Waveblaster 2 rough idle when warm

[Blake G]

So I have a 96 waveblaster 2 760 dual carb, starts right up cold and idles fine. Once out on the water and warmed up it will slowly develop a worse and worse idle until it sometimes stalls. Usually to get it to restart I have to give it some throttle. If i try to give it hard throttle after idling for more than say 15 seconds it sort of bogs but will even itself out. If I ride it around for a minute giving it some gas, then come to idle and go straight to WOT it feels fine. Only seems to be acting up at idle/when idling for longer and longer. Any ideas? I just rebuilt both mikuni’s with genuine kits. It had this issue before the rebuild, figured it was the carbs because of how nasty they were. Any input would be much appreciated as I am pretty new to these. Thanks!

 

[WFO Speedracer]

The kits don't include needle and seats and most likely that is where your issue is , needle and seat or the o-ring that seals the seat is most likely leaking. , how does it start , easily without the choke if so bad needle and seat. Basically I am giving you the symptoms of when they are not sealing ,one other symptom is if you cut gas off and it pick up for a second then dies usually bad needle and seat.

 

[Blake G]

Thanks for the quick reply! I always choke it when I start it and it fires up right away (but i can instantly take the choke off and it idles fine, almost like it didnt need it). I will try and start it cold with no choke to see what happens. Needles and Seats looked good when I did the rebuild but i’ve only rebuilt a handful of carbs. I did replace the seat O rings though. Everything in the carbs was pretty rough, I didnt see any ridges on the needles but maybe the rubber is just drying out?

 

[WFO Speedracer]

It doesn't matter how they look only if they hold pressure or not , without checking the popoff with a gauge you will not know if they are sealing or not

 

[Blake G]

I tried to check pop-off during rebuild, gauge wasn’t holding pressure. I assumed that wasnt right but once the Ski ran I figured it was maybe the tester I was using. I’m assuming its because the needle/seat wasn’t sealing? Lol I feel pretty stupid just glad to get some answers. I can pull the carbs back out sometime soon, the needles and seats should have markings on them for replacement right? And do you think im good to reuse all the gaskets and stuff I just put in?

 

[WFO Speedracer]

Yes you should be good there , next time if it isn't holding pressure find out where it is leaking from , soapy water will tell you pretty quickly , a lot of times it's around the seat o-rings , in your case I am betting on a bad needle and seat.

I think those use 1.5 needles and seats but don't quote me on that do your own research . Pretty much everything else runs 1.2 needle and seats.

 

[Blake G]

Well the blaster will start right up with no choke, but so will my vxr? The blaster is the only one having running issues, not sure if that means anything or not. I’m going to pull the carbs again on the blaster this evening and try to check popoff/look for a leak this time.

 

[WFO Speedracer]

The dual and triple carb stuff is always set up way to lean on the pilot circuit , so much so that they are very difficult to start even with the choke , that is why I asked , if it is starting with no choke at least one needle and seat is bad.. There is a lot of stuff that will make an engine run lean but not that many thing that will make it run rich .

 

[Blake G]

Just pressure tested both carbs, honestly seems like the needle and seat are sealing. However, both carbs seem to be leaking in the same spot at the base of the fuel pump block. Any ideas why they would be leaking there with new genuine gaskets just installed?

 

[WFO Speedracer]

Are all of the gaskets in there, Yamahas have a extra gasket that other machines with SBN44'S don't have . I usually sand the surfaces on the fuel pump with 400 grit and WD40 to make sure they are flat ,LMK if any of this helps , what is the popoff on the carbs coming out at ?

 

[Blake G]

Taking them back apart and putting them back together seemed to fix that leak but i still cant get them to hold all the way to popoff pressure. Ive gotten them up to about 45 psi without it popping off but then it tends to bleed off. any ideas?

 

[WFO Speedracer]

Are you wetting the needles with WD40 when checking the popoff ?

 

[Blake G]

Turns out i had the slightly bigger diaphragms in the carbs causing them to not seal against the weirdly shaped o ring on the pump side. The rear carb is popping off at 35psi and the front carb is popping off at 41psi.

 

[WFO Speedracer]

Correct popoff on those is 42-45 so on the one you are good , on the other one it needs to come up quite a bit, where are the needle levers sitting at on the lower popoff carb

 

[Blake G]

What exactly are the needle levers? I probably won’t be able to mess with the carbs for a few days now that I am back to work but i’ll check the next time I can. You don’t think it needs a different spring? I’m not sure if anyone has been in the carbs before or not, they were pretty rough.

 

[WFO Speedracer]

The part that opens the needle and has the spring under it , the pin is the fulcrum point so it is a lever , you can bend them slightly to make small changes in the popoff but in your case I doubt you can get that big of a change , you might want to get two new springs and go from there.

 

[Blake G]

The mikuni kits came with i think 2 springs, is there a way to tell what spring is what weight?

 

[Swordfish]

The 115 gram spring is just a touch longer. Just did a total rebuild on some B2 carbs as well

 

[Blake G]

Sounds good, thank you for the info guys! I guess ill try changing out the springs in the one carb to get both of the popoffs in that 42-45psi spec and get the ski hopefully running great!

 

[WFO Speedracer]

Hopefully that will do the trick.