Whats wrong with my 450's carb?

[Dan_187]

My bike has become hard to start after I ran race gas in it in and didn't fully drain the carb. It starts after I twist the throttle a few times even when warm. This tells me that its probably the pilot or leak jet because those are the jets that come into play when starting right? The bike runs pretty well when its running but a little sluggish off the bottom. Also my isle is messed up, sometimes it doesn't want to idle correctly and I have to turn the idle way up, and then other 5 mins later its ok again.

I don't want to take the whole carb off if I don' have to. Can I clean the carb properly with just removing the float bowl and cleaning the jets out that I can reach from there. What do you guys recommend?

[642MX]

Can I clean the carb properly with just removing the float bowl and cleaning the jets out that I can reach from there. What do you guys recommend?

You can clean the jets from removing the bowl, but its hard to get the passages clean. I'd remove it and do it right.

[mkporn]

pull the carb and completely clean it. I have seen this happen more than once....Isn't race gas great, just jet the damn thing properly and staop waisting money on the race gas, unless of course you have a ton of mod work done to the motor and it needs it.

The race gas does very little for a stock motor, other than lighten your wallet, smells cool, masks jetting problems a bit and you can tell your buddies you run race gas... If thats what you want then good on ya.

[grayracer513]

The leak jet has nothing whatever to do with starting, and unless your 450 is an '05 or newer, it doesn't even have one.

The pilot jet, and when the choke is used, the starter jet, are the ones involved with starting.

[Dan_187]

pull the carb and completely clean it. I have seen this happen more than once....Isn't race gas great, just jet the damn thing properly and staop waisting money on the race gas, unless of course you have a ton of mod work done to the motor and it needs it.

The race gas does very little for a stock motor, other than lighten your wallet, smells cool, masks jetting problems a bit and you can tell your buddies you run race gas... If thats what you want then good on ya.

I ran U 4.2 because I was in Glamis and wanted the most protection for my bike from predetination and wanted a few extra horses in the dunes.

The leak jet has nothing whatever to do with starting, and unless your 450 is an '05 or newer, it doesn't even have one.

The pilot jet, and when the choke is used, the starter jet, are the ones involved with starting.

My bike is an 06. Where is the starter jet located?

[grayracer513]

My bike is an 06. Where is the starter jet located?

Look on page 4-17 of your manual. If the main jet is in the center, and the pilot jet is at 6:00 o'clock, the starter jet is next to the main at 1:00 o'clock.

[BIG HAL]

pull the carb and completely clean it. I have seen this happen more than once....Isn't race gas great, just jet the damn thing properly and staop waisting money on the race gas, unless of course you have a ton of mod work done to the motor and it needs it.

The race gas does very little for a stock motor, other than lighten your wallet, smells cool, masks jetting problems a bit and you can tell your buddies you run race gas... If thats what you want then good on ya.

Don't listen to this guy he knows nothing about race fuel.. Don't use U4 anymore. If ya like VP use C12.. Or Track Tek 111!!! U4 evaporates and leaves a film in the jets and seat. Your gonna have to pull it and clean it.. Do not spray carb cleaner on the slide with the small flat o ring on it remove the slide first then proceed to spray the jets and such. As for the race fuel and stock motor. Pump fuel is designed for fuel injected catalytic converter automobiles!!! NOT 12:5:1 compression engines. Pump gas does nothing for the valves as Race Fuel cools the cylinder temp ans doesn't leave carbon deposits on the valves and piston.. It my friend is NOT a waste of money. Pump gas at one time was the same as race fuel today.. I dont run corn blended fuel in my bikes unless it's mixed 50-50 !!!!

[Ga426owner]

pull the carb and completely clean it. I have seen this happen more than once....Isn't race gas great, just jet the damn thing properly and staop waisting money on the race gas, unless of course you have a ton of mod work done to the motor and it needs it.

The race gas does very little for a stock motor, other than lighten your wallet, smells cool, masks jetting problems a bit and you can tell your buddies you run race gas... If thats what you want then good on ya.

oh geez another race fuel expert

[grayracer513]

Don't listen to this guy he knows nothing about race fuel..

He's entitled to his opinion just as you are. Leaded race fuels are more prone to leaving chamber deposits than unleaded fuels in general, and the valve and seat material in modern engines are designed to run quite well without any lead in the fuel.

