Triumph Repair: little power in first and second, vacuum gauge, manifold vacuum

Question
I hope you can help.  I have a 68 TR250. When in neutral, I get over 4000
RPMs but under load (go in to first) I only get a little over 3000.  I've adjusted
the points, check the fuel pump and made sure my carbs were lubricated and
functioning properly.  
Any ideas where to look next?
Rick

Answer
Hi Needham,
Just because an engine revs to 4K in neutral does not mean it is right. You need to do some testing to make sure the engine is sound first. Run a compression test. You should see 135 to 160 PSI on a compression test and little difference between cylinders. Then you need to set the ignition timing to specs. Then test the carbs by letting it idle and lift the spring loaded pin just under the side of the top pot and note the reaction and do it on the other carb too. If the engine speeds up and stays fast the other carb is too rich. If the engine dies, the other carb is either too lean or the two carbs are not in sync at the butterflies. If the carbs are correct the engine should drop off and run very slow like a two cylinder engine.
If you have done all that and it still will not run under load, you need to test the exhaust back pressure. First just put a manifold vacuum gauge on the intake vacuum and read the vacuum as you slowly raise the RPM. If it goes to zero you then need to test for exhaust back pressure. The back pressure should never go above 1.5 PSI at high RPM.
Howard