filled with enough potential costly heartbreaks, eh? Sh*t like this is inexcusable, and while this was not one of my personal motors that this happened to...it very easily could have been. I'm waiting to hear back from the parties involved. But, based on initial correspondence...I ain't holding my breath as far as them accepting any responsibilty.

There's a few different methods to peen or stake these threads. The important thing to consider, is that you don't want to just go in there with a hammer and punch and start banging away. The shaft is soft and can easily be bent or destroyed if not properly supported.

Here's a good article on how to do it properly with a few different methods and tools:

 

[Aquaholic]

So are you going to use Mikuni Screws now?

Where can these Mikuni Screws be found? Vendor Link?

Just scavenge the Screws from a Mikuni Throttle Shaft Rebuild Kit?

JetManiac, Watcon, and Highspeed Industries should be able to source these for anyone in need. I am under the gun to get this boat finished up and tested. It's going overseas. I chose to peen the existing countersunk screws, so as to get back to water testing. The boat ran well yesterday, with one of my backup motors. It's amazing how they can run with the throttle plate screws intact!

 

[E350]

I have never put a choke plate back into a carb. I have only removed them. But for newbees like me, obviously this PSA thread would apply to re-installation of the choke plate screws also...

 

[Sparkplug]

A automatic center punch is lot better for peening screws than using a damn hammer on your carbs.

To each their own

 

[kevbo]

Many auto punches will jump off the mark so be sure about your tools. Most riders will make a mess of peening screws because they won't spend the time fabricating a way to back up their hammer. Generally speaking, the only thing worse than worn out OEM parts are ones the owner tried to repair.

 

[E350]

I still don’t see a way to support the screw heads while peening the other end of the screws. How can that be done?

 

[kevbo]

I use a piece of steel bar stock mounted in a vise.

 

[E350]

Got it. I may buy a ~4"- 6" long piece of steel round bar slightly smaller than the diameter of the carb throat to keep around just for that reason.
Thanks @kevbo

 

[orangefinger]

This happen to us before but we caught it, the plate was loose and throttle / ski wasn't performing , sluggish ....

Did u notice anything while riding or did it come loose so fast and drop ?

 

[MADMAT]

Wow. Sucks!!! Should not even be able to happen!!

 

[WFO Speedracer]

Some of the 550 Kawasaki's came through without the screws staked, I remember the bulletin, the tool we used to stake the screws was a pair of linesman pliers with two handle extensions made from pieces of pipe , this was necessary to get the proper leverage to stake the screws

 

[Aquaholic]

This happen to us before but we caught it, the plate was loose and throttle / ski wasn't performing , sluggish ....

Did u notice anything while riding or did it come loose so fast and drop ?

This is a build I'm doing for Hassan. He's moved back to Saudi Arabia, but he's back in town for a few weeks. We were going to squeeze in as much water testing as possible, and then this ski, as well as an Edge, would get crated up and shipped. I just finished this build a few months ago. Since the clock was ticking...I decided to get some tray time on the ski before he returned to San Diego. I took the ski out 4 different times and it ran like a turd. Everytime. Totally unrideable. It had moments of brilliance, but each time I turned the steering hard left, or hard right it fell flat. I was trying every trick I knew to get it to run right and it wouldn't cooperate. The mindf*ck was that it is a recipe that I've used on my personal setups with the exception that this build was using a Zeel ignition...whereas in the past we've always run MSD. I tried different curves and even swapped out flywheels. Nothing worked.

Then, with time running out...I decided to pull this motor and throw one of my backup Dasa motors in, so that I could get this boat running with a baseline setup, that I knew was solid. I pulled his motor and threw it on the bench. After puling the head, I saw the telltale signs of something letting go. I immediately assumed that it was the crank going tits up. I didn't break the motor down any further, but I felt somewhat relieved to finally see what was going on. Or, so I thought.

Meanwhile, I throw this same set of carbs on my Dasa motor. Note: I still haven't noticed the missing throttle plate screw. And we were slated to test that following weekend. On a whim..and with a few extra hours to kill, I decided to break the rest of his motor down and get the crank sent out for a rebuild. When I split the cases...to my horror, I discovered that it wasn't the crank letting go..but in reality it was a screw that had been dancing around!! I assumed that I f*cked up and had dropped something in the motor. I was my fault. I was going to have to cover this expensive mistake!

However, it was tiny screw. It wasn't a screw I recognized. It's not any screw that I would be messing with on a motor rebuild or ski build. Well, maybe I somehow dropped it in there while running the ski with the flame arrestors off? Where the F*ck did this screw come from?

And, then it hit me! The light bulb when off... I peered down the carbs of my motor which was now sitting in the ski, ready to ride, and saw the smoking gun.
F*CK!!!

 

[Aquaholic]