Highway ‘misfire’. / stutter

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Nikonbloke
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Highway ‘misfire’. / stutter

Post by Nikonbloke » Sat Dec 14, 2019 4:10 pm

Hoping the hive mind can help me here. I’ve searched the forum and haven’t come up with anything conclusive, so . . .

I took the beast up the highway properly today for the first time since I acquired it. Normal early summer day here in Oz. About 28 degrees C, so not stupid hot ambients.

Bike idles nicely; isn’t all that snatchy when tickling along between 2000 - 4000 RPM; throws the tacho needle as you’d hope through all the cogs when you pin it (albeit mine is an NX and, thus, hits that ‘soft’ rev cut around 7200 - 7500 RPM. It’s getting an Oz-spec CDI box transplant early next week).

About 30 - 40 km into the ride, though, and while sitting at 110 km / hr / around 4500 RPM it started to have momentary loss of power . . . like it had a stutter for a second, or part second. Not a complete cut. More like a bit of a quick snap off the throttle, or or if you’d switched the crash switch ‘partially off-on’ super fast. What I also noticed was that if you opened it up a little, it seemed to momentarily stop. At times, it seemed to clear. For a good 10 km it seemed to clear pretty much completely if I sat on 120 - 130 km/hr / 5000 - 5400 RPM. Take an off ramp into a town and it was fine. Blip down, settle into ‘creep mode’ in, say, fourth gear at 2000 and it purred along at 60 km / hr smooth as. Also, when it was stuttering and you rolled the throttle open, it would cheerily punch up to 160 km / hr. At one stage, I pulled out of a rest area, sending it to the soft cut in every gear (though I gutsed out around 175 km /hr). Did exactly what it says on the box.

Trip back and I couldn’t find any ‘technique’ to eradicate it, or sweet spot to settle into. Brrrrrr, p, brr, p, brrrrrrrrrrrrrrr, p, brr, p, brr, p, brrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr, p, brrrrrrr . . . . 100 / 110 / 120 / 140 km / hr . . Did not matter. Still super smooth through small towns, and like shit off a shovel if you kicked down and gassed it up to speed leaving them, or to zip past someone while overtaking.

That’s the symptoms as best as I can relay them at least.

My theories include:

Fuel pump?
Fuel filter @ T (which I’m gonna check tomorrow)?
Spark plugs (which I might also change tomorrow)?
Plug leads? (What I don’t want to do, though, is change twenty things, fix it, and not know which change actually did).

The manifolds look OK and I’ve remedied that characteristic cracked cap doover on the RH carb. At first, I was thinking ignition / spark. / electrics. I’m drifting more towards fueling, though, as it was a bit like one of my old rally cars when you started a competitive having forgotten to switch from the ‘standard’ electric fuel pump to the ‘lets get into it’ one.

Grateful for any thoughts and / or comments (especially ones like, “piece of cake, mate. Just do dot dot dot”).

Cheers!

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Re: Highway ‘misfire’. / stutter

Post by HolerTogni » Sat Dec 14, 2019 7:45 pm

Hi Colin!

My spontaneous thoughts go to checking the side stand and/or clutch lever "kill switch" for correct contact.

Or checking the vacuum hose of the fuel cock and/or fuel tank breather related items.

Hope this helps and you can enjoy your "piece of cake" when solved the problem :wink: :roll:

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Re: Highway ‘misfire’. / stutter

Post by Nikonbloke » Sun Dec 15, 2019 3:26 am

Thanks, Holer.

Thoughts of the side stand did enter my mind at one stage. It did seem better (at times) on sections that were billiard-table smooth. Don’t think mine has a clutch lever kill switch. I’ll check that all the same.

As an update, this morning I pulled the tank and side plastics and checked the vacuum lines / manifolds / fuel filter / tank venting ... all good there (albeit I’ll renew the manifolds sooner rather than later).

All of which now has me thinking fuel tap / pump. Wondering how it would go switched to Pri on the highway (?) Would that me much different to an ‘old skool’ ‘off / on / reserve’ tap?

