carb woes

[tinman22]

Tomorrow I am going to weigh the floats. I know for sure they are all the same measurement but this is what i have. top black line is the factory "fill to here" line, Bottom line is the 16mm +/- 1mm line and fuel levels are marked on the hose. Floats are set at 1.125 measured at least 9 times. I think they are soaked and heavy.

 

[tinman22]

1 and 3 are consistently equal and low, 2 is good, 4 is usually low.

 

[Screwloose]

The above picture I believe would be someone here giving a great starting point at 28.5mm, and I see a Snapon driver in the background that suggests they like good tools and hence good workmanship. In reality you cannot get them very accurate this way as the floats are not horizontal to the carb body on every carb. But it works and gives a start up and idle without doing it on the bench cold. I think this photo would be intended to give a fairly accurate start, but not meant to be the final measurement. It works brilliantly for saving time. The 16mm size is correct for lean/rich setting, but needs done at engine temp.
I set my carbs cold on a surface table, and scribed a mark for the height using a vernier height gauge, then viewed the tubes against height blocks. I could not get them at cold anymore accurate than that. But it made little difference to the heights cold compared to running at temperature as they changed. It would have been easier just sticking to the 28.5mm height to get them started on the bike. This would be why most people on this site say they have had the carbs in and out many times over. I got virtually all my information from this site as many people have put info on this subject.
It is easy to overcompensate with the adjustment after running at temp, the nearer you get them the less the fuel level bounces, also when they bounce you get air in the tubes, so it's a bit of a battle the first couple of adjustments at temp.
When these carbs are brand new this would be probably allot easier to set up as more depends on the wear of the rubber on the needles trying to shut of the fuel, and the spring strength on them also. I ended up changing many parts to try and compensate for the wear.
This is just my evaluation but the fuel heights do change with temp, and wear in the moving parts makes the fuel heights change also.
Some photos below cold and hot running if that helps.

 

[02GF74]

as said above, can fuel starvation be ruled out? is the tank clean and fuel filter clear? and pump fully working? (there probably is spec for testing it in service manual )

 

[Screwloose]

Tomorrow I am going to weigh the floats. I know for sure they are all the same measurement but this is what i have. top black line is the factory "fill to here" line, Bottom line is the 16mm +/- 1mm line and fuel levels are marked on the hose. Floats are set at 1.125 measured at least 9 times. I think they are soaked and heavy.View attachment 74642View attachment 74643

I really do think you are very close for a first start up at temp. Its all effort from here on. My super accurate cold levels were a waste of time and I should have concentrated on adjustments at running temperature.

 

[Screwloose]

as said abouve, can fuel starvation be ruled out? is the tank clean and fuel filter clear? and pumpvfully working? (there prbably is spec for testing it in service manual )

I also cleaned the tank out and put a new filter in, you cant go wrong on that one for sure. I believe someone the other day posted the pump details.

 

[tinman22]

as said above, can fuel starvation be ruled out? is the tank clean and fuel filter clear? and pump fully working? (there probably is spec for testing it in service manual )

tank is spotless filter is new.

 

[Screwloose]

right you are. factory spec is 16+/- 1 mm. Below the line on the side of the carb.View attachment 74636

This must be about as bad a photo as it gets, I know its from the manual, but very poor for Yamaha.
The fuel height (if I remember right), comes from the centre of the diaphragm slider tube, then drops down 16mm from there.

 

[tinman22]

there is actually a cast line in the carb body rearward of the diaphragm cover. called the piston valve center mark in the book.

when i set up the carbs on my other 85' sean told me that 1.115 was the place to be and the factory setting would be rich. his logic on the setting was sound and founded in far more experience than mine with downdraft cv carbs.
I figured i would copy that set of settings over to this bike since it is set up exactly the same as the other one.

 

[Screwloose]

there is actually a cast line in the carb body rearward of the diaphragm cover. called the piston valve center mark in the book.

when i set up the carbs on my other 85' sean told me that 1.115 was the place to be and the factory setting would be rich. his logic on the setting was sound and founded in far more experience than mine with downdraft cv carbs.
I figured i would copy that set of settings over to this bike since it is set up exactly the same as the other one.

Wish I'd seen the centre mark on the body, it would have saved me time using a vernier height gauge to find that point.

 

[tinman22]

just found a really familiar post from 2007. Setting dry float levels on the bench from maleko89
and how 4 carbs set at 1.125 had four different wet settings hmmm.

