Float levels and other carb stuff

Before I start I'm not trying to make anyone mad or anything like that I am simply trying to straighten some stuff out for those of you who may have been confused. I am a Yamaha mechanic at a Yamaha dealership. I learned my carb stuff from a 30yr Yamaha motorcycle mechanic. I know what I'm talking about and he does too. If you have a comment on this post that is negative keep it to yourself. If you wish to add anything feel free.
1. If you have fuel leaking from your carbs while the bike is sitting it is usually a bad needle and seat. It has nothing to do with float level.
2. If you have a running issue during idle or up to 2900rpm it is usually an idle circuit issue. It has nothing to do with float level.
3. If you have a running issue after 2900 rpm it is usually a problem with the main fuel circuit. It has nothing to do with float level.
4. If you have trouble running with no air filter at all or with pods that are not properly done the problem is that CV carbs need to create a vacuum to work. The vacuum cannot be created properly with open air. It again has nothing to do with float level.

Now the reason i put all of that stuff on here is because I see this float level coming up over and over and it is never the issue. The float level is important in automotive applications. If you have messed with your floats then they probably do need to be set but that is the only time you should ever need to do anything with them. Yamaha books say you need to set them because early Yamaha bikes used a weird material in the floats that was not always consistent in how well it would float. In those instances the levels did need adjusted. We however do not have the bad float material in our xjs. The floats should never need to be messed with unless you have already done it or you are rough with the parts when you disassemble the carbs. The float level does nothing for how the bike runs unless your fuel level is too low to reach the jets. Again I am not trying to step on toes here. One more thing, you should never ever have to separate the carb banks. There is no need to do it and all you are doing is taking a simple carb set and making them complicated.

p.s. A CV carb is a CV carb no matter if it is the 4 on an xj or a single on a 4 wheeler. It is all the same concept.

 

I have a Question. If you should never ever seperate the carb banks then it is ok to leave the 20 plus year old shaft seals alone and just wait for them to fail and cause you to do all the work over again. If your not replacing those seals while you have the carbs off for cleaning then you are not doing it right your doing a half ass job on the carbs. I know i went through that. Pulled them off got new seals installed still leaked. Pulled them back off again to find two seals were smaller than the other six order new one measured all of them. Reinstalled them and had to go thru all the re-sync'n again. So if I had done it right and replaced all the old rubber seals the first time at least one of the carb pulls would not have happened.

 

The fuel level in the float chambers IS critical.

 

I didn't have to replace them on my 750 and i have never had to replace them in any other 20+ year old carbs that i have done and have never had any problems. my carb "guru" has found that if you don't stress the seals by separating them they will hold. They should only be replaced if they leak but in the end it is up to the owner. Just because something is old doesn't mean it needs replaced.

 

So if you do break them apart then it is a good idea to replace the seals while you have them apart?

 

So if you do break them apart then it is a good idea to replace the seals while you have them apart?

 

Try getting the carbs to look like this without breaking down the rack.

 

Thats what I am saying Wizard if you dont break them apart and replace the shaft seals then you are doing a half ass job on them. And it would PISS me off to no end if I took my carbs to a guru to be cleaned and rebuilt and he didnt replace everything. To me thats screwing the customer.

 

Cleaning:

Does NOT require separating the Carb Bodies and replacing Throttle Shaft Seals.

Over-Hauling: (Re-building, restoring, rehabilitating.)

Requires pulling everything apart and R & R'ing the Throttle Shaft Seals.

A good CLEANING with Passages Flushed and Diaphragm Piston Bore Scrubbing and Polishing, New Stainless Fastenen; Complete and Float Levels Set. Bench Synced and Pilot Screws Preset costs: $325.00 and Up.

Over-hauling. Base without complications adds 4-1/2 -to- 6 hrs. / $695.00
(Plus parts).

 

thank you RickCoMatic

 

So if you get the 325.00 job and the shaft seals fail within a week then the customer is SOL and has to pay for them to be replaced. If the complete job is 695 them why not go ahead and pay anothe 105 for a new set. If I pay some one over 300 to work on my carbs they better shine like a diamond in a goats ass and everything better be new.

 

Do it once and do it right.........that's the best and only advice that I can offer.

P.S. rubber isn't designed to last 30+ years in the environment of the carbs.

P.S.S. fuel levels determine whether the mixture is going to be relaively rich or lean. It takes "work" to lift and vaporize a liquid, and a given amount of pressure drop (what is called "vaccum") will produce a certain amount of "work" upon the fluid. If the level of the fluid is lower than designed, then a given amount of work will produce a lesser amount of lift....

P.S.S.S. air flowing thru the carbs (via the down-ward movement of the piston in the cylinder bore) creates a movement of air thru the carb throat. Moving air results in a pressure drop within this area, i.e. a "vacuum".


The basic rules of physics are pretty hard to argue with, and as far as science can tell, are somewhat universal.

 

Amen Len. if you are not replacing everything that is designed to fail then its not done right.

 

i've never replaced foam floats. nothing there to go bad.

brass floats on the other hand. i've seen go bad. and i just replaced my own.

in 1998 grandpa passed away and i inherited grandpa's 84 f250. first thing i fixed was the gas gauge. always read empty. the brass float had a hole and was completely filled up. grandpa bought that truck brand spanking new. the gas tank had never been taken off.

