Single Riva PowerBomb tuning advise

[sjetrider]

Any advise apreciated. Bought a new Riva PowerBomb from Thrust. Great seller by the way.
I am not real familuar with single carb tuning so figured I would ask some of you all who are.

My set up is simple on this ski.
Yamaha Suoerjet

62T cases
Your (Riva) single intake conversion.
Single 48mm Riva PowerBomb carb
Ported 84mm 64U cylinder
185 compression
MSD Enhancer
Factory B pipe
Lightened OEM Flywheel


I currently in the carb
140 pilot
170 main
2.0 N/S
65 grahm spring
Current pop off is 16psi

1 turn out on bottom and 1.5 turns out on top.

If I turn in to a crisp feel on bottom screw I get a hesitation when I let off the throttle and then gas again (seams lean). But if I back the screw out to get rid of the hesitation after mid throttle pass then it feels dirty and sluggish on bottom.

Please advise your suggestions.

 

[Mark44]

Tune with a tachometer and not to feel that will but you spot on. There is a good thread in the tech section from Randy at Watcon.

Mark44

 

[Winter X2]

make sure all your intake mani screws are tight and make sure your reeds are good. Carb could be tuned and you could be losing fuel. Just something stupid before you get to technical.

 

[CARBONX2]

At how many turns on the LS screw does it idle best?
If popoff and jet totals are correct, then need to raise pilot and lower main accordingly.

 

[sjetrider]

It begins to idle up at 2/3 turn on trlr.
My next option was going to be raising the popoff and increasing the lower jet?
Generally if I have a lean spot when I let off from half throttle and gas it again but not right from bottom I simply increase the pilot jet. But as I said it get dirty and less crisp when I increased the pilot from 137.5 to 140 unless I turn in to 2/3 turn out and then I have the lead spot.
I may try the increasing the pilot and decreasing the Main, but it seems like I would be richening the bottom and leaning the top that way. Maybe this carb is all about even overall jetting????? Again I am used to duals and non reverse jetting so I am thinking this one is just outside my thought process. I did email Riva for recomendations but from what I understand I cant really expect an answer from them.

 

[Matt_E]

Do you run a restrictor?

That seems like huge jetting and low popoff. Makes me think this carb has signal issues.
Anyways, back when I ran a single PB48, I used a 60 Main in the return line.
My jetting was far smaller, something like 130 Main and 115 pilot (I think, check the carb database thread).
Based on what I've read about PowerBombs in the past couple years, I think the design has changed to where that jetting no longer works.

If I turn in to a crisp feel on bottom screw I get a hesitation when I let off the throttle and then gas again (seams lean). But if I back the screw out to get rid of the hesitation after mid throttle pass then it feels dirty and sluggish on bottom

Sounds like it needs really low popoff (weak on signal)(, but it is so low that it loads up at low RPM due to shaking.

 

[sjetrider]

Do you run a restrictor?

That seems like huge jetting and low popoff. Makes me think this carb has signal issues.
Anyways, back when I ran a single PB48, I used a 60 Main in the return line.
My jetting was far smaller, something like 130 Main and 115 pilot (I think, check the carb database thread).
Based on what I've read about PowerBombs in the past couple years, I think the design has changed to where that jetting no longer works.



Sounds like it needs really low popoff (weak on signal)(, but it is so low that it loads up at low RPM due to shaking.

The restricter is not drilled out of this carb. I would normally run one but it appears to have the OEM 60 in the pump side. It may not be a 60. I will put one in line and see if that is the issue. I kinda thought the same as you (about it running like it had no restricter) but I checked it and it was not drilled out.

The ski runs ok, this is not a case of the ski running horrible buy any means, I rode it in the surf all weekend set the way it is and had a blast, but it could be crisper on bottom and I feel like it should be without the occasional hesitation. I really have to make it hesitate while testing most of the time.
Keep in mind I am no stranger to tuning and am looking for more info on a set up new to me and looking to get MAXIMUM power from this carb, not just decent power. I feel like it should be a good carb and should do better. If not then its off with its head and on to a full spec. or something else that provides maximum, crisp bottom end throttle response.

I do appretiate any and ALL input however as this is what I feel these boards are for. While it may not help me in this particular situation, it will certainly help someone else down the road or me on a later project.

thanks

 

[loictahiti]

I know, its very old thread, but I m in same situation with one 48 Powerbomb
Finaly, did you find THE good jetting ?
Thanks

 

[Mike W]

I know, its very old thread, but I m in same situation with one 48 Powerbomb
Finaly, did you find THE good jetting ?
Thanks

@sjetrider