ezveedub

iTrader: (17)

I believe the R should already have the cap. It was the MBX5 that had a the original tank cap, then it was changed to the MTX4 onroad cap. IMO, I would just get a tank.

Check here. Its part# H0864
http://www.nitrohouse.com/options_mbx5r.htm

Mugen Basher

iTrader: (28)

Ok well I have the mbx5r and the tank new is like 26.00 and I was looking at fleebay tryin to get a little cheaper...
here is the link I"m talkin about
http://www.amainhobbies.com/product_...oducts_id/2402

ezveedub

iTrader: (17)

Are you sure your need it? I believe the older cap was just a rubber/foam tank seal, but don't quote me on that.

Here is a pic of the newer cap top and bottom. If yours looks the same, then you already have it.

http://www.modelsinmotion.co.uk/spar...36&catcode=323

Mugen Basher

iTrader: (28)

Well I guess that is the one I have...
See the problem I'm having is that I'm gettin alot of bubbles in the line...
I have changed everything but the tank

Does anyone have an idea..

Eccentric

iTrader: (3)

Well if you're certain your tubing and filter are OK, then I'd say the tank is the culprit. Probably a leak in the pickup tube inside the tank.

Mugen Basher

iTrader: (28)

Well thats the first thing I look at.... I took the filter out and replaced the fuel tubing... I even changed motors....other than a tank do you know of anything else that would cause bubble to arise..

topcat-lll

iTrader: (1)

If you think it's your fuel tank thats leaking air, just take it off and place it
under water blow air into it using your exhaust back-pressure line close off
your fuel line and watch for bubbles.

Mugen Basher

iTrader: (28)

been there done that and bought the t shirt.... no bubbles......

i'm going for the last straw here

adz06

Raced the mbx5r today wil the reckwerk tuning steering balls, car was excellent never had one problem all day my engine on the other hand was giving me constant problems with stalling in all the heats started last in B final during the break tryed tunign it again so started the b final by 10 mins was 1st place with 1 1/2 lap lead on 2nd place driver car was flying then the dreaded tune started engine had overheated was so pissed like. Rcaing the GRP IRISH CHALLENEGE this weekend stripping down engine later see what is up check bearings etc if its done will have to retune my old rb ws711 and i have a novarossi plus 21-7 tink its is or somthing like that on its way to practice friday 5 heats saturday 2 heats sunday and finals.

Eccentric

iTrader: (3)

I meant that if you've already cleared (or replaced) the fuel tubing and filter then it must be the tank.






An external leak (crack in the tank itself) is only one of three ways that a tank can fail. This type of failure will give bubbles in the test you guys mentioned.

Failure #2 is a leaking cap (either due to a bad o-ring or a weak spring) will also give bubbles in the above test.

Failusre #3 (which I specificaly mentioned in my previous post) is when the pickup tupe inside the tank develops a leak. Your fuel tubing attaches to a nipple on the end of the tank. The nipple attaches to a pickup tube which draws from the bottom of the tank, sometimes through a filter on the bottom (can't remember if the Mugen tank has this filter).

If the pickup tube cracks, or develops a leak where it connects to the nipple (or the filter on the bottom if applicable) then air bubbles will get into the line once the fuel level drops below the leak point. Sealing the tank and doing the submerged pressurized bubble test will not yield bubbles with this type of failure. I had a revo tank develop this failure recently. Bubbles would appear in the line once the fuel level dropped below 1/3.

The easiest way to diagnose this is to try a known good tank. Borrow one if possible, or just buy a new one. They seem to go for around $10-$20 shipped on fleabay as long as you're patient.

T. Thomas

Are the bubbles happening before or after the fuel filter? If not beofre but after, your fuel filter can have a leak in it. Mine have done this and I do not run them anymore because of this. The stone filter in the tank is enough security for me.

Just one more thing to look at.

Mugen Basher

iTrader: (28)

Well I don't have a filter installed but the bubbles are coming striaght from the tank.... It looks like it is the tank but I'm just making sure my other options

ezveedub

iTrader: (17)

It could be the nipple itself where it screws into the tank. Maybe a small dab of threadlock or liquid PST on the threads only may stop it if its the nipple itself.

Mugen Basher

iTrader: (28)

I understand the air could get into anywhere and I will try it Beleive me I will try anything to make it work
Now I pressure tested the tank wouldn't i get bubbles from it

ezveedub

iTrader: (17)

Depends. Sometimes a leak can close under high pressure, but leak under very low pressure or vacuum. How many bubbles are being produced, as sometimes if its very small, it may not affect the engine. One other thing, are your exhaust gaskets sealing properly? If you have insufficient pressure to the tank, you may be drawing the fuel from the tank under carb vacuum. This will have the tendency to induce bubbles in the fuel when heat is present.