KR-1S.co.uk Forum

I'm not using the 35's

Why would a bigger carb improve power/bhp? Sorry if i'm being daft, i can fix bikes till the cows come home but the dark art or tuning is a complete mystery to me, as is suspension!

Ok bear with me but if you pop a bigger carb on a bike then surely (unless you jet down, which kind of defeats the purpose ) you will need to enlarge the airbox to cope with the higher demand of the larger carbs?

Am I completely on the wrong track here?

If anybody wants (subject to an engine being spotless) I would consider doing an engine or two for those racing over the winter.

This is the latest Bemsee dyno graph.
This is with the original bottom end (not the one that I used the last time), using the same Bob Farnham tuned top end, KR1S spannies and a KR1S CDI;


Power through the rev range is up, but still not that great - however, this is the bottom end that seized :'-(

There was about a 3hp increase using the Bob Farnham top end over a completely standard top end

I'm having this discussion with a friend on facebook who thinks that I should be running at 40:1 oil instead of 35:1 and it is that he thinks that killed the crank.
He thinks that the higher percentage of oil means that there is a lower percentage of fuel, therefore the mixture is too lean which caused the seizure.
I pointed out that the right cylinder was running richer than the left and it was the right side that seized. The AFR on the right was below 12:1 from about 9k through to peak, however, he believes that dyno AFR's aren't accurate.
Here is the condition of the leaner of the two pistons;
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I would have assumed that a piston would be more likely to seize than a crank, however the front and the back of both pistons looked clean.
Not only that, I don't think that going from 35:1 to 40:1 for the oil makes a significant difference in AFR.
For example, at an Air Fuel/oil Ratio of 12:1 (by volume) for 40:1 oil mix, there would be 12 parts air to 0.975 parts fuel and 0.025 parts oil.
The effective AFR by volume of fuel is 12.307:1.
And the Air Fuel/oil Ratio of 12:1 (by volume) for 35:1 oil mix would be 12 parts air to 0.97143 fuel and 0.02857, giving an effective AFR by volume of fuel of 12.35:1 making a difference of in ratio of 0.043

....and then he goes on to say that it wasn't the oil mixing ratio that was the problem, it was the oil and I should have been using Castrol A747.
Now I know that the Castrol oil is good, however, I also though that the Motul 800 two stroke oil specially formulated for high performance two stroke race engines such as TZ's, RS's and superkarts should at least be better than Lidl's own brand budget vegetable oil!

Personally, I think it was a tired old crank that had done over 24k miles, used, abused and thrashed that happened to have let go (it happened to a KR1S of mine once before at the end of a season).
If I'd had the engine instrumented up to the eyes, then I may come to a different conclusion


...I think my calcs make sense, anyone like to correct me?

Castor synthetic blends are by far superior oils. Your piston looks a bit cold and could do with a large dollop of compression.

I know that Ben (Luders) uses Motul 800 with no probs, however, as I used A747 in my TZ before, I think I'll use that for next season.
As far as the piston condition is concerned, my friend on FB says that it looks like its running too hot and the brown mark in the middle is signs of charred oil deposits.
Considering the depth of knowledge on this forum, I ltake more notice of what is said here than I do anywhere else

"Castrol A747 is only recommended for premix systems. Its viscosity is too high for use in oil injection systems.
Castrol A747 is recommended only for very high performance two-stroke engines.
If used in lower performance, lower revving engines, excessive deposit formation may result"

[?A747 is specified as default oil for racing RS/TZ (125/250) by the manufacturers?]
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as said
the molecular weight means the more oil you use the leaner the fuel mixture will be.

if a chainsaw can run flat out at 13,000 on 40:1 then your KR can too
the manual specifies 33:1 but like everything issued as a factory recommendation will be on the safe side.

Castor based oils wont stay miscible with fuels for long periods - you should shake your tank between consecutive race days - you probably have to drain you carbs and tank between meetings to stop clogging.
I'm only stating the knowledge that traditionally castor oil has offered superior (film strength) anti-seize lubricity. It could be that (more modern) synthetics offer the same extreme protection but with more fuel stability.
Motul can stay in suspension for months (between uses/meetings)
disclaimer: I have not used castor oil

it can't be ruled out that gearbox oil didnt play a part in the crown residue or failure

this was the other bottom end with the road crank that didn't leak gear oil

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I just meant there are multiple points gearbox oil can get to either cylinder on the KR - I think it really is a Random Probability which side will fail on with a KR - my experience has seen right hand side failures though

the disadvantages of castor oil is the burnt deposits and the useful life of the tank mix.
I think solubility is the main concern for the amateur racer that wont be discarding mixed fuel after a race meeting and the periods between meetings

http://www.foxvalleykart.com/oil1.html
"But alas, the report on castor oil as a 2 cycle lubricant isn’t all good. Some of the gums and other components that Mother Nature put in the castor bean don’t burn all that well and they can leave a gooey mess behind that can make piston rings stick in their grooves. And the parts that do burn can leave behind a significant amount of carbon on the piston crown and the inside of the head. Virtually all of today’s castor-based 2 cycle oils as described as being “de-gummed” but that is really a relative term. They have less gum and leave less carbon than their non-de-gummed cousins, but it is still something the user needs to be aware of. One other negative you need to be aware of is that castor-based oils have a disturbing tendency to “fall” out of solution in gasoline when they get below 50 degrees or so."


