NITROUS OXIDE ( nos / n2o ) advice forum

Well, I've confirmed that the issue with the engine is NOT with the nitrous system or the engine itself but with the CARB.

After resetting the carb to default settings with FRESH FUEL, I attempted to retune the engine but the damn thing WOULD NOT FIRE. I discovered that the original spark plug was fouled out and failed to make good spark so I replaced it with another. NO DICE. I also noticed that there was NO SIGN of fuel making its way into the engine because the new plug was BONE DRY, so I knew the carb was not doing its job.

Next, I took the carb COMPLETELY apart and cleaned EVERYTHING with compressed air. The fuel pump passages, the mixture valve seats, needle valves and ALL.

I reassembled everything and test fired the engine after resetting the mixture screws and IT FIRED right up! EXCEPT that after about a minute of running, I attempted to adjust the mixture screws, and of course this required burping the throttle around a bit, but then the engine went suddenly LEAN and died out very quickly. After that it would NOT start anymore and the engine FLOODED out.

So now I know that this carb is shot and in need of a rebuild , but I think I'll just move forward and go with the ALCOHOL CARB. So more nitrous, more power, MORE SPEED!!!

Trev, should I advance the timing for the alcohol carb with the nitrous/butane or should I keep it retarded?

I strongly suspect that the fault is with the metering diaphragm. Since both mixture adjustments wouldn't respond correctly, I think the diaphragm dried out and distorted over the months that I left this engine untouched and it either allows too much fuel to flow through or too little. I also cleaned out all of the little orfices where fuel comes out of and their check valves.

I have parts on order to replace this diaphragm and new spark plugs.

The alcohol carb is going in for now.

A hardened diaphragm will certainly cause problems.

Ok, so I have the new alky carb on and I'm using Denatured Alcohol as my fuel with 32:1 oil ratio for starters.

I made sure that the carb was reset as normal and attempted to tune the engine's low speed so I can get a stable idle and low speed response. EXCEPT that the engine couldn't maintain a stable idle much and I was fumbling around for a while to try and get things ironed out.

Now I've tuned small hobby nitro engines so I'm familiar with doing this in general, however this is not a small glow engine.

Everytime I richen up the low needle the engine rpm increases significantly and I have to lower the idle screw to close the plate, except that the idle remained unstable and the engine would stall. If I lean it out, the rpm drops and I have to increase the idle screw but then the engine dies again.

PLZ WATCH THIS

Could the timing retard have an affect on the idle stability?

I'm pretty confused with this thing LOL!

In my experience (although its many years since I've had to do this in practice), to achieve the optimum mixture, you need to aim for the highest rpm that the engine runs at smoothly and then reduce the idle to an acceptable level.

Timing adjustment has had very little effect on the 2 strokes I've worked on in the past but that's not to say that all 2 strokes will be the same and as it's a very easy job to switch it back to standard, I'd certainly give that a try.

Okay, I'M CONVINCED THAT THIS ENGINE HAS AN AIRLEAK SOMEWHERE.

I restored the timing back to stock, and as you've called it: it made no difference.

However this time as the engine lit, IT FRIGGIN' RACED LIKE CRAZY! I mean 18,000 RPM crazy! It got worse as I added more fuel so it has to be some air getting through and making this thing go nuts!

I even tried to use the kill switch to limit the RPM so that I can try to get some kind of control of this engine but NO DICE!

And it's tough to locate the source because any evidence is being burned in the engine. I tried spraying it down with some water to try to find the source, but nothing happened. This project is DEAD as of this moment.

Agree with your conclusion of an air leak but as there aren't that many places that can occur I'm sure you can sort it.

Got some parts.

The ones to note are the new diaphragm and cylinder gasket. The cyl gasket is double the thickness of stock so that TONS of nitrous can be used, but with the alcohol carb, I'll stick to the stock compression.

I still need to sort out the air leak before continuing with the project.

The airleak is fixed: the "steel reinforced" graphite gasket was letting air in. Damn graphite garbage! Anyway, I replaced it with a paper version of the gasket and tried the engine again.

The results weren't much different from before where this thing wouldn't run right on the alcohol, but perhaps I'm using the wrong type of fuel. I'm using denatured alcohol but I'm not sure it the spark ignition can handle that type of fuel. Should I change to a different alcohol fuel? Mix some small amount of petrol to help it idle?

I'm at a loss with this...

Which hasket are you talking about?

Alky can be harder to light so on that basis it would be a good idea to create a mix with petrol but you'll then have more of a problem determining the correct mix, so it would probably be a good idea if you started by using a small percentage of petrol in the mix.

Another option is to start with 100% petrol and start at 1% alky.

I added approx 12-15% petrol to the alcohol since it's common for street cars to adapt to E85 fuel just by increasing fuel flow and run normally.

I can't test for the moment because it's getting late.

w00t! Finally some progress with the this alcohol carb setup. As Trev mentioned, the alcohol fuel was too much to be lit off on spark alone and needed the help of some petrol to get the initial light-off. Without the petrol, the engine would either high-idle or flame out, there was no middle ground.

