Ace hesitation

Hi guys, new to the forum. Was directed here by a fellow ace owner I met at Chiswick Honda who said you guys knew your stuff when it comes to our beloved aces and cats.

I've had this problem for a while now and I can't get my head round it... my mechanical knowledge extends to the Haynes manual.... So either I've missed something or it could be something else.

What I've done to try and diagnose it -

Run through seafoam to try and get rid of any blockages (which I doubt as I also opened up the carbs to give them a quick once over and all looks clean and tidy)

Checked between the carbs and engine for any leaks.

Pulled all the coils and leads and checked their resistances (the only thing odd was the pickup coil which measured 105 ohms, but a quick call to yamaha said this shouldn't be a concern, they're only replaced if completely screwed)

I'm now at a loss, apart from taking it all apart and doing everything again but I'm not really sure.  Anyone have any ideas?

Thanks!

Out of curiosity, does it ever manage to rev higher than 4000rpm?

Doesn't the Ace have an Exup valve? Have you checked if that's working as it should?

Top drawer suggestion by BlueZed..

-edit- Here's a video to compare yours with:

Hi and welcome.

At around 4k the carbs move from the idle (jet) phase to main. I think you have one of two issues, the TPS isn't calibrated properly or there's a carb or two which isn't / aren't playing properly when moving over. As has been asked before, does this continue beyond 4k or does it clear off?
I got rid of my 'Cat because I could never resolve an idle issue - the opposite of your problem. In my case it turned out someone before me had a go at fiddling with the mixture screws and apparently some dirt where you can't see it.
I should add if the Haynes Ace manual is anything like the 'Cat version the TPS troubleshooting guide is somewhat misleading, mind you they at least did a slightly better job than Yamaha did in their factory manual!

Thanks guys,

you know I never thought to check the exup valve - it does rattle but I was always told "that's what it does" so I'll take a look at that first tomorrow morning as it should be nice and easy to rule out.

As for passing 4k - it does occasionally, I'll have a moment when it's running okay up to about 7-8k then hesitates and backfires and others when it just wont go past 4k and backfires and splutters. It won't redline at all.

Not sure what to do if it's the carbs, aside from cleaning them out I'm not very confident in working with them - and my 3 local motorcycle garages won't touch the bike because it's "too old"

Where abouts in London are you?, if you can get it to me I can have a look at it with you. I'm in SL2. I'm off Thursday and Friday this week if you can?

Well I tried getting the exup pulley cover off but the bolts have rusted to hell and pretty smooth - so not sure where to go here.

Haven't had a chance to look at the TPS - kicking myself really as if I had just turned the page in the Haynes manual I would have done it when I did the coils.

The White One wrote:Where abouts in London are you?, if you can get it to me I can have a look at it with you. I'm in SL2. I'm off Thursday and Friday this week if you can?

Thanks, I really appreciate the offer. Unfortunately I'm the other side, close to Essex in IG8 so a bit of a hog to get it anywhere!

If you rev the bike whilst looking at the Exup valve you should see it opening & closing with the throttle, it definitely shouldn't rattle at all & requires regular maintenance at least once a year.

robertcains wrote:If you rev the bike whilst looking at the Exup valve you should see it opening & closing with the throttle, it definitely shouldn't rattle at all & requires regular maintenance at least once a year.

Thanks, definitely top of my list of things to check. Contrary to what I thought, I always understood that it didn't need to be serviced and only checked if the error code shows up. Good to know though, if I ever get the cover off I'll make sure to add it to my yearly checks.

Hi & welcome to the site, hope you can get the ace sorted out quickly. It looks very tidy from what I can see on the video.

Paul

Right, exup cables are good so no problem there. Put the tps in adjustment mode and the reading was already at 5k. - is this what you were saying about misleading?

So not sure what else!

In fact, I just checked the fuel pump. Ohms are 2.4. Not the 4-30 specified. I also ran the bike a little bit without the pump and it's operating similarly. It doesn't seem to be doing much when I turn it over either. Could this be it?! Could a dodgy fuel pump be the bane of all my problems?!

Is it carbed or fuel injected?

The White One wrote:Is it carbed or fuel injected?

It's carbed

Just checked its carbed. Carbed bikes will run fine without a fuel pump although they get a little grumpy when running low on fuel as they are gravity fed. Have you checked fuel hoses for cracks/leaks and also have you drained your float bowls and refilled them when you turn the key on. You can run the bike and put your hand on the pump and it should vibrate about every 3 seconds. If not then its probably faulty.

If you have let it run low it may well have got something past the filters and into the carbs.

The White One wrote:Just checked its carbed. Carbed bikes will run fine without a fuel pump although they get a little grumpy when running low on fuel as they are gravity fed. Have you checked fuel hoses for cracks/leaks and also have you drained your float bowls and refilled them when you turn the key on. You can run the bike and put your hand on the pump and it should vibrate about every 3 seconds. If not then its probably faulty.

Couldn't feel any vibration, not that I can discern from the vibration of the engine anyway. Can't see any cracked hoses or lines, all and look good. I haven't drained the bowls - could this cause it? Could it be a dodgy float then? - I've ordered a pump anyway, £30 used so I can rule that out. Honestly I've tried everything I can think off except for stripping down the carbs thoroughly or getting into the valves and checking them.

Strangely though it did start running past 4k up to 7 when I took the airbox off to do another vacuum check - still sputters and backfires past that though.

The fuel pump will sort of tick every 3 seconds so you should feel a short vibration when it ticks. Maybe unplug the hose after the fuel pump and start the bike, it should pull fuel through if its working while the bike is running.

How is the fuel filter? (condition, size/flow rate)
It's obviously another potential cause of fuel restriction. :/

Does it match the required spec, or an aftermarket job which possibly doesn't?

The White One wrote:The fuel pump will sort of tick every 3 seconds so you should feel a short vibration when it ticks. Maybe unplug the hose after the fuel pump and start the bike, it should pull fuel through if its working while the bike is running.

I've packed up for the evening, but I'll give this a go tomorrow a logical thing to do, but I'm not much of a logical thinker!

Wooster wrote:How is the fuel filter? (condition, size/flow rate)
It's obviously another potential cause of fuel restriction. :/

Does it match the required spec, or an aftermarket job which possibly doesn't?

When I did the service about 6 months ago now I replaced it with a new one from wemoto - http://www.wemoto.com/bikes/yamaha/yzf_1000_r_thunderace/02-03/picture/fuel_filter/ so I'm hoping it's okay,

Was it running fine then? (I can't recall if you mentioned it already)

...just trying to rule out crud in the tank coming loose..

Have you checked on the filter? The plastic ones have a tendency to melt a bit if too close to a heat source.

When I serviced it it was fine, it was also fine for a short while after this.

Filter looked good to, I'll give it a check over again tomorrow. But there definitely weren't any leaks.

I really appreciate all the feedback guys.

Hi there, have you managed to sort this out yet? I had an ace not too long ago, cracking bike! ...you mentioned the cables were 'ok' on the exup, but were you able to actually examine the valve itself? If the cover and bolts were rusted, there's a good chance the valve is seized (or partially seized). The only other way to inspect is to remove the end can and link pipe (if you can) and look through the collector box.

These valves are notorious for seizing, most people change the pipes and get rid.

Regards,

Paul