on the debate of different blends of Motul 800 (whether its a road bike on the bottle or a dirt bike) - I doubt they would go to the effort of a mixing different blend on the bottling line or whether its just targeting a certain market or shop shelf with a label change.
Surely you would give a different formulation a completely different code? ?or is there anti-spark etc type issues for grass/forest type use?

you could do an experiment and put a petrol/A747 sample in a jar, and a Motul [or other brand] in another jar - subject them to conditions such as overnight temperatures in a van/pit garage and weeks undisturbed and see if there is visible difference - oil

I know when I used GPR2 instead of 2S there was (seemed to be) a noticible difference in performance (auto-lube). 2S was the Shell synthetic endorsed by Wayne Gardner at the time.

theres some very cheap 7-10mm USB borescope/endoscopes on Ebay and its no effort to insert one down a spark hole as part of a maintenance regime - less hassle and more useful than pulling off exhausts.

scooble wrote:I know that Ben (Luders) uses Motul 800 with no probs, however, as I used A747 in my TZ before, I think I'll use that for next season.
As far as the piston condition is concerned, my friend on FB says that it looks like its running too hot and the brown mark in the middle is signs of charred oil deposits.
Considering the depth of knowledge on this forum, I ltake more notice of what is said here than I do anywhere else

Charred oil is what you want, the clear parts of the piston are cooled by the fuel, those clean bits should be about 5mm from the edge of the piston in. When you get that the oil charring goes from black to brown then tan.

I've never had any of these 'gummed up deposits' using castor or castor/synthetic blends. Old R30 is bad if you leave it in the tank or float bowls. Takes 5mins in a ultrasonic cleaner to get rid of it.
Any spooge out the exhaust or excessive deposits is jetting and ignition not the oil.
Everyone with high end two strokes run castor/synthetic for a good reason. When synthetic oils stop working Castor starts working

i think your FB friend got a bit confused,if there is a black burnt area UNDER the crown then you have a problem,what TSI says makes sense regarding the carbon on the crown.
Ive always used 747 on the track,ive never had a seizure or excessive wear problems running at 30.1,wether its a tuned KR1,80hp TZ250,tuned h***a RS125 or a tuned RG5,
I jet for the day (weather/circuit type/rider),there is no other way of setting an engine,you cant Pre jet the week before,i wouldnt worry wether im putting out max HP for club racing as it really isnt the limiting factor to a good lap time,just look at the times of some of the guys on early TZR 250's and 350Lc's at YPM meets,there alot less bike than a KR1 in terms of capabilty.
Motul 8 is good oil but i do prefer to have the castor there for a track bike,i think this has to be one of the reasons for good engine longevity.
747 doesnt cause the problems that pure castor does (R30 etc),just drain the carbs after a meet whatever oil you use.

does anyone know how accurate the Dyna Pro AFR sensors are?

Looking at the colour of the plug on the 'leaner' side of the two, it looked like a health 'David Dickinson' type colour.
Anyway, the upshot is, is that I need a full crank rebuild on one, and an 'investigation' on the other.

I've had my 3xv on a dynapro dyno twice now:




Sadly we didn't use the sniffer on the final run, but I do have a pic of a plug chop from the right hand cylinder that was reading 12.5:1 on the sniffer:



Shows its very safe at 12.5:1. The left cylinder just dipped under 13:1 on the AFR (larger intake on the left hand airbox) I suspect if I plug chopped the left side it would show slightly leaner than the plug chop shown. My experience shows that the sniffer readings on James's dyno allow a good safe set up to be achieved. My 3xv did actually nip up on the dyno when the AFR was reading 14.5:1, the piston crown was still black and showed no signs of leaness. But the lack of piston cooling was the problem.

Dan

scooble wrote:does anyone know how accurate the Dyna Pro AFR sensors are?

Looking at the colour of the plug on the 'leaner' side of the two, it looked like a health 'David Dickinson' type colour.
Anyway, the upshot is, is that I need a full crank rebuild on one, and an 'investigation' on the other.

AFR isn't that accurate, EGT is much more reliable gauge to jetting/ignition.

Dan to do a plug chop on the dyno is worth doing but you need to do it in 6th gear with the highest gearing possible on. That way it takes a long time and realy loads the engine up. The normal 5 second run isn't long enough

Hi lozza,

Sorry i should have mentioned this, the plug chop i did was as the bike was set up on the dyno but on the open (private) road flat out in 6th for about 10 seconds.

Dan

Private road, flat in top must be a good driveway

On the dyno takes 20-30 seconds