jetting setup for 46 and 770 62t.

[jvann13]

I have 38’s right now and have finally got them jetted pretty well (based on my limited knowledge). I am sick of dealing with the duals. I am still a novice with jetting and it will be a lot easier to learn on a single, so please don’t try to convince me to stick with duels. I have done a lot of searches on this site and I think a single will be a good match with what I am wanting.

I have been searching to find the right set up but all I can find is jetting for the 701 with a 46. Can anyone give a good starting point for what I have? Is the jetting close to the same for 701 and 770 (I would not think so)?

My setup is:
Engine 62T Cases non ported.
62T Jug (OEM) 85 mm weisco (looks to be mild port not professional)
Carb OEM 38's prok arrestors (will be changed to new style ATP mani and 46 SBN)
Carbon tech reeds
Exhaust B-Pipe front and rear exhaust
Electical is totally redone by JSS.
Rad flywheel


What I think I will start with for jetting:
150 main
130 pilot
2.0 with a 95 or 80 spring. (need to get a pop off gauge first)

What do you guys think?? Any suggestion on what I might have missed?? Any advice??

PS: In a year or so I will be sending this off to get it ported and tuned by a pro. So that is not a option right now.

 

[jvann13]

Anyone??

 

[SUPERTUNE]

Sometimes I think singles are hard to tune...I like duals! (more HP)
Sounds like a good start, but might need a 2.3 needle valve W/80 gram spring depending on how high the compression is.
The ATP manifold likes richer jet settings than the conversion single manifolds and way different than 61x single cases.

 

[jvann13]

Thanks Supertune. I will stop and order the 2.3. It is the only needle valve I don’t have.

I am willing to loss a few HP’s for the simplicity of the single. When I need more power I can get the engine ported. I think that will more than make up for the loss in power from a single.

I know I am in the minority when it comes to wanting a single but I get pissed every time I have to pull the duals off the ski. Takes me like 3 min to change the jetting but it takes me 30 min just to get them on and off (the two inside bolts kill me). With the single I should be able get the carb off and back on in less than 5 min. I am sure I will be pulling the carb a lot to get it the jetting right.

What make the single harder to tune??

 

[SUPERTUNE]

Thanks Supertune. I will stop and order the 2.3. It is the only needle valve I don’t have.

I am willing to loss a few HP’s for the simplicity of the single. When I need more power I can get the engine ported. I think that will more than make up for the loss in power from a single.

I know I am in the minority when it comes to wanting a single but I get pissed every time I have to pull the duals off the ski. Takes me like 3 min to change the jetting but it takes me 30 min just to get them on and off (the two inside bolts kill me). With the single I should be able get the carb off and back on in less than 5 min. I am sure I will be pulling the carb a lot to get it the jetting right.

What make the single harder to tune??

This is why we use the aftermarket Boyesen intake manifolds (and sometimes Full Spectrum 49's) with the removable top plate.
Maybe because our engine packages require a lot of fuel so that just makes it harder for me...I put a single on a 862cc and with a 48mm novi carb, I had to use like a 160 pilot and 192.5 main!

 

[SUPERTUNE]

Here's some info that I ran across that Group K has stated about singles carbs...
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About Single Carb Setups

For reasons of desired simplicity and ease of tuning, some freestyle owners have converted their 62T cased engines to a single carb layout (running a single carb from 44mm – 48mm). Even though this is a setup that Yamaha has adapted to some oem models, we consider this to be a very poor choice for the 845 or any other any other freestyle setup for that matter….. here is why.

As mentioned above, maintaining the strongest possible inlet “signal” to the carbs is crucially important for any freestyle setup that is expected to have instant acceleration and precise fuel metering. Unfortunately, the “two into one” inlet manifold used for the 62T single carb conversion brings with it a huge increase in total inlet tract volume (much more volume than the individual runners on a dual setup). The increased volume of this manifold dramatically reduces the signal that is so badly needed for instant throttle response and precise fuel metering. Yamaha engineers were fully aware of this problem when they designed the very low volume 2-into-1 manifolding of the stock (61X) 701 crankcase/manifold setup. While this earlier 61X single carb case design is not “chic” technical fashion for hardcore free-stylers, the 61X cases are definitely the lowest-volume and highest-signal single carb manifold setup available. Even though the 61X reeds are slightly smaller than the 62T reeds, that difference does not out weigh the difference in inlet signal. The larger reeds of the 62T motor may be an advantage on an extremely high rpm closed-course racing package, but no freestyle setup needs to turn up into that extremely high rpm range.

