small engine coil bad?

Lamont in NC · Oct 15, 2021

Father reported his 2 stoke backpack blower wouldn't accelerate.
I didn't test it I just took his word and quickly checked the exhaust screen--it was not plugged and I didn't put it back in.
The air filter was filthy.
I just Installed new carb, fuel lines, fuel filter, air filter, plug. (yes, a dirt cheap kit off ebay--they work)
I demonstrated it ran like a champ.
Next day he says it isn't fixed--same problem.
I try adjust the carb but can't get it to accelerate either--idles great--not exactly bogging when throttling up just runs bad.
I have an induction tach I put onto it and at idle it shows 3,200 rpm give or take 60 or so. When throttled up it fluctuates widely from like 1,400 to 4,500. The tach usually shows leaf blowers idling at 3,000 ish and full throttle at 7,000 ish. Given the tach is actually just ounting ignition impulses could the coil be bad and only causing a problem when throttled up??? You can't get dirt cheap coils.

Thanks.

wore out · Oct 15, 2021

Conventional wisdom would be to try a new sparkplug before suspecting exotic problems. Have you done that?

Lamont in NC · Oct 15, 2021

Yes, I just Installed new carb, fuel lines, fuel filter, air filter, plug. By plug, I mean spark plug. In fact I've tried 3 (spark plugs)--one out of another blower that is working.

T.R.K. · Oct 15, 2021

It would sure help if you told us the make and model blower.

I fixed a Husqvarna trimmer that wouldn't rev up today by installing the correct RESISTOR spark plug in it. (NGK BPMR7A) It had a brand new Chinese plug in it. Some brand I never heard of. Some Husqvarna ignition modules must have resistor sparkplugs to correctly time the spark.

Even the 'E3' and 'First Fire' spark plugs don't tell you if they are a resistor sparkplug or not. At least I couldn't find any info online while I was looking.

guido · Oct 15, 2021

Lamont in NC,

Check the ignition coil gap. Bet you it's too close. Minimum gap should be.010.

If it's @ .010 open it up to .012, it should come alive if it's a good one, .010 to .014 is what most coils call for gap,

Guido.

Geo-TH,In · Oct 15, 2021

Clean all rust off flywheel magnets and ignition coil, then click on my $3 tool.
Always works for me. $3 is close to .010.
If flywheel wobbles try $4. Never had to use $4,
3 tool

Lamont in NC · Oct 15, 2021

Sure, Echo PB260L

Steve@Advance · Oct 15, 2021

Have you checked the exhaust?

Those are governed by a restricted exhaust and there may be a screen.

If too restricted it won't rev up. But that should not make it run rough, just slow.

Does a partial choke help? Or hurt?

Have you disconnected the kill wire at the coil?

544hydro · Oct 15, 2021

(quoted from post at 18:49:08 10/15/21) Have you checked the exhaust?

Those are governed by a restricted exhaust and there may be a screen.

If too restricted it won't rev up. But that should not make it run rough, just slow.

Does a partial choke help? Or hurt?

Have you disconnected the kill wire at the coil?

Ive had the same issue and it was the screen in the exhaust. Good place to check.

used red MN · Oct 15, 2021

I see looking at a parts diagram for the engine ..link.. it has a cylinder that bolts on to the crankcase. Some small 2 cycle engines like this have problems with the cylinder coming loose from the crankcase. Also I see the crankcase has two parts that bolt together. Those bolts need checked for being tight. Also bad seals on the crankshaft can make them perform poorly as well.
Parts diagram

Bret4207 · Oct 16, 2021

(quoted from post at 01:07:27 10/16/21) I see looking at a parts diagram for the engine ..link.. it has a cylinder that bolts on to the crankcase. Some small 2 cycle engines like this have problems with the cylinder coming loose from the crankcase. Also I see the crankcase has two parts that bolt together. Those bolts need checked for being tight. Also bad seals on the crankshaft can make them perform poorly as well.
Parts diagram

Agree, may be an air leak. I also suggest getting a Bosch or NGK plug. I have never had good results with anything other than Bosch or NGK in the last 20 years in small 2 strokes.

