I managed to get hold of a 10E carb. Friend of mine has a CV-R and liked to try another engine of me, so I can try his carb for a couple of weeks.

Will try to test it next weekend, will keep you guys informed !

Don't think I have any problem with the fuel flow from my tank, problem is same at full or almost empty tank.

Hi DP..MX.
Well I think I'm shelving the F1 project once again because I can,t get a cooling fan in there no matter how hard I try and I have found that the smaller battery is hard to find and will not have enough power to run an electric fan along with everything else.

So I want you guys to be the first to know I am cutting metal today on a prototype FS26 head with the intake port moved 90 degrees with a shorter intake track, curved flowing ports around the valve seats, and slightly higher compression along with some other tricks.
It will be a tricky machine job but I think I have it figured out. If It works out I will have them for sale. I will have to wait and see what the machine time is before setting a price.
I also am planning a trip to the RC Bike Nationals at SV Raceway in september if I can get it into my project superbike in time.

Alert the media!

Nolan Farmer
FPM

Tried a couple of hours last weekend tuning the engine.

With stock carb it's a nightmare. It can run very very fast on a very long straight, but it takes forever to rpm up.. Engine is far too rich stationair and middle area. If I lean it, the middle gets much better, but on top it simply dies. If it's tuned for good speed on top, it's very hard to keep it running stationair, and the smoke it produces when you drive away is insane.
I am using "low smoke" fuel !

But great potential !

So next step was the 10E from my friend. Checked it before I put it in... rubber are gone, mixture needle was broken.. Don't know what he did with it but it leaks air through the mixture needle... no option to even try.

Ordered yesterday a brandnew 10E-R, expecting it end of this week.
I thought about the slide, but the rotary just fits in very easily.
My goal is simply good stationair, don't care much about middle, it just shouldn't slow down the car, and a very good top. Everything that is better is just a bonus !

yeah, i'm still having issues tuning too. the perry pump works very well, and i'm going to follow dp's advice and restrict it a bit, it works so well. now i had to lean the top almost bottomed out, and the low was almost falling out. total reversal due to the perry pump.

now my problem is, that if i get the engine tuned to clean out well and rev hard, it gets too hot (it seems anything over 220-230 deg causes the same problem of leaning the engine due to inadaquate fuel flow. but it won't clean out otherwise. i'm going to try 10% nitro vs the 30% i was running. maybe i'ts pre-detonating at high rpm? or am i trying to overrev the engine? do these 4 strokers have a sweet spot where they clear out and rev hard, or are they limited to the very rich sound at high rpm?

also wondering if the carb is letting too much air in and killing the engine? its a small carb, but slightly larger then the stock orifice. it seemed the engine would run ok even with the throttle barrel at ~70%.

well, it's definately a challenge. trying to re-learn everything i thought i knew about nitro.

well, i just noticed that dp is using the vp-30 pump, and not the vp-20 oscillating pump i bought.... dp, have you tried the vp-20 pump? i did'nt order the 30, because it's supposed to be for 2-strokes. have you found that the 30 provides more consistant flow?
thanks again.

Yes, for offroad, the VP-30 works much better. The 20 is an improvement over no pump at all, but it doesn't have a real regulator in it. Its pressure adjustment nut just adjusts the spring tension on the oscillating part, so you still get fuel pressure variations caused by bumps and jumps. With the VP-20 pump, you can't get it to rev cleanly on a bumpy surface. The VP-30 is advertised as a regulated fuel pump (and it actually works!), and so it can keep constant fuel pressure no matter how much jostling is going on. It does need to be placed as close to the carb as possible to work well.

I usually tune the engine with no pressure and no pump on a smooth surface. Then, connect the pump as shown in the picture I linked to before, and try to make it work without changing your carb settings more than a little bit (leaner if at all). In effect, you now have a 3 needle carb. The low speed needle does idle, fuel pressure does transition and midrange, and the high speed needle does top-end. Keep in mind, fuel pressure effects all needles, so a big adjustment on the pump will require retuning both carb needles. Using this setup, you can make it run very cleanly, to where it doesn't miss under load, does not hesitate, and idles down instantly and reliably. You can also get much better fuel economy since you can get rid of any rich areas.

