Can't get Cyl 3 above 350° & fuel in vac line

Maintenance, repair, troubleshooting, etc.
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mvk24
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Region or State: New York
Motorcycles Owned Currently: 1992 yamaha xj600
Location: Long Island, NY

Fri May 26, 2017 7:51 pm

Hey guys been using all of your write ups over the years and my se a is riding well. HOWEVER it still feels like there's some ponies I haven't unleashed. I did a total rebuild to the carbs.( along with rebuilding the entire bike) New gaskets, New float needles, adjusted float heights (Thank you Radare) changed to #20 pilots and put brand new mains while I was at it. I used the bb trick to sync the carbs. And it has a brand spanking new fuel pump. New intake boots and new air filter.

Here's the 2 issues.

Using the infrared temp method cylinders 1, 2, 4 I can get to 500° no problem. However cylinder 3 will not go higher than 350° and it doesn't matter If I turn it 1 turn out or 7 turns out. Every combination of turns keeps cyl 3 between 200-350°. Thoughts?? I pulled the spark plugs and they're a little dirty but nothing crazy or fouled.

Second I know this sounds crazy but there is no thread on it anywhere online... I have fuel in my vacuum line. Yes I checked already over and over and it's 100% The vacuum line. I already rebuilt the petcock with new gaskets twice and I cannot figure out how or why a small amount of fuel would be bubbling with the passing air through the vacuum line. I changed the line twice also and I cannot figure it out. Like i said it's not the fuel line so it's not full its just like wet on the inside and I can see it bubbling slightly as it's idling.

The set of carbs I'm using are California that I got off a guy on here and I vacuum capped the 2 ports on the front of the carbs above cylinder 1 and 2. I'm trying to get the original rack back from my mechanic friend to swap all the parts over to those (NY) rather use 48 states carbs than have the California ones with the inlets all capped. Any insight would be great as I couldn't find either of these 2 issues in the archives over the past few weeks.

Happy Riding Fellas

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sleekitwan
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Tue May 30, 2017 1:49 am

Ok, i have done the carbs too, heck almost everyone here might have, and increased the pilot jet and got a 100 dollar dynojet kit, so the needle had a curve. Put the needle one notch lower down than middle and used the moderate main jet that came with dynojet kit.

Ok, my gut says look very closely at the diaphragm/slider of the suspect carb. THE TINIEST PIN HOLE will have massive effects pn the engine. Temporarily, if u find one, put a tiny dash of rubber inner tube cement on it, or just get a replacement.

Use a magnifying glass or some low pressure air method and soapy wAter.

This is also useful as a first job cos it can JUST be extracted this diaphragm, with the carb set in situ? U probably know that.

Set all the floats in the fuel bowl to give the max fuel level - there is bugger all in there!

These CV carbs are also prone to people putting the diaphragm not quite aligned properly. Allows leaks and all sorts.

Come back after the diaphragm check? Be very particular, NO PIN-HOLE OR TEAR NO MATTER HOW SMALL CAN BE TOLERATED!

Best of luck, will help further if this ain't it.
Current bike year 2000 Yamaha XJ600N also called Seca II or Diversion 600. On an older bike air cooling is a blessing, no sludge and complexity of badly-maintained liquid cooling. Other bikes were: BMW K100 roadster; Honda VF750S Sabre with anti-dive.

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sleekitwan
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Tue May 30, 2017 1:54 am

Sorry forgot to say, if just visually inspecting, hold the diaphragm in front of a bright light or sunshine. The pinhole will show well if u gently stretch a small area of rubber at a time?

This is the way I found a pinhole in a CV carb diaphragm/slider unit.
Current bike year 2000 Yamaha XJ600N also called Seca II or Diversion 600. On an older bike air cooling is a blessing, no sludge and complexity of badly-maintained liquid cooling. Other bikes were: BMW K100 roadster; Honda VF750S Sabre with anti-dive.

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radare
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Tue May 30, 2017 8:41 am

Problem is, Sleek, the idle mixture is affected by the pilot screw and jet entirely. The slides don't come into play until 1/4 or so throttle. Don't forget, too, that the US and UK bikes have different carbs. We have the BDS26 while you all got the 28 model. Different internals, jetting, etc.

MVK24: I've experience this myself and found that someone before me had replaced one of the carbs in the bank and it was flowing differently than the others. To remedy that situation, I had to jet that particular carburetor differently. I think it was a #17.5 when the others had a #20. This was in the first months of ownership of my red/black '92 and I didn't know much about the XJ. I replaced the entire bank, eventually.