Munich (Sigh). Passed through there in ‘96 on the way to Innsbruck (and other points). Beautiful part of the world.

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Re: Highway ‘misfire’. / stutter

Post by Rod.s » Sun Dec 15, 2019 3:57 am

Welcome to the forum and as you live around some amazing roads we'll expect to see many photos of Tumit, Jundabyne, Kahacobin and all the towns in between!!

As for the bike, it sounds to be the carburettors.

But for any bike that you don't know the history so do the usual, change the plugs, oil etc and expect some sort of fuckery from previous owners.

The issue is relater to fuel flow at constant rev's, when the throttle is fully open the carburettor effect is negated and instead acts like a fuel dump with little care for over fuelling. Remembering that these are CV carbs, the vacuum created will open the slide beyond what's expected for normal RPM related fuelling.
So at a constant RPM the carb settles into it's metered form, this when the tuning or lack of tuning shows it ugly head. At the 4500 and up RPM the carb is running off the slide needle and main jet, so if there is an issue with constant RPM it's found here and as you said, it doesn't change from 110-140Kph so it is not the needle or main jet. My guess is the float needle is sticking. This would not show its head under open throttle as the float valve is wide open and dumping fuel, now under metered fuelling the float is doing its job of not flooding so may stick and restrict fuel flow.

Without seeing the bike and riding it this is only an assumption :wink: I recently helped fix another TRX that had simple issues but after seeing the bike and riding it the issues were numerous and mostly related to the previous owners fuckery!

Vacuum can also show up with similar issues as once again the carbs are at wide open throttle the vacuum is negated and has little effect on the tuning of the carb, but drop down to a constant RPM where the carb needs to "work" and the vacuum starts to have an effect in leaning out the mixture and creating strange issues that are seldom constant, this is caused due to the engine vibrating creating an effect of closing or opening the vacuum leak randomly.

Once again this is at least a 25 year old bike with 25 year old components, as HolerTogni said check the vacuums hoses to the fuel pump and fuel tap, if either is giving intermittent faults there will be intermittent fuel flow.

The manifolds are prone to cracking these ones pictured were visually perfect but giving strange issues!! If you are replacing them only use genuine Yamaha ones.
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Last edited by Rod.s on Sun Dec 15, 2019 4:05 am, edited 2 times in total.
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Re: Highway ‘misfire’. / stutter

Post by Rod.s » Sun Dec 15, 2019 4:03 am

Nikonbloke wrote:Thanks, Holer.

Thoughts of the side stand did enter my mind at one stage. It did seem better (at times) on sections that were billiard-table smooth. Don’t think mine has a clutch lever kill switch. I’ll check that all the same.

As an update, this morning I pulled the tank and side plastics and checked the vacuum lines / manifolds / fuel filter / tank venting ... all good there (albeit I’ll renew the manifolds sooner rather than later).

All of which now has me thinking fuel tap / pump. Wondering how it would go switched to Pri on the highway (?) Would that me much different to an ‘old skool’ ‘off / on / reserve’ tap?

Munich (Sigh). Passed through there in ‘96 on the way to Innsbruck (and other points). Beautiful part of the world.
Check everything as the bike may have sat for months with crap fuel in the tank etc, the tap and pump can be removed and cleaned, some people replace the tap for a on/off/res tap as they have had fuel pooling in the cylinder and the pump is available on the Bay as a Chinese knockoff. I've never had any issues with either and have ridden over 60000k's on my black TRX and 5000k's on the red bike...
If it's not made in China, it's a fake!

