cruzin image??

General discussion about Street two-stroke Suzuki motorcycles.

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D&D CHASSIS
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Re: cruzin image??

Post by D&D CHASSIS »

Why can't you premix a gt550?
Vintageman
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Re: cruzin image??

Post by Vintageman »

The engines crank bearing etc. are designed to get oil from the injection lines (some oil lines are for bearings others are for piston skirt area etc.). If your premix it really won't reach these bearing areas well unless you modify things. For example some 2 strokes only have injection lines that the feed carb intake port, but the engine cases typically have passages that allow the mixture to reach roller bearings directly for example.

Still I always run a little premix with injection oil (nothing to do with your question but good insurance especially if you want to ride aggressively)
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tz375
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Re: cruzin image??

Post by tz375 »

The 550, like the 750, has CCI - Crank Case Injection. Unlike other two stroke manufacturers that basically injected oil into the inlet tract, Suzuki chose to pump the oil into the cases where it is fed to the main bearings. The mains have oil slingers around them which use centrifugal force to get the oil into the big ends and from there is spills out into the crankcase to be burned.

Premix can easily get to the big ends, so that's not a problem, but the slingers effectively shroud the main bearings so they will tend to starve for oil. On the TR750, Suzuki used different main bearings and seals and kept the pump for the crank and used pre-mix for the rest.

If a crank is being rebuilt anyway, it's easy to trim the slingers into spacers so that they do not obscure oil flow to the mains. It would also be useful to drill the crankcases to get oil down to the bearings like other two strokes have.
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Re: cruzin image??

Post by tricky1962 »

I'm sorry, which?

"Not on these engines" or..
Vintageman wrote: If your premix it really won't reach these bearing areas well unless you modify things.
The guy was talking about modding for maximum power
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tz375
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Re: cruzin image??

Post by tz375 »

Or just for more power. :shock:

The question comes up from time to time as to why not junk the pump and lines and go to pre-mix. The answers were that it's not that simple on a Suzi triple.
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Re: cruzin image??

Post by Vintageman »

tricky1962

Not the first time I have heard people say just run premix for more power on the Suz. It's not like an RD for example where take of oil pump and put a block off away you go I hope my explanation and TZ clarify why you just can't do this:. And the person reads wanting "more power" and is going to run it hard. Many have read such statements on posts and articles like this and have ruined their bikes in short.

If you google there is another article for modding a T500 for power. Runs both premix and the oil pump is still used for reliability during hard running. That article says something like if you want more more power on the last bend of the race disengage oil pump to get a tad "more power" maybe just enough to win by a nose. He also adds a disclaimer it will shorten life of motor.

I pointed out mistakes in the article and should have been reviewed back when. Since we put this article here for all to see it was worth clarifying and showing mistakes.. Us that return here regularly have a lot of experience with these bikes now.

This should prove to be a good post for others in the (if the next person reads its all)
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tz375
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Re: cruzin image??

Post by tz375 »

More power without the pump?

So small it's not relevant. Think about it. there's the friction in driving that last gear train plus the power to rotate the pump. Add that up and you get what? 1/4hp or so. People often fear that the pump might fail or that the old oil feed with its leaky or blocked oil lines will starve the bottom end of oil. Pumps are extremely reliable and oil lines can be cleaned and check valves replaced if necessary.

Vintageman mentioned Yamahas. I always run the pump on a street RD and always run pre-mix on my TZ's and teh bottom ends of both are basically the same. On a racer, we want lightest weight and no extra parts that could fail at 12,000. On a race bike we often want to change the oil:fuel ratio, but on teh street there is no need. An oil pump has a variable output and really works well.

But Suzukis are not Yamahas and changing a Suzi triple to pre-mix and have it live is not simple and has no use on the street
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Re: cruzin image??

Post by Alan H »

Hi Tz. The CCI is actually Crankcase and Cylinder Injection (originally called Posi-Force).
As you said though oil goes direct to the main bearings/seals and also direct to the inlet/cylinder area so no oil goes into the carbs. The inlet injector does oil mist the pistons/cylinder walls and big ends.
With oil in the carbs, the mixture has to be richened considerably as there isn't as much petrol in there by whatever ratio the oil/petrol mix is that you use. EG with a (say) 40:1 premix, then the jets may have to be 2.5% bigger before you start to try and calculate how much bigger they need to be if you fit pod filters or port it, or rev it higher. The Yamaha system basically just injects oil into the inlet just on the engine side of the carb(s), so there isn't oil in the carbs, but in effect it runs on premix. That's why you can premix a Yam without too much hassle. I think Kawasaki and possible Bridgestone had some sort of CCI system, but called it something else. It wasn't as sophisticated as the Suzuki CCI though. The pumps are very reliable and let's face it, running something in oil has to be good for it's longevity. The crank oil slingers are made to get used oil away from the bearings, so if you don't mod the cranks, the bearings don't get lubed.
Now the SRIS system can be blanked off if you run high revs mostly, it's just to recycle the oil from the bottom of one crankcase to the inlet of another after town running. The CCI system lubes better while using less oil and gives better engine reliability.
I've never heard of anyone tuning a GT550 for 'maximum power'. It's a bit small to race in the 750 class whatever you do. My A model is tuned for fast road (must get it on a dyno!) and has skimmed head and polished/matched ports - Mick Abbey chambers. He said he expected 'about' 20hp/cylinder. Good at low speed and very good at high revs. Not particularly economical though, as it tends to be spanked most of the time!
Think of how stupid the average person is, then realise that half of them are more stupid than that.
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tz375
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Re: cruzin image??

Post by tz375 »

Alan, good to hear from you.

2.5% change in jets is the same as a 100 to 102.5 or say a #200 to #210. Most bikes are not that finely tuned that a small change is even noticeable unless they are already close to the lean limit. It is good advice to be aware of the potential change but somehow people seem to think that a change to premix requires a significant change in jetting, and that's not really the case.

But on bikes of a certain age that were jetted lean to get through the first generation of emissions regulations and now running on an ethanol mix that causes a slight leaning, out may just push them too far.

60hp would be a significant increase over the stock 38 or so at the rear wheel from a GT550, so Mr Abbey must have worked his magic on those ports. That's almost as much as an RGV250.... Progress really shows up our old bikes as the slow lumps that they are.

FYI I have a 550 barrel on the bench with 44mm wide inlet port with no bridge and exhaust is currently 42mm wide and way up high compared to stock and so far no breakthroughs. The real issue is those tiny transfers and not a lot of meat to keep grinding through. Roofs can be raised a little and both sides can be widened a bit but not as far as they need to be.

This barrel is a badly worn spare, so it doesn't much matter if we break through into fresh air in search of horses. There may be some more hiding in there waiting to be found. I'd be very interested to see the dyno chart when you strap it down and thrash it.
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