whatnext

I have a KB 61 and I am trying get a tuned pipe to work on it. It is a Macs header and pipe made for the KB 61 engines. I have it on the test. I can't seem to find that sweet spot.What does it mean if It will only run excessively rich or too lean when it is running wide open? .I can't seem to fine tune it.

THANKS

1QwkSport2.5r

Is the header and pipe set pre-tuned or is the header about 7-8" long? If it's pre-tuned, which K&B .61? There is the old style baffled piston .61 and here's also the Twister .61. Two completely different engines that are setup differently.

aspeed

Running lean is the way full pipes are. Set it as rich as you can pretty much when trying to get your unloaded air rpms and playing with pipe length and prop diameters. Welcome to the forum? 3 posts.

1QwkSport2.5r

I would tune the pipe to the same prop diameter as the intended flight prop (remember you're tuning to literally one or two props only) but add 1-2" pitch and set the pipe to the higher pitched prop on the ground. Once you find your peak rpm on the higher pitched prop, then put your flight prop on it and go fly.

This may help a little with tuning the pipe and finding the peak rpm. https://youtu.be/KCIlP6_Z0pw

rgburrill

I like my lemon pie well tuned.

MJD

My Feedback: (1)

What prop are you using? That would be a good starting point.

Off the top, it sounds like your prop load is too high for the pipe tuning. If that is the case, the engine will either run rich and be stonewalled from staging into pipe resonance, or if you lean it enough to get the last few rpm & force the pipe into resonance to start boosting, the mixture will now go way lean and when you richen it it to compensate.. it will simply drop out of resonance again => this will result in the observation of too rich, or too lean, no sweet spot. On RCU it is rare to find anyone underpropping piped engines.

If you are running too big a prop you are obviously defeating the pipe system, which would be the answer right there. But if not, one way to diagnose/understand the pipe system is by underpropping the engine a bit to "know" that the load is small enough for a reasonably set up pipe system to stage. Perhaps a 10-7 or 11-6, which are enough shaft load for the engine but slightly under normal flight prop loads. If the engine stages fairly easily to the pipe and the mixture seems to be controllable/predictable, then you know you are close. If the engine won't stage on these props, something is up.

Or if you have the bits to do so, extend your existing pipe system by 3/4" - 1" and see how it behaves.

With a tuned pipe setup, it is normal for the mixture at launch to be set back 800 rpm or more from peak (depending on state of tune of pipe setup) so that the fuel flow is sufficient when the rpm jumps.

Generally for sport flying, tuning to max static rpm on the flight prop will get you a setup that works pretty well - the engine will overrun the pipe a touch at full speed but when under load such as a climb it will actually pull a bit more boost. For maximum all out performance the pipe has to be shorter, you gain a bit on top end but the trade off is tractability.

It's easy to know why the mixture changes - yeah it makes more power it needs more fuel, that is pretty obvious but it doesn't tell the whole story. For a given needle setting, the mixture is only "correct" at one rpm, it goes lean as rpm goes up and rich as it goes down. It might seem intuitive to think that with rpm increase, well then air flow speeds up and so there should be more suction to more fuel flow. True, there is more suction and you get more fuel, except for one problem - it does not change in linear proportion. As the rpm climbs from boost, the mixture shifts lean - when the engine stages to the pipe and tries to run 1000-1200 rpm faster or so, it will be leaner than when it started. If you're too far to begin with - hot hot hot.

maxtenet

Go to the O.S. engines website. They have a complete step by step explanation of how to tune tuned pipes. It is pretty comprehensive. I'd give u the link but this is a new iPad and I can't figure this damn thing out!��

Max

hsukaria

It would also help if you know what type of pipe you are using: Quiet, Muffled, or regular. See MACs listing: http://www.macspro.com/tunedpipes.asp

Here's the tuning info on MACs site: http://www.macspro.com/tuning.asp. Note that the K&B 61 is listed in the table. But as was mentioned already, make sure which version of engine.

For me, tuning with a Quiet Pipe was a no-brainer. I just had to make sure that I had it set rich enough at WOT for unloading in flight and that the prop is small enough (11x7). Plus cutting the header to the correct length of course.

I had more trouble tuning another engine with a Muffled Pipe. That type of pipe combined with the carb setup was giving me extremely rich midrange and the engine would quit at part throttle. it worked well at idle and WOT, but nowhere in between. I had to reshape the low speed needle and got it mostly fixed, but I need to fly it some more to prove it out.

