Braapp-Shack/SCARR Engineering 394 build, DONE :)

[srcarr52]

Wow, you REALLY open that exhaust up eh? You don't delete the heat shield as well, do you?

DO NOT remove the heat shield. It's there to make the air from the flywheel flow through the cylinder. Without it, the majority of the air would go straight out by the exhaust and the rest of the cylinder would be hot.

 

[RIDE-RED 350r]

I wasn't going to. Mind was a little blown there for a second, lol!

 

[jmssaws]

Jason what did that leave for meat from top of ring to top of piston? Did it leave at least .100

040 off leaves. 100

 

[redlinefever]

Thanks

 

[Moparmyway]

I love a good 394 !!

Thats after 5 pulls and hot.
It ain't easy getting this one started !

 

[jmssaws]

Here's the last one I did, ran it this morning some.

 

[RIDE-RED 350r]

Well, she is sooooooooooo close! I think I need a new carb, more on that later.

First thing I did was get the degree wheel on it and see where the timing number were after Shaun's work. Found exhaust to be at 108, transfers at 116 and intake at 75. Shaun raised the transfers for me as I do not yet have the right tools to allow me to raise them as much as they needed to be after having the base and squish cut, that being the case I knew I had some grinding to do on the exhaust. BTW: Shaun's work is top shelf, thank you Sir!

I raised the exhaust to 98 (boy was that some grinding!) and after much consideration I decided to leave the exhaust port at stock width for now. I can always go back in and widen it if I feel the need, can't put material back in once it's ground out. I also chose to leave the intake where it fell at 75 and opted not to widen it any. Looking at the piston skirt wear patter in the cylinder adjacent to the intake I decided I didn't want to remove any more piston skirt support as it looks like there already isn't a heck of alot. Again, if I feel the need, I can always go back in. I also found that I have 40 deg rotation from the time transfers open to intake closed and my thoughts are that I want to keep the crankcase compression strong. Over all I decided to play a little more conservative with this cylinder, they aren't making 394 cylinders any more, and I figure I'd like to try it as-is. I may go back in at a later time.

Here is the exhaust port, I'm really happy with hot it turned out. I think it's the best exhaust port I've done so far.








Some pics of it coming together

 

[RIDE-RED 350r]

Having a miserable time trying to upload pics... Got a couple up there but now it won't load any more...

Anyhow, on to why I think I need a carb....

Saw started and ran, high end responds to tuning very well and boy does it sound MEAN! However, the low end is a little lean and absolutely REFUSES to respond to tuning. It's idling a little too fast, idle screw is all the way out and throttle is fully closed, but still it's idling a little fast. Funny thing is that it still pops, doesn't sound lean to the point of a smooth lean bog... But the fact that I can't get it to richen up down low no matter what has me irritated. I swapped a carb from another 394 that had issues in just to see if the problem followed the carb and my 394 ran with the exact same querks on that carb that the other 394 suffered on that carb. I'm convinced there is something wrong with the low side circuit on my carb. I did put a kit in it, and also tried experimenting with raising the meter lever twice with only marginal improvement. High side still runs strong and responds well to adjustment. I set both H and L needles at 1.5 turns out for initial start up. High side 4-stroked well and I closed it down to about 1.25 turns and it cleaned up but still was safely 4-stroking a bit. I could cut it down a little bit more yet... Low side, still unresponsive and not rich enough. SO, if anyone has a KNOWN GOOD working 394 carb, I'm looking for one. Mine is the WJ39.

Compression: Pulled over 7 or 8 times with throttle wide open and she built 210psi. Holy cow does that thing have compression!

Overall, I'm real happy with how this has turned out, aside form the carb issue.

Note: new fuel line, filter, and carb kit. Carb didn't look bad at all inside....

 

[jmssaws]

You are leaving a lot of power on the table with the intake that high.

 

[RIDE-RED 350r]

You are leaving a lot of power on the table with the intake that high.

