Rev bogs with impacts, any clues?

[rotaxhippie]

My old school '03.5 summit bogs (acts like it runs out of fuel momentarily) when I land from a drop or even bouncing off a kicker sometimes. Its getting a little scary without throttle control sometimes. It also idles a little high when I come to a stop. Let me know if this issue sounds familiar or you might know what is causing it.

After the issue began I have changed the DPM, fuel pump, floats, carb boots with no help.

 

[Doo37]

check ur carb boots for cracks on the high idle and it sounds like u need carbs with splash bowls like race sleds have to eliminate the bog or make ur own

 

[winter brew]

Fuel slosh in the bowls I have been told. Check with the snocross guys, they would be the most likely to have a remedy. I have lessensed it by dropping float level a bit, but it still occurs at times.

 

[Reeb]

I've also found on only a couple sleds(or those that were recently rebuilt) that if the fuel line isn't routed the proper way it will kink during hard landings and crap out. Easy to check that one, otherwise....like Winterbrew said, drop the float level, but it won't cure it completely.

 

[byeatts]

I've also found on only a couple sleds(or those that were recently rebuilt) that if the fuel line isn't routed the proper way it will kink during hard landings and crap out. Easy to check that one, otherwise....like Winterbrew said, drop the float level, but it won't cure it completely.

If the fuel line kinked you still have a floatbowl full of fuel and would most likely cause a problem during WOT pulls.Winterbrew is most likely correct, I have found that over time the floats/ tab get deformed enough to raise the float level and and will flood the motor easily.Hanging idle cause by pulgged pilots and /or open fuel screws 1/4 turn

 

[Reeb]

You'd like to think so however I've personally experienced this about 3 times after rebuilding or swapping shortblocks and not running the fuel lines properly. Hard landing and go to punch the gas......believe me, it can happen. However, like yourself, I'd look into the floatbowls after reaffirming that all fuel lines are free flowing. Simple to check while your about to pull the carbs.

 

[byeatts]

You'd like to think so however I've personally experienced this about 3 times after rebuilding or swapping shortblocks and not running the fuel lines properly. Hard landing and go to punch the gas......believe me, it can happen. However, like yourself, I'd look into the floatbowls after reaffirming that all fuel lines are free flowing. Simple to check while your about to pull the carbs.

It would take several seconds on the throttle to deplete the fuel in the carb bowls and the engine movement pinching a fuel line when landing would be for a fraction of that time duration.You are correct lines do get improperly located during installs.

 

[Reeb]

I'm not arguing here but I am also correct in my findings. If it hasn't happened to you, then great, otherwise, please stick to the experiences you have had yourself.
Like mentioned, it has happened to myself once, and to two other sleds I've ridden after shortblock swaps. Hard landing and the sled does nothing but bog and I've had it stall once after about a 20ft drop. Once rectified, either by re-routing the fuel line or taking the carbs off and re-adjusting the float level, or replacing the DESS cap, or by replacing the killswitch(Same symptom, all different resolutions)......never once a problem. Although you might disagree, this is what I've found to be an issue that can possibly be resolved easily and without taking the floatbowls off. If this is not the issue, then tweaking the floats should be looked at. There are various fixes for the symptom described, but because they are not happening to us, in front of our faces, all we can do is help troubleshoot. I only offered my experience and since it's a simple check before you start tearing into other areas, why wouldn't you atleast inspect?

Now one has to also take into consideration that it idles high and our fellow snowester has also been in and around the carbs numerous times(at least that's how I read his original post) maybe it is something simple afterall.

Whatever the case, good luck in finding your problem.

 

[robandrus]

I've been having the same hanging throttle. I upsized my pilots and it didn't go away. Just got a bog, but mine is uphill. So for adjusting the floats do you want richer or leaner?

