Crucial 5ive B

[crucialRC]

Wassup guys I need your expertise. 1st off today I took the Losi 5b to the park for a quick run. I noticed that when i 1st opened the tank cap there was a crazy amount of vacuum that was released. Didn't understand why because the Losi has a vented tank bit I went ahead and filled with fuel and got a good 10min run in. She ran perfect for the whole 10min then she shut down on me. Go over to her and pull the starter and she start then when I put a load on her she cuts off. I look at the primer bulb and it's empty and every time I pump it no fuel comes into it. So I open the tank cap again and once again vacuum in the tank. I try to prime it with the cap off and still a no go. Its the 1107 carb on the 34cc DDM. Should the vent be an open screen or like the pic? What would cause the primer bulb not to pump?

 

[Z.hb71]

Wassup guys I need your expertise. 1st off today I took the Losi 5b to the park for a quick run. I noticed that when i 1st opened the tank cap there was a crazy amount of vacuum that was released. Didn't understand why because the Losi has a vented tank bit I went ahead and filled with fuel and got a good 10min run in. She ran perfect for the whole 10min then she shut down on me. Go over to her and pull the starter and she start then when I put a load on her she cuts off. I look at the primer bulb and it's empty and every time I pump it no fuel comes into it. So I open the tank cap again and once again vacuum in the tank. I try to prime it with the cap off and still a no go. Its the 1107 carb on the 34cc DDM. Should the vent be an open screen or like the pic? What would cause the primer bulb not to pump?

I don't have a 5b but I think your vent looks fine, but is internally messed up, I'd try s new vent first

 

[crucialRC]

I don't have a 5b but I think your vent looks fine, but is internally messed up, I'd try s new vent first

Ok but what about the primer bulb not priming?

 

[Z.hb71]

Ok but what about the primer bulb not priming?

Mmm that's hard. Id think it has to do with the vent but you said that it primes without the cap on which wouldn't be related to the vent (I think)

 

[crucialRC]

No it doesn't prime anymore with or without the cap on. Almost like the vacuum from the bad vent could've ruptured the primer diaphragm?? Just weird how both bad at same time.

 

[Z.hb71]

No it doesn't prime anymore with or without the cap on. Almost like the vacuum from the bad vent could've ruptured the primer diaphragm?? Just weird how both bad at same time.

Try a different carb and see if that works

 

[DougStar]

Hey curcial
Id test the line . Pull the hose off and try pull gas through without the tank...
Or the diafram under the prime could be faked

 

[crucialRC]

Try a different carb and see if that works

Yeah I'll swap it out for a new 990 I have packed away when I get home later.

 

[mark35]

My first thought was vapor lock as the 5b's are well known for getting hot but that wouldn't explain why it won't prime when it's cooled down.

 

[crucialRC]

Hey curcial
Id test the line . Pull the hose off and try pull gas through without the tank...
Or the diafram under the prime could be faked

I'll check the line when I get home cause it has the quick connects on them and I have another I can use to add an extension back to the tank.

My first thought was vapor lock as the 5b's are well known for getting hot but that wouldn't explain why it won't prime when it's cooled down.

Exactly Mark ? That's what makes me think the diaphragm is bad cause it won't prime hot cold or cap on or off.

 

[DougStar]

Keep us posted ?

 

[crucialRC]

Keep us posted ?

Will do brah

 

[mark35]

I've had another thought and this has happened to me with the same symptoms, mine was a perished fuel line in the tank.
Something else to try??

 

[crucialRC]

I've had another thought and this has happened to me with the same symptoms, mine was a perished fuel line in the tank.
Something else to try??

Yup. I will check if it after I bypass the fuel lines with my quick connects.??

 

[1Coopgt]

Sounds like your vent is clogged bro.

 

[crucialRC]

Sounds like your vent is clogged bro.

Yeah Coop, I will check that when i get home also.

But check this, I left the park and went over my in laws house for family dinner and for shits n giggles I went back out to the suburban to see if the primer bulb was still not working. Guess what, it was now working. So I took it for another run in his yard with no body on and this time no problems. After 20min running no problems and the primer bulb was still full and cycling fuel, but the tank still had a little pressure in it. So now the delimma....what is causing the tank vacuum issue? I'm still going to go home and check the fuel lines and tank vent tho.

 

[DougStar]

Now sounds like a heat issue.........

 

[crucialRC]

Now sounds like a heat issue.........

I thought so too but what about the tank pressure? If something is wrong with the vent wouldn’t that starve the carb also? I didn’t get a chance to check the lines and vent last night so I am going to check them both when I get home from work. I have never had a heat problem since I’ve holed out the body. Either way I’m going to find out today. Thanks guys??

 

[DougStar]

What manifold you running ?
On the carb

 

[crucialRC]

What manifold you running ?
On the carb

I assume stock manifold at the moment but I found something very interesting that needs to be posted. I pulled off the tank vent and tried sucking air through it. ?Nada. So being who we are, I took it apart. It consists of 3 parts. A plastic vent tube, rubber bladder, and cap. To my surprise the vent tube had a place where it should have been cut to allow air into the tube and through the cap. I cut a slit in the tube and reassembled and voila, the vent was acting properly. Reassembled the assembly and now I have to take her for a spin. I also noticed that the primer bulb seemed easier to push and seemed to fill up more.??