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**TownsendsFJR1300** · 06-23-2014, 01:09 PM

I too grew up on Yamaha Mikuni carbs on motorcycles for literally decades(sonce 1975, owned an XS650 besides an RD350, many YZ's, FJR, current FZ, etc). Just cleaned a Mikuni carb literally yesterday, off a CAT pressure washer, low speed jet varnished shut..

A carb is a carb for the most part. Typical varnish build up on the jets, etc.

If the plugs are wet and your not getting any fire, plug at least one of the spark plugs, plug it in the cap, ground and pull, checking for spark. It sounds as if there no spark, the plugs are wet, ether should fire but it isn't..

I don't know what the red light thing is about, someone else will have to chime in. Probably the key here, possibly (guessing) a kill switch or?

I would be looking for a kill switch or safety switch of some sort (if NO SPARK).

Of course the engine HAS to be in neutral to start (or if equipped, a fast idle-not in gear lever activated).

AND WELCOME TO THE FORUM!!

What is the year and model # of the engine so we can look at the parts fisch and probably find what that light is..

There's a "Purchase Yamaha Parts" section up above. Put in your info, you can find most EVERYTHING and is a big help in assembling/ diagnosing over the internet.

BTW, unless you literally broke off a piece of aluminum off the carb, you won't need a new one. Yamaha sells individual parts should you need a needle/float, etc...

**Wharfcreek** · 06-23-2014, 03:04 PM

Scott,

Thanks for responding. The model is a F8MSHA.....which I find confusing because all I see are F8SMHA version......w/ the MS/SM inverted. But, I CLEARLY read my label, and it is definitely a F8MSHA. Build date appears to be 10/01, making it an '02 according to the local Yamaha dealer.

As to carb, I pulled it yet again just about an hour ago.....and it had gas and 'seemed' to be OK. I also decided to pull the fuel pump and just go through it as well. A LOT of scale inside it......so I cleaned it up and got the scale off the reed valves. The diaphragm was perfect, so I didn't replace it. Likewise the top gasket was fine......so I really didn't need to do anything more than just clean it and make sure the surfaces of the reed valve contact points were free from debris. I then re-installed it......and I don't think it will need any further attention.

Here's a little 'up-date'.....and this is where I think I need someone with some specific knowledge about this: When doing all this in the past hour, I also had the plugs out just to make sure I didn't see anything goofy and confirm that I did, indeed, have the correct plugs (a BH6HS I do believe). I gave the engine a couple of pulls with the plugs out.....just to clear the cylinders....and I noted that the little red light I'm asking about was blinking constantly throughout the pull cycle. OK I thought.....still not knowing just what that little light is all about. So, I put the plugs in, pulled the choke out, and gave it one pull and it started to run!! As I had no hose hooked up, I quickly grabbed for the kill switch...but I think it died out on its own. Anyway...... I grabbed the hose, gave it some water, and attempted to re-start it......and again..... NOTHING!! But, NOW I'm seeing odd things with that little light! Instead of blinking constantly as I pull the cord....it seems to blink only once.......AFTER I complete the pull cycle. It's like something charges up from my pulling, and as soon as I quit pulling and that rotating motion stops.....it's like there's a discharge...and the little red light blinks once....and that's it!!

So, I pulled all the wires out of the very nice little connector rack.....and removed each wire connection and checked to make sure I didn't have a corroded connector. All were fine. I tried disconnecting the white wire that comes from the kill switch.......and tried pulling again.....and again......the same flash at the end of the pull cycle. This appears to be a 'single-fire' coil......which in my motorcycle world means that the coil is basically firing both plugs simultaneously on each power cycle. Basically this is what many 'twin' cylinder engines do...since there's no harm in firing the plug at the top of the exhaust cycle. But, I checked to see if I had ANY kind of visible spark at the gap of either plug ....... and now....nothing!! And, again...... I'm stumped! However, I now know that running out to buy a carb or fuel pump is going to be fruitless until I solve this ignition problem.

