Moss Motors, Ltd

Anyone ever experience this problem?  I think the fans are pulling too much juice and throwing the timing off because I used the brown wire from the to the ignition relay from the fuse block to power my fan relay.  Any thoughts?

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Dave Kiernan

www.airforce.com
www.dosomethingamazing.com

DK,

No, the fans coming on will not affect the ignition timing no matter where they get their power. Timing is a mechanical function of the positioning of the distributor on its axis. The engine probably slows down because the fans impart a significant electrical load which in turn demands more of the alternator, which therefore puts a load on the engine which drives it. It may indicate that the fans, which were not a proud moment in the history of efficiency anyway, are in need of service.

I usually take them off, disassemble them, clean the internals and lubricate them before reassembling them. You could do that or chuck them and buy one of the aftermarket high efficiency units with its own sensor which are sold everywhere, even in Utah!

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Thanks Bill, I was thinking that it might be time for them to go.  They have been a problem since I first bought the car.  I think I may have to differ to the professional for some of the remaining problems:  backfires, extreme rpm drop off when accellerating and runon to name a few.  I think I maybe doing more harm than good.

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Dave Kiernan

www.airforce.com
www.dosomethingamazing.com

Update:  I installed a Hayden 10" fan last night and removed the old ones.  The drag on my RPMs is gone, however, it does run a little hotter.  Is this normal?  I set it up as a puller as there was more clearance on the engine side of the radiator.  I keep saying like above, "this time I'm taking it to a garage, I'm in over my head and I need a pro!"  but I still keep monkeying around with it.  Now I notice a drop in RPMs when the lights are on.  I've been planning to relay them but I don't think that will solve the RPM problem, the draw is still the same, its just not going through the switches, right ?

Different area:  How shaky is the timing mark allowed to be?  I keep thinking that the timing is retarded and that is cause of my very bad throttle response/backfiring/very hard starting/rough idle.  I have to rev the engine to above 3000 just to go from stop and I'm backfiring with cool engine on throttle up.  When I set the time before, following the Haynes instructions, I did so with vacuum advance disconnected and plugged.  I adjusted the distributor and set the timing a 10 degrees BTDC.  I then reconnected the vacuum advance, according to the manual, and the timing advanced 20 to 30 degrees.  This does not seem right, the book say a "slight advance" when it is reconnected.  Any thoughts?

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Dave Kiernan

www.airforce.com
www.dosomethingamazing.com

Hmm, I know the vac advance is taken from different parts of the inlet different on different carbs and works differently in combination with the distributor - I just don't know which is which. I remember that you switched from a ZS to single HIF - can you tell if the vacuum connection is in the same part of the new carb - or is it unchanged and taken from the manifold? Could this be part of the problem?

How does it run if the vac line is disconnected and plugged?

Wish I could offer more help on this, but it's well outside my experience.

Ed

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I want my MGB

There is no vacuum port on the HIF carb.  A big problem is I did not document where things were connected before I installed the new manifold.  I couldn't even tell you if was connected prior to the new manifold.

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Dave Kiernan

www.airforce.com
www.dosomethingamazing.com

Hmmm, we need motorbill!

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I want my MGB

Ed, I think your right.  I found this reference in an old post from last year.  The thread is 1972 B Idle Problem and the post was by firemanpheonix and Mac:

firemanpheonix:

"as soon as I reconnect the vaccum line she jumps to ~2000revs. I have tried setting the timing back with the vacuum hooked up but then she has no power."

Mac:

"AFAIK the HIF does not have a vacuum port on the carb (at least the 73-74 variant did not, see below). The distributor that was used with HIF carbs these years used manifold vacuum to the vac advance.

Manifold vac is high at idle and drops when you crack the throttle. Ported vacuum is low at idle and rises when you crack the throttle. 

I can easily imagine distributor with a vacuum advance that expects to get port vacuum operating as you describe when fed manifold vacuum...and there'd be a drop off as the throttle is opened. 

You should be able to check with a tach and timing light (easier with a dial-back timing light and its built in tach) . At idle you have xx degrees total advance (with vac line on) and xx total advance with vac line off and plugged. If the two are about 10 degrees different (higher with vac on)...that's the answer. Then with the line connected, check total advance as you crack the throttle a little. Does it drop? more confirmation.

