Today was the first time my engine bogged down on me. I was going about 25 and I kicked it up to 4th. I pulled back the throttle and I hear "bog bog bog" and then my engine dies.

To make sure, I did the same maneuver and it did the exact same thing.

Things I recently changed:
Spark plugs
Air Filter
Battery


I did take the gas tank off and had to put back the fuel lines.


Other considerations:
My gas is a bit low (I tried reserve same thing though)
Bike starts fine and runs great, no bad sounds
After it died It was easy to start back up.
1997 CBR 600 F3

I am thinking it has to do with me yanking the throttle.
I am pretty sure it has nothing to do with my carbs even though engine bog is linked to carbs.

Perhaps sparks or fuel lines?

Any advice would be love!

 

anything near 25 mph and 4th gear doesnt match at all unless you got a 60 tooth sprocket on the rear....does it do it when your in 2nd

 

thanks nickels. and good question!

No it does not do this in 2nd. I was thinking like you and so I went down to like 5mph but in 2nd. I then goosed the throttle. It kinda bogs (always does) but it did NOT die on me.

Yeah and the 25mph and 4th gear isnt something I rarely do. Not good on the engine for sure. But I never had it die on me like that.

something up with my fuel mixture? I didnt change the idle. Idles great actually.

btw new filter is K&N

 

25mph and 4th gear? there isnt a bike around that wouldnt bogg down in that same scenerio. Unless like nickels said, you have a huge sprocket on it. My guess is the bike just can't recover from such a low rpm under that heavy of a load. It bogged until it just flooded out the engine. You should try to keep your rpms up .... I would suggest no lower than 3500 rpms, and only if your cruising. If you decide to get on the gas at all, drop the gears until your rpms are above 5000 or so. If your going to get on the gas hard, make that 7000 rpms or so. Of course, this doesnt count for first gear....

What rpm is the engine at when your going 25mph?

I doubt there is anything wrong with the bike, just keep the rpms up if your planning on giving it a lot of gas.

 

Thanks a bunch justa,

I am quite sure my rpm was less than or equal to 3500. Didnt see it but I can kinda hear it. But your right. going slow and in high gears will obviously bog the engine down. But I never thought it could actually kill the engine?! This has never happened to me b4.

I thought it was fuel starvation but your saying I flooded the engine? Could you tell me mechanically how that works? I understand that the large amounts of fuel came from the act of goosing the throttle. However, when I goose the throttle the same amount but at a higher rpm and correct gear, the bike is not flooded right? How come the bike cannot take the fuel when I am going slow and in high gears, but it can take that same amount of fuel when I am going fast and in the correct gear? I hope my question makes sense.

Now that I think about it, the engine bogged at first and I then yanked the throttle and it died exactly then. That's exactly where I flooded it?

Can you also tell me then why my described scenario could not be fuel starvation? I know you are probably dead on right but I would like to learn.

This is my thinking:
When I would run real low on gas the engine would "bog" a bit, and I would have to pump the throttle or open it wide to keep it from dying. I would then switch to reserve quickly and the problem would desist. This is fuel starvation is it not? So from this experience I can say that it is quite different from the flooding incident. In the flooding problem, opening the throttle wide kills the bike, but in fuel starvation opening the throttle wide can keep you alive for a bit.

However, they had the same engine "bogging" noise! Same noise but from two different reasons? One reason is fuel starvation and the other is from low speed at high gears. damn this is confusing me, how can these two different situations create that same engine bogging sound? And to top it off flooding an engine versus starving it are exact opposites of each other!

I admit the bike had zero problems yesterday b4 the small tune up I gave it. And when I was running the bike today it was all good except for this one case.

im the problem huh?

dude and thanks for listening to my rambling, im just interested in this kind of stuff and would like everyone's input and wisdom!

 

What those guys said.. in that gear at that speed you're probably at 2k rpms or lower which is practically idling. You're probably going to bog when you gas it at anything below 5k or so if you're goosing it. So make sure you downshift a couple clicks!

For me with stock gearing, 2nd gear gets the job done for 25 mph.. probably around 5k rpms, which is right around where I like to keep it for cruising.

 

+1. Is this your first bike?

 

Thanks for all the help. I asked my father about this also and this is what he says:

At a low speed in high gear, you are putting too much strain and load on the engine, thus the engine is working harder to pull the bike. This results in the engine rpm slowing down. As the engine rpm slows down it is sucking in less air/fuel mixture to the intake.

When we open the throttle we are primarily controlling the air (air valve). If we pull on the throttle we get MORE air and this also draws in fuel with it via venturi effect. More air=more fuel (at their respective ratios).

However, in my case where the engine rpm was low and the engine was weakening due to the load of 4th gear at around 25mph, the engine was not sucking enough fuel and air. So when I yanked the throttle I did not "flood" the engine, I made it too lean with too much air and importantly too much air TOO FAST. Thus, my engine died immediately.

Two things to understand:
Other than the accelerator pump, the engine turning and creating that suction is the only time when the fuel is drawn. Opening the throttle is more air than fuel.

The engine was having a hard time sustaining itself BECAUSE it was sucking in less fuel and air; by opening the throttle at that time, I was sucking in air and fuel but more air because the engine was not turning fast enough draw the fuel accordingly to how much I pulled the throttle.

He doesnt know jack about bikes but he did say that I may have flooded the engine when I goosed the throttle since that is a time when the accelerator pump does come on. However, it is most likely due to the air I pulled at that exact moment when the bike could not take it without becoming too lean.

Summary:
1. Engine RPM is low
2. Due to High Gear Load
3. Less Engine RPM=Less fuel and air mixture drawn into the intake valve
4. Throttle primarily controls air (air valve)
5. Opening the throttle wide when the engine is drawing small amounts of air and fuel (due to low engine RPM) would give me more Air than fuel as the mixture hits the intake.
6. This is so because, there is too much of a difference in engine rpm and how much throttle (air) you are pulling.
7. Thus, causing the bike to become too lean too fast.
8. Engine shuts



He explained it better and I guess you guys are correct! I was being an idiot not the bike.

 

nope my 2nd bike. When I kicked it up to 4th at 25mp even my brain was saying "this is not normal wtf are you doing?"

I admit it was foolish

 

Maybe your carbs need cleaned. It should not die from cracking it open at 3500 RPM.