Compression experiment
Thread Starter
|
Tourer
Joined: Aug 2019
Posts: 288
Likes: 141
From: Dental city
Compression experiment
My 07 Road King 96” has a “hot start” problem. The starter kicks out/back and screeches when the motor is at normal operating temperatures but never on cold starts. I cringe and avoid “hot starts” whenever possible. When on a long ride yesterday I brought along spark plug wrench. After about an hour of riding I simply pulled the plug wires and loosened both plugs several turns to release the compression. I retightened them and tried the starter…..No screech or kick out! Down the road I repeated the test a couple more times with the same results. I’ve concluded it’s the compression when the motor is at normal operating temperatures that is causing the starting issue and not the compensator or starter. I wonder how many compensators have been replaced needlessly?
I thinking having compression releases installed is the best solution but I’m still considering other options. Any thoughts?
I thinking having compression releases installed is the best solution but I’m still considering other options. Any thoughts?
Last edited by I Like Pie; Sep 16, 2021 at 03:03 PM.
Stellar HDF Member
Joined: Jun 2017
Posts: 2,231
Likes: 653
From: Atlantic Canada, eh
I wonder if this is what is going on with my bike.?
When warm, if I stall it, or shut it off it WILL NOT start within the first 2-ish minutes, no matter what I do, though it cranks fine.
Ive never tried this cold...only when bike is hot ( I think)
Ill have to run a test.
Drivetrain 100% stock
2004 rkc 88 tc
When warm, if I stall it, or shut it off it WILL NOT start within the first 2-ish minutes, no matter what I do, though it cranks fine.
Ive never tried this cold...only when bike is hot ( I think)
Ill have to run a test.
Drivetrain 100% stock
2004 rkc 88 tc
Outstanding HDF Member
Joined: Dec 2008
Posts: 2,007
Likes: 353
From: Ohio
Compression is often higher with a hot engine vs cold. This is partly due to the fact that ring seal is better when the engine is hot. Also a hot engine will heat up the intake air expanding it. That increases the compression as well. Just these two things are enough for a kick back on some bikes. One solution is compression releases. Another is S&S Easy start cams. And then there's possibly a tuning solution to retard the spark. But before you spend money check to make sure you don't have a large carbon build up in the cylinders with an endoscope.
Stellar HDF Member
Joined: Jul 2009
Posts: 2,825
Likes: 2,140
From: Hope Mills NC, bye CA!!
Trending Topics
Seasoned HDF Member
Joined: Apr 2011
Posts: 6,185
Likes: 2,134
From: W. Texas
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Road Master
Joined: Jun 2019
Posts: 952
Likes: 528
From: Richmond TX
Your '07 never had this problem before, right? It's hard to imagine the compression improved over the years, although now that I type it I suppose you could have a carbon build up. However..... wherever the motor is stopped you'd think at least one valve would be open on at least one cylinder if not both. I wonder if the time spent pulling spark plugs isn't enough time for your problem to clear. Could be temperature related wrt the starter motor, could be a starter solenoid as per the post above. Compensator? Never had problems with mine, maybe engine temperature has an effect?
I would try a starter solenoid and then a start motor long before I pulled the heads to get compression releases installed. Another good thing already mentioned would be a battery load check and thorough cleaning of both ends of both battery cables. Weak battery or loose connections could have your starter solenoid 'bouncing back' when your engine is warm? Good luck getting it sorted.
I would try a starter solenoid and then a start motor long before I pulled the heads to get compression releases installed. Another good thing already mentioned would be a battery load check and thorough cleaning of both ends of both battery cables. Weak battery or loose connections could have your starter solenoid 'bouncing back' when your engine is warm? Good luck getting it sorted.
Stellar HDF Member
Joined: Jul 2009
Posts: 2,825
Likes: 2,140
From: Hope Mills NC, bye CA!!
I will tell you from experience that it is a compensator issue. Upgrade the comp and make sure your battery is good and you can forget about compression releases. This may be the most discussed topic around, that and what kind of oil to use...