'81 CB750C "Rock-It" (X-Basket Case)

I'm confused, not difficult really. You said you had good flow from the petcock then later you say just a few tiny bubbles. Do you mean good flow with a few bubbles of air in it?

When you had the petcock off the tank did you manage to get the internal tank filter out as well and clean it. They are a PIA and sometimes wont come out. Are you sure the tank cap vent is OK and not causing a vacuum and is the fuel filter on the right way if its not bi-directional.
 
If I take the fuel hose off the carb connection and open the petcock it flows like crazy. I did pull the small bowl off the petcock and the new filter screen I had installed still was clean. Tank, petcock, filter are not the issue. Something past that in the carbs is not letting fuel flow. After sleeping on it I am wondering since this is the first time running with the actual fuel tank if something made all 4 fuel valves stick.
 
Hoosier, I don't know anything about CB carbs. But is there a vacuum tube to the carbs themselves? I've seen them get pinched / clogged on other bikes and it's enough to dry out the bowls.
 
There was a vacuum controled fuel shut off valve on the 81 CB750, affectionatly known as the Spawn of Satan... but with them being so problematic I removed mine and capped off the vacuum port during the rebuild.
 
That would be really unlucky to have all four blocked in the same place at the same time. which would lead me to think it is the Carb T between 1&2 or the fuel lines blocked.
What happens if you unscrew the bowl drain on number 4? If it keeps flowing well past a bowl full then fuel delivery to bowls is not blocked and the problem is elsewhere.

The tank filter I was refer to is inside the tank a 3" plastic mesh tube that controls the reserve.
 
notlob said:
That would be really unlucky to have all four blocked in the same place at the same time. which would lead me to think it is the Carb T between 1&2 or the fuel lines blocked.
What happens if you unscrew the bowl drain on number 4? If it keeps flowing well past a bowl full then fuel delivery to bowls is not blocked and the problem is elsewhere.

The tank filter I was refer to is inside the tank a 3" plastic mesh tube that controls the reserve.
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That is the plan of action I planned to take tonight if time permits. Open the bowl drains on 1 and 4 and verify fuel flow of the outboard carbs.
 
peteGS said:
I've been missing out HD, she sounds great! Haven't logged into DTT for a bit and missed it :-[
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Hey Pete! Thanks, I am the same way with theGSResources. Haven't been on there in a long time.
We had plans last night with some friends, good time and all but didn't touch the bike. It rained here again last night so mowing is postponed... guess I gotta go out to the shop. ;)
 
MAN!
Something went horribly wrong with fuel tank cleaning process this time.
Opened the float bowl drains and only got a dribble of fuel out of all 4.
Pulled #1 bowl off and it was FULL of some grainy, amber, sludge!
I tried to remove the float thinking I could spray carb cleaner and examine the float valve seat but it was stuck solid!
I pulled the entire carb rack and disassembled them again... sprayed out the bowls. The jets, drain screws and accelerator pump came apart easily but the float valves and seats were corroded something fierce. Had to use needle nose pliers to extract them. I have the bits re-soaking in the Berrymans now and bought two cans of spray carb cleaner. It's been about 3 hours later and things are starting to come clean.
Drained the two day old fuel out of the tank and it was brown and cloudy. The inside of the tank is covered with a thin rusty film. Rinsing it out with Kerosene now then I'll do it a few times with fresh gasoline and see how it looks. One of the steps I used at some point went WAY wrong once the gasoline hit it. :-[
 
Bugger! What'd you use to clean it? I'm still happy I did the POR 15 treatment on mine... holding up and it's getting on for two years down the track now...
 
Nope, no liner of any kind in the tank, PO15 or Kreem. I used the same process I did on the Suzuki tank that still looks shiney two years later. Had used "The Works" to remove the rust, then flushed with rubbing alcohol, lastly a coating of Marvel Mystery oil to prevent it from rusting while in storage. I just must not have gotten all the contaninant out or it reappeared inside the tank that I couldn't see while I had it stored.
Carb bits are cleaning up well so all is not lost.
 
Hoosier Daddy said:
Nope, no liner of any kind in the tank, PO15 or Kreem. I used the same process I did on the Suzuki tank that still looks shiney two years later. Had used "The Works" to remove the rust, then flushed with rubbing alcohol, lastly a coating of Marvel Mystery oil to prevent it from rusting while in storage. I just must not have gotten all the contaninant out or it reappeared inside the tank that I couldn't see while I had it stored.
Carb bits are cleaning up well so all is not lost.
Click to expand...

Good luck with the cleaning, you guys seam to have a plethora of tank and carb cleaning chemicals we cant get hold of here. Dont forget that filter inside the tank or you'll never get everything out of the tank.
 
Got the carbs cleaned back up over the weeked, lost of soaking and spraying. I flushed the tank several times until the fuel ran out clear. Reassembled and rode her again last night. Seems to be running fine once again. Now is the waiting game to see if it STAYS that way.
 
Was a nice day out so I grabbed a few pics. Not ready for the "Before and After" thread yet, but she is getting close.

Rock-it2_zps01958943.jpg


Rock-it3_zps3adf91be.jpg


Rock-it1_zpsa4d85a00.jpg
 
Thanks guys, it is really appreciated. I still have some minor cosmetics to sort out, need 4 screws for the tank emblems, 4 fuel line clamps, and need to cut and bend some aluminum I picked up for the side covers.
Let's just hope when I get home tonight the gas stayed in liquid form.... craziest damned thing. ::)
 
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