Super Jet Front cylinder flooding after carb rebuild

Location
Oregon
I just installed a b-pipe ltd chamber, ADA head 35mm domes, and SBT carb rebuild kit on my otherwise stock 2000 RN. Set the carb screws to recommended settings, I also used the new spark plugs as recommended. The jets are 135 main and 75 pilot. The ski runs rough, but won't even come close to idling, and at full throttle it can't even come close to getting up on plane. For some reason I can't get the front cylinder to fire. It seems to me that it is being flooded with excessive fuel. That is my guess because with the new plugs I could tell the front cyl was not burning, but the rear one was. The front plug was wet with fuel, but still looked brand new as if no combustion was occurring. To eliminate possible problems I switched the front and rear plug wires and put a new plug in the front (so it wasn't fouled) to see if the front one would now burn. No go. Still only firing in the rear. My guess is that I have screwed up the carb rebuild and put something in the wrong place causing too much fuel to dump into the front cyl. I checked for spark on the front and rear wires and I'm seeing spark on both. Any ideas on troubleshooting this? This is my first ski and my first Mikuni 38 rebuild if you haven't already gathered that. P.S.The carbs look to be synced very well.

Thanks in advance for any help
 

shepster

Living the dream!
Hi, I would pull the carbs again and double check your work. Seems to be related to carb as you said you have just done them.
Make sure the needle valve isn't getting stuck open and all diaphragms are in the right places.
 
Location
Oregon
Hi, I would pull the carbs again and double check your work. Seems to be related to carb as you said you have just done them.
Make sure the needle valve isn't getting stuck open and all diaphragms are in the right places.

I pulled them off already and double checked that the jets were installed properly and that the needle was not stuck open, also double checked the hi and low speed screws. As far as the diaphragms being in the correct place, I don't have much to go off of here. I took the carbs apart before my carb rebuild kit arrived (like an idiot), so I don't know exactly how the diaphragms are installed. I have a small diagram of how the diaphragms go in, but it's not real clear. I have them installed in a way that I thought best matched the documentation I do have. I could really use a better diagram or some pictures of an actual carb. If I can't get anything I do have a buddy with an identical ski that I could probably pull off the carbs and see how they should be, as long as I don't screw his up too. :thinking:
 

tom21

havin fun
Location
clearwater FL
3 things come to mind, there is a bur on the little bar that lifts the needle and I had a set of carbs that the needle hooked on it and it held the needle open and it just poured and poured fuel. pretty hard to miss if this happens.

did you replace the needle and seat? if you did, did you do it with the sbt ones or genuine mikuni? if you didnt and you didnt do a popoff test then you may have old leaky needle and seats.

did you change the springs? its possible you mixed them up or that they are not the same pressure. one will get fuel and one wont get it at the same amount as the other. again you would have to have a popoff gauge to set this up and confirm it.
 
Location
Oregon
3 things come to mind, there is a bur on the little bar that lifts the needle and I had a set of carbs that the needle hooked on it and it held the needle open and it just poured and poured fuel. pretty hard to miss if this happens.

did you replace the needle and seat? if you did, did you do it with the sbt ones or genuine mikuni? if you didnt and you didnt do a popoff test then you may have old leaky needle and seats.

did you change the springs? its possible you mixed them up or that they are not the same pressure. one will get fuel and one wont get it at the same amount as the other. again you would have to have a popoff gauge to set this up and confirm it.

Are you talking about a burr on the metal bar on the diaphragm that pushes on the needle lever? I think something like this may be occurring because the last time I tried to run it with the flame arrestors removed I noticed fuel pooling in the front carb just by looking at it from a standing position in the tray. At the time I wasn't trying to diagnose a problem, so I didn't pay much attention. I did not replace the needles and seats as they didn't come in the SBT rebuild kit (unless somehow I didn't see them in the package). I did replace the stock springs with 95g springs. I think they are silver compared to the stock ones having a brass color, or vise versa so I don't think I mixed them up, but I will definitely check to make sure. I do not have a pop-off gauge, but I will ask around to see if I can find a friend that has one. On a side note, the ski ran well before these mods.
 
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some photos would help, for sure.

- run it on the trailer, at idle you shouldn't see fuel dribbling in. If it is, the needle/seat is leaking or stuck.

- triple check that you are putting the correct spring, and the same spring, in both carbs. Mikuni changed their spring colors quite a while back, I have no idea what comes in an SBT kit...but for new genuine Mikuni springs, the 95g is a dull silver color and is the only one of the 4 (115g, 95g, 80g, 65g) that are wound the opposite way. (Yeah, that only helps if you have others to compare it too, I know). The real test is to use a pop-off tester.

- make sure that you rebuilt the fuel pump side of both carbs correctly...put up some pics and we can tell.

- I'd also make sure that you don't have a broken reed just in case.

- You have bigger problems than this, but just FYI...I prefer to sync carbs using a snail synchrometer. If you don't have access to one, putting a long tube in the carb throat and listening to the pitch of the two carbs is better than just eyeballing it.
 
