• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

MGB Choke on SU-HS4 1971 MGB

Share this page

P

PRBrauer

Freshman Member
Offline
Everyone,
I'm the one trying to figure out why my newly acquired 1971 MGB died on its way to its new home. Was running on a couple of cylinders like it was being drowned. One possibility is the choke on front carb might have been stuck because it drove great for several miles before it puttered and died. Got it started again and home. I have been trying some of the suggestions (those that I can while waiting for routine maintenance parts). Being a newbie with only a Haynes manual so far (more on the way), I am trying to understand how the choke works on these HS4 carbs. From what I can gather the choke actually lifts the jet assembly. Is that right? How is it related to the fast idle screw? I also noticed while digging around that only the rear carb had a choke return spring attached, there wasn't one on the front carb that supplies the cylinders I thought were being drowned. In addition, the throttle spring on this same carb isn't looking so hot either. Since I putz with the carb (moving the piston up and down and getting a better idea of the design), the engine seems to be running on all fours (went around the block). I wanted to take it down to the station tonight and fill it with new gas but the weather is bad here (not like FL though). Just to see if I could get stranded somewhere. It still seems very rich (gasy smelling) but it may be because I have exhaust manifold or manifold seal problems too. So how do the chokes work on these Bs? /ubbthreads/images/graemlins/crazyeyes.gif
 
Here is an experience I just remembered. I had a friend that bought a '71 MGB and his carbs were flooding a lot. This car had sat for several years without running. His problems were flakes of stuff in the bowls of the carbs and stopping up the jets and also sticking the needles open. Also stuff was coming in from the filter and coming into the filter from the tank and clogging the filter. It started running fair after cleaning out the carbs and pipes replaceing filter etc. But he eventually had to replace the tank because of so much rust. The top of the tank had holes in it and when he filled it up gas ran over the side.
But after all this it ran great.
The area where rust attacks the tanks besides internally is on the top of the tank below the floor of the trunk.
Bob
 
Thanks for the tip. However, based on the info I have on what was done within the last year or so is that it has a new gas tank (it looks new too), filler tube, new fuel sender unit and fuel pump. The previous owner had it a few months and only put about 100 miles on it. The previous previous owner (PPO) was a mechanic who took it in the shorts when it came to fixing it up (talked to him on the phone before buyint it and he was ranting on himself about the money he spent but said it was a good car, however he stated he never wanted to see it again and he meant it-- bitter reminder I guess). I have a copy of his hand written notes as to what he replaced and spent on it). So I don't really think the tank is rusty. Can one see deep enough inside using a flashlight to see anything or must you remove it and shake it (just kidding about shaking it)?
 
If it looks new its probably OK. My old one had a baffle so you couldn't see beyond that looking in the hole where the fuel gage is and where the fuel pickup is located. I don't think you would see much looking in the neck either with the rubber connection to the filler pipe off.
Since it looks new, I would probably look elsewhere. How does the inside of the carb bowls look? Is there any trash in there?
Bob
 
Pulling out the choke cable does two things...closes the choke and raises the idle. The first 3/4 inch of choke pull raises the idle and the next inch or inch and a half closes the choke. When you release the choke cable back to the first step the idle remains higher until the cable is pushed the whole way in. That is probably what you are seeing.

It sounds like the missing return spring on you front carb may be permitting the choke to partiall close. This will happen especailly at low RPMs or when there is a lack of vaccuum to keep the choke open...fix the spring and tighen up the manifold and I bet it will run much better.

Oh, one more thing...both carbs feed the mainfold which in turn feed all four cylinders...the front carb should effect all four, not just the front two cylinders.

Bruce
 
Back
Top