Sluggish and Popping…

[JBryan91]

Hello everyone.

I have been chasing a random popping condition on my max for a while now. I can say for certain that:
Has clean 87 octane and clean filter
Good fuel pump
Good coils/spark/plugs
Carbs have been professionally gone through and sonic cleaned
Gone Down to 150 mains. Everything else is stock.
Vboost has been adjusted
Have synced carbs with digi sync to 58 kpa on every one @1100 rpm.
Coils all read 3.3-3.5 ohms
Pressure Sensor reads 2V
Running delkelvic 8” slip ons.
No exhaust leaks whatsoever.
All rubber has been replaced with genuine Yamaha

Bike is not pulling as hard as I think it should. Kinda sluggish. I’ve ridden a bunch of bikes and this one has no balls unless you’re running the pi$$ out of it. Can’t really feel “vboost” kick in. Servo does cut on and cycle with key on though. The engine pops briefly on start up. I have done the “shotgun” by lvlhead multiple times. The rear carbs (#1,#3) a/f screws do not affect the idle at all. Only the two front carbs (#2,#4). I’m not sure what I’m missing.

 

[MaxMidnight]

Apart from the random pop on start-up when else do you get it i.e. on acceleration, steady speed or decelerating?
I would normally associate popping with an air leak in either inlet or exhaust systems.
Inlet can be checked by spraying and Easy start aerosol around the inlet and listening for the revs to rise; the exhaust by close inspection for sooty deposits around the joints.

The 2V pressure sensor reading only indicates the output at ambient manifold pressure. The voltage will drop if you reduce the pressure (apply a vacuum) and increase as it goes above ambient.
You would need to measure the output voltage between -600 mm Hg and +600 to confirm it is operating correctly.
All that said I don't ever recall reading of one that has failed.

Have you done a plug chop to establish what the mixture is doing? (see attached).

Until you can establish if you have the correct air/ fuel ratio you will just be guessing.
If you have the time then 'chopping' should point you in the right direction. However (and tadahh! here it comes) IMO the quickest way would be to get a base line dyno run. That will give you factual measurement from which you can move forward.

 

[Fire-medic]

In my experience, 'popping' is due to a lean condition.

What does your gas tank look like inside? Do you see shiny metal?

 

[JBryan91]

Apart from the random pop on start-up when else do you get it i.e. on acceleration, steady speed or decelerating?
I would normally associate popping with an air leak in either inlet or exhaust systems.
Inlet can be checked by spraying and Easy start aerosol around the inlet and listening for the revs to rise; the exhaust by close inspection for sooty deposits around the joints.

The 2V pressure sensor reading only indicates the output at ambient manifold pressure. The voltage will drop if you reduce the pressure (apply a vacuum) and increase as it goes above ambient.
You would need to measure the output voltage between -600 mm Hg and +600 to confirm it is operating correctly.
All that said I don't ever recall reading of one that has failed.

Have you done a plug chop to establish what the mixture is doing? (see attached).

Until you can establish if you have the correct air/ fuel ratio you will just be guessing.
If you have the time then 'chopping' should point you in the right direction. However (and tadahh! here it comes) IMO the quickest way would be to get a base line dyno run. That will give you factual measurement from which you can move forward.

Thanks MaxMidnight! I do not get any popping on decel. I thought i heard it quietly and briefly yesterday through a WOT pull in the midrange. Subtle is a better word to use. It seams to do it at the end of a throttle blip and idling. I have wasted two cans of brake clean looking for any air leaks to no avail. There is no obvious exhaust leaks or sooting that i can see. AAAAAND i would do inappropriate things for a local dyno, just don't tell my wife.

I will try a plug chop in a day or two. I get off work late and don't want to piss the neighbors off.

In my experience, 'popping' is due to a lean condition.

What does your gas tank look like inside? Do you see shiny metal?

Thanks once again Fire-Medic!

Gas Tank has shiny metal!

 

[JBryan91]

What stumps me the most is what other system is involved that would cause both rear a/f screws to still not adjust after thorough cleaning? Are #1 and #3 connected somehow? PAJ1, PAJ2, main jet air bleed, and carb mixture screw passages are spotless.

I forgot to add the bike runs as aforementioned on 2-2.5 turns with 150 mains. If I go to 3 turns on a/f it sputters severely. If I go to anything below 2 it starts to get hot.