So, a low temp setting on #3 probably points to a rich condition in that carb. What pilot jets do you have in the others? And are you comfortable reducing the pilot in that particular carb to compensate?

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mvk24
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Tue May 30, 2017 9:00 am

radare wrote:
Tue May 30, 2017 8:41 am
Problem is, Sleek, the idle mixture is affected by the pilot screw and jet entirely. The slides don't come into play until 1/4 or so throttle. Don't forget, too, that the US and UK bikes have different carbs. We have the BDS26 while you all got the 28 model. Different internals, jetting, etc.

MVK24: I've experience this myself and found that someone before me had replaced one of the carbs in the bank and it was flowing differently than the others. To remedy that situation, I had to jet that particular carburetor differently. I think it was a #17.5 when the others had a #20. This was in the first months of ownership of my red/black '92 and I didn't know much about the XJ. I replaced the entire bank, eventually.

So, a low temp setting on #3 probably points to a rich condition in that carb. What pilot jets do you have in the others? And are you comfortable reducing the pilot in that particular carb to compensate?
Hey Thanks Sleek and Radare as always. I went to 20's in all 4 carbs and kept the main jet size but just replaced them with new ones while I was at it. I can throw the 17 back into that one if you think it'll rememedy the situation. If I already have the carbs off I might as well check the diaphrams for safe measure of future problems. I never touched the slides or needle (10 cent rejet) as i didnt totally understand the procedure so i just ordered my jets from Bikebandit.com and did a rejet, new float needles, set float heights. My biggest pet peeve is these are California carbs I got off here (much appreciated) but I really don't like having 2 ports vacuum capped incase they melt or fall off a state away from home lol. I want to swap over the good parts and jets to my original NY rack but my buddy that tried to rebuild them as a project has misplaced the entire rack as of now (very upset about that). Do you think I'll end up with better all around performance if the 17 is bringing that cylinder to the 500° Mark? I never even though to have mismatched pilot jets sizes in the same rack. I have seen 2 or 3 carbs on eBay for like 100$ that look like they need a cleaning idk if it's worth ordering another 48 states set and seeing what happens.

Side note do you have any thoughts on the fuel gurgling in my vac line? I can take a picture of it to show it's seriously not the fuel line mis installed.

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radare
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Tue May 30, 2017 9:19 am

The other thing you might look at is float height. It can cause the same effect as pilot jet sizing. If your #3 float height is out-of-wack, you'll also experience problems. Maybe that's the better way to go first. Set them wet, not dry. It takes patience and isn't fun, BUT, once set, they should be right indefinitely.

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radare
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Tue May 30, 2017 9:21 am

Oh, and for the fuel in the vac line: The rebuild kits for the petcocks don't tend to work too well (from what I've seen). I suspect you are leaking fuel into that vacuum line from the petcock. My advice would be a new vacuum actuated petcock (OE, genuine) but, well, you know.

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mvk24
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Tue May 30, 2017 9:59 am

radare wrote:
Tue May 30, 2017 9:21 am
Oh, and for the fuel in the vac line: The rebuild kits for the petcocks don't tend to work too well (from what I've seen). I suspect you are leaking fuel into that vacuum line from the petcock. My advice would be a new vacuum actuated petcock (OE, genuine) but, well, you know.
I tried that Acerbis a few of the guys were using but it didn't seem to work. Should I try to get a new version of the original or do you have another After market suggestion. There is a Belgium or polish company that was making exact oem of some of our components. I got a brand new fuel pump from them maybe they make the petcocks too

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mvk24
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Tue May 30, 2017 10:01 am

radare wrote:
Tue May 30, 2017 9:19 am
The other thing you might look at is float height. It can cause the same effect as pilot jet sizing. If your #3 float height is out-of-wack, you'll also experience problems. Maybe that's the better way to go first. Set them wet, not dry. It takes patience and isn't fun, BUT, once set, they should be right indefinitely.
What's the method for wet float heights again? I thought it was some sort of meter that I didn't have so that's why I did it on the bench.

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Jimbo
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Tue May 30, 2017 10:49 am

Here is a youtube video link of how to check the float height (wet test method) while the bike is running. Video was made by a XJrider member.

phpBB [video]


All you need is some clear fuel line.

Another tip: I replaced all of my fuel lines with clear fuel line so that I can visually see the fuel flow and fuel quality at a glance.

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