Fuel coming out of exhaust Z1

Hi all, hopefully someone can help me.

I've completely rebuilt my Z1B, taken 6 years, I'm not fast. But this is the first time I've actually posted here, but have used this forum hundreds of times to get answers, thanks to all. Here's my problem;

• I’ve had the engine running, and have actually even ridden the bike. It started really well, bit lumpy, but otherwise pretty good, very happy considering I’ve had every nut and bolt off.
• Then I started getting a problem on carb\cylinder #4. It would start fine, but only fire on 3 cylinders, #4 was cold. Strangely, I could fix it by draining the carb bowl, then starting it again and it would work fine, until the next time I started it. Did all the basic checks but decided the carbs had to come off, not my favourite job.
• Bought new jets etc for all 4 carbs. Set the float height manually to 24mm. Balanced the carbs on the bench. Gave it all a good clean, put the carbs back on the bike...eventually. Why is that so hard?
• Started the bike up, carb #4 worked fine! Now carb #1 is doing the exact same thing as carb #4 used to do, except draining the float bowl doesn’t fix it.
So here are the symptoms:
- Bike starts really easily, even idles on 3 cylinders.
- #1 cylinder is cold, lots of fuel coming out of the drain hole on the exhaust, (this is about half way down the exhaust near the foot rest.)
- Plug has a good spark.
- Have swapped the leads, problem stayed on #1.
- Spark plug is very wet.
- Reset the ignition timing, all looks good.
- Compression isn’t brilliant, all cylinders on about 125, but I might have a cheap gauge? (New valve guides, rings and honed.)
- Leak down test is very good.
- I checked the float level using a clear tube, and it was off, even though I had set it to 24mm manually. So I set the level again, and it looks perfect.
- With the engine off, petcock on, there is no overflow of fuel from any of the carb drain tubes.
• So here’s what I’m thinking:
- I keep thinking it must be the carb, as this cylinder was working fine before I took the carbs off.
- But if I have a spark, and there is fuel getting through, why does it not fire? Could it be that it's just gas, and not a gas\air mix. I’m presuming that because there is so much fuel coming out of the exhaust drain hole.
- The valves must be working correctly to allow fuel in, and out, and the leak down test was perfect.
- I've read on this forum that it is probably the float level. OK I get that. But if the float was sticking then the fuel would come out of the overflow, it wouldn't make it to the cylinder. Unless I have two problems, sticking float and blocked overflow.
- I also understand that gas is probably in my oil now, didn't think of that. But am I OK to continue testing, I don't want to change the oil every time I test the carb!
- I've attached a short video to show just how much fuel is coming out of the exhaust! (And a picture of my bike!)

Appreciate anything you can send my way.

If its not firing on one cylinder, even if the carb is set up perfectly, fuel will eventually make its way into the exhaust. The cylinder will suck in fuel firing or not.
When you swopped the plug leads did you try swopping the plugs also? "iffy" plugs will sometimes spark perfectly against the head when checking for spark but may not when under compression in the head.
New plugs is the first thing I'd try before taking the carbs off again..

no video attached.

Thanks Warren3200gt, good thinking but not the issue. They are all new plugs, but I swapped just in case, but still the same issue.

(I've tried uploading the video again.)

Hmmm, if not that it must be air supply to that cylinder. If you have cleaned the carbs and are 100% sure all the passages are clear I would try turning the airscrew out to lean off that cylinder. If it fires with the airscrew way out you must still have a partial air passage blockage.
I assume you bench synced the carbs before fitting. vacuum sync when running? even if that cylinder is not firing you should still be able to vac sync them.

Warren3200gt wrote: Hmmm, if not that it must be air supply to that cylinder. If you have cleaned the carbs and are 100% sure all the passages are clear I would try turning the airscrew out to lean off that cylinder. If it fires with the airscrew way out you must still have a partial air passage blockage.

I think the same, it's not getting any air. I've tried to lean it all the way out, no difference. I think that either there is some serious blockage in there, or I've done something stupid, wouldn't be the first time. I believe it might be time to take the carbs off, again!

totally random, you are sure you screwed the slide to the lifter on that cylinder? and have bench sync so all slides are lifting equally. Once firing on that cylinder then a vacuum sync to even the vacuum draw.

Yes I did a bench sync on all four slides, 0.7mm. I figured once installed and running, I could then put the gauges on to fine tune, but I guess there's no point doing that until I can get all four cylinders firing.

Check the pin hole on the bottom of the brass choke pick up is clear. Actually if that was the case you'd have no fuel on choke to that cylinder so probably not. so looks like carbs off and sonic clean, airline blow through of all passages is your only option.

Yes I think it's time to take them off again, getting good at this! Really appreciate your time, I'll post more when I figure this out. Thanks.

So you can remove the spark plug and see a spark when running?
Be very careful, if you are getting gas in the exhaust system.
I am not familiar with a Z1 exhaust but on my bike a working cylinder can touch off the raw gas in the pipe and cause a explosion and possibly damage to the system

Assuming stock VM28's here.

If the enrichener (choke) plunger is not seating and sealing when the choke lever is fully down, an extremely rich mixture will be introduced into that cylinder. Check that the plunger on the problem cylinder is seating completely when the choke lever is down.

Good Ridin'
slmjim & Z1BEBE

I was wondering about the choke too