- Joined
- May 8, 2008
- Messages
- 15,018
- Reaction score
- 1,190
- Points
- 113
- Location
- San Diego, Ca.
Does that valve have 2 hoses? One for fuel to the carbs and on that get vacuum?
high rpm when transmission isn't engaged
- Thread starter 87fz600
- Start date
Does that valve have 2 hoses? One for fuel to the carbs and on that get vacuum?
87fz600
Junior Member
It's got two hoses, one to get fuel to the carbs and one goes to the top of one carb. Jblk9695 says its a vacuum hose to actuate the fuel valve. When I blow pressure into the hose there is no free flow at all. It's like blowing into a completely clogged hose but the hose is clear and valve is clean. Was curious as to whether its supposed to eventually give way since its a vacuum. Wouldn't the air supposed to be a sucking action and not a blowing action which is what comes out of the nipple on top of the carb. If this isn't working correctly could that be a cause of the high rev?
- Joined
- Feb 7, 2009
- Messages
- 12,549
- Reaction score
- 1,197
- Points
- 113
- Location
- Cape Coral, Florida, USA
It needs VACUUM to operate, not pressure.... Where tha air hose attaches is a vacuum port, it sucks air thru the carb/venturi. There may be a PRIME SETTING on the valve that will allow fuel to flow without vacuum. Try disconnecting the fuel line and point it into a can. Turn the valve (with the engine off) and see if fuel flows in any position, reserve may work without vacuum.
If you have a spare, small lawnmower gas tank or such, you can by pass the vacuum valve (cap that off if by passing) and try the bike. Eliminate or verify the valve one way or the other.
You mentioned giving the carbs a quick cleaning. I would strongly suggest re-checking the main and idle jets as they have very small holes and clog easily(especially the idle jets). Pull them OUT and MAKE sure you can SEE THRU THEM.
As stated previously, it does sound like a vacuum leak, most likely the intake tubes from the head to the carb's. I'm sure their made of rubber and being 24+ years old, I wouldn't trust them. Even if you don't see any cracks, they may not be tightening down flat on the head or around the carbs allowing air in. A check of the spark plugs may show a white (lean) plug verifying this...
Good luck
Last edited:
87fz600
Junior Member
Is the vacuum hose supposed to go to the boot between the carbs and heads or into the top of one of the carbs? One carb is different from the rest having another outlet near the choke and it has a nipple on it. I will post pictures of it once I get to my computer instead of my cell phone. doing a thorough carb clean right now.
Jblk9695
Elite Member
- Joined
- Aug 9, 2009
- Messages
- 1,603
- Reaction score
- 56
- Points
- 0
- Location
- Back in San Bernardino, Ca.
If possible take a photo down the throat of the carbs from both ends, just curious what the butterfly's and vacuum slide look like. Not sure about the vacuum line for the fuel valve but some photos of the carbs will help.
Jerry
Jerry
87fz600
Junior Member
I cleaned the carbs and put them back together but I will be back down to work on the bike on Monday so I'll take the covers off and take pictures. Here is the picture of the carb with the super cool extra piece lol. One awesome upside down picture...easily corrected by standing on your head or turning the computer monitor upside down...your choice. Dumb camera man I am haha
- Joined
- Feb 7, 2009
- Messages
- 12,549
- Reaction score
- 1,197
- Points
- 113
- Location
- Cape Coral, Florida, USA
On the second picture, the one with the covered nipple would provide vacuum for the pet****.
Are there nipples on the intake rubber mounts? There should be another set of nipples (one on each carb) in that area for syncing the carbs. Syncing involves checking the vaccum between all 4 carbs and adjusting accordingly. Looking at Babbits parts fisch, you'd adjust the sync with a vacuum gauge by turning those screws in or out (once running correctly) and getting an even vacuum pull from all 4 cylinders...
I could not find the intake boots on the parts fisch......
Last edited:
87fz600
Junior Member
Yeah there are nipples on the rubber mounts. The second hose from the pet**** went to the nipple on the rubber mount, not the carb. It's supposed to go to the one on the carb? I don't have any clue what was done to this bike before I got it so I'm teying to figure it out and get it running like it should. Thanks again everyone for your help.
Oh yeah, the pictures are the same carbs I just put the cover back on to show which one I was talking about. That's the only one like it out of the 4.
Oh yeah, the pictures are the same carbs I just put the cover back on to show which one I was talking about. That's the only one like it out of the 4.
Last edited:
- Joined
- Feb 7, 2009
- Messages
- 12,549
- Reaction score
- 1,197
- Points
- 113
- Location
- Cape Coral, Florida, USA
The fuel valve just needs a vacuum to operate. That covered nipple, being the only one, is most likely what thats for.
The other 4 nipples on the intake boots are also vacuum, for syncing the carbs once assembled. They should be capped when NOT SYNCRONIZING. If their open, you will have a lean condition big time . They should be capped otherwise...
