Non plastic floats buoyancy testing??

[16VGTIDave]

Okay. I'll be the first to admit I don't always grasp the concept but please explain to me the value of using plastic tube to verify that the carbs are overfilling? If I was actually trying to ascertain the correct fuel, I could understand the rationale. But as the fuel level just keeps rising until it overflows, I'm not sure what I would be reporting back. Did you actually read my original; post or perhaps you found the long words confusing?.

@Fentible I'll try to ignore your flippant attitude yet again, and I'll continue to share with everyone who views this thread some of the 40+ years mechanical experience and some of the lessons I've learned. But let's be clear: You @Fentible are the one asking for, and obviously needing, help with your bike. I certainly have nothing to gain from this discussion, other than being the recipient of your attitude and insults. I don't owe you anything. It's certainly not like you've been valuable or contributed in the 3 years you've been a member, with only 65 posts (as of this point). You appear to only come here with your hand out asking for help, and don't return the courtesy. You are a leach, so cut the BS.

Carrying on with the problem at hand. You've set the float levels as per the manual, with the carbs upside down and measuring with a ruler or callipers. To the best of your ability, which you @Fentible have previously documented. If done correctly, that is fine for a stock bike with all new and/or serviceable parts. Now, you install the carbs on the bike. Is the bike stock and in like new condition? Have the front springs collapsed some? Are the clamps lowered on the forks to give a sporty rake to the bike? Taller shocks in the rear? Larger diameter rear tire? Smaller diameter front tire? Gas tank moved higher? Is the pressure vent valve in the gas cap functioning correctly? What is the specific gravity of the gasoline you are using? What is the vapour pressure of the gasoline? What is the temperature of the gasoline? Anything else that may have changed the positioning of the carbs or the fuel pressure at the needle seats?

Now, considering all those factors, what is the actual fuel level in the float bowls? You don't know. Got it? You DON'T know. What you do know is that it is high enough flood the engine. If the carbs are perfectly level, then you need to look at the floats, their adjustment, the needles and seats, and the gas cap. But, are the carbs perfectly level? Are the carbs tipped lower towards the engine? Probably, based on your previous descriptions, but that is just a guess. Regardless, this is why the actual fuel level in the float bowls needs to be determined. Once you know the actual fuel level, you can then determine the correct action. It may be as simple as lowering the fuel level 1 or 2 mm by adjusting the floats correctly.

Can we stop with personal attacks now and stick to fixing bikes?

 

[MrStubb]

I want to be such a smartass but I'm afraid I'd offend someone who's advise & opinions I greatly value. Suffice it to say that all of this snarky sharp penned banter gives me gas!!! Now it's off to the gunk bucket for a good soak!!!!!

 

[Fentible]

Hi Chris, I tested the floats in some gasoline and although they do float but my concern was that they were 95% submerged. This is why I wondered if they were sufficiently buoyant. I compared them with some old GPZ1000 plastic floats which were about 50% submerged. Unfortunately I didn't feel that this was a particularly valid test as it wasn't like for like.

As for measuring float heights I use a set of digital Vernier calipers. For the initial static measurement, I inverted the carbs and clamped them level in a vice, removed the float bowl gaskets to measure and set them at 24mm from the gasket surface to the heel of the float (the highest point when inverted). Now the bike has previously run well at this setting, with a really steady idle at 1200rpm.

Since I have been unable to prevent the fuel level slowly rising, I have tested various float heights using this measurement protocol, to no avail. Its currently set at 26mm. I did wonder about the height setting quoted in the Haynes manual (32mm) but everything I have read suggests that this is a misprint and goes agaist the fact that the bike has previously run well at the lower height setting.

If I was listenng to someone explain this problem to me, my first recourse would be the float valves. However, Ive replaced them twice with brand new items since it flooded the engine and without success. I really can't just keep buying float valve sets, although without any further evidence (see point 3+4 below) I might just accept they are poor quality pattern parts.

• I have checked the float bowl vents are clear
• I have checked that the floats are free to move and aren't catching on anything with and without the float bowl attached. I did read about a guy who discovered that the float was catching on an expanded gasket but that's also not the case with this set of carbs.
• I have altered the float heights between 24-28mm without success
• I have fed fuel into the carbs with the float bowls removed and even light pressure on the floats is sufficent to stop the fuel flow into each carb
• With the carbs fully built up, I have blown down a hose connected to the carb fuel inlet and can hear the air hissing out, if I then slowly invert the carbs till they are upside down, I can no longer blow down the tube.
• If I orient the carbs as if they were fitted to the bike and attach a small fuel supply, after a few minutes I can see fuel lying at the point the jet needle enters the emulsion tube in the carb venturi. It doesn't flood out but if I leave it overnight the level in the temporary tank will drain down.

