SU advice needed badly

My car (1977 MGB that has been retrofitted with two SU carbs) was running fine; however, I noticed that the rear float chamber was lose. I tried (unsuccessfully) to tighten it but managed to knock out the hose that runs from the carb to the bottom of the float chamber thus draining all the gas from the float chamber. I was able to get the hose back in and I filled up the chamber with gas to the level I thought it was at before it drained. Upon starting the car it ran very rough and wouldn't rev above 1,000 rpm. Idle speed was about 400 rpm. Using the manual choke seemed to not make any improvement. Any advice as to how I can correct this problem. Does this sound like a float problem or did I foul something else up

unknowingly. I did not remove or alter any other parts of the carb when attempting this repair.

Today I ordered new gaskets, float, grose jet, etc for the affected float chamber from Moss hoping it would solve the problem. Any advice on this would be greatly appreciated as I would love to avoid having to tow the car to the shop to cure this self-inflicted problem.

I assume you have HS4's.... You didn't mention ordering the main jet. It has a fairly fragile plastic tube that takes the gas into the carb.

When you pulled the tube loose from the bowl and replaced it you could have gotten the rubber washer or "O" ring jammed into the hole plugging up flow or you could have crimped the plastic tube (Inside the spring). If you bend them to the point they crimp (bend in half) they are trashed.

At about $15.00 for a loose one or part of a kit they are not worth trying to salvage.

What I think has happen is you aren't getting fuel into the carb you pulled the hose out of. There are two O ring washers that go on the hose before you place it in the float. If you didn't remove them and slide them over the hose before installing it you probably have a blockage. If you want to varifie this. Spray some starter fluid, carb cleaner, or gas into the throat. If the engine wakes up you found your problem.

I think this could be what happened because I don't remember there being any washers on the hose at all when I reconnected it. They probably fell off. Also, when I put the hose back in it was difficult to tighten properly. It took two or three attempts before it would stop leaking gas. Do you think the hose is most likely a goner?

Thanks for the help.

Sounds like you knocked off the jet hose that runs from float bowl to jet (small black hose). Just putting it back in may not work and it's plugged. Get yourself a good manual (Haynes or Bentley) they will show the proper way for hose etc to be assembled. There is a small flat washer and rubber gasket involved along with a threaded fitting. The float bowl is not designed to be tight, rather it's mounted thru a rubber gasket affair. Mine have ~80K on them and they just seem to bobble around. You may wind up pitching the Grose jet...they seem to hang up with the most minute trash, even though filtered. I've got a couple gathering dust...

BTW...some may argue, but I find it's far easier to affect repairs such as this if you take them off the car

I dought you lost them. They are still there. You almost have to pick them out with a scribe or something. You have screwed the hose up trying to stop the leak. If it was me I would replace the jet. You want to ask them if it comes with the O rings.

Thanks for the advice, I'm learning as I go. I've only had the car for about 3 months. Regarding the float chambers, what confused me was that the front one is firmly connected to the side of the carb while the rear one was "bobbing around." That's why I thought I should tighten it. Also, the hose on my carb is actually clear plastic with a flexible metal cover on the outside.

What you have is the right OEM type of jet. What was refered to above is a cheap aftermarket type. The reason you have a loose float bowl is the rubber buffer has deteriorated.

Thanks for the advice, I'm going to get a new hose and washers, etc to get this fixed. Hopefully, it will be pretty straightforward. Any advice as to how much gas I should put in the float chamber before I start it up?

allen; replace the su with a weber 45 dcoe and manifold. your toubles ARE OVER

Your troubles will just begining. Believe me a DCOE is not for a beginer. You don't have to put any gas in it. The fuel pump will do that.

I'm with you Tom!!! From my last couple of weeks of getting serious about the engine again, I realize that SU's are the way to go!! I will bet they may only need a little tweek at 50,000 miles and that will be because the vaccum has changed with the engine!! If anybody is having trouble setting their SU's, go to Skye's front page!! The only thing it is lacking is that down is rich it and up is lean!! Other than that, go nuts!! :o)

For right now I'd just settle for getting the car drivable. I'm going to replace the jet hose and hope for the best! I was really surprised that knocking one carb out of commission had as much affect on the engine as it did.

well yeah, that is half your fuel supply... hang in there, u will get it worked out.

Not only is it half your fuel supply, it's pretty much the only supply to two of the cylinders! (Unlike Tony's Corsa, where the two carbs on one cylinder bank both feed into a plenum supplying all three cylinders on that side.)With one carb dead, the cylinders normally fed by it have to try to suck their fuel through the crossover pipe - and that's not very efficient.

These things are good to know. Well, my parts are on order and I'm hoping to get back on the road by Saturday.

Thanks!