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MG MGB Technical - Points gap / timing problem fixed...now carbs

Hey again. Well, the replacement temp used distributor solved a lot of the problems. The cam is tighter then on the one that was installed and the vacuum cannister works. Now I can see why they say to remove the vacuum line when setting the timing. There is a noticable difference.

Now I can get on to the next problem. This has been there since I got the car but I needed to straighten out the ignition before tackling the carbs.

The car idles beautifully at about 1200 rpm with the choke in. However, it barely runs! A lot of sputtering and no power at all.

If I pull out the choke about 3/4" then it runs beautifully, but won't idle. It will stall almost immediately when removing my foot from the gas pedal. So, during the test runs around the block over the past couple weeks I pull out the choke to run and push it back in every time I come to a stop sign!

I know the carbs are difficult, but if there is some quick advice based upon the symptons I'd appreciate the guidance. I do want to learn about them, and this is a good opportunity, but I'd also like to see the car running right!

Thanks,
BH Davis
BH Davis

BH, Sounds like your carburetors need a complete synchronization and adjustment. One reference with some small photos is here.
http://www.mgbexperience.com/article/mgoc-basic-4.html

The reference above is for HS carburetors, your car should should have HIF carbs. Mixture adjustments on the HIF carb is with a screw, rich and lean is opposite what you would expect. Turn the screw out CCW to lean, turn it in CW for a richer mixture. Here is a link with detailed photos of HIF carb rebuilding.
http://www.chicagolandmgclub.com/photos/hif_carb/

If you are going to work on an MGB there are several web sites that have MGB repair and service data. One of the most informative sites is maintained by Paul Hunt. I would advise bookmarking his site along with others you find with valuable information.
http://www.mgb-stuff.org.uk/hammerframe.htm
Under Hammer and Spanner, click on fuel, SU Carbs and Setting up for carburetor information.

Actually SU carburetors are simple devices with very few part. Setting them up isn't difficult but you do have to be precise with adjustments to get them properly synchronized. When you get bogged down post you questions here for help.

Clifton
Clifton Gordon

As Clifton says setting-up twin SUs isn't difficult but it does require patience and care to get each stage right before moving on to the next. When you *have* got them right only ever make the same adjustment to both carbs in the same direction. If you start fidling with the carbs individually you will have to go right back to the beginning. Whilst HSs *may* require half a flat richening for winter and weakening for summer HIFs should not. I used to check mine (I have both types on two cars) for balance and mixture at every service but always found them spot-on, so now I don't even check them once per year. Done right, and not fiddled with, they do hold their tune well.
Paul Hunt 2

Interesting about the possible winter richen and summer leaner on the HS4's. I am at 5,280 feet in Denver so wonder if that exacerbates the problem. Didn't know that but my experience with winter starting seems to support it.

I got mine set for me 6 years ago and haven't touched them and car still runs great.
J.T. Bamford

Clifton,

Thank you for the input. I visited those sites over the past few days and have even printed out the instructions/guides.

I will either dig into this myslef now over the next week or two or just take the car into the local "Where British Cars Aren't a Dirty Word" garage!

Thanks,
BH Davis
BH Davis

I have a 1972 mgb car has sat for many years. I have replaced fuel pump,tank filters. Car is idling very rough. The hoses that attach both carbs that eventually lead to the charcoal canister that should just take vapors, when I disconnect the hoses from the carbs it runs better but there is quite a bit of gas dripping from the tube from the carb. What is the problem? Thanks for any help.
Shawn Allen

This thread was discussed between 07/05/2006 and 17/05/2006

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