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Non BMW question...help?


kmac

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I am helping a friend fix a 2004 Yamaha V-Star 1100.

It sat for months and would not run. It is carbureted with twin Mikunis.

 

I knew the carbs were gummed up as all carbs are if they sit anymore with modern fuel. So I pulled the carbs off and they were not terriblely gummed, but the jets were clogged enough so as not to run.

 

I completely cleaned the jets and blew out all ports and venturies....one carb at a time so there was no parts mix ups.Drained gas tank and fresh fuel put in.

I have rebuilt dozens of carbs in my life of riding so I am confident in my skills.

 

I put this bike back together and it fires right up, warms up and I test ride it, it runs but it blubbers on take of and then runs very odd, surging on power. I realize I must have missed something. I pull it all back down, this time I soak every part of each carb, one at a time again, take tiny copper wire and make sure every jet, venturi, port, and opening is clean and blown thru with compressed air and all seems good.

 

I put it all back together and now it fires up even better, warms up fine and once in the revs it pulls VERY strong with NO surging, runs perfect....except,

If I let the clutch out at low rpms it lugs a bit then pops once or twice, then pulls great. If I rev up the motor before letting out the clutch, then let the clutch out slower while the motor is at a bit higher RPMs then no pop and great pull...it is just that low rpm pop under load...no popping when not under load. I do not remember if it pops in all gears if I shift at low rpms or only 1st...I do not short shift very often so I am not sure.

 

What is is guys? Jetting?

It is BOX stock with stock jets and stock exhaust. Help, what do I check now?

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Back when I used to wrench and ride British, there was a saying that I still remember. "90% of all carb problems are ignition, and 90% of all ignition problems are carbs".

Since you have been in the carbs and they look good, start looking at ignition. Maybe the plugs are fouled?

Happy Hunting

Steve

 

 

 

 

 

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+1 on possible fouled plugs

 

I've personally seen this happen with old fuel and the plugs looked good! Just replace them to rule them out and check back with us. :lurk:

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Probably ought to post this in the "non R and K bikes" section.

 

I did not post it there because that specifically says "F and G bikes and airheads".

No mention of non-BMW brands and I am "Talking" about motorcycles so I went with "Motorcycle Talk"...sorry if that is the wrong choice, a mod can move it if it is in the wrong place. Thanks for the heads up.

 

Plugs will be my next thing to do. I am still concerned if the pilot jets still possibly have some crud in them. I soaked them in carb cleaner spray that I sprayed into a cup and soaked them and then used a strand of copper wire and worked it thru the pilot jets. But man were these jets tiny and it seems as if ANY particle that I may have missed could cause the popping. I hate to think I missed anything, but since I have to pull off the tank and airbox to get to the plugs so I might just pop the carbs back off and re-check the pilots.

 

What is everyones favorite carb cleaner? The gallon can soak type, Berrymans or McKays or other?

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Probably ought to post this in the "non R and K bikes" section.

 

I did not post it there because that specifically says "F and G bikes and airheads".

No mention of non-BMW brands and I am "Talking" about motorcycles so I went with "Motorcycle Talk"...sorry if that is the wrong choice, a mod can move it if it is in the wrong place. Thanks for the heads up.

 

Actually, you posted this thread in Bike Related.

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Most carbureted bikes built in this century are not jetted anywhere near ideal, but are compromised to pass emissions requirements. You can buy a jet kit that addresses the problem for your particular model, or you can find a website that is model specific and find out what the cool guys are doing.

 

In other words, "They all do that......This is how you fix it!"

 

Here is one solution: http://www.maxairengineering.com/mm5/merchant.mvc?Screen=PROD&Product_Code=MK-YVS1-P

 

I am sure there are more, and less expensive ones, too.

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I am on my way to get a set of plugs for it, but I think I am going to Re-RE-check the pilot jets. I hate modern fuel.

 

What is you folks favorite carb cleaner soak?

Is Seafoam really effective at cleaning a carb?

