[Aaron407]

I'm looking for some feedback about my plugs in the middle of break-in after a full rebuild on my '96 Formula Z 583.

Quick background: after a failed rod bearing on the mag side shortly after a top-end rebuild, the engine was completely rebuilt, including a replacement crank, end bearings/seals, cylinders, pistons, all gaskets, etc. I'm running both premix and injection during the break-in. It's currently running 350 mains on both carbs to make sure it doesn't lean out due to the additional oil. Jet needle clips in the middle. Runout on crank checked out within spec. Carbs were fully cleaned.

I have had virtually no WOT, but plenty of mid-range and a few very brief WOT touches. It seems to be running fairly well, but the mag side plug does seem to be showing a lot more oil than the PTO side and has fouled once so far (granted it was during warmup on a fairly temperate day). I had "tested" the oil pump with a drill when it was all apart and confirmed that it would bubble a bit of oil out of each tube, but that was about the extent of testing it and there was no way to confirm actual flow rate.

Anyway, are the photos below somewhat typical? There shouldn't be one side running significantly richer than the other, especially since the crank seals were replaced and there are new carb boots in place. I'm more wondering if this suggests the oil pump is pumping more to one side than the other. I'm thinking I might pull it into the garage, pull the carbs, and run the engine off of a drill with the plugs out while monitoring the oil on both sides to compare the output. Other than that, any suggestions?

Mag side plug:

PTO side plug:

 

[Aaron407]

In my quest to figure this out, I rebuilt the fuel pump in case there was a leaky diaphragm letting extra fuel into the mag side where the impulse line is connected. I also recorded oil flow from each injection port while spinning the engine with a drill on high speed and the pump held open. First in the video is the PTO side, then the mag side. There's a huge difference in the oil stream - it actually blew/splashed back on the PTO side, but was a clean direct stream on the mag side. Is this simply due to the rotary valve on the PTO side opening from the top but opening from the bottom on the mag side? Should this have any impact on things? Before anyone asks, I absolutely nailed the rotary valve timing when I reassembled, and the machine starts and runs well.

Here's the video:

Rotax 583 Oil Injection

youtube.com

 

[Aaron407]

I'd love any feedback on this. The rebuild of the fuel pump doesn't seem to have made a difference in mixture - the mag side is still black while the PTO side is brown. I'm guessing it's probably not a great plan to reduce jetting while still in the break-in stage running extra premix oil as it probably can't be read accurately, so maybe I should leave it as is for this tank and finetune on the next tank. I'm just a bit confused as other documentation suggests that the PTO side should be the one running richer with identical jetting, whereas mine is the mag side. Or maybe it's just the extra oil that's making it black, but I would have thought oil consumption/effect should be roughly equal on both sides.

 

[nm9stheham]

Good videos. I wish I knew enough to help here. I saw the blow-back on the PTO side and had to wonder if the piston rings were yet fully sealed. Were the cylinders honed prior to installation? How many miles of riding?

 

[David H]

Maybe just to get a conversation started.

So, you are running premix? What ratio?

Both plugs look rich but not crazy rich IMO. They look safe so I would take some comfort in that.

 

[Aaron407]

Yep, cylinders were honed before install. I've only put 30 miles on it since the rebuild, though, so the rings may not be fully seated yet. Hard to say. Compression has gone up from 120 to about 130 on both sides since the rebuild, so they seem to at least be starting to seat. In terms of the oil blow back, it's also possible that the intake airflow at WOT when the pump would be fully open would just suck all the oil in. I just can't help but wonder if that can explain differences in oiling, but I haven't seen anyone else having tested them like this to actually know.

I am running about 40:1 premix in the tank along with the injection. It's definitely nice to not worry about them being lean at any rate, but I do worry if the PTO side isn't getting the oil it should, maybe due to the blowback, which could cause it to not be as black.

 

[Aaron407]

Well, the problem swapped sides when I swapped the carbs, so it seems to be a carb issue of some kind. I'll be pulling them and giving them another thorough clean, put in 340 jets, then I'll test again.

 

[David H]

put in 340 jets, then I'll test again.

