Any and all carb experts

anyone that has seen my posts of late know I'm having issues with the xj700 airhead I got a little bit ago.

The carbs are set up correctly, sync'd etc, etc. I've been in contact with another forum member on this quite a bit. The bike will start hard, and there is no power from idle to 4k, then it takes off. Both of us are thinking vacuum leak somewhere. The diaphragms are good, no apparent holes, cuts or shrinkage. The vacuum line for the petcock (off no. 2) is new. I pulled the intake manifolds and gaskets and rtv'd them all together and then rtv'd them to the head, and tightened. I also rtv'd the base of the vacuum ports on the manifolds, checked the rubber vacuum caps and insured the intake boots were plyable and hole/crack free. The throttle shaft seals (the two I could get to without breaking the rack) appeared good. Soft, and in good condition. No apparent tears, holes etc.

So, the q is-where else could I have a leak from? I haven't remounted the carbs because it has been a nightmare. I figured I'd get everyones input first. Thanks!

 

Does the bike idle properly?

Easy-test:
Try spraying some starter fluid (or some other flammable substance) onto the other v-seals, and even though you RTV'ed them, onto the manifolds while you're idling.

If it revs, you've got a leak there.

 

The bike will idle no problem after you get it going.

When the throttle is twisted hard (like you normally would) it'll go, putt, putt, putt, putt, (until 4k) then VROOOOM! I tried the spray over the boots trick to no avail.

 

i remember your posts i think, you took a pic of the outer shaft seal? If this is same member or not we recommended you spary different things around the carbs, unlit propane torch will raise the idel if there's a leak, WD40 will make the cylinder smoke out the exhaust if there's a leak. No one will say for sure till you break the rack and change the throttle shaft seals, fuel rail o-rings, and mixture screw oring (at the bottom of the mixture screw). Let us know about the spraying stuff results.

to be honest, I had that problem forEVER. It ended up being (I think cause it still not done) a crack i couldn't see unless I bent the intake boot apart. AFter I replaced it I had high expectations. Last thing for me was to look at the valve gaps and see if it needed shimming. They were all tight and i'm finishing that job today. If all 4 holes don't fire on startup i'll be looking at the TCI.

When you start the bike cold put two hands all two header pipes and feel if they're getting hot equaly. let us know! if you ever checked for spark and didn't follow the correct procedure (which I didn't know about or ever heard of cause I'm not a mechanice w/ former training) you could have burnt something in the TCI. Here's the TCI link I plan to follow if they're still not all firing/getting hot equally:
http://xjbikes.com/Forums/viewtopic/t=1 ... t+tci.html

 

What kind of intake are you running, stock airbox or something else? Do you know what size main jets are installed? I'm thinking you may have a mixture problem.

 

You say your carbs are all set up properly??? What do the bottom 3rd of your spark plugs look like. I'll bet they are a way different shade than the top 2/3rds of the porcelin. I may be thinking way off here so I'll try to find that other thred and see what you have done so far.

 

ok read your other thred..
-who synced your carbs and how?

 

All four pipes get H O T.
Spark on all four. I've tried two other known good tci's.
Main jet is a 307, pilot (the bottom pilot) is a 368.
Plugs after the only run (35miles) were tan, nice and tan.
The bike is bone stock, stock airbox, intake boots, airbox boots.
Carbs were sync'd by me with a motion pro sync guage.

 

i am no expert, but maybe this chart will help. not sure if your 700 is very different from my 650, but should your pilot jet be bigger than your main jet? my main is 110 and my pilot is 40. it would make sense if either your enrichment circuit was clogged or dirty, or pilot jet size were off and causing your problems because they run the show at start up and low rpms.

***per ricks carb cleaning instructions in the float bowl--Near the frame rail -- you'll see a very small diameter brass tube sticking-up from the Carb Body.

That's the Siphon Tube. This tube supplies fuel up to the Cold Start Enrichment Circuit. The tube has a very small fuel metering port at it’s open, bottom end. That tube extends into the special well designed for it in the wall of the Float Bowl.

The Siphon Tube, having such a small metering port, and extended into the Float Bowl well -- supplies fuel to the top end. It's size and the relatively small volume of fuel within its supply well allows fuel to be drawn-up the Siphon Tube with the relatively low vacuum drawn on it when starting-up the engine.

Probe the opening on the tube and insure that the metering ports supplying fuel to the special well the tube extends into, on the Float Bowl, are clean and allow fuel to fill the Fuel Bowl’s well. The fuel drawn-up through this narrow tube from the small well is the needed supply for cold starting. This is the Cold Start Enrichment Circuit’s vital fuel supply.***


also, i just completely tore down my carbs and rebuilt them. time consuming, but manageable and not that expensive. and this was my first set of carbs. i would, without hesitation, recommend this. instead of wasting all of this time and energy guessing, do things right from the start. once the carbs are good then move on. in the long run, you will probably spend less time, money, and most definitely have less frustration. plus, i think that having that kind of detailed knowledge about your bike is irreplaceable.

 

Hey midnight, that is a great chart. It looks pretty accurate and summarizes pages of literature! Very curious where you found it. Thanks!

 

i agree, it is a great visual. sorry, i looked for the website, but couldn't find it. i saved this chart while doing some research before tearing my carbs apart and thought it might help me tune if i go with a different filter setup. i take it's accuracy with a grain of salt, but it looked close enough for me to believe.

oh, and i am not 100% sure the article i found was necessarily talking about hitachi carbs either. i see that needle clip position is on the chart and i don't believe most of our carbs have a needle clip or adjustable needle. but it is still nice to see how those things affect the throttle range. so take that for what it's worth.

 

great chart.

I believe I found the problem. I'm slilghtly embarassed by what I think it is, but we all make those 'what was I thinking' type errors sometimes. I'll let you know how it all works out today after I finish...I went in the right direction yesterday and got close...just not quite close enough.

 

Nothing is working here.
new plugs, again, idle mixture is at 2.5, floats are at 12mm dry, and wet test is still low. If I go any more, it overflows. One cylinder fires, no 4. Spark on all 4. I did put rebuild kits that included new seats and needles in it...The only time I had it running was with stock needles and seats with the float levels at 15mm dry. I'm going to swap out the rebuild kits for the oem parts and if that doesn't work, I'm pushing it into a corner until I get the urge to look at it again....

 

You didnt mistakenly put the floats in upside down did you?I clean my carbs every year and last time I was distracted and accidently put mine in upside down I knew right away what I did when it didnt start right up.But we live and learn lol.

 

well i hope for good results in the AM. My problem is hopefully the two broken wires I found under the boots at the coil end of the plug wires. maybe you should check your resistance there. I haven't since I installed them a few months ago Brand New but somehow they broke!!! it was only enough spark to idle and sometimes rev up slooooowly- I'll post results by lunch tmrw

 

nope, with the two spark wires re-crimped starts a theh slightest touch of the button, but still won't rev, just puts. DAAAAAAAAAAAAAAAAAAAAAAAAMN its TCI time...