So here's my newest question: Could this be a pick-up issue?.....if so....any easy way to tell?.....if not.....what do I do to confirm what it is? There's a little label on the top of the engine that says to disconnect the yellow wire to the micro-processor to get engine to 'limp into port' mode. I'd sure like to know more about that.

Time to go buy a good service manual...............

Thanks, Tom D.

**Wharfcreek** · 06-23-2014, 04:27 PM

One Hour later: Well, I just went out to the back yard, gave the starter cord a pull.....and the little red light is blinking away like it did last time. Or course, I've done nothing other than come inside and eat lunch and type a few memos on the computer. So, what ever was 'failed' would appear to be working now....for the moment. I'm going to go hook up the water and see what happens.....but I suspect it will 'flare' from an initial dose of fuel....then quit from a loss of ignition.....and I'll bet I'll see the little red light quit blinking as it's rolling to a stop.
WC

**TownsendsFJR1300** · 06-23-2014, 04:54 PM

Here's you electrical parts fisch. Part #17 seems to be your "light": "emergency signal light assembly"

Re it starting after leaving the plugs out, sounds like it was flooded and dried out.. Rodbolt likely knows, an owners manual would likely have something re that light. I did a search and couldn't find anything. (With the name Yamaha calls it, I have to doubt/guess, per your dealer, its ON all the time)

http://www.boats.net/parts/search/Ya...201/parts.html

**Wharfcreek** · 06-23-2014, 04:55 PM

Another quick update: Just got off the phone w/ yet another Yamaha shop.....and got some conflicting info. I got the engine to fire again, but it again died.....and I noted that it was actually 'firing' and running off the ether while the little red light was NOT blinking. So, in checking w/ yet another local shop, this place is telling me that the red light is a low oil pressure warning light...which makes sense to me. He said the 'blinking' while cranking is 'normal'....but not indicative of anything. Basically....according to 'Chris the Mechanic'...the red light will blink while cranking....then go 'off' when running....unless engine loses oil pressure at which point it will come on. So, I guess I need not worry further about the red flashing light. Also, this engine may just have 'weak' spark.....so that may be why I can's see it when I tried looking. But.....it did fire....and it actually gave me about a 10 second run....then quit again. This time I'd go for 'fuel' as being the source of the problem.......and I may be back to taking that carb off....AGAIN.....and hauling it down to the local Yamaha dealer and talking to Chris in person....carb in hand...and getting his opinion. $30 for a needle.....???? WTF!! (F for Frog) Oh well........if you wanna play, you gotta pay!! WC

**Wharfcreek** · 06-23-2014, 04:58 PM

Scott.......

To quote 'Shultzie' (if you're old enough to remember him)...... "I see nothing......."

Did you attach an electrical diagram? Looks like that light is a low oil pressure warning light and nothing more? If you can confirm, that's great!!

Thanks,

Tom D.

**Wharfcreek** · 06-23-2014, 05:14 PM

Scott,

Got it! Had to log out then log back in, but now I see the attachment. Many thanks! As you figured....it looks like that's a low pressure warning light and NOT illuminated all the time when running. Now I'm back to 'carb' problems......and looking more like I may just bite the bullet and spend the $350 for a new one. DAMN!! Oh well.............

**TownsendsFJR1300** · 06-23-2014, 05:14 PM

Originally posted by Wharfcreek View Post

Scott.......

To quote 'Shultzie' (if you're old enough to remember him)...... "I see nothing......."

Did you attach an electrical diagram? Looks like that light is a low oil pressure warning light and nothing more? If you can confirm, that's great!!

Thanks,

Tom D.

No Tom, thats strictly a parts site (up above here in RED). It won't show the wiring diagram, just the harness to purchase. You can key up on the various parts.

Its possible that oil pressure switch has failed and is shutting the engine down. (I'm not sure if it would shut down altogether or do a limp mode thing).

