"Jaberoo" down (Mildura this time)

[geoffreywh]

Daffydd...... Rotec flat slide (updraft) carby. Large tapered funnel inlet (in place of Cub type air box) with K&N filter on the front 8" cube shaped airbox with carb heat flap. I don't like the right angle in the airbox, but the ram air negates the change of direction. I Have equal CHT's and r/h cylinders 100f hotter than left!... The Rotec Fuel (" injector") would work better so much than the Bing. ( In my opinion) To the guy with the XL600 I think you are on the right track. The TBI ( very similar to a flat slide mikuni ) atomises fuel better than the Bing and Soooo much better that the Marvel

 

 

[Dafydd Llewellyn]

Thanks, Geoff; I need to digest all this info. I'm currently working with a 2200, and naturally the 3300 is a different kettle of fish.

 

 

[jetjr]

Daffyd, a issue with the swirling and use of carb heat may NOT be the temperature difference but the fact in Jabiru carb heat air enters ina different direction and upsets airflow differently

 

I can even get similar effect with "half" carb heat

 

The heat sure richens mixture. And can act to drop a hot egt situation. Perhaps the evening of egt has nothing to do with temp of oncoming air

 

Im far less concerned with actual CHT or EGT levels but the spread thats the killer i think and why im keen on simple port EFI

 

 

[Dafydd Llewellyn]

Yes, multi-point EFI sidesteps all this difficult airflow business; but the certification difficulty of it means it won't happen quickly, I'm afraid. So I think some attempt at sorting out the airflow problems is a necessity until the EFI can be done. After all, there are people on this thread who want lots of development testing before the product goes on the market; that's surely true of any EFI solution. I like the idea of using the existing carbie as the throttle-body for an EFI system; that reduces the "hidden function" issues - one could use it to start the motor, thus testing it at every engine start.

 

I do suspect that the root cause lies largely in the existing airbox. May know more in a week or two; guessing gets one only so far.

 

 

[jetjr]

I agree the airbox is the cause of the issue , however throat is surely too sensitive to changes

 

On the upside theres maybe simple fixes to steadying airflow, even changes upstream of filter seem to have big effects

 

What about different foam style filters panels or just increasing size of scat to reduce velocity?

 

 

[Dafydd Llewellyn]

Yes, looking at possibilities now.

 

 

[Oscar]

Going back to the lead fouling issue for a moment, here are a couple of piccies (apologies for the quality) of one of the heads I have on a dummy engine I'm using for R&D purposes for developing cooling set-ups etc.

 

I have no idea of the history of these heads, they were donated to me for the R&D work ex a rebuild. They appear fairly much uniformly as this one, though there are noticeable differences in the amount of fouling between them all, indicating probably BOTH mixture and cooling differences between pots. There are no signs of warping /leakage normally evidenced by burnt oil deposits. They are thick-finned 'Mk.II models (i.e. with the exhaust pipe chamfer - style rather than the original flat-port and gasket heads.

 

The lead build-up is fairly evident on the head: there is a patch - just to the right of the inlet-side plug hole - that is 1.7mm thick.

 

 

The valve guide is good, well within tolerance, and the seat is ok as well - but have a look at the leading on the valve stem!

 

 

 

[Old Koreelah]

Please Mr. BP can we have ordinary lead-free petrol of guaranteed quality?

 

 

[dlegg]

I agree the airbox is the cause of the issue , however throat is surely too sensitive to changesOn the upside theres maybe simple fixes to steadying airflow, even changes upstream of filter seem to have big effects

 

What about different foam style filters panels or just increasing size of scat to reduce velocity?

I notice on my jab airbox setup that the k&n airfilter goes in back to front compared to a vehicle panel setup. Looking at the filter I can't see as how it could make a difference in flow. My filter is square in size, same measurements, and if installed horizontally rather than vertically, static rpm drops 150 revs, and full throttle runs much rougher. So even seemingly minor changes has a big effect on tuning.

 

 

[geoffreywh]

The inlet tract looks really wrong, from the inlet duct on the side of the fuse, then a tortuous path with scat hose causing all sorts of drag to the awful "cobra head" again with some scat hose, to a plenum of sorts (Much too small) with different length pipes to the inlet. It is not so much "why does it run so unevenly" more like "why does it run at all" I would have rather seen a 10" x 2" pancake filter straight onto the carb. With the carb heat arranged accordingly. Rotax get their air from under the cowling so it should work for Jabiru 3300? I wish the one I care for was 19- reg

 

 

[coljones]

Mr Shell is looking at 100NL as we speak. The Lycoming guy mentioned it at today's AOPA Seminar at Bankstown.

 

 

[Dafydd Llewellyn]

Do, please, look at a typical design standard before you decide how it should be re-designed. Here's one; it's an extract from CS-VLA. they are all pretty similar. In my lexicon, SCAT is a four-letter word.

 

INDUCTION SYSTEM.doc

 

INDUCTION SYSTEM.doc

 

INDUCTION SYSTEM.doc