29 replies to this topic

[paulrockliffe]

i do it so the metal sleeve that the needle goes into is flush with the bottom of the piston.

Theres a thick metal barel that the needle goes into, which seems fixed into the piston, then the needle has a non-tapered cylinder that goes into this barrel, the non-tapered bit of needle sits flush with the piston, but in this position it can move vertically so the taper of the needle is inside the piston by a few millimetres and can also fall out of the piston all together if the needle is floating.

Hmmmmmmmmmmm.

[blacktulip]

oh right, how is your other one fixed?

[paulrockliffe]

oh right, how is your other one fixed?

They were both set with the needles not all the way into their guides, but the diagram that was just posted shows they should be as far into the guides as they'll go, so maybe they were just fitted wrong in the first place.

I put them all the way up and both were fine, then as soon as I tighten the dashpot cover the piston stops falling all the way again! I've taken the needle out and with the dashpot tightened up there isn't a problem, so I guess the needle is still rubbing slightly.

[paulrockliffe]

I undit the locking screw slightly, so the needle is floating and it's fixed it. I just hope the needle doesn't slide out!!!

[minimender]

oh right, how is your other one fixed?

They were both set with the needles not all the way into their guides, but the diagram that was just posted shows they should be as far into the guides as they'll go, so maybe they were just fitted wrong in the first place.

I put them all the way up and both were fine, then as soon as I tighten the dashpot cover the piston stops falling all the way again! I've taken the needle out and with the dashpot tightened up there isn't a problem, so I guess the needle is still rubbing slightly.

Yep , you will have to centralise the jet.
take the bits off , centralise it then tighten up then put all bits back (in a nutshell)

[dklawson]

Since these are HS2s, you need to do the following.

With the pistons out on the bench, insert the needles into the bottom such that the square shoulder of the needle is flush with the bottom of the piston. Then tighten he grub screw that holds them in place. Both carbs need the needles set flush with the bottom of their pistons. It's important that they're both flush with their pistons when you adjust the mixture.

Remove the jet tubes. Remove the dashpots if you've fitted them. With the vacuum chambers and pistons fitted to the carb body the piston should lift and fall freely without binding if you lift them with your finger through the carb throat. If they don't move freely, remove the vacuum chambers and clean everything. by the way, the vacuum chambers are matched to their pistons. If you think you might have mixed the parts up... try the sticky piston in the other vacuum chamber.

Once the pistons lift and fall freely, reinstall the jet tubes. As per Haynes and others, run the jet tubes up until they are flush with the bridge in the carb throat. Loosen the jet bearing nut. This will allow the jet to move radially. Lift the piston up and let it fall to the bridge. With the piston down, tighten the jet bearing nut slowly but securely. Repeat the lift and drop test. If there is binding... loosen the jet bearing nuts and repeat again until the pistons can be lifted and dropped smartly on the bridge with a "click".

Once the jets are centralized you can set their nominal "start" position and hook up the choke linkage arms.

[AstonMartin]

My Dear Friend,

I also have a twin HS2 set up in my 998 mini. I had way more problems then you, but i solve each of them good. Your problem of the piston didn't want to sit down completely was very simple, make sure the neddle is perfectly straight, a bend needle can be a very paintful thing for your wallet.

My needle was bent, and it shos wear near the base, the wear is nearly flat, becaue the piston keep sliding up and down during the running time in the past few years, the jet, acts as a file ground my needle side flat, fuel optimization is very important, i was running super rich even i lean out the carbs, each carb feet two cylinders, (suppose you know). the number 3 & 4 cylinder was running lean, because it was lean out, but the 1,2 cylinder still run rich, how do i know, i clean the spark plug each time i tune the engine, the 1 ,2 spark plug is full of soot, and 3,4 were so white, so i know there is somethign wrong withmy 1,2 side craby, and after looking it closely at the need, and ah ha, the needle base is no longer truely round, one side is flat, this is enough to cause my air care fail. The professional mechanic didn't even know, i found out that by myself study the hell out of the carb, the needle is really the heart of the carb, wrong needle or damage needle is the cause of power, emission, and fuel ecomony key.

I change the needles, and now the car is running fine, i know twin SU can help increase the HP and volumatric efficiency of an A- Series engine, but twin carbs will occupy lots of space under hood, it is a B ITCH to work with, even now i am experience of tuning both carbs, which mean make them hiss at the same , without too lean and to rich , carlibrate the best. I still fine the twin carbs garbabe, they are not efficiency as individual throttle system , i think it doesn't make much of a difference, except it looks cool, when pepole see it is a antique on older engines.

I have a HS4 or 1.5 Single carbs, sitting on the shelf and i will be replacing the troubosome, twin SU with it, I am not using the car in race performance way, so i think the single HS4 can offer me ease of maintenance, more engine bay room, , enough power, and most important help me to pass aircare, since i live in Vancouver B.C, if i cannot pass air care, i cannot insure, the car.

Please don't get me wrong, i am not saying the TWIN SU are totally Garbage, it help Cooper win races in the past, the design is great that give my 998 a very fast acceleration, lots of fist punching torque.. and sounds fabulous when it hitzzzzz.

I will sell the twin carbs 1.25 along with the manifold, linkage, velocity stacks, to anyone who is interested for USD 300 nego

[dklawson]

AstonM., you said that on your car's carb needles you observed "and it shos wear near the base, the wear is nearly flat ". On HS2 carbs this is an indication that the jet and needle are not centralized properly, not necessarily that the needles are bent. Bent needles tend to hit the jet tube at a point well before the base where they enter the carb piston.

I agree that for most street cars a single larger SU is easier to setup and adjust.

[AstonMartin]

My dear friend,

Thank you for explaining that well, you get my point. I mean the same thing, but just couldn't explain it that well. I mean the jet and the needle does not line up properly, (not perfectly center), so the base of the needle keep rubbing the jet. That what cause the base to ground flat (wear out)

Once the needle is not round, the fuel cannot atomize evenly, or may have bigger dropplet, causing uneven combustion which lead to emission.

Second though is that when you want optium performance for the engine that fitted with twin SU, is pretty difficult, especially when you dont' have a carb tunning tool, it is a measuring device that measures the volume of air passing through the carb.

I dont' have this tool, so i followed the book, and i use the old fashion inaccurate way to tune my carb, by listening the hissing sound through a 18 inch rubber hose. Well,i get i pretty close but i think is not perfect.

Well, after hours of tuning the car starts to run ok, but i think both carbs still running not the same, but is close enough. If i can get both the carb even, then i think my car can go really smooth.

Can't wait to install my 1.5 SU on to the engine.,the installation will be much faster, and the tuning will be easier.

wanting to do this for a long time, but was thinking of converting a VTEC , but now i change my mind, classic is good.

Hey volks, i am buying another shell, with glass and door minus engine, and will build up a TDI engine powered RWD mini cooper, will post progress soon.

Let me know what you guys think.

Cheers

[dklawson]

I use an airflow meter to balance my carbs. Some say that balancing with the rubber hose works just as well as the air flow meters. Like you, I've never known how close I was with the carb "hiss" method.

For Stromberg carbs there is another balancing tool that I've used. The tool is a kit consisting of plastic rods/dowels and pieces of bent wire. You remove the dashpots from the carbs and replace them with the plastic rods (which are a press fit into the dashpot sleeves). The pieces of wire are inserted into the exposed end of the plastic rods and they are bent 90 degrees so that the tips of the pieces of wire (one from each carb) are pointing at each other (and nearly touching) with the engine "off". With the engine running, you adjust the air flow so the wire tips are still pointing towards each other. I've never compared this method with the air flow method. I presume this tool is also available somewhere for SUs.

Good luck with your projects and keep us posted with your results.

[paulrockliffe]

Thanks for your input people, after much swearing and messing abut the carbs are on and the engine setup......

.....kinda.

I'm able to balance the carbs and get roughly the right air/fuel mix, so I've got rid of the airleak. I can even adjust the idle right down to zero now too, so definitely heading in the rght direction.

BUT..... The engine is still idling eratically! I'll post a video of it this weekend if you're lucky. Anyway, can you please give me as many potential causes as possible, everything that's worth checking etc etc.

I'm completely stumped!

I want to just take Jason to a garage but he's not MOT'd. Can I book an MOT and have the garage sort the carbs then MOT him, or is this not legal?

My head hurts! Just want to drive to Bingley next sunday!

I use an airflow meter to balance my carbs. Some say that balancing with the rubber hose works just as well as the air flow meters. Like you, I've never known how close I was with the carb "hiss" method.

For Stromberg carbs there is another balancing tool that I've used. The tool is a kit consisting of plastic rods/dowels and pieces of bent wire. You remove the dashpots from the carbs and replace them with the plastic rods (which are a press fit into the dashpot sleeves). The pieces of wire are inserted into the exposed end of the plastic rods and they are bent 90 degrees so that the tips of the pieces of wire (one from each carb) are pointing at each other (and nearly touching) with the engine "off". With the engine running, you adjust the air flow so the wire tips are still pointing towards each other. I've never compared this method with the air flow method. I presume this tool is also available somewhere for SUs.

Good luck with your projects and keep us posted with your results.

[Jammy]

As long as the erractic idle isn't too bad, it should pass the MOT (as long as it gets through the emission tests).

[paulrockliffe]

As long as the erractic idle isn't too bad, it should pass the MOT (as long as it gets through the emission tests).

I'll put a video up so you can see at the weekend, it's not ridiculous I don't think, but not a million miles away. I only have a visual emmissions tests, so I'm not worried about that! Ideas people!!

Cheers.

[AstonMartin]

Yeah, paulrockliffe, post a Video so that we can see what is going on. A picture worth a thousand words.

You guys know what i think about this forum and the www.tdiclub.com forum, i think both of these forum's members are very very nice, they are willing to help each other, without being sarcastic. Although i am a newbie, i find these two forums are useful when compare to the 16vmini.com forum, those members's nose is on the forehead, i joined them last week, and i left a message, and the reply was BS..making me mad. I will never reply anything again, i didn't even response after i heard the BS. They accusing me cannot weld up a chassis because i cannot fabricated a shifter. Totally different things.

I said i had a problem of designing the shifter , not i cannot fabricate the shifter, all i want is opinion and some simple advise, if you cannot offer, i don't mind, but not step on me :xxx. Oh well, just want to let you guys know how well you guys are.

Cheers

[paulrockliffe]

No video yet, sorry, have been busy all day, but I started Jason up again and drov him about my yard a bit and h seems to be idling ok now. I dunno, think I'm gonna book an MOT and then test him all week to make sure he's gonna be ok. Maybe I dont have a problem. Once he's got a ticket he's going to get a proper once over from someone who knows about mini engines and then rolling road tuned, so if there is a problem it will be sorted!