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Discussion Starter #1
Bought a 03 1100 VTwin that was not running. Pulled carbs cleaned and reinstalled. Ran but was way to rich. Checked jets and found someone had put way to big of jets in it. Took Carbs to MC shop. Bought jets they recomended due to type of pipes on bike. Was better but still way to rich. Plugs last about 30 min before fouling out. And by fouling out I mean charcoal black both cylinders. Changed out jets again to factory jets. Same results so I went another step down on main jet. Runs for 30 miles and turns the plugs into charcoal. Took it to MC shop they went through carbs adjusted float level, fixed exhaust leak and said it was good. Drove it home and around town and sure enough at 31 miles the pluges fouled out. The thing runs perfect before the plugs foul out. Makes no sense. Cannot figure out were the extra gas is coming from. I even went as far as to plug the choke holes to verify the choke injector wasnt leaking by. Got the same results. Its back at the shop now driving them crazy. Just wondering if anyone has ever heard anything like this? Thanks for any advice you may have.
 

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Pulling my hair out!

Yes they are the correct carbs. They match all the literature I have looked up on the bike. The bike came from the original owner and he's not smart enough to change out carbs.
 

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Any other mods done to the bike besides the exhaust? What jets do you have in the carbs now? Does it just flood out driving along or when you come to a stop? Since the MC shop and you both have been through the carbs with the same results (unless both of you are overlooking the same thing) that kind of says look elsewhere. What about fuel pump pressure? It may be too high for the needle and seat to overcome. Just a thought.
 

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If it's too rich then it"s too much fuel or needs more air. Check and look into air supply What's the filter look like? Maybe try a high flow filter? Check and make sure air box doesn't have a nest in it? This happened to my Dad's bike had it stored for a couple storage years, after, it ran similar to yours except his ran rough. Who would have thought.
 

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Again obvious but no chance it's NOT a fuel problem? IE leaking so much oil into the cylinder that it's actually oil you're seeing on the plugs.

If that were the case it should be leaving the most God Awful cloud of blue smoke you've ever seen, but hey strange things happen sometimes. I wouldn't even bring it up except that I've seen it happen so ya never know?

If it really is running that rich you would expect the exhaust to black as coal.
 

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Not knowing anything about the bike...it's impossible to tell you what direction to go. We don't even know the size of jets you are using, what brand they are, how the bike is set up......etc etc.

From the sounds of things...something in the carbs is not put together right or the floats needles are stuck
 

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Discussion Starter #10
Lot of good responses thanks. Let’s see if I can answer the questions in one reply.

-Any other mods done to the bike besides the exhaust?
No other mods except straight pipes that have been on the bike since it was new.

-What jets do you have in the carbs now?
Jets are back to factory OEM Yamaha parts.
Main jet 110 (112.5 is factory. down sized trying to reduce fuel)
2nd main jet is 42.5
Pilot jet 17.5
Needle is factory needle as well with no adjustment.

-Does it just flood out driving along or when you come to a stop?
Does not flood out when driving or stopping. Runs perfect. Other than some backfiring when you rev it up and the smell of unburnt fuel you would have no idea anything is wrong until the plugs foul out.

-What about fuel pump pressure?
Very good question. Was discussing that very thing with the MC shop. I would think if it had too much pressure that it would cause fuel to come out the overflow when the key is on but the motor isn’t running. I find it odd that it even needs a fuel pump. Was debating on trying it without a fuel pump to see what happens.

-If it's too rich then it’s too much fuel or needs more air. Check and look into air supply what’s the filter look like?
Been down that road already. Even ran through a set of plugs without a filter installed at all and it still did it. Completely dismantled the air box as well. Heard of that problem before.

-If it really is running that rich you would expect the exhaust to black as coal.
Just get a little puff of soot when you rev it up and get a good back fire. The ehaust smells of unburnt fuel.

-Not knowing anything about the bike
2003 Yamaha 1100 VTwin only has 10K miles. I am the second owner. I know the original owner well. The pipes are bubs or bubas something like that. They are straight shot pipes and have been on the bike since it was new. Ran fine until owner let it sit over a year and the gas gummed everything up in it. The 1st owner’s son tried to rebuild carbs. He ended up putting way too big of jets in the carb. Had a 120 in the 2nd main jet. Never got it to run correctly. Then it was left sitting for a couple of years before selling it to me.