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Location
Oregon
I got a hold of a pop off gauge, from what I've read the Mikuni's are about 12# pop-off with the stock springs? I'll check what my 95g springs are giving me for pop-off, then I'll throw the stock springs back in just to see the difference. I'm also taking a depth micrometer to measure the fulcrum distance from the face of the carb down to the metal fulcrum. Maybe this was bent during installation? I'll post results tonight.
 

tom21

havin fun
Location
clearwater FL
no 12is way low, stock is like 50 to 60. if you have the stock springs I recommend putting those back in. when you are checking the popoff you are also checking the condition of the needle. with the stainless cover off and the diaghram out you depress the lever for the needle and spray some wd40 in the seat. block off the return and install the pump on the inlet side and pressurize. it should pop. if it dribbles then the needle is worn. note the pressure it pops off at and repeat 2 more times to confirm.

you probably swapped a different pressure in and have mucked it up a bit.

also as aramis pointed out you may have messed up something in the fuel pump side but I know from experience that those springs are probably at least some of your issue.
 

tom21

havin fun
Location
clearwater FL
I should have also said to seperate the carbs when testing. you can do both at the same time but usually one pops and the other doesnt. you could hold the needle in to check the other if you want to be lazy. been there, done that. im not perfect either lol. and im really lazy too.
 
Location
Oregon
Well, my pop-off gauge only goes to 30 psi, and I tested it up to 30 with every spring I had and none of them popped off. So I assume I need a different gauge that goes up higher? Here are some pics of what I'm doing and how I have the diaphragms installed. Note that the filters for the needle seats were removed for pop-off test and pictures, but they were installed while trying to run the ski. Also, I measured both the fulcrums at .012" above flush of the surface (I believe to be) that the manual says it should be flush with. These are the stock fulcrums and I have not bent them or changed them since the ski ran before carb rebuild.

IMGP1611.jpgIMGP1613.jpgIMGP1615.jpgIMGP1616.jpgIMGP1617.jpg
 
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tom21

havin fun
Location
clearwater FL
yes, you would need a gauge that goes higher than 60 if your stock setup is 50-60. this is why I said just put your stock springs back in. its better if you test the carb with the fuel pump installed this way you can also check for gasket leaks while you check pop off. maybe you have a bike pump with a gauge on it you can fab something up?
 
Location
Oregon
yes, you would need a gauge that goes higher than 60 if your stock setup is 50-60. this is why I said just put your stock springs back in. its better if you test the carb with the fuel pump installed this way you can also check for gasket leaks while you check pop off. maybe you have a bike pump with a gauge on it you can fab something up?

tom21, I'll try it with the fuel pump installed tonight if I can find a new gauge. Thanks

Diagram on page #3. If you have the 65g spring in there pop off should be 32, if its the 95g spring then 43

http://www.hotproductsusa.com/Catalogs/06._Intake_Systems_Section.pdf

Thanks motozachi, I'll try to come up with something today that goes up around 60 psi.
 
Location
Oregon
So I managed to build my own pop-off tester, and I'm getting a consistent pop-off on both carbs of about 47-48 psi with the 95g springs. I had a buddy come over and he checked the way I installed the diaphragms and gaskets in the carbs with the diagram. We both agreed that everything is installed right.

I'm starting to wonder if it may have something to do with my coil or ebox. I had the ebox apart when I installed the OCD tidy bilge kit, but I know I checked to see if the ski ran after that and it did start right up (although I didn't actually ride it). I kind of ruled this out due to the results of switching the plug wires around like I discussed in the first post of this thread, but now I'm not sure. :dunno:
 
the stock e-box only has one coil, so both plugs always spark at the same time, two times per revolution. If one plug is sparking, and the other is not, then the problem is in the plug wire / cap and not the e-box.
 
Location
Oregon
Do you have the oem f/a?

N&S are not included with oem mikuni or a/m carb kits.

Chris, does oem f/a stand for flame arrestors? If so, yes I do have them. If it means something else, I apologize for my lack of carburetor vocabulary.

the stock e-box only has one coil, so both plugs always spark at the same time, two times per revolution. If one plug is sparking, and the other is not, then the problem is in the plug wire / cap and not the e-box.

aramis, both plugs spark when plugged into the boot, but the rear wire seems to jump spark much further than the front wire when I try to get it to arc across to the cyl head.

First I'm going to check my reeds just to make sure they're not mysteriously broken, then I'm going to take my buddy's 38's off of his RN and see if my ski will run with his carbs on it. If it does run at least I know my problem is in my carbs, if it doesn't run the problem is probably in my wires/coil correct? Then I'd probably just order a new coil from Chris. Does this sound like a decent plan of attack?

Thanks guys
 
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munki63

Epoxy is my duct tape
Location
Canada
Sounds like your coil, the wires from the coil to the boots arnt the sturdiest thing, Durring your build you could have unintentionally damaged the wires, if your not getting the same spark on both plugs replace it, it's that simple.... You could try cutting your wires back a couple inches and reattach the boots, if your lucky that will fix your problem
 
Location
Oregon
Sounds like your coil, the wires from the coil to the boots arnt the sturdiest thing, Durring your build you could have unintentionally damaged the wires, if your not getting the same spark on both plugs replace it, it's that simple.... You could try cutting your wires back a couple inches and reattach the boots, if your lucky that will fix your problem

munki, I'll do some experiments tonight or over the weekend to try and narrow it down. I just read through your g3 build thread, looks awesome. Did you get to ride it yet or did the snow hit already up there? Where in Canada are you? I visited Quebec City about a month ago, I liked it a lot... Just curious if you're from that area.
 
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