I mixed in approximately 15% petrol and there was some measure of improvment in the idle quality, but not enough to maintain a steady idle without creeping to a flame out.

Now that I've mixed in an additional 10% more or less of petrol, I was able to maintain a decent idle to at least begin power tuning with load. The alcohol certainly takes some getting used to because it causes the engine to load up with fuel much easier than on petrol. This means that the engine will idle at around 6000 rpm then down to around 4000 upon load up. On alcohol only, the idle went from 6000 to 3000 then 0... it was so frustrating!

Hopefully, I can tune it to satisfaction then have a go on the nitrous!

If all goes well, this thing should haul boulders!!!

Well gents,

It appears that I will have to change up the fuel side of the SFBK nitrous system for my current goped setup. Today, I happened to get the goped running on petrol again since the alcohol setup proved troublesome with idling. With petrol, I was able to discern that this engine cannot handle the excess fuel that vaporizes inside the nylon pipe, as short as it is, is enough for the engine to bog down and stall out from continued fuel ingestion.

I think that this is due to either one or both of the following:

1) The lack of direct drive prevents the engine from rotating long enough to pass the fuel through and continue normal combustion, which leads to the engine flame out while still moving.

2) This engine, with its larger transfer ports, draws in the fuel much faster into the combustion chamber that it becomes over rich and flames out unlike the much smaller ported stock g23 engine. And without direct drive, there is no way that the engine can pass through this excess fuel.

So, I will have to change the fuel medium so that it cannot vaporize in the nylon pipe. And that means using either petrol or some other fuel (preferably high octane) that remains liquid once the pulsoid closes and that should eliminate the excess ingestion of fuel and make awesome power.

By he way, I was scared to death after I tried it out today and kept accelerating towards the curb at the end of my street! It's a good thing that the engine cut out when I let off the nitrous!

at being scared when still accelerating when heading towards the end of the test strip.

Before you do anything else can you tell me exactly what you are experiencing again, please.

By the way you are a man after my own heart, venturing where no man has gone before and your latest experience reminds me of a similar one of mine.

It was when I was racing my street based but HEAVILY DOSED UP V8 Rover powered Escort.

To ensure my unique Duo-Noids fired instantly, I set them up in a way that caused them to be slow to shut off, which wasn't a problem on the Drag strip but I should have kept that fact in mind. when I was asked to give a nitrous demo to one of my brothers on the road.

The road that passes my premises has a short straight section followed by a 90 degree bend (and I mean an ABRUPT 90), so I used to do my resting and demo on that straight and shut down for the bend.
So I lunched the car to scare the crap out of my brother but when I shut off it just kept pulling at almost full power. LUCKILY straight on and off to the right a little, there was a VERY SHORT rough track leading into a field which also LUCKILY had an OPEN gate to it at this time, so I steered the car up the track and into the field.
My brother was seriously impressed and had no idea that I was crapping myself due to the lack of control of the power but to save face I let him think it was all intentional. ;-)

Luckily from that and all the other knowledge I've gained since then, I now know how to make the power delivery INSTANT ON AND OFF.

ROFL

Yes, I was pretty terrified because the scooter would not accelerate much and the clutch would continue to slip from lack of torque, but on the nitrous it kicked the front wheel up a bit and the clutch gripped to allow full RPM acceleration. Once I realized that I was going faster than expected on such a short road with the end approaching ever so quickly, I let off the gas and the engine cut out and I was able to hard brake enough to avoid a catastrophe!

Anyway prior to this almost incident, I had tuned the carb to its best on some fresh petrol and I static tested the nitrous on it. Now the carb was set optimally on the low speed so that it would sharply accelerate, any richer caused a further delay in rev up and any leaner caused the hollow-sounding hesitation indicating too lean. When I tested the nitrous on optimum low speed setting, the engine revved up as normal yet once I released the gas the engine almost died but I was able to save it by opening the throttle and passing that bog through, then it would continue to run as normal. I then richened the low speed some and the engine would stall out with the same test despite trying to pass the bog through by actuating the throttle. On the lean setting, the engine accelerated but would idle almost normally without much bog at all.

Also when I test the system with the air cleaner off and the two pipes are exposed, I put my finger close to the two nozzles and I can tell that there is a significant lag between the nitrous and the butane. Now, both of them seem to discharge simultaneously, except the nitrous empties itself out of the longer pipework much faster than the butane because the liquid butane continues to flow about .75 to 1 full second after the nitrous has emptied its pipe. And along with my carb adjustments, this leads me to believe that the fuel lag is killing my engine when I let off the nitrous button.

I hope that explains what I'm experiencing.

By the way, this was the 2.5 BHP hit with 5N and 5F

I'm pretty sure that I could make you a small inline pressure valve, that would open at the max pressure and shut when it dropped A LITTLE.
If you placed that as close to the injection end of the propane pipe as possible, it SHOULD cure the problem and even if we can't make it as pressure sensitive as to shut off immediately, it should certainly shut off soon enough to seriously reduce the problem.

TOP MAN!!!

YES! I was thinking the same thing with something like a relief valve that would close when the flow begins to degrade!