Hi,
I changed membranes of carbs, cleaned carb at same time, checked float levels. But carb no 1 or 2 is overfloating (from bigger hose) when machine gets warm.. I tried to syncronize carbs, but vacuum is much higher in second cylinder, and after removal of vacuum measurement hose, I noticed smoke coming out from intake :dash2: Valves are also adjusted and new piston rings installed...
Any idea? to stop overfloating... I'm for my first time synchronising carbs, so if I'm totally out of proper range with second carb?
See attached picture of smoke coming from intake..
br Jyrki
The overflow of the carbs is most likely crap stuck in the float needle or a stuck needle. Smoke from the top of the engine is likely oil that dripped during valve cover removal or the valve cover gasket (bolt grommets as well) leaking. If the smoke clears up after a few runs then don't worry about it. If it continues then look for signs of oil where it can leak from the valve cover.
Hi, smoke is coming from underpressure measurement connection, after removal of measurement hose, so from intake manifold/connection. I will clean again the carb...
Burnt intake valve?
Hopefully not... I noticed that sealing rings between carbs are not in the petfect condition, so I chabged those O rings. Next step to try..
What makes intake valves burning?
Tight valves. When the gap is under spec the exhaust valves can't close completely. This lets combustion gas past as well and cooks them.
Typically, it's an exhaust valve that "burns". Exhaust valves see the extremes of temperature that intake valves typically do not.
As the engine runs, the exhaust gasses erode both the valve seat and the valve itself. This causes the valve to recess into the seat area, which reduces the clearance at the cam lobe. Left long enough without the clearances being checked and the valve can get into a situation where it does not close fully on the valve seat. This only accelerates the valve wear and can result in a burned valve as a localized spot will usually fail first. This causes a localized area where exhaust gasses will "jet", which causes even faster errosion in that one localized area. If its left long enough, you end up with this type of damage:
(https://volvoforums.com/forum/attachments/volvo-s90-v90-40/8899d1371884017-burned-valve-gasket-failure-cause-burned-valve.jpg)
Intake valves are closed when combustion occurs so the narrow sealing area between valve and seat don't see the same combustion heat as exhaust valves. Combine this with the fact that when the intake opens it only passes clean (and relatively cool) air and fuel and the intake valve is thermally more stable. Intake valves typically don't have thier clearance wear down as fast as exhaust valves, but if it started "tight" and was run for extended mileage without a valve check, you can get into a valve "burn" situ on intake as well. Poor valve sealing on the intake side is far more likely to be insuffeceint valve clearances than a burned valve. You will notice the engine coughing back through the carbs long before you end up with a burnt intake valve. Be cautious when thinking it's a burnt valve if your bike is "carb coughing", lean and rich mixtures can cause the same behaviour (ie: carb coughing). Check the valve clearance and then go into the carbs next if it's coughing back.
Burnt valves occur due to insuffecient sealing at the valve and seat interface. The most common cause of this sealing issue is insuffecient clearance at the cam lobe/lifter....
:)
Yea, what he said... Check your valves even if they sound alright. A tight valve is silent and can cause a failure. A loose valve will not, ie. a Tappy valve is a happy valve...
Consider this a Public FJ Service Announcement (PFJSA). Seems like a Trump text when put like that. :shok:
Quote from: great white on June 03, 2017, 08:54:28 PM
Intake valves are closed when combustion occurs so the narrow sealing area between valve and seat don't see the same combustion heat as exhaust valves.
Aren't exhaust valves also closed during combustion?
Noel
Quote from: ribbert on June 03, 2017, 09:32:57 PM
Quote from: great white on June 03, 2017, 08:54:28 PM
Intake valves are closed when combustion occurs so the narrow sealing area between valve and seat don't see the same combustion heat as exhaust valves.
Aren't exhaust valves also closed during combustion?
Noel
Except when they are out of adjustment and allow hot gasses past them.
Quote from: FJmonkey on June 03, 2017, 09:35:53 PM
Quote from: ribbert on June 03, 2017, 09:32:57 PM
Quote from: great white on June 03, 2017, 08:54:28 PM
Intake valves are closed when combustion occurs so the narrow sealing area between valve and seat don't see the same combustion heat as exhaust valves.
