Tuning dual 44's - couple of questions

[wildman326]

My motor is cut to 55mm at waist of exhaust, cleaned up intake & boost ports, sleeve sides raised 13mm, race finish, cases filled and fingerported.

Re-cap:

2.3 NS
65 gm spring
doubled up fingernail valves
112.5 pilot
102.5 main
drilled out return to 3/32 or so (not critical)
70 main jet in return line (after T)
1.25 turns out on bottom
1 turn out on top

and

stock flame arrestors
stock intake filled in on sides and bottom to match reed stuffers in
carbon tech reeds on Kawi cages
1/4 inch intake spacer to compensate for longer reeds

I don't know if I mentioned this before or not, but my carbs don't dribble at idle. They don't load up. There is no hesitation that I have found.

I think that a stock or aftermarket intake (with non kawi reeds) would work equally well and intend to try it later in the season. I'm going to take another stock intake and fill it in for v-force reeds. I personally prefer the stock intake. It's nice to have the carbs linked when you take them off, plus they're cheap. I'd probably use the Brazina intake if I had more $$ and less desire to tinker.

 

[Matt_E]

My cylinder should be identical to yours. Mine is currently at 83mm bore.

I run dual OEM 44's on a Riva manifold (w pump sides facing out), with VForce2 cages and reeds, and ported, but not filled 62T cases.

I'll give that jetting of yours a try. You run a B-Mod, right?

 

[wildman326]

I run a b LTD, but have a mod and was considering trying it out. I've heard that the limited has more bottom end . . . and that the mod is good for strokers and 84mm or bigger bore. How does that work? When you get to 84mm why is the mod suddenly better?

 

[Matt_E]

I imagine it has to do with the volume of air being expelled through the exhaust.

 

[wildman326]

I imagine you are right, I'd like to get a little more in depth answer.

 

[waxhead]

the bigger engine can afford to give away some lowe end compared to the 701 and so a pipe tuned for more top end works well in this situation

 

[wildman326]

I called Paul this morning. He said that a mod is good for anything that isn't stock, be it 81mm or 86mm. I'm putting on my mod pipe tonight.

This is very exciting. It's like free HP. And I don't have to order any parts . . . :cheer: :cheer: :cheer:

 

[Matt_E]

I called Paul this morning. He said that a mod is good for anything that isn't stock, be it 81mm or 86mm.

But why?

 

[Mile9c1]

The mod lets you turn more RPM's. But if you run it wet, you won't get those extra RPM's in my experience (I don't have a tach, but wetter = lower RPM's on all pipes).

 

[wildman326]

OK. The shorter pipe sends a return wave that facilitates more flow. On a stock motor you dont have as much flow, so the longer waves are better for stock. Flow in should equal flow out. Now I know this is not very scientific, but the final answer was "there are formulas . . . " and that was about it.

 

[Matt_E]

Actually, air in = air out explains a lot about these motors to me.
I am just a hack, but I am happy with my porting results. (And now I want to make sure the carbs are setup the best way possible)
I am still waiting on more jetting to arrive. I need to drive to Seattle and back tomorrow, so I should get a chance Saturday.

Of course, Sat I also need to make sure the ole Bayliner runs so I can get rid of it.

 

[wildman326]

Well, the mod pipe may have made a little difference, but I'm glad I didn't pine away and save and search and worry.

The rear cylinder seems to be running a little lean, is that normal?

 

[Matt_E]

It is, in boats with heavier loads. Yamaha sitdowns quite frequently have the rear carb jetted richer than the front (or middle & front).
GroupK has a good article on this.

Uneven popoff could be to blame, to. Did you check it with a gauge?

 

[wildman326]

No, I was too anxious to ride. I should have. Perhaps I will tomorrow.

 

[Matt_E]

Heh...same here. I still don't have my jetting I've been waiting for. So much for asking for USPS priority.

I remembered that I have some 105 mains, so I just stuck those in there (instead of the 110's). I doubt that will cure the rich off idle condition, but I suppose I could always add more oil to get back to the breakin mix. So I can at least ride this weekend.

 

[wildman326]

What is your carb set up?

 

[Matt_E]

24 psi popoff (2.0/95g)
115 pilots
105 mains now

(OEM Dual 44's on Riva manifold w/ VForce2)

 

[wildman326]

Hmmpf. I don't know what to tell you. Before we found this "Team Scream" set-up we went with 120 pilot 110 main 1.5 NS and 95 gram spring (I'm not 100% sure on the spring. That worked great. Then you know how it is, someone says "This other thing is better . . . " and were on to that.

 

[Matt_E]

I am starting to realize that there is more than one way to skin a cat, err, tune a carb.

And actually, the setup you got listed is somewhat similar to what I run now. The low speed combo with that higher popoff should be very close to my 2.0/95g 115 pilot
As you know, too high a popoff can be compensated for with bigger low speed jets, and vice versa.

 

[Matt_E]

Alright...I figured out part of my problem. I had the FA's off today and reved a couple of times, and found the primer line to be leaking into the carb throats rather severely.

I moved the take-off fitting to the return line - I Hope that fixes that situation.
I also doubled up the fuel check valves.
Unfortunately, I still don't have my jetting. Dammit.