Author Topic: 88 flstc sluggish and backfiring (Read 828 times)

hogget · « **on:** April 02, 2021, 01:03:41 AM »

after sitting neglected in the garage for about a year, i pulled the heritage out for a run yesterday - started fine, but i noticed it was backfiring on overrun and was very sluggish on acceleration - otherwise ran ok for a 120 mile ride
today i checked the soft inlet manifolds for cracks - none - and replaced the voes hose - it was a bit cracked and tested the voes - its fine - filled with new fuel - but no improvement, still sluggish and backfiring
sounds to me like an air leak on the inlet side for the backfiring, but not sure about the sluggishness
any ideas???
thx rory

Scotty · « **Reply #1 on:** April 02, 2021, 02:01:57 AM »

Pull the carb off and take it apart and clean all the jets and passages in the carb.
Sitting around for a year + the fuel has probably dried and blocked the tiny holes in the jets and passageways.
While you have it of if you have the means replace the manifold with a one piece and new seals.

Hossamania · « **Reply #2 on:** April 02, 2021, 05:26:36 AM »

A couple new spark plugs probably wouldn't hurt either.

JW113 · « **Reply #3 on:** April 02, 2021, 08:02:59 AM »

Yep, sounds like the textbook symptoms of gunk in the pilot jet circuit. As Scotty said, pull carb, clean everything. And don't forget those little holes in the bottom of the bore near the throttle plate (i.e. transfer ports).

-JW

RTMike · « **Reply #4 on:** April 02, 2021, 08:31:29 AM »

david lee · « **Reply #5 on:** April 02, 2021, 12:37:05 PM »

Quote from: JW113 on April 02, 2021, 08:02:59 AM

Yep, sounds like the textbook symptoms of gunk in the pilot jet circuit. As Scotty said, pull carb, clean everything. And don't forget those little holes in the bottom of the bore near the throttle plate (i.e. transfer ports).

-JW

had that happen before. blocked pilot jet after sitting and not draining the carb

hogget · « **Reply #6 on:** April 02, 2021, 03:47:19 PM »

thanks guys, will give that a go
should have said it has a screaming eagle carb on it - from new, but the same principle applies and it has a pilot jet, so i'll get to it

Burnout · « **Reply #7 on:** April 02, 2021, 04:45:27 PM »

Which Screaming Eagle carb?

Some of those carbs offered should never have been bolted onto a motor.....

hogget · « **Reply #8 on:** April 02, 2021, 08:09:55 PM »

checked the carb (keihin 40mm pumper - 33 years and 40k miles)- pilot was blocked - back together, but no difference
changed the plugs (6 years since last set), seems much better,but still backfiring in the pipes on overrun - crack the throttle a bit and it stops, so will check the exhaust flange gaskets
will fit a fuel filter
thanks for the suggestions

Hossamania · « **Reply #9 on:** April 02, 2021, 08:20:14 PM »

In-line fuel filters don't work well in general. Check the screen on the petcock. I have seen them swell and deteriorate over time.

guido4198 · « **Reply #10 on:** April 05, 2021, 03:28:40 AM »

Another vote AGAINST inline fuel filters. I've seen them be the source of more problems than they solve. If your tank and petcock are in such bad condition that you need a fuel filter...you don't need a fuel filter, you need to pull the tank and petcock and solve THOSE problems.

