Runs great until fully warm, looses power backfires and dies

[NEWFISHER]

They say 19 year old Swiss guys can fix them, I guess I need to start learning to yodel?

After getting the front ride height dialed in Sunday, I took it up in the woods for some light wheeling and lock to lock full stuff to check clearance and listen/feel for any suspension issues. After a backwards downhill bounce and a 3 minute drive onto the gravel road, the Pinz backfires a few times, looses power feather throttle and dies. Cranks over well and wants to start 1 time out of 20 trys. On the 21st-ish try, it stumbles, clears its self and then idles. When throttled, will backfire and die or if I put it on gear and under load will die a within 10 feet. Sometimes will idle for several minutes until it dies.

I let it sit overnight and changed the fuel filter, has fuel pressure on pump to carb side, checked all connections for the SSi , test voltage from ignition switch and everything looks good so I fire it up. Sync the carbs( were not far off) and take off. It warms up, runs super smooth as always when warm, then after 5-8 miles, looses power, backfires then dies. Repeat the same process except this time the muffler rips open on one backfire and attempt to start.

It runs great until Sunday and when cold, runs great, smooth, idles well, pulls throttle well in all gears but then after warm and several miles, acts like its running out of fuel. It has a Andre Stainless tank, clean lines and filter, good pressure, all lines tight and no leaks, sync'd carbs. It back fires when the problem happens, so im assuming fuel is getting into the carbs and ultimately the muffler because it now sounds like a dragster and the muffler looks like an open face taco.

Ignition switch cleaned with contact cleaner and feels snappy and tests good. It seems temperature related after warm and 5-8 miles driven. Let it sit overnight and all is good until the next 5- 8 mile drive.

Ive read a few threads, searched " backfire" , have a schematic sent from SSi , but havent tested the coil or ignition when its acting up.

Im ruling out valve adjustment , timing and carbs because it runs to well, smooth and great power when its started the next day , warmed up and driven 5-8 miles.

Anyone go through this?

My wife is getting good at flat / strap towing me

Thanks

[edzz]

Sounds like ignition related. The ign switches can sometimes be funky. I don't know the SSI systems however if it were me i would setup a temporary circuit to provide power to the SSI system / coil to rule out every thing between the SSI system and the battery +24v terminal. sounds like your getting plenty of fuel BTW, sorry to hear about your former muffler.

[NEWFISHER]

Oops.

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[pcolette]

Are you using the original fuel pump or an electric?

For a backfire strong enough to split the muffler, it seems like quite a bit of fuel had to get in the exhaust system. Any chance that your carb floats are sticking?

[Haf-e]

Sounds like a coil failure - I would change them out to eliminate that possibility.

With a regular (single coil) ignition system - a bad coil would cause the engine to stop running. With a (multi-coil) system - the engine will run partially with one bad coil.

I think the SSI uses two double ended coils? That would knock out two cylinders. and the engine would run as described - barely. Some coil failures open only when they get hot which only occurs under load - so they can idle ok...

One good tip is to use a infra-red thermometer on the header tubes to see which cylinders are not firing... there would be a big temp difference.

[Jimm391730]

Check the valve clearance; the clearance may be just barely enough to properly close when cold, but as it heats up they might not be closing completely -- a partially open exhaust valve would both force fuel/air mix into the exhaust, and then ignite it... and tight valves do give much improved power as long as they can close.

The warm/cold difference seems to point out a mechanical issue.

[NEWFISHER]

Thanks guys. Going to start with compression test , valve adjustment first to verify all good there. Rick with Pinz SSi has been very helpful with diagrams and places to test. I ordered carb kits from EI too. It just runs so good at first until it decides to fail and then nothing but cranking to start and backfiring with the occasional getting it to idle then dies as its put in gear with a load on it, which makes me think coil. This morning it fired right up again. I have the dog house off and will start checking valve adjustment/timing tonight.
Thank you for the responses, words of wisdom

[Texas710]

Open faced taco...! Good description, sorry about the muffler.

Valves are a good place to look, wondering if an advance could cause that as well, I know I had a bike that was not advanced right and it would idle just fine but no power under load.

[Andre]

Pull the cover off the drop in timing wheel on the SSI unit. double check that the timing hasn't changed. When I first got my system, i hadn't checked the screw that held the timing wheel on and it was allowing the timing to change. It would loose power and back fire because it would move so far out. installed a lock washer on the screw and problem was solved.

[NEWFISHER]

Thanks Andre for the tip.

Here's what I know so far:

SSI screw checked and is tight. Checked timing and the SSI led comes on just a camel hair past TDC on clockwise rotation ( will adjust after test drive)

Adjusted all valves. Spark plugs look okay. Nothing standing out, most were tighter than 0.20, but sounded loose when engine running? Compression good. Cyl #4 valve cover internally darker than the others. Most likely last in the row on an air cooled engine. Harleys have rear cylinder temps greater than front too.

I received the carb kit from EI, called Jim L to send them to have him go through them, but he is swamped and my turn around time didn't sound good so I grabbed a buddy who is fantastic with Rochesters ( a crazy stupid carb), Webbers, Holly's etc. and had him go through them. He found several issues that would cause a backfire and flooding condition. missing orings, loose bodies that I had lock tighted but had the screws pull out. He installed nut serts, checked all components for warpage on a 600 wet stone and reinstalled them.

It starts, runs, idles better with less fuel enrichment aka choke, still cold blooded as hell and didn't die on my first test drive. Crossing fingers for a longer drive with no flat tows

I am waiting for some numbers from Jim L and hope to inject this thing

[Jimm391730]

Adjusted all valves. Spark plugs look okay. Nothing standing out, most were tighter than 0.02,

I hope you meant 0.20mm valve clearance, cold. 0.02mm would have been WAY too tight (but would give very noticeable increase in power, assuming they seat!). FYI, 0.20mm = 0.008".

[NEWFISHER]

Adjusted all valves. Spark plugs look okay. Nothing standing out, most were tighter than 0.02,

I hope you meant 0.20mm valve clearance, cold. 0.02mm would have been WAY too tight (but would give very noticeable increase in power, assuming they seat!). FYI, 0.20mm = 0.008".

Yes, mistake. Corrected to 0.20mm thanks for catching it.

[NEWFISHER]

I beat the muffler closed and goober welded the seam, have to say I almost left it as it sounds fine just looks like crap. I didn't want to test drive with an open muffler, tune etc. Test drove over to the muffler shop to dumpster dive some "new old stock" mufflers and it ran well, no backfire and dying. 10 minutes in to the metal scrap pile, I found a 6" x17" round 2 inch in and 1 out with a hanger tab for what looks like an older Mercedes sedan? Looks like it will work. I'll get it welded up and a further test drive.

[NEWFISHER]

You have do what you have to sometimes! Thin metal, wind blowing and not having the tire off I am surprised it looked this good!

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[NEWFISHER]

Here's the scrap pile replacement. The part number burned off befire I could remember to snap a pic. Its 1 inch longer , fits perfect, sounds great and was free! I will try to update the info on the part number if the muffler shop remembers it.

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