more carb questions

[bchaffin]

So I have been working on my bike for about 2 months now (when I find the time). I have pulled the carbs and gone through them completely. I installed some inline fuel filters. My question is when I turn it to prime I can clearly see the fuel going through the filter but when I put it to on and it is running I cant see it flowing any more. The bike stays running but when you roll on the throtle it sputters and dies. What could be some issues to look into?

[brcree]

carbs

After reading many threads in here I understand that prime is used for runnen your bike, "on" is for tuning and runnen bike as you work on it. Vacuum system I believe, must be in use for the "on" to work, could be wrong. Anyone else help out?

[WMarshy]

Possible kink, trace your line and make sure its not pinched. There are some diagrams some where on how to route them. Do a little search and it will keep you busy. Lots of other possibilities but start with the easiest... How well did you clean them? Browse through the tech tips on how to clean your carbs and you might find something that you missed..?

[WMarshy]

PRI is only used to "prime" your carbs if you have ran out of fuel. It lets gas flow regardless if the bike is running or not. Our bikes have a vacuum operated system that is closed when the engine is off and 'opens' when the bike is running, when in the 'ON' position. I always use on while riding and/or tuning, no real other reason to use PRI other than stated above.

[CatatonicBug]

After reading many threads in here I understand that prime is used for runnen your bike, "on" is for tuning and runnen bike as you work on it. Vacuum system I believe, must be in use for the "on" to work, could be wrong. Anyone else help out?

Not really. "Prime" is used for tuning, or for filling the carbs after you've taken them out and emptied the fuel from them. It bypasses the vacuum diaphragm and allows fuel to flow without the engine turning. "On" is used for everyday use. The turning of the engine creates a vacuum that allows the fuel to flow.

[brcree]

carbs.....

Just tryen to get a handle on this item.......if you are not runnen a vacuum system and use straight fuel lines with filters is there still a vacuum?

[CatatonicBug]

Just tryen to get a handle on this item.......if you are not runnen a vacuum system and use straight fuel lines with filters is there still a vacuum?

The vacuum system is part of the bike... If you have the stock petcocks, you connect a line from the petcock to the intake boots (the one used for sync'ing the carbs). Of course, if you choose NOT to connect things that way, you are forced to bypass the diaphragms by using "Prime" all the time.

[bchaffin]

How well did you clean them? Browse through the tech tips on how to clean your carbs and you might find something that you missed..?

I have taken the carbs apart a couple times now. The first time I thought they looked clean so I just did minor cleaning. Bad idea. This last time I took every thing off the carbs cleaned every thing with carb cleaner and blew every thing out. I still need to sync the carbs and do some final adjusting just thought I would see the fuel flowing more then I did.

[WMarshy]

The only way your not using the vac in your fuel system is if:

1. you ditch the Octy, on the later models, or
2. go to full manual petcocks, for the earlier style that had the diaphram inside the petcock valve body


What size jets are you using, did you do a bench sync and check float height?

[CatatonicBug]

Gravity does a lot of the action, but not all of it. There is a siphon effect once the lines are full of fuel. You might try filling the lines before attaching them, and get all the air out first. This might not be the issue, but it might be worth a shot...

[DGXSER]

So, you look to have a standard. This means you have vacuum operated petcocks in the ON and RESERVE positions. When in the PRIME position, as stated, you bypass the Vacuum valve inside your petcocks.

On the Special models, they use the OCTY or a separate single vacuum valve to control fuel in the ON and RESERVE functions. Again, it is also bypassed in the PRIME position.

You stated that your bike is running good in the PRIME position, this would indicate your carbs are not the issue, your petcocks are. If you forgot to hook up the vacuum lines, or your petcocks are not working properly, then you will starve for fuel when in the ON or RESERVE positions. What you describe is exactly what happens when the bike is fuel starved and it will slowly run out and die.

Basically, PRIME does as stated and bypasses the vacuum valve(s). It can be used to run the bike continuously. Thunderstruck was left on PRIME when I got it because the OCTY was shot and no one repiped or fixed it. Take note though, running on PRIME eliminates the reserve function, so when you sputter out of gas on PRIME, your done, wlecome to the walking brigade!!

[bchaffin]

What size jets are you using, did you do a bench sync and check float height?

I believe it has 138 main jets in it. I did check the float hights and I still need to put my guages on the bike to sync the carbs.

[Ken Talbot]

If you forgot to hook up the vacuum lines, or your petcocks are not working properly, then you will starve for fuel when in the ON or RESERVE positions. What you describe is exactly what happens when the bike is fuel starved and it will slowly run out and die.

Cracked vacuum lines can also cause trouble - they leak so you end up without enough vacuum to fully open the diaphragm in the petcock.