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David is a Technical Moderator, for Baron's Custom Accessories Technical Forum
Your engine had been running fine. Recently it has started running poorly or backfiring, 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 Road Star 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.
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.
Bulldog
Barons Custom Technical Form Staff
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Finding Intake Manifold Air Leaks
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#1Darkwingduck commentedEditing a commentThere is a capped vacuum port on the manifold of my 04 rodie, the manuel show it going to a hose but is vague on what, or where, said hose is supposed to run to. Can someone point that out for me? I do not see any un attached hoses for this to povent to. Been running rich with occasional backfire on hard acceleration out of first. doesn't seem to have the top end power shes had before. A slight high pitched wheeze off the top end of throttling. I'm going to give the carb a spray out and port the manifold. noticed a possible gap spacing between the air filter housing and the carb intake... I let a shop work on her awhile back and it seems ever since then I've been coming across things not re-attached properly... hmm -
#2Darkwingduck commentedEditing a commentShes always burned rich, I assumed it was the jetting the shop did for the big air breather that the previous owner put on and cobra pipes..
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#3Darkwingduck commentedEditing a commentUpon further reading I see this bikes AIS has been removed and plugged. so the cap on the manifold will stay, the vacuum hoses on the top of the cylinder head are still running to open hoses, do i disconnect the 2 or plug them?
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