importance of the correct return jet sizing
- Thread starter ryan0
- Start date
- Location
- Norwich United - Kingdom
I did all my initial set up at 1000 rpm, finally got race car running quite well, now fine tuning.
- Location
- Asheville, NC
Im glad I just stumbled across this thread... My ski runs great but I've always felt it could run better. After getting it tuned in last season I haven't had any issues except my ski drinks gas like nobody's business... Plus, I have black spooge out of the tail pipe to the point that exhaust soot is starting to collect on my dash. I highly suspect this return jet might be the missing link to an even better running ski. As of now, the ski starts and runs great all day long but I have a slight bog after nose stabs and tail stands. Im interested to see if this return jet makes a good difference! Will update eventually 
- Location
- Charlotte, NC
According to the novi instructions posted on page 1 by the OP, pressure should be checked at idle-2500 rpms with boat moving in the water. I checked mine on the trailer. Since then I purchased a liquid filled gauge and want to run a hose through the hood to check pressure while in the water moving like novi instructions say. I'll try both and see if its different
I just did this, or at least tried, on two skis last night. I ran a line through each pole and zip tied the gauge to the bars.
In both cases the pressure didn't even budge the needle on the gauge idling on the trailer, barely moved it idling in the water, I had a little over 1 psi riding as slow as possible (not on plane), and was about 2psi riding just barely on plane.
Both skis I am not willing to ride sustained wide open and if I was I definitely wouldn't be able to watch a gauge. The tamer of the two I could kind of grab a handful and get a general idea of what the gauge was doing. I couldn't tell you if it was going to 5psi or 6psi, but somewhere in there. I left it at an 80 main jet for the restrictor.
The rowdier of the two no way I could get even the faintest clue what the gauge was doing at wide open. I left it at 60 main jet partially because this one seemed lower on fuel pressure overall and it had old NOVI carbs and the 60 is what both the NOVI instructions and the builder said to use, and at idle it was if anything low on pressure according to my gauge. This surprised me it was a bigger motor so I was expecting higher fuel pressure.
Near as I can tell I'm in the ballpark with both of them, but after trying to do it, I'm having a hard time believing anybody is checking freestyle skis anywhere near wot. I don't see how it would be possible.
In both cases the pressure didn't even budge the needle on the gauge idling on the trailer, barely moved it idling in the water, I had a little over 1 psi riding as slow as possible (not on plane), and was about 2psi riding just barely on plane.
Both skis I am not willing to ride sustained wide open and if I was I definitely wouldn't be able to watch a gauge. The tamer of the two I could kind of grab a handful and get a general idea of what the gauge was doing. I couldn't tell you if it was going to 5psi or 6psi, but somewhere in there. I left it at an 80 main jet for the restrictor.
The rowdier of the two no way I could get even the faintest clue what the gauge was doing at wide open. I left it at 60 main jet partially because this one seemed lower on fuel pressure overall and it had old NOVI carbs and the 60 is what both the NOVI instructions and the builder said to use, and at idle it was if anything low on pressure according to my gauge. This surprised me it was a bigger motor so I was expecting higher fuel pressure.
Near as I can tell I'm in the ballpark with both of them, but after trying to do it, I'm having a hard time believing anybody is checking freestyle skis anywhere near wot. I don't see how it would be possible.
hornedogg79
dodgin' bass boats
I didn't check my fuel psi but switched to an .035" mig welding tip(.889mm) after reading this thread a few years ago. Before my ski would fall on its face if my low speed adjusters were less than 1.5turns out. Always had fuel droplets on my f/a's, black wet plugs, and sludge out the pipe. Now I'm able to run them at 7/8's and everything is crisp and clean. Plugs look like they're supposed to. It took care of a lot of head scratching for me. Setup is full spec 44's, external fuel pump, ss865.
- Location
- Charlotte, NC
Interesting. I checked my superjet with a 735, tnt ss chamber pipe, 200 psi with dual 44s and was getting 3.5psi psi at idle with ski strapped on a trailer. That was with a 70 restrictor. Went to the 80 jet and it was at 2.5 psi. Ski idled noticeably smoother with the 80 jet. I want to try again with a new gauge and not on the trailer. Also tried a buddies ss900 with dual 46s and got 3.5 psi with the 70 I had. Had nothing bigger to try at the time but have a 90 for it now to try
- Location
- Charlotte, NC
It's very strange how the higher fuel pressure almost causes a lean condition off idle. Mine was the same way with the 70 jet. Ran better the more I opened the low screws. Put the 80 in there and it was noticeably better
- Location
- Charlotte, NC
The first gauge I bought was a mr gasket from local auto parts store. New gauge got on Amazon and its liquid filled. 1st gauge isnt liquid filled and the needle moved all over the place. Was very difficult to determine actual number. Sounds like you might have a bad gauge.
I'm using a liquid filled gauge, but it is a cheap one from amazon. The bouncing of the needle is not too bad, but the accuracy of the gauge is definitely something that could be questioned since it's just a cheap amazon no name gauge.
Just did a quick calulation, it only takes about a 40 inch column of gasoline to make a psi of pressure, and when I was checking on the trailer I had the hoods off and the pole all the way up, so I am probably loosing around a psi at the gauge just from that when checking on the trailer.
Just did a quick calulation, it only takes about a 40 inch column of gasoline to make a psi of pressure, and when I was checking on the trailer I had the hoods off and the pole all the way up, so I am probably loosing around a psi at the gauge just from that when checking on the trailer.
- Location
- Norwich United - Kingdom
Hi All - good replies, thanks
I am now up to 6 psi fuel pressure using the changed Pop off valves,springs etc. I have 8 of the SBN carbs on the V8, each bank of 4 fed via a separate electric fuel pump. Each bank of 4 has return pipe to the tank. I have 1mm ( 0.040") orifice in each return pipe. Currently I am using 3.5 litre fuel per MINUTE!
I am now up to 6 psi fuel pressure using the changed Pop off valves,springs etc. I have 8 of the SBN carbs on the V8, each bank of 4 fed via a separate electric fuel pump. Each bank of 4 has return pipe to the tank. I have 1mm ( 0.040") orifice in each return pipe. Currently I am using 3.5 litre fuel per MINUTE!
- Location
- Charlotte, NC
I'm not sure how your situation will apply since you're running something I dont think anyone on here at least has tried. Just out of curiosity, why run the sbns on a v8 instead of a carb more designed for that type of application?
hornedogg79
dodgin' bass boats
Just some interesting food for thought. I have an Ultranautics Jetstar here that uses a single SBN 44. The return is capped shut from the factory.
- Location
- Norwich United - Kingdom
I decided to go SBN for safety reasons. I race in Hill Climbs & sprints, something like Pikes Peak. If I had/have an accident and car turns over with the float chambered carbs, there would be lots of fuel spillage - potential fire. THE SBN's offered a good solution and, once tuned, do provide a very good system. I was tempted towards EFI but at 77 years old it was too much of an unknown. Dont forget - installing with horizontal crankshaft, all OMC carbs were not suitable. We are now looking at a new V8 engine with EFI directly injected into cylinder heads - only exhaust port involved, EFI infinitely tuneable via my new team members! - ANY ideas/thoughts?
- Location
- Norwich United - Kingdom
Hi Kevbo - With 8 carbs involved, the return at a highish pressure is VERY important. With 6 psi it evenly distributes fuel to all 8, fills all chambers, allows the Pop Off valves to function and finally clear any air etc. back to the tank. Multiple SBN's will not function without an effective return line.