Nitro Troubles

[timberwolf]

Working on an alky saw, runs well on straight meth, but when I start to add some nitromethane I just can't get enough fuel in to keep the RPM down. I have drilled out the carb passages enough I would think it should flow, also tweeked the needle valve, but no luck. Even with the HS all the way out it's still half a hair lean with no more room for adjustment.

tried a couple carbs, no luck,

I added a bit of length to the pipe, but that still did not do it,

I could make a steeper coned pipe to clamp the high rpm, but I still need more fuel adjustment.

Any tips on how to get more fuel through the carb???

Do I need to retrofit a bigger carb on?

Thanks

 

[Mr.]

What saw and what carb and what exactly did you drill out?

Fred

Pics of the carb would be helpful.

 

[ccicora]

How much Nitro are you using? Also are you using an ignitor? What is your pop off preasure? Have you done all the work on the needle and seat? What kind of nitro are you using? Are you starting to see a patern here??
Lets start there and work forward...

 

[Crofter]

Is the fact that the rpm wants to go high the only indicator that it is running lean? Can an alky saw have its no load rpm limited by mixture in the same manner as when running gas?

 

[timberwolf]

Saw
260

Carbs
Wt 17D
Wt 581

opened restriction from jets to under the frost plug, did not think of the needle valve seat! Maybe thats the bottleneck.

Chris, pop off preasure, sound like I have something to learn here.

Using straigt methanol cut with meth/15% niromethane so I have been working from 0-10% nitro, ok to 4-5%, but not more. For oil, you know what I use now, the stuff that mixes with meth, and the correct amount.

I have tried some acetone as an ignitor, but have not found it nessicary or any advantage.

 

[ccicora]

Pop off preasure is the preasure needed to open the needle valve. By changing this you can richen or lean the carb out. I will admit I'm still learning in this area but Have a beter grasp than I did before I started playing with my own alky mixes...

 

[Mr.]

Sorry I'm out on this one, never did an 026. I would look at Tillotson off a 70cc saw and go from there. You can make it work. If you go bigger PM me I'll send pics.

Fred

 

[timbrjackrussel]

Info on alcohol fuel properties

http://journeytoforever.org/biofuel_library/ethanol_motherearth/me1.html

 

[stihltech]

pop off

OK, Chris will shoot me, but I am going to tell you what I know about it.
Frankenstein,my hotsaw, was lean no matter what I did. A certain saw guy decided to lower the pop off pressure by making less tension in the inlet lever spring. Voila, no more lean.

 

[ccicora]

I'm going to tell your wife!

 

[ShoerFast]

Sometimes the fastest way is "slowly"

Timberwolf

Sometimes the fastest way to get somewere is slowely.

Nitro is heavy stuff. methanol is .792 @ 68°F (lighter than water) and pure nitro is 1.139 . Establishing a regulated tank pressure could help overcome the inlet restance.

If your getting it to run well at 4 -5% , you may not see much "umpt" till your well into 20 - 30 % ,,,, but may need to see it run well at 10% before you mix it at 15%,,,,, just a step at a time

Methanol can run well at about a 6 : 1 ratio,,,,,, it makes it' s own O2,,,,, adding nitro really starts the party, 100% nitro will run at 1.3 : 1 , you may need to do your tune work on a dyno or in wood?

Just an idea, as lean nitro will detanate and burn things !

Kevin

 

[ccicora]

Timber,
ShoerFast brings up a good point Air..... And I'm not talking the air in the motor but in the fuel tank. You are going to need to modify the breather and make it flow more air so you don't make a vaccume.

 

[timberwolf]

I have been working it up slowly, Started by geting it going on ethanol, then meth, then 2% nitro, then 5%, and ran out of carb ajustment on 7.5%, went back to 5%.

I have got a couple ideas now to do some more work on the carb, I think thats where the problem at.

I think I will also build up a new pipe designed to run alchol rather than a gas pipe adapted to work, will build it to shut down the RPM quicker above 14,500.

Thanks for the info guys, that thread on the jorney to forever is a good read (read it a couple times before), it helped me to get as far as I have, much to learn.

That could be a factor (the fuel tank), I noted the rpm tended to climb after a bit of time at WOT, had dismissed this as heat, but it's easy to address so will look into that also. Good point!

 

[ehp]

Brian the easiest way for me to try and tell you is this, methanol has a octane rating on 130, nitro is only 45 so you can run more compression with methanol than once you start adding nitro so I would say ifyou want to run nitro lower your compression. Most small saws that are on pipe run less than 180 pounds if running nitro, sure you can run 250 pounds and make 3 cuts but most times the saw if fighting its self threw the whole cut and doesnot cut fast. Muffler saws are different cause they donot have the effects of the pipe drawing the fuel charge threw the tranfsers ports, you can make the pipe do different things but most times it doesnot make you cut faster

 

[timberwolf]

I am ok on the compression, at a bit below 180.

Still having trouble getting enough fuel at HS while not going lean at LS.

Seems the more fuel I get in the faster it wants to turn, I would say 180 degrees from gas when you go rich on gas the saw looses rpm. I was thinking on a pipe designed to keep the RPM from running up. But again though that may work with gas I am not sure the same rules apply to nitro.

I have another carb to try, maybe I will have it right this next time.

 

[ehp]

You will need to make a high speed circuit in your carb to pass move fuel, right now my high speed jet nozzle is .250 inside diameter with just a screen it there so lots of room . Did you drill out your needle and seat ? plus if you are starting to really pass some fuel you will need to make your vaccuum for your carb bigger, a bigger hose and fittings for your carb

 

[timberwolf]

Thats where I was working, but maybe I have been a bit on the conservative side with the drilling.

 

[ShoerFast]

2 strocker nitro,,,,,

Timberwolf

Just from the hip,,,,, as I dont have much experance with 2 cycles on nitro,,,, but I would think that you may need a little more pipe on nitro (?)

The reason that gas slows down rich so well is it just cools the cylinder temp a little, and makes the gas less drastic, it should be the same effect as with methanal and nitro, but there less senisative to mixture changes, thats why I'm thinking you may need to get close with your tune under a load, than even if it may be still way fast, it has a better chance not burning up before you get there (?)

Just .02 cents worth

Kevin

 

[ehp]

measure the rubber end of your needle and seat, you need to keep your drill size around .010 smaller than your rubber end , now normally when you drill your needle and seat out your needle will leak abit and remember that you have changed the position of the needle cause you drill the hole bigger so this lets the needle sit down father into the carb, so sometimes you need to make your pop off pressure alittle higher and the easiest way to do this is put a little JB Weld under your spring, you know the hole the spring seats in that runs your needle and seat . It depends on how thick you make this to each carb there is no set rule but most times it doesnot take much

 

[timberwolf]

Rick, For me it's all just fun, but it was good to have EJ there, he was open to share ideas, but hey all info is suspect to a certain degree, it is after all a race. I don't think he told me any lies and if he did they must have been good ones.

Beter yet having some strong saws there showed that a woods saw does not cut it against alky saws, nito ect. It raises the bar and puts some fun into to it to saw better and build a faster saw, I wont say better saw because a woods saw and a race saw are two different things.

Ed, I think I was headed in the right direction by what you said, I just had not gone far enough. It is increadible the amount of fuel that needs to get trough.