Yamaha Zeal nightmare!!!!!

[RonR]

Hey all,
been a while.

The bike has had this problem since i got it 6 months ago. If you are gentle with the throttle the bike will go fine all day. If you hammer it for even a second it goes great until it comes back to idle at which point any bit of throttle makes the bike go chuggalugg. It's like there is a huge flat spot from idle to about 5000rpm. Anything above 5000rpm is usually ok. This even happens at standstill. I was told by a dealer that the pilot jet may be blocked. So today i pulled apart the carbs and pulled out the jets and cleaned them out with CRC carb cleaner and compressed air. They looked beautiful! Put it all back in, started it up, it ran well. Took it around the block and gave it some, but the problem still remains. Humongous flat spot at anything below 5000rpm. It might take about 6-7 seconds for the bike to clear that flat spot zone at 5000rpm. But tomorrow, I can bet that the bike will run nicely until it is hammered again. The problem usually clears up after sitting for a few hours, then returns when the throttle is used enthusiastically. (10,000-12,000rpm)

Can anyone please tell me what else could be the problem. Please don't tell me it's the carbs again (my hands are freaking killing me ).
Could it be the fuel filter or fuel pump?? Anything that is an easy fix? The carbs must be ok now (all clean, and pilot screws all 3 turns out). --[the pilot screws were all different turns. one was 2 turns, one was 3.5...]

Super desperate!
Cheerio

Johnny

[breakaway]

Have you balanced the carbs?

[RonR]

i'm not especially carburettor minded, so I don't believe i know how to balance the carbs. Is that just making sure all four butterflies are open the same amount? Cos they looked like it. And besides i didn't touch the butterflies. I just opened the caps on either side of the carbs and cleaned out the muck inside and the jets.

How do you balance the carbs? Do i need any special equipment? expensive?

j

[Grub]

You need some kind of vacuum indicator to balance carbs.

You can make up your own gauge with a bit of tubing, some wood and a bit of brake or AT fluid.

[Hitcher]

Zeals, like most inline-four 250s, have a flat-spot in their power band. My Zeal's flat-spot was at almost exactly 6,000rpm. While irritating (appearing as it did at about 100kmh in top gear), Zeals do not mind getting their necks wrung, and a bit of anticipation about where and when power may be needed was generally all that was required.

[breakaway]

You can make up your own gauge with a bit of tubing, some wood and a bit of brake or AT fluid.

My mate has one of those, built it himself with aquarium tubing (I think) and used water with red food coloring instead of brake fluid. Works real well. He says "Total Cost? About $30"

[The Pastor]

how clean is the air filter?

[jonbuoy]

Don't think it will be just balancing, out of balance would make a rough running/idle. Unless they are massively out of balance which they won't be unless you've stripped them off the bike and had all the linkages apart. More likely a fuel blockage somewhere.

[RonR]

The bike doesn't have the flat spot when it hasn't been ridden for a few hours (or say overnight). It won't have the flat spot if i don't rev it hard, or above about 9,000rpm. If i do rev it hard/quickly to anything above about 10,000-12,000rpm, the bike will have a flat spot from idle to about 5000rpm. It has a burbling sound and no matter how much i twist the throttle, it will take ages for it to clear that burbling stage and rev to 5000rpm where it finally runs ok again. A few hours later it is usually ok again. This leads me to believe it is a fuel/carby problem as it seems that something is settling (fuel??) or the carbs are flooding or something.

I haven't synch the carbs cos i don't know how (yet), but all 4 butterflies looked very even. One thing i didn't do is spray carb cleaner with the butterflies open. Don't know why... silly me. Other than that the jets are clean, pilot screw is set 3 turns out......

And thanks erik, that post was really good. I might have to check out the idle mixture screw and leads too.

[Coldrider]

Have you cleaned the fuel tank filter, sounds like petrol starvation.

[Paul in NZ]

Well you have made a start.

Firstly - I'm guess in uses a CV carb? Hence when you turn the throttle, the butterflies open BUT the slides wont lift? That means if (say) its flooded to buggery and the plugs are wet it won't rev hard enough to lift the slides to clear it's self (for example)

250/4s are very prone to loosing performance if the valves and rings are not sealing well - before you co any further I'd suggest a leakdown test at a bike shop. Failing that a compression test would be better than nothing.

Assuming thats OK the next thing is to check all the electrics out. Is the battery good? Are the coils OK, are the HT leads OK, no broken earth wires, dirty connections etc. Its a good idea to keep everything clean in the electrical dept and an extra earth strap or two never hurt.

If thats OK - what are the sparkplugs like?? Good condition?

When was the last time it had it's valve clearances checked? Those Yamaha engines must have proper valve clearances to have any chance.

Now - Lets look at the fuel system.

When you had the carbs off - did you check the float chambers for dirt? Look at the float needles, float levels and main jets etc. While you are in there look at the needles and needle jets - check for wear and also check the carb diaphragm and that all the vent holes to the top chamber of the carb are clear and (if fitted) have the proper O rings.

Check the fuel flow from the tank - often the fuel tanks get full of crap and condersation. Hold the tank over a container and check the fuel runs clear from the tap. Check the fuel filter and the pump (if fitted) and that the pump works properly and that it fills the float chambers and then stops.

Check the tank is venting - ie air can get in to replace the fuel going out.

Phew - that should do it for now....

[FROSTY:Me]

Wot he said BUT
My gut feeling is you have a torn cv diaphram or two.
Bad news-expensive to replace Good news 1) you dont have to remove the carbs and 2) you may be able to repair em.
Haul the lids of the carbs and have a looksee at the rubber diaphrams--good chance theres pinholes and splits in the rubber close to the edge.
I've had success using bicycle tyre glue to seal up the splits

[RonR]

Wow. Thanks for the lengthy replies guys. As for the diaphragms, they are ok. No holes, splits, or tears. I wish it was just that simple.

Can valve clearance checks and adjustments be done simply or is it a major deal? I really don't fancy pulling apart the whole engine. And this "leakdown test" and compression test... expensive?

I am thinking maybe i should just take it to a bike shop and let them sort it out. A couple hundred i can live with. Over $400 or $500, you must be kidding.

[RonR]

Problem solved.

As i removed the airbox from the bike, i noticed that 3 of the plastic carb slides were closed while 1 was open. After removing the carbs i examined the diaphragms and the slides they are attached to. The diaphragms were fine. No cracks, splits, tears. However 2 of them weren't sliding into the carb easily at all. In fact they needed some force to slide nicely. I ended up giving them a light sand with some 1000grit wet/dry paper until they went in smoothly. Now they spring back nicely

Took it around the block for a fang, and it was GREAT! No more flat spot, no more lagging.

So thanks to all for the input. I can almost call myself a carb expert (in my mind at least)

J

[jonbuoy]

Good for you mate, its a nice feeling when you fix something yourself.