Topic: New member...cb550f pic new build...runs out of fuel @ open throttle

[pannonia]

Hi, I'm a new member, and have been putting together a fun bike which now works great, except for the seat pad which i still need to make, and the fact that when open throttle at higher speeds runs out of gas and stalls. details: the carbs have been rejetted and work great, no flat spots, k&n pods, inner baffle drilled. my guess is that the bike sucks a lot more fuel than it used to/ supposed to and the engine stalls when it can't get enough fuel due to the limiting flow of the petcock. one, i am not sure if my hypothesis is correct, so would like to ask here, second: if it is correct, has anyone found a suitable higher-flow petcock replacement? my bike is a 75. thanks!

[DJ_AX]

So you're saying it's running way too lean... do the plugs agree?
Maybe the float level is just low.
Did you do the 3k tune up?

And welcome to the site...

[pannonia]

it does not run lean. i have not checked the plugs but it runs just fine until it runs out of gas at open throttle. does not turn lean - not a mixture issue. it literally runs out of gas. float bowls empty (not lack of fuel going from float bowls to cylinders).
thanks for the welcome!

[xnoahx]

Clogged in tank fuel filter?

[bollingball]

First off if it is running out fuel have you had the petcock off you should have a in tank filter is it clean.? Has a PO put a in line filter in? You can still get the in tank filter from Honda. Take a length of fuel line and time how long it takes to fill a given amount of fuel into a container with the filter. Then time it without a filter.
Ken

[bollingball]

Also make sure the vent is open
Ken

[Fritz]

If the petcock was the limiting factor, you bike must have real poor fuel economy, like 5 mpg.

So, clogged filter or vent hole in gas cap might rather be the issue. If you are using an in line filter, throw it away and renew your petcock screen.

Cheers
Carsten

[pannonia]

Thanks for all the replies.
The reason I do not believe it is a venting issue is that the vent is open, plus if it were clogged/unvented then once the bike stalled while running it would not start up again until the gas gap were removed, i would hear the vacuum when i did, etc.

The reason I do not think it is a clogged in tank fuel filter is that it was cleaned well before reinstalling on clean tank withh new gas. proper masking during painting, etc.
The reason I do not think it is an inline fuel filter is that i replace them and the fuel lines,  all is new
Now - there was kink in one of the lines i thought had been causing it, but i removed the inline filter from that one to help eliminate the kink, but issue still happens.

I am not positive about any of the above not being the issue, just sharing my thought process and would definitely encourage anyone to help figure out where i may be making wrong assumptions.

The comment that if if the petcock is the limiting factor, i must have really poor fuel economy leads be to believe that even with engines tuned to require much more fuel than mine (my carbs are rejetted wtih 120's i think, k&n pods, inner baffle drilled) but i have not done any crank or cam or head/cylinder work - all is stock 550. so if others who have done serious tuning are able to use the same  stock petcock, that would really help me exclude that hypothesis as a potential cause, and may force me to revisit other potential culprits? Can someone confirm that they are runnign similar/ more highly tuned-to-need-more-fuel-than-mine setups with the original petcock?

And again - not a carb tuning issue, the bike runs great wtih no flat spots.

I don't think it should matter but I'll say it here; the plugs are all new D7EV NGK that i found $10 for 4 on eBay.

Thanks again for all the help, I promise to update on the solution, as it will be found...

[pannonia]

sorry, i have question on one of the previous comments, about throwing away the inline filter. i was thinking that the filters are new so they must be ok, but now i am wondering if others have found that the mere presence of an inline filter can cause problems, even if new/clear? Hard for me to understand how that could be the case, unless it was that the inline filters caused a secondary problem of kinking, but i figured i'd ask more about that comment. thanks!

[TerryK]

There is no way your stock CB550 is pulling more fuel than a stock petcock can supply. I'm guessing your float levels are way low.

BTW, how do you know for sure it's a fuel issue? Could very well be ignition related.

[Fritz]

I was thinking that the filters are new so they must be ok, but now i am wondering if others have found that the mere presence of an inline filter can cause problems, even if new/clear?

It's just my opinion. Read the full discussion at http://forums.sohc4.net/index.php?topic=33389.0

However, Terry's right: If you think that you fuel line, vent and petcock are good, and are confident that it's a fuel issue, you might have a look at the float levels.