Odd engine rythm when not on the gas

[Taavinen]

Ok, sort of hard to explain, but basically when i am rolling along any speed (eg 35mph for example), i am holding the throttle slightly open to maintain speed. Instead of giving an even Purrrrrrrrrrr sound, it almost sounds like it is missing, but you can give it boot and it does not miss at all. Sort of feels like it is getting worse, and is not so smooth on take off unless the revs are up.
A few things to note:

*I had the carb's sync'd 2 weeks ago, had problems with backfiring thereafter, went to yami (different place) they said the carbs were out of sync. I have checked the linkage for setting t e carbs during sync and it does not appear loose. It has a slight forward back movement on the sleeve but no wear when you try to swivel it so no obvious wear IMO

* I have opened up the stock exhaust (first there was small hole put in the baffle - made it a little more deep sounding, but not louder. Then i drilled 1/2 inch holes in the backs of them.

When the carb's were re-sync'd and tuned this was all done at yami with the open exhaust (which the mechanic was not impressed about saying "you've F**ked your exhaust" pointing out how one exhaust handles most of the load and is balanced by the other exhaust.

I am planning on getting the carbs rebuilt in a week or so as the bike sat for a long time prior to me buying it.
Is it the carbs that are probably causing this issue or could it be the exhaust?
Are the carbs potentially going out of sync again? And if so, why??

 

[richwrench]

My exhaust is drilled the same way & I have NO problems with idle or off-idle. If the bike has sat for a while, I'm sure the problem is in your carbs. It doesn't take much to plug up the tiny holes in the jet block. Rebuild, resync, & I'm sure you'll be fine.

 

[MaxMidnight]

Not sure what the 'mechanic' means by 'one exhaust handles most of the load and is balanced by the other exhaust'.

Given that the system is symmetrical and goes into a collector box then provided that you have the same size openings in both silencers one would expect that a similar amount of gas would flow through both?

It isn't uncommon for a motor to feel 'different' when floating between a driven (applying throttle) and closed throttle state and it can feel like it is hunting (a back and forward 'pulse').
Most engines can be made to do this but it depends on your driving style if you ever notice or induce it.

Usually applying a tad more or less throttle will stop the sensation.

Assuming that the carbs are synched, air filter is clean and the ignition system is in good condition then the only sure fire way to establish what is going on would be to put the bike on a rolling road and measure what the air/ fuel ratio is doing when you get the condition.
You can often waste a lot of time and money by trying to guess what the problem is - it's far better to base your diagnosis on facts! :ummm:

 

[one2dmax]

A cruise surge can usually be cured by enlarging the PAJ2 jets (stock is 170 - use a 177.5 mikuni or 190 dynojet). Every engine is different as is every reaction to changes. Jets are cheap and they would be easy to try (located under the carb slides).

Sean

 

[gamorg02]

shimming the needle may help too depending on what rpms its missing @

 

[SpecOps13]

I have a half inch hole in the center of each muffler and 5 half inch holes around the end cap area. It has a slightly rhythmic idle but is smooth as glass off idle and warm. Sounds like it's either how you're riding when you detect the rhythm or it's jetting. I'm at sea level and have stock jetting.

Good Luck,
Dave

 

[ripinanroarin]

I have a half inch hole in the center of each muffler and 5 half inch holes around the end cap area. It has a slightly rhythmic idle but is smooth as glass off idle and warm. Sounds like it's either how you're riding when you detect the rhythm or it's jetting. I'm at sea level and have stock jetting.

Good Luck,
Dave

Mine was the same set up. Rythmatic when cold, but went away after warming it up. Just before I sold it...I put the chrome covers on to hide the holes,.and the rythmatic sound disapeared completly.

 

[mivmx]

I have a similar sound since I drilled my mufflers. I just think it's talking to me now that it can. Nothing to worry about.

 

[eatatjoz]

Cracked intake boots could also cause an erratic idle.

 

[Taavinen]

Intake boots are all good. When i float along it almost sounds like it is out of tune til you raise the revs a little. Just feels like it is maybe hesitating and jerky when floating, but straight away responds with ANY increase in throttle. Maybe it is just like this cause i modded the muffler? I called yami about ordering parts for the rebuld. The mechanic got on the phone and reckons:
1. It is cause i drilled out the mufflers
2. He says i should be running the carb cleaner that they gave me to add to the fuel for about 1000km and see how it goes before i think of rebuilding the carbs.
I guess i am keen to build them now as it is annoying when i am riding it, and the bike has sat for a long time so figured why not just rebuild the carbs for good measure

 

[naughtyG]

When he talks about your exhaust, your mech is simply full of shite and uses your drilling as an excuse for his own shortcomings. (most yamaha mechanics today are clueless when it comes to Vmax - they are trained to service current bikes not 25 year-old ones..)

