Pre-Break in carb tuning

[NickCawks]

Good morning all! I just have a quick question. I've tried searching for an answer, but cant seem to come up with exactly what I'm wondering about.

This is in reference to a 657x, but I don't think it makes much of a difference.

I am still in the process of breaking in my motor. I know the best method of confirming the tune is correct is to slap new spark plugs in and run WOT for a bit then check the plugs. The problem is that I'm still in break-in and cannot go WOT.

Is there any particular and recommended method for confirming that a tune is at the very least okay during this process.

I started with the low speeds out 1 1/8th turn. The factory settings ask for 1 1/4th, but the 1/8th was done to compensate for the altitude I'm at.

From there I have been riding for 15-30 minutes at a time. Then pulling up to the beach and feeling the side of the motor and grabbing the top of the spark plugs. I recall hearing that the spark plugs should be hot, but not too hot to hold so that's been the main factor that has caused me to richen up the mixture. Does this seem reasonable?

In doing it this way I have noticed that the mag side cylinder is has been significantly hotter than PTO side. Due to this I have been very slowly richening the mag side carb. A question has occurred to me. Does the mag side just tend to run hotter than the PTO side? Or am I correct in thinking that this is a sign that the mag side carb is too lean?

Thanks in advance for your guys' responses! Carbs are one thing that makes me nervous and I never feel as if I know for sure that I'm making the right decisions with them.

 

[AKnarrowback]

Did you do a carb rebuild when you did the motor rebuild?

Are the gas lines new, you removed the original grey lines?

When the motor was open were all the coolant passages clear of sand, salt anything that would block coolant flow?

If you can say yes to everything above then set the carbs to the factory specs, run the proper heat range plugs, check them every once and a while to make sure you don't have any white or grey color on the plugs.

When you say you adjusted the low speed screws in one turn for alttitude I assume you are running at a higher elevation. If this is true then factory specs in a good set of carbs will not hurt the motor.

How are the plugs looking now? I'm guessing they are very dark with a little hint of brown on the electrodes, but not light brown.

The cylinder temperature differences you feel are from the cooling jacket flow, the carb mixture is not going to produce enough temperature difference to feel through the water jacket without doing damage to the motor.

A wide open chop and stop is a tool for checking the main jet, something you should not need to do on a stock calibration.

For some good carb info go to

General Technical Articles

And read up on the carb tuning pages.

 

[AKnarrowback]

Not sure what model you have, but the 657x was only used in 3 machines from what I remember. I have a stock 94 xp with the 657x running all stock carb specs except for the pop off pressure. The machine runs great at 80F and I ran it yesterday at 37F on the same carb calibration. If it was a sled dialed in for +10F and I was going to run it hard at -30F I would be concerned about burning the motor.

My point here is that the stock configuration for the carbs on the Sea-Doo is plenty safe and you should not have to worry about hurting the motor at all provided you have carbs that are clean and in good running condition and the fuel system is free of green goo and air leaks.

You are right to be cautious about carbs and hurting the motor. In my experience 90% of burned motors in sleds are carb related for any number of reasons, not calibrated for an aftermarket pipe, failure to rejet for lower elevation, not cleaned on a regular basis.

The Bombardier test and tune crews spent a lot of time dialing in machines before they gave the thumbs up on what the "official" specs are for that model for that year. They ALWAYS built in a safety factor that runs the machines a bit on the rich side but still providing good performance. The Rotax motors with the rotary valve seemed to be able to handle wider temperature and alttitude changes without requiring carb changes. My old 90 Mach 1 with the 580 could run from +40F to -45F without rejetting, my indy 500 piston port motor needed three jetting changes to deal with that much temperature change.

 

[POPPS]

AK is correct, the engineers carb their skis so that they run in a wide span of temperatures, and oxygen levels. I would not be doing any WOT tests till the motor is broken in. And, really, unless you are racing, doing a WOT plug chop is unnecessary. If the motor has no issues, and proper carburation, the plugs will always look like light ale.

 

[NickCawks]

AK - Yes to all your questions. The only reason I did not go right to factory setting because at my altitude (around 5k) is the stock settings cause it to load up unless at WOT. This is especially compounded by the lake I go to having the claim of the largest no-wake zone in CO.

