400ex possible fuel issue

[SlammedRanger 1,556]

450 tank have its own cap? Or did you use your 400ex cap? Did you try running no cap? It has to be lack of fuel flow. Be prepared if you try a fuel pump you will need to put a return line back into the tank or regulater to slow the flow. Otherwise you are 100% going to push passed the float needle and have fuel running out the over flow tube.

[SlammedRanger 1,556]

Not to mention if the fuel flow isnt able to fill the carb bowl fast enough it wont be able to feed the fuel pump fast enough to keep primed so its not gunna really work anyway. It has to be a tank vent issue. We can rule out petcock. Carb.(Unless you got 2 with the exact same problem? Not likely) Time to run it on a bottle with a vent hole in the top and see if it runs perfectly fine.

[Dorman10 3]

450 had its own cap. I ran it with the cap on and off. Ran it with a bottle too and it still has the issue. Had a vent cut in the bottle and everything. Could it be electrical, like in the stator and firing?

[SlammedRanger 1,556]

Honestly at this point it could be anything. But we confirmed its running the bowl out of fuel. It doesnt make any sense. Stator, coil, cdi. None if those are gunna have any control over filling that float bowl. Gravity fills it. Does it do it when engine is cold and hot? Could it be getting so hot it boils the gas in the fuel line? Im grasping at straws here my man. Nothing about this makes any sense. Unless you have 2 bad carbs in the exact same way and one is brandnew right out of the box bad? Wow thats a stretch! The main jet didnt maybe fall out or something? That would pull so much fuel so fast it maybe could out run the gravity feed?

[SlammedRanger 1,556]

Make 100% sure all the vent lines arent kinked. Pinched. Blocked. Again grasping at straws.

[Dorman10 3]

What would be the ideal main jet for me to use with the set up i have:

440big bore kit

stage 3 hotcam

ported heads.  
slip on HMF pipe

[SlammedRanger 1,556]

Stock carb i would be guessing somewhere in the 180-190s. Pilot jet will be 45 or 48 i would guess also.

[Dorman10 3]

Ok so this is going to sound weird, but blowing in the hose to the gas cap seems to keep it running on top end, like it needs pressurizing. 

[Fishfiles 20,145]

your fuel cap vent is clogged up , do a video search of fuel tank  vent blockage , how to check and results   

[Dorman10 3]

Taking apart the carburetor now to see if something from the tank went down in it. The floats in the carb aren’t doing their job anymore because it leaking gas out to the run off hose

[Fishfiles 20,145]

Leaking gas out the "run off tube "is a sticking needle valve , you'll got ethanal gas around where you at 

[Dorman10 3]

It’s like it’s not letting enough fuel flow down to the carburetor, but nothing it’s stopped up from all we’ve tested

[SlammedRanger 1,556]

Yeah man im stumped. As long as gravity hasent changed it has to work. The fuel flows out of the tank down the fuel line into the carb. There is a direct connection from the fuel line nipple on the side of the carb and the float bowl. The only thing left in this process is the float needle. I wonder if something was in the fuel line and got into the original carb. Then when you put the new carb on the same stuff was still in the line and went in the new carb and did the exact same thing? Maybe sand or dirt or something? That would stop the float needle from moving freely. Which would then slow the fuel flow into the bowl. This new symptom of leaking out the overflow is telling us the float is sticking for what ever reason.

[shadetree 5,880]

just a shot in the dark, but...what size is the fuel line ?, and do you have an inline fuel filter ?, if both are too small ?, it will cut down on the fuel flow to carb !.

[F250 guy 107]

I'd look over your carb and tank again, something still isn't quite right, did ya get it all cleaned? Probably unrelated but I run Sunoco Non Ethanol Fuel it's the only stuff I run, if you can find it in your area I highly encourage you to get it.

[Honda 400X 2]

Hey Dorman10 did you ever figure out your problem? I have same exact problem and done EVERYTHING you have done and nothing!

[Misterclean 421]

If its a fuel flow problem then I would do a flow test at the fuel hose where it connects to the carb nipple and another test out the bowl drain valve. A clogged bowl vent will do this as well. If the valves are too tight it will have these same symptoms. Hope this helps.