87fz600
Junior Member
I'll cap the one on the boot that the hose went to and run it to the carb once my tank gets here and let you guys (gals too for those reading this) and let you know how it goes. Tank should be here sometime next week. Could the hose being mounted wrong be the cause of the high idle? I couldn't find any more air leaks before we removed the old tank but I will check again once the new one is installed.
Jblk9695
Elite Member
- Joined
- Aug 9, 2009
- Messages
- 1,603
- Reaction score
- 56
- Points
- 0
- Location
- Back in San Bernardino, Ca.
Has it always idled at 4-6k? IMHO that is very high for just a vacuum leak and I would still suspect something mechanical but with out being there in person its hard to tell. Keep as informed and hope it turns out to be something simple
Jerry
Jerry
87fz600
Junior Member
It doesn't stay idling that high, it'll randomly shoot up there and once it starts it happens more frequently during the ride. Once in gear and the clutch is slowly let out idle drops back down to normal. Makes me have to half engage the clutch at lights to keep it from being so high or turn the bike off at a stop. A few times I have been riding then I suddenly get a loss of power and I die out. Won't start back up without the choke being opened. Another issue completely I'm sure but I can deal with that at a later date. I'm more worried about the high rev for fear of damage to the engine and burning out the clutch. I figure the die out is the engine being starved of air. tackling harder issues first.
- Joined
- Feb 7, 2009
- Messages
- 12,549
- Reaction score
- 1,197
- Points
- 113
- Location
- Cape Coral, Florida, USA
The vacuum hose, not really. I'd pay super close attention to the rubber carb to head boots if the carbs are SPOTLESS, especially gthe ones that changed the the idle when sprayed.
As stated earlier, you hook up an auxilary gas tank to the main fuel line and eliminate the stock tank and valve for testing purposes. Cap off ALL vacuum line openings if doing this.....
Something also not noted, there is SOMETIMES a metal screen filter INSIDE THE GAS TANK over the fuel valve inlets, if those are clogged, that would limit fuel delivery and cause havoc...
The carb bowls usually have a drain screw on the bottom. Once the bowls are aledgedly full, open the drain screw on each carb(catch the outcoming fuel in a small container) and verify fuel is getting to EACH CARB.
Good luck....
Last edited:
87fz600
Junior Member
Sorry I haven't been posting. Had a busy past couple of days. I won't be back to working on my bike until the 25th when my tank gets here. I can't work on it at my apartment complex and the closest place is an hour away. I will continue to keep you all posted with what I find.
87fz600
Junior Member
So the new tank is on. Started up and rode fine. Went to bring it home and the rpm skyrocketed again during shifts. Made for a hard shift and I think its beginning to mess up the gears. Carbs were completely cleaned and parts lubricated for smooth movement. Don't have the cash for new boots so I'll try a ghetto seal with flex seal or jbweld and see if there is a difference. Hopefully the gears didn't get shredded. New tank is in great shape though so at least something positive happened.
- Joined
- May 8, 2008
- Messages
- 15,018
- Reaction score
- 1,190
- Points
- 113
- Location
- San Diego, Ca.
Don't put JB Weld in the boots. You could clean them (Don't soak them) with some acetone and rub them with some black RTV silicone compound. Let them set up for a day. All you should need it a thin coat on the outside of the boots.
You said it ran okay after installing the tank and then started doing the higher idle symptom? Is this symptom temperature sensitive?
You said it ran okay after installing the tank and then started doing the higher idle symptom? Is this symptom temperature sensitive?
87fz600
Junior Member
Could very well be. I didn't even connect that in my head lol. Thanks for the tip on the boots. Flex seal is a spray rubber so I figured that might work but atv silicone is cheaper and easier to access. What could the high temp issue mean? Or cause it? What would cause this? I put up a search for a new engine, transmission and carb set up so I may just redo the whole mechanics.
Last edited:
87fz600
Junior Member
So someone mentioned to me it sounded like my choke was open. With the plungers down, is there any way the carbs will act like the choke is open? Could engine temp cause this? Is there any engine that will be a simple bolt on swap other then an identical engine as they are hard to come by. Specifically a fz-750 86-88? Any knowledge of a swap like this beIng done?
Jblk9695
Elite Member
- Joined
- Aug 9, 2009
- Messages
- 1,603
- Reaction score
- 56
- Points
- 0
- Location
- Back in San Bernardino, Ca.
Shouldn't cause hi idle with the plungers down unless the choke cable is to tight and pulling them open when you turn the bars.
Might try Ebay for a used set of carbs but no guarantee that they would solve the problem.
Jerry
Might try Ebay for a used set of carbs but no guarantee that they would solve the problem.
Jerry
87fz600
Junior Member
Then its not the choke cuz its not a cable set up. Little piece of metal on the side, no cable...its a bar that is manually pushed on the side of the carbs to open or close the choke.
Similar threads
