Down on power and sounds like a lawn mower - post carby rebuild (FLHP/1996 big twin evo)

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Down on power and sounds like a lawn mower - post carby rebuild (FLHP/1996 big twin evo)

FLHP1996
5 years ago

Hi all,

Just wanting to see if i can get some guidance on what to check next and if other people have experienced similar issues.
The motor on my bike is a 1996 big twin evo (frame is a 1984 FLHP) and in the last couple of months I've started to experience some issues.

After running for approximately 15 - 20 minutes, it seems like the bike almost goes into limp mode. The power drops, the engine starts to sound like a lawn mower or a two stroke motor, you try to accelerate but it doesn't really go anywhere, revs don't increase. The bike starts to vibrate as you're trying to pick up revs but it refuses to accelerate and sounds horrible. Sometimes I can tell it's starting to happen because the engine gets really hot (first Harley so not sure if this much heat is normal) and i can feel the bike gradually losing power. It still kind of rides OK but i can tell it doesn't have the same power and eventually it goes into limp mode. Sometimes if you drop a gear and continue to hold the throttle open, all of a sudden the revs pick back up and the bike goes again (it feels like something is stuck and finally lets go).

I've rebuilt the carby and replaced the cylinder sleeve along with the plastic diaphragm. i replaced several spring, o rings, the float needle (and readjusted it to the correct angle) and the diaphragm in pump. I cleaned everything up and put it back together. The bike ran great once i got the carby back on the bike. The bike seemed to work fine for a couple of hours and then as i was getting home it started doing the same thing. If i let it cool down for 30 - 60 minutes it starts up and runs fine.

The issues seems to occur when the bike gets hot - either riding in hot conditions or in traffic. It has also happened a couple of times when i would fill up a full tank of fuel (i'm not sure if this is related to the issue or just a coincidence).

I'm still thinking this is a carb problem? Could it be that the carb is getting flooded? but why doesn't the issue present itself as soon as i start the bike?
After the carb rebuild it ran well for a couple of hours (i thought it was fixed because it didnt have any power issues in the first 30 minutes) but it's come back.

could it be a dirty tank, fuel filter and is it common for the evo's to overheat?

Any suggestions/ideas would be appreciated.

Thanks

Evo
5 years ago

Mate, its an evo so it doesn't have a limp mode. As stated, check your VOES but Evo's are a very simple animal, you only need spark, fuel and air. I am leaning towards your coil playing up. It if has a slight crack, it will play up when it gets hot so that you will go from two cylinders to one and back again making for the viberation and lack of power. Would be worth checking.

FLHP1996
5 years ago

Hey mate,
Thanks for your reply.
I've definitely seen the VOES (black vacuum looking thing) hanging around the carb/manifold but didn't know what it is.
I'll get it off the bike tomorrow and just go ahead and replace it.
I'm not sure about the timing. i'll have to look at that tomorrow as well. Although how do you adjust ignition timing (i know how to do the cam timing)?

Yes, i'm running electronic ignition.

i've had the bike for about 12 months. i bought it from my cousin who's had it for over 10 years. it was built by him mate.

thanks again for your help.

FLHP1996
5 years ago

Quoting Evo on 10 Jan 2019 10:00 PM
Mate, its an evo so it doesn't have a limp mode. As stated, check your VOES but Evo's are a very simple animal, you only need spark, fuel and air. I am leaning towards your coil playing up. It if has a slight crack, it will play up when it gets hot so that you will go from two cylinders to one and back again making for the viberation and lack of power. Would be worth checking.

Hey mate,
Thanks for the advice.

I know it doesn't have limp mode, just didn't know how else to articulate the symptoms.
That's definitely another things i'll be checking, although i think it was changed a couple of years back. Any idea how to work out if it's faulty?

Thanks

daddyracer56
5 years ago

clean fuel tank & cock & check fuel flow for any restrictions etc & set fuel bowl level 7/8th's full bowl, also check all main wiring terminals & give ign key a wiggle , if not better replace ign system completely pick-up & coil
cheers

tussuck
5 years ago

If its fine cold and then turns to chit when warm then it does lean towards a electronic issue. I chased a similar issue and it ended up being the Ignition module in the cam nose. Replaced with a new Ultima one and have not looked back since. Assuming heat related then:
Coil
Ignition module
battery on its way out
- Regulator buggered and cooking battery
- Alternator buggered and cooked Regulator which is cooking battery
- Check these with a multimeter and see what voltages are happening at battery.
And lets not forget earths getting frayed
Redo the all the nuts on the fuses etc as well.

FLHP1996
5 years ago

Thanks mate. I've just ordered myself a manual and i'm also thinking it's probably not timing but will be one of the things i check.
The coil was changed about two years ago so i'm thinking it might not be that either but will definitely keep it in mind.
I think i'll start with the fuel and move from there. i'm planning to take the tank off, give it a good clean, remove/clean the petcock and change the fuel filter.

Thanks again.

FLHP1996
5 years ago

Quoting daddyracer56 on 12 Jan 2019 12:33 AM
clean fuel tank & cock & check fuel flow for any restrictions etc & set fuel bowl level 7/8th's full bowl, also check all main wiring terminals & give ign key a wiggle , if not better replace ign system completely pick-up & coil
cheers

Thank mate, I'll be giving it a clean on Saturday. hopefully it fixes the issue.
I adjusted the fuel bowl according to the instructions when i was rebuilding the carb but it wasn't to 7/8th full. you think that's a better set up?

Any tips on cleaning the tank?

Thanks

FLHP1996
5 years ago

Quoting tussuck on 12 Jan 2019 01:39 AMedited: 12 Jan 2019 01:40 AM
If its fine cold and then turns to chit when warm then it does lean towards a electronic issue. I chased a similar issue and it ended up being the Ignition module in the cam nose. Replaced with a new Ultima one and have not looked back since. Assuming heat related then:
Coil
Ignition module
battery on its way out
- Regulator buggered and cooking battery
- Alternator buggered and cooked Regulator which is cooking battery
- Check these with a multimeter and see what voltages are happening at battery.
And lets not forget earths getting frayed
Redo the all the nuts on the fuses etc as well.

Thanks mate, i'm going to try to work through the list. Coil and ignition is the next on the list once i get the fuel system cleaned up.

Topics

Down on power and sounds like a lawn mower - post carby rebuild (FLHP/1996 big twin evo)

Down on power and sounds like a lawn mower - post carby rebuild (FLHP/1996 big twin evo)

FLHP1996

Evo

FLHP1996

FLHP1996

daddyracer56

tussuck

FLHP1996

FLHP1996

FLHP1996