Engine Stumbles, coughs, backfires - Harley Davidson Forums

Go Back   Harley Davidson Forums > Harley Davidson Tech & Mechanical Forum > Exhaust System Topics
Log In 

Exhaust System Topics New and old exhaust system discussions. Fitment issues to sound bites and suggestions. Post them here.

Engine Stumbles, coughs, backfires

Thread Tools Search this Thread
Old 10-14-2011, 11:57 PM
Trek Trek is offline
Senior Rider
Join Date: May 2008
Location: Spokane Valley, Washington State
Posts: 408
Default Engine Stumbles, coughs, backfires

I installed a Thundermax and the bike ran wonderfully for a month. Then all of a sudden it started running very lean. Literally ran great to a stop, then when I restarted the bike ran crappy.

The Thundermax seemed to try and add fuel as it got better but it would not go away. It being a stumble/cough/misfire at 30 mph and 2500 rpm's on up, very light throttle positions.

I put the stock ecm back on. Same problem. Bike runs fine at speed, but not idling around town, unless I lug it at 2000 rpm's....

Any ideas? Harley Dealership just says everything is crap and I need their version of a tuner. I already have the TTS and that map worked just fine...

Appreciate any ideas.
Reply With Quote
Old 10-15-2011, 01:30 PM
nevil nevil is online now
Ultimate HDF Member
Join Date: Jul 2008
Location: southeast PA
Posts: 5,053

It's possible it could have nothing to do with the tuner. An intake leak will cause it to run lean and not run well. I replaced the intake seals twice on my Dyna and it finally runs like it should with the TMax. Also found a leak in the fuel line inside the tank and replaced that.
I would reinstall the TMax, load the correct map again, reinitialize according to Zipper's instructions and see if that makes a difference.
Of course the dealer will bash the tuner because they didn't sell it to you. Properly set up it should pull like a freight train.
Reply With Quote
Old 10-17-2011, 12:19 AM
Trek Trek is offline
Senior Rider
Join Date: May 2008
Location: Spokane Valley, Washington State
Posts: 408

This problem has been resolved. So, after hearing that my TTS map and the Thundermax were poor substitutes and that they would have to install Harley's tuner. Fortunately, they did not know how to flash the ECM so could not get their computer system to communicate with the bike's ecm. So they were encouraging me to send the ECM in to HD for flashing, buy this and that from them for close to 900 dollars.

I said thank you, paid 133 dollars for their fine diagnostic work and the wash job, and took my bike home. Since it was running just like a car would if it had plugged injectors, I bought a can of Redline injector cleaner that my Indy shop guy sold me, run it through the bike. Cost me another 6.00. Put it in the tank, added non ethanol fuel and rode home.

Reinstalled the Thundermax, reinitialized the Thundermax, and went for a 100 mile ride.

Results: Not one single misfire, or decel pop bike ran as smoothly as ever!

I was sure it was a poor connection somewhere since it started running cruddy all of a sudden. Well, I went through another "School of Hard Knocks" and found that I could solve the problem with a really simple solution.

Oh well...
Reply With Quote
Old 10-17-2011, 06:36 PM
Hillsidecycle.com Hillsidecycle.com is offline
Join Date: Oct 2009
Posts: 6,632

Glad it worked out.
315-495-6650 tel/fax
Palmer's Performance Products
Complete H-D Machine Shop
Case Boring, Cylinder boring
Surface Grinding
Complete Cylinder Head Shop
High-Performance Engine Kits
Super-Flow Flow Bench
Crank Rebuilding
Direct Link Dyno Tuning
Goodson HD Tooling Manufacturer
Walk-in Retail Store
Reply With Quote

Similar Threads
Thread Thread Starter Forum Replies Last Post
Power Vision 2 question BeeRAD56 New "Rushmore" Models 8 03-31-2015 10:16 PM
2008 Sportster 1200 Low - Coughing die4toys Sportster Models 7 04-27-2014 08:18 AM
Thunderheader problems chevypilot Exhaust System Topics 2 03-09-2014 07:58 AM
Need some tech help....'02 FLHRCI Navyrep1 Touring Models 6 07-11-2011 03:27 PM
02 Rdkng police engine miss shellsburg18 Ignition/Tuner/ECM/Fuel Injection 17 10-21-2009 02:28 PM

1550, backfires, cough, harley, lite, poor, pops, run, stumbles, throttle

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

All times are GMT -5. The time now is 03:33 PM.