woodburner

Lucky as I am... it IS indeed a "91" model... [:@]

1QwkSport2.5r

There a ton of these floating around. I got mine free. They will run just fine with good carburetion. Perry carbs for these are $50 USD. And work well from what I've heard.

woodburner

Having a real hard time starting this thing... sometimes it starts and runs like a charm, sometimes it doesn't even hint at firing.... I'm running straight 0/20 FAI fuel on a OS 6 plug.

1QwkSport2.5r

The sportsters have some hefty compression, so it should run pretty well without nitro. If it were me though, I'd use a long-reach glow plug. As for the not firing - They like a good prime like every other engine. If you're hand flipping it, prime it until its good and wet and backflip start it. That is if its got a good amount of running time on it already. If its new, you may need an electric starter. The compression was pretty lax on mine before it was broke it in, After a gallon or so the compression really came up. As always, make sure your glow driver is getting the plug hot enough. If the glow is good and bright, and its getting fuel, it should start easily. If you're using old fuel, swap out for some fresh stuff and if the glow plug isnt shiny and new, maybe swap that too. If after all of the usual stuff it still wont start for beans, try adding 3% by volume of acetone to give the fuel a little extra volatility.

Mine backflip start on one flip if I prime it 6 flips or so with the carb plugged. Works almost every time. I run mine on 5% nitro 20% castor though.

earlwb

The OS plugs are 3/4 length, in between a short and a long glow plug. Like 10qwksport2.5r stated a long plug would work better as it puts the glow plug element slightly lower down towards the combustion chamber.

woodburner

It now has the original K&B plug it came with...still not starting even with a fully charged ni-start. Might be the hot weather here (around 93° right now)... fuel is fresh. Time to order a new electric starter I guess...

Thanks guys!

woodburner

Finally got it started again. It likes a really HEAVY prime before flipping, and even then a LOT of flipping. It also leaks a lot of fuel from the needle valve thread... but I'm running it very rich during the break-in.

earlwb

I tend to cheat and use a electric starter most of the time. Sometimes for nostalgic purposes or just to show that it can be done, I'll hand flip the prop to start the engines. I either use a chicken stick or gloves as those prop blades are sharp. usually the engines won't start easily by hand if they are hot. You have to let them cool down. But many years ago when I was first in the hobby we didn't have electric starters, and when they first came out most of us didn't use them.but after you start using one, you get spoiled pretty quickly.

1QwkSport2.5r

I didnt have a starter when I broke my Sportster in either, it took a few tries before I got it going. I used a McCoy hot plug (#59) right off the bat, though.

Break the sportster in like you would a lapped iron/steel engine. After 2 gallons of fuel or so, the compression should be much better and it should start and idle a lot better.

woodburner

How's that about the CENTER hole on the internal pipe? It's just a tube... can't open it any larger.

1QwkSport2.5r

I took my baffle out altogether. Mine had too much backpressure. You could drill the existing holes bigger in the baffle but at the expense of noise. Drill enough holes and you might as well have just chucked the baffle in the first place.

turbo.gst

My Feedback: (8)

The Sportster 's muffler really robs power. I got a low DB BCM sport for mine. It is extremely quiet, plus it adds several hundred rpm. It is not a cheap muffler, but it fits so many engines I have ( ST 45-60BB, HB 40-61, K&B 61-65, Webra Blackhead/ Silverline .61). I have since bought a low DB BCM Sport muffler for many other engine as I am so happy with it.

My Sportster felt terrible when NIB. I broke it in with 25% oil. It took at least a gallon to get it to have good manners. Now, it is a one flip start every time and at a ridiculously low idle. I enjoy using the .65 every time I take it to the field.

1QwkSport2.5r

Other than the carb being snotty, my sportster runs well. Last time i ran it i got it to idle at 2200rpm with a good k&b carb. I am going to be getting a mig27 foamy from a friend that one of my sportsters is going onto. I'll probably get Perry's for them and make a couple mousse can pipes. My wife has 3 aluminum hairspray cans I can use.

