[Dave in DE]

If your applying choke to run well, the ski is running far to lean.
I'd rebuild carbs with Mikuni kits while your in there. And be sure to get the high/low screws correctly set.
You may want to consider the the carb upgrade from the sticky below the drilled return in greenhulk how to's.

The 1200 came from factory running very lean. They have a known tendency to have a lean cyl seizure. The upgrade fixes this. I've read, in place of flame arrestors you can drill holes in the factory air box cover for increased air flow.
My concern is if your needing choke to run your very close to a seizure.

 

[Dave in DE]

Missed the check valve issue. No way to check them I'm awere of short of visual inspection. They should be flat with no wrinkles or creases.

 

[Peteysparks]

I started reading the carb upgrade post and my head is spinning. I started removing the parts of the carbs for the return mod and the check valves look good. I do have a D Plate installed. I don't want this to be any more complicated. It seems others have followed the recipe and still have issues. My bog at acceleration seems to be a common thing. Would also like to get rid of it or improve. BTW The carbs were rebuilt last end of season. I only need to choke a little to eliminate the acceleration issue once it's going and up on plane I can push the choke back in and it's fine and goes fast. Do you think the return mod will fix this? I just didn't want to open up the can of worms if I don't need to. My ski is for cruising more than going fast. Although, a little rush of speed is always a fun thing. Thanks Dave!

 

[Dave in DE]

I don't think the return mod will fix the issue unless it's from on carb not getting enough fuel. Then it may help. May want to try coming out on you low screw a 1/4 turn this may help issue as well. Opening the high side screw a tad may not hurt either. 1/8 turn or so.
What do your plugs look like?

 

[Peteysparks]

The plugs are oil fouled. This is because I still have a gallon or two of break in gas left in the tank. Not sure if that may be contributing to the problem. I’ll be filling it up with some ethanol free in the coming months. I was even thinking of pumping out whatever is left first. I guess I need to drill out the plugs first. I think I see the plugs but want to be sure. I’ll check into that. All the carb components look really clean. I’ll be drilling out the return and cleaning everything this weekend. See attached are these the plugs?

 

[Dave in DE]

It's hard to tell from pics, but I believe I'm seeing an H in the second pic just above the plug that the arrow points at. That would be the high screw. So yes that's your plug. Should be a L by the one on the other side.

I'd leave what oil that's in the tank and just fill with fresh fuel.
Forgot your still breaking in fresh motor.

 

[Peteysparks]

Dave, I really appreciate your replies. Keep them coming. I drilled all three carbs tonight for the return mod and tapped the return fitting with a 95 jet. I meticulously kept the shavings under control with compressed air and carb cleaner after wash. I flushed everything... even took apart the large diaphragm, and flushed everything with carb cleaner. Everything looked good including the check valves and gaskets. (My mechanic rebuilt them end of last season) I also went ahead and ordered a SBT pop off pressure gauge and pump. I also checked the needle/seat lever to make sure it was level with the housing. Used a razor blade. All good. Since I’m keeping everything stock what’s the pop off pressure range for the three carbs? Is it 47? I have the silver spring. I’ll also drill out the plugs and do what you suggest with the screws. Maybe I should check the factory settings first? What are they? I’ll see where mine are first. I’ll admit, I have reservations about messing with them but a 1/4 or 1/8 of a turn should be a little insurance right? Some pics attached.....

 

[Dave in DE]

Pics look good. ? great job.
Once you get the plugs out recording and saving the factory set up will give you a set point to go back to if need be. And a great idea.
Not certain on the pop off but the number you posted sounds correct.

I believe if you drill a very small hole in the plug install a small sheetmetal screw you can then pull the plug out with pliers. Would be worth a shot anyway. There not real tight. Late model car carbs used the same system so you couldn't adjust them.

 

[Peteysparks]

I got the plugs out of the first carb. WOW! I need to go relieve some stress...LOL So I'm trying to decipher the information I found on the Mikuni website. I downloaded the manual for the Super BN carbs. If I'm correct my 1200 has triple BN44-40-43 carbs. Here's the link: Mikuni American Corporation For the spec chart on page 19 and I can do process of elimination and find which carb is mine. Looks like the low speed is 1.0 turn and high speed is .75 turns. These of course are counter-clockwise out from seated. I found the high speed screw to be a 1/4 turn from seated. I think I braised it while drilling and spun it in a little. The plugs are really thick and seem to be right up against the screw. This requires lots of patience but i think I have it down for the other two. In any case I just want to get everything back to specs and then do what you said with both screws. I'm going to read through the information. I'll probably find what the pop off should be. Thanks again Dave!!

