backfiring thru Carbs

Okay, I'm not sure if this should be in this forum or the Carb forum, but here it goes:

On my 1980 KZ550c, I have gotten to the part of the resurection on this bike that I am trying to get it started. Now, I know that I have a few things going against me as I go into this (carbs still over flowing while petcock on prime, vacum line not hooked up yet, bike hasn't run in 3 years... yada, yada, yada...), but it the attempt to start the bike, it has back fired through the carbs a couple of times. My first thought is that this is a timing issue. Would that be correct?

The bike hasn't started up and run yet. I did manage to get it to run on a couple of cylinders for a couple of minutes a few times and, I think, on all four once, but it just wouldn't keep going. There's still allot of investigating to do, but I was wondering if I need to put the timing on the top of the list.

Well KB02, If your bike has been sitting for a couple or years you might want to go throught the carbs and make sure gas is getting to the chambers. By your description of "backfiring thru carbs" i might suspect leak in your intake valve. If you dont already own a compression tester you might want to purchase one and get a compression test of all cylinders. They should all be right around the same general value for your specific bike.As for your bowls over flowing, this sounds like your float needles are not working properly. This could be because they are either not making a good seal with the float needle seat(caused by deposits inhibitting proper seal)or your float assembly is not pressing your neddle up into the seat.

You can start down many rabbit trails with a bike in this condition. I wouldn't worry about backfiring through the carbs till the bike was actually running... If this thing were mine here is what I would do:

1. check compression - check all four cylinders with plugs out holding throttle open. Lack of compression will make all the other exercises just that... exercises. If you need to rebuild the top end, it is hardly worth giving advice regarding backfiring

2. If the compression checks out, FIRST make sure the cam timing is spot on... DO NOT TRUST that it is correct. Once you are in there, you can adjust the valve clearance. DO NOT attempt to start the bike until the valve clearances are correct AND the cam timing is correct.

3. Adjust cam chain if it has a manual adjuster... no sense the cam chain popping off the sprocket if you get it running

4. IGNITION TIMING... it can be checked statically with the bike not running.

5. VOLTAGE TO COILS - Even if everything else is peachy, if you have low voltage to the coils, the bike won't tune easily, will foul plugs and not run well... it WILL BACKFIRE THROUGH THE CARBS. Check the article on coil powering in the FILEBASE section

6. Don't bother try and run the bike without disassembling, cleaning and rebuilding the carbs. If they are done right, you will have far less trouble tuning the bike to run right.... carbs are the last step as you probably noted. Part of the "carb job" is cleaning the inside of the tank. Phosphoric acid wash is best (be careful of paint) as it kills and washes away the rust. You might consider a new aftermarket petcock and use an inline fuel filter as a bike that has sat WILL have fuel delivery problems otherwise.