Case porting?

[ShreddinSD]

So, I was waiting on parts at one point and decided to finger port a case. I think I made a big mistake. I was going to leave the engine stock except for bolt ons for reliability but had idle time and this is what happens…my question is this: can porting cause an engine to fall on its face around 6000 rpm once it’s hot? I know that I have altered the case volume which will impact vacuum and compression in the entire engine, and now that I think of it would likely cause the pulse signal to not be as crisp. Is that what’s happening? This is a second case that I’ve molested, I’m realizing now that when I ingest water I want it to hit all these surfaces and vaporize before it hits my piston and rings. It’s power vs reliability and since I’m always chasing big air in salt water- the colder the better, I should be prioritizing reliability. So, how bad have I messed this case up? I plan on going back to the stock upper half on my fresh sp today but it has some damage where the FPP limited chamber was rubbing. What are thoughts on this? Any advice? I wish now that I had asked these questions here before getting so far into it.

 

[Storbeck]

I have very similarly ported motors that run great, I don't' think you did anything but improve performance with that case porting and trimming the bottom of the sleeve the way you did.

$.02 from a rando on the internet, but with a bit of credibility because I have actually done it very similar to what you did.

 

[ShreddinSD]

Well, I did look around at what others had done before I went at it…That’s not my first attempt. Luckily I had a few cases laying around. I did resolve at one point to leave the engine stock and reliable but….So, the last $200 stock engine ran like a top in till I ingested some water and broke a ring. Im actually looking for that $.02 before it costs me more and lost time on the water.. So thanks!

 

[kevbo]

Your porting is basically what the factory did on sxr800. The carbs must always be retuned whenever any change is made. Open the top screw and leave it on the rich side of peak power. It’s more difficult to melt a piston that way. If it is the 178 degree the exhaust port it can be raised a little without hurting response very much. I wouldn’t go over 2mm. Then make sure the pipe responds quickly, if it doesn’t lower the pump load.

 

[ShreddinSD]

That’s what I thought. I figured it’s probably worth 5hp- but at the risk of throwing cold water right on my pistons. By lowering the ex port 2mm I’d essentially be making it an SXR with thin cylinder walls right? I had this setup pretty dialed and hitting hard with instant throttle response
My settings on sbn44:

Green ski
135 high
100 low
2.3 n/s
Black spring for 17# popoff

 

[kevbo]

I was referring to the exhaust open duration. The small pin single carb cylinders were 178 degrees open. The early sitdowns were 178 for single carbs and 184 for twin carbs. Most of the big pin cylinders ran 192. These high ports make great power with a pipe but can also be very slow to respond. Low ports are the most user friendly but make less power. Make sure the sleeve doesn’t rub the crank when mixing various cylinder and crank combos. The SXR stuff is more difficult to find used, I’ve never measured one.

 

[ShreddinSD]

So I finally sat down, got in the right state of mind and thought this through again. It does seem like a fuel problem, fuel pump problem. I thought it would be one of the check valves but the big diaphragm had stretched. To the point that it wasn’t pumping at high rpm once it had been ridden and stretched out a little.
It sounds to me like since my riding style has improved I may want to raise the ports on that next build. Or not. Dammit. I haven't had a good shred sesh in a long time. I gotta get back together so I can go get right!‍

 

[waxhead]

1100 Waveraider Performance Modification

1100 Waveraider Performance Modification 02-26-2014, 03:11 PM Written by Wax This is the build up of engine up for my triple conversion for my wave blaster. I thought maybe you guys would be interested in the build and results. As you can see here, I’m just adding the J-B Weld to allow me to...

www.waxracingproducts.com

Have a read through here.
This was an engine i ported years ago

 

[JC-SuperJet]

"an engine to fall on its face around 6000 rpm once it’s hot?"

Assuming the Rev Limiter is set right and the Temp Sensor is not causing this, then:

If you can't tune this out, I would test the Coils ( Ignition, Charging, etc). Stator Coils with Layer Shorts usually start malfunctioning once they get Hot.

And also rule out any Air Leaks, with a Leak-down Test, that develop when the Engine Parts get hot and expand. (Crank Seals, Gaskets, Case Mating Surfaces, Warped Cylinder Head)

 

[Pro-pulsion]

My experience with this symptom has always been with MSD enhancers. Either they flat out die without warning or the adjustable rev limiter dial failed and the ski wouldn't break 6200 RPM. If you're using an enhancer then try a stock CDI and see what happens. It wouldn't surprise me in the least if you're running an enhancer and this just started happening.

 

[ShreddinSD]

Wow. Great thread. It seems like you could get that crank spinning fast enough with 33* timing! So Wax, can a Kawi 1100 ever hit like a 750 with a pipe? Not sure if you’ve done any Kawasaki 1100s but it’s been a while since that post so probably… Kinda, almost lights a fire under my ass to get back on my X3 project. But I think hawk it and get your thruster sxr setup and raise my exhaust port to 38.5mm might be a better move. The new chamber looks like it would hit more mid to high correct?

 

[ShreddinSD]

I sat down and put on my thinking hat for a while and Realized it was probably a fuel problem. Probably a cracked check valve in the carb. When I pulled the fuel pump apart the large diaphragm that actually pumps was stretched and won’t lay flat. I think it was taking a little bit of riding for it to stretch and become a real problem then it tightened up a little when it was put away for a day. So it runs fine first thing again. One of the changing problems- like an air leak.

Not running an enhancer-yet. So honestly I haven’t heard enough great things about them to make me want one. Isn’t there a different OEM coil that might work better? I’ve run Yami WR3 or OEM SXR coils. I read that the zeel will improve spark but have not tried it to find out yet. It seems to me that the strength of the spark would be dependent on the coil and the heat range is dictated by the rating on the plug. I’ve heard many say “spark’s spark” so I changed my focus to when the spark’s going to spark

 

[kevbo]

My experience says keep at least 1.6” between the port and deck on 750s. If you raise the exhaust port higher it takes better tuning skills to get good response.

