Struggling 3-fo-six

[Dolkitafreak]

Been working on this 346 for a hot minute now, just for some reason isn't running the way I'd like. Whole build was inspired by a redhead I ran a year ago so I wanted to give it a go.

Saw had squish and base cut (.075") and I was seeing ~185psi at my elevation, I wanted more. I then had the chamber welded and its blowing 230 now, nifty. The Jred had 240, and finger ports. My numbers (I need to check my notes but I believe I remember correctly) are 101-118-82, I am not running fingers currently. My saw and the jred are running walbro 359 carbs. Similar muffler mods (big *a-hole out the front). Jreds numbers are similar to mine (I know numbers aren't everything, starting point though). My transfer roofs are flat both main and secondary, I feel I should have angled secondary more upwards.

Saw runs okay, but wouldn't hang with the jred I don't think. Someone told me they think compression may be holding it back, so I'm gonna stick another base gasket in and see what its like. Currently winds up to 14.4ish with a little four stroke. Square work chain in the video. Any helpful advice, questions, etc. is more than appreciated.

https://youtube.com/shorts/TbfcOS2dXSg?feature=share

 

[huskihl]

How far is the timing advanced? A little advance will help, but too much will definitely prevent higher RPMs

 

[Dolkitafreak]

How far is the timing advanced? A little advance will help, but too much will definitely prevent higher RPMs

Timing is stock.

 

[huskihl]

Timing is stock.

Well that’s a turd LOL

 

[Dolkitafreak]

Well that’s a turd LOL

Indeed, I'm not thrilled lol. I really figured with the exhaust that high it would spool higher. Just hasn't hit that magic feel yet.

 

[huskihl]

Indeed, I'm not thrilled lol. I really figured with the exhaust that high it would spool higher. Just hasn't hit that magic feel yet.

Yes something is up with it. I would try a different coil. I’ve seen 17,000 out of a 104° exhaust

 

[Dolkitafreak]

Yes something is up with it. I would try a different coil. I’ve seen 17,000 out of a 104° exhaust

I can make it turn higher its just lean when doing it. Coldish I can make it hit 15.5, once it gets some heat in it then its lean. Someone asked if the carb was good, I may try another. I'm just discouraged at this point!

 

[srcarr52]

I think you have way too much intake duration such that you've killed your crankcase compression, especially with that short of blowdown I bet it's back flowing the transfers at higher RPM.

 

[Dolkitafreak]

I think you have way too much intake duration such that you've killed your crankcase compression, especially with that short of blowdown I bet it's back flowing the transfers at higher RPM.

Raise to 75 maybe?

 

[Dolkitafreak]

I think you have way too much intake duration such that you've killed your crankcase compression, especially with that short of blowdown I bet it's back flowing the transfers at higher RPM.

I could absolutely see this being the case, uppers had to be raised quite a bit, and by the time I case matched and rounded the divider in the lowers, there is a whole lot of volume!

 

[srcarr52]

Raise to 75 maybe?

You could epoxy the intake and get it back to 75-77 you'd be in better shape, you'll probably gain some RPM but probably not a lot of torque. It's also a lot more ex duration than I've ever ran in one. I've found that smaller bore saws like less duration all around, they just don't need that much time*area to fill/exhaust the small cylinder.

 

[Dolkitafreak]

You could epoxy the intake and get it back to 75-77 you'd be in better shape, you'll probably gain some RPM but probably not a lot of torque. It's also a lot more ex duration than I've ever ran in one. I've found that smaller bore saws like less duration all around, they just don't need that much time*area to fill/exhaust the small cylinder.

I would tend to agree, the saw I'm attempting to copy was just a mean sob. Normally on a 50cc motor I'm 104-105 and 78ish on intake.

 

[Bjorn]

I think you have way too much intake duration such that you've killed your crankcase compression, especially with that short of blowdown I bet it's back flowing the transfers at higher RPM.

Hello, Will crankstuffers help the crankcase compression, When running hi intake duration like 82 btdc.

 

[srcarr52]

View attachment 302788 Hello, Will crankstuffers help the crankcase compression, When running hi intake duration like 82 btdc.

Yes! I had forgot that 550 crank stuffers will fit on a 346 crank with a little modification.

 

[Dolkitafreak]

View attachment 302788 Hello, Will crankstuffers help the crankcase compression, When running hi intake duration like 82 btdc.

With stuffers your intake timing should be just fine! I am unsure what is causing the issue you messaged me about.

 

[Dolkitafreak]

I think I'm fighting a few issues here, just figured I would share my thoughts.

1. Blowdown, with my exhaust as high as it is, I think the saw would benefit with more blowdown.
2. Transfer staggering, currently my uppers all have flat roofs and open at the same time, I think if my secondaries pointed upwards at the plug and opened 2-3 degrees later it would likely help.
3. Intake is low, but not sure if it is low enough to be causing me issues, my thinking was at high rpm you don't have much time to fill the case. Intake isn't wide, just low.

Thoughts, concerns, general comments of "you suck, get outta here"? all welcome and appreciated.

 

[srcarr52]

I think I'm fighting a few issues here, just figured I would share my thoughts.

1. Blowdown, with my exhaust as high as it is, I think the saw would benefit with more blowdown.
2. Transfer staggering, currently my uppers all have flat roofs and open at the same time, I think if my secondaries pointed upwards at the plug and opened 2-3 degrees later it would likely help.
3. Intake is low, but not sure if it is low enough to be causing me issues, my thinking was at high rpm you don't have much time to fill the case. Intake isn't wide, just low.

Thoughts, concerns, general comments of "you suck, get outta here"? all welcome and appreciated.

I agree with 1 and 2, 3 depends on the carb size.

 

[Dolkitafreak]

I haven't decided what to do, I'm not sure if this cylinder can be saved or if I should just toss it and start again.

 

[srcarr52]

I haven't decided what to do, I'm not sure if this cylinder can be saved or if I should just toss it and start again.

Epoxy!

 

[Dolkitafreak]

Epoxy!

What about blowdown issue? Will epoxy hold in the upper transfers? Already planned on it for the intake.