STILL need some help with tuning!

[Waternut]

I can understand not wanting to go total loss when you ride surf all the time. Plus total loss and a high compression head would easily cost about $1000 used and closer to $2000 new together. I would think if yamanube could afford that, he wouldn't be running the frankenstein motor that he is.

I've got a 135 main jet I'll send you if you want to try it but that seems excessively small compared to what you're running. Surely someone in that crew down there could hook you up with a handful of jets to try. Takes 5 minutes to swap jets on the beach and you'll instantly know if it made it better or worse. I can't see pulling the intake grate helping any. If the prop was too big, it wouldn't be snappy off the bottom.

 

[D-Roc]

Stock with WW cone.

go measure it and see what "stock" is.

 

[D-Roc]

]I can understand not wanting to go total loss when you ride surf all the time. Plus total loss and a high compression head would easily cost about $1000 used and closer to $2000 new together. I would think if yamanube could afford that, he wouldn't be running the frankenstein motor that he is. [/B]

I've got a 135 main jet I'll send you if you want to try it but that seems excessively small compared to what you're running. Surely someone in that crew down there could hook you up with a handful of jets to try. Takes 5 minutes to swap jets on the beach and you'll instantly know if it made it better or worse. I can't see pulling the intake grate helping any. If the prop was too big, it wouldn't be snappy off the bottom.

yeah good point, but it may be part of the solution to getting this combo to work good. unfortunatly.

 

[yamanube]

I can understand not wanting to go total loss when you ride surf all the time. Plus total loss and a high compression head would easily cost about $1000 used and closer to $2000 new together. I would think if yamanube could afford that, he wouldn't be running the frankenstein motor that he is.

I've got a 135 main jet I'll send you if you want to try it but that seems excessively small compared to what you're running. Surely someone in that crew down there could hook you up with a handful of jets to try. Takes 5 minutes to swap jets on the beach and you'll instantly know if it made it better or worse. I can't see pulling the intake grate helping any. If the prop was too big, it wouldn't be snappy off the bottom.

I have a decent selection of jets, my powerbomb has been everywhere from 115/130 up to 150/160 with similar issues. I don't plan on putting a 135 main jet in it.

 

[D-Roc]

how much pop off have you changed?

 

[yamanube]

how much pop off have you changed?

In the PB I ran a 2.5NS with 115g spring and 95g spring and 1.5NS with an 80g spring and 65g spring (to try out both extremes) in the 44 I have run a 2.5NS with 115g and currently 2.0 with 80g.

 

[D-Roc]

this is what my powerbomb came with from riva as a single.
Main Jet: 135
Pilot: 150
N/S 2.5
Spring 115
Pop off 20-22lbs
Low adj.....1 turn (tune for idle)
High adj.....1 turn (tune for highest rpm)

i came up with different jetting when for when i switched to duals.

 

[BruceSki]

Raise the compression.....

I ran a borrowed 760 62T motor before for a short time. The first thing I was told is, the only way this thing makes power is with compression. Bump it way up. Get #.0 to mill and oring a 760 stock head for you. thats your cheapest way out and he is semi-local.

 

[D-Roc]

man, no one can say you haven't tried stuff!!!!

 

[Waternut]

I have a decent selection of jets, my powerbomb has been everywhere from 115/130 up to 150/160 with similar issues. I don't plan on putting a 135 main jet in it.

Didn't the powerbomb require an inline restrictor adding complication while the OEM carb has it built in?

On a side note... If you can't get this engine tuned fairly soon, it is my recommendation that you work towards another used top end or cylinder. High compression and total loss is AWESOME. However, buying a high compression head or total loss as a band aid to something that you can't fix isn't a wise choice in my opinion.

 

[D-Roc]

The TL and compression it is what is needed to compensate for the port timing of the 760 cylinder. without it, it may never get tuned to the point that it works better than a 61x cylinder without the tl and head. i think getting the oem head milled like was suggested is a pretty cheap way to gain some power.

 

[Jr Freestyle]

what is your reduction nozzle diameter?

hahaha

 

[D-Roc]

Also I am running a 14/18 concord and as CarterB and I discussed the other day it is likely overpitched BUT I have run it on all my motor setups in the past 5 years, including a bone stock '06 superjet and they all seemed to push it very well.

haha?

 

[yamanube]

I really don't think TL ignition is the only way to make this motor run well, I am not the only person to run 760 cylinders on X cases. I think you guys may be over thinking it a little.

 

[D-Roc]

your right, matte and motoman both did it and they used some compression to get the desired performance. you have tried alot of jetting, tried a smaller carb. but still not compression. also the other thing that is probably different from mattE and motoman is your pump setup. the prop is kinda steep and that cylinder may not have ideal bottom end porting so with an overpitched prop the motor could be working a bit harder trying to push the water out of your oem sized reduction nozzle. it was just a thought. tl will help your bottom end, but that is not an option for you as stated. if your not slipping your prop at all you could open the reduction nozzle. i have mine at 85mm

 

[BruceSki]

I did it on a borrowed motor that was already tuned with dual 44's.

I know that it had a bunch of compression though. that's all I was suggesting.



I was running the same pump setup I ran with a similarly (bolt-on) modded 701. 12/17 mag swirl with a TBM pump cone.

The ski ran just about the same. I lost a touch of bottom end snap, but gained a bit of midrange/top.





All my information is out the window though because nube is running 61X cases.

 

[yamanube]

I appreciate all the help guys, I don't want it to seem like I am disregarding any suggestions I just have a limited budget at the moment and don't want to throw parts at it that don't help solve my issue. I am much less concerned with making a bunch of power as I am with making smooth, consistent power. This motor really launched my REV, just gotta find the right combo in my stupidjet.

 

[D-Roc]

good luck, let us know if you figure it out.

 

[KTM434]

If you still havnt figured it out and you wanna try bumping your compression on a budget you could try a stock 701 head on the 760 cylinder. That will give you 185 psi compression although its not the best setup to run permanently its a quick way to tell if compression is the missing part of your equation. I swapped a 760 into one of my B1s and it has a Protec pipe so i needed the exhaust mounts on the 61x head to mount my pipe so I ran that head on the 760 temporarily until I bought my ADA head and 760 domes. Although the squish was not too tight to run I did have some detonation and I blew a couple headgaskets (cheap ones I got from a friend). I do agree that you may be masking a problem but that prop is a steep pitch so if you dont have the money to buy a prop, head, total loss, etc. this could be something just to try

 

[yamanube]

Picked up a billet head that should put me up around 185lbs but won't likely have my ski together anytime soon to try it out.