Running on 1.5 cylinders

[SuperJet-Dave]

The motor has been running rough for while (2 seasons at least). Put in a new CDI, new spark plug wires (via jetskisolutions.com... great job!), new spark plugs. 4.2 k-ohms between boots as expected. Running a little better, but still rough. I pulled one boot from the plug, and runs similar. Can start the motor this way and runs similar. Put boot back on. Start motor. Pull the other boot from the other spark plug, and engine stalls. I can start the motor this way, but will not idle, need to pull the throttle to keep running, but it does keep running, barely. Spark plug in this cylinder is a little wetter and browner than the other, after 1 ride. I have rebuilt carbs last season and did not effect the rough running. Checked all the bolts on the motor head and exhaust connection (except 1 I could not get to). All seem tight). Ski rides ok, just seems to have a reduction in power (like maybe 20%).
BTW, this is a 2004 Superjet with Pro-tec head, Coffman exhaust, b-pipe.

ARRRG. Need help! ANY SUGGESTIONS on what the heck might be going on?

 

[Harbor]

Do a compression test next

 

[SuperJet-Dave]

165 psi in “good” cylinder, 155 psi in “bad” cylinder. While not ideal/perfect, the compression test seems to be acceptable. Within 10% of each other.
Also swapped the spark plug wires (simply switched which spark plug the wires went to) with no impact. So it is not the coil.

 

[Quinc]

reeds?

 

[Harbor]

Iam not so familar with the protec head, it's seems odd your compression with what I assum is a fixed dome oring'ed head is still only 165 in the good hole ? Both seem lower than I'd expect. You'd think atleast 175 in the good hole, my R&D put out at least that, actually closer to 185. Wonder how accurate your gauge is? Are you using the long reach adapter in the plug hole ? It's threaded long like the spark plug, the short reach adapter lower the compression number by around 7-9 psi. 155 should still fire though just odd.

Anyways it could be a lot of things. Air leak, cyl lean, cyl rich, restricted idle fuel circuit, reed pedal, carbs idle out of sinc, You might have a look at your piston wash, also verify your not leaking water into the low cylinder steam Cleaning the piston. I'd assum you richeden up the low cylinder already via the low screw ? Leaned it as well, was there any change ? You could remove the air filters and watch for spray back out of the low cylinders carb will it idles to rough check the reeds. Do a engine pressure test.

 

[SuperJet-Dave]

Iam not so familar with the protec head, it's seems odd your compression with what I assum is a fixed dome oring'ed head is still only 165 in the good hole ? Both seem lower than I'd expect. You'd think atleast 175 in the good hole, my R&D put out at least that, actually closer to 185. Wonder how accurate your gauge is? Are you using the long reach adapter in the plug hole ? It's threaded long like the spark plug, the short reach adapter lower the compression number by around 7-9 psi. 155 should still fire though just odd.

Anyways it could be a lot of things. Air leak, cyl lean, cyl rich, restricted idle fuel circuit, reed pedal, carbs idle out of sinc, You might have a look at your piston wash, also verify your not leaking water into the low cylinder steam Cleaning the piston. I'd assum you richeden up the low cylinder already via the low screw ? Leaned it as well, was there any change ? You could remove the air filters and watch for spray back out of the low cylinders carb will it idles to rough check the reeds. Do a engine pressure test.

Yah, I bought an Actron compression gauge for $30, and it bounced around a bit, so I kind of averaged the numbers. I used the long adapter. The high cylinder was at 175 the first time, then when I did it again was more like 165. The low cylinder was more like 165 the first time and then was 155 the second time. When I checked last year, they were more like 195 each, with a loaned tester from Pep Boys. (I tried the loaner again, and it was broken, so I ended up buying the Actron). So... the actual numbers are suspect, but the <10% diff is likely real. I adjusted the low adjuster richer and leaner with not much change (I think they are at 1.25 turns out now). The spark plugs tend to be wet, So if anything it is likely running rich??
I removed the air filters, rev'ed the motor, and noticed some more spray coming out of the carb with the lower cylinder psi. Does this mean the reeds might be damaged on that side?

