Classic/Antique Car Repair: XKE Power Loss, piston engines, fuel compression

Question
Hi Howard,

It's me with the 1970 XKE again.  You gave me such good advice the last time, I thought I would ask you another question.  A problem just started yesterday and I've been trying to fix it all day today with no luck.  It seems as if every time the engine warms up, it loses all power.  It will continue to idle but any attempt to rev the engine and it almost stalls.  If I turn the engine off for several minutes it will return to full power but only for a minute or so.  I thought it might be the fuel pump as it seems to pump quite slowly but I've been able to rule this out by temporarily installing another fuel pump that performs much better.  As I started before, it seems to be related to the warming up of the engine.  The longer I leave it off, the longer it will run normally but it seems to always return to a state where it develops no power beyond an idle.  I've cleaned and gapped all of the spark plugs, replaced the distributor rotor and checked the gap on the distributor points.  I'm at a loss.  Do you have any suggestions?

Glenn


Answer
Hi Glenn,
Your problem does sound Carb / fuel related. However, your discription of the problem does not pin point the fault to me. You will have to do some tests and do them at the time of failure, meaning when it is hot and doing wrong.

As you know all piston engines only require 3 things to run. Compression, Fire & Fuel. Compression is not going to be there at idle and go away on a rev up so that leaves Fire and fuel. Fire can be OK at idle and fail on a rev up but it is usually associated with backfiring and very harsh missfiring which I didn't hear in your discription. So fuel is the most likely. Too much fuel or too little fuel will give you loss of power. Look at the exhaust smoke when you rev the hot (no powered) engine. If it is an excess of fuel you will see a definate excess of black smoke. If not, then it is a lean condition. As I remember there is a large sheet metal cover that connects the carbs to the air cleaner. You need to remove this. I use a oil squirt can full of gas for this test but you can use a spray can of WD-40. Keep fire equipment handy and rev the engine untill it is running badly and spray WD-40 into the carbs. If it helps the engine run, it is for sure a lack of fuel. As I remember the 70 "E" type had two Stromberg carbs, is that correct? If so remove the four phillips screws from the top cover of each carb and inspect the rubber diaphrams for holes or tears. Remove the pistons and inspect the needles to see that they both are in place and lightly spring loaded toward the engine. Be very carefull not to bend the needle setting them down. Then with a strong light shining down into the open top of the carb. Blow a quick hard puff like you are saying Pooooo! directed at the open jet that the needle was in. Do not get so close that you can't see the jet opening when you do this. You should see fuel come to the top of the jet and maybe overflow a little just after you blew at it. This roughly checks the float level in the carb without disasembling it.
Let me know what you find up to this point. You can contact me via my E-mail longez8@bellsouth.net