Running a little Seafoam or similar fuel conditioner/cleaner is a good maintenance routine if the bike sits for any number of months each year.

You got the right idea in wanting to rebuild carbs on a bike that has sat, but I would not order ANY parts until you've taken them apart and had a good look, as it's impossible to say what you will and won't need to renew and some of those parts are VERY expensive.
Also do NOT get any 'carb kit' as they are all pretty crap, just order what you need from Yamaha or even better, Sean Morley.

 

[kevman]

Cairns Yamaha suck and their mechanics know sfa about Vmaxes.I had the hole punched in the exhaust when I first got it and then I drilled holes to make it louder.Brett does a good job on all the vmaxes in town and it would be better to get the carbs pulled apart and cleaned.Brett is a perfectionist who does great work :worthy:.He's tuned mine twice and it goes like a scalded cat .Cheers Kevman.

 

[Taavinen]

Cairns Yamaha suck and their mechanics know sfa about Vmaxes.I had the hole punched in the exhaust when I first got it and then I drilled holes to make it louder.Brett does a good job on all the vmaxes in town and it would be better to get the carbs pulled apart and cleaned.Brett is a perfectionist who does great work :worthy:.He's tuned mine twice and it goes like a scalded cat .Cheers Kevman.

Hi Kev, thanks for your input. The bike started stalling the second day i had it (actually round the cnr from Brett's shop) and so i took it to Brett for that and then again to fix a leaking clutch slave. Damn straight he does a good job, it seems like most of the Vmax's in town are worked on by Brett ( The man has a picture of a Vmax on his business card!), and he is very reasonable in Price. I think i will just be done with it and get the carbs built. Brett quoted a good price

 

[Taavinen]

Cheers NaughtyG. You are about the forth person (on and off this forum that has mentioned that). Re-parts, i will get a mechanic to do it, and i know he will only order what is needed

 

[Taavinen]

Bike started playing up even more today. First the idle dropped a few hundred rpm by itself, and now it is stumbling, popping and back firing. Have booked in with my local mechanic Brett to fully rebuild the carbs, that is 2 weeks away, so will be riding the mountain bike for about 3 weeks :bang head:
Was hoping to put Sean's muscle kit thru, but can't afford it and the pipes together and need the bike on the road ASAP

 

[Taavinen]

Can you guys suggest parts that probably SHOULD be replaced when the carbs are done (besides gaskets obviously). Don't want to have to go back into them again.
My mechanic said he would totally go over the bike as well for eg vacuum leaks, faulty parts, checking valve clearances etc to hopefully finally get it running right.

 

[naughtyG]

Can you guys suggest parts that probably SHOULD be replaced when the carbs are done (besides gaskets obviously). Don't want to have to go back into them again.
My mechanic said he would totally go over the bike as well for eg vacuum leaks, faulty parts, checking valve clearances etc to hopefully finally get it running right.

If you look at my carb rebuild thread you can see what I replaced, which wasn't much. I basically got new fuel bowl gaskets, and the seals under the jet blocks and associated o-rings.
I was lucky as all four of my slide diaphragms as well as all four of my coasting enrichment diaphragms were in excellent shape - if any of those have holes or are torn they'll need replacing, and are rather expensive.
You can check out the slides diaphragms without removing the carbs - actually you take 'em out to do the shotgun..

 

[Taavinen]

Thanks NG. Was told by yami today those diaphrams are $185AUD each :surprise:
Either way i don't care. I wanna see this beast running right and kickin some Harley arse

 

[one2dmax]

I have everything on hand you need for a normal rebuild. Typically it runs around $150 for all the parts. Shipping would be simple.
Sean

 

[Taavinen]

Ok SHOTGUN'D the carbs today. Was actually a bit of fun and a good learning exp. It has definitely shown improvement. It accelerates smoothly now.
The only problems that remain are all during floating:
*It still gives a brr..brr.b..brrr.b.b.brrrr if that makes sense.
-It DID not do it when i bought it.
*It also continues to POP at the exhaust.

Any ideas? Or is this probably due to drilling the exhaust out?