Logic suggests that if fuel continues to seep into the float bowl after the float valves should have shut it off then the only items that can affect that process are the float needle, needle valve seat or the floats. Having tried all of the above several times, even leaving it for a couple of weeks to go away and think about it I seem to be left with the actual floats as the only question mark. I have rebuilt numerous sets of carbs fom singles to multis and never had this problem.

 

[Fentible]

@GTI Dave, strangely I still do appreciate your input but perhaps if you were a little less condescending and maybe consider the manner and content of your own posts to total strangers it might have helped avoid the initial conflagration. Not that I feel I need to explain, but the reason that I only appear intermittently is that this is not actually my bike (Triumph Speed triple, Tiger 955i and a 1970 Benelli 650 Tornado personally), I'm trying to help a friend with limited mechanical knowledge and as you rightly state, any discussion will still help others so please don't belittle my limited input . At 40+ years repairing, riding and yes occasionally crashing bikes we are at the same level so I agree lets both stop the BS, we can both still learn
Again @GTI Dave
Right, I get what you are suggesting but I can't actually achieve a fuel level. If I place a clear hose against the side of the carb all I see is a gradual rising in the fuel level to the gasket mating surface at which point fuel leaks out of the emulsion tube. So literally I have nothing to measure unless you want to know the initial fill level in which case i will check tomorrow. Altering the float height makes no difference within the parameters 24-28mm. Lowering below 24mm would only help increase the level of fuel in the carb and I would try the Haynes recommended 32 mm if it were not for the fact that the bike previously ran well on a float height setting of 24mm. It is a stock 1980 XS400SE (S4G5). Nothing on this bike has changed (aside from 2 x brand new float valve sets) since it was running well and then drained the tank contents into the sump over this winters layup.
As previously stated I have successfully rebuilt numerous sets of carbs, these have me stumped. Where do I go next?

 

[Fentible]

Okay after on GTI Daves advice. I checked this; at the previously set level of 24mm float height and with clear tube up the side of the carb, there is an initial fuel fill to approx. 2mm below the gasket surface but which then slowly creeps up till fuel appears in carb mouthThe R/H carb (as sat on bike) is worse than L/H carb which creeps up more slowly. Set float level to 26mm and the initial fuel level is about the 3mm mark but I get exactly the same results slow creep on L/H carb, faster creep on R/H carb.

 

[xschris]

22mm is what plastics floats call for. If level is correct then the float valves are not sealing. Are you using OEM valves or an aftermarket set. Make sure also that your petcock shuts off when the bike is not running if you have a stock petcock.

 

[16VGTIDave]

My first though, after reading that the floats are 95% submerged when tested, is that they have absorbed fuel. Uncommon for this type of float, but not impossible. However, further consideration leads me to believe that this is normal. Look at the carb and float bowl, consider where 3mm below the gasket surface is. The floats would have to be mostly submerged with the fuel that high.

I'd suggest adjusting the floats to lower the fuel level, to see if the level can be positively controlled by the floats. Some increase in the level is acceptable, as the spring in the needles will allow for some variation in the fuel level. But the fuel level must (obviously) be controlled before the carbs overflow. If that works, make note of the fuel levels and adjust the floats as required to achieve the correct fuel level. Regardless of what the height of the floats end up at. As I said previously, the float height is just a starting point, the fuel level is the desired result.

If the fuel level can't be positively controlled by adjusting the floats, and since there is a difference between the rate the levels increase, moving the floats to the other carb (adjusting height if required?), would allow one to confirm or eliminate the floats as the problem. If the different rate follows the floats, they are the problem. If the rate of increase doesn't follow the floats, then the only logical conclusion would be defective float valves as @xschris mentioned.

The only other test I can think of would be to weigh the floats and compare to a known good set. There shouldn't be more than a few 10ths of a gram difference.

 

[BBS360]

My floats are out so I gave them a quick weighing.
8.8g for one and 8.7 for the other

I wouldn't call them a known good set as I haven't gotten my bike running yet but these floats haven't touched gas in years so they're definitely not saturated.

