Hawk is here, yay!

[Emerikol]

Dan, I can tell you from personal experience with my Hawk that running the 39T rear sprocket will get you up to about 68 mph at about 6,200 RPM. I bounce off of 70 occasionally, but the bike is really too light for those kinds of speeds. I get some really wicked headshakers going on after about 62-65. Any small upset in the road surface causes huge oscillations back through the handlebars. I'm sure most of that will disappear once I burn through the stock knobbies and get some more street-oriented tires on, but for right now I treat the Hawk like my Ural: It will do 55 forever, 65 occasionally, and 75 once (Usually over a cliff....) Just my thoughts on what I know with my bike, your mileage may vary.

[Megadan]

I get zero headshake or other stability issues at or past 65mph and I am still on the knobbies. Might want to check your wheel and/or headstock bearings or front wheel trueness and balance. My only enemy is the wind.

[Emerikol]

Dan, front wheel is true and balanced, and the head bearings are greased and tight. Not sure where the headshake (oscillation, really) is coming from, but I know I run higher tire pressures, and that likely has a lot to do with it. I just keep it down around the 55-60 mark and I don't have any problems. It's a super fun bike to tool around on, and if I need to do any serious overlanding I take out the DR. I'm going to need to take them Missus bike out today. It has 67 miles until the 1500mi oil change. I want to get that done before we go to Arizona. Have a great day everyone.

[pete]

And they lock up under brakes quite easy on lose surfaces..
i am on my 3rd set of 700s on my XT660R... but then the XT is a bigger
heavyer bike to stop in a hurry as well as having a 320mm front disc rotor..


..

[Megadan]

Originally Posted by pete

And they lock up under brakes quite easy on lose surfaces..
i am on my 3rd set of 700s on my XT660R... but then the XT is a bigger
heavyer bike to stop in a hurry as well as having a 320mm front disc rotor..


..

I kind of expect that with any less aggressive tire. I would imagine the Avon's I am looking at would be even worse at locking the brakes than the 700's. Just kind of the way of things.


In other news, I went ahead and ordered one of these guys. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
The irony of spending more on the adapter than I paid for the carburetor. is not lost on me. Admittedly, I didn't actually pay for the carburetor directly, but it is still funny.

I had the option between that and a slightly bigger unit designed for up to 34mm carbs. This one is a bit smaller with the inlet size reduced to 28mm, but the mounting flange options mean I can either try it on the stock intake, or directly to the head, plus I can always machine out the center to 30mm. This one also works with the carb I currently have without needing to buy a reducer/adapter.

[Megadan]

So, here are my options and drawbacks with:hmm this adapter.

Option 1. Mount it directly.to the head.
Pros.
-The carb is close to the intake port with a straight ahot in.
-likely the easiest way to fit it and will clear frame. Will also make pod filter sit more inward.

Cons.
- Carb is angled back more than I would like. Not a deal breaker, but will possibly require adjusting float level to compensate.

I do happen to have a 15 degree rotax carb socket that would work perfectly, but it is designed for 38 to 40mm carbs, so it will not work with the 30mm oko or Adapter I purchased. I would love to find one like this for 35mm spigot diameter, but I haven't had much luck.

[Megadan]

Option 2; Mount it to the exiating intake.
Pros.
- Angle of carb will be more level.

Cons.
- Intake run from throttle slide to intake valve will be a bit longer. This may not really be a bad thing per-se, but it just represents potential turbulence/restriction.
-Fitment may prove to be an issue in regards to the air cleaner side of things as the inlet of the carb will move further out and forward. I have a few simple ideas to solve this, but compared to the bolt to head approach it requires extra work.

[pete]

Only use it for riding up hills the carb will always be level...

it's not really a issue... but you could make a wedge shaped spacer ...
or mill the face of the manifold on a angle...


.....

[Megadan]

Those are options, but I decided to go a slightly different route. I went ahead and setup an exchange on this adapter for the larger unit and I am going to bump up to the 32mm OKO. This will give me the spigot diameter to work with the Rotax carb boots I already have.

