MGB 71 MGB Won't Start

[MikeH]

Hi All, I have a 71 MGB that won't start. Earlier this year the head cracked in the number three exhaust area. I found a used head that had been gone through, it looked ok, and installed it. The car tried to run on two cylinders so I then did a leak-down test and had air escaping through the 3 and 4 intake. Had my machinist check the head and he resurfaced the valve seats. I reinstalled the head and did a compression test. About 100 #'s on each cylinder, I have a cheap test kit so I don't know about accuracy, but all were close together. The car will now start with starting fluid, will not run, and nothing without starting fluid. Valve lash is right, carbs and timing are close. I don't understand why it will start( not run ) with starting fluid and won't without. Any help will be appreciated.

Thanks, Mike

71 MGB Wires and OD
63 TR4 Surrey Top

 

[JPSmit]

I'd check fuel flow to start - disconnect at carb, have someone turn over the engine and see if it pours into a container.

If no flow trace back to sort out why (including checking if you have gas in the tank - don't ask me how I know.

Assuming the carbs are good, my next hunch would be timing. I've had the timing close but not close enough to get the air really sucking. I suspect the starting fluid is both more volatile and in finer particles making it easier to start. As I recall, on my first startup, we got it going with fluid but, I had to loosen and adjust the distributer while turning it over to get it to run.

 

[bob67bgt]

JP sounds correct about not getting fuel. Also check that the needle and seats are actually opening. I have seen Grosse Jets stick shut and no fuel could get to the bowls. I have also run across 2 people that had massive intake air leaks because they left washers between the carbs and spacers blocks and or the heat shield. My guess would be a misplaced washer. Bob

 

[davester]

I think bob means gaskets, not washers, and I'd agree that would be something to check. My. Troubleshooting sequence would be:

1. Check all gaskets and fittings for vacuum leaks, including the gulp valve (which I'd probably block off for the purposes of testing. Also check that one of the metal plugs hasn't fallen out of either end of the intake manifold rail.

2. Do you have enough gas? How old is it? Stale gas won't work.

3. Check fuel pump output at carb inlet.

4. Pull float bowl top and check for gas and debris in bottom.

5. Check if jet tubes are clogged and if jet nuts are set at 12 flats from bridge. Also, does the choke properly move the jets down?

6. Report back.

 

[bob67bgt]

No,I mean washers. I have seen hobbyists remove carbs and put the nuts and washers back on the intake studs. When reinstalling the heat shield they forget to remove the flat washers thus creating a major air leak. Its just something to check while you are hunting the problem. Bob

 

[DrEntropy]

Bob, we oughta get together a list of the "sins" we've seen over the years that've been perpetrated on the cars. :laugh:

 

[MikeH]

Thanks for the replys. I believe that everything is installed properly. Fuel level is right in both the bowls and jets. Choke moves jets as it should. Hard to check vacuum on a non running engine.

Thanks, Mike

71 MGB Wires & OD
63 TR4 Surrey Top

 

[bob67bgt]

Doc, That would be a interesting list. I got most of them written down from that 73 i purchased a few months ago. Mike, If there is fuel then there must be a vacuum leak somewhere. It fires on a spray so your ignition system should be good enough for the car to run. I have also seen the rear core plug fall out of the intake manifold when a car is shut down. That was a interesting problem the first time I ran across it. Good luck on the hunt for the problem. Bob

 

[davester]

As with Bob, I had one of those plugs (the front in my case) fall out and give symptoms just as described. It took me an eternity to find the problem. A fubar gulp valve can give similar symptoms.