Outer crank seals / Carbs

[Andy4k6]

Hi, I'm back again.

I have been testing my engines again today and on the whole they seem to run fairly well mechanically.

I have found 2 issues though which I hope you can advise on.

The left engine when started on the hose revs to 3500 and doesn't wish to come down and if it does it's only to 3000.

The right engine seems to idle at 2000 rpm and although it will rev up I have to move the throttle more than 1/4 before anything happens. The throttle cable is correctly adjusted.

I know adjusting the idle is fairly easy however I am about to rebuild the carbs on both engines shortly and I am concerned with this being 21 years old and still on the factory engines which have never been rebuilt ( paint all unbroken on everything except the cylinder head bolts) could I be having outer crank seal issues causing one of the issues?

How can I tell without striping the engine and carrying out a vaccum and pressure test?

Also once I have rebuilt the carbs how will I know if I have a problem or not as I will be tuning the carbs and if I do have leaking seals will I not be masking the issue when I am tuning by upping the fuel going into the engine?

Many thanks

Andy

 

[racerxxx]

Well go thru the carbs, but the boat should idle at 3K, not 2K. That way in the water the idle should drop to roughly 1500 rpm. The only way to test the crank seals is thru a pressure test.

 

[Sportster-2001-951C-Stock]

A couple quick and dirty ways I've used before are to test if the idle changes when spraying a volatile solvent such as carburetor cleaner around the seals, or an idle change from dropping some motor oil on the seal while running to temporarily enhance sealing.

The second method is to run the piston to the bottom of the hole and connect an air compressor to the plug hole, plug the exhaust and carbs if the intake tract leaks using rags or tape and maybe a cooling hose or two to create some small amount of crankcase pressure in the crankcase, don't exceed more than a few psi to avoid popping the seals out.

Then while pressurized slightly ( plenty of air will be leaking from various places, such as out the pisser vent and through your rags stuffed into the exhaust) spray some soapy water around the crank seals, rock the crankshaft back and forth and watch for air bubbles appearing in the soapy solution.

Otherwise, the service manuals describe removing the exhaust pipe and installing a gasketed plate (this can be made of plywood and use a piece of rubber innertube as a gasket). This method of sealing up all openings allows for a true rate of leak check and is quite reliable.

 

[Andy4k6]

Thanks for the info,

Can the outer seals be replaced with the engine still in the boat or is it a crank out job?

Many thanks

Andy

 

[hotrodssnova]

I didn't see what boat you have. Usually, the case has to be split to get the pto side seal out.

 

[Andy4k6]

Sorry I should have said.

It's a 1995 speedster fitted with 2 657x engines.

Would you recommen rebuilding the carbs and take it from there?

Many thanks

Andy

 

[hotrodssnova]

Well, I would. But being that old of a boat, rebuild is probably in your near future. You definitely have to split the case to replace crank seals on the 657x.

 

[Andy4k6]

I'll be honest I'm trying to avoid removing and stripping the engines.

Although I'm certain I have the skill to do it time and money are not on my side. I also don't have the alignment tool.

The engines have never been rebuilt although the heads have been off both of them at some point. Non of the drive bearings or impeller bearings showed any signs of ware and appeared to be the original ones.

The boat has been laying around for 10-12 years and I don't think it had much use in florida before being imported into the uk. So any issues with it are most likly going to be age related instead of wear.

I will rebuild the carbs and give it a water test / tune and see if it runs well or not.

What symptoms should I be looking for other than it permanently being too weak?

Many thanks

Andy

 

[Sportster-2001-951C-Stock]

Rebuild the carbs? Based on previous discourse I would say absolutely! But, aren't there any confirming symptoms of hesitation usually associated with detonation? I would fully expect you should be experiencing some form of hesitation, this would definitely confirm the mixture is too lean.

The reason is, clogged carbs are a primary cause of premature piston meltdowns (overheating the aluminum piston from the crown on down), second only to failing piston ring seal.

Normal engine wear vs lean carburation:

Usually in the case of tired piston rings due to normal wear it's not the center of the piston that gets torched first, the side of the piston usually is damaged due to heat from combustion gas blow-by past the rings down the side of the piston damages the thin oil film lubricating the cylinder wall and piston skirt galling takes place due to the lack of lubrication. This is why ALL 2-strokes are destined to seize if not rebuilt prior to the event.

Lean carburetion causes elevated combustion temperatures, due to abnormal combustion (detonation occurs, by definition combustion ends prematurely). The piston as it heats, expands normally within limits of the design clearance tolerance but in the case of detonation the piston expands too much due to the excess heat of lean combustion and actually becomes an interference fit in the cylinder to the point the oil film cannot provide lubrication, then galling of the piston skirt takes place or the top of piston might actually melt.

Many racers searching for the best optimum power try to run as close to this pont as possible b/c the engine often makes it's most power at the knee point of being on the hairy edge of too lean. This isn't practical for the daily driver recreational user, it's best to be a little on the fat side.

