Bad porting by Nmotion?

[300EXrider356]

Alright so the story goes, I send my motor to Nmotion to get ported and polished and a new wiseco piston, get the whole bike back together, then I break my leg yay! so I just got off my crutches about 2 weeks ago, and Ive been trying to get my 440 to run good but I cant. Its running way to lean, I bought a new 450R carb but nothing worked, went all the way up to a 220 and got a little better each time. So i threw on the old Edelbrock, went all the way up to a E30 needle, and it was still to lean, I just want to ride, I took it apart last October and i havent really been able to have fun since!
Anybody got any ideas?

[Dill]

air leak?

[300EXrider356]

no i got a new boot to the engine, and the filter boot seems to be fine, which leads me to believe that they shaved to much off?

[JW450R1]

Was it a full port job?.Did they install over size valves?.

[400exrider707]

Have you tried changing any other circuits in the carb other than the main jet? What pilot are you running, what needle, wheres the fuel screw?

[honda250xrider]

have you ever tried a bigger carb, i've had a same problem on a very built motor where it would not run decent at all with the stock carb nor with a 2mm difference. went from 34mm to a 38-40mm and adjusted it from there and it ran perfect.

[GPracer2500]

How are you determining that it's too lean?

[parkers30]

did you change/replace the exhaust crush gasket when you reinstalled the head?

[400exrider707]

This is funny actually because I recently read about the 520 Nmotion buildup on ******** or somewhere, its on the Nmotion website, and they recommended this guy putting in a smaller carb with way lean jets. He ended up with a 39FCR with something like a 150 main and this was done on a dyno so it was jetted correctly! I find this rather amazing. He too started with a high main like a 210 or 220 or something similar, and ended up with a 39mm carb with a 150 main. Crazy!

[underpowered]

400exrider707 is right. believe it or not, sometimes richer is leaner and leaner is richer. try going back down, i would start at like a 175 or so MJ in the 450r carb. bigger is not always better.

[dork]

if they changed the cross section alot and or the short turn then you may have a lazy port that will raise your bsfc's but not efficiency. it will want a lot of jet but not make better power. what cam do you have? you may want to try a needle with a richer taper so the main jet will have more control over the needle jet area.

[wilkin250r]

For the life of me, I can't see any way possible that the ports would completely screw up your jetting. It will CHANGE your jetting, sure, especailly on the top end because it changes airflow characteristics. But it can't screw up your jetting completely.


So, just as been asked previously, how are you determining that it's too lean?

[300EXrider356]

I am determining It's to lean just by the fact that it wont rev out, its like it was being starved for fuel i can get to about half throttle then it just starts cutting out. Also everytime I go up on a needle(Edelbrock) it seems to get a little better. I origionally had a E-25 needle which is what I had before the port, but went up from there. Ill try the 450 carb one more time, with a smaller jet, I think I started at like a 190 last time or something. If that dosnt work I'll take it down to Nmotion and see If they can help any with there dyno and since they built the engine. Also for dork, I have a HC stage 2 and the Edel. dosnt have jets.

Please correct me if I'm wrong, I've never been to good at jetting and this is my first engine build:chinese:

[Hammer trx450r]

Did you try calling NMotion?:rolleyes:

[mad440]

im going to suggest a different view instead of going bigger with fuel go more air. take the main back down to a reasonable number 170 or so then take your air box lid off and see if it will rev out. my 440 did that to, i wanted to keep my lid because i ride no matter the conditions and i didnt want anything to get in it. but my motor would never rev out at all so i kept uping the main jet and it did nothing then my uncle suggested more air so i took my lid off and it revved out all the way but my main was way out so i got it dialed in and runs perfect. and if you do want a lid k&n makes a lid/air filter that really dosent effect the open airbox flow, but it keeps the crap out real well.

[300EXrider356]

I already have a outerware lid(I dont know what its called) but I will try your guys's suggestions once I get back in town, I'm in florida right now:devil:

[wilkin250r]

A lean condition will generally rev out really well. Often, you will get several loud Pops. This is usually the only indication of a lean condition before you overheat and melt your piston.

A rich condition will gurgle and sputter, and often will not rev out well.

Without being there in person, I would say that if it doesn't rev out well, most likely it is rich, not lean.

[400exrider707]

Originally posted by wilkin250r
A lean condition will generally rev out really well. Often, you will get several loud Pops. This is usually the only indication of a lean condition before you overheat and melt your piston.

A rich condition will gurgle and sputter, and often will not rev out well.

Without being there in person, I would say that if it doesn't rev out well, most likely it is rich, not lean.

Agreed.

[300EXrider356]

Alright guys I ll try that when I get back, it just didnt make sense to me that i would go leaner than what I was at before they did the engine work.

[GPracer2500]

Originally posted by 300EXrider356
....it just didnt make sense to me that i would go leaner than what I was at before they did the engine work.

The size of the hole in a jet isn't the only thing that determines how much fuel that jet delivers. The other side of the coin is the vacuum signals (created by the engine) the carb uses to move fuel through its circuits.

In other words, a 150 main jet won't always deliver X units of fuel. A 150 may deliver X+Y or X-Y depending on depending on the vacuum signals seen by the carb. Its not terribly unusual for some engine work to actually need smaller jets. It's not that the engine doesn't need as much fuel. It's that the engine is able to push more fuel through the same size jet.

[Dill]

Originally posted by GPracer2500
The size of the hole in a jet isn't the only thing that determines how much fuel that jet delivers. The other side of the coin is the vacuum signals (created by the engine) the carb uses to move fuel through its circuits.

In other words, a 150 main jet won't always deliver X units of fuel. A 150 may deliver X+Y or X-Y depending on depending on the vacuum signals seen by the carb. Its not terribly unusual for some engine work to actually need smaller jets. It's not that the engine doesn't need as much fuel. It's that the engine is able to push more fuel through the same size jet.

especially when going to big bore or high compression pistons. They will draw more fuel through a smaller mainjet than engines with weaker intake signals.

[300EXrider356]

I guess that makes alot more since now since i upped the compression to 12.5:1
Thanks for all the help guys!;)

[wilkin250r]

It wouldn't suprise me, either, for yet another reason.

There are two aspects to the "signal" that the carburetor recieves from the engine. One is vacuum, the other is called the Venturi Effect, and it's based on airflow.

Basically, the more airflow you have going across a hole, the more vacuum is created through that hole, and it's not a linear relationship. Twice as much airflow doesn't result in twice as much fuel, it results in FOUR TIMES as much fuel.

So let's say you flow 10% more air, that would result in about 12% more fuel, which would be rich. Plus, you probably started with jets that were larger than your original, so now you're REALLY rich, and you only went up from there.

If I were you, I'd start with your original jets, and do some plug chops.

[krt400ex]

Originally posted by 300EXrider356
I am determining It's to lean just by the fact that it wont rev out, its like it was being starved for fuel i can get to about half throttle then it just starts cutting out.


that is rich...not lean. lean would allow it to wind out and it would be running really hot