loosing power

[jefferson]

If your bike won't rev out then the carb is rich which can be caused by missing vent lines off the carbs. The vent lines need to be in place and routed as they were from the factory. They should terminate in the hollow frame space under the battery. There is a hole there that they go through. Check and see.

[Rikugun]

I can see where pinched hoses would cause fueling issues  - bowls slow to fill/lean perhaps? But I would not have thought missing vent hoses would be necessarily detrimental. What process is at play?

[Guerrero]

well today again.run for some 30min to work.everithing run perfect.but almost at the end somehow engine died,and while hot,could not start.drained battery.left to cool for 20min,and started from half turn  :D will change jets to half size smaller.lets see how that goes.

p.s. but actually after i upgraded to full power version the stumble what i got ,and why i started this thread has gone completly.runs smooth.today even could rev up to some 8k (did not need to do more) and the power increase is quite nice. so i am happy with atleast that.

I guess,if i will be able to complete the problems with hot starting,then my V is ready to go for full time job =)

p.s.s. i think that handlebar mirrors and drl i put on looks quite nice.and leds are draining much less voltage.actually voltmeter is not showing any voltage drop,when i turn drl on.that is nice.tail lights aswell with led bulbs.

[jefferson]

The issue with the vent hoses is at speed there is higher pressure under the tank where the open vents are. If the vent hoses are run to the area they are supposed to be then they get atmospheric pressure and thus don't run rich. Higher pressure in the bowls will act on the fuel and give you a richer mixture.

[The Prophet of Doom]

I thought the vent hoses ran to the enricher / choke circuit.  I'll have to have another look when the weather is better

[jefferson]

The vent hoses run off the top of the carbs at the rear left corner, on the 83's anyway. I am pretty sure the 82's do also. It takes a fairly long hose to reach the spot they need to go to.

[Guerrero]

i found only 1 hose running to that hole.if i am right?the hole before the absorber?between battery and tci.

[jefferson]

I'm not sure what you are calling an absorber, but the hole is in the top of the frame section between the battery and tci. There should be a separate hose from each carb going into the hole unless they were y'd together into one

[Guerrero]

i am not sure how it is called on english,but i gues motorcycle absorber(in google at pfotos it shows the right thing,what i ment) =) ok,will look closer at that.as i can see,only one tube is going in to that hole from top.But i am not sure where is it starting,from one carb or both.

[pinholenz]

Didn't know that about the vent tubes. Makes sense but more tubes floating around sure will clutter things up.

Guerro, my bike isnt too happy starting from hot either. I suspect that it is valve clearances as has already been mentioned. I'm looking to get them sorted before next season so I can eliminate one more variable.

I am glad to hear that you are now running without a stumble. What did you do between the two posts to get rid of that?

[Rikugun]

The issue with the vent hoses is at speed there is higher pressure under the tank where the open vents are. If the vent hoses are run to the area they are supposed to be then they get atmospheric pressure and thus don't run rich. Higher pressure in the bowls will act on the fuel and give you a richer mixture.

I thought that's where you were going with that which would explain why they route them to a "calm air" place.

[jefferson]

I am thinking that alot of the hot start problems are due to the heat soaking of the carb. and thus the fuel. Then you also have the air underneath the tank that is hot from sitting above the engine. What you have is hot thin air that doesn't send a good signal to the carb and the carb is full of really hot fuel. Probably not a very good recipe for firing up. If there is a breeze blowing I would think that pointing the bike into the wind when you park it would help with removing the hot air when it is parked.

[Guerrero]

pinholenz-i just upgraded to full power and the stumble disappeared.
It would not be a problem if V would start harder when hot,if coming from shop or something=) as Bike is getting cool really fast,if compaired to car.But biggest problem,than in a traffic if V dies,and the lights go green,and i am sitting in a middle of the road.and cant do a thing.darn.

[Rikugun]

There are several things you've done to fix the hot starting problems - eliminating the YICS and replacing the cracked rubber intake manifolds, etc. I did the same things and they helped, but replacing the throttle shaft seals eliminated the symptoms completely.

[Guerrero]

that is interesting theory.need to have a look at that

Rigubun,but could you explain me please,how it works,and how it would help?

[Rikugun]

Again let me stress getting my bike to the point it is now required a bit of time, trial and error and going through the electrical, fuel and cooling systems several times. Hugely important is clean fresh fuel exiting a clean tank to clean carbs. A fuel filter is added as extra protection, NOT because it is needed outright.

I started with a good top end i.e pistons, rings, cylinder walls, and valves all in serviceable condition and valve lash in spec. Not knowing the health of the top end doesn't guarantee success or failure but without these basic elements in place, you are wasting your time.

The last thing I did was change the throttle shaft seals. It was not a magic bullet but rather the last piece of the puzzle in my case. The original seals are hard and leaking air. You can not adjust the carbs or re-jet to tune the problem away.  The vacuum leak they provide is variable and temperature sensitive.

I can not explain the entire process in this post but do encourage you to search the forum and you will find quite a bit of information on the subject. The process is easy for some and challenging for others. For some it is beyond their abilities and must be entrusted to a competent mechanic.

Depending on many factors some bikes can run OK with the old seals but many do not. Some owners are often chasing gremlins that may be simply worn seals. More often the case is multiple problems making accurate diagnosis and repair difficult.

[The Prophet of Doom]

Nice post Rikugun - and all quite true.
You neglected to say that getting those screws off the throttle valve is a complete arse and you will probably end up drilling them out,  The seals are available from Yamaha for about $6 each I think.  There's a part number on the forums somewhere on the forums, and one of John's excellent videos.

I'd also check pilot screw for correct adjustment and carb sync, as these are major adjustment fault areas.  One would hope Guerrero did the lash when he replaced his cams.

[Rikugun]

I purposely left specifics out of my post. There are too many variables and steps to cover and I'd end up droning on for several pages.

[The Prophet of Doom]

Good point Rikugun, can't have you droning on.  Asking "what's wrong with my bike" is a bit like asking "how big is my tockley"  No-one can say except by going round and seeing for themselves.

There comes a time when a man has to read the manuals.

[dingleberry]

When did the analogy "how long is a piece of string?" become redundant? :o