Exhaust reverberation..WTF??

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Apr 4, 2011 | 05:10 PM

chipdavey

Thread Starter

Intermediate

Joined: Jul 2009

Posts: 32

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Exhaust reverberation..WTF??

OK thanks folks for the great advise I've recieved from all, on here before. Here is my problem. I have an Evo big twin on a softail, and I am experiencing what a mechanic friend tells me is "exaust reverberation." He says all big twins do this. OK, so heres the deal. A stock 80" big twin, Andrews EV 27 cam, S&S E carb, 2 into 1 exhaust with baffled muffler and a new 6-speed. At 70 to 73 MPH in 6 th gear and 55MPH in 5th, I am experiencing some major sluggishness, at higher RPM, and higher speed it does go away, 80+ in 6th, and 60+ in fifth. Its happening at the same RPM, but I dont have a tach. I am wondering if anyone out there might have had the same, or similar problem? If so what would you recommend to resolve this? Thanks I know their has to be some pretty smart folks out there? And I hope to hear back from some of them. Thanks

Apr 4, 2011 | 06:42 PM

Dr.Hess

Seasoned HDF Member

Joined: Aug 2007

Posts: 8,198

Likes: 3,087

From: NW AR

Sounds like it's not jetted right. I'd guess you need to go one leaner on the intermediate jet. If I was to guess.

Apr 4, 2011 | 07:15 PM

K9r

Intermediate

Joined: Mar 2009

Posts: 37

Likes: 0

Could it simply be because of the six speed gear ratios your not "on the cam"?
More specificaly reaching those speeds at a lower rpm effectively lugging the engine.

Apr 5, 2011 | 02:58 AM

grbrown

Club Member

Joined: Jun 2007

Posts: 45,429

Likes: 2,898

From: Bedford UK

You're lugging the motor at those speeds! On stock gearing in fifth gear your bike will be turning just 22mph per 1,000rpm. So at 55mph your engine is turning at just over 2,000rpm and in sixth at the road speeds you mention it is probably turning only a little faster.

You are asking too much of your bike! Gearing is high and killing your poor motor. Either run the engine at higher revs in a lower gear, or consider changing gearing to give your motor an easier time. Any 'problems' in the exhaust are a distraction.

This is a hobby topic of mine, so I will be happy to discuss further!

Apr 5, 2011 | 08:28 AM

woodnbow

Tourer

Joined: Nov 2007

Posts: 334

Likes: 2

GrBrown's nailed it... BTW, the term your wrench was looking for was 'exhaust reversion'. We all use that term, I suspect very few of us, myself included, really understand it. RB Racing has a pretty good tutorial on the subject FYI..

Apr 5, 2011 | 10:14 AM

#1rocketman

Road Captain

Joined: Mar 2009

Posts: 734

Likes: 0

From: Southern Missouri ( ozarks)

My problem on my ole 92 was kinda similar,although i didn't have a 6speed.I did have an S&S carb and it acted sluggish at cruising speed.Plus it just didn't run all that smooth,period. Got to looking at it and someone in the past put a G carb on it.The motor had a cam in it and whatever else I'm not sure. BUT the G was just too much.I bought an E and the bike ran better than ever...hell like a totally didfferent bike!

Apr 5, 2011 | 10:27 AM

1997bagger

Seasoned HDF Member

Joined: Aug 2008

Posts: 5,078

Likes: 2,150

From: Ohio

Harleys pull air backwards thru the exhaust and can travel to the head in one direction and then has to push it back out on the exhaust stroke in the other direction causing a collision, this is my basic (redkneck) understanding (reversion) from AFR readings and why excessive lean conditions show up in the exhaust when proper fuel is present in the cylinder.

2 into 1 exhaust slow down reversion because one pipe is being evacuated from the other pipes spent gases exiting. TD's have reversion and drag pipes are the worse.

Chipdavey, the members are onto something, not too many HD engines are strong around the 2000 range, grab your favorite beverage (maybe 2 or 3 beverages) and have a indepth conversation with Grbrown, the engineer is going to come out of him.

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Apr 5, 2011 | 12:17 PM

grbrown

Club Member

Joined: Jun 2007

Posts: 45,429

Likes: 2,898

From: Bedford UK

Both 4-stroke and 2-stroke engines use pressure waves in the exhaust to improve performance and essentially over-fill the cylinder - that is what tuned exhausts are all about. In the case of a 4-stroke, when the exhaust valve opens it sends a shock wave down the pipe, which travels faster than the gases themselves. Meanwhile the inlet valve is filling the cylinder with fresh air/fuel mixture, while scavanging the spent exhaust gases. Some of the fresh charge follows the spent gases out of the exhaust valve. The pipe length and features in the muffler reflect that shock wave back up the pipe, so by the time it gets back to the valve it pushes the spilled new charge back into the cylinder, just before the valve closes. Siamesed pipes, such as a 2-into-1 on twins, can be tuned to give better performance, by playing the pipes off against each other. No modern engine builder or manufacturer could consider making their products without optimising exhaust performance.