From previous experiences on other bikes with similar cylinder sizes I don't expect it to misbehave, but I do see the biggest issue being the port restriction on the stock head since it is only 30mm. I will test it out on the stock head, and see how it behaves. Obviously if I don't like it I will simply convert back to the Fakuni until I can get around to doing the ported cylinder head, which I can port match and blend the extra 4mm diameter of the flange with a taper.

I can always go back to the 30mm idea if the 32 doesn't work out, but it will take a lot more time and effort to try and sort that out. As I said, from my previous experience with similar cylinder sizes, the engine should respond rather well across the rev range, but until it can be put into practice it is all just speculation at this point.

Worst case scenario would be a small loss in the lower revs and a gain up top with a marginal effect on throttle response (being a bit more touchy). Given my riding style and use of the bike I personally wouldn't mind that trade off. Best case scenario, and something I have experienced in the past, would be a strong gain in the mid-range and top end. This has been evidenced on GL1000 enines, which run a 32mm carb with a 28mm venturi that step up to a 35mm down-drafts with a 32mm venturi, and especially on a 40mm carbs with a 35mm venturi. While obviously apples to oranges, the individual cylinders are similar in displacement, 2 valve heads, and have an identical powerband and rev range. So it makes me optimistic. If I end up with the same kind of powerband (useable from idle to 3000, good from 3000-4000 and strong from 4000-8000) then I will be plenty happy.

Guess I will find out.

[pete]

Originally Posted by Megadan

Those are options, but I decided to go a slightly different route. I went ahead and setup an exchange on this adapter for the larger unit and I am going to bump up to the 32mm OKO. This will give me the spigot diameter to work with the Rotax carb boots I already have.

The 32mm carb has a 40mm OD out let... if I remember correctly...



..

[Megadan]

Originally Posted by pete

The 32mm carb has a 40mm OD out let... if I remember correctly...



..

That is precisely what it has, but the flange adapter has a 34mm ID to work with carbs up to the 34.

[Megadan]

It's almost like these intakes were designed to drive you insane. Not one bolt pattern on either end of the intake manifold is centered. Carb side AND the head side are slightly offset, so neither adapter will work as is. This 34mm one could work, but obviously there is a drawback to it without port matching. It may be possible to drill a new pair of holes to center it up, but the casting won't allow them to sit as deep into the head.

So that leaves me with the second option, offset the port matching as seen in the second picture. It would allow a bit more wiggle room in reshaping the port for a taper this way to really kick up the velocity, and the offset moves the centerline of the intake port up a bit as well which would give a slightly more direct shot at the valve. This would split the port work into two main sections. The first half would be mainly focused on the upper left, and the second half would be on the lower right, which is where a lot of work is really needed around the valve radius and valve guide end to help open up the airflow some.

All of that said, short of making my own flange adapter at least, my only option is to either find something I don't think exists - a socket style intake for the CG250 that angles in the same direction as the Hawk/TT250 intake manifolds do - or write off the idea of a flat slide on a stock engine.

I am not opposed to making an adapter, but I was hoping to find a solution that didn't require fabrication. At least I know I can make it work with the ported head, so that's something. I was just kind of hoping to see if there would be any change in performance on an unmodified engine as well.

[hertz9753]

When I see Rotax I think rotary valve engine. Not that a hose won't work but I am curious.

[Megadan]

Originally Posted by hertz9753

When I see Rotax I think rotary valve engine. Not that a hose won't work but I am curious.

Certain Skidoo and Polaris snowmobiles and watercraft used a Rotax engine in them that had angled carb boots to help level out the carburetors. I initially bought them attempting to find a solution to an ITB setup for my Goldwing, but decided to go a different route. They are just about the perfect angle to make the carb and adapter work on my Hawk, and not too hard to find. If I can get it to work, then I will definitely post up the model they came from.

[hertz9753]

I was thinking about the Can-Am Bombardier 500cc 4 stroke motorcycle engine.