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Re: Highway ‘misfire’. / stutter

Post by cobbadiggabuddyblooo » Sun Dec 15, 2019 4:07 am

Rods pretty well nailed it for you .
77,000km on the clock
Look down inside the inlets and just check there’s no carbon build up from tight inlet valve tolerances which the early TRX’s suffered from..
Could be another cause with just a slight leak from the inlets. Trx runs horribly rich from std so light throttle under load at 100kph may be a culprit too so hard throttle may mask this but it will rear it’s ugly head again in the hi RPM range.
If it’s like hitting the limiter at 7500 through the gears I’d be hedging towards valves as the limiter kicks in at 180kph and 9500rpm under 180kph.
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Re: Highway ‘misfire’. / stutter

Post by Rod.s » Sun Dec 15, 2019 8:15 am

cobbadiggabuddyblooo wrote:Rods pretty well nailed it for you .
77,000km on the clock
Look down inside the inlets and just check there’s no carbon build up from tight inlet valve tolerances which the early TRX’s suffered from..
Could be another cause with just a slight leak from the inlets. Trx runs horribly rich from std so light throttle under load at 100kph may be a culprit too so hard throttle may mask this but it will rear it’s ugly head again in the hi RPM range.
If it’s like hitting the limiter at 7500 through the gears I’d be hedging towards valves as the limiter kicks in at 180kph and 9500rpm under 180kph.
Yep great pick up Brian! defiantly check the valve clearances :)
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Re: Highway ‘misfire’. / stutter

Post by Nikonbloke » Sun Dec 15, 2019 4:07 pm

Rod, Brian...thanks heaps. That’s excellent and all completely logically. Gives me a great starting point.

Weirdly, after I’d had a little search around with the tank / plastics off this morning (where I checked heaps..did peer down inlets, too. Recall them being clean. Will do again) I took it for a run around the ‘Cotter Loop’ this arvo. Only one stutter on the way out and smooth as on the run to Uriarra Crossing (as close to a few kms of highway as you’ll get out that way). Mind you, I did switch the fuel tap to Pri before I left Cotter Campground. Has me leaning to the float needle and seat. Think I’ll start there first.

But, yeah... I was pretty much gonna go right through it anyway. Maybe ‘whatever’ will show up in starker contrast once I swap the CDI unit out to an Australian delivered spec one as well.

Yes, Rod...there’s some pretty country around here. I’ve been through a lot of it in the Jeep. Lob’s Hole / Ravine; Coolamine Homestead; Jounama Homestead; Island Bend. I’ve spent a shirt load of time in Jinders / Thredbo...love that whole area. Do a fair bit of mountain biking around there as well. I’m also the worst fly fisher in the known universe. (Fly fishing is just an excuse to walk a stream after two hours 4WD-ing off the main road in low range anyway) lol

Thanks again, fellas.

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Re: Highway ‘misfire’. / stutter

Post by Snod Blatter » Sun Dec 15, 2019 7:14 pm

Rod.s wrote:The manifolds are prone to cracking these ones pictured were visually perfect but giving strange issues!! If you are replacing them only use genuine Yamaha ones.
Why is that? I've fitted some Chinese ones off ebay and was very impressed with the way they fitted. Can I expect ludicrously short life from them?

(Sorry about the slight thread hijack! To stay on topic though my original rubbers were heavily cracked when I replaced them last year.)
'95 4NX with K&N filter, Motad Venom cans, YSS PD valves, Ohlins fork springs, 530 C+S, Green CDI, 11/16 radial master cylinder, +30mm jack up dog bones. Enjoyable money pit.

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Re: Highway ‘misfire’. / stutter

Post by dicky » Sun Dec 15, 2019 10:57 pm

Maybe ‘whatever’ will show up in starker contrast once I swap the CDI unit out to an Australian delivered spec one as well.
If you haven't already spent money on the 4UN CDI unit then I'd strongly recommend saving up a few more dollars and getting an Ignitech unit (http://www.ignitech.cz/en/vyrobky/tcip/tcip.htm).
It makes a very noticeable difference in the bikes performance.
Even if you have spent money already I'd still recommend it, the only thing the 4UN will give you over the 4NX is removal of the Japanese market limiter.

