Topic: Bike Running Poorly on Reserve - Problem Solved

[Tom C]

Just putting this up here so that perhaps the next time this problem happens to some other noob he will do a search and find this post.

I've been slowly working on the restoration of this 74 CB550:



A good friend did the paint job on the tank and side covers.  The inside of the tank is in good shape. 
I haven't ridden her too much since the tank was painted, but the other day I took her out far enough to run her down to the reserve tank.  Once she was on reserve she ran very poorly until I filled up the tank at the closest gas station.  If felt like there wasn't enough fuel getting to the carbs to keep them all happy.  Once filled and switched back to to the "on" position on the petcock she ran fine. 

This particular bike has this type of petcock:

..when the petcock is set to reserve, fuel enters the petcock bowl through the gap between the copper tube of the petcock and the center hole drilled through the bottom of the fuel tank, shown here:


If there is gunk or paint remnants in that hole it will slow down the flow of fuel when the bike is on reserve.  That's what happened to me. 

When I got home from that ride I tested the fuel flow on both main and reserve settings of the petcock.  Fuel flow through the main circuit was fine, fuel flow through the reserve circuit was a dribble.  It was enough to keep me going at about 25 mph for my 6 mile ride to the nearest gas station. 

I fixed the problem by scraping the excess paint out of the center hole of the petcock mount and re installing the petcock.  Now I have good fuel flow on both the main and reserve petcock settings!   

Anyway I hope this doesn't happen to any of you but if it does perhaps you'll find this post helpful.   

[Robbo]

Nice looking bike

I had a similar issue on an original CB350four (not at all paint related though) and had to disassemble the petcock and clean out the reserve flow channel.  That area tends to get a buildup over time.


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[bryanj]

Small point it cant be both 72 and a 550

[Tom C]

Thanks Bryanj, it is a 74 CB550K0, not 72 as I said in my first post (since corrected).  My first SOHC/4 resto was a 72 CB350f.  I get the years mixed up sometimes.  Along with most everything else...

[bryanj]

Wait till you get to my age, you get the days mixed up then-----special on virus lockdown

[Capistro]

With this dual outlet petcock, how are the fuel lines supposed to be set up?  Is one outlet for 'on' and the other 'reserve'?  Or do they both flow together?     

[PeWe]

Both flows in parallel.
One hose for carb 1-2,
2nd hose for 3-4

Important to shut it off when parked. Not good if carbs overflow and fill engine. My carbs are OK, but I do not take the risk.

I saw a bent rod from a CBX1000 yesterday that had been started after carbs had overflooded and filled engine.

[Deltarider]

One hose for carb 1-2, length should be 18cm
2nd hose for 3-4, length should be 30cm
Ideal internal ø is 5,5mm.
Abstain from inline filters!

[jonda500]

Important to shut it off when parked. Not good if carbs overflow and fill engine. My carbs are OK, but I do not take the risk.

I saw a bent rod from a CBX1000 yesterday that had been started after carbs had overflooded and filled engine.

I leave my fuel tap on reserve at all times in case I leave the bike parked for weeks - if my fuel tap is left turned off and the fuel in the float bowls evaporates enough to use up the tiny bit of fuel in the rubber lines between the fuel tap and the two metal tee's between the carbs, the 'o' rings on the tee's dry out and fuel pisses out under the carbs the next time I turn it back on   
n.b. if the overflow rubber tubes and tubes in the float bowls are clear the engine cannot flood...

[Deltarider]

That's why I keep my carbs always in their natural state: wet. Also in winter. So far I did not have to replace any O-rings at the T-joints. They're 45 years old...

[jonda500]

I sure wish I'd known to request harisuluv to NOT replace those fuel tee 'o' rings when I had him restore my carbs!