hey there, I'm hoping someone can help me out a bit here.
I have a 74 Z1 900 that's been redone from top to bottom. the only thing that hasn't been touched (that much) is the carbs.
the bike starts just fine but until the cylinder head temp reaches about 310 degrees (which is nearly imposisble on cooler days) the bike will sputter, backfire out the carbs and exhaust. I have to leave the choke on until it reaches that temperature or the bike will be un drivable and backfire a lot, with the choke on at least it can accelerate and does not backfire that much. When it warms up after about 30 minutes of riding and keeping it at slightly higher RPM's it seems to run fine and idle with the choke off, I can let it sit for a while and let the temps drop to about 120 degrees or so and fire it back up and it will run just fine. but it's very annoying having to take it out for a 30min spuddering and backfiring nightmare pre-ride before I can actually ride it.

also, I don't know if this is a carb problem, but if I use more than 1/3rd of my tank I have to fill it up again or it will act like it's running out of gas

 

How do the plugs look? If they are fine, check your vacuum lines and if all else fails clean the carbs. Good luck, and welcome to KF!

oh yeah, and PICS!!!!

 

I had some time today so I pulled the plugs and cleaned them, I found that cylinder #1 was not firing which would explain why it was running so rough the last time I had it out.. So anyways I cleaned it and it seems to run better, the same as before though, still takes some time before it will idle correctly. I think when the season is over I will send it over to a guy I know who has a motorcycle shop and helped me out big with my GSXR carbs when I had it. They probably are past due for a rebuild.


anyways since you asked I'll post a pic.. you probably won't like what's done to it though.. lol (don't shoot me)
Still needs some cosmetic work but I purchased the bike pretty much like this.














GSXR 750 Front forks, wheels, bandit rear suspension, gsxr tail light, ect.

 

Not my style but looks nice, someone obviously took the time on it. You say you bought it in that condition, did it also have the sputtering problem when you bought it? Carbs are very VERY finnicky when it comes to those air cleaner pods, its very hard to get them to work correctly. If you have the stock airbox I'd try to go back and see if it helps.

Also does the 1/3 tank issue go away if you take the fuel cap off? could be a clogged vent.

 

when it was stock the last owner said it did have backfiring issues, I think he said it was pretty much the same issues from when it was stock with the stock air box to now with the cone filters.

The fuel cap actually leaks bad when I fill it up to the top full, if I get on it in 1'st gear and gas will pour out of the cap like it's not even there, I don't think it was doing this the first few times I put fuel in it, just recently over the last week I have noticed it, but I only had time to ride it a few times at night before so it could have been happening.. The seal is brand new, The spring is doing it's job providing even pressure on the seal. I will look into it further tomorrow and try to ride it with the cap popped to see if that makes a difference. I think some of these problems may be related to the cap, which is why I mentioned it.

 

Nice, some more attention to detail and this will be a Rocker! Did I say that I think it is a good looking ride?

What is wrong with this statement?

 

probably a lot.. lol
I'm talking hot day, in traffic, and I have the trail tech gauge with the temp sensor that sandwiches in between the head and stark plug. like i said on cooler days riding around it's nearly impossibly to get it above 260, and on those days the bike just won't work correctly.

also, cyl #1 is fouling instantly now.. and poping the gas cap doesn't work. I'm not going to worry about it anymore, once my rebuild kits come in I will have it done.

 

hahaha, that just seems really hot! I am not familiar with your temp setup but that just seems too hot. I would prolly toss a compression gauge on each cylinder and record the numbers for good measure. Record the fouled plug look as well along with the plug specs. Oil fouled? Gas fouled? Burned off? lol that kind of thing. Good luck on the progress.

 

haha I guess I didn't specify units.. 300F is 148C if that makes it seem better.

anyways the plugs are dry, and have a thick layer of Black carbon covering everything. they turn like this within 10-20 min of riding.

 

stay with F degrees. lol

Replace the tank cap gaskets and that will of course stop the leak and most likely the 1/3 tank full of fuel issue. Not sure if a replacement cap is needed, but a check in your fiche should be of usefull information.

Have you pulled the rack back off and verified cleanliness and adjustments yet since your first post?