Carb kits and parts are available from Keyster (https://www.motorcyclespareswarehouse.c ... -parts-kit) , among others.
It is well worth while buying some viton seal kits from Blair at Litetek in Thailand (https://litetek.co/Carb_Kit_Yamaha_TRX850.html) to eliminate any ethanol tainted fuel problems.
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Re: Highway ‘misfire’. / stutter

Post by Rod.s » Mon Dec 16, 2019 2:15 am

dicky wrote:
Maybe ‘whatever’ will show up in starker contrast once I swap the CDI unit out to an Australian delivered spec one as well.
If you haven't already spent money on the 4UN CDI unit then I'd strongly recommend saving up a few more dollars and getting an Ignitech unit (http://www.ignitech.cz/en/vyrobky/tcip/tcip.htm).
It makes a very noticeable difference in the bikes performance.
Even if you have spent money already I'd still recommend it, the only thing the 4UN will give you over the 4NX is removal of the Japanese market limiter.

Carb kits and parts are available from Keyster (https://www.motorcyclespareswarehouse.c ... -parts-kit) , among others.
It is well worth while buying some viton seal kits from Blair at Litetek in Thailand (https://litetek.co/Carb_Kit_Yamaha_TRX850.html) to eliminate any ethanol tainted fuel problems.
Talk to Brian about one, he had a few that he was selling, not sure if he has any left :D
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Re: Highway ‘misfire’. / stutter

Post by cobbadiggabuddyblooo » Mon Dec 16, 2019 4:06 am

I bought a pair of the cheaper inlet manifold rubbers and had issues tightening them to seat correctly and they would start to pull to one side when nipping them up.
A little sideways movement on the carbies and it would pop off.
Problem sorted by fitting genuine ones from Yamaha.
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Re: Highway ‘misfire’. / stutter

Post by Nikonbloke » Mon Dec 16, 2019 1:16 pm

Thanks again, guys. Good advice.

Fitted the 4UN brain box this arvo. That’ll do me for now. I have read a little about the Ignitech ones , , . They do sound good and I might look into them further down the track. Would love to get this issue sorted first. Thanks for the links, too!

Just as an aside . . . Yes, I did give her a short road test after swapping in the 4UN CDI. My my . . . don’t they sound awesome up there around ‘eight five’? Oh, look! No need to play with the speedo internals either! Yay!

Typical me, though. Now I’m thinking to myself, “Hmm . . . It’s never been revved that hard before most likely. Wonder what sort of conrod stretch they have around 7000 v (say) 8500-ish and if there’s a lip in the bore the top rings need to worry about?

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Re: Highway ‘misfire’. / stutter

Post by Snod Blatter » Mon Dec 16, 2019 11:17 pm

cobbadiggabuddyblooo wrote:I bought a pair of the cheaper inlet manifold rubbers and had issues tightening them to seat correctly and they would start to pull to one side when nipping them up.
A little sideways movement on the carbies and it would pop off.
Problem sorted by fitting genuine ones from Yamaha.
I honestly had no such problems, the only difference was that the holder nubs for the jubilee clips were on the opposite side so tightening the screws was even more awkward than the original ones. But they fitted perfectly :dontknow:
'95 4NX with K&N filter, Motad Venom cans, YSS PD valves, Ohlins fork springs, 530 C+S, Green CDI, 11/16 radial master cylinder, +30mm jack up dog bones. Enjoyable money pit.

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Re: Highway ‘misfire’. / stutter

Post by Rod.s » Tue Dec 17, 2019 9:50 am

Snod Blatter wrote:
Rod.s wrote:The manifolds are prone to cracking these ones pictured were visually perfect but giving strange issues!! If you are replacing them only use genuine Yamaha ones.
Why is that? I've fitted some Chinese ones off ebay and was very impressed with the way they fitted. Can I expect ludicrously short life from them?

(Sorry about the slight thread hijack! To stay on topic though my original rubbers were heavily cracked when I replaced them last year.)
The main issue is the unreliable quality of the rubber used some are terrible and other are crap, the rubber breaks down quickly and is to soft :( they may last 4 years or 5, but I'd be surprise if they last anywhere near as long as the factory versions.
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