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  1. #1

    Join Date
    May 2006
    Okinawa Japan

    Need help chasing down a problem

    Actually maybe two problems:

    Ski - 1200R with the following basic set up:

    Stock, no porting 66v cylinders with sea-doo valves and Riva pro series heads w/41cc domes.

    Riva boost bottle intake w/Novi 48s, 3 fuel pumps and vapor separator. 105 in the return

    Triple pipes with FP water box and pipe inserts

    MSD total loss ignition – using BR9ES plugs instead of BR8ES-11 plugs. Fuel octane is 93.

    Also using Riva’s micro touch water injection into the FP water box

    Hot tach III with EGTs

    Problem 1:

    At idle (which is very rough and unable to smooth out with low speed screw adjustments), the mag cylinder seems to be not firing. The EGT stays almost ambient until I rev the motor then the EGT goes up. So it’s firing when the Rs are up. Also, both the mag cylinder and pipe stinger feel cool relative to the other pipes/cylinders but warms up when the engine is reved so I'm sure it's not a bad EGT probe. Ski runs fine in the water at higher rpms. The problem only exists at idle speeds.

    I've double and triple checked the following so far:

    Checked the plug cables. They meet specs.

    Double checked the MSD – the pickups are working and the ignition is making the coils fire the plugs.

    Double checked the timing set up on the MSD.

    Triple checked the timing on the pick ups

    Rejetted the carbs

    Pop off pressure on the 48s with the boost bottle is set to 25. I thought that might be the cause but the ski doesn’t load up so I think the pop off pressure is ok.

    Compression is 145/145/150 for the mag/center/pto cylinders. Testing done with throttle wide open and sea-doo valves untouched. Domes are 41cc

    I didn’t pull the intake manifold but did use a mirror to look at the M16 reeds while the carbs were off and they looked intact.

    Thought it might be the Start Retard function of MSD ingnition box might be the problem - maybe not allowing the timing to return to normal at 1000rpms like its supposed to - like it's delayed a little. But if that were the case, all 3 cylinders should be affected, not just #1.

    BTW - static timing for mag and center is set to 27 degrees and the PTO is at 25. As mentioned, I rechecked that and the pickups haven't moved.

    Don’t know what else to check without pulling the motor apart and even then, not sure what’s going to cause a problem at idle but not at WOT…Usually it’s the opposite…

    The second problem is a surging that's developed at idle after installing new fuel pumps and the vapor separator. It may be related to the main problem or not...basically, the idle speed revs up for a few seconds - not much, then drops down for 30 seconds or more...The VS is working like it's supposed to - absolutely no air is getting through to the carbs which are also getting plenty of fuel.

    Anyway - any thoughts, suggestions, help etc will be greatly appreciated.

    Thanks again,


  2. #2
    WATER WOODY's Avatar
    Join Date
    Aug 2005
    Minden, Nevada, United States
    Whats the plug look like on the mag? Could be a bad N/S or spring in that carb allowing it to dump fuel at idle,causing it to run rough,then clears out when your at top speed.Its just 1 thing to look at.

    HOLY %$#^&%^&!!!!!!!! RAYINJAPAN.....were have you been!

  3. #3

    Join Date
    May 2006
    Okinawa Japan
    Thanks for the reply mate!

    I've been checking out the forums but not posting much. Haven't been out on the ski's much either for various reasons but hoping to get back into it hard again. Back in Okinawa again after retiring from the USAF while up in mainland Japan...

    I just replaced the N&S & spring while rejetting - went to 2.0s and dull silver instead of 2.5s and gold springs. Pop off didn't change much (from 22ish to 25).

    The mag plug has been oily/wet after idling so I'm pretty sure the fuel is getting to it. Part of the reason I rejetted/changed N&S/spring was to see if maybe it was getting too much fuel but the problem still exists.

    I'm also wondering if another problem exists within the carb body causing too much fuel at idle but can't figure it out. Makes no sense to me:

    New plugs - check.

    Spark - check.

    Fuel - check.

    Compression - check.

    Timing - check.

    Firing at ilde - no!

    It's got me scratching my head hard which isn't good cause I'm losing enough hair as it is...

    I didn't pull the sea-doo valves off cause they shouldn't cause a problem like this. Any other ideas?

    Thanks again for the reply,


  4. #4
    WATER WOODY's Avatar
    Join Date
    Aug 2005
    Minden, Nevada, United States
    Ray,try pulling your FA/water sock off the Mag carb and see if it clears up some only at idle though.Dont take a chance on running it hard with that one naked carb on there,just at idle.It will get more air and lean it out some.Just an idea.Might need to rebuild them.One thing at a time though.Good to hear from ya!