Maybe tell us what you find inside. Mains, pilots, air screw, needle clip.

 

[Aaron407]

I do know there are currently 350 mains, 40 pilots, and I confirmed 7DL7 needles with clips in position 3 yesterday. I am curious if I find anything plugged at all, though. I also had set the float heights according to the service manual, which apparently states a 38 rather than 40 mm carb basis, so I'll be checking those as well.

 

[nm9stheham]

That is indeed odd. I was going to suggest looking at the exhaust system carefully for the blow back.... Are you sure there was nothing near the carb inlets to cause a low pressure area to make this happen?

 

[Aaron407]

That is indeed odd. I was going to suggest looking at the exhaust system carefully for the blow back.... Are you sure there was nothing near the carb inlets to cause a low pressure area to make this happen?

Everything looks perfectly normal at the intake side, and the exhaust was fully cleaned during the rebuild. There isn't a bunch of oil making it back to the airbox anyway, so it would seem that it's all ending up being carried into the engine at any rate (obviously a good thing). I'm guessing it's related to the rotation of the rotary valve, but I really don't know. The machine seems to run strong at any rate, and I'd expect some kind of running issue if there would be an exhaust restriction on one side causing blowback as it also wouldn't be able to pull fuel in properly. I'd be very interested if anyone else could test this out on their 583 to see if it looks the same.

 

[Aaron407]

Also, one thing to keep in mind - the plugs were pulled when I was testing it, so the general flow dynamics of the engine might not apply (e.g., there would be zero compression). I don't think my drill will have enough torque to test it with the plugs in.

 

[nm9stheham]

Ah, OK all bets are off then as they say. You just need a bigger drill LOL. It seems that you are making a lot of good observations BTW.

 

[Dodosmike]

Aren't the specs for main jet different on PTO and MAG sides? Forget which is larger.

IS the "wetter" side the richer side?

If it was me I'd be cutting back the oil on the pre-mix and see what plugs look like then.

 

[Aaron407]

According to the proper spec info, both sides use 340 mains from the factory. The service manual that showed staggered jetting was also referencing the wrong size of carb (38 instead of 40 mm), which caused some confusion. Since the wetter/blacker side switched when I swapped the carbs around (with the same size of jet), the problem seems to be within one of the carbs. I'm not sure if they're both supposed to be running in the leaner or richer form of what I see on the plugs, so they're both coming out soon for a thorough bath.

 

[Aaron407]

As for cutting back the premix oil, likely by diluting it, I'm a bit hesitant as I'm still breaking things in.

 

[Aaron407]

So, I pulled the carbs tonight and gave them both a good clean with carb cleaner and compressed air. Everything looked good inside, nothing plugged nor built up. All components are identical between the two - main/pilot jets, needle jets, needles, needle clip positions, etc. I put 340 jets in place of the previous 350s, confirmed the float arm heights in both, confirmed the floats still float (in case one had a hole and was filling with fuel), matched the air screw positions, confirmed the throttle slide heights were identical at idle and WOT, fine-tuned throttle freeplay, synced the slides, confirmed the oil pump calibration, and ran it with a fair bit of mid to high throttle for about five miles.

And, it made no difference. Although it runs like a champ, the cylinder with the same carburetor that was running richer before still runs a bit richer. Since the issue switched sides when the carb did, I'm trying to decide if I should slightly lean out the richer side. I wouldn't really feel good about it since it doesn't make sense, but maybe I should try running a size smaller for the one main jet? I don't like the idea of running different needle clip positions, but maybe I'm just paranoid. Or, since it's not running in a risky lean condition, maybe I should just run out the rest of the premix and see what it looks like with just injection oil before making changes. Or just stop worrying since it seems to run well.

I'm open to any suggestions!

 

[snow n go]

My 2 cents worth, run out the premix,
Start running a tank of fuel sans oil.
After a few miles of fuel sans oil check plugs again.
So, tune it for the way you actually will be running it.

 

[Aaron407]

My 2 cents worth, run out the premix,
Start running a tank of fuel sans oil.
After a few miles of fuel sans oil check plugs again.
So, tune it for the way you actually will be running it.

I think that's probably a good plan.