400ex carb help

[doublejz]

So I just went out to break in the new 416 build. I fired it up and it shot right up near WOT. :mad: My tach said 15k but yea, I'm not believing that.

Anyway, I have a 175 jet, 2 turns out, curtis sparks exhaust, no airbox lid, 416 11:1, hot cams stage 2, 108 race gas. I also tried adjusting the throttle stop cable/knob but it didn't make a difference (assuming its not idling on the pilot jet.. just a guess).

Any suggestions before I pull everything back off and pull the carb out. This is the first time I've messed with a 400ex carb so I could have totally fubared something up when I had it apart.

TIA

[slightlybent47]

Remove or dis able the choke, Better yet remove the choke plate.
Reduce your octane to 105 or less.
108 is a little hot for 11.1

[doublejz]

Choke is already gone. Also 42 pilot jet installed.

[slightlybent47]

Did you check the little fuel screen that sits in the fuel intake hole?
Where the fuel line plugs in the carb, there is a little fuel screen, most don't know its there.

[slightlybent47]

Try blowing out all the vent tubes, sometimes they get clogged with dirt.

[slightlybent47]

Is it a 400 carb or a 450?

[slightlybent47]

You may have to try several jet combinations till you you get it rite.
It's a pain but well worth it when she runs like a scalded dog.

[doublejz]

Is it a 400 carb or a 450?

Its a 400 carb. My thing is that I don't see how the main jet would come into play at idle. Should only be using the 42 pilot jet, right?

[doublejz]

Its a 400 carb. My thing is that I don't seje how the main jet would come into play at idle. Should only be using the 42 pilot jet, right?

So I pulled the carb back out and tore it completely down, put it back together and it's fine now.. other then it being way rich.

[slightlybent47]

It don't take much varnish to mess things up.
And you may have just over looked something the first time.
We've all done that.
Maybe something just didn't quite line up rite the first time.
I could do this all night. lol


Main thing shes workin now, thats all that maters.

[doublejz]

yea.. I'm guessing it was a vacuum leak or an o-ring/gasket landed up being off a little.

[slightlybent47]

Glad you got it worked out,

[doublejz]

Just wish I knew why the float or valve keeps getting stuck dumping gas outta the over flow.

I'm also having an issue where a 175 jet with 1 turn out is almost where I want it but still a little rich but 172 at 3 turns out is a tad on the lean side.. I cant find a happy medium to where I have some room for adjustment debating in temperature/altitude.

[CJM]

The float valve is likely worn out or dirty.

As for jetting, pick a happy medium really is the key here. A carb will never be perfect b/c it can compensate on the fly like a true fuel injection system will.

[slightlybent47]

Those float valves can get saturated and don't float like they should, and with a dirty needle and needle seat, can give you fits.
I'd stick with the 175 for a while till you get a real good feel of how it runs, then try another size. That way you have a better chance of feeling the difference in the two different sizes.