Aren't exhaust valves also closed during combustion?
Noel
Except when they are out of adjustment and allow hot gasses past them.
That's true Mark, and a tight inlet valve would be subject to the same thing but the context above was of a theoretical cycle.
Noel
Quote from: ribbert on June 03, 2017, 10:04:43 PM
That's true Mark, and a tight inlet valve would be subject to the same thing but the context above was of a theoretical cycle.
Noel
Fair enough, just a gentle poke. Something for us to remember when I get to visit the land down under. Its been too long since my wife has seen family.
Hi, many many thanks for your replies and hints! My first time checking valve clearances of yamaha after machinerebuild...I will open the engine and check if there is damages on valves. So on I am on learning curve with Yamaha ☺
Quote from: ribbert on June 03, 2017, 09:32:57 PM
Quote from: great white on June 03, 2017, 08:54:28 PM
Intake valves are closed when combustion occurs so the narrow sealing area between valve and seat don't see the same combustion heat as exhaust valves.
Aren't exhaust valves also closed during combustion?
Noel
Well, I know you know what I meant because of your experience. But for the benefit of those that don't have as much mechanical knowledge: yes, they are both closed during ignition.
I was keeping it simple as the discussion only required a simplistic answer. Without posting a novel on the combustion cycle and engine construction, it's easy to pick holes in a short internet forum post. People typically don't want to read several paragraphs on an internet forum, they just want a simple answer.
:hi:
Both valves are closed during ignition but only the exhaust valve sees the higher combustion temps as it deals with evacuating the spent charge. The "Blow" part of Suck/Squeeze/Bang/Blow.
:sarcastic:
The intake valve does not see the same temperature swing for several reasons from boundary layer effect to the cooling properties of the intake charge. Not to mention that its small profiles (ie:edges) are not exposed to the high temp exhaust gasses so its relatively protected from the rapid heating effects by the virtue of it's effective increased mass by being in contact with the valve seat/head while the "hot" part of the cycle is in progress.
The only cooling (essentially) the exhaust valve gets is the contact area with the valve seat where it can conduct it's heat to to the head, although boundary layer also helps protect it (like it also does for the intake valve) during the charge ignition.
:hi:
Hi, I checked valve clearances: in cylinder no 2 one intake valve was too tight and both exhaust valves were also too tight > causing high temperature > melting? some of vapor/gases escaped also to carburetor causing overfloating? Is this a school example what happens when there is not enough clearance for valves? I afraid that also mixture has been probably too lean, only 2 rounds open for mixture screw. Do I need to do something for cylinder head? See picture no 1. Also some markings in piston, picture no 2. Valves and valve seats looks like to be ok..
it's always hard to tell from pictures on the internet, but the valves pictured don't appear to have any damage.
The cylinder head and piston crown look as if they've had previous damage. Looks like something came apart at one time and was bounced around, marking the head and piston crown.
Not ideal, but should be usable in a street driven bike.
If you're getting fuel overflow from the carbs, you need to get back into the float bowls and clean the needle shut off areas. depending on how neglected or molested the bike is, you may want to confirm the float levels are correct.
Get your valves set correctly, then get you carbs cleaned, then get the carbs properly set up and sync'd. this shoudl have the bike running at least acceptably.
Unless your compression is bad that is. But if you have the head off now, there's no way to check compression without putting it back together. If compression is low, you're looking at a rebuild. With that piston damage, if I was doing a rebuild I'd be going up an overbore to get fresh pistons in there along with a fresh bore and rings. It's a "if you're in that far, you might as well go all the way" thing...
Maybe polish the seats a bit with the paste? This is more of a question than a suggestion.
Quote from: FJmonkey on June 03, 2017, 10:31:58 PM
..... Something for us to remember when I get to visit the land down under. Its been too long since my wife has seen family.
Mark, have you been to Australia and from which part is your wife's family? If you feel like sharing, I'm curious as to how a yank got lucky enough to snag an Aussie Sheila for a wife? :biggrin:
Air fares have never been cheaper and the exchange rate heavily favours US visitors. It's also the off season for many of the things that will bite you, eat you or kill you.
Noel
Noel, I will send a PM.
I sent a PM...
