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Carb swop

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Carb swop

Postby Matt » Tue Jan 12, 2016 6:25 pm

Has anybody swopped a 32mm carb to 40mm carb on 2200 engine lately. Was it worth the effort. Did you get a power increase or was it a none event. I'm looking at doing the same thing but would like to know if its worth the effort before I ago ahead.

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Re: Carb swop

Postby Steevo » Tue Jan 12, 2016 10:20 pm

All I can say is don't do it!!!

Did mine last year. Quite a bit involved for very little gain and has a few downsides.

First off you need a new sump and induction manifold. Depending on what you have already, almost certainly a complete set of new induction pipes. I had mine cut and re-welded. If you do not have the later design heads and later design pistons then you will not get the full benefit of the upgrade. I already had the new heads but had 4 new pistons put in.

On most, you also need to modify the firewall else the new carb will hit (I had to have a little indent put in to mine, difficult to explain, it's like a little bracket on there but creates an indent to make room for the carb).

Once you have done all that and spent all that money, you will get a little extra power especially on climb out (I noticed the extra power straight away) but the 32mm carb idles much better than the 40mm carb and you get better fuel economy on the 32mm carb.

There was a variety of other little items I had to buy as well. At the end of the day, it was a lot of money spent but the gains don't warrant it.
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Re: Carb swop

Postby Steevo » Tue Jan 12, 2016 10:41 pm

Matt

Some actual figures for you.

After the upgrade, I get around 100fpm better climb, cruise speed the RPMs are 50-75 less than before to achieve the same cruise speed, static RPM is 50-100 RPM better.

Before upgrade the engine would idle smooth at below 700RPM, after the upgrade it runs rough below about 800RPM. For fuel it uses 1-1.5 litres more fuel per hour. To get the idle anywhere near smooth at lower RPM, I had to play around with different jets.

Full speed is irrelevant as you can almost achieve VNE with the 32mm carb.

One last minor point, it's now confusing buying parts. Usually they list parts by engine serial number ranges. Now I have to mix and match. If I sell my aircraft it will be very confusing for the new owner if he doesn't know exactly what has changed.
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Re: Carb swop

Postby Matt » Wed Jan 13, 2016 7:23 pm

Hi Steevo,
Thanks for posting. Been most helpful. What I was looking for was an increase in power to decrease me takeoff roll. I operate out of a short strip and wanted an increased safety margin.
I managed to pick up a second-hand sump and manifold. Been offered a used carb. I don't really want to go about modifying my bulkhead or my induction pipes. I'm not changing my pistons either. So looks like I'm going to give it a miss.
I posted on the official Jabiru tech forum and they advise not changing the carb. I did think they were going to advise to do it. They are going to post a list of Mod's that they recommend for my serial number engine. I'm interested in what they have to say.
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Re: Carb swop

Postby Steevo » Thu Jan 14, 2016 11:50 am

Matt,

It may not be as bad as that. My engine serial no. is 589 so an early engine. It started off with the smaller heads and mainly early design components. If you have a later engine, you may not have to change the pistons or the induction pipes (although induction pipes are highly likely). Depending on the build, you may not have to modify your firewall. The induction pipes can be cut and welded so they go in the right directions for the new manifold.

You do not have to change pistons anyway but if it's the earlier pistons then the compression is slightly different so it means you will not get the full benefit of the conversion (maybe 80hp rather than 85hp, but that's still better than the 65HP the standard 32mm carb engine had), but you will still get some benefit especially in climb performance and shorten your take-off roll slightly.

As long as you have the large heads, new sump and induction manifold you have a fighting chance of doing it with purchasing just minor things like nuts and bolts, if you already have the new sump, manifold and carb.

Even so, I still feel the 32mm carb is better suited to the 2200A engine in general. But if you want to get close to the full 85HP then you will have to do the swap.
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Re: Carb swop

Postby Matt » Thu Jan 14, 2016 3:12 pm

Steevo,
Mine isn't much newer than yours s/n 675. The real ball ache for me is my hanger is in the middle of know where, with no power. So its easier to remove the engine to any in depth work. I'd rather not do that again. The last two winters its been out.
I've asked Jabiru if the 32mm carb will work with the newer sump.
They have suggested changing to a larger diameter, reduced pitch prop, a climb prop. Which I have thought about before.
I was thinking how much do the newer heads and pistons contribute to your power increase?
They also suggested checking for brake drag and wheel alignment to reduce rolling resistance. Which is another good idea


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Re: Carb swop

Postby Garyo » Thu Jan 14, 2016 4:52 pm

what about the Hercules prop? a local had 1 fitted in Norfolk and said it climbed better and had a better cruise for fuel burn.. he did the LAA paperwork for it so should be straight fwd.

my jab s/n 1041 has the 40mm carb, I also have a cobra neck and there is loads of room before the firewall, but mine is a UL450 if that's any difference
tick over on mine I can get smooth to 500 rpm and a little lumpy on mag check, I can go to 400 rpm but starts hunting. but why would you want to have such a low tick over and risk an engine cut, I keep mine at 700 to 800 rpm. clean mag drop etc
fuel burn 1 up is around 8 to 10 ltr per hr. 2 up if I am not slogging it is 12 ltrs p h
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Re: Carb swop

Postby Matt » Thu Jan 14, 2016 6:10 pm

There are a couple of prototype mods for Hercules props on Ul and Ul-450. Not much on the approved props list for the SK. I'd probably email Hercules to see what they have to say.
I don't know if there is a difference between the SK and the UL in terms of bulkhead clearance.
Got my tick over set to 700 rmp. Tried it lower, didn't like it. When I first got the aircraft it was set to 1000. The thing didn't want to land!
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Re: Carb swop

Postby Steevo » Thu Jan 14, 2016 9:31 pm

Gary

Mine was about the same as yours when I had the 32mm carb. But now my fuel burn is minimum 12 litres. There is no way I could get that low in the rpm. I have always run my idle rpm at about 850 which it does run fine at but if I was to go much below 800 the engine would not be smooth at all. At around 650-700 it would cut out.

When I first planned to do this, everyone told me not to do it, even Gary Cotterell who did most of the work. He said he had never seen a 2200 with a 40mm carb run as nice as one with a 32mm carb. The 40mm carb was only put on there because Jabiru needed it for the 3300 engine and they didn't want to maintain different sets of parts. Plus Jab were always being criticised because they claimed the 2200 with a 32mm produced 80hp. In every independent test the max they could get out of it was between 65 and 70hp.

In all honesty, I should have spent the money on something else and listened to everyone's advice

Some of it may well be that the engine is still not run-in after the upgrade. I have only managed 6 hours since it was done.

Gary did say that not all firewalls need to be modified and it depends on how it was built, but most he has done did need doing. I cannot get a cobra head on mine. I probably could just about squeeze it in but there it is literally a tight fit before any scat hose goes on. Mine is an SPL-450 (aka a UL-450 that you need a different license to fly).

The long and short of it is that it was a very expensive upgrade that has given me a tiny bit more power but now has more downsides than before.

Steve
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Re: Carb swop

Postby Garyo » Fri Jan 15, 2016 12:54 pm

mine was supplied with the engine and the aircraft built with it in 2002/3
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Former Owner of
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Jabiru 450 UL
Engine serial 1041
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No Exhaust temp sensors
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No bells and whistles
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