You may want to disconnect or ground the harness by-passing the oil pressure switch (obviously if you have no oil pressure it could be very bad) and see what happens.

From what you post, initial cranking, its letting it spark. Then, once it STARTS, it doesn't sense oil pressure and shuts down...

Something, on ANY ENGINE, especially with issues, check ALL GROUNDS connectors etc. Could be something as simple as a bad ground at the coil, etc..

**TownsendsFJR1300** · 06-23-2014, 05:28 PM

Originally posted by Wharfcreek View Post

Scott,

Got it! Had to log out then log back in, but now I see the attachment. Many thanks! As you figured....it looks like that's a low pressure warning light and NOT illuminated all the time when running. Now I'm back to 'carb' problems......and looking more like I may just bite the bullet and spend the $350 for a new one. DAMN!! Oh well.............

Your fixing to have a spare carburetor and still have issues.

IMO, invest in a shop manual and go thru the carb again.

Its very possible the main carb to bowl gasket may be installed incorrectly holding the needle open (seen it happen) or something else. Its a carb, you've been thru numerous, same operating principle.

Confirm spark 100% of the time, (eliminate spark being an issue or carb being an issue). Confirm the oil pressure switch isn't killing spark, etc. A wet spark plug, the engine won't start..

The original owner sold you a fixer upper(known), no doubt in my mind the carb itself is fine, may be assembled wrong, someone changed jets screwing with it, it needs to be gone thru with a fine come OR as you stated, drop $350. Me, I'd rather find the issue..

**Wharfcreek** · 06-23-2014, 05:58 PM

Hey Scott,

I'm going to have to get that manual. I'd like to confirm your thought about the oil pressure switch....though seems to me that the circuit being 'warning light' activated.....shouldn't be any shut down involved. If there was.....no point in a warning light......it would just go on as the engine quit.....so you may never see it.

As to the carb itself.....I here you about the money situation. I don't particularly want to drop $350 on a carb only to find it was something else. My ONLY reason for thinking I may need to bite the bullet on a new one is that the 'bore' ...where the float needle goes up and down....that bore has deteriorated badly in my carb. So did the needle itself. The 'etching' that has taken place is horrible! So, the question is: Will a new float needle run smoothly in that bore.....or will it hang up and 'stick'...either up or down....just because the hole is so badly deteriorated? I've run into this before....where everything else is OK....but because the float needle valve didn't get a separate and 'serviceable' housing.....the aluminum around the float needle just gets so eaten up that you can't get a float needle to run smoothly any more......so the carb either floods.....or starves. And...you can play hell trying to come to that conclusion!!

Like I said, I'm generally pretty good with carbs. I've rebuilt probably no less than a thousand.....if not twice that. People bring their carbs to me....and I'm the one who points out the finer points about transition ports, fuel delivery passages, jetting, air and vacuum ports and jets.....and even accelerator pumps if so equipped. And, I've confirmed fuel IS making it's way through the idle circuit and the transition circuit. I CANNOT get the main jet or the idle jet out of the carb....they are simply seized in there so badly I fear I'll butcher them in trying to get them out. So, the 'emulsion tube' as I refer to it...or the 'mixing' tube as some call it......I can't get that out either. So, I'm simply hoping that since the main jet is 'covered' by that plug......and fuel is delivered through what I guess is some kind of metering jet (beneath the idle jet).....I'm hoping that the emulsion (mixing) tube isn't also plugged. These tend NOT to be plugged, even in badly contaminated carbs....which is not to say this one isn't. But, I think my problem is still in the needle valve....and then getting fuel to the main and idle circuits. I'll probably go pull it again...and work on it some more tonight. For now, I'm heading out to the Chesapeake Bay and seeing if I can catch a fish or two!!

Thanks Scott!

Tom D.

**TownsendsFJR1300** · 06-23-2014, 06:44 PM

Tom,

The corrosion is generally (you likely know) from water sitting in there. Wether from ethonol or ?, who knows. Didn't know about the corrosion internally previously... In the future, please post anything unusual/done to the engine recently, etc, it may help in the diagnoses.

