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MG MGB Technical - Won't Start-Need Clues

Posted earlier about fuel pump. Thanks for the help. Won't start now and need clues about what I've probably messed up. History-car stopped running three times at different speeds (acted like fuel starvation), but would restart after a few minutes except for the last time when it was towed. Got it going but rear carb(HIF) was gushing gas. Removed carbs, cleaned etc. and then car would not start. Had local mechanic a block from my house check it out and he said it was firing (I wasn't there to see it) and that it was a fuel problem. Didn't want to leave it there because he didn't know MGs. Since, I have replaced fuel pump (after market w/regulator set at 1.5), rotor/distr. cap, and used Moss carb. rebuild kit to replace jets etc. Oh yes, new battery. Still, no start. Cranks but no sputtering, coughing, or other signs of life. Plugs are dry, fuel pump is pumping to carbs (measured for 1 pint per minute), and checked for loose connections. Now comes the stupid questions-could I have gotten the carb throttle linkage upside down or something, screwed up the needles ???? Is there a way to jury rig something to check and see if it is firing from inside the car (don't have anyone to crank it for me)? The no start situation began after I first removed the carbs to clear sticking float. I'm using the Clymer and Haynes manuals for instructions. Nearest MG garage 50 miles away-need clues!!! Thanks, sorry about the long post.
Lowell Wakefield

Where does the gushing gas come from? The Jet hole, a connection, etc.?? This is the first thing you must fix.

1. Spark - Do you have a strong or ANY spark at the electrode of the plugs??

2. Correct firing order -

3. Timing - Is #1 firing at TDC on compression stroke.

4. Carb linkage - Can't you see if the butterflies open????? You should have the air cleaners off while you are working on the engine.

These are the first questions that need to be answered. You need a Moss catalog to reference the correct part names when asking questions. If you don't know how to proceed with the above checklist, just ask. Your question is NOT too long. These are the kind of mysteries that the folks on this bbs thrive on. Just make Sure you let us all know what it was when you finally get it sorted out.
Fred Horstmeyer

Thankyou for your response Fred. The gushing has problem is fixed. As I stated, I don't know if I have spark, ecept for the mechanic's word and am looking for a way to jury rig a way to tell from inside the car as I don't have anyone to crank for me. This car ran and started perfectly on a daily basis until this suddenly started, so I don't think that firing order or timing has anything to do with it. Yes, the air cleaners were taken off when I rebuilt the carbs, so I can see that the butterflies do open. I have the Moss catalog (that's how I ordered the rebuid kit) and everybody else's too. The main thing I don't understand with this no start problem is how it went from instant start to no start unless I had electrical and fuel failures at the same time. Or is it the forest and the trees ?
Lowell Wakefield

Lowell,
Fuel starvation-might be creating a vacuum in the tank, next time try removing the gas cap and listen for a "whoosh". Or maybe a dirty fuel filter if you have one.
You can check for spark with an induction timing light if you have or can borrow one.

Mike
'79B
Mike Janacek

Thanks Mike-plenty of fuel getting to carbs now. No access to a timing light. Might try rigging a volt/ohm meter to a plug wire and setting it up where I can see it when the car is cranked. Anyone know what the meter should read if it is getting voltage ?
Lowell Wakefield

Lowell: Throw some starting fluid down the carb throats and see if she'll fire.
Luis

Lowell,
Please don't feed the voltohmmeter with a plug wire, or that'll be the end of the meter. Tie or somehow fasten a spark plug so that the curved electrode at the tip is against a well-grounded piece of metal, ie, the engine block or head. Get in and crank the engine and look around or under the hood so that you can see if the plug is sparking. Should be a fat blue spark. If anything less, replace your condensor on the distributor and see if that fixes the problem.

Best, Joe
Joe Ullman

Do you have spark at the plug electrode? Pull the plug, reattach the plug wire, turn the ign on, hold it with a WELL insulated grip and ground the electrode where you can see it spark.

This will check the plug wires, coil, points, etc. all at once.

Report back.


The next item will be to check the timing, which is easier than you think.
Fred Horstmeyer

After much cranking the plugs should smell strongly of fuel if not be soaking wet i.e. flooded. If they are dry with no smell that implies no fuel is gettuing through. If you remove the air cleaners and lift the pistons then blow down the carb overflow pipe you should see fuel coming up the jet. If not you have a problem in the carbs. Whilst the air cleaners are off and you are lifting up the pistons check that the butterflies are moved from closed to open when you pull on the throttle cable sheath. Unfortunately I do not know a way of checking if the choke jet is functioning and unless your ambient is pretty high you probably will need choke, all you can do is look at the cams on the interconnecting spindle. Other than that it is a matter of checking that you have a spark going to each plug by laying it on the block and cranking as described previously, but remember that bad plugs may well spark in free air but not under compression. Then you need to check each cylinder is getting its spark at the right time i.e. just before TDC on the compression stroke and not the exhaust. You can check which is which by turning the engine by hand with the plugs removed, the compression stroke will blow your thumb off the plug hole on the compression stroke and not the exhaust. Firing order is 1-3-4-2 *anti*-clockwise, and bear in mind that although No.1 plug lead should come off the cap at about 2-o'clock if a PO had the drive dog out and put it back wrongly No.1 could come off the cap anywhere. Also check that the dizzie is fully seated in the drive dog and not just resting on the top. But given the earlier history one has to suspect the carbs.
Paul Hunt