Lamont in NC · Oct 16, 2021

One of the plugs is NGK

Lamont in NC · Oct 16, 2021

Everything is tight--a bit of dust but no oily dirt around seals.

Lamont in NC · Oct 16, 2021

as noted it was the first thing I did.

Lamont in NC · Oct 16, 2021

was and is dead on .010 coil is tight

Lamont in NC · Oct 16, 2021

dead on .010

Lamont in NC · Oct 16, 2021

disassembled further.

Nice and clean inside with only light dust--no oily residue. Looked at both seals and they look good. Cylinder is tight to block and I see no evidence of leaking crankcase.

Coil gap is/and was, set at .010

Disconnected coil grounding wire--didn't change a thing.

Tried reving it slowly and it'll go from 3200 to like 4,800 nice and even then gets a missing sound and the inductive tach starts to fluctuate greatly as noted originally 1,200 to 5,400 or so. Lowering the throttle will start to produce good running sound at about 4,800 again.

As I can see it the only thing it could be is the coil doesn't iike high rpms. But why so good at low speed?

Lamont in NC · Oct 16, 2021

tested coil with ohm meter. 2,000 ohms plug socket to ground.

For comparison:
I have a running homelite blower who's coil tests 3,000 ohms.
I have 2 tihl BR320s which both initially started at like 6,000 and went up over about 10 seconds to infinate--I never could get a reading on them again. WTF?

guido · Oct 16, 2021

Lamont in NC,

Its probably O.K. Still I would suggest trying another WIDER setting. Doing so will slightly retard the timing a bit, this will make sure you burn all the gas going in.

If the wider gap has no effect, I suspect you may have some kind of fuel issue. Use the choke to see if that improves it running. To check the head for tightness, grab the spark plug, and see if you an feel any movement of the head,

Guido.

Geo-TH,In · Oct 16, 2021

Time to try another coil, spark plug.

When it starts to stumple, what happens if you add a little choke?

Try new gas. Different oil mix.

Could be you have a crankcase leak.

If all else fails, target practic time.
I refuse to work on 2cycles.
I have a 20v leaf blower. BOSS loves it to clean garage with.

Easy start. California compliant. Haha

rlp in Co. · Oct 16, 2021

Sounds like it is running lean on gas. Did you adjust the needle screws?

Bret4207 · Oct 16, 2021

(quoted from post at 13:02:19 10/16/21) disassembled further.

Nice and clean inside with only light dust--no oily residue. Looked at both seals and they look good. Cylinder is tight to block and I see no evidence of leaking crankcase.

Coil gap is/and was, set at .010

Disconnected coil grounding wire--didn't change a thing.

Tried reving it slowly and it'll go from 3200 to like 4,800 nice and even then gets a missing sound and the inductive tach starts to fluctuate greatly as noted originally 1,200 to 5,400 or so. Lowering the throttle will start to produce good running sound at about 4,800 again.

As I can see it the only thing it could be is the coil doesn't iike high rpms. But why so good at low speed?

The seals may be okay, but seals can leak in one direction and not the other. If it's not a carb adjustment, if trying a little choke doesn't help, if a slightly wider coil gap doesn't help...have you checked the plug wire from the coil to the plug? Any sign of broken insulation? Could be the coil, but IME when a "solid state" coil goes bad they go bad altogether. They aren't like a tractor coil that goes bad when hot from what I've seen. I'd try another Bosch or NGK plug first before assuming it's the coil.

Texasmark · Oct 18, 2021

I just had one on an 18 hp BS V twin. Turns out an good sized rat crawled up under the air deflector cowling, on top of one of trhe cylinders and once getting in, couldn't get out. Over time the cylinder and I guess the coil got hot and it finally died.

small engine coil bad?

Member

Well-known Member

Member

Well-known Member

Well-known Member

Well-known Member

Member

Well-known Member

Member

Well-known Member

Well-known Member

Member

Member

Member

Member

Member

Member

Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Similar threads