The Lucas pn for the distributor used with the 73-74 AUD 550/AUD 630 HIF carb is 41491. The 72 (used the AUD 493 HIF) used the 41370 distributor. Part number can be found on the body of the unit. I have AUD550 and 41491 distributor. (both out for rebuilding while I use an earlier set of HS4s and it's distributor borrowed from my 71 GT). I have no specific knowledge of the AUD493 carb (i.e. I am not positive it does not have a vacuum port, but I think it does not). I suspect that the 491 and 370 distributors would swap insofar as this characteristics, although their advance curves could be different (mgbmga.com has some details on different distributors)."

I wonder if this has any relevance?

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Dave Kiernan

www.airforce.com
www.dosomethingamazing.com

Update:  Thanks for all the advice!  I disconnected the vacuum advance and re-timed it last night.  WOW, what a difference!  The most enjoyable ride I've had in a long time (since I bought it)!  Lots of take off power, no backfiring, no run-on (I used the manifold port that the VA was plugged into for the anti run-on valve control pipe).  What are the long term implications of not using the VA?  Is my VA broken or just not getting the vacuum at the right time?

 

P.S. I also changed my oil last night and my oil pressure is high idling its around 65-75 and at speed its around 85, the level is right at MAX and immediately prior to changing oil, the pressures were within specs, 20s and 80s according to the manual.  I'm watching johnc's oil pressure posting to see how his turns out.

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Dave Kiernan

www.airforce.com
www.dosomethingamazing.com

Excellent news!

Yes.. the thread from which you quoted described the vacuum connection differences that I was attempting to explain, but I had only a rudimentary knowledge . Now I want to go and do a little more reading on this subject and the various configurations.

Cheers,

Ed

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I want my MGB

Happy Happy Joy Joy... just passed safety and emissions!  Legal and back on the road!  Just realized my timing is still a little advanced 10 degrees at 1000 rpm as opposed to 1500 rpm, oops.  Could anyone tell me if i can just ignore the vacuum advance and leave it disconnected?  I found a chart that shows the mechanical advance is all in at 4500 rpm.  Is that true?  If so I think I can live without the vacuum.

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Dave Kiernan

www.airforce.com
www.dosomethingamazing.com

DK,

Check to see that your mechanical advance is correct at the max at 4500 RPM. If so, and assuming you can get an idle with which you are happy, you're good to go. Just make sure there is no vacuum feed port opening into the manifold/carburetter(s) which would cause lean running. Enjoy that car, man. You've worked for it!!

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Bloody marvelous! Congratulations

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I want my MGB

Wow, this has been a really long thread!  All for something that is probably very simple.  Most folks are probably thinking "Dang, how many months to change out a manifold and tune it back in?!"  Well, thanks to all of you guys this dumb Airman finally got it put back together and running great!  My eternal gratitude to you all!  Now on to other things; where should I start?  Seatbelts, working but sticky, carpet; torn and moldy; top, torn and leaky; rust spot, small but annoying; gas gauge, working but jumpy; seats, torn and very hot in the Utah sun (I'm thinking tan would be nice, but wow, $$$$, maybe with my reenlistment bonus).  Hmmm, any suggestions?

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Dave Kiernan

www.airforce.com
www.dosomethingamazing.com

It all takes longer than you would ever think... Don't worry about time - here's my experience.

When I first started work on my car, it lived in LA with my wife, and I lived in the UK for 50 weeks of the year. Yes that's right folks. Married in 2002, finally living in the same country in 2006... to my wife that is . As you can imagine, this left little time for project work.. on my car, that is. Still, I managed to rebuild suspension front and rear, and get familiar with the cars construction and the areas that needed attention. The enforced time away from the project motivated me to read read read. Haynes, internet articles, Moss catalogue, bulletin boards, so that I was well armed with tricks and tips and the proper information next time I had a chance to work.

Now I live with the car (oh, yes, and my lovely wife...) there has been time to tackle some things I considered really advanced jobs like engine and gearbox - things I never thought were within my grasp, as someone who had never owned a car before!

Still, there are always the little jobs, and the not so little. My car needs further attention to the bodywork and a decent paint job. Then again, I have to replace the petrol gauge sender, which presently reads from "full", drops quickly to around half, then goes up again before dropping very slowly. If you run until it reads 1/4, there's only about a teaspoon left.
It's all part of life's rich journey on and off the road - a friend told me that "you'll be distraught when that car is finished" Luckily that will be some time yet....

Cheers,

Ed

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I want my MGB