Zeal misfiring @7k - what next?

Hi everyone,

So I bought a zeal around 12-18 months ago from eBay. It was in rubbish condition, but I was only looking for something to get me through my L's before moving on to something more appropriate. To date I've put <50km on it.

Aside from the engine issues I'll address in a minute, I've put new tyres, resprayed it, re-upholstered the seat, fitted new bars/grips, replaced bushes everywhere, digitized the dash and generally put a lot of hours into it getting it to a rideable condition. It starts straight away, idles and runs while parked just fine.

Buuuuut.... the damned thing has a horrible misfire at 7rpm under load. It revs fine to 12krpm+ when stationary, but only maybe 3-4 times it has pulled through to more than 9krpm while riding. It still has an FZR250 exhaust with the EXUP removed, but the problem is worse than the flat spot that particular exhaust would create - it completely hits a wall.

It feels like a fueling issue, like the float height is too low because it gets worse the longer I ride, so I checked that and it was fine. Maybe it's heat related?

Did a plug chop, and found it was a little lean on 3 & 4.

Checked the fuel pump - fine. Then I cleaned and rebuilt the carbs with a LiteTek kit just to be sure, a few dirty jets but nothing too bad. While I was in there though I found someone had cracked off a jet housing nut and I replaced it - I thought this might be the issue, but no.

Then I moved on to compression, which was very low @ <110psi (and extremely low on 3) but unlikely to cause the issue I thought. Regardless, I rebuilt the top end with new pistons & rings and now have great comp. While I was there obviously I did valve clearances and shimmed a tight-ish valve that was borderline spec - just in case.

As far as airflow is concerned, I've run the bike with & without the airbox, and other than obvious fueling differences, the issue is still present either way. Also choke on or off, the issue is still present at the same spot. I've also inspected the boots from the head to the carbs, they still appear to be reasonably flexible for their age, and no cracks that I can discern. The vacuum balance line between 3 & 4 seems to by 2x -3x as long as the the one for 1 & 2, is this normal?

How often do the coils go in these bikes? Everyone always says "get in those carbs" but I'm wondering if it's a coil or CDI unit issue? Are there some solid coil test specs out there for these bikes? Can I test the CDI unit?

The other thing is could it be worn needles? Spending another $200 is not really something I'm keen on... and it feels like they're not too bad, under 7k the bike is very responsive to all throttle positions/transitions.

I'm about ready to throw the whole thing on eBay as a parts bike, I've spent far too much time pulling it apart and putting it back together, I'd actually rather be riding it by now.

Thanks in advance for any input you guys may have.

Regards,
Jared.

 

Thanks for the welcome! Hopefully I will be able to add something to these forums over time!

I guess flat spot isn't the right word, it simply won't pull past that point at all. I would fit a standard exhaust, but I don't have access to one easily/cheaply. I would have thought being 4-1 rather than 2-2 that I would lose mostly bottom end, but it is very responsive down low and even more so with the new piston/rings. The zeal does not have a servo for exup, although from what I've read it isn't all that hard to retrofit - but ideally I'd do that/CDI & cams from an FZR all at the same time if I was really going down that path. I have thoroughly inspected the carby boots and was surprised that they seem to be fine. I know the cracks can be hard to see since I had seen some posts somewhere on it so I checked thoroughly.

1) Plugs gapped to spec - but have replaced twice so will check - thanks
2) Hard to know. The lack of effect (on the dead spot itself) of choke and or/air filter makes me suspect that it is not fueling. Obviously it's doughy with the choke on and lean without the filter, but the problem itself is unaffected.
3) Where can I possibly be getting vacuum leaks? The head-carb boots are fine, and the two balance lines appear fine as well. I've greased each point and everything pretty tight. Is there a line I'm missing though? Gosh I hope so!
4) Yes have checked stator + rec/reg and they're fine.

Plugs are tight, I only just installed them (again) after rebuild.
Good point about the header, I'll see if it's all true bolted up true. I've had similar issues on my other bikes with pinhole leaks and the like, but it usually presents itself as a 'popping' on deceleration.

Fuel pump appears to be the original (or at least has quite a few years on it). It pumps/primes up if I've drained the carb bowls, clickety click click.. click.......click..........click. It seems as though it gets up to pressure pretty quick, but obviously it's inaudible with the motor running. After a plug chop there was plenty of fuel in the bowls though.

Air filter is old, and was reasonably dirty but has been cleaned (dry non-oiled paper filter). I've run it without the filter to be sure it wasn't too restrictive with no change. I've even run it without the entire air-box with no change to deadspot.

Sincerely, thank you very much for the help guys, I'll check a couple of things and report back!

 

Mixture screws are currently at 2.5 turns out. I've tried one turn either way, but it seems to run best/cleanest at 2.5 turns.

As above. I've just pulled it down again to test coils (as in tank/airbox off), and will try leaner/richer again since it's pretty easy to do. I think I need a dummy fuel tank so I can test ride without going through so much hassle haha.

I had thought this may be the problem originally, and especially because I have replaced it with an alternative tap (non OEM - the original design with plastic knob is horrible AND expensive). But in all my adventures I had completely forgotten about this, maybe it warrants further investigation. Unfortunately I can't find the original broken tap to try at the moment, I may have inadvertently thrown it out.

Also I just tested the coils.
2-3:
Primary 4.4ohm
Secondary (leads only, no caps) 15kohm
1-4:
Primary: 4.1ohm
Secondary: 15kohm.

I just read a thread below mine that says 2.2-3.2ohm on the primary. Am I a fair way off with my primary resistance or is it unlikely to cause issues?

Thanks again guys, it's nice to see such an active forum.

 

Thanks Damus.

I just checked 1,2,3 again. No leaks at all that I can find. Visually inspected the carb boots again, and I tried spraying WD40 around the carb boots while running to listen for any changes - with no change. Don't get me wrong, I hear what you're saying and I appreciate your input. I'll check and check and check again though to be sure!

I took it for a quick spin before putting the airbox back on, to see if it changed anything. It had a little throttle hang without the airbox (slightly lean) so I added 1/2 a turn of fuel to it. It rode a little worse (to be expected), but definitely still hit a ceiling at 6-7krpm. If I can properly describe it, it's like hitting a rev limiter, and hard. I'll try and find my gopro and get some footage this week.

The other thing is, without the airbox on you can hear what sounds like a flutter, like the throttle slides are fluttering as it misfires. I've also noticed that despite the rebuild/teardown/seals/clean, those slides seem to be a little sticky and sometimes unresponsive? This is what made me chase vacuum in the first place. I inspected the diaphragms and they're all in decent nick and will hold pressure if pressurised.

I'll try the needle position, I had tried it one clip either side earlier on before the rebuild with little to no positive effect, but I might go to the extreme and see how it rides. It kind of feels like it wont get onto the main jet, more so than a needle problem but it might show me which direction I need to go. I'm worried about doing a plug chop because I'd rather not load the pistons up just yet, I've heat cycled them a couple of times but I'd rather not stress them more than i have to just yet.

 

One other thing... It's currently got a tank of 98 in it because it's what I had lying around for other bikes. I've read here somewhere that these bikes don't like anything other than 91? Now I've personally not heard of a bike/engine that runs worse on 98 than 91, and I'd pretty much just written that off as nonsense but if there's a chance I'm willing to give it a shot. Anyone?

 

Thanks Linkin. I believe he's referring to the pickup/alternator/stator coils, not the ignition coils though. The two stage stator idea extends beyond my knowledge though, and google was of no help on that one.