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Help with 4 stroke flameout?

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Finally caved in and bought a 450 4 stroke to help a 40+ vet guy clear some obstacles that have been giving me fits on my 125 if race day track conditions were less than ideal ( read most races ).

Bought a totally mint original owner 05 RMZ 450 (for $1,800) and have had it out on two practice days. The bike ran great, starts great, handles great, and is a complete blast to ride. Raced it moto for the first time, went out in pre-race practice, no problems. In the first moto, decent start, got into a set of switchbacks diving in deep and braking hard and the bike dies but I'm able to pull in the clutch and catch it in time with enough momentum and bump start it and keep going... happened two more times in the moto @ different spots all in tight turns.

Second race decent start again 2/3rds into the first lap and dive into a deep rutted sharp hairpin and the bike dies and not enough momentum to bump start it and now I've got bikes piling up behind me cause it was a wet, one lined mucky turn. Can't get the bike started cause my boots are all muddy, have to push the bike off the track and roll it down a hill to bump start it and now I'm really hot cause I've never had to deal with this before.

All three times I rode the bike the temp was in the 60's... I have no experience with these bikes but love the power, spent the end of the day with my son and his motos and I didn't have time to ask around so I'm asking here... Jetting?

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Bikes do not flame out, Jet engines do.

From what you described, you simpley stalled. You need to check and set the fuel screw. Also make sure the hot start works properly.

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

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No way to tell if your jetting is off based on what you said but if the bike pulls cleanly from low rpms, then jetting is probably not a big factor.

Most guys coming off 2-strokes have a hard time with flame out until they get used to clutching in turns and when brake sliding the rear end. Spend some time getting used to disconnecting the drivetrain whenever you are going to rapidly slow or stop the rear wheel and you'll be done with the flameouts. A flywheel weight helps too.

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your just not used to the engine braking that 4 strokes have. They stall easier because of this.

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