Diagnosing Low Max RPM: Margaret Thatcher Needs her Coffee!

During the practice day for the 2013 LeMons Capitol Offense race, it was hard to NOT notice our MGB GT had somehow dwindled to an upper limit of 4500 RPMs, which means the very important upper 20% is missing, right in the power band. The poor girl is weak already, and a limit of 4500 would literally (and figuratively) knock us out of the race.

Sigh.

We check the pedal linkage, it was OK.

The accelerator cable was making grinding noise; we sprayed into the cable all we could with silicone spray, to some-but-little effect.

Scot noticed the butterfly gears on the Weber DGV Downdraft Carb were not articulated 100%, so we bent and adjusted the cable bracket all we dared to extend the motion, and then greased the hell out of it. To no effect.

We were getting driver stints in between tweaks, and by the time we fixed the butterfly gears it was time for LeMons Tech Inspection, which we failed, so we dropped the whole "Upper 20% power missing" because Tech had rendered us with a "Upper 100% power missing" situation.


After the sobbing subsided (2 weeks later) I finally got back to diagnosing the issue.

First up: Fuel Delivery.

We had previously had mega-carberator problems with gunk at Summit Point 2011, so that was a thing.

Remembering the Jet Ski in-tank fuel filter I had added 2 years prior, I decided to make sure the carbs were getting enough coffee fuel.

1) get a glass jar, clean it out, drill a 3/4 inch hole in cap (or whatever size your fuel hose is, 'natch)



Guinness does not come in clear bottles, so you'll have to resort to 9 oz poison bottles.

2) disconnect fuel line from carb.

Might want to make sure fuel pump power is OFF before doing this, dumbass.



 3) stuff this thing in that thing:

Probably illegal in New Jersey.

 

4) apply power to fuel pump, count how many seconds it takes to fill up bottle (6 or so seconds). Do not drink, though it would be healthier than what originally came in the bottle. I messed up timing this, in that (1) I didn't run the car first to purge the air, and (2) I didn't use a timer, but counted one-mississippi.

Pretend this pic is rotated 90 degrees counter clockwise.

5) now, don your best Saran Wrap Fetish Gear, and give your Fuel Cell a proctal exam:

Definitely illegal in New Jersey!

6) wave to neighbors, note which ones wink, reach into fuel cell and fish around for fuel pickup and in-tank filter:

This may feel uncomfortable...

7) remove said filter (and small connecting hose):

Possibly clogged filter removed, immediately wash arm with 30 gallons of soap

 

 8) change crappy-ass "Fuel Pressure Regulator" which is actually just a friggin fuel restrictor from 4.5 PSI to 6 PSI; retest fuel flow, receive same damn 6 second time.

Crappy ass.

 9) Be sure to leave bottle cap in fuel line so that you look like the complete tool that you are, buttclown.

Honest, it's a heat shield!

10) test drive that bad boy - 5500 RPM, bitch!!!!!   Dunno if it was the pressure regulator (probably), clogged fuel filter (probably), or the need for a saran wrap proctologist exam (probably)... but whatever - I'm happy.

Last check I need to do it run it HOT, and see if 5500 is still reachable; not too worried since the 4500 limit was all day, even once cooled. Sounds fun.

Rev Limiter for MGB Survival

We surmised that we over-revved the MGB engine in the first race of 2012, because:

    1) there was no tachometer

    2) there was no speedometer

    3) the engine is underpowered, causing drivers to floor it all the time, for the entire 14 hours

    4) the 4 speed manual transmission really really needs a 5th and 6th gear, causing drivers to floor it all the time, for the entire 14 hours

So we installed a tachometer from another MGB and rotated it so that 5250 is pointing straight up - she really could use a "shift now" light for gears 1, 2, and 3 and a "sit back - you're just along for the ride at this point" light for 4th gear. Some day.

We installed a Rev Limiter instead since our driver pool is often hungover and barely focusing on the road ahead much less the little numbers on the tach.

The Rev Limiter we ended up with was the Procomp Single Stage Rev Limiter PC2031, and it did just fine as far as well could tell. 

1-800-Dial-a-Prayer!

Also on the menu was a new fuel pressure regulator, the Holly Fuel Pressure Regulator had died after a failed attempt at rebuilding the internals with new rubber and filter element. Oops.

All those pretty blue AN fittings were a real pain to match up, but they sure mate nicely and are clean etc etc. Soooo un-MGB like.

MGB Fuel Pressure to Weber Carb should be about 4.5 psi and very shiny.

Bogging Down Exiting Corners - Weber DGV Accel Pump?

During our last few races (ok, all of our races), I've noticed the ol' chap tends to hesitate when exiting corners. Up till now I've assumed that's just the carb being slightly dirty or temporarily starved when stomping on the gas (right after holding your breath through the tight corners).

It's been nagging me for a year now; something's wrong, but not sure how to troubleshoot it without having someone hang on the hood while we drive around the track?

Then I stumble across this little gem of a description from the Pegasus Auto Racing Supplies catalog:

Accelerator Pump Diaphragm Assembly, Weber 32/36 DGV

 
If your car bogs down exiting corners, your accelerator pump may not be pumping! When the throttle is opened all the way from idle, the accelerator pump should deliver a shot of fuel directly into the carburetor throat. If this shot is not visible (with the engine off), the diaphragm may be ruptured.






