? About Cylinder/Port Height & Timing

[Pro-pulsion]

I'm about to mod my exhaust ports and while I have the cylinders off I also advanced my timing by a couple mm. Awhile ago on here if I remember, I read that the old-school freestylers & racers back in the day would sometimes remove the base gaskets and use sealants instead so they could lower their ports without modding the cylinders...aside from opening up the exhaust ports. Apparently it makes a very noticeable improvement on certain skis, more so on the Kawi 650's. My question is, if I lower the port height by lowering the cylinders, would it be best to stay with the stock timing or will I still be ok with the small advance? My reason for asking is because I have not yet found out if the freestylers & racers did both or only stayed with one or the other.

 

[SUPERTUNE]

It's more complicated than just that. Carbs, pipe, pump setup, compression ratio and head design all have a roll into how much you can do with advancing the timing.

 

[the WaTeRhAwK]

It's more complicated than just that. Carbs, pipe, pump setup, compression ratio and head design all have a roll into how much you can do with advancing the timing.

Lmao. all the Bolt-on junkies are like "uh...what the...huh!?!?"


LOL

 

[skithis]

I would imagine that if you just seal the bottom with sealant itll just be a constant headache over a little low end on a machine that is already not very fast. I would save your money and buy a superjet or a 750sx.

EDIT: now that i read your post again it doesnt say which machine you have.

I'm running a riva cdi and 2 degrees advanced on my 61x. Although I cant comment on the difference because I also ported and piped at the same time.

 

[Cannibal]

A very respected member of this board has been running his kawi w/o a base gasket or problems for years. It is an old trick and one that still has merrit.

Make sure you verify quench though.

 

[junkyardj]

the hole no base gasket thing seems sketchy to me, why not just get a head and widen the exhaust port a bit

id be worried about a air leak all the time(thats just me)

 

[the WaTeRhAwK]

id be worried about a air leak all the time(thats just me)

if you clean the mating surfaces good with a non-oil based laquer thinner, and use 1211 with everything tight, it shouldn't be an issue.

 

[Pro-pulsion]

It's more complicated than just that. Carbs, pipe, pump setup, compression ratio and head design all have a roll into how much you can do with advancing the timing.

It is a Kawi 650, I'm not looking for speed because I just want to get into a bit of freestyle.
It has:
- 42mm Keihin carb
-stock head, just polished and deburred
-compression ratio is stock at 7.2:1 having a 76mm bore and 70mm stroke with 145 compression on both cyl.
-the exhaust ports measured out at 55mm wide, I have not modified the ports, only polished them. I think this engine was ported before I owned it
-stock pump with a replica WetWolf short pump cone
-stock impeller
-Westcoast complete exhaust
-stock waterbox
-stock eletrical

Waterhawk, I'm not a bolt on junkie, if I were I wouldn't be asking questions, I would just do it. I stand behind blueprinting first and modifying later but when you have a 400 dollar ski which wasn't meant to be a great freestyle ski to begin with, sinking a ton of time and money on blueprinting isn't worth it. I just want a little more than stock performance and am only going on what I can find for data about tried methods that worked out. Granted nobody went into detail about what other mods they were using when they went with certain mods, but they still mentioned that they worked. If I don't ask first then I could grenade the engine and really be kicking myself for not asking.

I have heard the "get a SJ" statement all too many times and I will stand my ground, if anyone cares to sell one to me in as good of shape as my Kawi for the same 400 bucks I paid for it, which means clean condition hull and good engine, and includes free shipping then I will gladly take it. Otherwise please refrain from the politics, I do want a SJ, but it's next to impossible to find one here and what I have was all that was available at the time. In fact I have yet to find another stand-up ski for sale since and I have been looking because I want a SJ, 750 SX or 800 SXR to pop up. IMO, I'd rather have something I can get out on the water with now, then be standing around on the sand while all my buddies are out rippin it up and I'm regretting not buying what I have because I listened to everyone say don't get it. Now can we all just move along and get past the politics please. :Banane35:

 

[SUPERTUNE]

One of the things that don't allow me to know what really to do is I don't have any experience using 42mm Keihin carb other than some limited use on a race 785 on a laydown manifold.

I know if your really good with Keihin carbs, you can get some pretty good results with them, but info and tuning parts are harder to come by.
I used mostly aftermarket dual round body 38mm carbs when we raced back in the late 80-early 90's in mod class, then did a lot of limited racing using a taperbored single SBN 44 mm on a intake conversion kit manifold.

