Stumble at cruise speed

[edharrison]

Ihave a 97 Max that runs a little glitchy at 3000 - 4500 revs, I have shotgunned the carbs replaced plugs / leads caps, sorted charging system, replaced airbox rubbers and done all the recommended checks for vacuum leaks fuel filter and so on, diaphrams look fine, needles stock, tried two tanks of seafoam too, does not look rich or lean from plugs - I'm stumped.

Checked resistance at plug boots - fine, maybe coils???

Its stock except for stainless front downpipes and supertrapps running 8 disks with closed caps, A/F set to 3-1/2 turns at the moment.

Idle fine,

pulls fine under load at any revs

3000 to 4500 rpm stumbles at steady throttle,

gets slightly worse when warm


Any ideas please?


thanks Ed

 

[gennro]

Do your coilpacks have cracks in them? Most likely they do.

 

[edharrison]

Rear two look ok - I really dont like the idea of getting the fronts out, rather do COPS but only if I can be somewhere near sure it will help....moneys running out !

Ed

 

[naughtyG]

Ed I used to have this problem on my '86, mostly around the 4.5k range on the motorway.

Tried many things, but best solution ended up being shimming the needles, that did the trick. Not expensive to do so you can have a go without breaking the bank!

Basically you want to get some really small washers, I can't quite remember if they were 0.004inch (which is 0.1mm) or 0.4mm thick but if you search this issue here there's a thread with the answer or ask Mark (Maleko) as he knows!

Then you pull out your diaphragms and slides, get the needles out and replace with the washer just under the holding clip - basically raising the needles very slightly.

It worked for me!

PS: COPs are real easy to try out too, you don't need to remove the OEM coils until you're sure it helps and COPs go for very little ?? on fleaBay as most modern crotch rockets use them. You can make temporary harnesses very easily too, and if it works for you get the top quality fully made harness from Gannon (88vmx12) if he still has any.

 

[edharrison]

Thanks - needles were shimmed with one washer on each but the dealer used star grip washers so I removed them as they did not help and would doubtful have been accurate!

I will get some decent washers and try that, cops is on my list but a bit expensive for me right now, wouldnt have a clue on making up harnesses so Gannons are on my shopping list soon.

Seems to run slightly better cold then starts missing / stumbling from 3000rpm but clears past 5000rpm but only plays up at steady throttle, annoyingly right where most of my cruising revs are!

Ed

 

[naughtyG]

Well I hope it helps! If you get COPs with their original wiring you can usually simply crimp standard flat spade connectors and plug those straight into the max's coils connectors, then tape over to keep dirt and liquid out. Not pretty or very 'pro', but it works and would allow you to see if your coils are the culprits. I've seen s/h COPs going dirt cheapo on fleaBay..

Did you have the problem when those star grip washers were on too? It may be that your carbs need the kind of cleaning that only removal can do, check out my carb rebuild threads with photos it was a lot easier than I thought to do! Sometimes the rubber plugs and o-rings in the jet blocks can get worn and they are cheap to get and replace - if you do it yourself! Here's the first one:

http://www.vmaxforum.net/showthread.php?t=5830&highlight=clean+carb

 

[edharrison]

Superb write up on the carbs - too scary for me, it looks like saving money time for a trip to the dealer (not the one who used star washers as needle shims)!

The star washers did not seem to help but it costs virtually nothing to try some good washers so will do that first.

Found coils on eBay but how do you know what way round to wire them from the VMAX connectors to the two spades on the modern coil tops???


Thanks Ed

 

[RaWarrior]

I have this exact same problem, and I've been chasing it for over 2 years now. Still have yet to figure it out. I've done everything shy of a total carb rebuild, that may be coming this spring. Converted to COPs, new plugs, played with jetting/needles, got the charging system to work perfect (14.4v), tried swapping MAP sensors. Nothing has fixed it.

Mine is very intermittent. Sometimes the bike will run 100% perfect for weeks at a time, then randomly start acting up. Just a slight(but noticeable) misfire under steady throttle at highway speeds. It doesn't respond to small throttle changes, you've gotta really juice on it, at which point it takes off strong and crisp. Then it'll randomly stop again. The randomness of it makes me think it's electrical, but when it's "acting up" I can manipulate the problem with throttle position, which makes me think it's fuel. I don't know. It's not a huge problem, I've kind of just gotten used to it. But still annoying. Like how my damn blinkers get all wacky and flash weird when idling, since the bike loses 4 volts between the battery and blinker relay. **** yamaha wiring. I can't just run another line, since then power backfeeds and the the lights would be on all the time even when the key is off.

Be very wary of dealership carb work. More often than not Vmaxers who bring their bikes to yamaha shops for carb work end up taking them to someone else to get fixed again. If you can remove the carbs yourself(which is not that difficult, they all come off as one rack), send them to Dannymax or Sean and they will rebuild them for you, at a cost much lower than a dealer will charge and you'll be sure they're done right. Then just slap the rack back on your bike and go. You can remove the carb rack in around 5 minutes. Remove airbox lid and scoops, remove airbox(4 clamps), remove carbs(4 clamps), disconnect throttle cables, pull off fuel line, done.

