fuel level issue or normal?

I used colortune yesterday and today was going to be carb sync day. Instead of an auxiliary tank I have the bike's own tank up and back on saw horses to allow access to the various adjusting screws. Petcock is on Prime, of course. I find that when it's been on Prime, for any length of time, I'm getting some fuel out one of the overflow hoses (haven't directly observed which one, yet). I am concerned that this could be an indication that fuel level is too high, but I don't know if this could be a typical effect of running engine from Prime setting. I do hereby confess that in carb cleaning/renewal, I skipped over checking fuel level. Someone please advise if my symptom (fuel out overflow line when running via prime) is a sign of too much fuel in one or more carbs. Thank you.

 

You answered your own question. Wet setting the floats is critical to making sure that the floats, and needle valve are working properly. This will affect the performance of the bike also as incorrectly set float levels will change the fuel/air mixture, and cause the bike run irratic.

The correct order should be vacuum sync. Then color tune. Any changes in the vacuum sync will change the fuel/air mixture. Making the color tune inaccurate.

Ghost

 

Hey Ghost, the bike manual says that carbs "must be set properly before synchronizing" I took that to mean fuel/air mix also.

 

If you put in new Float needles and seats - it's possible one of the float needles isn't seating well. I just rebuilt my carbs and put in rebuild kits - including of course float needles and seats, and 1 of the 4 wouldn't shut the gas off completely when the float went up. Fortunately, I was setting float levels at the time on a bench vs. having the carbs back in the bike so it was easy enough to correct the problem. I went through my old valve seats and needles and found a set that looked pristine and put them back in - worked fine after that. I've read elsewhere on this forum that some of the valve seats received in cheaper rebuild kits are prone to these issues due to lack of good quality control from the manufacturer. Having the tank on prime would not cause your issue - the carbs shut themselves off via the float needle and seat. It's hard to imagine that it's a float level thing also, as the float tang would have to be grossly out of wack for the float not to engage the float needle at all - and it sounds like you didn't mess with those. New float needles can be about 1mm longer than the originals - so if you replaced the originals, then it would actually be shutting the gas off sooner - so your float levels would be too low vs. too high. Also, did you put the screens on your new valve seats? If not any piece of gunk can get in the valve seat and keep the valve needle from sealing off the flow of fuel completely.

 

I believe I read in the posts here somewhere that Rickomatic has had experience in "truing" up some of these new valve seats that aren't working correctly (if that ends up being your issue).

 

Regardless of why your gas is overflowing, Ghost is right, you have to get the fuel levels correct or it will mess up the rest of your process of getting the bike running correctly.

 

You are correct on the statement in the manual, but the manual does not cover the air/fuel mixture. The air/fuel mixture is a variable setting.

The bike maual does cover the floats, and fuel level settings. It is those settings that the manual is refering to being set before syncronizing the carbs as they can, and will affect the carb sync.

The fuel/air mixture is based on the vacuum of the carb. When you change the vacuum of the carb. You change the carbs ability to pull the fuel into the air stream.
More vacuum = more fuel = richer mixture.
Less vacuum = less fuel = leaner mixture.

With four carbs ganged together you need to have all four cyinders working equally. This is why the vacuum sync becomes important. It adjusts each carb for the differences in each cylinder so that all four cylinders are doing an equal share of the work.

Once the vacuum sync has all four cyilinders working in balance. You then adjust the mixtures to make the cylinders work to peak efficency.

While not required. You can then go back, and recheck the vacuum sync to verify that the mixture adjustment did not throw the vacuum sync out. It is a process of going back and forth to completely dial in the carbs. And yes. A major P.I.T.A.

But it all has to start with the correct settings on the floats, and therefore the fuel level.

Also note the absolute requirement of the valves clearances being in spec before doing a vacuum sync on the carbs.

Fear not! You now have the knowledge to make that bike scream as it was meant too.

Class dismissed! :lol:

Ghost

 

Thank you, Ghost. Your explanation is both thorough and comprehensible to a guy who WASN'T born with a wrench in his hand! In the spirt of the "maxim" If it's worth fixing; it's worth fixing right, I will remove the carbs and get with the fuel level program. Appreciate it!

