high rpm when transmission isn't engaged

[cavaliernik]

I'm not having quite the same issue*, but i have an 86 fz600, and it appears that the pet**** vacuum line may have been connected to one of the manifold boots (is this the right term for the boots between the carbs and heads?) because one of these nipples was open, and the fuel lines were disconnected when i got it. The previous owner had drained the fuel.

Could one of you confirm if the pet**** vacuum hose should be connect here or to one of the carbs. Or does it not matter?

*My bike won't rev past ~2000. Last night i discovered a crack in one of the manifold boots which might have something to do with it, but i'll post a thread about this once i resolve the crack and my fuel delivery issues.

 

[Motogiro]

I'm not having quite the same issue*, but i have an 86 fz600, and it appears that the pet**** vacuum line may have been connected to one of the manifold boots (is this the right term for the boots between the carbs and heads?) because one of these nipples was open, and the fuel lines were disconnected when i got it. The previous owner had drained the fuel.

Could one of you confirm if the pet**** vacuum hose should be connect here or to one of the carbs. Or does it not matter?

*My bike won't rev past ~2000. Last night i discovered a crack in one of the manifold boots which might have something to do with it, but i'll post a thread about this once i resolve the crack and my fuel delivery issues.

The petc0ck vacuum line should be connected to a nipple anywhere after the carbs There should be no open nipples or leakage after the carbs.

 

[FinalImpact]

A couple of things:
If the carbs have not been completely gone through, they could have internal leaks as the temperature changes DUE to hardened seals. Example would be the primers leaking fuel. But a small amount of rust or dirt can plug critical ports. Like Scott said, the ports are tiny. They must remain clear for it to run correctly. I would add an external fuel filter AND "it must have a metal cannister" for fire safety.

The RPM shoots up because the air fuel ratio is incorrect. Either TOO much Air or Not enough Fuel.
-floats stick Up, shuts off fuel, runs lean, RPM rises and then it starves for fuel and tries to die. 1 carb can do this.
-floats stick Up, shuts off fuel, runs lean, RPM rises, runs rough, roughness shakes float free, fuel restored, runs OK.
-dirt in idle or main circuit of carbs, shuts off fuel, runs lean, RPM rises, runs rough, roughness shakes dirt free, fuel restored, runs OK.
-Fuel flow diaphragm looses vacuum. It runs lean, RPMs rise.
-Single carb sticks open, RPM rise, AFR is whacked for the other cylinders.

You are still at a process of elimination. Dirt in the fuel system can plug and cause all of this in one or all of the carbs. So can a sticky butterfly, a vacuum leak, a cracked hose, OR those mounts to the carbs...

Do you own a vacuum gauge?
Can you grab a 50cc syringe at the store?

With these two items you can test the hoses and diapharm for leaks. Test the fuel shut off and simulate the engine running by applying vacuum to the engine shut off valve.

Let me know if you're interested. both are cheap.

 

[FinalImpact]

I'm not having quite the same issue*, but i have an 86 fz600, and it appears that the pet**** vacuum line may have been connected to one of the manifold boots (is this the right term for the boots between the carbs and heads?) because one of these nipples was open, and the fuel lines were disconnected when i got it. The previous owner had drained the fuel.

Could one of you confirm if the pet**** vacuum hose should be connect here or to one of the carbs. Or does it not matter?

*My bike won't rev past ~2000. Last night i discovered a crack in one of the manifold boots which might have something to do with it, but i'll post a thread about this once i resolve the crack and my fuel delivery issues.

In your case:
A large crack is ugly. . . lol haha!

OK -all kidding aside, the carbs would not pull in fuel and this could limit RPM, but it would have to be a pretty fair sized opening. Follow your plan and start a new thread when its back together. See you then. . .

 

[87fz600]

I'm going to have my carbs cleaned by someone far more experienced then I as this is my first bike. I cleaned my carbs on my atv but I think these are far dirtier. One of my buddies said to fill a pan with gas and let them soak. Not sure if it'll work so once I scrape together 200 I'm just going to have them professionally rebuilt. While they are being worked on I will cover the boots with the thin coat od RTV so it eliminates both of those possibilities. Very excited to be back on the pavement again.

 

[TownsendsFJR1300]

I think that's a good idea re the carbs, a lot cheaper than a new engine... Your problem seems to be somewhere in the fuel intake system.