JohnnyCashPan · « **Reply #11 on:** April 05, 2021, 04:51:58 AM »

As long as you're chasing crud in the fuel system replace all rubber fuel lines. If it sat for a year with old fuel in it, they could be flaking off internally.and adding to the problem.

hogget · « **Reply #12 on:** April 06, 2021, 05:59:36 PM »

thanks for the feedback - will have another shot at it today taking into account the above, because its still not running right

hogget · « **Reply #13 on:** April 06, 2021, 07:28:10 PM »

so, carb apart again, jets and passages cleaned and blown thru, new fuel line, no filter
tanks are in perfect condition - must admit i was surprised
screen in fuel tap is fine, had some loose crud on it but no way would that amount have restricted flow
checked exhaust flange nuts - all tight and dont appear to be leaking
took it for a ride - no change - still sluggish and backfiring
i want to think its fuelling, but not sure what else to check
thanks again for your advice
rory

Scotty · « **Reply #14 on:** April 06, 2021, 11:05:04 PM »

Quote from: hogget on April 06, 2021, 07:28:10 PM

so, carb apart again, jets and passages cleaned and blown thru, new fuel line, no filter
tanks are in perfect condition - must admit i was surprised
screen in fuel tap is fine, had some loose crud on it but no way would that amount have restricted flow
checked exhaust flange nuts - all tight and dont appear to be leaking
took it for a ride - no change - still sluggish and backfiring
i want to think its fuelling, but not sure what else to check
thanks again for your advice
rory

It has all the signs of being fuel but perhaps pull the nosecone cover off and check the pickup is not leaking or burnt it could be on it's way out.

FSG · « **Reply #15 on:** April 06, 2021, 11:32:19 PM »

Quote from: Hossamania on April 02, 2021, 05:26:36 AM

A couple new spark plugs probably wouldn't hurt either.

brother did a LOT of work on a friends Evo Heritage last year only to eventually find a new set of plugs cured the problem

hogget · « **Reply #16 on:** April 06, 2021, 11:50:17 PM »

thanks scotty, i was thinking it might be electrical/battery but didn't know about the pickup (have had probs with batteries on other elec ign bikes recently)
will check that as well as testing charging circuit and running voltage - battery 'seems' fine - heaps of grunt to start and registers 12.7v with ignition off
thanks again

Hossamania · « **Reply #17 on:** April 07, 2021, 04:54:45 AM »

Check the tank vent, gas cap for air flow.
Could the voes be acting up, not allowing ignition advance?

Scotty · « **Reply #18 on:** April 07, 2021, 12:21:58 PM »

Quote from: FSG on April 06, 2021, 11:32:19 PM

brother did a LOT of work on a friends Evo Heritage last year only to eventually find a new set of plugs cured the problem

Not wrong and cheap to do as well.

JW113 · « **Reply #19 on:** April 07, 2021, 07:09:47 PM »

Popping and backfiring on deceleration? A common culprit of that is old dry or cracked intake manifold O-rings, the ones that go around the manifold spigots and against the heads. Also, check your VOES (if you have one) to make sure the little diaphragm in there is not cracked. Need a Might-T-Vac or something similar to check properly.

-JW

kd · « **Reply #20 on:** April 07, 2021, 07:51:58 PM »

.... and exhaust gaskets or muffler joints.

hogget · « **Reply #21 on:** April 07, 2021, 09:21:08 PM »

while i'm at this, does anyone know where to get a new air cleaned for the screamin eagle carb - it has k&n F026A6 on it, but can't find that anywhere online (it too is 33 years old)

hogget · « **Reply #22 on:** April 07, 2021, 11:00:02 PM »

checked the pickup - looks ok to me, but i've never seen one before
have checked voes, new plugs, exhaust mounts to heads and and muffler are ok
haven't yet checked gas cap venting, manifold o rings or battery/charging - this will take another week because i'm doing the 100/100/100/100 ride (on the 100th day of the year, bike and rider >= 100 years old, 100 mile ride and at least 100mph) tomorrow and then out of town
thanks again for all your suggestions - i'm sure we'll get there in the end
rory

hogget · « **Reply #23 on:** April 07, 2021, 11:30:35 PM »

meant to attach this pic of the pickup
[ You are not allowed to view attachments ]

Scotty · « **Reply #24 on:** April 07, 2021, 11:59:44 PM »

Looks like something melted in the pickup in the top left corner.

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Author Topic: 88 flstc sluggish and backfiring (Read 828 times)