You know what today is? DAY I GOT COOKIE!!!

Problem may still be elsewhere, but boy does that description fit! With all the crap and junk and dirt and bits and crud and grime and filth and rubbish and mud and garbage we pulled out of the tank and carb and filters at 24 Hours of LeMons Summit Point Capitol Offense 2010, it is very possible this contraption is hobbled.

Thanks Pegasus for the schoolin'. Order placed.

[UPDATE 2012-04-08] Either we don't have a Weber DGV, or Pegasus sent us the wrong part... either way, it don't fit no way no how. We need the part shown in photo above; the part we received was not 'square' and the brass pin in the middle was mush skinnier and was not spring loaded.

Bob found and took out the old part, and it looks like there could be a little leakage around the circular shape of the rubber is.

We put the original piece back in until we get our hands on the unobtanium accel pump...

Race Report: Where the Elite Meet to Cheat 2011

Where the Elite Meet to Cheat at Charlotte Motor Speedway was a riot as expected. Plenty of this report snipped & edited from Driver Dave's email.

We finished the race with a blown head gasket; 53th place out of 66 entries; we were in the pits the last 4 hours with the engine ripped apart. A noble effort!

 

Rain. And more Rain. And no windshield wipers. And no RainX (plastic windshield).

Friday: set up day: Judge Phil comes over with a friend and says something like “this is my friend Randy, he’s a pretty good driver and your car really caught his eye… any way he could sneak a few laps in it sometime?” … Carl is in a great mood and of course said “hell yeah”… good karma and all that. Also - it's always a good idea to do the penalty-wielding judges a favor.

Tech Inspection: should move under-hood fuel filter closer to pressure regulator so it is more protected and doesn't flop around; brake light switch may need adjustment (woops - more on that later).

Paddock all set up Goldbrick style: XBOX, fridge, leather couch, snacks. We'll unload the car sometime... oh wait did anyone remember to actually bring the car?!?!?!

Saturday, Race day one: we finished the first hour as the top class C car.  Carl was driving in the rain and doing a great job.  Until he passed under yellow - scratchy plastic crap windshield with no wipers was almost ok until it stopped raining and muddy water coated it.... oops. Penalty: driver change *whew* Second hour we had a terrible driver transition and refueling.  Dropped 30 laps back of top C car.

Then Ray got the best black flag in the history or racing.  He gets stuffed by some other car on a corner and ends up hitting some cones (mandatory black flag here.)  His penalty was to sit out for an hour... OR...  Let Randy Pobst drive our car during the penalty. Randy is a professional car roadracer.  Check out his info on Wikipedia.  So, during that hour Randy posted 60 laps, one of the top 10 fastest laps on the track (1:21), got us back to within 5 laps of the lead!  He was doing stuff we didn’t know the MG could do.  UNREAL! It's written up here: http://www.thetruthaboutcars.com/2011/09/randy-pobst-lemons-mgb-gt-handles-well-bad-brakes-low-on-power/

I had forgotten to replace my lucky stick-shift knob with a "real" one... sorry Randy!

Randy dropped the rear tire pressure to 2 or 3 psi below the fronts, so now Front 29psi, Rear 27 psi; also said the rear drivers side would "clunk" on the one hard left, and that we really should adjust the pedal travel.
 
Then the problems started....  While Kurt was driving, he got flagged for brake lights.  Took us 2 HOURS to fix the stupid brake light switch on the MG.  So, we were well behind.  Dave made up some of it and was having a GREAT hour.  Posted a 1:24 lap and was trying to emulate Randy.  Was gaining 1 lap every 4 laps against the 2nd place C car and 1 lap every 5 against the 1st place C car.  Then Dave says he turned into a moron and ran out of gas while on the track...  Lost everything he’d gained waiting for the tow truck.  "I’m advocating a gas gauge Carl..." We added 7.5 gallons... so that is our new volume (thanks for measuring that Dave!) Max went out... into the heavy rain... zero visibility.

We finished day one pretty well though.  160 laps even with none of Kurt’s last 20 laps in the rain registering - several transponders were not working in the heavy rain towards the end of day one.  We were only 30 laps out of 2nd C class car.We were 47th place, "good enough" with all that lost time.

I guess 43 is old enough to smoke, so what the hell was I supposed to say?

Sunday, Race day two started well.  Ray was putting in some good laps.  Posted a 1:28 lap time!  Then 1/2 hour in the car started overheating.  When we looking it over, discovered water in the oil... unfortunately AFTER we refilled the radiator.  We’ve driven it without water before, so sent it back out!

Exhibit 1: A major disadvantage of having a light colored paint job

Kurt was driving when he was black flagged for the oil pooring out of it... :( 

We cleaned it up (drained everything; replaced oil filter plus oil change) and let it idle for a good 15 minutes; revved it a few times. We were thinking of sending it back out with new oil and no water.  

Judge Phil drove up and so no f@(#)%^ing way. Probably a good call.

 

So, we had no choice but to try to replace the head gasket.  Judge Phil assured us it was an easy job... Then disappeared...  We had some generic too-thick cork for other gaskets and decided to go for it. With four hours left we tried.  Couldn’t get it done by the time they called the race 1/2 hour early with lightning.