As you probably know, many racers rebuild between races and while rebuilding this gives them the opportunity to investigate and compensate many performance parameters, such as by inspecting the underside of the piston crown around the wrist pin for traces of carbon they can determine if the piston crown is overheating (there should be no carbon deposits from fuel decomposing underneath, on the bottom of the crown). Also while torn down, they make note of the quantity of oil puddled in the crankcase, the general rule of thumb is the puddle should be enough to just wet the cranks wheels, no more. If not, they consider increasing the ratio. BTW, increasing the ratio might involve rejetting to compensate for lower octane as the fuel is further diluted by lubricant. Yes, these are the pros who might rejet carbs during a race to compensate for changes in temperature and humidity.

This is a lot to go through thus simply isn't practical for the average Joe, we're more willing to give up the extra 50RPM and 5ftlbs of torque in favor of simplicity and longevity.

 

[Sportster-2001-951C-Stock]

Although I'm certain I have the skill to do it time and money are not on my side. I also don't have the alignment tool.

any issues with it are most likely going to be age related instead of wear.

I will rebuild the carbs and give it a water test / tune and see if it runs well or not.

What symptoms should I be looking for other than it permanently being too weak

Andy

Yes, I concur with your approach, it's not as if you can drive down the street and exchange for a reman as some folks here are able to do. Thus, I can imagine your approach must be considerably more thorough and cover more territory.

Honestly, tools are of great value and can pay for themselves quickly, sometimes this isn't the case.

I agree concerning age, barburetors tend to corrode with age, especially the aluminum variety, these aren't a corrosion resistant zinc alloy.

First confirming symptom of being too lean is hesitation, 2nd symptom is the engine runs like a raped ape at WOT. When tuning a 2-stroke, you want to hear some occasional 4-stroking burble, especially when the engine is unloaded. Ideally the engine 4-strokes with no load and as you progressively apply load it clears out and begins firing every stroke this is the sweet spot.

If you were to go to the 2-stroke dirt bike races or perhaps you recall from days gone by, at the start line the racers will rev their engines in anticipation of the go signal. Listen carefully to these 2-strokers revving and you'll notice the engines don't seem to be firing on every compression stoke but as the rope drops and the racers release the clutch those same engines sound completely different, they're no longer sounding like they're missing, you can definitely hear the cylinder clean out and begin hitting on every compression stroke. The reason is, a 2-stroke must be kept on the rich side of the knee point to avoid detonation, an unloaded engine isn't making heat and as the engine becomes loaded, dynamic conditions require that previously excess quantity of fuel.

We used to know our tune was getting close when we could pull in the clutch and twist the throttle and hear the 4-stroking, then as we engage the clutch this quickly and reliably transitions to firing every compression stroke. In fact, we didn't used to have electrics or the primitive mechanical carb rev limiters, our rev limit was in the mixture tune. That rich mixture rev limiter strategy kind of went away as manufacturers were forced to comply with emissions limits and rev limiters were implemented into the new CDI systems.

 

[hotrodssnova]

Nicely said sportster! Do the carbs, and then try the spray trick on the pto side. That will tell you something. The mag side should be completely sealed. The starter, mag housing and mag cover, and harness all are water tight. You won't get any spray in there.

Edit
I would think the rv seals would give out before the end seals. Opinions? Experience?

 

[Sportster-2001-951C-Stock]

Andy, something else we lightly touched on previously but didn't completely discuss, is cooling. You had said you were confident water is circulating through with good flow as the engine is revving and making power. Idling and low speed only requires the jacket has filled with water (pisser tell-tale is trickling), flow volume not nearly as important until the engine begins making real power then flow is absolutely necessary.

So your description of water gushing from the jet pump hose seems adequate but I want you to examine how you assembled the engine. Specifically, I want you to consider how much sealant you used during assembly b/c many times I've seen where a ton of some slimy silicone sealer was used, so much that water flow was blocked by the excess quantity of sealer.

Generally I avoid using sealer when possible b/c I hate having to clean that goop off when those come to me caked with it. Torqued properly and in good condition surfaces rarely leak when assembled with care, cleaned well so no remnants of gaskets and sealers are present before assembly. Of course sealers will be necessary in some cases, such as hose barb threads and water jacket through-bolts, water jacket stud nuts, and such. Usually just enough to fill the threads, a thin coat basically.

Just in case some of this sparks your fancy, trying to cover all the bases here...

 

[Andy4k6]

Wow such a lot of useful information there!

Thank you very much for taking all that time.

I have never stripped the engines or had the boat in the water, so I'm unable to advise how it drives (there is so much needing work as most of it was siesed or needed work).

The engines have been run twice out of the water in my ownership and seem to run ok other than the issues above.

One of the cylinders needs a repair as part of the edge that holds the water seal has corroded away so while I'm taking the head off that engine I'm going to do the other and change the seals and can inspect both engines while I'm there.