 

[byeatts]

I'm not arguing here but I am also correct in my findings. If it hasn't happened to you, then great, otherwise, please stick to the experiences you have had yourself.
Like mentioned, it has happened to myself once, and to two other sleds I've ridden after shortblock swaps. Hard landing and the sled does nothing but bog and I've had it stall once after about a 20ft drop. Once rectified, either by re-routing the fuel line or taking the carbs off and re-adjusting the float level, or replacing the DESS cap, or by replacing the killswitch(Same symptom, all different resolutions)......never once a problem. Although you might disagree, this is what I've found to be an issue that can possibly be resolved easily and without taking the floatbowls off. If this is not the issue, then tweaking the floats should be looked at. There are various fixes for the symptom described, but because they are not happening to us, in front of our faces, all we can do is help troubleshoot. I only offered my experience and since it's a simple check before you start tearing into other areas, why wouldn't you atleast inspect?

Now one has to also take into consideration that it idles high and our fellow snowester has also been in and around the carbs numerous times(at least that's how I read his original post) maybe it is something simple afterall.

Whatever the case, good luck in finding your problem.

I did not intend to step on anyone toes,From the engineering viewpoint the carbs hold aprox 4 oz, of fuel and that fuel will need depleted before the engine will starve,takes several seconds on the throttle for this to occure.Simple Physics will support that a brief momentary supply delivery deficiency only while the sled lands will not cause the symptom's suggested.I agree many have experienced this same problem,Myself included ,Could they be mis-diagnosed?Fuel is delivered via the main jet due to a differential of pressure .Fuel flows up through the main since the atmospheric pressure is lower in the venturi than in the float bowls and while landing the float bowl pressure will briefly increase due to sloshing / forcing additional fuel up through the main jet and flooding the engine,the DPM function is to reduce pressure in the float bowls thus altering the fuel delivery.A higher than normal float level will magnify these affects. kinked fuel line symptom's will surface on Wot. pulls however not till the float bowl supply is depleted.

 

[byeatts]

I've been having the same hanging throttle. I upsized my pilots and it didn't go away. Just got a bog, but mine is uphill. So for adjusting the floats do you want richer or leaner?

Hanging throttle can be plugged pilot circut.poor cable adjustment,vaccume leak,leak at top carb cover,cracked hose to the fuel pump which will not allow pump to function at full rate [which is also an air leak}cracked reed boot,restricted fuel tank inlet.Rave valve gasket leak,not likely the float level.The hammering up /down of the sled will raise the float level over time since the tab becomes distorted from the constant upward force,not lower float level.. The most probable cause which will cause both hanging idle "AND "WOT bog is cracked hose/line to fuel pump [hose air leak = hanging idle and Fuel pump not pumping full rate due to air leak =starves for full at WOT}

 

[Reeb]

I did not intend to step on anyone toes,From the engineering viewpoint the carbs hold aprox 4 oz, of fuel and that fuel will need depleted before the engine will starve,takes several seconds on the throttle for this to occure.Simple Physics will support that a brief momentary supply delivery deficiency only while the sled lands will not cause the symptom's suggested.I agree many have experienced this same problem,Myself included ,Could they be mis-diagnosed?Fuel is delivered via the main jet due to a differential of pressure .Fuel flows up through the main since the atmospheric pressure is lower in the venturi than in the float bowls and while landing the float bowl pressure will briefly increase due to sloshing / forcing additional fuel up through the main jet and flooding the engine,the DPM function is to reduce pressure in the float bowls thus altering the fuel delivery.A higher than normal float level will magnify these affects. kinked fuel line symptom's will surface on Wot. pulls however not till the float bowl supply is depleted.

Nor am I arguing that the mechanical/engineering standpoint either. However, and RKT will argue till he's blue in the face, sometimes, even through all the math.....some things don't add up. Sometimes the math just doesn't add up(even if it does on paper) real world experience tells different. This is one of those. I've had a technician argue with me until finally we tried it my way. Yes, it may not be conventional, yes it may not make sense, but if you try it and it works......how do you explain that one? Not saying that in this instance I am right, but because of this experience, it would be worthwhile for this fellow to at least check to see if anything is routed wrong or pinching as it might save him from pulling the carbs off.
I do understand your POV and the engineering behind it, hence why I didn't find the problem on the hill as I went through the exact same thought process you're explaining. However.....a shot in the dark gave us the results needed in 3 different circumstances.......it's worth a look no?
Personally, I like to subscribe to the KISS method when applicable.