As for the plug's current shape, I just reused my plugs from before the rebuild. They only had around 10 hours on them and I wanted to save the fresh plugs I have for when I can go WOT so they are not much help.

The top-end just got a bore and hone and the shop I go to cleaned them up really nice for me and the water jackets were exceptionally clean. I also did a very thorough cleaning of the rest of the pieces before reassembling as they had been sitting disasembled for a month and had picked up a decent layer of dust. I will double-check all the water hoses and make sure there are no unseen clogs. Do you have any suggestions on things I should check to make sure that my cylinders are staying evenly cooled?

The ski the motor is in is a 95 GTX. So far I have gone through about 2/3rd of a tank with the rebuild. The ski is running great and feels good. It has been nice to take the break-in period very slowly (in some ways) as I have been able to feel that the rings are beginning to seal a little better each time I take it out which is noted by slight power increase and better throttle response each time. At this point, I have still not taken the ski over 75% throttle and for the most part, have been yo-yo-ing between 30-50% (just enough to get it on plane). I have also been able to put this thing through a pretty wide range of ambient temperatures due to the time of the year. The ski has functioned well between 50-85 degrees F.

I feel fairly comfortable that the carbs are not putting the motor in a lean condition and are more or less in a good place. My main concern was noticing that difference in temperature between the cylinders which is the main reason I posted. I also want to note that neither side is hot, both are warm and allow to place my hand on them for extended periods of time, but the mag side cylinder is probably a solid 3-5 degrees hotter (I think I need to bring the laser gun out next ride so I can be exact in my numbers). I feel it also worth noting I have been putting significantly less importance on holding the sides of the motor then I have been on holding the spark plugs. at one point the mag side spark plug was just slightly too hot to hold in my hand for an extended period of time while the PTO side remained at a temperature that was easily held in the hand. Because of this I richened up the MAG side (by like a 1/16th turn) and noted that the plug was then able to be held.

Thank you guys for the responses. I had this thing rebuilt at the start of summer and then had a piston seize on me which was the cause for the second rebuild. I am very much trying to avoid this happening again which I think has me a little paranoid.

 

[mikidymac]

Never reuse plugs on a new engine. Seriously it’s $5 worth of plugs.

 

[AKnarrowback]

Why did it seize after the first rebuild?

 

[etemplet]

Why did it seize after the first rebuild?

That is a very important question.

 

[NickCawks]

Never reuse plugs on a new engine. Seriously it’s $5 worth of plugs.

It wasn't really a money decision just didn't know it mattered.. why does it matter? They are still pretty new and and spark just fine.

Why did it seize after the first rebuild?

According to the machine shop the way the piston looks indicated that the ski was run at wot before the engine was warm. I did give it a solid 7-10 minutes of warmup and not sure if I believe this was actually the issue. It had also just been moved from 5k altitude to sea level. I think this played a bigger part. I did reset the carbs to factory settings and was trying to get it from the ramp over to my brothers neighborhood which was about a 5 minute ride. Was gonna do a more serious test and tune once I got there. About half way there a piston ring siezed and the motor just puttered out.

 

[AKnarrowback]

A "four point seizure" is common on sleds that are run hard without a warm up, but it rarely takes the motor to a point where it won't run unless the abuse is repeated. On water craft it can still happen, but after warming up for 7 minutes it should never have been the cause of piston damage.

Do you still have the old piston, if so take a pic and post it.

 

[NickCawks]

I do and I posted it on the last post. Did it not show up?

 

[mikidymac]

Running lean from either poorly adjusted or dirty carbs and/or fuel system.

You did not seize it from a cold seizure, that's basically a myth on a stock ski.

As far as the plugs if you have contamination on the plugs from a seizure it can cause pieces to come off on the new engine and also make checking the new engine for being rich or lean difficult. For $5 it is better to be safe than sorry

 

[POPPS]

In 90 % of the cases, fuel starvation from the carb, or the fuel delivery system is the main cause of seizures.

 

[NickCawks]

The carbs not being rich enough was pretty much my conclusion.

I did pretty thoroughly clean the plugs but I get what your saying. I will make sure to out fresh ones in and not make this mistake again.