 

[user 16790]

could the little springy bits in the needles be upsetting the fuel level by not being even in their movement

 

[Screwloose]

Changing the needles and seats worked good for me. The springs and viton tips were worn, resulting in unstable readings at the fuel level.
The viton tips go hard through lack of use also, and do not seat/seal as good as they used to. The old springs were clearly weaker than new needles springs. So I further suspect that some fuel was pushing past the viton tips at running, even although the float heights were correct at a bench set-up. It may also be the case where viton expands/contracts when aged with temp's and dry/wet.
The above is just my own experiences with these carbs, I find they are like individual little creatures all with their own characteristics, sent to play with your mind. In my view if the bike has not been started for a couple of years or so, and fuel was left in the carbs to rot away, then its a strip-down and renew the needles as a minimum, not to mention getting the carbs totally cleaned out. I fought a battle for an entire week with these carbs, lost, then came back with a vengeance and cleaned re-newed and set-up and eventually won.

 

[Fire-medic]

If I have carbs apart on a new-to-me bike, the float needles get replaced as a matter of course. I generally-don't replace the seats, they just get cleaned.

 

[Screwloose]

If I have carbs apart on a new-to-me bike, the float needles get replaced as a matter of course. I generally-don't replace the seats, they just get cleaned.

That sounds fair to me, as I’m not so sure changing the seats helped me in any way with only 17k miles on the clock It’s doubtful they were worn.
The seats were already in the re-furb pack, and I seen on this site it was easy to change them by just pushing them out with a clamp, and pushing out the seat caps at the same time as the seats.
I think it was yourself FM that said to do the seats and caps together that way and it worked a treat, 20 mins and the seats with caps were out the 4 carbs.

 

[Fire-medic]

Certainly if you have the set of seats and needle valves, you probably should replace the set. I normally buy just the needle valves, aftermarket, and replace those. Some on here would rather use only OEM, and for most of my stuff it is OEM replacement, but the needle valves I get K&L pieces for about $4/apiece, and they have worked for me.

 

[Parminio]

Certainly if you have the set of seats and needle valves, you probably should replace the set. I normally buy just the needle valves, aftermarket, and replace those. Some on here would rather use only OEM, and for most of my stuff it is OEM replacement, but the needle valves I get K&L pieces for about $4/apiece, and they have worked for me.

The problem is the cheap kits. Their needle valves are HUGE compared to the OEM valves and they restrict flow. Your bike will run fine until you really get on it and then towards the upper end of the RPM range you lose power because you are literally running out of gas.

 

[Screwloose]

Your idea worked great on the caps and seats. The only small extra part I done was to drill very slightly the cap securing dimples that are stamped on the body, then run a sharp knife on the dimple inside diameter just to be safe on not tearing up the cap rubber seal.
Changing the seats was the only fulfilling task on the whole carb job that I enjoyed, everything else was a damn struggle.

 

[Screwloose]

The problem is the cheap kits. Their needle valves are HUGE compared to the OEM valves and they restrict flow. Your bike will run fine until you really get on it and then towards the upper end of the RPM range you lose power because you are literally running out of gas.

I tried to get OEM parts, but over here in Scotland it can be a struggle getting anything for this bike OEM. Fowlers in Bristol is the best supplier and if they don't have it you generally have to wait. The Carb top and bottom OEM rubbers I waited about 3 weeks for and cost me about £180. Hopefully Brexit will change all that and allow easier access to the US for bike parts. For instance there is nobody in the UK that I can find has a valve tool, or sells one, or has a drawing to make one.
I did notice that the seats I bought were slightly different in the sense that the outside diameter locating taper was slightly too far back (just a few though), and allowed the seat to drop in a bit further than the original seat, so I used Loctite shaft retainer to hold them in. The needles were verging on exact copy as I measured them (Touratech I think was the make and probably not available in the US), but the prong that locates the valve to the float was wrapped all the way around and had to be partly clipped off as it needs to be an open prong just as the original is. In the spring time I'm pulling the carbs out once more for a final adjustment and inspection, so hopefully nothing is amiss, or moved.
Trigger is moving like a rocket, but there is still fuel level bounce at mid temperature on tick-over at #4, hopefully this will be solved, if not I'll be considering a full OEM kit from the US.

 

[Parminio]

You'll have to wait and see what happens.

From what very little I know about Brexit, rather than having an EU trade agreement with the United States, you now have absolutely no agreement at all.