 

[Sportster-2001-951C-Stock]

Okay then that's the right approach, and don't hesitate to ask Q's as you make progress, we all learn something new most every day. The BRP factory shop service manual for a ski that uses your same motor will help in many ways if you haven't downloaded one just yet. (FWIW)

 

[Andy4k6]

Yep I already have the seadoo manual for the boat which has been a big help already.

Are there any carb stripdown videos or threads knocking about? I don't think I will need one but a bit of advise always helps.

Also for the rebuild do I need to strip it down to every last piece because most of it seems to be clean and working well I just need to change the filters, seals and diaphragms and give the inside a clean out.

I still have loads to do before I'm ready for a water test but I'm hoping to get it on the water before September. I just hope I don't need crank seals or anything else as I'm already about $4500/ £3000 into the boat and have loads still to do.

I'm really grateful of all the help I'm terrible for over worrying about things and the excellent advise really does help spur me on with the project.

I keep thinking about make a project thread, I might get on and make one might help the project move on a little further.

Andy

 

[Sportster-2001-951C-Stock]

The carbs shouldn't need to be completely disassembled, no need to remove the butterfly shafts for instance. For the needle mixture adjusters you can turn them inward till the seat lightly on their stops and count the turns so you can duplicate the original position and/or compare it to specification.

Specification settings should work well, if not the carb probably isn't clean and that can be a challenge as the tiny passages do corrode and thus become restricted due to the natural corrosion.

Maybe you have the Mikuni SBN owners manual, there are some good drawings and description of how the carbs operate. You're probably familiar with the float type of carbs and these really aren't much different except these are using the metering diaphragm to regulate the quantity of fuel in the small metering chamber as opposed to a float bowl.

Engine vacuum travels inward trough the orifices and pulls the rubber metering diaphragm inward, this pushes the metering arm against it's tension spring and lifts the rubber tipped metering needle off it's seat allowing fuel to enter the metering chamber from the fuel pump inlet side (through a passage from the opposite side of carb).

Keep your original metering springs and avoid bending the metering arm, you should also attempt to confirm "pop-off" pressure once the metering arm/needle/seat/spring are in place before buttoning everything back up. "Pop-off) pressure is the amount of pressure on the fuel inlet passage required to force the rubber tipped inlet metering needle against the metering spring and off it's seat. This pop-off pressure is a baseline that's dependent on airbox restriction and dynamics of the vacuum signal inside the intake manifold. Factory spent hours tuning this for good low speed operation, and if it's kept close to this there won't be any low speed lean hesitation or excessive over fueling.

Also if you'll notice, most of the screw heads look like standard phillips head screws but there's a dot on the head by the X, denoting a JIS Japanese standard screw head design, it's similar but the geometry isn't exactly like a Phillips, the dimensions are a metric version. Maybe you're already familiar.

Anyway, the screws are quite tight from the factory if the carbs have never been rebuilt due to they may have put quite a lot of torque on them, use thread locker or just there's been some galvanic reaction over the years. I want to advise, you'll need a good quality screwdriver most of the time, with hardened bits not an el-cheapo worn out Phillips from a dime store. It helps to press hard while breaking them lose to keep the bit from twisting out and boogering the head of the screw. You might discover a bit of heat from a small pencil torch helpful in case one or two are particularly stubborn.

You'll need to remove the high and low speed mixture adjustment screws and probably the high and low speed jets located under the kidney shaped metering plate inside the metering chamber under the metering diaphragm. This will allow for blowing the crud out through the passages, sometimes there's a surprising amount of junk in there.

If the carb was hesitating coming off idle to begin with and you discover the thimble shaped fuel filters in the inlet side aren't totally plugged, the reason usually is corrosion in the low speed "Pilot" metering circuit you just read about.

In the case of my 951 carbs, there was an imperceptible amount of corrosion in the pilot holes causing hesitation and even after stuffing a wire through them still some hesitation existed. Not recommending this in your case b/c the carbs are tuned quite differently and not the same model (951 uses the SBN-46mm "i"(mproved) but my solution involved going to a larger pilot jet to compensate and get her on the fat side enough to eliminate hesitation. Hopefully you won't need to fuss about opening up the pilot passages or try getting more fuel through them and a good cleaning does the trick.

There are numerous cases where posters have given up on cleaning their old corroded carbs following several attempts and installed brand new ones which of course completely eliminated their lean hesitation issues.

Sounds like you've got the concept, take your time and be meticulous, devise methods to test and inspect. For instance, one of my favorites is placing a dry paper towel in the jet pump outlet for a few days after having changed the pump oil in case the cone fill plug is leaking I can witness this on the paper towel before losing the lubricant into the water and damaging the pump bearings.

Cheers!

http://www.mikuni.com/pdf/sbn_manual.pdf

 

[Andy4k6]

Wow, you really know your 2 strokes and carbs

Thank you very much for the info and link they will come in seriously handy.

I only use decent tools where possible, I'm an ex mechanic and still keep all my snap-on and Mac tools to hand. Can't do a quality job without quality tools.

Andy