When to change carbs

[Phatboyz]

I am redoing the topend on my bike this month. I just ordered a new cool head. I didn't get the domes cause I was not sure what size I need. I have FMF pipes and silencers (The original fmf pipe) and newer power core 2 i think. I have't looked at it in awhile. I belive that last time I rebuilt I was a .80 and now I think that the scratch is going to take it .100 but I won't know until I get to the machine shop. My elevation here is 923FT I ride mostly woods so low end/mid is what I am looking for. I usually run 92/93 so what cc dome do you think that I could use?

 

When do and what size carbs?

Edited December 8, 2004 by Phatboyz

[Ducman]

21cc domes, maybe 20 with 93 but that is pusing the envelope and probably wont work with timing advance.

 

bigger dual carbs when you get some serious porting done or a 2 into 1 carb will improve power and throtle response from bottom to top a lot on a stock to mild ported motor.

[svtkid78]

You should have had your head modded if you are .080 over now. Once you go over.060 you need to get big bore domes. I would run 21-22cc.

[Phatboyz]

I am not running a stock head now. You say that make big bore domes? I thought about a port job, I really didn't want to buy new carbs yet. Can I get away with out them for awhile? I know that I won't make peak power until I change them. The stock size is 26mm? Would some 28mm of an 77 RZ400 work? I can make intakes. Have vertical and and endmil.

 

Edited December 9, 2004 by Phatboyz

[Ducman]

Those 28mm would probably work with the stock manifolds and intake boots. You'd just need a new throttle cable if you still have the TORS on the stock carbs. Stock is 26mm. If your .080 now, I'd get new sleeves installed (either stock or bigbore) or get a good set of used cylenders with a few bores left and then get the porting done. I think standard domes work up to .080

[Phatboyz]

I got a twist on it. I have acouple sets of cylinders. I'll mic them in a second

 

I measured these with a dial caliper, Not a bore guage

 

Cylinders I'm running 65.5mm

Cylinders I have 64.7/65.05

 

I think that I'm going to take the smaller ones and match them to 65.5

 

I got a noss head off ebay yesterday. What domes do you think that I should run.

Edited December 9, 2004 by Phatboyz

[Banchetta]

I got a twist on it. I have acouple sets of cylinders. I'll mic them in a second

 

I measured these with a dial caliper, Not a bore guage

 

Cylinders I'm running 65.5mm

Cylinders I have 64.7/65.05

 

I think that I'm going to take the smaller ones and match them to 65.5

 

I got a noss head off ebay yesterday. What domes do you think that I should run.

291083[/snapback]

I'd call Dave at Noss and ask him for the dome size. He knows best w/ elevation and compression. Some domes will vary from manufacturer to manufacturer. As for carbs. Larger carbs will take away hp unless you have porting done. Your better off w/ stock carbs and will gain quite a bit over larger carbs, especially on the bottom.....

[Phatboyz]

Well as for porting I could do it myself if I knew alot about two strokes. I have ported car cylinder heads a few times and the Old XR's that I used to ride I opend the intake for a straighter shot and hogged out the exhaust to match the inlet of the headpipe. I could do these cylinders if I knew where to cut. I'll start another post to see if someone can guide me in the right direction. I have seen a few porting pics on here so I have an idea. Open up the intake windows slighly,taper the bridge. The transfer ports on my cylinder look ok, except of one that I will blend.

[Banchetta]

Well as for porting I could do it myself if I knew alot about two strokes. I have ported car cylinder heads a few times and the Old XR's that I used to ride I opend the intake for a straighter shot and hogged out the exhaust to match the inlet of the headpipe. I could do these cylinders if I knew where to cut. I'll start another post to see if someone can guide me in the right direction. I have seen a few porting pics on here so I have an idea. Open up the intake windows slighly,taper the bridge. The transfer ports on my cylinder look ok, except of one that I will blend.

291474[/snapback]

Two strokes are totally different. The height of the ports are extremely important and change the power curve dramatically. There is no mechanical valves in the two strokes so porting changes everything. Just be careful and do a LOT of research.