1995 WaveRaider DLX 701 62T missing at partial throttle only

[Zak]

I have a 1995 WaveRaider Deluxe with the 701 62T engine with dual 38 mm carbs. I just put an SBT rebuilt engine in it and rebuilt the rear cylinder carb at the same time (reused the original pop-off spring and arm). I also switched from oil injection to 40:1 premix. All jets, needles, flame arrester, etc are factory stock.

The ski runs fine at low speeds and at 3/4-WOT, but there is a portion of partial throttle where it sounds like it loads up and starts to miss. It runs fine from 0-7 mph and 35 mph and above. Trying to target anything inbetween 7-35 mph, however, usually results in the missing condition. I'd say this is happening around 1/4 - 1/3 throttle. Once it starts to miss at low throttle, if I go to a higher throttle percentage, it will continue to miss for a bit until it clears out and then starts to run fine.

I have tried a new set of plugs, but that didn't seem to affect the condition. I have also tried the stock pop-off spring and the longer spring from the SBT carb rebuild kit without much difference. Any ideas what I should try next (pop-off spring, low speed jet, etc)?

Thanks,
Zak

[Technical Support]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

What happened to your original engine and what repairs were made? Where are your carb screws set at?

[Zak]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

The old engine seized the rear cylinder with no symptoms before the seize. It ran fine right up until it seized. I don't know what caused the seize, so I switched to premix and rebuilt the rear carb to cover my bases. The new rebuilt engine is from SBT.

I put the carb screw settings on the rear carb back to where they were (High speed screw 2 turns out / low speed screw 3/4 of a turn out) after the rebuild. I believe the front carb screws are at the factory settings since I have never messed with them. I have tried adjusting the rear carb low speed screw with no improvement.

Could there be that much difference between the rebuilt engine and the old engine that the jets would need to be changed? Could something have gone wrong during the carb rebuild that could be causing these symptoms? I'm leaning away from ignition issues since it seems so throttle position related.

Thanks,
Zak

[Technical Support]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

Your rear high speed is only supposed to be out 1 1/8. You are almost a full turn too rich, which will make it run like crap. And yes, it's possible you did not build the carb right, and more likely, you ALSO should have done the front as well. If something got into the rear wouldn't you think the front could also be effected?

[Zak]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

The high speed screw is the same two turns out that it was when the old motor was running fine, but if you think it might work, I'll try turning it in to see if that helps. It was my understanding that the high speed screw would not have much affect at the throttle positions where I am having the miss. Full throttle, where the high speed screw is most important, seems fine. From what I have read, the pop-off pressure or low speed jet is more likely to be affecting the 1/4-1/3 throttle position where I am getting the miss.

I realize that there could have been an issue with the carb rebuild, but I was hoping someone here might have an idea of what type of problem to look for that might cause these symptoms. I'd suspect that the list of problems to cause these fairly specific symptoms (runs fine from 0-7 mph and runs fine from 35-50 mph but misses when targeting 8-30 mph which requires about 1/4-1/3 throttle) would have to be pretty small. Tearing the carb apart isn't going to help much if I don't know what areas to look more closely at.

When I rebuilt the rear carb, I didn't find anything amiss. There was a very small amount of particles in the filter, but nothing was clogged. I did remove the jets in the front carb to make sure they were clear, but I didn't see any reason to go further since the old engine ran fine and the front cylinder had no issues.

Thanks,
Zak

[uncle-buck]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

I had a similar problem with a Venture 700. It ran poorly between 5 and 15 mph. Rebuilding the carbs helped a little. Broke part of the body on one carb by accident - so I bought a pair of "take off" carbs. Now it runs great.

Go with tech's advice first. Rebuild the other carb and start with stock settings on both. Then, go from there.

[Zak]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

I'm pretty sure it is the rear cylinder that is missing. I don't see how rebuilding the front carb would help that. I had never changed the high-speed screw settings, so I have a feeling they were stock to begin with (even though they didn't match what the Tech said). The old motor also didn't have this problem with these same settings. I did try turning in the high speed screw to the recomended setting, but the miss problem remained unaffected.

Thanks,
Zak

[skraggy]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

And how are you so sure it is the rear cyl. missing ?

And did you check the reeds before reassembling ?


And I would agree with Tech....Rebuild both carbs...Even if one is not bad....
That would be kinda like just changing one spark plug.

[Zak]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

The front sparkplug looks normal, but the rear sparkplug looks wetter if I bring it in after it has been missing.

I did check the reeds and they looked fine.

Zak

[SP]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

get a pop off pressure guage and read the pressure the needle pops-off while the return line is pinched, that can even be done in the boat.

For sure when replacing a motor, rebuild the carb, thats a given.

For sure you should see what the old setting is on the front carb by counting the # of turns before it gently seats.

My guess is it's a pop-off pressure or carb needle problem.

When you rebuilt the carbs did you leave the needle arm flush with the adjacent carb bidy or just .020 above (a must)?

[Zak]

Re: 1995 WaveRaider DLX 701 62T missing at partial throttle only

SP,

I'll have to look into getting a pop-off gauge. When I first put the carb back together, I used the original needle arm and spring to (I thought) avoid any pop-off pressure issues. The needle arm, therefore, should have been set correctly in relation to the carb body. I have since tried the needle arm and the longest spring from the SBT rebuild kit with no improvement. I'm not sure what I would do to raise the pop-off pressure further than it is now. Would I be able to find a stiffer spring than the OE or the long one from the SBT rebuild kit?

Thanks,
Zak