 

[Harbor]

Oh ok, Yea my R&D was actually 187/192 but was boarded .5 over. Ideally try to use the same gauge each time like you did, that's good, That new gauge might be suspect like mentioned or you've got top end wear... Also things like fuel/oil sitting on top the piston can make an initial higher reading till it dissipates and changes in cranking rpm during the test can sku the numbers lower, like when the battery start fading slightly on successive tests but still cranks seemingly normal.

You might make sure the suspect cylinders carb isn't dumping fuel at idle, if not already checked. Also the other checks mentioned.

The reeds on that cylinder could be suspect if it's spitting out more than the other carb. One thing I hate but is part of the equation some times is taking stuff apart and not finding anything. I had a ski here and used a bore scope to inspect the reeds thru the carb and intake throat. I could see all the edges of the reeds sitting on the reed cage and was able to iliminate obviouse damage on those without taking the ski apart. They were carbon V-Force reeds though...

 

[Harbor]

Attempted to use my home fiberbore scope to view stock reeds, little too dark, maybe week battery, but I hate this one, that's why it's at home lol.. It has a small light source compared my snap on I have at work which is much brighter. The stock reed cages have that rubber lip the reed sits on.. was easy to check reed and rubber with the manifold off

Good luck..

 

[Freakrider]

In my experience pro-tec orings didn't last very long from it's one piece design and engine vibration. Engine builder Chucky told me the same thing and advised me to switch to an ADA design which is much more reliable in this regard.

 

[SuperJet-Dave]

Oh ok, Yea my R&D was actually 187/192 but was boarded .5 over. Ideally try to use the same gauge each time like you did, that's good, That new gauge might be suspect like mentioned or you've got top end wear... Also things like fuel/oil sitting on top the piston can make an initial higher reading till it dissipates and changes in cranking rpm during the test can sku the numbers lower, like when the battery start fading slightly on successive tests but still cranks seemingly normal.

You might make sure the suspect cylinders carb isn't dumping fuel at idle, if not already checked. Also the other checks mentioned.

The reeds on that cylinder could be suspect if it's spitting out more than the other carb. One thing I hate but is part of the equation some times is taking stuff apart and not finding anything. I had a ski here and used a bore scope to inspect the reeds thru the carb and intake throat. I could see all the edges of the reeds sitting on the reed cage and was able to iliminate obviouse damage on those without taking the ski apart. They were carbon V-Force reeds though...

I am not sure how to check if it is dumping fuel when idling, because the throttle is not open and cannot see into the carb. I am probably missing something in what you are saying.
Never messed with the reeds before. Can you inspect and replace them removing the intake manifold, with the motor in place, or do you need to remove the motor? Do you just look for physical damage to the reeds, and if there is some replace them? There seems to be several aftermarket options/materials for reeds. Some quite pricey. Any reason to not get the OEM reeds (full Yamaha OEM new assemblies can be found online ranging from $42 to $145 each).. quite a range!?
Also assume I need to replace both gaskets (8 in the pic). Do you also replace the plate (7 in the pic)?
Thanks.

 

[SuperJet-Dave]

In my experience pro-tec orings didn't last very long from it's one piece design and engine vibration. Engine builder Chucky told me the same thing and advised me to switch to an ADA design which is much more reliable in this regard.

Thanks, that may be a next step if I end up not finding damaged reeds. Do you know if o-ring wear would show up as low compression in a compression test? (showing my ignorance here ;-) )

 

[Harbor]

I am not sure how to check if it is dumping fuel when idling, because the throttle is not open and cannot see into the carb. I am probably missing something in what you are saying.
Never messed with the reeds before. Can you inspect and replace them removing the intake manifold, with the motor in place, or do you need to remove the motor? Do you just look for physical damage to the reeds, and if there is some replace them? There seems to be several aftermarket options/materials for reeds. Some quite pricey. Any reason to not get the OEM reeds (full Yamaha OEM new assemblies can be found online ranging from $42 to $145 each).. quite a range!?
Also assume I need to replace both gaskets (8 in the pic). Do you also replace the plate (7 in the pic)?
Thanks.
View attachment 356905

On the fuel you just look in carb at idle and see if fuel is dumping or dripping out of the bomb sight onto the throttles blade. The manifold can be removed in the ski and inspected. The reeds need to be not broken or cracked/distorted, need to sit flat and seal on the rubber just under them, the rubber can't be distorted or delaminating from the reed cage to name a few.

