Single carb on RN confession

[XtSuperJet]

Hello guys, well as you probably read my other post about jetting recommendation for my new Novi 48 single carb with riva intake manifold. Well here is the story.

I thought (after doing a research in here) that single carb would solve my problems when it comes to surfing which is what I mostly do. I bought the single for ease of tuning and taking off for cleaning. What I had on mind (after reading almost all of the “single carb” posts in here) was, I would get better low end kick, might even be better than my stock 38s at the cost of not being able to run WOT for more than several seconds. Guess what, that just did not happen. The freaken single carb was just about the dumbest mod that I have ever done for my poor ski. It ran smother, but weak. I mean the thing just had no torque, and I did tune them right, at least for the low end, it did not bog or hesitate, it would be like, gas it and she goes, but it just did not have the arm ripping power that I had with my stock carbS. I spent the whole day trying to get it to at least hit as hard as my stock carbs but I just could not. So what did I do, I put my stock carbs back and oh my god, I almost cried of happiness, the power/torque is back, and I can run the ski at WOT for as long as I want. Now I know that single is just not the thing for me. I could live with spending an extra hour in taking my dual 38s off for cleaning every once in a while but I sure can not live with the power loss from going to single.

Bottom line, dual carbs are the way to go, I read that way too many times, but I just had to try it for myself, now I am a believer.


Ahmed

 

[unclehulka13]

Were you using that crappy 650 kawi manifold on the spacer/adapter plate? If so, i suggest you try some x cases or an atp manifold.

 

[waxhead]

yeah but think of the extra fuel economy you got on the single

 

[Mike W]

Are you sure it was jetted right? What was your jetting?

 

[XtSuperJet]

yeah I was using 650 kawi manifold on the Riva adapter plate.
I have 155 main, 135 low and 95 spring with 2.0 or 2.3 needle/seat. now that I think abou it, right of idle she seemed ok, but anything above half throtle was just flat weak. the thing that made me give up on the single so easily is just the fact that the performance that I got out of it (even if it was half way tuned right) was nothing compared to my stock 38s. I think it would have worked better if I had 61x case that as well as the fact that I will always have to becarfull of how much I run WOT for.

Ahmed

 

[SuperJETT]

That jetting sounds rich to me.

I also had a single 48 Novi on my ski, replaced dual 44's with it, then went with oem dual 44's, and the power was the same, just smoother.

Did you have a return line restrictor? Good fuel pressure?

Something was wrong if it wasn't better than your 38's.

 

[XtSuperJet]

I did have return line restrictor (60 main jet). But maybe I was on the rich side however, if it was rich enough, the RPMs would go up slowley right? in my case, the rpms will shoot right up as soon as I hit the gas, but she would not rip. it almost felt like it had slipping clutch in it (feeling wise that is).


Ahmed

 

[Matt_E]

What was the impeller used?

 

[sjetrider]

What was the impeller used?

i WOULD ASSUME IT WAS THE SAME PROP HE RAN W/ THE TWIN 38'S???

 

[sjetrider]

That jetting sounds rich to me.

I also had a single 48 Novi on my ski, replaced dual 44's with it, then went with oem dual 44's, and the power was the same, just smoother.

Did you have a return line restrictor? Good fuel pressure?

Something was wrong if it wasn't better than your 38's.

DONT MOST CARBS W/ FUEL PUMPS ON THEM ALREADY HAS A RESTRICTOR FOR RETURN FUEL? Would you need ANOTHER ONE????

 

[Matt_E]

DONT MOST CARBS W/ FUEL PUMPS ON THEM ALREADY HAS A RESTRICTOR FOR RETURN FUEL? Would you need ANOTHER ONE????

Most aftermarket carbs do not have a fuel line restrictor, pump or not. The restrictor is not part of the fuel pump, even on carbs that do have them.

 

[FL-cracker]

Sounds rich up top..... did you at least turn in the high speed to see if it got any better? If it got better as you turned it in, you need a smaller high speed jet.

Always remeber to do a hot stop, to ensure you dont lean it out too much.

If you do a hot stop (from WOT), and the plug is black of fuel you know your too rich!

 

[Endo]

Older carbs with the round pump required a restrictor.

 

[SuperJETT]

I did have return line restrictor (60 main jet). But maybe I was on the rich side however, if it was rich enough, the RPMs would go up slowley right? in my case, the rpms will shoot right up as soon as I hit the gas, but she would not rip. it almost felt like it had slipping clutch in it (feeling wise that is).


Ahmed

That's strange. I was running a similar setup, ported 701 with Speedwerx dry pipe and MSD total loss, and noticed no loss in power switching to the single 48 with an external fuel pump.

 

[XtSuperJet]

I tried messing with both needles to see if it will get better, I opened the top end to 2 and half turns (from one turn) and it got better in the high end. it also got better down below when I leaned the low needle a bit. so I know I was a bit rich on the low jet and lean on the main jet. I did not bother much with rejetting since I know that I will never get it rich enough up top (after reading SuperJETT post where he had the main out along with external pump and it did not do him much good). I might have got some more rip down low by leaning the low jet and or messing a bit with the pop off. But to be honest, I just could not see it hitting as hard as my stock duals espesially in the mid range and up. maybe my stock carbs are just perfectly tuned to start with.

oh I have been aloways using skat trak 12/17 prop.

I have heared of very few succesful stories when it comes to 62T and singles and that just put off my fire, but again, I am the kindda person who have to try for themselves to be a beleiver, and now I am.


Ahmed

 

[Matt_E]

I'm very happy with my single 48 Full Spec. Hits harder than my dual 44's did, can go WOT without a problem.

 

[Takeastand SJ]

I have a 62T, lots o porting, 84mm, etc with a single 48 powerbomb and it rips. Your single wasn't tuned correctly, I can't offer much help though because I wasn't the one who tuned mine.