 

[Fentible]

22mm is what plastics floats call for. If level is correct then the float valves are not sealing. Are you using OEM valves or an aftermarket set. Make sure also that your petcock shuts off when the bike is not running if you have a stock petcock.

Sorry for the late response, away for the night after going to see ELO live in concert. Absolutely incredible set. Jeff Lynne is a brilliant musician. 35 years since I last saw them in 1981.

Chris, carbs are off the bike at the moment so simply using a remote petrol source (permanently on).Switched to a manual tap on the bike after the rebuilt one so obviously failed during the winter stand and several months after working properly. When you say plastic, these are the black rubber(?) variety. Setting to 22mm would simply increase the fuel level based on my readings with the previous 24 and 26mm height. I am also not aware that OEM float valve sets can be obtained, I have searched for them so am using currently available pattern parts from suppliers I believe to be genuine.

@GTIDave, I think you are absolutely right about about how much the floats would be submerged but If they had lost buoyancy they would still apply less pressure on the needle valve. In truth I am struggling with the lost buoyancy concept. I will try raising the height of the floats as that might compensate for any lost buoyancy and report back. Good point on swapping the floats, I'll also try that to see what if any difference it makes.

@BBS360 Many thanks for the weight comparisons, I'll compare them against mine.

Thanks to all again for your input, it genuinely is appreciated.

 

[MrStubb]

Sorry for the late response, away for the night after going to see ELO live in concert. Absolutely incredible set. Jeff Lynne is a brilliant musician. 35 years since I last saw them in 1981.

Chris, carbs are off the bike at the moment so simply using a remote petrol source (permanently on).Switched to a manual tap on the bike after the rebuilt one so obviously failed during the winter stand and several months after working properly. When you say plastic, these are the black rubber(?) variety. Setting to 22mm would simply increase the fuel level based on my readings with the previous 24 and 26mm height. I am also not aware that OEM float valve sets can be obtained, I have searched for them so am using currently available pattern parts from suppliers I believe to be genuine.

@GTIDave, I think you are absolutely right about about how much the floats would be submerged but If they had lost buoyancy they would still apply less pressure on the needle valve. In truth I am struggling with the lost buoyancy concept. I will try raising the height of the floats as that might compensate for any lost buoyancy and report back. Good point on swapping the floats, I'll also try that to see what if any difference it makes.

@BBS360 Many thanks for the weight comparisons, I'll compare them against mine.

Thanks to all again for your input, it genuinely is appreciated.

WOOHOO!!!! Another ELO fan. I was turned onto them my sophomore year around 1975. Really makes me an OLD FART

 

[xschris]

Here is another thought. How are the o-rings that seal the valves into the bodies. Also make sure the valve retainer clips are screwed snug. If those are not sealing you can get fuel overflow. This is how I test valves. Turn the carbs over and gently blow into the fuel inlet. If no air pushes through then they are fine.

 

[Fentible]

WOOHOO!!!! Another ELO fan. I was turned onto them my sophomore year around 1975. Really makes me an OLD FART

Mildly of topic mr S, but been a fan since 10538 Overture 1971/2

 

[Fentible]

Here is another thought. How are the o-rings that seal the valves into the bodies. Also make sure the valve retainer clips are screwed snug. If those are not sealing you can get fuel overflow. This is how I test valves. Turn the carbs over and gently blow into the fuel inlet. If no air pushes through then they are fine.View attachment 26130

Hi Chris, sorry already tried this, post # 23, points 4+5. I am at work tomorrow and Tuesday so likely I won't get back into the garage till Wednesday. So its not that I've gotten bored, simply time management.

 

[Fentible]

Okay, after several trials I found that a float setting height of 29mm would stop the fuel level creeping up but which left the fuel level at roughly 15mm below the level of the float bowl join. Working back to a 27mm float height produced some interesting dynamics. Fuel creep was seemingly halted and the fuel level in the float bowl settled at a shade under 10mm. After 5 hours the fuel level in the temporary tank (funnel on rubber tube) had drained down and the fuel level in the right carb had gone down 2mm and that on the left carb went up a similar amount (edit: ignore this I realised that I had knocked the plastic tubes altering the fuel levels relative to the pen marks). A very small quantity of fuel pools in the top of the emulsion tube on the right carb (the photo doesn't make it clear), yet the fuel level never got anywhere near the carb/floatbowl join, so where is this fuel coming from?? I can't see any leak anywhere else and the blue paper towels I placed under the carbs had no indication of any drips.