As for the COPs, any coil from any modern sportbike will work. The two wires that go to the stock coil packs just plug into the two tiny spade terminals on the COP(they're wired and work the same way). There is a big COP thread somewhere, think it's a sticky. It has all the info you need.

I would try to get a set of COP's with the donor bike's sub-harness so you can steal the connectors. It's possible to get some female mini-spade and slip in there, but I'd rather have the original waterproof connectors. Also, the connectors are pretty universal. I run harness connectors from a R6 and coil sticks from a GSXR750 and they're identical and fit perfectly. Try to get your sticks from a gixxer, they use Denso sticks. Yamaha's use Mitsubishi, which have been reported to be more problematic.

I originally paid $30 shipped for a set of 4 sticks from a R6, and the sub-harness. I then switched to Densos, and paid $20 for the set of four. Yes, they're like $100/ea from a dealer, and no, that doesn't mean $50/ea from some salvage yard is a good deal. Poke around, there's tons of listings on ebay for coil sticks. Just search "gsxr coils" and you'll have a plethora to choose from. Find the best deal and go for it.

 

[Rhoy Carter]

Have you tried the a/f screws at 2 - 2.5 turns out?

 

[Itgoes]

That's a lean condition....could be as already mentioned cracks in the boots, or needles need adjustment.
Try choking the motor a tiny bit and see if it goes away.

 

[edharrison]

Thanks Ive tried numerous AF settings, it makes very tiny differences but does not cure it, when I did the shotgun the screws and jets blew through easy and no visible gunk in there.

RAWarrior - According to one source it is the pilot circuit that is responsible for 4000rpm steady cruise so maybe carbs for us both....very frustrating, if yours is intermittent could be sticky float - I will do COPS soon as its one more thing off the list!!

Dont think its lean but will shim needles and turn out 3-1/2 turns on the AF and try again.



Ed

 

[edharrison]

Are 2006 FZ1 Yamaha coils ok for the job - found some cheap?

thanks

 

[naughtyG]

Just about any will work, but as previously mentioned by someone it's prolly best to go for Honda/Suzuki ones as they use Nippon Denso which according to everyone here have proved more reliable so far than the Mitsubishi used by Yamaha.

Just make sure they come with their wiring!

 

[edharrison]

Thanks - more experimenting Today - put 6 disks / closed cap on the supertrapps and tried 2.5 / 3 / 3.5 & 4 turns out on the A/F screws - still stumbling but when you go out on the screws low RPM pulls a bit harder under load.

Tomorrow I will shim the needles and try various A/F settings and disks then post my results, hopefully it may help someone who gets the same issues at some point!

Ed

 

[tothemax93]

My bike was acting just like your describing. 4000 rpm stumble and weak up through. I know you tried this already, but the shotgun cleared it up 100% for me. I also had a time before I did the shotgun that I thought it cleared itself up. It seemed to be running back to normal. and then it started to act up again.

 

[edharrison]

Done the shotgun again this morning, shimmed the needles with one washer and will test ride a lttle later....

UPDATE -- Sadly no improvement - going up to two shims on needles and 8 supertrapp disks...

UPDATE #2 -- Still poorly but faster for sure!

Do I really need needle shims or am I masking the issues going way too rich -- , stock airbox / filter, Supertrapps closed caps 8 disks, stainless larger bore downpipes with no crossover????

Ed

 

[mgosset1]

i run my a/f screws at 2.5 turns out and it runs great...

 

[RaWarrior]

The larger bore headers w/o crossover could be playing games with you as well. I'm not an exhaust whiz, but know that things like crossover pipes and pipe diameter/length can have noticeable effects on how a motor runs.

So the problem is concentrated in the midrange? as in the idle is ok, and past 4500 or so it's OK?

If shimming the needles didn't help, maybe try going the other way and lean it. There's no simple way to lean out stock needles, but another way is to put in a bigger PAJ #2 (the jet that lives behind the diaphragms). This is an air jet, so a bigger jet=more air=leaner.

You may want to get a set of adjustable needles and lose the stockers, gives you more tuning power. Stock ones were non-adjustable to try and prevent people screwing with the mixture and thus affecting the "tailpipe emissions".

 

[edharrison]

Thanks - one thing I noticed doing the shotgun, 3 out of 4 carbs ejected some fuel from the needle jet hole, one didnt but air blew through all...

I have tried no shims and its worse, idle is fine, up to 3000rpm is fine, above 5000rpm is fine. under load is fine - problem is only at steady throttle between 3000rpm and 5000rpm - right where you need steady cruise throttle!!. With two shims it definitely pulls harder though

My gut tells me its rich (73 miles to fuel light last time lol) but it acts lean.

Even with the original headers it was the same, it does worsen slightly when warm which is a rich symptom but also a coil symptom.

Oh and just to be sure PAJ#2 has a much bigger hole than PAJ#1 - Just checking the PO didnt mess up!!

Got a friends compressor tomorrow to do yet another shotgun but with more pressure than a hand blower!



Ed

 

[naughtyG]

Ed, be careful not to overblow air in there - good pressure yes, too much no! There are some fragile bits inside the carbs too..