I still would strongly suggest, if you can swing it, new carb to head boots, their 24 years old. The old ones will be comprimised just by their age, just eliminate that potential problem once and for all....

The old ones can be leaking on the surface that actually bolts to the head or the surface area that clamps on the carb hardened up to a point that it isn't sealing fully when tightened down causing havoc...

 

[87fz600]

I will more then likely do that since I found some for 40 bucks complete set. One question I do have is should I stay with the k&n air filter pods or try to find an original air box? I got a buddy who has been working on bikes for years that's gonna help me clean my carbs the right way. Good way to learn to do it right.

 

[TownsendsFJR1300]

I will more then likely do that since I found some for 40 bucks complete set. One question I do have is should I stay with the k&n air filter pods or try to find an original air box? I got a buddy who has been working on bikes for years that's gonna help me clean my carbs the right way. Good way to learn to do it right.

With the K&N pods, you'll most likely flow more air thus changing the air / fuel ratio...

If your going to do a lot of bad weather riding, I personally would go back to the stock air box to keep rain/water, etc from soaking the filters, clogging them up, possibly stranding you.

Should you keep them, you can use them without the stock box but check your spark plugs once the bikes running correctly. On a full power pull, (wide open thru all the gears, turn off immediatly) let the bike cool off and pull the spark plugs. If their burning lean/whitish, you need a richer (larger) main jet. A good burning plug will be tannish looking... Do a search, there's many threads on what a good burning/well jetted machine spark plug should look like..

Better to have it a little rich than too lean. Too rich, it'll build up carbon much faster than it should and gum up vlaves/rings, etc...

 

[87fz600]

You sir are a god send...now if only you lived next door to me. Haha. I'll check it all out...aGould be late this following week. I hate my stupid apartments rules.

 

[TownsendsFJR1300]

You sir are a god send...now if only you lived next door to me. Haha. I'll check it all out...aGould be late this following week. I hate my stupid apartments rules.

Wish you were closer, I like a good "what the hecks wrong with this?" project!

Carbs are the biggest offender, especially of older carbed bikes. The orifices are pretty small and clog easily, especially with the ethonol crap if they sit for any lenth of time... An older bike just adds to the problem as rubber deterorates, seals shrink, etc...


Getting someone familiar with carbs going thru them should help. Hopefully its a simple low speed jet or orifice clogged. Also, I've cleaned carbs on weedeaters that the hole was so small I had to use a wire from a wire brush as a needle was too big. Clamp the wire in a needle nose vise grip, bend accordingly and be very, very gentle....

Good luck

 

[87fz600]

Haven't had the time to tinker with the bike but I was told how to tell if it was the carbs or the boots and figured I'd post for comments or for others experiencing the same issue. Fire it up with gas tank off to the side to allow access to the carbs. Once started, put pressure from different angles on the carb assembly. Would cause the leak to change in size if It's the boots causing a variation in the idle. Will hopefully be able to do it this week but can't order new boots until the first. Just a little check in for those checking the thread.

 

[87fz600]

I also really want to get the original air box but I can't for the life of me find it. Found the boots for 65. Had found them for 40 but I can't find the site again.

 

[87fz600]

So I'm almost positive the idle is in the carb holder boots and carb. However it will no longer be my issue because I'm trading the 87 fz6 for a 90 ninja 600r and a 92 ninja 250. I feel like a trader cuz I love my fz but the trade gets me extra money from selling the 250 and without a job that's needed. Thanks again everyone for the help and input.

 

[TownsendsFJR1300]

Just as an FYI, last week I had to sync some carbs on a Yamaha Royal Star V4 1300. The bike had less than 400 original miles on but is an early 80's model... The bike ran very rough initially and back fired badly on decel. The sync was out real far (better than 60mm) and once in line ran much, much better..

The spark plugs seemed to burning ok except one which was odd looking... We sprayed some carb cleaner around the boots while idling and you could hear the RPM's raise about 100RPM for that boot.

Accelerating down the road, the bike now sounded reallly good but slowing down that boot was pulling air causing some serious back firing....

 

[87fz600]

I'll tell the guy they may need syncing too then. Told him about the boots and carbs being cleaned better and he's fine with it. I had some plans for the fz but no funds so made it rough. Plus the 600r has a sportier ride position so I'm kind of excited. I'm 6'5" and 240# so the fz was thin and small but still a blast. heart will be with yamaha and will get one that suits me better with funds eventually.