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kvb34441

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I love my vmax to death, I do, but shit just keeps breaking. Recently, cylinder number 4 went dead, so I replaced the spark plugs, wires, and boots. When I fired it up, it sounded really bad, the right pipe sounded like a flip flop being slammed on the ground repeatedly. The left pipe seemed fine. Not only that, but white smoke was pouring out of the right pipe. So I pulled the plugs, did a compression test on all 4 cylinders, got 60 on both right cylinders, 115 on the left two. Then I did a wet compression test by pouring a tiny bit of oil into each cylinder and compression got better. Immediately, I thought it was the piston rings. Now i'm not to sure. I did an oil change, and added in some "engine life extender" I don't exactly remember the brand. Now, the right pipe doesn't smoke anymore, still flaps but not as badly. It also idles way higher, at about 1500 rpm and rev hangs pretty badly. I turned the idle adjuster all the way clockwise and counter-clockwise, nothing. What's odd, is that it still accelerates just as ferociously as it always did. I wanted to get you guy's opinion before I take it to a shop and pay a couple hundred bucks or so to have it diagnosed.
 

Parminio

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Have you checked your oil to see if it's contaminated at all? (Maybe a head gasket went)

Have you hooked up a set of sync gauges to see if the vacuum matches the compression loss?
 

kvb34441

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well like I said, I did an oil change, the oil that came out was definitely do for a change, but it wasn't awful. The oil thats in there now is perfectly fine. I haven't checked vacuum yet though. Say it was a head gasket, about how much do you think someone would charge to replace it?
 

Parminio

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A lot. I don't think the typical shop would touch it for less than 1000 dollars. You'd be better served getting an upper kit and doing it yourself.

I'd run the vacuum check to make sure you're losing vacuum on the same two cylinders you're losing compression on.
 

MImax

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when were the carbs last cleaned? I’ve learned that these definitely require a good cleaning more frequently than you would think and it can account for a lot of issues. I kind of had a similar issue recently and I cleaned the carbs and did one of those top end valve cleaning chemical solutions and that seems to have cleared it up for now. It’s at least very cheap and easy to do for a start.
 

Pighuntingpuppy

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Dirty carbs don't cause you to lose compression.
Technically, yes...they can. Here is how. If a carb is over fueling a cylinder, it will wash the oil off the cylinder walls. As you know, oil completes the sealing process. If there is no engine oil properly lubricating the cylinder, poor running, hard starting and no starts can result.

When I worked for the dealer some years back, the coolant temp sender would flip out. Read -40F all the time. This would cause the injectors to hold open at their maximum time. This over fueling would eventually cause the engine to lose compression and eventual no start. How we would remedy it was replace all spark plugs, replace the coolant temp sender, add a smidge of oil to the tops of the pistons via the spark plug hole and oil change. Then we would drive the hell out of the vehicle to clear out the exhaust of unburnt fuel. They would smoke so bad that you could almost do a trip around the block and run into your own exhaust.

Moral of the story....yes, dirty carbs can make an engine lose compression.
 

kvb34441

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As a matter of fact, I recently ran into a yamaha mechanic and thought I might as well see if he could tell me what might be wrong with it. I described it all to him, and he told me it could in fact be a carb issue. He said that if the pilot jets are either stuck, or just set incorrectly, that would lead to the high idle, and he said it could cause carbon build up on the piston rings. I'm taking it to a shop today, I'll let you guys know what they tell me.
 

Parminio

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So I pulled the plugs, did a compression test on all 4 cylinders, got 60 on both right cylinders, 115 on the left two.
If that's the case, the carbs have nothing to do with it. It could effect the bike while it's running, but not with the plugs out on a turnover compression test.
 

kvb34441

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well the reason i'm considering that theory is because the bike is just as fast as it ever was. I was out riding it the other day and beat the hell out of my buddy's 2015 5.0. I'll be honest, I'm not too well versed on the inner workings of carburetors. However, from my understanding, the pilot jet controls how much fuel there is at idle. And like I said, it idles at 1500 rpm even AFTER turning the idle adjust screw entirely both ways.
 

Parminio

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That's part of why I wanted to see the results of the vacuum test. If the carbs aren't pulling the same vacuum you can sync them and see if that sorts it. If they are then that eliminates that problem.

I've seen where someone "rebuilt" a carb set and lost the tension springs but figured they weren't that important. He didn't realize what carb syncing was and that without those springs it was impossible.

You have a set of vacuum gauges it takes you 10 minutes to find out.
 

Fire-medic

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That's part of why I wanted to see the results of the vacuum test. If the carbs aren't pulling the same vacuum you can sync them and see if that sorts it. If they are then that eliminates that problem.

I've seen where someone "rebuilt" a carb set and lost the tension springs but figured they weren't that important. He didn't realize what carb syncing was and that without those springs it was impossible.

You have a set of vacuum gauges it takes you 10 minutes to find out.
Oh my!

VMax synch screws.01.jpg

A lack of adequate synchronization of the carburetors 'hangs-up' the idle at an increased rpm's.
 

kvb34441

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I brought the bike to the shop, they can’t look at it thoroughly until about Saturday. But they said that from what they heard from it running, it’s probably a carb issue.
 

Parminio

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You should invest in a set of vacuum gauges. You could find out yourself in 10 minutes. A decent set runs around 100 bucks.

Hell, for that matter Newnan isn't that far. If it's rideable you could have brought it here and hooked it up to mine.

Besides, you'll need a set to keep your carbs in sync anyway. It's supposed to be done annually.
 

Fire-medic

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You should invest in a set of vacuum gauges. You could find out yourself in 10 minutes. A decent set runs around 100 bucks.

Hell, for that matter Newnan isn't that far. If it's rideable you could have brought it here and hooked it up to mine.

Besides, you'll need a set to keep your carbs in sync anyway. It's supposed to be done annually.
Or whenever the carbs are off the bike to be worked-upon. You can get a set of bourdon tube gauges for much-less than $100.

I have one of these, lots of adapters for different bikes:

They're $45 delivered.

I also have a set of 'wet' Motion Pro 'sticks.'

My oldest set is like these:
$36, delivered.

They're almost 40 years-old. Still work fine.
 

Ted Drum

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Have you checked your oil to see if it's contaminated at all? (Maybe a head gasket went)

Have you hooked up a set of sync gauges to see if the vacuum matches the compression loss?
I love my vmax to death, I do, but shit just keeps breaking. Recently, cylinder number 4 went dead, so I replaced the spark plugs, wires, and boots. When I fired it up, it sounded really bad, the right pipe sounded like a flip flop being slammed on the ground repeatedly. The left pipe seemed fine. Not only that, but white smoke was pouring out of the right pipe. So I pulled the plugs, did a compression test on all 4 cylinders, got 60 on both right cylinders, 115 on the left two. Then I did a wet compression test by pouring a tiny bit of oil into each cylinder and compression got better. Immediately, I thought it was the piston rings. Now i'm not to sure. I did an oil change, and added in some "engine life extender" I don't exactly remember the brand. Now, the right pipe doesn't smoke anymore, still flaps but not as badly. It also idles way higher, at about 1500 rpm and rev hangs pretty badly. I turned the idle adjuster all the way clockwise and counter-clockwise, nothing. What's odd, is that it still accelerates just as ferociously as it always did. I wanted to get you guy's opinion before I take it to a shop and pay a couple hundred bucks or so to have it diagnosed.
 

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