Bog
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Cruiser
Joined: Apr 2007
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Bog
Okay so I got a 45mm Mikuni on my 103" big bore FLHTC, I have a definite bog or power bog in certain areas. Around 70 mph if I gas it, it spits and sputters for about a good 4 seconds, then goes. I also experienced this in other areas. Seems to delay before it really takes off?
I have heard maybe dirty jets in my carburator? Or completely plugged jets? Do you guys think this is the problem? Dealer I calledsaid the carb probably needs to be retuned?
I have heard maybe dirty jets in my carburator? Or completely plugged jets? Do you guys think this is the problem? Dealer I calledsaid the carb probably needs to be retuned?
Outstanding HDF Member
Joined: May 2007
Posts: 2,304
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From: Florida
RE: Bog
ORIGINAL: FX4 Level II
Okay so I got a 45mm Mikuni on my 103" big bore FLHTC, I have a definite bog or power bog in certain areas. Around 70 mph if I gas it, it spits and sputters for about a good 4 seconds, then goes. I also experienced this in other areas. Seems to delay before it really takes off?
I have heard maybe dirty jets in my carburator? Or completely plugged jets? Do you guys think this is the problem? Dealer I calledsaid the carb probably needs to be retuned?
Okay so I got a 45mm Mikuni on my 103" big bore FLHTC, I have a definite bog or power bog in certain areas. Around 70 mph if I gas it, it spits and sputters for about a good 4 seconds, then goes. I also experienced this in other areas. Seems to delay before it really takes off?
I have heard maybe dirty jets in my carburator? Or completely plugged jets? Do you guys think this is the problem? Dealer I calledsaid the carb probably needs to be retuned?
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Cruiser
Joined: Apr 2007
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RE: Bog
Not sure what jets exactly, it has SE heads, SE jugs and SE pistons, Andrews 260 cams, mikuni 45 carb. Also have the SERT.
Dealer just told me today it is loading up, too much gas, so I am taking it in to run on the dyno to thin out the air/fuel mixture I guess.
Dealer just told me today it is loading up, too much gas, so I am taking it in to run on the dyno to thin out the air/fuel mixture I guess.
Road Master
Joined: Jul 2005
Posts: 1,061
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From: Fort Worth TX
RE: Bog
Well being that it is a carb bike and quick way to see to check a carb issue. Pull the choke out in the rpm range that is is running poorly. If it gets worse you are too rich if it improves you are lean. What do the spark plugs look like?? We often see plugs that are just plain worn out. Some will let the bike idle too long with choke on, and foul the plugs. etc. Start with the basic's first. A new set of plugs gapped and start from there. IF you take it for a short ride and the plug is solid black well yes you are overly rich. New jetting adjustments are needed. I have the Mik tuning book on my site under tech info if you do not have one. It will get you in the ball park. Whacking the throttle wide open on that set may be part of the issue. Increasing the rpm / gear selection when you open the throttle.
A dyno tune would be the best thing to ensure the afr is correct across the board.
A dyno tune would be the best thing to ensure the afr is correct across the board.
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Joined: May 2007
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From: Florida
RE: Bog
The 260 cams are a top end cam this means the lower rpms are going to suffer, this along with a mechanical slide on the carb can and will cause some low rpm stumbling when you wack open the throttle.
I call 1500 to 2500 low rpm cruising with a cam like your running, so if you are cruising at 60 mph your tacking about 2400 to 2500 rpm....when you snap the throttle open at this rpm the slide goes wide open and your getting some reversion from the overlap of the cam and the engine will studder because the air flow doesn't know which way to go....if you go higher in the rpm range (like 3000 to 3200 rpm) and snap the throttle open the engine should take it because the overlap is working for you at this engine speed.
You might get some of this out with a good tune but I doubt it, I think it's an air flo and cam overlap problem.
I'd keep up myrpms or change the primary gearing to achieve a 3.37:1 final drive...this will raise your rpms to mph ratio and keep you on the power band of that 260 cam. Personally I think your way over cammed for a 103'....I get 117/119 with a .590 lift cam and 105/110 with a .510 lift cam in the 103' consistently.
I call 1500 to 2500 low rpm cruising with a cam like your running, so if you are cruising at 60 mph your tacking about 2400 to 2500 rpm....when you snap the throttle open at this rpm the slide goes wide open and your getting some reversion from the overlap of the cam and the engine will studder because the air flow doesn't know which way to go....if you go higher in the rpm range (like 3000 to 3200 rpm) and snap the throttle open the engine should take it because the overlap is working for you at this engine speed.
You might get some of this out with a good tune but I doubt it, I think it's an air flo and cam overlap problem.
I'd keep up myrpms or change the primary gearing to achieve a 3.37:1 final drive...this will raise your rpms to mph ratio and keep you on the power band of that 260 cam. Personally I think your way over cammed for a 103'....I get 117/119 with a .590 lift cam and 105/110 with a .510 lift cam in the 103' consistently.
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Cruiser
Joined: Apr 2007
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RE: Bog
Doc 1, wow thanks for all the helpful info! I kind of knew a little about cams, but didn't knwo that much!
I agree with the RPM's being too low to open the throttle up and it pukes, that is exactly what I thought too, that I am cruising at too low of an RPM? I am use to my old sporty, so I guess maybe that's why?
So do you think I should be cruising in 4th gear at like 60-65 mph instead of 5th? I know that is where the power band is strong.
Again thanks for the help!
I agree with the RPM's being too low to open the throttle up and it pukes, that is exactly what I thought too, that I am cruising at too low of an RPM? I am use to my old sporty, so I guess maybe that's why?
So do you think I should be cruising in 4th gear at like 60-65 mph instead of 5th? I know that is where the power band is strong.
Again thanks for the help!
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Cruiser
Joined: Apr 2007
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RE: Bog
Thanks for the info guys! I am getting 112/109 currently, so you are saying that I would get even more HP and torque with a different cam?
So should I be running more in 4th gear at highways speeds witht that cam so I have instant take-off power? It feels weird to be running that high of an RPM consistenly but I am use to my old stock sporty!
So should I be running more in 4th gear at highways speeds witht that cam so I have instant take-off power? It feels weird to be running that high of an RPM consistenly but I am use to my old stock sporty!