Sputter at 1500rpm

Last weekend I had the benefit of attending the MA Carb Clinic, which was a ton of fun. My bike purrrrrs like a kitten now, but I did notice one little hiccup on the way home.

After riding about 45 minutes at around 70mph, the bike sputtered from a stop around the 1500rpm area. Sputtered so much I thought it was going to die out. I revved it up to get it out of the band, and I was off. At each stop light/sign, it did it again. Beyond 1500rpm (give or take a couple), it is smooth as silk.

Carbs were pulled and cleaned, balanced, and syncronized. I haven't had a chance, yet....but I am going to pull the plugs to see what they look like.

Any first ideas?
wolfmajor

 

Got a bit of crud from your fuel tank? Did you buy cheap gas at a cheap station? Laugh if you must but it can happen. Do you by chance have an inline filter installed as of yet Wolf? If not, you should do so at first opportunity. Sorry, this is the only variable I can think of right off the bat. Hope you find it!

 

Did you put an inline fuel filter on after cleaning the carbs? Also has it cooled off weather wise in your area? My Seca would always run like that after a cold front or rain came through. Turns out it was condensation in the tank. Haven't had this with my Maxim but the Seca was reliable in this respect.

 

Max, you might have the culprit right there. Wolf, what shape is your fuel filler cap seal in? If it is cracked (and most are by now) you could run into condensation contaminiation issue. Good point Max!

 

Great insight, guys! Let's see if I can answer all those questions.
I did have the tank cleaned and conditioned about 2 years ago....so hopefully, it wasn't in too bad shape.
Yes, I purchased gas on my way home early in my trip at a station I have never been to. Was it bad or cheap gas?? I have no way of knowing!! (hmmmm....)
I did (or should I say RickOMatic) installed an inline fuel filter. Never had one there before. Brand spanking new.

Yes, the weather has cooled off a bit lately from where the temps had been hovering.
I did notice that this didn't happen at the beginning of my trip but did happen at the end when it got really warmed up from a long highway drive.

Fuel filler cap seal? Well, I'll have to check that out in the morning. Never looked at it before.

Thanks for the suggestions. I'll be back tomorrow with more info!
wolfmajor

 

Don't forget ... this is the bike with the petcock that wasn't sealing and leaking-by. The petcock's vacuum diaphragm was "altered" to allow it to shut-off when no vacuum is present.

With the "working clearance" of the aftermarket vacuum-operated diaphragm -- effectively REDUCED by .025 mm -- There is the distinct possibility that the vacuum diaphragm does not OPEN sufficiently under conditions where low vacuum occurs. Red lights, low-rev ops, cruising no-load in top gear, etc.

Test by riding in varying conditions ... or trying to duplicate the condition which causes the sputter.

Sputters? Yes.
Retest with petcock set to PRIME.

Sputters? Yes. Tuning issue ... we'll have to have a look at your plugs and possibly reset the mixtures.

No ... Petcock at fault. We'll have to throw that kit in it. But, we need to be absolutely certain that the kit IS NOT generic and is the right one for that bike!

 

Good point, Rick. I'll test out these conditions on my next ride. Hopefully, tomorrow. (Haven't checked the weather, yet.) I have to tell you - I love that the petcock doesn't leak all over the side stand anymore!

I'll let you know about the plugs, too.

 

No real insight just what I lived with. Funny thing is I haven't run into anyone else with a Seca who has the same problem. Of course it may have much to do with the humid south. While you're at it tonight Robert, check out my post about my cylinder being shaved. I will pick it up tomorrow and start reassembly.
Wolfmajor, I would look to make sure that the fuel filter does not put the fuel line in a rise. I doubt Rick wouldn't know about that :wink: but it can slip out of the retainer and create a hill for the fuel to climb.

 

I'm all over that ... the retainer caused the line to kink. She has down-sloping flow from the Petcock's fuel outlet ... into a angled length of gas line ... on to the clear Fram inline filter ... out and down the supply line.

Not a drop of contaminated fuel went into the carbs before they were hooked-up to the tank. My aux tank for tuning has both an internal and external filter.

Since we ran the bike a good deal while syncing (real tweak-the-hell-out-of-it; sync) ... I'm betting the problem is going to be that petcock vacuum valve. We might be able to solve the vacuum problem by "Doubling-up" the vacuum's off the manifolds.

I could fabricate two short lengths of vacuum line running to a "Y" fitting and then over to the petcock. I have my doubts about trying to tweak the petcock vacuum valve assy again ... I'm sure any further stress on the thing is just asking for trouble. I'd rather get her running OK with a bandaid fix; than have the bike laid-up waiting for a part.

 

Yep, looks like she either picked up some bad gas or it's the petcock. ONce she flips it over to prime while it is sputtering we will most likely know.

 

The reasons I suspect the Petcock are: a) It's a generic aftermarket job. I'm not too happy with the way everything fit -- especially the most important part ... the vacuum valve. You cant tell me that they didn't know that thing was leaking-by. When a petcock is functioning properly ... you're able to remove the tank and set it aside without worrying about gas running out of the tank all over the place. b) We had everything humming when the bike was running straight off the aux tank we had hung while tuning. That's effectively like running the bike on Prime -- right there! My feeling is that Wolfmajor should voice a complaint to the shop that set-it-up like this and demand it get done to her satisfaction. We found evidence (reversed fuel bowls) -- that who ever did the job was careless and sleepwalking. Nothing upsets me more than paying for steak and getting hamburger!

 

Here here Rick. Bad service is something that should be brought to the shops attention ASAP. If the management is worth its salt, they will want to nip inattentiveness in the bud straight away to prevent lawsuits.

 

Out of curiosity, I checked with a source at a local Yamaha Dealership. The Dealer is bound to supply service customers with NEW -- Genuine YAMAHA Parts ... unless they contact the customer and get the authorization to substitute NON Genuine Parts or, in some cases -- a suitable working part from salvage. The customer must be notified and authorize the substitutions. Without a consent from the customer; the only parts used for repair are supposed to be Genuine Yamaha.
***(And, if the parts ARE Genuine Yamaha -- the customer should be guaranteed that they fit, are installed right, not leaking and work like they should.)***

[w-m ... I got yer back if you feel like sticking-it to the guy's who messed you up!]