[Honda 400X 2]

So I already figured it out.. believe it or not it was gearing.. i have a 05 400ex motor in a 350x frame. I went to a 36 in the rear because my bike on 5th was screaming like it wanted to blow up and felt i needed to shift to 6th which there isn’t..  now it rides awesome and no more running out of fuel because i was over reving.. 350x frame is much lighter more aerodynamic and just 3 wheels on the ground.. i had checked all fuel flows i swapped petcocks, fuel lines, fuel cap and even carb and did nothing.. thanks for replying!👍🏻👍🏻

[Misterclean 421]

28 minutes ago, Honda 400X said:

So I already figured it out.. believe it or not it was gearing.. i have a 05 400ex motor in a 350x frame. I went to a 36 in the rear because my bike on 5th was screaming like it wanted to blow up and felt i needed to shift to 6th which there isn’t..  now it rides awesome and no more running out of fuel because i was over reving.. 350x frame is much lighter more aerodynamic and just 3 wheels on the ground.. i had checked all fuel flows i swapped petcocks, fuel lines, fuel cap and even carb and did nothing.. thanks for replying!👍🏻👍🏻

Ok but it does not sound logical to me. I'm 62 now and have played with gearing (for fun) for at least 35 years now and have never experienced anything like this. I've geared dirt bikes so tall that they wouldn't top out in high gear. 105 mph on my YZ 250 is a fairly recent example. An old 1978 RM 400 went so fast fast that the unbalanced front tire was literally hopping off the pavement. 

[Honda 400X 2]

No idea man.. all i know is i put a 2005 400ex engine in a 86 350x frame and seems like it was under geared.. when i was on 5th topping out on the road for a long period of time gunning the throttle it would starve eventually but normal riding in the trail it road perfectly fine.. this will only happen at wide open throttle in the street once it hit max mph and about 2 miles later..I would know it will starve because the second it would act up i shut the fuel valve off and stop the bike I would drain the carb and nothing will drain out..

[Misterclean 421]

12 hours ago, Honda 400X said:

No idea man.. all i know is i put a 2005 400ex engine in a 86 350x frame and seems like it was under geared.. when i was on 5th topping out on the road for a long period of time gunning the throttle it would starve eventually but normal riding in the trail it road perfectly fine.. this will only happen at wide open throttle in the street once it hit max mph and about 2 miles later..I would know it will starve because the second it would act up i shut the fuel valve off and stop the bike I would drain the carb and nothing will drain out..

That's new information for me. Wide open throttle for two miles! LOL That's hard on an engine! Perhaps the fuel was boiling because of the excessive heat built up in the fuel hose. If you have an inline fuel filter then remove it and just rely on the filter built into the petcock. Fuel does funny things when hot and gravity fed thru a filter media. Also re route and/or insulate the fuel hose. Hope this helps.

[SlammedRanger 1,556]

Im trying to figure out how its not running on the rev limiter? Unless you did one of those cdi boxes that removes the limiter. Wide open throttle for 2miles would be banging the limiter the whole entire way. I will say from experiance the 400ex motor built right will handle anything. Stock form with out a limiter the valves are floating hard and it wont last very long before your pulling a piston with a valve sticking out of it from the engine. My .02

[Honda 400X 2]

So i have no fuel filter and even ran it without petcock filter.. i never run it that hard for top end but when it happened i had to see what was going on with it.. it definitely was under geared i had to drop the rear sprocket on it and it fixed everything now it run like a champ.. 

 

 

No idea man.. all i know is i put a 2005 400ex engine in a 86 350x frame and seems like it was under geared.. when i was on 5th topping out on the road for a long period of time gunning the throttle it would starve eventually but normal riding in the trail it road perfectly fine.. this will only happen at wide open throttle in the street once it hit max mph and about 2 miles later..I would know it will starve because the second it would act up i shut the fuel valve off and stop the bike I would drain the carb and nothing will drain out..

[Aaroncurry 0]

On 3/21/2020 at 6:45 PM, Dorman10 said:

I need some help guys. I have a 02 400ex with a big bore 440 kit, stage 3 hotcam, ported head, and brand new carburetor currently with a 200 main jet in it, yet it seems like it still running out of fuel on top end. I’ve tried every jet from a 148 to a 200 and I’m having the same issue. It runs good and hard up until I’m going through 4th gear around 60mph and then it just started shutting down like I’m out of fuel. Sometimes if i keep playing with the throttle i can keep it running before it shuts off, but most of the time it just shuts off. It will crank back up without hesitation after about 5 seconds like I’m having to wait for the bowl to fill back up with fuel. There is no black smoke coming out the pipe or anything to show that I’m running too rich. I just need some help, so somebody please tell me what they think is the problem 

Just wondering if you ever got your problem fixed, having the same problem with my 400ex and can’t figure out what the problem is

[Honda 400X 2]

Fixed mine by going one up in front sprocket. I was winding out on top end and screaming for more fuel. Guess it was wayyy too much rpm