 

Wiley Dan, thank you also. I didn't change any float-related parts, so that stuff is all original. I will check the float valves to see that they still function, check thoroughly for obstructions, and of course, take a look at the valve seats, which I also omitted earlier!

 

Jobee,
You need to update your signature so we know what bike you have. If you have a 550 the carbs are different than a 650 or 750

MN

 

What the book actually says:



Which is not related to your issue; but is as equally important as precise float levels.

 

I was just looking at another thread and it looks like you are working on an XJ 700. I think that your bike would have Mikuni carbs on it. If it does check the o-rings that are around the seats. Those like to shrink and not seal anymore when they get old.

MN

 

Bigfitz, my" book" is the Yamaha 1985-86 Yamaha XJ 700X service manual on CD (done by Cycle Hippie). pdf file p. 2-11, and I did quote directly the sentence immediately before the note you quoted. However, it's not outlandishly important, since I understand the principle now. MN-Maxims, you are correct about which bike and carbs, so I will absolutely check that o-ring as well! To everyone... valve clearance havebeen properly adjusted with new shims (where required) from XJ4ever. Clearances weredouble-checked afterwards.

 

Fitz

The OP has a 700 Maxim X waterhead, and is correct in the statement about the manual. It is in the X manual about having the carbs set properly before syncing. This is what caused all the confusion as that statement is not included in any of the other manuals. I had to verify this for myself.



You are also correct about the absolute requirement to have the valves in spec before syncing the carbs

Ghost

 

Hello again. I believe I have created confusion because of my lacking signature and multiple threads. I apologize for that. First off, signature is updated, bike is as MN said, XJ 700 waterhead. I have taken the carbs off once again due to the fuel overflow issue, and found that the o-rings around the valve seats are indeed brittle and need to be replaced. I think I may have set these, with o- rings still in place, directly into carb cleaner before I became a poster/reader here.Outside of o-rings, the seats look to be in excellent condition. Since I have another order to make, I'll be getting the stuff necessary to check fuel levels properly (drain nipples & tubing). In addition I believe it makes good sense to refurb the petcock, since it's one more old item which could give headaches later. BTW, since I cannot find anything visually wrong with the float bowl valves, and the springs work properly, is it okay to continue with the originals?

 

If the needles and seats are good then just install new o-rings and use them. I like to polish the insides of the seats with some 00 steel wool just to make sure the float pin moves as freely as possible.
When you wet set the floats you'll know if everything is ok

MN

 

thank you for the polishing advice, will do. will also use magnifying glass to examine the needles more closely than just naked eye.

 

Oh yeah, just disassembled petcock. It is aboslutely screaming for a refurb. took pictures every step so as not to screw myself later.

 

Sounds like your on the right track, let us know how it goes.

MN

 

thank you, I will

 

Some reference material in case you need it for that petcock rebuild.

Rebuilding the Yamaha Vacuum Fuel Valve w/pics

Ghost

 

Thank you very much, Ghost.

 

... and a tip of the hat to Bigfitz for creating these excellent instructions

 

Been a while since I posted. I need to finalize my order to xj4ever, then when my stuff comes in (float valve seat o-rings, petcock rebuild kit, clear hose with measuring marks for fuel level checks) will get cracking. Have read with interest a couple of recent postings about finicky fitting with the petcock rebuild kits, and hoping I can sort that easily enough if it occurs to me. Another question, does anyone know of an easier way to set up the carbs for the fuel level check than the PCV creation pictured in the instructions posted on this site?

 

The clear tube wet set is really the only way to get the right float height. It takes a little time but well worth it in the end...

 

The clear tube wet set is really the only way to get the right float height. It takes a little time but well worth it in the end...

 

In regard to the PVC "fixture" I just clamp the rack in my (carboard-padded) bench vise and use a small level to ensure that it's level in all directions.

 

bench vise solution sounds reasonable. I can test drive that while I'm waiting. God knows I got no shortage of cardboard. Thanks.