Carb tuning...

Trevor Johnson · Posted: Mon Nov 29, 2004 10:54 pm Post subject: Carb tuning...

I was wondering if anyone could direct me to a good website(s) that outline carb tuning for a delorto/rotax 257. I have a rough idea of how to do the tuning, but am fully aware that knowledge is speed (or something like that....)

Thanks all.

TJ

Robert Lawson · Joined: 10 Nov 2001 Posts: 2219

Trevor,

look here: www.greenflag.net

Tom has everything you'll need.

Trevor Johnson · Posted: Wed Dec 01, 2004 4:18 pm Post subject:

Perfect, that is pretty close to exactly what I was looking for. In particular the parts about the idle circuit and the idle jet selection.

We had a pair of engine seizures this summer that we are not quite sure the cause. I was thinking an air leak after the carb, Dad was thinking the idle jet possibly as we have never done a heck of a lot with that. We are your main jet, needle changing, imulsion tube type o guys.....

Thanks!

ted dale · Joined: 25 Oct 2004 Posts: 611

I mormaly keep going smaller till is seizes then go back one size

Trevor Johnson · Posted: Thu Dec 02, 2004 12:35 pm Post subject:

Reggie Brown, Jr · Joined: 25 Sep 2004 Posts: 310

God i love being at the track with you ted, never fail to make me laugh. that should be on your business cards, priceless. hope all is well

reggie

Johnny West · Joined: 03 May 2002 Posts: 1180

When jetting, I just use the largest jet. Then I jam a tooth pick in the hole to lean it out. Very Happy

I have blown up a few this way. Not sure why Question

_________________
Johnny West/West Racing

Riley Will · Posted: Fri Dec 03, 2004 10:12 am Post subject:

The correct way to jet a Del'Lorto carb is to use their comparative main jet charts. These charts give you a comparative main jet size for each 10% of throttle opening. Not many people know that for a given needle/clip position/nozzle that there is only 1 correct main jet size. If you are happy with your low-mid throttle response make sure you leave the 0-50% throttle opening values the same. To tune for max EGT at 100% throttle pick the needle and nozzle combination that changes your 100% value the direction you want to go. Many people make the mistake of going too small on the main jet and end up choking the fuel distribution curve down to the 70% comparative main jet size. That means that after 70%, your fuel distribution is a hope and a prayer.

Software can be had from www.pfpservices.co.uk to make this easier. I believe that Green Flag and Herdan Corporation can get you paper charts if you need to go this way.

If you do not have this software or the charts, do not change your jets until you do. Without these tools I would be in the dark and rolling the dice with set-up.

By using these tools along with our Mychron Extreme, I can get my front and rear cylinder to read exactly the same to no more than 5 degrees C different from each other at an EGT value that I know we make the most HP with.

You must read and rely on your data to determine other things like EGT recovery time and spikes. The Mychron Extreme system allows us to monitor H2O, EGT Front, EGT Rear, and Throttle position.

At the sort of performance that we are tuning to, reading the sparkplug/piston/pipe is not accurate enough. I bet that this is the same for many competitors out there right now considering the development of Superkarts in North America. I do read the piston and plugs for detonation. I also measure piston sinkage with a special tool from www.vhm.nl. Too much EGT will manifest itself with a sunk piston crown before you have any other sort of piston related failure.

All of the above points come from an extensive testing database. Real world track testing cannot be beatten along with comprehensive note taking. Some sinkage is OK, up to 0.15mm on a typical 125cc cast piston, then you must replace the piston assembly.

If anyone on this list has tuned their 125cc engines with Del'Lorto carburetors the following may be of interest. Our BRC250FE twin cylinder engine will use between a 210 and 235 needle/nozzle/main jet combination for most tracks. Given the same ambient conditions and elevation, the next most critical consideration is length of straight. This determines how long we are pulling in each gear. If all conditions are similar from a short straight (ie. Laguna) to a long straight (Road Atlanta) our 100% needle/nozzle requirements dictated a main jet increase from 212 (Laguna) to a 235. This was entirely down to maintaining the same EGT levels between the 2 facilities. Consequently we won both events with 0 engine failures.

I hope that this information helps and enlightens those who may be searching for it. For any other information regarding how to jet a Del'Lorto please ask me, I am happy to help if I can.

www.brceng.com
_________________
Riley Will
BRC Engineering
rwill@brceng.com
(403) 216-0630 wk.
www.brceng.com

bill gillespie · Joined: 23 Jul 2001 Posts: 54

hi riley,

whatever happened to "lean to the ping" ????
best regards,
bill

Riley Will · Posted: Mon Dec 06, 2004 9:32 am Post subject:

Bill, I was wondering if you were still around Shocked

Good to see you posting again. You guys still have the Stockman RS? I was at RA and had a blast. I left the kart in Georgia so I can attend more races down there. The tracks and people were awesome.
_________________
Riley Will
BRC Engineering
rwill@brceng.com
(403) 216-0630 wk.
www.brceng.com

Larry Dobbs · Posted: Mon Dec 06, 2004 10:09 am Post subject:

Hey Riley,
You can leave a kart in California with me!! Just don't forget to leave the keys!

Trevor Johnson · Posted: Mon Dec 06, 2004 10:16 am Post subject:

bill gillespie · Joined: 23 Jul 2001 Posts: 54

hi riley,
hunter and i kind of dropped off the radar for a while after my mom passed.......racing had to take a back seat for family. like the phoenix , we have now risen from the ashes, and have acquired an excellent ralt rt41 atlantic car.....we are cnverting it back from toyota to cosworth power, but should be up and running in the spring. we sold the stockman to help with finances, and i believe it has changed hands again. hunter was amazed at the performance of a good fe 250, but our heart was with you and your program. the atlantic opportunity came up, and we had to take it.
max props and kudos on your luguna and r/a results....i'm glad the long hard work paid off for brc eng.......your calgary facilities are most impressive, and was matched by your families' kindness during my visit.
i hope to see you in georgia, and maybe hunter can do an arrive and drive sometime with you down here.
best wishes and happy holidays,
bill