Luis=tried, no joy-Fred, tied plug to top of valve cover, got spark. Paul, blew thru overflow from carbs and can see no fuel. Butterflies open when throttle is opened. Car always starts w/o choke down here. I guess it's time to pull the carbs again and double check my assembly. Got any thoughts on what to look for?
Lowell Wakefield

Sounds like no fuel in the float chambers, or jets (both?) blocked. Try slackening the screws on the float chamber lid (bottom of carb) and draining any fuel into a container, then retighten the screws. Then turn on the ignition and listen. An SU pump (or an aftermarket that stops when the float chanbers are full) will chatter for two or three seconds then slow down and stop. If you get that then the float chambers are being filled. If there is no chattering, particularly if you got nothing out when slackening the float chamber screws, no fuel is getting in, check the float valves, blowing through the fuel inlet pipe and testing that the float can open and shut the valve.
Paul Hunt

Paul-went ahead and replaced plugs and condensor just in case-no difference. Before your last post I took off the piston chambers to check for fuel flow. The front carb shot fuel in the air, but the rear did nothing and apparently is not getting fuel (not a blocked line). Beginning to suspect my original thought that I screwed up the reassembly of the carbs. In your experience (or anybody elses), would totally messed up carbs produce a situation of not even a cough when trying to start? Just trying to set my mind at ease about the ignition side of things. Worn out for the day, will take carbs of in a.m. and start again.
Lowell Wakefield

Until paul answers again, I would say that in my experience

1. I never need a choke unless it's below 30*f

2. With even 1 carb working it should at least kick. Try the starting fluid in the carb trick.

3. Is it possible to turn the dist with your hand? If the pinch bolt is loose, it can move and cause the problem you have.

4. Do paul's timing check. Just b4 your finger gets blown off, check to see if the rotor is pointing to the #1 plug terminal in the cap.
Fred Horstmeyer

My 73 with HIF ran rough following new engine installation - however it smoothed out with choke pulled. I surmised that maybe the main jet was blocked on one carb since on the HIF units the rotary choke valve provides a separate fuel path, unlike the earlier models which lower the main jet. Rebuilt both carbs with kits, since I didn't know which might be blocked, and all was well.

Good luck, Barry
B.J. Quartermaine

Like Fred I would say that even with only one carb pumping fuel you should get something when cranking it particularly as the balance tube means that some mixture from one carb will get to the other two cylinders.
Paul Hunt

Have had all the fun I can stand for one day. Took carbs off and disassembled again. Don't know if it means anything but there was a difference (slight) in the length of the needle valve and the jet needle that Moss supplied and my old ones. Knowing the B used to run with the old ones, cleaned them up and reinstalled. Squirted carb cleaner thru fuel inlets to check flow and if valves opening up. At least on the bench, the pistons pump and the fuel squirts, so we shall see. If it doesn't at least fire tomorrow, then I'll go for the timing per Paul (Fred the distr. will not turn by hand). Now, if anyone has read this far, let me tell you the really stupid trick I pulled. Somewhere (near the start I would say) along the way I managed to put the fuel inlet hose (front carb) on the overflow fitting and vice versa. Kinda think that would mess with an SUs mind! Don't expect that to cure original problem, but it might have a fighting chance of running now. Naturally I discovered this after I tore down the carbs again. Will post tomorrow, please don't laugh too hard.
Lowell Wakefield

Lowell

That's only slightly worse than me reconnecting my plug wires 1-3-5-2 assuming the distributor rotor turned clockwise (like the front pulley). I now tell everyone to be sure they go counterclockwise when assigning leads!

Good luck, Barry
B.J. Quartermaine

Bolted down the carbs again. Can see fuel coming out of the jets when I raise the pistons and no overflow anywhere. Low battery now, so I'll post again when that problem is resolved.
Lowell Wakefield

Charged battery. Started! Don't really know what the original problem was since alot has been done. I guess it's a matter of perseverence. Thanks so much for all the help from everyone.
Lowell Wakefield

1-3-5-2? Now that *is* silly ... ;-)
Paul Hunt

Thanks Paul, that makes me feel better!!!!!!
Lowell Wakefield

1352- maybe that is "missing" on one cylinder? Among other things.
Ken R
Ken Rich

Sorry for the typo - just noticed the comments!
Barry Quartermaine

This thread was discussed between 06/06/2002 and 11/06/2002

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