Hard to Start 2003 YZ 450 When Hot

I have a question regarding a 2003 YZ450 that is hard to start when the engine is hot. It starts OK when cold but when hot it takes so many kicks but it helps to give it a steady 1/8 throttle and then it takes about three kicks. This is so strange since you normally give it no throttle when starting. This implies to me that it is too lean and a little throttle squirts in some additional fuel. Is this thought logical?

It has a White Brother’s header and aluminum muffler. It ran lean when this was installed giving the popping noise going into turns. Right now it has a 52 pilot (45 is stock) and a main jet 2 sizes larger than stock. Could it be too rich causing it to be hard to start? It still occasionally pops going into turns so this makes me think that it is not too rich.

Has anyone else had issues like this or might know what is the cause? The valves were recently adjusted and that did not seem to help.

Thanks,

Jay

I have a question regarding a 2003 YZ450 that is hard to start when the engine is hot. It starts OK when cold but when hot it takes so many kicks but it helps to give it a steady 1/8 throttle and then it takes about three kicks. This is so strange since you normally give it no throttle when starting. This implies to me that it is too lean and a little throttle squirts in some additional fuel. Is this thought logical?

It has a White Brother’s header and aluminum muffler. It ran lean when this was installed giving the popping noise going into turns. Right now it has a 52 pilot (45 is stock) and a main jet 2 sizes larger than stock. Could it be too rich causing it to be hard to start?

Actually, it sounds like your problem is that big ol' pilot.

The need to open the throttle usually is the result of a too rich condition and reveals the engine's need for a bit more air when starting. I assume you are also using the hot start during this procedure(?)

Popping on deceleration can be caused by a lean idle mix, but that's not the only reason. It is very commonly caused by an air leak in the exhaust system, and since that's when your trouble started, I'm betting that's what it is. What you have likely done is to cover over an air leak with an excessively rich idle mix. The two most probable points for the air leak are at the midpipe/header joint and the header/head, especially if these are slip joints.

It also needs to be understood that absolutely no harm comes to your bike from decel popping unless it's so severe that there's a danger of blowing the muffler apart, and a certain amount of it is pretty normal for a correctly jetted engine.

Yeah, these bikes are hard to start and pop with rich jetting also. IMO the popping is LOUDER with the richer jetting.

Do you foul plugs?

Another vote for a pilot thats to big. I have gone down on mine and it now starts in one kick when it's hot even after I dump the bike. Takes two or three when it's cold and been sitting for a week.

I found most of my poping was due to intake valves being to tight. I'm still working on a few issues but it's much better now.

38 pilot .. was 42 I'm between 4k-4.5k ft

Thanks for the feed back. I bet you are right and it is too rich or there might even be an air leak! This forum is great!!!

Jay

Go to the 48 or stock pj and see if this helps - :ride:

One thing I meant to mention in the first post. The spark plug is white. From my 2 stroke experience, this implies to me that it is too lean. Does plug color mean as much in a 4 stroke as it does in a 2 stroke? It could also mean it is lean in other parts of the powerband and still rich on low end.

Thanks!

One thing I meant to mention in the first post. The spark plug is white. From my 2 stroke experience, this implies to me that it is too lean. Does plug color mean as much in a 4 stroke as it does in a 2 stroke? It could also mean it is lean in other parts of the powerband and still rich on low end.

Thanks!

Dont assume you can read a 4 strokes plug color. do a search, several people have lengthy articles on why you cannot read the plug color as you would a 2 strokes.

You be careful with those offhand remarks there, mister. :ride::banana:

He's right, since lead was removed from the gasoline, reading plugs for mixture is pretty much impossible. They'll come up white unless the plug itself is the wrong heat range or you're burning oil.

You be careful with those offhand remarks there, mister. :banana::busted:

He's right, since lead was removed from the gasoline, reading plugs for mixture is pretty much impossible. They'll come up white unless the plug itself is the wrong heat range or you're burning oil.

Im just trying to figure out if I should lube with moly or moly or moly or calcium....Can anyone help me. :ride:

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