Yes, tuning these engines is completely different from 2 strokes, and with a pump, you are adding another variable to learn. When tuned for maximum performance, they will act lean while warming up (high idle, lean bog, sometimes dying if full throttle is sustained for more than 0.5-1.0 seconds), then as temp builds up, they start running really crisp and strong at full throttle. This is more noticable with the bigger thumpers, but you will notice it a bit on the .26 when you get close to the bleeding edge. As you start tuning closer to the engine's maximum potential, a good cooling fan becomes very important. Without it, you'll notice a sharp loss of power as it gets too hot. Here's a picture of the fan setup I have on my .26:

As you can see, it's close to the engine, and the drive pulley is much bigger than the pulley on the fan. It moves air with ENTHUSIASM, and I haven't had trouble with overheating unless it's too lean, but if it's too lean, it won't run good to begin with.

As with any engine, you tune it for how you are going to be running it. For a small track, you tune it leaner on top (don't hold the throttle open very long, since you won't be on the track), and for a wide-open track, like an oval, you tune it rich enough on top to reliably do top-speed passes without missing or losing power.

Almost forgot to mention, I never got the .26 to run correctly using the 90 degree manifold. I've only had success with a straight manifold, both the stock setup and this one:


Here's a shot of the whole truck, just 'cause:

thanks dp. i think i might order the vp-30. i just finished running the jato, and the restriction + lower nitro definately helped. i could actually get it to run an entire tank of gas. the engine doesn't get above 230 deg. now, even when running very lean on top. it also doesnt seem to miss on the top as bad- when i lean it down, it actually cleans out.

i see what you mean with trying to tune it to be crisp. it will die occasionaly when it is close to perfect on the top end. especially after going full bore, then turning and gunning it again. it tends to die - probably due to lean bog. (or maybe i'm too rich on the low end?) it also acts inconsistent- likely due to the bumpy road i'm running it on. the low end seems to be the most difficult to tune, as it will run on virtually any needle setting and perform the same.

It's probably dying because it doesn't have constant fuel pressure. If the carb is more than an inch to the left or right of the fuel tank, you'll experience lean while turning one way and rich while turning the other way. That combined with a bumpy surface makes it impossible to tune for maximum performance -- you'll always have to be pretty rich with a fairly large idle opening to avoid flaming out. The regulated fuel pump fixes this problem, letting you tune MUCH leaner on top, midrange, and idle.
This is when using a fuel with high % synthetic oil and high nitro comes in handy, because you don't have to run it as lean as a lower nitro content fuel to get good performance. I'm not saying a lower nitro content won't work, but you might notice it running hotter because you'll tune leaner to get the power out of it. I've also found a high nitro fuel produces a more stable and consistent idle over longer runs, and in my experience is easier to tune with.

2 strokes do not have this problem in r/c cars, because their air/fuel mixture has to go through the crankcase before it gets to the combustion chamber. You can pinch the fuel line on a 2 stroke and it'll run for 3 - 5 seconds on what's in the crankcase. It acts like a buffer, so the small transitional fuel pressure changes they experience in an r/c car do not have any effect.
A properly tuned 4 stroke will only idle about a half second after pinching its fuel line, and dies instantly if the throttle is open even a tiny bit. This is because the air/fuel goes directly from the carb to the combustion chamber. That makes them EXTREMELY sensitive to fuel pressure changes, particularly the kind generated by jumping (0 gravity = rich), landing and traveling up the face of a jump (lots of G's = lean), and if the fuel mass is not centered on the carb, turning, accellerating, and braking.

thanks dp, excellent info again as always. the vp-30 is on it's way. i'll update when it gets here....

Here I found from Japanese web site, an aluminum make clutch shoe, which is high grip type, for use with 4-stroke engine, they claime used to pull out the efficiency of the 3D clutch to full, I'll buy one for test...

How did you get the 3d clutch to fit the FS26?
I thought they could only be fitted to SG shafts

Where can i get the 4troke racing videos ? ... the ones in rcpics.net are not available anymore ...

thanks,

.

Oh, RCPics takes stuff down if it's not super popular. The Hank video is on my Comcast webspace, so it is still available. If anyone has a place to host the Summer Rage videos, (they are 11 - 20 MB a piece) please send me a PM.

Thanks.

My small movies are still available, see my post one page back.

It's from a on road, running the 26 engine.

Not as great as the stuff from DP ! But trying to get close.

I'm still waiting on the new carb to arrive..

@ DP. I see on the pictures that you run the same fan as me, but you mentioned a bigger pulley on the crankshaft ? What diameter are you using ?
I have the pulley which came with the fan, how much rpm can that little fan handle ? Running the engine at full speed it already runs very fast to my idea.