Get XiED(tm)! Performance Parts

Don't let the Harley heat monster ruin your riding.
Reduce  Engine Surging
Improve Throttle Response
Reduce Engine Ping


HD 2007/2008 Engines

High Heat on 2007/08 HD engines

HD 2007/08 Performance Recommendations

Cool your exhaust temperature with the Wide Band O2 upgrade for 2007/08 HD

Harley Camshaft Specification Tables

HD Twin Cam Engine Builds
TC 128 HP 95 CID
TC 100HP Street Engine

The basics of Fuel Injection explained

Rammer Performance Air Cleaners
TC Performance Heads 100+HP

Pro Tuning on a Shade Tree Budget


Finding Intake Manifold Air Leaks

Your engine had been running fine. Recently it has started running poorly, maybe when its warm, maybe when its cold or sometimes the problem just seems to come and go. The problem shows signs of both a rich and lean running carburetor. You have done the obvious like change jets, replace spark plugs, check plug wires and replace your air filter element, but the problem persists. You and your mechanic are quite frustrated because you can't seem to identify the problem.

Erratic symptoms like these can be the sign of an air leak at the intake manifold or carburetor.

The design of the Harley-Davidson engine and the intake manifold make it prone to air leaks. Improper installation and age are two major contributors to the condition. Symptoms usually develop just after working on or around the carburetor.

Finding an air leak at the manifold is simple. All you need is a can of penetrating oil (like WD-40) with the extended nozzle attached. With the engine idling, direct a heavy spray of  the penetrating oil at the manifold gasket area and base of the carburetor. When the spray hits the area leaking, there will be a distinct change in the sound of the engine. If the air leak is major, the change in sound will be quite obvious. Smaller leaks may only create minor changes in the sound.

The engine temperature need to match the times the problem most frequently occurs. If you accidentally spray the exhaust system, you may get a little smoke. The penetrating oil can be cleaned up by washing the bike after the engine cools.

Most carburetors have vacuum lines or fittings attached. The vacuum line(s) normally run to the VOES and on late model bikes, the fuel petcock. If you suspect an air leak, just replace these hoses. You can get vacuum hose at your local auto parts store. Replacement of the hoses is the best way to eliminate vacuum leaks here.

The CV carburetor has one additional area that can create problems. The slide has a neoprene diaphragm at the top. If the diaphragm is installed improperly or develops cracks, an air leak will occur. Problems are most likely to develop just after re-jetting or  making modifications to the carburetor. Make sure you properly install this diaphragm after upgrading your CV carburetor. The diaphragm must be properly seated or an air leak will develop.

Using this information, you now have the means to identify the cause of may baffling performance problems on your engine.

Table of Contents
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Modification, Installation, Maintenance and Tuning Index  will help you find most of the information you want on one page.

How to get Professional Tuning Results at home
Testing the Innovate Motorsport LM-1 portable air fuel meter

Profession Tuning on a Shade Tree Budget

Veypor VR2 Data Logger and Instrument Panel
Video Installation and Demo
Purchase VR2

Engine Performance
How to Build a
TC96 2007 Engines
TC88 70HP Stage1  
TC95 128HP Stage 3
TC95 100HP Street
TC96 2007 Stage 1/2
EVO 64 HP Stage 1
EVO 74 HP Stage 2
EVO 82 HP Stage 3
EVO 95 HP Stage 3
883 to 1200 Upgrade
Shovelhead Modifications

New EFI for EVO and TC

Performance Gallery
Horsepower Gallery
Evolution 80
Twin Cam 88/95
Evolution Unlimited
Sportster Unlimited
Drag Strip Gallery
Land Speed Racing Gallery
CV Carburetor
Modifying the CV carb
Tuning a CV carb
Selecting a cam
Install a TC 88/95 cam
Install a Big Twin cam
Install Sportster cams

Camshaft Specifications
Twin Cam

Exhaust Systems
EVO Exhaust Testing
TC Exhaust Testing
Khrome Werks AR100 test
Making Drag Pipes Work

Shop Manual
Carburetor Troubleshooting
Finding Manifold Leaks
Cylinder Heads
Pistons and Cylinders
Belt Drive
Shop Manual Appendix
$20 Bike Lift
Plug Wires
Spark Plugs
Engine Tuning
Nitrous Oxide
Motor Oil
Stutter Box
General Information
WEB Links
Buy Books and Manuals
Performance Calculations
Estimate Horsepower
Estimate 1/4 Mile Time
Estimate Top Speed

Engine Displacement
Exhaust Length
Gear Ratios
Air Density

The Nightrider Diaries
The ramblings of a genius a, a madman and something in between.

Where is Sifton Cams?

Autocom Active-7 tested

Harley-Davidson EFI
-EFI basics explained
-EFI modifications explained

183 HP, 2 carbs, 2680cc

Copyright 1997-2006  Stephen Mullen, Oldsmar, FL -+-