The energy content of race fuel vs. pump is such that a fuel like U4.2 is worth about 1.5 hp in a properly jetted 450, but whereas you can get that kind of gain from, say, a $600 pipe and good jetting, the gain from the race fuel will cost you easily twice that in a year's time. And you have to keep on paying for it. Worth it?

Yamaha pegs the fuel octane requirement for all of their 12.5:1 racing 4-strokes at 95 Research Octane, which equates to about 90-91 by the (R+M)/2 method used in US pumps. Even at 13.5:1 octane is rarely an issue.

Pump premium probaly should be avoided in areas where it comes with more than 10% ethanol, but otherwise, it really works OK for almost everyone. As far as blending race gas with pump, it's a bit like mixing chocolate ice cream with dog crap. Even at 50/50, the result is bound to be a lot more like dog crap than ice cream. You'd be much better off adding 10-15% toluene, and it's a lot cheaper, too. (requires richer jetting)

[Ga426owner]

Don't listen to this guy he knows nothing about race fuel.. Don't use U4 anymore. If ya like VP use C12.. Or Track Tek 111!!! U4 evaporates and leaves a film in the jets and seat. Your gonna have to pull it and clean it.. Do not spray carb cleaner on the slide with the small flat o ring on it remove the slide first then proceed to spray the jets and such. As for the race fuel and stock motor. Pump fuel is designed for fuel injected catalytic converter automobiles!!! NOT 12:5:1 compression engines. Pump gas does nothing for the valves as Race Fuel cools the cylinder temp ans doesn't leave carbon deposits on the valves and piston.. It my friend is NOT a waste of money. Pump gas at one time was the same as race fuel today.. I dont run corn blended fuel in my bikes unless it's mixed 50-50 !!!!

yep.....

U4 and U4.2 are completely different - no residue with U4.2 unless it is left in carb for several weeks or longer & Yes C12 50/50 is great also

To the threader

HOW LONG WAS THE U4.2 LEFT IN THE CARB???????

I have my doubts that this is the issue - run some pump gas through it and see if it clears up. Also temp changes will cause what you are seeing.....

You can remove the tank - remove top carb cover and bottom 17mm drain from carb. Then remove the needle jet - allenhead on top of carb, spray carb cleaner in the carb and this may clear up issue / also you can remove pj and mj if you like all of this is easy to do. THe idle may be a separate issue altogether

[Ga426owner]

He's entitled to his opinion just as you are. Leaded race fuels are more prone to leaving chamber deposits than unleaded fuels in general, and the valve and seat material in modern engines are designed to run quite well without any lead in the fuel.

The energy content of race fuel vs. pump is such that a fuel like U4.2 is worth about 1.5 hp in a properly jetted 450, but whereas you can get that kind of gain from, say, a $600 pipe and good jetting, the gain from the race fuel will cost you easily twice that in a year's time. And you have to keep on paying for it. Worth it?

Yamaha pegs the fuel octane requirement for all of their 12.5:1 racing 4-strokes at 95 Research Octane, which equates to about 90-91 by the (R+M)/2 method used in US pumps. Even at 13.5:1 octane is rarely an issue.

Pump premium probaly should be avoided in areas where it comes with more than 10% ethanol, but otherwise, it really works OK for almost everyone. As far as blending race gas with pump, it's a bit like mixing chocolate ice cream with dog crap. Even at 50/50, the result is bound to be a lot more like dog crap than ice cream. You'd be much better off adding 10-15% toluene, and it's a lot cheaper, too. (requires richer jetting)

Grey we all know what opinions are like....right?

I have had great experiences with both U4.2 and C12....and not so good experiences with U4.....I only run race gas period and as long as you are jetted correctly for it it will make more HP and the bike runs much better with it. It does cost $$$$ though. Is it worth it? It is to me:excuseme:

[BIG HAL]

yeah an EXPERT! Been using it since 81.. And as for the deposits none!! Opinions are like dog crap nobody likes it.. fact is like Ice Cream, real!!! I dont even get a glowin red pipe @ Idle anymore.. how bout them apples.. I did rejet the thing.. i run TT111. The old Phillips 66 B32

[todds924]

I ran U 4.2 because I was in Glamis and wanted the most protection for my bike from predetination and wanted a few extra horses in the dunes.

