http://en.wikipedia.org/wiki/Edmund_BurkeBasically, change when it is needed and shown to be needed, but stay the course if no change is needed. Thus Burke supported the American Revolution for it was needed change given the British attitude to American of the 1770s, but Burke opposed the French Revolution for it made changes that were NOT needed, even if an improvement. Thus the test for a Conservative of the Burke School was simply, was the change needed? not that the change was good or bad (Change for the Good was a viewed as a "Liberal" movement).
This view of Conservatism must be viewed in opposition to that of a Reactionary, who wants to undo changes that have been done, and "Economic Liberals" who want to free Business of government Regulations. Yes, that sounds like the GOP of today but the historical name is "Economic Liberals", thus prior to the 1930s what we call "Liberals" today, called themselves "Progressives". It was FDR who popularized the name "liberal" for left wing causes, something rare in Europe to this day, and unheard of prior to FDR,. This change in American political Terminology was FDR trying to show his New Deal was NOT some radical program (As the Progressives had advocated for since the 1870s), but just another liberal program, like the pro-business liberal programs of the GOP since the Civil War that freed business from regulations of the State.
This has been one of the problem of the GOP since about 1900, they are really a pro-corporation party (Economic Liberals) who want Government to do what is best for Corporations. Social Liberals started to leave the economic liberals in the 1890s when it became clear that given a choice between greater profits (and lost lives and Income for the poor) and taking care of the working class and poor, Economic Liberals backed Corporation and opposed labor). Labor then moved from being a GOP dominated group to a Democratic Group (Basically more in the 1920s and 1930s, but the movement was on by 1900). Blacks followed labor, starting in the 1930s, but increasingly in the 1940s and 1950s (As the Democratic Party embraced Civil Rights, which the GOP had embraced since 1854). The difference between the parties became clearer over time. The Democrats supported Civil Rights with little restrictions, but the GOP always sided with business when it came to conflicts between business and Civil Rights.
Thus a Solid Conservative is someone who is pro-business, and care less about anything else (including social reforms, such as improving the Rights of Labor the Rights of women and minorities and the environment) except to the degree needed to get elected. The problem is that even the GOP knows they can not get elected on just a pro-business ticket so the GOP runs candidates on Social issues, but, once elected, ignores those social issues if the proposed reform interferes with business. The problem is being for these non-business groups brings those groups into the GOP, and sooner or later they want a real say in who is the GOP candidate.
Thus the GOP dilemma, McClain is NOT 100% pro-business, he has and will compromise the interest of business when other issues are as important (Civil Rights, labor rights, the environment, medical care etc). Huckabee is the same, not 100% pro business (He actually believes it is the duty of Government to help ALL the people, not just business). The GOP need people who support candidates like McClain and Huckabee, but the GOP leadership don't want them in control. Thus neither can be a "Solid Conservative" for both are in the Burkean School of being Conservative as opposed the the Economic Liberal School of Conservatism.