I removed the jets High-117.5 Low 87.5. These are probably stock USA setup. I read the European stock specs are the way to go. I believe with the dull silver spring (what i have) my pop off should be around 45psi.
European Specs-
Main Jet 135
Pilot Jet 92.5
Low speed Screw carb 1 = 1 1/4 carb 2 = 1 1/2 carb 3 = 1 5/8
High speed screw Carb 1 = 7/8 carb 2 = 3/4 carb 3 = 7/8
Why are the screw turns different?

 

[Dave in DE]

I know it's off but that is correct. All three carbs are set different. I won't pretend to know why. Clueless.

The European skis didn't have catalytic converter either. So I'm told. The US ski had to meet all the EPA bs. This required them to go very lean to get emotions low enough.

 

[Peteysparks]

Not sure what I’m going to do yet. At this point I’m going to check the pop off and go from there. Any links or source to get the high and low mixture screws to factory specs?

 

[Peteysparks]

So I've been reading lots of posts here and GreenHulk. I think I've found the root of my original issue with the bog on 0-25% throttle. I'm certain the mechanic I used for the carb rebuilds last season didn't replace the needle and seat. I'm sure there was a couple gaskets he didn't replace either. I can't even understand why he would do this? I was able to get the seat out but ended up marking it up so bad it's useless. Guess that's just what happens when the o-ring is so bad it's frozen in place. It is the 1.2 factory seat. Three are on order with three new rebuild kits. All genuine Mikuni parts. The o ring on the seat was in bad shape. I have a jewelers loupe to see this. Definitely not replaced recently. Most likely original. I'm just going to do a full rebuild and leave the original jets.

One question I have is what do I use to smooth out the machined surfaces on the pump side of the carb. Very fine sandpaper? I notice some minor corrosion or surface discoloration in a small area where the gaskets press against. Everything else looks remarkably clean.

 

[Dave in DE]

Either fine sand paper or a fine scotch Brite pad. Will clean it up.
Just be sure to flush well before assembly.
Use a little 2stroke oil on the o-rings as you assemble them. Helps slide it in place without tearing them up.

 

[Peteysparks]

The fine sandpaper worked great.
I’ve started rebuilding the carbs with the I series Mikuni kits. The spring that comes with the kit is listed as the 115gm. Looks to be the same size as what was previously in the carbs. I have everything stock including the 117/87 jets and 1.2 needle/seat. Should I be using it? Is this the factory setup with the high pop off? My pop off pump only goes to 60psi. The chart I have shows pop off of 85 psi for my combination. This post from greenhulk suggests this may be factory setup for the 66v motor. What do you think. See replies from Water Work.

(You need to put everything back to stock,stock jets,stock springs (dont worry about pop off) 1.2n/s & 115 gram springs.

The key is to drill out the mixture screw caps so you can adjust low speed mixture screw & set them to 1.5 turns out & highs at 1 turn out, bolt carbs on & it will run perfect. From idle slam the throttles & it comes out like a rocket.

I see in your first post you say "stock settings" so I assume you havent drilled out the mixture screw caps.)

POST LINK

Pop Off Too Low on Stock 1200 PV (66V)? - Greenhulk Personal Watercraft Performance Forums

PWC Performance modification discussion for the 2-stroke Yamaha Waverunners GP1300R and others.

greenhulk.net

 

[Dave in DE]

My 800's factory are low 80's for pop off. So yes that will work. I would say the 1.5 & 1 turn out will get you in ball park and running. You can fine tune from there if need be.
Unfortunately I just don't have stock info for carbs on 1200's. I found this same info below from "Water Worx" on green hulk just as you did. I trust his info. Id trust that set up.

 

[Peteysparks]

A lot has happened since my last post. Got everything back together and it started right up. Idling 100% better than last October. Never used the choke whether it sat for minutes, hours or days. It started right back up. I did have a slight hesitation when hitting the throttle. I know under load in the water is the only way to see real conditions but I felt something wasn’t right. I decided to do Oside Bill’s recipe for the carb/accelerator disconnect upgrade. Before disconnecting the carbs I was curious to see if the accelerator pump was working. Just had a feeling. Well guess what, carb #1 wasn’t getting gas! Found the sprayer tube had a blockage. This most likely was the cause of my original hesitation issue on acceleration last season. I was so sure I blasted out everything on the carbs. Live and learn! I’m currently getting everything needed for the upgrade. I’m following the recipe that someone in the thread tried with the stock air box. I’m leaving the chokes intact and disconnecting the pump cam. Everyone is telling me to remove the screen but I just don’t feel it’s a good idea. It’s there for a reason so I came up with the next best thing. At least something is better than nothing. See attached. What do you think?

 

[Dave in DE]

That's the way I've always read it. If you don't use after market flame aresters drill the factory box full of holes