If the needle bore is etched up and the needle CANNOT close FULLY, slide up and down as designed get a good seat, yes I agree, the carb body is toast.

It'll also leak internally (and likely externally) and potentially work its way into the engine (depending on the tilt of the engine) and very likely run rich (your wet plugs) and foul them out(no spark).

IMO, replace the known, corroded carb, then go from there..

**BTW, smell the engine oil and check the level to make sure it hasn't been diluted with fuel.**

As a side note,
I just worked on two mowers yesterday, one being a Honda engine (clogged carb). Got it running pretty good. The owner mentioned, it'd leak gas out the carb over night. I got done with it, left the fuel ON (on purpose), sure enough, puddle of fuel under the engine OVERNIGHT.. Pulled the carb off, the aluminum body and aluminum needle seat was fine. The rubber tip on the needle had such minor wear it wasn't visable without a magnifying glass.

I confirmed this as the leaking area putting fuel to the carb, UPSIDE DOWN, NO float bowl. The needle would NOT FULLY seal and sure enough, fuel very slowly seeped out... Just that little bit, a hardened rubber tip, caused this fairly major leak overnight... Your carb sounds easily 10x's worse..

He didn't want to put a needle (carb kit) in it, (it was already apart, same price on my end). Buttoned it up and he was aware what it needed to fix that very hazardous issue...

**Wharfcreek** · 06-23-2014, 09:50 PM

Scott,

Carb work is 'such fun'!!!......lol I've been pretty lucky in the past.....and actually resurrected old CV carbs that have sat for over 20 years OUTSIDE in one case. The old 'bike out back against the barn' deal.....and, a Yamaha XS650 at that! I recently rebuilt another set of XS carbs that probably had about 10 years since their last use. One of those was literally filled with green 'gas fungus'! I still find it hard to believe that there is species of 'mold' that grows in fossil fuel.....but.....'yup'!! .... and it can be some pretty nasty stuff!

The carb on this OB was full of crap.....mostly in 'powder' form....some of it even granular...like sand. But, the real problem is the 'scale' the builds up.....and I've not found anything that will eat that off. My only successful resource here is just patiently 'scraping' it away under a magnifying glass with some 3X specs on. I use everything from a small Xacto knife...to a small screw driver that I've specially sharpened and shaped just to be used as a scraper on carbs. I also use guitar strings to route out carb passages...which works REALLY well!! Since guitar strings are all sold in identifiable gauges....you can tell from checking a known good jet size and checking it against one in a carb. As for this carb.....I feel as if the passages are all OK....but like I said....I'm VERY skeptical about the float section. Tomorrow I'm going to remove it ....again....and run it to the Yamaha dealer and get a second opinion. I'm also going to buy the needle, for the ridiculous price of $30....and see if that maybe solves all the problems.

Not that I have ANY desire to spend $365 on a carb.....but one thing that might be worth mentioning here is the 'reliability' factor.....and the cost of getting 'stranded' because the carb screws up while out somewhere. Frankly, that's where 'peace of mind' becomes 'priceless'!! Ya know, I may go pull that carb now (dark outside...but 2 bolts.....I think I can handle it!!....and spend some more time looking over that needle bore. Guess we'll see what happens tomorrow.

Thanks for all your help Scott! I really appreciate it. Surprised that no other person commented here. Seems a bit unusual, yes/no?

Later,

Tom

**rodbolt17** · 06-24-2014, 07:01 AM

that red lamp is indeed a warning for oil.
as long as its out when running your ok.
however even if its ON the motor will run.
until it mechanically seized.
sounds like you have no fuel in the carb or a clogged main jet passage.

**chrissy t** · 06-24-2014, 07:10 AM

If you buy a new carb, maybe I can make a deal for your old one. I only need the throttle shaft from it.Let me know,thanks , Rob

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