Think so?? I remember you posting some numbers earlier in this thread for 78 on the intake, but if I recall your transfers were a couple of degrees higher than mine. That's why I decided to leave it at 75 for the time being. I may yet go back in after running it a bit, nothing has been ruled out.

I really appreciate the advice you have given along the way.

 

[RIDE-RED 350r]

Trying pics again....

 

[jmssaws]

I will use 78 if the exhaust is 101+
At 98 you need more intake or you waisted your time raising it that far.
Intake duration won't hurt these saws,since Shaun raised then that far I'm sure he had around 80 and 98.5 to 99 on the exhaust.
Your to far under square.

 

[RIDE-RED 350r]

OK, you've convinced me to go back in. I got the exhaust at 98 right on the nose.

 

[RIDE-RED 350r]

Thinking about my carb issue... When I put the new kit in, I noticed that the pump diaphragm (opposite side from the metering diaphragm) was black and pretty thin. My kit came with two tan weaved looking diaphragms that matched up to the black on I installed. Is there a chance that I need to put the old black diaphragm back in?? Is it possible that the reason for my low end issue is the different color/material diaphragm? The old one looked fine..... I almost remember this happening on another 394 I did... I could almost swear I swapped the old diaphragm back in and it solved the problem.

 

[huskyboy]

Thinking about my carb issue... When I put the new kit in, I noticed that the pump diaphragm (opposite side from the metering diaphragm) was black and pretty thin. My kit came with two tan weaved looking diaphragms that matched up to the black on I installed. Is there a chance that I need to put the old black diaphragm back in?? Is it possible that the reason for my low end issue is the different color/material diaphragm? The old one looked fine..... I almost remember this happening on another 394 I did... I could almost swear I swapped the old diaphragm back in and it solved the problem.

Can't hurt trying, nice saw btw! My ported and stock 394 are pretty fussy on the low side but nothing that can't be tuned out, def sounds like a carb issue though on your carb by the way you describe it.

 

[RIDE-RED 350r]

I just went back out, took the carb all apart and put it in carb soak. Going to let it sit in the soak till tomorrow afternoon. When I put it back together I'm going to put the black diaphragm back in. The issue is isolated to the low side, top end runs fierce and responds well to adjustment.

I have never removed the welch plug in the metering diaphragm side. Is there anything of consequence under it that I should check/clean?

 

[jmssaws]

Intake block on upside down?
Gasket or Sealant on the base?
Did you put seals in it?
Flywheel side one drove in crooked?
Sounds like a airleak to me

 

[jmssaws]

You don't have enough impulse from either the block or airleak.
Raising the metering arm don't change it?
You should be able to flood the *s-word out of it

 

[RIDE-RED 350r]

Running a gasket for the cylinder base. I would be thinking air leak too, but the high side runs consistent at gravity and responds predictably to adjustment. The issue is isolated to the low side. Idle screw is backed out to the point that the throttle butterfly is closed and it still idles kind of fast, just a whisker under clutch engagement. It's not a smooth lean bog sounding idle either, that's what is weird. I really think I have an obstruction in the low speed fuel circuit. Carb is all taken apart and sitting in carb soak solution now, going to let it soak till tomorrow afternoon.

Bottom end has new OEM bearings and seals.

I had one of these 394 carbs beat me in the past... Ended up replacing that carb and all was cured.

 

[beaglebriar]

Running a gasket for the cylinder base. I would be thinking air leak too, but the high side runs consistent at gravity and responds predictably to adjustment. The issue is isolated to the low side. Idle screw is backed out to the point that the throttle butterfly is closed and it still idles kind of fast, just a whisker under clutch engagement. It's not a smooth lean bog sounding idle either, that's what is weird. I really think I have an obstruction in the low speed fuel circuit. Carb is all taken apart and sitting in carb soak solution now, going to let it soak till tomorrow afternoon.

Bottom end has new OEM bearings and seals.

I had one of these 394 carbs beat me in the past... Ended up replacing that carb and all was cured.

Pull the Welch plugs they aren't hard to replace.