I see alot of people recommending it for FI bikes that have sat, and the can says it is good for carbs also. Any success?

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Afternoon kmac

 

(IF), your problem is in the carbs, & it kind of sounds that way, you are fighting 2 things.

 

The first is varnish in the jets & fuel/air passages caused by sour gasoline turning to varnish. Common carb cleaner & other carb cleaning operations as well as compressed air will easily clean this up.

 

The second is a type of corrosion inside the aluminum air passages & other areas of fuel or air flow. This is caused by remnants of moisture in the fuel & alcohol in the fuel causing galvanic, or corrosion/oxidation issues. This type of passage restriction is very difficult to deal with as no solvent or compressed air will effect it.

 

The oxidized passages (if present) almost always need manual cleaning with soft wires or something to break the oxidation loose & push it through. Unfortunately using anything stiff like piano wire can damage the small restrictions in the passages. I have had limited success using my friends ultrasonic carb tank that heats the cleaning fluid as well as the ultrasonic.

 

Another thing that can cause all kinds of carb issues is if the carbs have vacuum diaphragms on the slides. Any vacuum leakage or stiffness in the rubber diaphragms can cause the slide to lift incorrectly, delay lifting, or with 2 carbs not lift at the same time as the other carb.

 

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Thanks DR.

That is kind of where I am looking right now.

I put new plugs in today but I said while the tank and everything was off I would re clean the carbs.

I bought a can of that Berrymans carb dip with the plastic basket. My only problem is I can not get this big double carb set up in the can.

 

Thanks for all the help.

 

I never claim to be real sharp, more like sharp like a marble.

 

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Moved again....whatever

 

Anyway, I think I figured out what I did. I am honest and not above discussing my mistakes...lol, to many to actually discuss all of them, but in this case:

 

I am still soaking the pilot jets just to make sure but as I slowly and methodically disassembled the carbs for this 3rd time I pulled the right carb diaphragm cap off and noticed the tiny O-ring that seal a vent port to the top of the carb body was down inside the diaphragm cavity and not in place where it should be.

 

Completely my bad and operator error here.

 

I will let you folks know if it works and thanks again for the help.

 

Now my question is, there is a T between the carbs that goes directly into the underside of the diaphragm. On the T is a block that looks like a check valve like a big version of what is on the tank vent line on a dirt bike, but it is clear in both directions when I blow thru it. What is it? A filter?

 

It is open to the air and just sits open in a pocket under the airbox that is NOT connected to anything. It does not even go into the airbox.

 

Anyway now when I blow gently into it both vacuum slides go up evenly, so I think they will work now. My guess is without that one O-ring in place one diaphragm was leaking a little bit so when you began acceleration one diaphragm started to open and the other one took a second longer causing the pop stutter.

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Afternoon Kmac

 

I'm not familiar with that crossover device but it could very well be a filter of some sort.

 

Engine vacuum lifts the TOP of the diaphragms so the bottom of the diaphragms need be vented to allow lift. Or possibly some sort of delay device to slow down the slide lift.

 

If you had a leak in one of those diaphragms that can make the engine run like crap on throttle up as one slide will lift but the other side will be lazy or no lift at all.

 

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Hey Kmac,

 

When I pick up old airheads, I buy a gallon can of carb boil and after dissasembly of the carb, allow all pieces to soak overnight at least. Replace all the rubber pieces as well, especially the diaphragms as they tend to be a big culprit when all else is well. Little O rings are always replaced. Very inexpensive insurance to make sure the little ankle biter issues are solved.

 

 

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Runs like a champ now. Amazing what a good service can do for a bike. The thing handled like such a pig when I was test riding it, so heavy on the steering.... Once I got it running right I completed the rest of the service and fluid changes and checked tire air pressures, wow, it had like 15 psi in the rear and 12 psi in the front, brought them up to 32 psi front and 34 psi rear and now it turns MUCH better. Still not a BMW, of course, but for a big fat cruiser couch, it turns much better.

 

All in all it runs great now....for a couch anyway. lol

Thanks folks.

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