Whatever it is it is common to both cylinders and both carbs. Plugs come out looking identical (charcoal black).

I have smaller than factory jets installed and ran with out air filter with straight pipes. Everything says it should be starved for gas but it isnt. Where is the extra gas getting through?
 

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This may be a stretch, but it may prompt some thinking. You said the carbs were gummed up, correct? Any mechanic I have talked to who is good at carbs claims that if you don't use at least a whole can of cleaner on them, you didn't use enough, and some strange things can happen if there is the slightest amount of gum left inside. I wonder if there is a chance that somewhere inside the bowels of the carburetors there is a spot that is still gummed and causing the gas to be squirted instead of sprayed into the cylinder. I would think this would cause it to run rough, but I've also learned to never say never. It just seems to me that if the plugs are fouling that fast, it would have a hard time running at all. You said the float level is good, but are the float needles (or seats??) sealing and doing their job? There could be a little gum around the seats and could be letting just a little bit too much fuel into the bowls, and since it has a fuel pump, they shouldn't leak when the bike isn't running. I dunno.....just throwing out some food for thought.
 

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Discussion Starter #13
What do you mean by second main jet? There is only one sir
Negative the parts breakdown shows all three jets and calls two of them "MainJet" and the other pilot jet. Dont quite understand it myself but every carb breakdown I have seen for these carbs call two of them "main jet".
 

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Discussion Starter #15
This may be a stretch, but it may prompt some thinking. You said the carbs were gummed up, correct? Any mechanic I have talked to who is good at carbs claims that if you don't use at least a whole can of cleaner on them, you didn't use enough, and some strange things can happen if there is the slightest amount of gum left inside. I wonder if there is a chance that somewhere inside the bowels of the carburetors there is a spot that is still gummed and causing the gas to be squirted instead of sprayed into the cylinder. I would think this would cause it to run rough, but I've also learned to never say never. It just seems to me that if the plugs are fouling that fast, it would have a hard time running at all. You said the float level is good, but are the float needles (or seats??) sealing and doing their job? There could be a little gum around the seats and could be letting just a little bit too much fuel into the bowls, and since it has a fuel pump, they shouldn't leak when the bike isn't running. I dunno.....just throwing out some food for thought.
Anything is possible at this point. I cleaned them multiple time and the MC shop has cleaned them. Pretty sure they are clean. I cant stress how well it runs until the plugs foul. It will take off as fast as you can hold on and cruise at 80mph and pur like a kitten. It makes no sense. You would think it would run rough at some point but it doesnt.
 

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Negative the parts breakdown shows all three jets and calls two of them "MainJet" and the other pilot jet. Dont quite understand it myself but every carb breakdown I have seen for these carbs call two of them "main jet".
Tht's where you have to know exactly what you're working on. Even though Yamaha called the air jet a "main jet" in the parts breakdown, it's actually an air jet and is normally never messed with. There really is only one fuel related main jet.

A couple of silly questions..... what plugs are you using..and how far up the site glass is your oil? Also, are the small o rings still in place on the top of the diaphragms?
 

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Discussion Starter #17
Tht's where you have to know exactly what you're working on. Even though Yamaha called the air jet a "main jet" in the parts breakdown, it's actually an air jet and is normally never messed with. There really is only one fuel related main jet.

A couple of silly questions..... what plugs are you using..and how far up the site glass is your oil? Also, are the small o rings still in place on the top of the diaphragms?
-Good to know. Wondered how they called them both main jets.
-Running factory specified plugs NGK BPR7ES if memory serves me correctly. Would have to look at home at my collection of spark plug boxes. :) I should have bought stock in NGK!
-Oil is 1/2 sight glass not running. Is this correct?
- Small orings are in place but I have not replaced them. What is the purpose and what do they do?
 

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Heres another stupid question, just covering bases and I see no one has touched it yet...have you adjusted the air fuel screw (PMS screw)?

Yes it seems obvious but you never know...
 

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Heres another stupid question, just covering bases and I see no one has touched it yet...have you adjusted the air fuel screw (PMS screw)?

Yes it seems obvious but you never know...
I tried several time but probably made it worse. I assume the MC shop did when they rebuilt the carbs. Idled really well. I haven't touched it since then.
 

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another silly and maybe stupid and unrelated. But did the previous owner disable/bypass/remove the AIS and maybe not do a proper job of it? Most people remove/bypass it when they change to non-stock pipes - just a shot in the dark
 
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