I love the sound of my sportsters. Can't wait to fly one.

woodburner

What makes the Sportster's carbs so bad? I mean, mine leaks abit, but I'd like to understand more about the mechanical 'flaws' on mine. BTW my .65 is the 91 model.. the US ARMY drone engine.

turbo.gst

My Feedback: (8)

The carb on the drone engine was changed to make them cheaper to produce (as they weren't intended to idle anyway). All of mine are K&B #5800, some being Remote Needle Valve and most have the Needle mounted to the carb. I have 12 of them. I was afraid that the Modeler Direct sale was going to be the end so I loaded up on them. I would like to play with a drone carb and compare the internals with a stock 5800 version.

The stock muffler works well. They leak at the seams and look messy. Trying to gut them and make more power works, but the BCM makes more power and is quieter. I have people wonder what kind of engine I am flying when they see it in the air first. They have to come check it out as they refuse to believe it is a Sportster. It is a very nice application. As I said, the reason I bought my BCM is that I had so many engines that it fits( about 30). It might not be practical for everybody as they run about $50, but it is one of the best choices I have ever made. I love the combination!

1QwkSport2.5r

The carbs on the "91" engines is hit and miss. My two "91" sportsters have defunct carbs, but a buddy has one of the "91" engines and with his carb (looks the same as mine) the engine didn't miss a beat - it throttled perfectly.

Some work fine and others dont.

codycarlisle25

I made a bushing for my Sportster that allows me to mount a carb to the bushing. I saw that K&B did something like this on the 6.5cc and Webra did one for the Dynamix(.61) to fit the 91 Webra. I have played with that (Dynamix) one on a ST 90. The only real issue is that it raises the carb centerline about 3/8". I have only used on the bench at this point on my Sportster 65. I don't have any expensive tools, just a lot of patience and a bucket full of carbs from years of looking for them at swap meets. I encourage you to try it, it adds yet another fantastic dimension to an already great hobby!

1QwkSport2.5r

I've actually been on the hunt for a pair of carbs for my engines for awhile now. Because of the neck size of the K&B carb, its hard to find any carbs from other engines to fit. I'd like to get a pair of Italian SuperTigre carbs from the S.90's. The venturi isnt much bigger and should suit my Sportsters just fine. My future flying buddy might be able to make me a couple sleeves to fit the smaller neck of the ST carb into the enormous Carb opening on the Sportster since he has a lathe.

I just cant find any guys with Italian carbs they're willing to part with, nor any guys with K&B carbs willing to let them go.

I gotta find something soon as I can probably have my enormous Goldberg Mig-27 Target drone ready to fly in a weekend. The guy I'm getting the plane from has two of these, and he's gonna assemble his while I assemble mine and we're going to go fly them together with Sportster .65 for power. Should be a fun day.

I'm going to add an extra channel to the plane to add a rudder to it. Originally it has ailerons and elevator only. I'm also going to put landing gear up front and have it be a taildragger.

woodburner

I bought one of those MiGs at Perry, GA for 10 bucks but never flew it. I think I even gave it away, can't remember now.....

codycarlisle25

I had a buddy fix up one of those 'Drone Migs' to really look nice. I tried to find some pics, but can't. He had to put a .90 on his as it needed alot of power to fly. He didn't keep it very long. When I asked about it, he really enjoyed getting it ready to fly. He couldn't remember the flying weight.

1QwkSport2.5r

They are big planes. I think the length of the fuse is roughly 5 feet or a little longer. If the .65 with a MCP isn't enough oomph, I have a ST S90K I can run on it.

earlwb

1QwkSport2.5r I think you are going to have to bite the bullet and just buy a Perry carb for the Sportster engine.
I have bought and used Perry carbs myself. I have one that fits the Sportster engine also. If one of the engines I have has a bad carb on it, I'll switch it out for the Perry carb.

I think those foam MIG target planes were not really intended to have a lot of paint on them, or live long enough to get fuel soaked either. So they are probably quite light without all the paint, etc.

Sport_Pilot

H'mmm, triple expansion? Must be quite.

Sport_Pilot

Does K&B not sell their carbs? Just a tad better than the Perry carbs IMO. Especially the latest one with the wire detent on the idle disk.

turbo.gst

My Feedback: (8)

K&B does sell the carb, but I think it is a cost thing( like $46). If you can find someone who has an ASP .91 - 1.20, have them check the carb neck diameter. Those replacement carbs are $14. The perry site shows .625 for the neck diameter on the Sportster .65