 

[MaxMidnight]

Apart from the link via the V Boost tubes (which link the left pair and right pair of carbs so not relevant to your issue) the only other link I'm aware of is the fuel delivery.
When you say it splutters or runs hot is that at idle or do you get this on the road at higher revs?
Whilst the idle circuit provides fuel throughout the rev range this reduces significantly as the needles and main jets take over as can be seen from this generic illustration..


If the adjustments you cite affect the running on the road then my gut feel is that you have another problem with the carbs. That the rear pair do not make any difference to the idling of the bike suggests to me there is still a blockage somewhere in the system.

 

[Fire-medic]

MM, isn't it true, that generic diagram is for an 'old-style' carbureted system? Nothing to do with a CV carburetor, where the diagram is mentioning, 'throttle valve cutaway?' There is no throttle slide cutaway to a CV carburetor.

That brings me back to the days of my CL77 Honda Scrambler, where I used to use two same-sized drill bits, like 1/16" resting in the venturi and sticking out of the throttle slide cutaway, to get the carbs synchronized. You would mess with the threaded throttle cable adjustment sticking out of the threaded throttle slide cap, so both slides moved simultaneously. Not too-long before that, Milhous Nixon had been elected POTUS, and it was the year I paid much-attention to the person pulling birthday-dated ping pong balls out of a container.

Yes, I believe that if your below the CV cap screws 'do nothing' to influence how the bike runs, the air/fuel circuits operating off them, are somehow obstructed.

 

[JBryan91]

I’m just going to have to pull the carbs apart myself further than the shotgun method suggested. I’m irritated that I paid $550 to have them “cleaned and rebuilt”. I’m mechanically inclined just not on quad CV setups. I was hoping it was something simple…

 

[MadMark]

I’m just going to have to pull the carbs apart myself further than the shotgun method suggested. I’m irritated that I paid $550 to have them “cleaned and rebuilt”. I’m mechanically inclined just not on quad CV setups. I was hoping it was something simple…

I think that's what will end up being your problem from what been said. Even the best mechanic/carb builder can't get it right 100% of the time. No fault to their ability or experience, sometimes things happen. That's why I always fix everything myself. Unless I can't find the time or it needs fixed immediately.

 

[JBryan91]

So I started on #3 and #4 tonight. Everything looks clean and nothing out of place. However when taking jet blocks off the rubber gasket looks new, but flimsy and not well made. It looks correct but is slightly larger and does not sit flat on the carb body. One can assume that it might be plugging small passages when squeezed flat with jet block in place and tightened.

First time this deep in a carb as well. Can I spray carb cleaner in every little hole I see or is there particular ones I need to avoid? TIA

 

[MaxMidnight]

MM, isn't it true, that generic diagram is for an 'old-style' carburettor system? Nothing to do with a CV carburettor, where the diagram is mentioning, 'throttle valve cutaway?' There is no throttle slide cutaway to a CV carburettor.

I did say it was a generic diagram and the point I was trying to illustrate was that whilst the idle circuit operates throughout the rev. range the needle and main jet control the majority of fuel flow.
Whilst I am happy to be corrected, apart from the reference to the throttle cut-away, the diagram is a reasonable representation of a CV carb?
Perhaps float height should replace cut away? (Ref Factory Pro carb tuning guide)

 

[JBryan91]

Carbs are clean and back together with oem Yamaha gaskets. Synced and still can’t adjust rear a/f screws. pops occasionally and runs as before. Anybody want to buy a 95 max?……

 

[JBryan91]

Carbs are clean and back together with oem Yamaha gaskets. Synced and still can’t adjust rear a/f screws. pops occasionally and runs as before. Anybody want to buy a 95 max?……

I feel like an idiot but after I ran the bike for a minute and did a plug chop like MM suggested. I started with the easiest plug in the rear left and pulled it to find NOTHING. It had no deposit. The color was not biscuit, not foul, not wet, not black or sooty. So I reinstalled the plug and started the bike without the plug boot attached. I then verified that the plug boot, when grounded on the engine block was arcing and firing. So for grins and giggles, I pulled the plug boot on cylinder three and no change in tone. The bike still ran as it always has…..

HO-LEE-CHIT

 

[Fire-medic]

Well, when you get the primary circuit operational, and you hit VBoost, you're gonna love that bike!

