Topic: CB550F Fuel Issue

[rcollins09]

Hello everyone. I have been having issues with my 76 CB550F supersport stalling after a 4-5 miles cruise to work. I can get to work fine stay there all day. Start it up like a champ with the electric start and then ride it home…. runs great to I get right by my house 3-4 miles and bogs and shuts down. I have done ALOT of diagnosing of all the electronics and everything is good from stator, battery, rectifier, regulator, points are fine, valves are adjusted properly etc. After thinking the issue was electrical and doing all the previous tests I finally figured out it was fuel starvation. When I get to the same exact spot it dies I notice that fuel lines were empty but the tank is full and the petcock is clean and open. I have been noticing my fuel tank starting to hold alot of pressure. When I loosing the cap it releases all the pressure and fuel begins to rush into the carbs. I let them fill back up and the bike starts right back up. I know the fuel cap has a vent on it somewhere and Im sure its plugged or clogged is there any way to clean it out? I have been looking for a new cap but have had no lucking finding one. Its the one that is under the metal fuel door (supersport).  Does all the technical gurus think I am right with my final diagnosis? Love to hear any opinions. I have read hundreds of faqs and posted from twotired etc and have learned a ton. I think all I need is a new cap but i want reassurance.

Thanks,

Ryan

[DJ_AX]

Yep... that's it.
On my cap the vent hole is pretty obvious.. not sure about yours but I'd bet it's repairable. Maybe someone else will chime in.

[rcollins09]

I figured if see it plain as day to but i see nothing on this dang thing…there is a vent in the tank itself where it looks like it would drain gas if you spill in the resets part of the tank but there is nothing on this cap anywhere.

[LesterPiglet]

That's odd. If it's not the original cap get your tiniest drill bit and put a tiny hole in it. The hole in my cap is obvious, it's in the middle of the raised part you grab to unscrew it.

[bollingball]

Hold up don't start drilling it comes apart.
Ken

[TwoTired]

I figured if see it plain as day to but i see nothing on this dang thing…there is a vent in the tank itself where it looks like it would drain gas if you spill in the resets part of the tank but there is nothing on this cap anywhere.

Lift the bail and look for a triangular hole that it hides in the ridge/step on top.

[bollingball]

This will explain how it. If the rubber seal is cracked this is a good time to replace it Honda still has them or you can make one. scroll down for some pictures easy fix.

http://forums.sohc4.net/index.php?topic=35056.0

Ken

[TwoTired]

This will explain how it. If the rubber seal is cracked this is a good time to replace it Honda still has them or you can make one.

http://forums.sohc4.net/index.php?topic=35056.0

Ken

Er....
The F model has a completely different fuel cap arrangement from the early K models.  In 77 the fuel cap changed again for both models.

Cheers,

[bollingball]

This will explain how it. If the rubber seal is cracked this is a good time to replace it Honda still has them or you can make one.

http://forums.sohc4.net/index.php?topic=35056.0

Ken

Er....
The F model has a completely different fuel cap arrangement from the early K models.  In 77 the fuel cap changed again for both models.

Cheers,

Sorry about that. When he said he had the fuel door I thought it was like mine. Do you have any pics of this cap and how to fix it?

Ken

[bollingball]

TT when you say lift the bail what do you mean? I have never had one of these caps and can not visualise what they look like.
Ken

[TwoTired]

75 and 76 F model tanks, both CB550F and Cb750F had this cap style.
Click the picture and you can see a triangular hole in the top.

Cheers,

[bollingball]

75 and 76 F model tanks, both CB550F and Cb750F had this cap style.
Click the picture and you can see a triangular hole in the top.

Cheers,

OK thanks TT First time to see one like that. So the inside does not come apart like mine?

Ken

[rcollins09]

So is there anyway to fix this style cap then or is my hunt to find a new one continue? So annoying that my bike wont run right due to a gas cap. But o well

[TwoTired]

I've never had to take one apart.  The top metal component appears to be "crimped" onto the lower metal bit.  That might be a challenge to replicate, assuming you could undo the crimp for dissassembly.  There's a big honkin' spring inside it, presumably pushing against that crimp.

 Did you check the hole was clear?  Fish any wire through it?  Can you blow through the hole?

I'd be tempted to dunk the whole thing in "Metal Prep" before attempting to take it apart.  Mine could use cleaning.  Maybe I'll try that on my rusty one.  But, I have 3 aquarium air pumps the refurbish, and a window fan to repair first.  The chores are stacking up.   

Cheers,

[lostmykeys]

 I started a thread a week or so ago about this very subject.
 I got a reply from Bollingball about how to take the cap appart to clean.My cap is different than the pictures he provided.
 I'm working on a 78 f3.
 My bike was cutting out at 85 mph or if I was running steady at 65 to 70 mph and I applied more throttle it would bog until I let off and be fine in the 65 to 70 mph range but would pull itself to 85 before cutting out again.
 My gas cap has a ridge on the top so that it can be unscrewed with a hole in the middle of the ridge.On the bottom of the cap there is a U shapped loop.
 I dont have the bail on my cap and after looking over the cap with the rubber seal removed I couldn't find a triagular hole anywhere.
 So today I took my 1/16 drill bit and my Dremel and drilled from the existing hole in the top of the cap until I saw the bit come out in the U shapped loop in the bottom of the cap,went thruogh it like butter.
 I speant more time making sure to get out any metal shavings with carb cleaner and compressed air.
 I put the cap back on and started the bike,the first thing I noticed was that the bike warmed up faster the second thing I noticed was when I was at the speeds mentioned above the bog turned into just a slight hesitation,but then the bike would start pulling hard again.
 At this point I'm back in the garage rerouting the fuel line and inline filter so that it has the shortest route to the carbs and the line is running at a downward angle from the petcock to the fuel inlet on the carbs.
 I had my fuel line and inline filter running downward before but I suspect that I had too much line before.
 So part of the problem may have been there was too much slack in the fuel line so that at higher speeds the air preasure could move the line and hold it in a possition that may cause fuel starvation.

[lucky]

Do you know how far a motorcycle will go on JUST the fuel in the float bowls?

3-4 miles in many cases. Check that your float bowl vents work. Make sure they are not pinched.

[rcollins09]

Just to finish this thread I ended drilling a very small hole where the original vent was suppose to come out and the issue has been fixed. If people want I can take a picture. Rode the bike for 2 hours today and road like a champ…although on occasion when I stop at a stop light or stop sign and go to take off it kind of bogs/hiccups a but right when I let out the clutch..no idea whats causing that but i can live with it!