 

True, floats themselves rarely if ever need to be replaced.

stunnuts; Float levels ARE critical to how these bikes start, run and idle. This has been proven through experience, for many people and on multiple bikes. Yamaha specified it as part of the regular maintenance, and went to great lengths to explain how to check the levels with the carbs on the bike. It's in the FACTORY service manuals.

RickCoMatic's post is right on the mark, as are Wiz, chacal and the others. We speak from direct, hands-on experience, not what somebody told us.

Back when this stuff was NEW it never needed to come apart as far as breaking down the rack, and wasn't intended as part of the "maintenance scheme." But that was 30 years ago, and throttle shaft seals don't last forever. We quite often have to take things a tad deeper than simple "maintenance."

All you've really proven with your post is another good reason NOT to take our 30-year old bikes to a modern Yamaha dealership.

 

Boy stunnuts, throw around words like "always" and "never" and you open yourself for some criticism.

I will agree that floats, once set, should not change. Unfortunately there are very few of these motorcycles that have not had at least one ham fisted previous owner (or Yamaha mechanic) work on them.

Butteryfly shaft seals do seem to hold up well. Until a ham fisted PO (or Yamaha mechanic) lets them soak for a couple days in a bucket of carb cleaner. Then they're likely shot.

Float levels are important, but not the be all end all as they often seem to be in discussions here. Fact is that if the jets are wet and the carburetor isn't flooding they'll usually run (pretty well even). All the precision involved with wet levels has more to do with keeping the EPA happy. Still, there is no harm in setting them properly, and there won't be any question that running issues must be something else.

But here's what is going on in the threads you seem to have an objection to: The authors are trying to make the point that the only way to ensure the motorcycle runs properly is to make sure that everything is within spec. Otherwise it's a bit of a crap shoot. They're trying to impart a methodical approach rather than having someone yank the carburetors half a dozen times hoping that this time whatever is poked or pried will solve the problem.

Still, there is valuable information in your post. Unfortunately you trumped the message with the attitude it contained (despite the disclaimer at the top). Let me give a crack at presenting it in a more useful manner:

Tips:

I learned my carb stuff from a 30yr Yamaha motorcycle mechanic. Between us we've seen a lot of situations and want to offer the following suggestions for dealing with carburetor issues.

1) If you have fuel leaking from your carbs (sitting or running) it's usually a bad needle and/or seat. Bad ones will never adjust reliably, check them before investing time into setting the float level.

2) If you have a running issue during idle or up to 2900rpm it is usually an idle circuit issue, it's unlikely to be a float level issue. They need to be thoroughly and carefully cleaned.

3) [I would ditch this. If the idle circuit is ok the main isn't likely to need cleaning either. More likely there is a problem with the ignition system or fuel delivery to the carbs]

4) You will likely have running trouble with open air intakes or pod filters unless the carburetor has been properly re-jetted. CV carbs are very sensitive to air pressure changes at the intake. Change the intake characteristics and you get to enter the exciting (and tedious) world of jetting carburetors.

Finally, it is unnecessary to break the carburetor rack to clean them. Breaking the rack adds a lot of work in re-aligning the carburetors, getting all the springs back in properly etc. Don't brake the rack unless you are doing something more than cleaning

 

i don't think there's such a thing as a 30 year motorcycle mechanic.

aroound here. the dealer won't fix bikes older then 10 years.

around here. the mechanics weren't even born when i drove my brand spanking new yamaha off the show room floor. at the ripe young age of 18.

they do however. change my tires. and flush hydraulics when need be.

so i don't completely rule out the dealer.

 

my $0.02....

I think some people are missing the point that we're giving advice to strangers we've never met, and on bikes we've never seen. The only way to properly help them over the internet is to explain everything as simple as possible and have them check everything even if it may not need checked.

How do we know how well someone knows engines from the "I need help won't start" type thread? Maybe they started on lawn mowers when they were 5 ,maybe this is their first time with a wrench.

Maybe the floats are good, maybe not. Don't know until you check. Takes a few minutes and costs next to nothing.

I bought my XJ with the carbs in a box. Should I not have checked the floats and their level?

I got a deal on it because the PO was not able to clean and adjust them properly and gave up. I spent a couple hours cleaning with Rick's guide, my first trip through these types of carbs, and then set the float levels to the new needles I had, bike fired up and I've road it for 3 years now. Every spring I pull the rack off the bike and clean them out and check everything, even the float level. Didn't move but I know for sure. I do not split the rack for this clean/check.

and not a slap at you stunnuts, but the "mechaincs" I've dealt with recently at dealerships near here both Bike and Auto are nothing more than parts changers who change what the book and/or their computer tells them. The book is not always right and even more so when you're now 30 years past it's publish date with who knows what modifcations made along the way.

 

We're pretty lucky in the seattle area to have enough vintage and cafe enthusiasts to warrant a few shops in the area that cater to old bikes. Even so, most folks can't see paying shop rates of $60-100 an hour to fix up an $800 craigslist find.
Awesome resources for things like shim pools to go swap what ya got plus a buck or four for what ya need.

 

thank god I haven´t seen this thread before I decided to check my carbs float level. it was all about float level, acceleration stopped @ 5500 rpm.
carb float level

 

Sorry about everyones toes here. : )