Custom Fighters - Custom Streetfighter Motorcycle Forum banner

1 - 20 of 27 Posts

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #1 · (Edited)
Fuel intake issue?

So. Today I tried to tackle my problem with the bike not starting.
Tried to start her a few times but nothing. She turns over fine but no combustion.
so i took off a plug and it was completely dry!
..so were the other 3. I took off my fuel line and when i turned
the petcock on Prime - nothing. Now i did a bit of reading and my 3 option petcock (reserve, prime, on) is supposed to be a vacuum one, right? Meaning it has an extra vacuum hose coming into the petcock and basically it requires air to pump out the fuel from the tank. So i figured it wasn't getting air. I opened up my tank's cap and what do you know - we have flow (rhyme unintentional). So i just took off the tank's overflow/breather hose since i figured the lock mechanism it has (with a small ball inside) must be broken or something.

Put the cap back on and fuel continued to poor when in prime. Small success. Then i set it on On and tried to start her but not a drop came..
When i reconnected the fuel hose and set it on prime - nothing. I mean even without cranking there should still be fuel pouring from the... Err... 'overflow hoses' or what not, right?

Any thoughts to what my next step is analyzing this issue?
Feel free to ask stuff for i'm not sure i was very clear. Also, all sorts of education on the hoses and vacuum system is greatly appreciated and welcome, if anyone is bored enough at work or something.

cheers
 

·
sickboy
Joined
·
3,544 Posts
Cant remember what bike you have but them diaphragm carbs (assuming) and vacuum petcocks can be a pain sometimes. I find if you use some starting fluid to get it running the vacuum from the bike actually running will get things flowing again.
 

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #3 ·
Yammer '89 XJ600 and diaphragm carbs indeed. Alright then. I'll get her going with starter fluid or injecting fuel straight from the spark plug holes and I'll get back to you see how it works out.
Thanks for helpin out.
 

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #4 ·
I've been thinking about this now.. and the starter fluid/fuel injection solution seems kind of a temporary fix.. or isn't it?
Cos I'd like to get to the bottom of this so it'd start on it's own every time and not need a mandatory fix like every two months.
.. if my point makes any sense
 

·
Vtwin
Joined
·
3,945 Posts
Re: Fuel intake issue?

I've dealt with this type of petcock on my drz, when it is on prime the fuel should flow regardless of if the engine is running/cranking, that is what the "prime" setting is for, to get enough fuel for the engine to fire creating the vacuum and opening the petcock, the vacuum feature is only suppose to work when it is set to ON

Set it to prime to fill the carbs then switch to on to start

From what you said earlier it sounds like your fuel cap may be creating an air lock in the tank


Sent from Motorcycle.com App
 

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #6 ·
Indeed. But the prime only works when i don't have the fuel hose connected.. I mean, prime should allow
the fuel to flow regardless of any hose set up I have. Even if there is an air lock by the cap - the fuel should flow until the free air runs out in the tank, right? So to recap:
Main fuel hose disconnected from the petcock - Prime - Fuel flows fine
Main fuel hose connected - Prime - No dice
Main hose connected/disconnected - On - Starting - No dice

Thoughts?
 

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #7 ·
Oh also my tank's cap is air-tight/non-breathable whatever you want to call it. That's why it has that separate hose,
which I've now removed. What kind of options do I have for switching out the cap? I saw UF cut out his top part of the tank and replace it with a newer tank's part which had a flushed cap - looked real sweet. But are there any other ways or is cut and weld my only way to go 'bout it?
 

·
Vtwin
Joined
·
3,945 Posts
Indeed. But the prime only works when i don't have the fuel hose connected.. I mean, prime should allow
the fuel to flow regardless of any hose set up I have. Even if there is an air lock by the cap - the fuel should flow until the free air runs out in the tank, right? So to recap:
Main fuel hose disconnected from the petcock - Prime - Fuel flows fine
Main fuel hose connected - Prime - No dice
Main hose connected/disconnected - On - Starting - No dice

Thoughts?
That being the case I would have to say the carbs are plugged or for some reason or another not allowing fuel past the needle valves....have you tried blowing into the fuel inlet on the carbs themselves? With say an air hose....not really a recommended practice but...maybe if ya get desperate


Sent from Motorcycle.com App
 

·
Super Moderator
Joined
·
3,021 Posts
Can you take off the fuel valve and disassemble it? Maybe it was rebuilt at some point and something installed wrong?

Later, Doug
 

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #10 ·
Doug - but i've had it start with this same set up before as well..

Whip - its weird that ALL spark plugs are dry. If this were a carb issue, wouldnt there be small problems in different cylinders? I mean, carbs are all separate right? As thus, its kinda unlikely that they all got the same issue..?


I'll take the carbs off thursday and give them a clean just in case. Also gotta check if the diaphragms are all tight.
 

·
Vtwin
Joined
·
3,945 Posts
Re: Fuel intake issue?

Not sure how yours is setup but I've seen both, one with rail style that feeds each carb and one that the first carb gets the fuel line and the rest are fed of that carb


Sent from Motorcycle.com App
 

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #12 ·
Umm... both the 1st and 4th carb have a fuel line going to them from the petcock and then the 2nd and 3rd carb
are connected just to each other ... Now that I think of it, doesn't make a whole lot of sense :confused:
 

·
Vtwin
Joined
·
3,945 Posts
Re: Fuel intake issue?

Hmm...that is kinda strange, but if ur getting fuel to the carbs in those fuel lines then the block has to be IN the carbs somewhere, either clogged or some sort of air or vapor lock

Don't most carbs have some sort of breather to the float bowl?.....so the air displaced by the entering fuel can escape?


Sent from Motorcycle.com App
 

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #14 ·
Excellent question (I think?)... now how do I check that? :D
 

·
Vtwin
Joined
·
3,945 Posts
Re: Fuel intake issue?

Hmm...my drz had a CV carb and I believe there was a port that went from where the cv boot is down into the bowl area....really the only reason I know this is from shooting wd40 through all the ports to clean it and thought it was strange that one of then shot all the way through

....I'm really just brainstorming here so if anyone else can jump in by all means


Sent from Motorcycle.com App
 
  • Like
Reactions: ants

·
Legit goon
Joined
·
1,466 Posts
Discussion Starter · #16 ·
Yeah, I know. Really wish CF wasn't such a desert in the Summer season... But thanks for
hanging in here with me Whip.


So... I just took off my carbs (MUCH freakin easier the second go around!) and... damn! Everything looks decent
and still clean. Also, there was some fuel in the carbs - plenty for sure to start the bike! So I'm definite now that..
a) my prime doesn't work on the petcock when the fuel line is connected
b) there must be some air lock or escape or what not, not allowing my system to be in a vacuum state or something somehow not allowing the air to move and pump fuel around?

I was a bit iffy about one of the diaphragms but since the needle moves back up (or down?) when I compress it,
everything should be o.k. right?

I'm so damn pissed cos everything should work just fine and yet I'm missing something ... :hairpull: :hairpull: :hairpull: :hairpull:

Someone please toss some more ideas my way! I'll check my fucking chain slack if that helps you figure some shit out at this point ..
 

·
Vtwin
Joined
·
3,945 Posts

·
Watch the world burn
Joined
·
1,046 Posts
Maybe a dumb question...but is there enough gas in the tank? Have you tried running it in reserve?

*edit* the only reason I ask is because my father-in-law was convinced his 4 wheeler's "on" didn't work and would leave it in reserve. I filled the tank and the on position works fine, he had just run it low on gas.
 
  • Like
Reactions: ants
1 - 20 of 27 Posts
Top