The manifold and reeds I have is for sale, about $50 shipped to you and it has new gaskets and plate and is ready to go if it helps you....

I'd do 7&8 and the reeds and the carb base gasket not shown...

On the oring, if leaking you can get a sorta intermitant water flow and spitting out your over board water pissers, also it can lower compression and also can clean the top of the piston some.

To pressure test your crankcase/intake system plug your exhaust close to the manifold if possible, usually disconnect the head pipe from manifold and place smooth rubber Matt in lace of the gasket and bolt back together. Remove carbs and do the same with rubber... Then use a pop off pump and pump via the pulse fitting to 8 or 10 pis.... It should hold the pressure and not leak for at least 30 minutes. If it won't hold use soapy water in a spray bottle to attempt to locate a leak.. Front crank seal under mag cover, rear crank seal, intake gasket, cylinder base and case halfs etc

To pressure test your cooling passages, plug all your water lines and use the pump to pressurize via one head cooling nipple with spark plugs out.... It should hold pressure too....

 

[SuperJet-Dave]

Great info. Thanks.
If I can get some gaskets quick, I will remove the manifold and check out the reeds. Going on weeks vacation in a few days with the skis and not sure I can get it done beforehand. Can I replace the reeds without pulling the motor? If so, I might have a chance of getting it done prior.
Also, I assume I can remove the manifold with carbs attached, then I do not have to worry about the carb/manifold gasket. Is this a correct assumption. Sorry for all the basic questions.

 

[Harbor]

No I don't think you get the manifold off and back on with the carbs still attached. The upper outer bolts and tight and close to the carbs.. see pic, it's behind the carb stud...,

You can leave the engine in the ski

 

[SuperJet-Dave]

No I don't think you get the manifold off and back on with the carbs still attached. The upper outer bolts and tight and close to the carbs.. see pic, it's behind the carb stud...,

You can leave the engine in the ski

Thanks! The pic helps. The reeds are attached to the manifold. Not sure what I was thinking before...

 

[SuperJet-Dave]

Well I took out the reeds and they actually look ok. See pic. I will put the reed and manifold assembly I purchased anyways. Although I doubt it will make a difference since the original appears to be in as good a shape as the replacement.

The cylinders and pistons both appear to look and move ok.

Any other suggestions out there?

I won’t be able to test right away since I have the motor dismounted and driveshaft disassembled awaiting parts for another project.

 

[BEastman]

my stock superjet had the same problem, would not idel, on the spark plug there is a cap, tighen that bi+c# sounds stupid but it worked, it went for crap to brap in two mins lol. and do you have oem fuel/water seprater?

 

[SuperJet-Dave]

my stock superjet had the same problem, would not idel, on the spark plug there is a cap, tighen that bi+c# sounds stupid but it worked, it went for crap to brap in two mins lol. and do you have oem fuel/water seprater?

I checked the spark plug caps, and they are fully tight. No surprise, since they are new. A nice simple thing to remember to check though. Thanks.
The ski does not have a fuel/water separator.

 

[mbrick]

I checked the spark plug caps, and they are fully tight. No surprise, since they are new. A nice simple thing to remember to check though. Thanks.
The ski does not have a fuel/water separator.

I think he means the aluminum nut on the top of the spark plug, and not the plug boot on the coil wire. Yes, these will rattle loose and vibrate and then get metal dust in there and cause really annoying problems.

I'd suggest running solid top plugs to prevent it altogether, if your head uses the H length or E length there is a BR8HS (NGK 6715) and BR8ES (NGK 3961) solid top available.

 

[Quinc]

there is a BR8HS (NGK 6715) and BR8ES (NGK 3961) solid top available.

Know of any websites or ebay acutions that have these at a decent price?