All that said, we contend that the exceptionally strong inlet signal of the 845 makes dual 44s as easy to keep in tune as any single carb setup. Can a single 46/48 on 62T cases work okay on the 845??.... Likely so… would it equal the response or acceleration of well jetted duals?? …. No way.

For owners that are absolutely dead set on running a single carb setup anyway, we would strongly recommend they consider using 61X cases instead of the 62T cases. It bears noting that on our single carb 61X packages, we modify the stock 61X manifolds to further reduce inlet manifold volume and increase signal …. It makes a difference in throttle response that can be easily felt on any single carb engine setup.

 

[jvann13]

Thanks for the info supertune. If I go back to duals i will have to get one of the after market intake manifolds.

I hope to have my new set up ready to test this weekend. I will report back.

 

[jvann13]

Alright. After running into a few snags, I am working on the jetting.

I have tried the following

First: Spring 80
Seat 2.3
Main 155
Pilot 132.5

Second: Spring 80
Seat 2.3
Main 155
Pilot 130

It runs ok on top (still a little rich but ok).
The bottom is consistent but kind of blubbery or rough. It is like this from idle to somewhere between quarter and half throttle. At this point is cleans up and pulls strong to full throttle. What should I try? The smaller pilot did change much if anything. I think it is the spring and seat. I am not sure which way to go.

 

[oxnard111]

Take a look at my post. I ran this exact same jetting before I ported my cylinder and it ran well. I just had the screws turned in a little more than on the ported cylinder

http://www.x-h2o.com/threads/53061/post-704785#post704785

take a look at post #4 and post #6

 

[ATS_Aaron]

It runs ok on top (still a little rich but ok).
The bottom is consistent but kind of blubbery or rough. It is like this from idle to somewhere between quarter and half throttle. At this point is cleans up and pulls strong to full throttle. What should I try? The smaller pilot did change much if anything. I think it is the spring and seat. I am not sure which way to go.

1. Check your pop-off with a gauge. Almost every carb guy I have ever talked to recommends about 18 psi pop-off on a freestyle ski.

Setting up the low speed stuff is pretty easy. The following is from GroupK:

LOW SPEED ADJUSTMENT 0% to 35% throttle range - In 90% of all cases, the low speed mixture screw can be accurately set without riding the machine. Secure the boat on a submerged trailer or standing in about three feet of water. With the engine completely warmed up, set the carb up to a slightly higher than normal steady idle. Turn the low speed mixture screw in or out in 1/4 turn increments. As you get closer to the ideal setting, the engine rpm's will increase. If the idle speed is increased by this mixture adjustment, turn the idle speed adjustment screw down and continue the same process in 1/8 turn increments. At the ideal mixture setting, 1/8 turn in a richer or leaner direction will cause a very un-steady idle and cause the engine to die. To confirm your perfect low speed mixture setting, touch the kill button during idling...and then touch the start button about ten seconds later. The engine should restart instantly and idle steadily without touching the throttle.

If you find that your ideal mixture setting is less than 1/2 turn out from bottoming, you should probably consider going to a slightly leaner (smaller number) internal low speed jet. If you find that your ideal setting is beyond 2 turns out, you should consider a slightly richer (larger number) internal low speed jet.

I have been slowly getting my ski dialed in this summer and I am amazed at how what seemed acceptable just 2 months ago would constitute a total dog by how my ski runs now. Stick with it and don't give up just because it rides "OK for now."

Aaron

 

[jvann13]

Thanks guys. I am going to get this right.

My plugs are just plain wet. Not sure what that means?
It is drinking fuel like a big bore stroker.

I think I will try:
Spring 95
Seat 2.3
Main 150
Pilot 130

Any comments??

 

[kevbo]

Are you sure its rich enough at WOT? Using other peoples carb specs is inviting disaster. Make it fourcycle at full throttle and lean in from there. Your flame arrestor will play a big roll in determining the correct main jet with oversize carbs.