Hi! I think I found reason for overfloating of carbs: I bypassed gasoline pump and cables from reserve switch I took off.... bike is 1988 model. No overloating any more. This hint I found from some UK site ( somebody had changed needles etc) Does anybody knows the reason for excess fuel pumping or function principle for fuel pumping?
Check out this video. FJ1200 Faulty Fuel Pump (https://www.youtube.com/watch?v=jZDub9xT-qI).
Simple test - plug in fuel pump without fuel lines attached - put your finger over the outlet and turn the key on - a good pump will shut off immediately to within a few seconds - a faulty pump will run for much longer or not stop at all. If this happens then the fuel pump will overflow the carbs.
If the pump shuts off then you can attach the inlet line & attach an outlet line and drain it to a container (e.g. water bottle) - turn the pump on and let it cycle - when it shuts off confirm if the gas flow also stops. If the pump still gravity drains - and depending on your float heights - this may cause it to overflow also.
You can also check the contact points for the pump, but I think it just wouldn't work at all if they were faulty. (I'm guessing)
If it is doesn't shut off then you can only replace it with OEM ($$$$$), used, or aftermarket like RPM sells Electric Fuel Pump (http://rpmracingca.com/proddetail.asp?prod=fuelsystem%3AFP&cat=39).
Good Luck
Thanks! I will check tomorrow! Is there difference between inlet and outlet of fuelpump hoses? I wonder if I have mixed them causing this problem...
If you have the oem pump, both inlet/output ports face forward. The inlet (from tank) is the upper port, the outlet (to carbs) is the lower port.
Quote from: Pat Conlon on July 05, 2017, 01:06:30 PM
If you have the oem pump, both inlet/output ports face forward. The inlet (from tank) is the upper port, the outlet (to carbs) is the lower port.
On mine, both ports are at the same level to each other.
The one closest to the outside of the frame is the inlet from the tank.
The one closest to the engine is the outlet to the carbs.
Yep, Alan you are correct :good2:
http://www.partzilla.com/parts/search/Yamaha/Motorcycle/1989/FJ1200W/FUEL+TANK+NON+CALIFORNIA+MODEL/parts.html (http://www.partzilla.com/parts/search/Yamaha/Motorcycle/1989/FJ1200W/FUEL+TANK+NON+CALIFORNIA+MODEL/parts.html)
Quote from: jyrki on July 05, 2017, 10:03:59 AM
Hi! I think I found reason for overfloating of carbs: I bypassed gasoline pump and cables from reserve switch I took off.... bike is 1988 model. No overloating any more. This hint I found from some UK site ( somebody had changed needles etc) Does anybody knows the reason for excess fuel pumping or function principle for fuel pumping?
But did you find a reason for the smoke from intake manifolds?
Hi, I suppose it was fule fumes, not smoke... as there has been excess fuel. Damages in cylinder head and piston: I found some rests of sandblasting sand in valve stems (there is a minor slot around stems, there there was stucked some sand corns, bloody machinery company...). Next steps: checking function fuel pump, checking wiring, checking float bowl hight, adjusting carb balances, adjusting idle mixture, bypassing fuel pump, etc... Hopefully I get to ride this weekend.... Looks like that I have to really earn my riding, but anyways, this is interesting hobby! To get to know my bike...
Hi again!
I noticed that there is big underpressure difference in second cylinder, when I tried to balance carbs. Underpressure was like 0,5, and other had around 0,1 bar. What is reasonable underpressure? I didn't suceed to balance that second cylinder carb... Air leakage somewhere? attached picture from cover of carb: it has given some back pressure hits also, as slide has hitten on top of cover... Mayby I should check all seals in carb number two...
I hope that you are not doing the same beginners mistake as I did when I first started to play With the carbs, that is adjusting the air/fuel mix screws in an attempt to sync the carbs and overseeing the actual sync screws that are sitting lower on the carb.
At the time I did somehow manage to get the engine to run nicely but today I see how out of adjustment everything was.
Also, without Reading through the entire post again, has anyone thought of the possibility that the carbs might be set up for gravity feed but are actually run With fuel pump causing the initial problem of overfloating and the issues that come With it...
Just my thoughts in this.... :yes:
Magnus