Floats at 27mm height showing fuel level in carbs

Inside the venturi showing the top of the emulsion tube and the point the fuel pooling occurs

Showing how much the fuel level in the temporary tank has dropped in 5 hours. No spillage around carbs.

See edit in post Again no leakages detected aside from the fuel pooling at the top of the R/H carb emulsion tube.

 

[Wolfe_11B]

5 hours of fuel sitting in a wide mouth container open to the air will evaporate that quickly. Same with the fuel in the bowls, they are open to the air and the gas will evaporate. The fuel showing up at the top of the emulsion tube is probably simply gas vapor making its way up the tube and then condensing on the brass. I think you are over thinking this.
Put the carbs back on the bike, use a good petcock, make sure to have it in the off position when not running, and go enjoy the bike.

 

[Fentible]

Thanks Wolfe, I had thought about the evaporation theory but thought the speed and amount was a little excessive but hey I've been wrong before. I'm also left wondering why the fuel only appears in the R/H carb and not the left. I did wonder if it was simply some sort of capillary action but after leaving them over night and seeing that there was actually a fair bit of fuel on the carb mouth floor (R/H only see photo below), I'm left wondering how its actually getting there as the fuel level in the plastic tube hasn't risen above the previous 10/12 mm below the float bowl join line. That said, it is possible I am overthinking and I doubt that would unduly affect the running of the bike I am going to try these on the bike as are and leave the plastic tube on while its running to see what is going on under dynamic conditions.

Showing fuel on the floor of the carb after being left connected to a fuel supply overnight, this appears on the R/H carb only and as the fuel level in the plastic tube is still well below the floatbowl/carb joint how is it getting there??

 

[16VGTIDave]

At this point, now that a reasonably stable fuel level has been established, I'd concur with Wolfe. Get the carbs back on the bike and go for a ride. Once the bike is fully warmed up (about 15 minutes of aggressive riding), you will be able to judge the fueling. I'm going to guess, with the fuel level as low as it currently is, the bike may run slightly lean in the mid rpm range at full throttle. 4000 - 7000 rpm.

If the needles are adjustable, raising them a groove (lowering the clip!) may cure this. If the needles are not adjustable, they can be shimmed up with tiny washers.

 

[Fentible]

Right Dave, I thought about it running a bit lean so Ive compromised on float height at 26mm and since my post this morning (about 5 hours ago) the fuel level, as indicated in the plastic tubes, has been holding steady at 3-4 mm below gasket face. Something it wasn't doing a few days ago and other than playing with the float heights I'm at a loss as to what has changed. I still can't understand where the fuel is coming from that is pooling at the top of the R/H emulsion tube, but am going to ignore it for the moment. I'm busy this weekend with house and wife projects so probably won't get over to bike till next Tuesday. I'll post the results as soon as I can. Thanks again for sticking around and helping out.

 

[Fentible]

Carbs fitted back onto the bike with plastic tube attached to float bowls to monitor fuel levels.
Open fuel tap, carbs fill and settle at about 4mm from the gasket mating surface.
Bike starts using choke, switch off the choke after a few seconds and bike settles into tick-over, occasional stumbling but nothing I would worry about.
As I am refitting some fasteners the bike cuts out, really difficult to restart, impossible on starter but does eventually fire up using kickstart.
Same sequence ticks over for a few seconds then cuts out, fuel level remaining stable in carbs. After several more tries the bike refuses to tick over and simply fires and cuts out.
I only had a few tools with me so took the plugs out, they looked fine colour wise although I felt the spark was a bit weak. Am I looking at a dud battery, didn't have tester with me
Remember, bike was running fine prior to winter lay up, coils, plugs, points and condensors and battery all new.

 

[MrStubb]

From your description I think the fuel delivery issue is solved. Now it seems to me that there's an electrical issue that requires attention. I'd start looking at all of your connections It seems these bikes have connection issues from corrosion. My first thought would be with the charging system from the stator right up thru and including the battery itself. My bike didn't run reliably until I had these all taken apart cleaned & tightened up. Being such a small battery for this size bike it really needs to be at it's best charge all the time. And if the generator system isn't up to the task something's going to suffer. Being an 80 with electronic ignition it seems possible that's where your loss is happening Similar to where my issues were.