Back in the day we mostly just milled and re-cut squish for added compression and use only the stock Kawasaki OEM headgasket.
Yes, we always advanced the timing on 650's stator plate as that would really help, but can cause havic on the stock milled head using the OEM metal headgasket as we cut them about .050 thousandths. As

On the mod engines we used PJS one piece thick cast heads with the moly stud kit and milled the stock cylinder to run the Ultimate green composition head gasket for a much better seal than the metal headgasket.

Just go for it and learn from it, as that's how I did it...

 

[Pro-pulsion]

I'm only going by a posting I read on one of these sites...can't remember which one...but the poster said that he advanced the timing by a measurement on the plate of 2mm. He said that should offer the best performance for these skis. I'm always a little reluctant to max things out like that so I didn't go the full 2mm, I went about 1 or just a touch over. Initially when I posted this I had already pre-set it to 2mm but I ended up wanting to play it a little safer so I backed it up a bit that night. Did you ever try the "no base gasket" theory? The only time I have heard of any negative feedback about it was on this thread. Aside from this, most people had no experience related knowledge so they couldn't offer any insight.

 

[SUPERTUNE]

The .020 no base gasket trick IMO doesn't make that much difference on a stock ported engine, raising the compression ratio is more of the equation to the gains in performance from doing this than lowering the port timing by only .020. 650 SX exhaust port timing isn't near as high as the 750 SXI and dual carb models.

 

[Big Kahuna]

if you clean the mating surfaces good with a non-oil based laquer thinner, and use 1211 with everything tight, it shouldn't be an issue.

If done right, you would not even need the sealant. Personally I do not like this way. (No Gasket). I know Tricky had to do it to get proper squish until he could get correct domes.

 

[Cannibal]

Why is everyone so afraid of running without a gasket? Your case halves don't have a gasket, just two macined surfaces and some sealant.

There are a couple products that come to mind made specifically for this type of thing. One is Permatex Aviation Grade Formagasket, and the other is Loctite 515. I am sure there are others as well, and I know people just use 1211 or YamaBond without issue.

I learned about this from an old engine builder still doing it today. I should be assembling my engine today, and as long as the squish comes out correct, I will not be running a base gasket on this ported small pin 750.

 

[the WaTeRhAwK]

If done right, you would not even need the sealant. Personally I do not like this way. (No Gasket). I know Tricky had to do it to get proper squish until he could get correct domes.

I've yet to know of a "right" way to do it without using 1211 or yamabond/equiv. sealant.

how are you sealing the mating surfaces without "sealing" them?

 

[Pro-pulsion]

I was actually considering using the CNH (Case New Holland) anaerobic flange sealant. When I worked with the Case dealer we used it quite often to seal hydraulic transmissions and that stuff worked amazingly well. It not only withstood the temperatures, but it cured in minutes once torqued and held up against any pressure in the trannys. One of my thoughts for this were also to get a little bit more compression out of it without milling the head. Another thing I was considering, and again based off of info found on these sites...was to only clean up the transfer port heights. I measured them all and they vary about one mm in height both in casting and to where the chamfers are ground at their highest. Some have poor surface matching to the cylinder ports as well. What I copied into a text file from the postings was to flatten the roof of each port and I would also like to balance out the chamfer heights too. My understanding would be to make them look like this: --- instead of on an angle like this: \

Does this suggestion sound right? The ports will not be higher than stock, but more internally open only at the roof tops, and equal in the highest stock height. The center port on both cylinders is about 3mm lower than the rest and the casting has a very sloped back wall leading toward the top of the port, similar to the second diagram above. I don't think those ones should be cleaned up because of their height and shape being almost identical on both cyls. With how they look, they make me think that they are directly related to the intake manifold ports. Any thoughts about this?
Here's a couple of pics regarding the chamfer heights and difference between the center ports and the rest.

 

[X2guy]

Don't worry so much about the port chamfering difference. Cleaning up the ports and matching the sleeve with the cylinder casting will help. You will get an increase in compression by removing the gasket but that's about it. Just do it and see what happens. Don't worry aboiut the timing advance you have now. Way back when I ran a 650 in my X2 I had mine set about 5 or more mm. Can't remember what advance it was exactly but I remember the seperation in the lines.

 

[kevbo]

The big problem with a 650 is in the fact they have to be tuned right at the edge of meltdown in order to make good power. Anyhow, you taking on a very expensive and time consuming task.

 

[Pro-pulsion]

Thank you very much guys, I really appreciate the good tech info. I'll set the timing back to stock and just port match the transfers. The exhaust ports looked like they were stock when I first polished them but when I measured them last weekend I found that they were about 72% of the bore. I'm guessing someone has already been in there and opened them up. I can't thank all of you enough though for mentioning just how much is involved with one change here or there. I'm going to get it all back together this week then and hopefully get out for a test run this weekend :fingersx: