Morris Minor Forum

I’ve got a 1275 that runs only when I shoot a little gas from an oil can into both carbs ( filters off). Runs great for five seconds at a time. Fresh gas, carb bowls fill up, lots of gas coming out the float shutoff needles ( dual carbs) when top of bowls are removed. I know there’s no flooding because priming gets it running every time
Seems like the carbs need cleaning somewhere, I didn’t drain them when I should have, 23 years ago, just the tank. So would shooting carb cleaner into the throats hurt anything or is there any other easy fix? Maybe shoot cleaner at the bottom of the bowls? I have a manual on rebuilding them but don’t really need another project right now
Thanks



Edited 1 time(s). Last edit at 2025-05-07 09:36 PM by Rick406.

Sometimes there is a bit of rust or dirt in the little pocket as the bottom of the float bowls. Check for this and clean it out. Then most SU carbs have small tubes that lead from the float bowls to the jet at the bottom of the carb. Make sure this is not clogged. When the float bowls are full, remove the "bell" covers to the carb along with the piston and main needle. You should just be able to see some gasoline at the bottom of the jet if fuel is flowing from the float bowl to the jet.

John F. Quilter
Eugene, Oregon USA

Jey tubes are plugged. Replace the jets.

Thanks for the advice, I took the carbs off, cleaned them and the bowls which had enough dirt to block the fuel. The jets were very easy to blow through. The piston chambers had a lot of dirt in them so I'm glad I got it apart. Back together, the fuel still wasn't getting to the intake so I took it apart and found there were two O rings in each fitting on the bottom of the bowls which were quite bad off so I replaced them with one good O ring each carb. Don't know how thats going to work until I replace a bad needle/seat thats flooding all of a sudden.

It's good to know how these carbs go together. Now I know how to drain the carb for long term storage. (crack the brass fitting on the bottom of the bowl)

SU carbs almost always need servicing after the car has sat.. the 'economy' way to do it is remove float bowl lids and the dashpot with piston, spring and needle as an 'assembly'. and stand it upright in a suitable container so as not to damage the metering needle ( I uses a small box with hole cut for needle to pass through) you can then blow through the jet and connecting tube to float bowl with compressed air to clear it .) with dash pot off you can better access the choke linkage ..blow it off with comprssed air and check for movement.. and douse with light lube such as WD 40 and check for free movement again.. Next remove dash pot from piston and clean it with some rattle can carb cleaner.. and do same with piston..IF you turn it anything but upright, you will lose the dashpot oil ( wise to change it anyway as part of the service) in which case, after the piston is satisfactorily clean, rest the piston back in upright the box. and add some oil to the inner tube.. to about 1/2 way up (do NOT overfill..should be 1"- 1/14" from top) then place it back in the carb along with spring, and refit the dash pot..tighten screws then check for smooth operation ( it should drop in its housing with a 'clunk') then clean the float bowl lid(s) and inspect the float valve(s).. all it takes to comprimise them is a small amount of gum or varnish from dried up fuel on the tip or in its seat.. so make sure they are clean.. it is safe to use carb cleaner to clean 'viton' if used sparingly.. (Do NOT soak the float valves in carb cleaner.. simply use it to clean them off) with that done, re-fit the float chamber tops, turn on ignition and check the float valves are doing their job..and if all is good.. you are ready to run the engine again..



Edited 1 time(s). Last edit at 2025-05-12 11:44 AM by tjt77.

Thanks for the good advice. I did get the pistons cleaned up and operating well. However I noticed that both needles were loose where connected to the piston, is that normal? It made it so easy to re-install that I left them that way. Seems like a long time ago I saw one or two that were tight in the piston. It seems like if they are supposed to be tight they might be hard to get centered. Thats good to know I can clean the rubber tip of the needle with carb cleaner because Im about to order new ones. I did use cleaner to clean the seat but that didn't help any. Also good to know I've been overfilling the oil tube. Why does the jet move up and down? I think its moving when the throttle is half to fully down? I'm guessing it increase the fuel for higher speeds.

