High RPM's. Something hanging?????

[Got3now]

After a year long restoration of my 79Z I fired up the bike this morning. What a beauty! It raced up to 4000 RPM's as I quickly shut it down. I checked the idle adjustment screw and it is all the way backed off. I can only assume the slides are hanging up???? Any thoughts. The Tee's between 3-4 and 4-5 were long gone. I didn't put anything there as seen in the attachment. I trust that is not a vacuum source.

http://i186.photobucket.com/albums/x43/ ... C02268.jpg

[Got3now]

I pulled the tank, checked to ensure the choke was not hanging up causing the butterflies to stay open. Visually backed off the idle screw off the plate. Pushed the throttle plate to ensure it was closed. Your thoughts??

[Got3now]

Pulled the slide covers off. All smooth. Now I need help!

[Got3now]

I did a complete rebuild of the carbs following Mike Nixon's book. I did not sync the carbs as they appeared untouched from the factory with yellow paint.

[steve murdoch icoa #5322]

The missing tees will not be a problem. If the choke was hanging up i don't think it would rev that high.
I would guess that it is something with the throttle cables and/or controls causing the revs to race. They can be cranky with improper routing, sticky throttle sleeve. I always look for the simple fixes first.

[daves79x]

Your carbs are likely way out of sync. Yellow paint means nothing. If you separated the carbs, you will have disturbed any correct positioning of the throttle plates. You probably need to pull the carbs again and carefully bench sync them. Then they'll be close enough for the bike to run and idle. Could be some other things, but that's the most likely. Correct position of the throttle plates is the front bleed hole just BARELY starting to be exposed. If you find some further than that - that's the problem. It only takes one or two.

Dave

[bikeymikey748]

What they said and also ( don't ask how I know ), if you have completely disassembled the carbs make certain the throttle plates are PERFECTLY centred in their bores.

[Jeff Bennetts]

A couple good suggestions above, just a FYI, you have to also check the carb slides after you torque down the carb tops.

You can get the slides in a bind if you don't index/center the carb tops as you tighten them down, you'll notice the carb top screw holes are oblong to allow a couple mm's of adjustment.

[Got3now]

Thank you for the posts, still running at high rpm's.

I removed the carbs and checked the slides. They were smooth as I was able to push them each up with my finger and they returned nicely. Also while on the bench, I checked the throttle plate where the cable attach. They had quite a bit of spring snap back and all plates returned closed, again nicely. I didn't close the position of the throttle plates any further as they were closed down nearly completely, but not just showing one hole. Perhaps a bit more here and there. I really couldn't see anything wrong. SO, I put them back on and same problem. I bought six vacuum type gauges to sync the carbs. I had mercury type but chose to upgrade. I broke the sync nuts loose and backed out the screws about a 1/4 turn, started the bike and same thing. Hung at 4,000. So I kept backing them out without any change..

I am at a loss. The bike starts nice, only has 5300 kilometers on it.. So I am thinking it is not an advance issue??

I will crack the slide cans loose as an effort to fix, but don't think that will help as the slides moved freely when on the bench. The cables are new and work well. I think it could be a little better but am confident they allow the plates to return to the closed position.

Absent any other suggestions I will take the carbs off again, bench sync them, and seek to ensure the plates are centered and returning completely. ( I am confident all is well here but I am running out of ideas).

The bike has new intake boots. Pilot jets set at 1 1/2 for now..

http://i186.photobucket.com/albums/x43/ ... C02294.jpg

[daves79x]

I think you are vastly underestimating the importance of EXACT positioning of the throttle plates. "A bit more here and there" won't cut it. And your method of backing the sync screws off "about 1/4 turn" is the wrong approach. The sync screws move the throttle plates directly and each bank is connected such that each one effects the others. I'm thinking you made matters worse. Please do remove them again and bench sync them, but you need to be absolutely sure about how to do that. From the look of the gauges, #6 is hanging 4 & 5 open also.

Dave

[Got3now]

I will take them off again this evening when I get home.. The engine was off when I took the photo so the gauges are not reflective of anything. When checking the plates, to ensure they are perfectly centered, is there any perferred method? I can't imagine they are hanging up but have to look at everything once again while I have them off.

[Got3now]

Well I bench snyc'ed the carbs tonight. I thought I was going to be smiling by the end of the night but same problem. Yes, adjusting them on the bike was doing it blind, and they were well off when I put them on the bench. This lead me to think my problem was solved. Unfortunately, it was not. Photos show before. #4 was open quite a bit more than the others. This was a result of trying to adjust them on the bike while running.. One thing for sure, they are dialed in right now.. Throttle plates perfectly aligned, all plates just barely showing the first hole. Engine still racing. Throttle cables move freely, and snap back/return to closed position. Slides are returning to the bottom. Cans are not hanging up the slides.

[tevan]

Did you check the piston vacuum line from the top of carb and goes to the carb throat? It is the hole that you see when you pull the top off and it is under the black cap with a screw. The hole looks big but it is a size of a wire brush brissle at the very top. I overlooked this once and that was my problem. The slides moved freely with my fingers but when I installed carbs it hung like you are saying on 2 carbs. I had high revs also. I cleaned that line and presto it was fixed.

[Got3now]

Well it has been some time since I went through the carbs but I did remove the black caps and completely stripped the carbs, soaked them, rinsed in soap and water, blew out with cleaner, and air. Put small cleaning wire through the passages. I trust that I cleaned all passages and they were clear. I followed Mike Nixon's book. I don't recall if he mentioned that passage in his book and it is out in the shop. Sounds like it could be worth a try. Is there a way to figure out which one may be the problem?

[Got3now]

Is this the passage you are referring to? Of course I am referring to the passage from the bottom up. Disregard the writing in the photo.