Convert to Methonol Fuel

[evelrod]

My son-in-law races a Yamaha 250 four stroke in the "Over the Hill" groupe (gad, he is only 35!!!) and must compete against 450's (quite successfully so, too!). As in years long past I raced a couple of bikes (Bultaco and Husky) that I converted to methonol with great success, I sugested he might try this idea on his 2003 Yamaha. Problem---I am over 30 years older than the days of my conversions and I have no idea of what it would take to convert these newer bikes aside the trial and error approach that I used in the past. Don't get me wrong, it definately still works but is a bit time consuming and expensive. What say you?

Rod

 

[Metalguy]

Jet it rich to start with and slowly keep leaning it down to find the power. If he drains and flushes the tank and carb he won't have to be concerned with corrosion either. But all he's likely to get is ~10% more HP, so tip the nitro can.<g>

 

[patprimmer]

Rod

I know how long you have been around, so I feel a bit self concious about telling you how to suck eggs.

My main concern would be compatibility of components with methanol, as modern motorcycles might have plastic tanks and lines, carby floats, gaskets etc.

If you know what plastics are used, I can find data on them for you.

Fuel lines are normally significantly oversized for gasoline but might not be large enough for methanol.

Needle and seat, emulsion tube wells, idle fuel passages etc can also be a restriction. Sometimes just substituting a single carb with twins overcomes that problem, but on a single cylinder, that might not work so well. I guess yours is a twin cylinder, but probably already has twin carbs.

If you do go to twins, and the single was about the correcr airflow, reduce venturi size to give a 10% on total airflow increase to compensate for the air displaced by the extra fuel.

If you don't change the venturi size, still increase the cross sectional area of the main jets by at least 250%. Some guys even say to double the dia which is a bit under 400% increase.

If you change the venturi size, correct for that, then increase by another 250%

Raise the compression to as high as you can get it.

If it's convenient, you can get rid of some weight by halving the size of the cooling system, that is, if it is water cooled. Probably not worth the trouble though on an existing set up.

Make sure the oil is suitable for use with methanol. Some turn to custard a lot easier than others. See what the sprint car guys run.

We run Kendal or Penzoil raceing 50 in our drag car, but that is a different set of circumstances to your motor cycle.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

Thanks Pat. I feel self concious every time my fat belly passes it's reflection---

The bike is my son in laws race vehicle. He runs in the old guys class (30+, ha ha) and must compete with up to 450cc bikes on his 2003 Yamaha 250 (now 262cc @ 14+:1 CR) watercooled single cylinder four stroke.
I did a lot of methonol conversions in the late 60's and early 70's, mostly Amal carbed conversions, hillclimb stuff and the like. I know most of the basics involved ( I tend to the 400% area, it's difficult to get too rich on methonol) but am woefully ignorant when it comes to the modern units. Technology has come so far in motorcycles that I have been left behind. What I really needed was to perhaps find someone who has already done the &quot;suck it and see&quot; stuff so I don't have to do it again.
I will check into the compatability issues and the type carb involved. All I know is that it doesn't seem to have a float bowl??? My guess at this point is he will continue to use leaded racing fuel (as I stated in another, related forum).

Metaguy, thanks. In the past it was quite common to get ~20% power improvement from the air cooled two strokes and the side benifit of MUCH easier starting and broader torque curves necessary in hillclimbing. I did a couple of fourstrokes for the mini-bike racers of the times but, no power figures were ever taken ( a fuel burning 5 hp B&S powered mini bike would EAT a stock 250cc bike of the time)


Rod

 

[etatv]

Rod,
I have bee on this quest myself for the past year. I race oval track ATV's and want the extra torque that I can get from switching to methanol and upping the compression. The standard response that I get from the motor builders is &quot;send it to us and we can do it for you&quot;....forget that.
Here is what I have been able to gather on this subject so far.
You WILL need to drain and flush the entire system each time you use it to avoid corrosion. Most guys will have a small tank of gas to run the bike on after they are done racing/playing for the day. I would imagine that better materials could be found for the tank and lines as Pat indicates, but the engine is still aluminum, and a puddle of metanol in the bottom of the crankcase will wreak havoc. In my sprint car days, we would shut the fuel off and run the engine dead to get the fuel out of the engine, but still had to clean the system all the time to avoid problems.

You also need to open up the fuel flow to the carburettor, usually by removing the stock petcock and replacing it with larger tubing.

As far as I can tell, everybody that is running methanol is using a retrofit Mikuni &quot;power jet&quot; kit and Mikuni carb/s. This kit is consists of an additional emulsion tube that is fit into a hole that you machine into the carb bell on the air filter side. This tube connects through a hose to the fuel bowl. You then put the largest main jet that you can in the carb, and tune by using the power jet.

I haven't done it yet because of this.....afraid to blow-up my motor experimenting.

The information that I haven't been able to pry out of anybody is, will I need a stronger ignition (most likely), how much ignition advance should be added since methanol burns slower, how much compression should be added to be optimal, and should the port timing be changed any to take advantage of metanol (probably not applicable to you).

I believe that the Yamaha 250 & 450 have a TPS on the carb which is used to adjust the ignition timing map, so you would have to deal with this also...I could be wrong about this.

Guess I will just have to bite the bullet and do a little experimenting.
Hope this helps, good luck on your endevors.
Ed