Later HS2's used on 1275's have spring loaded needles that aren't firmly arrached to the piston. This allows the needles to self-center in the jet.

The jet should not move unless you operate the choke. The jet should be all the way up for normal operation and down when the choke is engaged for a cold start.

many thanks. These needles aren't spring loaded as far as I can tell, they're quite loose. Should I tighten up the screw on the side of the piston?



Edited 1 time(s). Last edit at 2025-05-13 10:15 PM by Rick406.

If the needles are as loose as you say and not the spring loaded type it seems like they would fall out of the piston. Can you easily pull them from the piston?

Got the carbs back off, I was wrong, the needles are spring loaded. Which I think means they’re later types? But I thought these carbs are 1972-74, according to one old post that says the AUD459 tags indicate 72-74. Anyway the motor still isn’t starting without priming. Piston work well, tubes are clear. One jet is still a little sticky on the choke but whatever the problem is it’s affecting both carbs I assume, because if one carb delivered gas I’d at least get two cylinders firing (I think) The sticky jet was stuck in so bad I had to take it out with its nut and drive it out of the nut with a punch. But since it starts by priming it’s not a choke problem. Any suggestions much appreciated

the jets gum up in their tube when left sitting.. this prevents the jet from sliding sufficiently low to enrich the mixure for cold start.. you can often lossten them up by lowering the jet as mauch as possible , dousing it with a penetrant such as WD 40 and working it back and forth until the varnish and other residue melts away, allowing the jet to move more freely.. minimally you need air filters and dashpot assy off to make this work....

It’s starting now, idled nice a couple minutes but now it needs some adjusting. Fixed the sticking jet so it chokes but now the other one stays choked. Reading the manuals.

Thanks, I got the jets moving up and down using carb cleaner. One was enlarged from hitting it with a punch to remove it from the locking nut and I filed that down. But it's still extremely choke sensitive. I read thats because the choke also sets the idle mixture. But it doesn't seem to be able to do anything but idle to high or too low....the throttle works OK. I'm thinking the jets are worn out. I put another pair of carbs on that work much better. One leaks out the bottom of the bowl so off they come again for an O ring. I modified an open end wrench to make removal faster. I heated it up and bent it and ground the outside of the jaws way down. I think BP Northwest has the jets for those.

You might want to replace the jets.. these are precision parts and any damage from a punch will comrimise them.. once damaged they are hard to correct. regular O rings dont usually seal the jet in the float bowl either.. they have a 'square' section seal which abutts an aluminum washer ..the jets are ofen installed 'off center' too.. you need a jet centering tool if the main body of the jet holder is disturbed.. its false economy to take short cuts with SU carbs.. they are simple enough, but wont work properly if comprimised.. key issues that cause less than smooth operation :- wear in throttle shaft and bushings.. float valve comprimised.. float comprimised ( the older brass floats are soldered.. residue from ethanol in fuel attacks the solder, causing float to leak).. the plastic floats in HS carbs also give issues over time and tend to develop leaks .. best to replace with solid 'niprophyl' floats to insure against problems..metering needles often suffer damage too.. they are often bent from previous carelessness, and can corrode, usually at the 'thick' end, which effects low speed running.. frankly there are few short cuts that work with SU carbs.. best advice is to rebuild them properly with no short cuts .. do it right once and you can forget about it for a decade or more..

Thanks, I will go ahead and get the kit. I learned a lot R and R'ing the carbs 15 times. Every time some "improvement" failed, I'd get another idea on what might work and take them back off. I hate waiting for parts.
fortunately there are several ethanol free pumps in my area.
British Parts NW does have the kit for my bad pair. But half of the 20 or so kits they list are not available.
If anyone knows where to get just the square O rings I'd appreciate knowing where