  5. #5
    I'm gladd I cought this post! I am having the same exact problem too!

    I just got my boat back together today and found the same problem. My set up is a bit different though.

    Riva Pro series head 37cc 160psi

    Dominator manifold

    V-force3 reeds w/spacer

    46mm Novi's 162.5H 140L 2.5N/S 115 gold spring

    3 external fuel pumps

    Advent Ignition

    I seem to be getting all the same symptoms as you. Rough idle, idle serge from time to time

    At an idle the mag pipe is stone cold and the other two are warm. I dont have an EGT on my boat. If I bring it up in rpm it seems to start warming up. I have not lake tested it yet, I am going tomorrow morning. I am just running it on the hose at home for now.

    I have double and triple checked the pop-off and it checks out good. I just put brand new needle and seats in as well as new springs. I did have a N/S problem a little while back flooding my #3 cly with the same symptoms. I automaticly thought it was the N/S again, but the popoff checks out.

    I talked to Tim at novi and he said that it is a good possiabliity that I could have a stretched diaphram. This wouldnt show up in the pop-off test but when the motor is running the diaphram is holding the N/S open and flooding the clyinder. This is the problem I had with my #3 cyl a few weeks ago. I replaced the diaphrams in each carb, I can t believe this would be my problem again? It just might be your problem though!!!!!! I would check that out.

    Keep me posted, hopefully we can figure this thing out. I'll let you know how I make out this way.

    I am also running a 100 main jet in my return line. I'm at 1 psi at idle which is right where I want to be.
    Last edited by HCP Designs; 09-27-2007 at 11:08 PM.

  6. #6

    Join Date
    May 2006
    Okinawa Japan
    WW & HCP - Thanks for the input...

    WW - the only thing left as far as rebuilding the carbs is to replace in the carbs is the diaphram - might have to try it since that's about the only thing left.

    HCP - That's strange that you're having the issue again after replacing the diaphrams. Did the problem go away for a while after you replaced them? Do you have the part # for the diaphram for the Novi 48s?

    I don't know what else to check so this weekend, I'm gonna leave it tied down on the trailer and back it into the water, start it up and then keep messing with the low speed screw until hopefully I solve it. Come to think of it, I might pull the low speed screw and inspect it then put it back in if ok. In theory, the low speed screw and the low speed jet control the idle so maybe my screw is messed up and I don't know it.

    Or it could be the following from the Mikuni tuning manual:

    “As the fuel in the chamber is drawn in by engine suction…” The engine suction only occurs at low rpms, then Air Velocity takes over.

    I need to double check the fuel flow at idle for that carb. Maybe I have an air leak that is causing low manifold pressure so the carb isn't flowing fuel until the air velocity takes over and draws enough...maybe that's whats causing the surge too...

    Damn - I really don't want to tear the ski apart just to double check it. Pulling the pipes is a pain in the arse...

    Anyway - Thanks for the help - I'll let ya'll know what I come up with...


  7. #7

    Join Date
    Aug 2006
    Ray, I've seen a simular problem a couple of times, and it was actually the plug wire broken internally. I would not have ever thought that a solid wire would break down inside, but it happens. It would have a spark, but I noticed it was a bit yellow, so I tried a test with the plug gapped way wide, and it wouldn't spark at all then.

    Another time on a Venture, I found the pickup coil in the stator for #2 cylinder had a broken wire also, it wasn't even kinked where it was broke, but when I checked it after it failed continuity test, I pulled on the leads and it pulled apart the vinyl insulation to exposed a burned and broken wire.

    Just some thoughts, good luck.

  8. #8
    Here is the part # 6R7-14541-00-00. The diaphram is for a super bn carb. I dont believe there is any differance in the diaphrams between 48's and 46's

    With me having a stock ignition(besides the advent) and you having MSD I find it hard to believe its a timing problem. But who knows.

    I pressure tested the motor before it went back in, everything ok there.

    Like you I really think its in the carb too. My novis are pretty old and my linkage is getting really worn out. I'm having a really hard time sinking the carbs. Especally at Idle. When I adjust the idle It almost takes one full turn of the idle screw on the #3 carb before the linkage catches up with the other two. Thought this might be a problem too.

  9. #9
    LT1GMC, If this were the case would it pass a resistance test? I tested everyting yesterday and it was ok in my boat.

    All three wires and coils were within spec and all on the high end of spec? Can you replace just the plug wire in these skis. I've seen people do it when the move the CDI boxes in their GPR's. But everytime I look at them it seems like they are part of the coil.

  10. #10
    All hail the Chief! fullboogie's Avatar
    Join Date
    Nov 2005
    Ray, I don't have any input on your problems, but it's good to see you posting again! Welcome back!

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