 

[ShreddinSD]

Well that’s right where I’m at! I need to go ride,thinking is giving me a headache

 

[waxhead]

Wow. Great thread. It seems like you could get that crank spinning fast enough with 33* timing! So Wax, can a Kawi 1100 ever hit like a 750 with a pipe? Not sure if you’ve done any Kawasaki 1100s but it’s been a while since that post so probably… Kinda, almost lights a fire under my ass to get back on my X3 project. But I think hawk it and get your thruster sxr setup and raise my exhaust port to 38.5mm might be a better move. The new chamber looks like it would hit more mid to high correct?

Yes i have done a stroker 1100 kawasaki. the trick with them is they are more of a revy engine due to the square bore ratio, Its actually a more correct design in ratio but a lot of other issues hold them back. With the right squish clearance and timing you can make them fry a prop hard off the bottom. I am about to start a 5mm stroker west coast triple exhaust port cylinder for my gen 2 x2 build. I will put the pics and details up on that one
* I will see if i can get some pics of the 1100 engine I did but im not sure how many I have. I used a Di cylinder as the porting was to high in the carb 1100 with the stroker crank.

 

[waxhead]

My experience says keep at least 1.6” between the port and deck on 750s. If you raise the exhaust port higher it takes better tuning skills to get good response.

1.6 inches, Damn you mericans. Now i have to convert it
ok well 1.6 x 25.4 = 40.64
with a 133 mm rod and a zero deck you end up with 185 exhaust duration.
That would make a tough engine with good response if all other things are right then the exhaust port is a good height, Awesome advice for a touch engine.
I tend to go a little higher but I have a little tuning experience.
I like to go about 196 degrees exhaust or thereabouts.
Thats 37mm
37/25.4 = 1.45 inches for you mericans

 

[Storbeck]

1.6 inches, Damn you mericans. Now i have to convert it
ok well 1.6 x 25.4 = 40.64
with a 133 mm rod and a zero deck you end up with 185 exhaust duration.
That would make a tough engine with good response if all other things are right then the exhaust port is a good height, Awesome advice for a touch engine.
I tend to go a little higher but I have a little tuning experience.
I like to go about 196 degrees exhaust or thereabouts.
Thats 37mm
37/25.4 = 1.45 inches for you mericans

One thing to keep in mind the kawi engines have the pistons WAAAAY down in the bore at tdc. Usually .055" or so (1.4mm for Wax) from what I've measured.

So that 1.6" down is actually a lot lower than that, especially the transfers, very low duration. An a ton of squish clearance.

That's why I like to leave the base gasket out so I can get decent squish clearance and use the 29 stamp cylinder to get around 190/124 with no base gasket, which is what I like to do but it seems to be an unpopular opinion.

 

[ShreddinSD]

You know what? I was running no base gasket years ago and had the electrode somehow bend and close the sp gap. Only explanation I could find was that carbon deposits were hitting it but I can’t really believe that. So I thought it was just due to intense vibration and heat. I used to break the insulator free from the base a lot. So it would slide up and down. “Variable gap spark plug” better than split fire!

So too much squish is not good? I kinda thought too little could cause deto and that was the only concern there.

 

[waxhead]

You know what? I was running no base gasket years ago and had the electrode somehow bend and close the sp gap. Only explanation I could find was that carbon deposits were hitting it but I can’t really believe that. So I thought it was just due to intense vibration and heat. I used to break the insulator free from the base a lot. So it would slide up and down. “Variable gap spark plug” better than split fire!

So too much squish is not good? I kinda thought too little could cause deto and that was the only concern there.

If the piston hits the head then there is nothing there. you cant deto whats not there. Piston should hit the head at 1000 rpm more than you will see
Im not sure how you managed to close the gap when the plug is in a dome ??

 

[Pro-pulsion]

While I'm not well knowledged on electronics I believe that the way the better spark is generated through the CDI would be more capacitors, bigger capacitors and better control of discharge to the coil. In the basic function of the coil, yes you are correct in that it is the output to the plugs but if you only give it so much charge then it will only be able to put out so much discharge. Think of it like connecting a 1.5 volt AA battery to it vs. connecting a 9 volt square cell to it. The 1.5 is only going to give the coil what it can to generate a magnetic field on the primary winding which is going to be very small. Toss on the 9 volt and the magnetic field is going to be about 7.5x stronger. The stronger the magnetic field the stronger the output on the secondary winding which is going to your spark plugs. The bigger the bolt of lightning across the spark plug the more thorough the ignition. The Zeel has so far been very reliable. I have been running mine for about 3 seasons now, this being the third, and I trust it a lot more than the enhancer. I've been left stranded floating from 2 enhancers and had one fail in the adjustable timing dial switch limiting me out to 6200 RPM. It had great holeshot response but there was nothing else past the low side of mid range. I put a stock CDI back in and got my full power range again just minus the holeshot boost and 9000 rev limit. As for the diaphragms in the carbs expanding, that's an ethanol thing doing that. I have taken apart so many carbs using genuine Mikuni kits, Keihin, SBT, Winderosa, they all do the expansion thing when soaked but recover after drying up about an hour later. The only kits that haven't done that were the WSM kits but since 2020 they were forced to source out cheap components because of the global supply chain issues and the last pair of kits I installed did the expansion thing when I had to take the carbs off for tuning adjustments. Mikuni however as of the last couple of years have become much better about it and from what I have worked on, they don't seem to be doing it either as much or at all.