This quote," the plug boot, when grounded on the engine block was arcing and firing," refers to the plug boot, with a spark plug in it, and with a good ground to the block/frame (somewhere) was arcing and firing, yes?

Just so you know, the cylinders are numbered LR #1; LF#2; RR#3; RF#4. Draw (print) a capital letter N, starting at the LR.

 

[JBryan91]

Well, when you get the primary circuit operational, and you hit VBoost, you're gonna love that bike!

This quote," the plug boot, when grounded on the engine block was arcing and firing," refers to the plug boot, with a spark plug in it, and with a good ground to the block/frame (somewhere) was arcing and firing, yes?

Just so you know, the cylinders are numbered LR #1; LF#2; RR#3; RF#4. Draw (print) a capital letter N, starting at the LR.

Don’t judge me I reverted to my “bush mechanic” method and used a screw driver inside the boot then held close to block. You can definitely hear and see spark. The bike ran as it always has with #1 and #3 boots pulled off. Explains why a/f screw wouldn’t adjust on #1 #3

Yes I’m aware of the order of cylinders. Sometimes I get it bass ackwards due to the order when you sync and adjust.

This Texas heat is not helping my brain any…

 

[Fire-medic]

Expecting a parallel-twin of 600 cc to pull like a VBoost stock bike, well, if you haven't ridden a VMax properly operating before, better bring some clean BVD's when it's firing on all four and 1200 cc. Here's hoping that you sleuth out the issue.

When I hit behavior like this, I go back to the carburetors. I'd also look at the valves to see if things are happening when they're supposed to be happening. What about the rear primary coils? Are they plugged in properly?

 

[JBryan91]

Expecting a parallel-twin of 600 cc to pull like a VBoost stock bike, well, if you haven't ridden a VMax properly operating before, better bring some clean BVD's when it's firing on all four and 1200 cc. Here's hoping that you sleuth out the issue.

When I hit behavior like this, I go back to the carburetors. I'd also look at the valves to see if things are happening when they're supposed to be happening. What about the rear primary coils? Are they plugged in properly?

Carbs are spotless and rear coils are not split and ohm out at 3.3. Ever heard of weak spark but good coil readings? Gonna get a compression tester and test when I return Sunday night.

The engine has always fired right up with a little choke and ran “smooth” otherwise with random occasional popping. I do not hear excessive lifter or top end noise. Whatever is wrong I think #1 and #3 share it.

Also wouldn’t hurt to check the crankcase for fuel in the oil. God I hope the cylinder walls haven’t washed down. I’ve only ridden this bike to work once and to a friends house…

 

[MaxMidnight]

...after I ran the bike for a minute and did a plug chop like MM suggested.

Suggest you do another chop but this time hold the revs at (say) 4K. If the cylinder is firing I'd expect to see some evidence of that.
You would also expect to feel heat from the headers.
Did you pull either of the front plugs to compare how they look to the rear?

 

[Hayden Belcher]

I feel like an idiot but after I ran the bike for a minute and did a plug chop like MM suggested. I started with the easiest plug in the rear left and pulled it to find NOTHING. It had no deposit. The color was not biscuit, not foul, not wet, not black or sooty. So I reinstalled the plug and started the bike without the plug boot attached. I then verified that the plug boot, when grounded on the engine block was arcing and firing. So for grins and giggles, I pulled the plug boot on cylinder three and no change in tone. The bike still ran as it always has…..

HO-LEE-CHIT

So wires or coil?

 

[JBryan91]

So wires or coil?

Coils are good. Not sure on the wires and boots. I found an older forum in reference to plugs and wires and found that you can order an NGK SB05F and get 7mm copper core wire at auto parts store. When the boots arrive Friday, I’m gonna build me a set and put it on the bike to see if that fixes my problem.

Suggest you do another chop but this time hold the revs at (say) 4K. If the cylinder is firing I'd expect to see some evidence of that.
You would also expect to feel heat from the headers.
Did you pull either of the front plugs to compare how they look to the rear?

The front plugs look excellent.

I know that this is not the correct way, but I did a cold compression check with a compression tester and got 120 psi on every cylinder. I’m terrified to continue running it to get a warm compression check because I don’t wanna further wash down the rear cylinder walls. The oil smells like gasoline.

My next question for the experts is would a faulty CDI box, allow the front two cylinders to get adequate spark and weak spark for the rear?