My bike is an 06. Where is the starter jet located?

You ran U 4.2 in your bike at the dunes with your STOCK JETTING? And it still runs? That thing was running LEAN for sure. Not good.

[Ga426owner]

yeah an EXPERT! Been using it since 81.. And as for the deposits none!! Opinions are like dog crap nobody likes it.. fact is like Ice Cream, real!!! I dont even get a glowin red pipe @ Idle anymore.. how bout them apples.. I did rejet the thing.. i run TT111. The old Phillips 66 B32

I am glad it's working for you, no offense meant. There is no argument that Higher Compression motors need race gas from me, but the fact is a stock 4smoker motor does get benefit from high Oxygenated Fuel such as U4.2. It does add some complexity to jetting, more cost but bottomline once the bike is dialed in ...more power.

[BIG HAL]

I agree with you Oxygenated Fuel is like N2O more air.. I use non Oxygenated Fuel due to 50 mile races that we do 12.00 per gallon um no.. TT111 is 7.00 per gallon Premium is 3.40 almost half..

[Dan_187]

yep.....

To the threader

HOW LONG WAS THE U4.2 LEFT IN THE CARB???????

I have my doubts that this is the issue - run some pump gas through it and see if it clears up. Also temp changes will cause what you are seeing.....

You can remove the tank - remove top carb cover and bottom 17mm drain from carb. Then remove the needle jet - allenhead on top of carb, spray carb cleaner in the carb and this may clear up issue / also you can remove pj and mj if you like all of this is easy to do. THe idle may be a separate issue altogether

I left it in the carb for about a week.

But there was only a very little bit of fuel because I ran the carb dry until the engine stalled before I put it away, so there wasn't a lot of fuel in the carb. I just think my carbs clogged because for the first time my bike is hard to start and when I give it shots of gas with twisting the throttle it starts up. Also I has a hard time idling correctly. All this started happening after the Glamis trip. I highly doubt my valves would be the culprit. I just seems to have trouble getting fuel at the lower RPM levels.

[Dan_187]

You ran U 4.2 in your bike at the dunes with your STOCK JETTING? And it still runs? That thing was running LEAN for sure. Not good.

I'm no expert but if there is better fuel for the same amount of air wouldn't that make it run RICH instead of lean? I don't think you have to rejet for race fuel, 450s run like champs these things aren't finicky 2 strokes.

[todds924]

I'm no expert but if there is better fuel for the same amount of air wouldn't that make it run RICH instead of lean? I don't think you have to rejet for race fuel, 450s run like champs these things aren't finicky 2 strokes.

You would THINK that it would make it richer but the U 4.2 will make a stock jetted bike run LEAN. When i use the 4.2 i have to go from a 160 main to a 170 and a 45 pilot to a 48.

[Kent Rathgeber]

You would THINK that it would make it richer but the U 4.2 will make a stock jetted bike run LEAN. When i use the 4.2 i have to go from a 160 main to a 170 and a 45 pilot to a 48.

I don't know about the rejetting. I have been told by race mechanics (Blackfoot Yamaha) that I don't need to rejet my 07 YZ450F if I'm running U 4.2. I run the 4.2 because when I crash or stall, the bike starts easier. It's worth it to me in a race. Not so much when practicing. I'm too cheap (hey, it's about $100 for five gallons here in Alberta of VP U4.2) to run it all the time.

[todds924]

I don't know about the rejetting. I have been told by race mechanics (Blackfoot Yamaha) that I don't need to rejet my 07 YZ450F if I'm running U 4.2. I run the 4.2 because when I crash or stall, the bike starts easier. It's worth it to me in a race. Not so much when practicing. I'm too cheap (hey, it's about $100 for five gallons here in Alberta of VP U4.2) to run it all the time.

Kent, You don't notice any difference in running condition when you switch between the two with the same jetting? I tried that at first thinking i didn't need to re jet....My bike spit flames like the "Munster Mobile" with the 4.2 and stock jetting. LEAN. An example i know of is this...Team motoworld rider David Vuillemin<this was back in 06> was running a 170 main/45 pilot/45 leak/2 turns on the fuel screw with his race gas, richer all the way through compared to stock. I got a chance to work on that bike when he turned it in at the end of the season. Ask Eddie over in the Jetting forum, he'll tell you the same thing.