MJD

My Feedback: (1)

Do you figure it was higher tank pressure in the midrange because of the muffler? Sounds like the typical troubles you get when you use a pump on many regular carbs.

whatnext

Ok first of all thanks for the replies.And secondly I should have made my explanation in my first post a lot more clear.
Here is what is should have typed in the beginning.
I have a KB 61 pumper that was modded by Clarence Lee.He did the PDP mods and he timed it for a pipe.
Now this engine was new old stock that I bought .I bought a Macs header and tuned pipe made for the Kb 61.The engine ran like a top for about 2 or 3 gallons of fuel/It then started to act up.I was told that the diaphragm in the pump was shot..Now then I also had a Nib KB 61 modded by Clarence Lee.All that was done to this engine was the PDP mods,no timing for the pipe.This is the engine I am trying to get a tuned pipe to work on.
Now, this tuned pipe I am trying to get to work on this engine is the same pipe and header I used on the pumped Lee modded timed for a pipe engine.I cut the header to length and it worked almost perfect.
Could it be the header is now too short for the non pumped and timed engine?

again thanks jimmy

hsukaria

You can re-use the pieces of header that you cut off back in and see what happens.

hsukaria

Not sure. This engine doesn't have a pump, but the shape of the low speed needle was very blunt. There was a very large gap between the LSN and the jet tube and the needle did not enter into the tube until throttle was down to 3/4. At 3/4 to WOT, I could tune the HSN to work fine. But as soon as the LSN began to enter the jet tube, it was too rich instead of too lean because I has to back out the LSN quite a bit because it was so fat. I tapered the LSN to a more gradual slope until it was at the inlet to the jet tube at almost WOT. That allowed the LSN to meter the mix from idle up to WOT and reduced the rich mix at part throttle. But I still have not flown the plane much to make sure it is good at all operating conditions.

I hope that makes sense. It took and lot of head scratching and asking questions to figure it out. It was my first pipe tuning other than the Quiet pipe on an OS 61FX. That tuned pipe and header were designed up front for the 61FX and no tweaking required.

PS. I think that the exhaust pressure at part throttle is typically too low to cause an excessively rich mixture. It does have impact on tuning at higher throttle settings. My problem was from 1/4 to 3/4 throttle. Reshaping the LSN fixed most of that.

MJD

My Feedback: (1)

If you are trying to turn the same prop that would make perfect sense. The pipe timed engine will turn faster on the same load. You'll need to run the same rpm range, or re-tune the system for lower rpm to find out what is going on. That can be done by adding in more header to reduce the rpm range of the pipe system, or testing a smaller prop to see if it behaves when you let the rpm get back up to where the other engine was, will both tell a story on that subject.

If it behaves better - pretty much voila now you know. I think the issue could be this simple, personally I'd recommend treating it as such until some other factor reveals itself.

whatnext

Well I added about a half inch piece of the cut off header back into the coupling and It will now fine tune on the top end. It's on the test stand.The transition from low to high seems a little sluggish.Should add or takeaway from the header length? It idles real well.

jimmy

hsukaria

May be time to try a smaller prop?

That is where I hit the proverbial tuning wall, good idle and top end but rich mid-range.

Do you know what type of pipe you have, quiet or muffled?

MJD

My Feedback: (1)

Assuming you have the low end needle set at the sweet spot, which it sounds like it may be.. i.e. not too rich causing loading and stumbling on acceleration, or too lean starving it dry when you open the barrel.. just go farther in the direction you did and watch the effect. More header or less prop - if it behaves even better then the answer is simple. If not, then other factors may be at play.

whatnext

Well I have this thing running unbelievably good.It's on the test stand .It will idle all day around 2100 rpm.It has instant throttle. It went from around 11.4 k without a pipe, to around 12.3 with the pipe.-
-11-8 APC
10% Coolpower with 5 ounces of castor.
Fox long reach with idle bar.

thanks for the help
jimmy

hsukaria

So how did you get it fixed? Added more length to the header? By the way, a more typical prop for an application like yours would be the 11x7. But no arguing with good numbers like yours. But checking out performance with the 11x7 might be educational if not entertaining.

whatnext

I added the small pieces that I cut off the header back into the coupling, which makes the header longer.I filed the pieces down until it started running good. I sure hope in runs in the air like it does on the test stand..These ole KB engines run real good,not the most powerful but I think adding this pipe will do what I need it to do.The carb. on this one is a good one too,real easy to adjust now that the pipe is set.

MJD

My Feedback: (1)

It's good to hear that the problem was as simple as that in the end. Some folks never seem to get their pipe troubles licked. On a standard timed engine you won't get such an aggressive boost as with the higher timing, but you should at least get back your open exhaust horsepower. And a much better sound..