8 replies to this topic

[radgator1]

Let me start by admitting I'm pretty much clueless on the mechanical issues of Mini's and pretty much all other cars so apologize in advance.  But anyway, my Mini was an SPI that now has a rebuilt very fast road build engine and rebuilt twin carbs that I bought several years back on ebay.uk (the carbs, not the engine).  After years of delay after delay, everything was finally put together recently by my local mechanic in California, and although he is a good mechanic and most importantly honest and fair, he has never worked on a Mini before and has never seen SU carbs unfortunately.  Anyway, he got everything pieced together and called me the other day to say he tried to start her up and it it started for a few seconds but flooded out quickly and fuel didn't stop flowing for some time when accelerator released.   Pulled the plugs, dried them off, tried again, same thing.  Is it possible that the carbs have no needles and the car would still start?  I asked him if the needles were in them and he said "good question" and said he didn't "feel them".  Do rebuilt carbs come w/o needles or would that be very out of the ordinary?

 

So if it is in fact the case that the carbs are needless then I need to buy some.  What would you recommend for a 1430 that I hope to use to cruise around town in and occasional spirited rides in the local mountain roads, or even track days?

 

Another item possibly worth mentioning is that when he installed the new fuel tank and mechanical fuel pump, he used the SPI fuel line that was already in place under the car and capped the return line I believe, then ran braided line the to the carbs.  Could that be causing the problem?  I saw in the other "rebuilt engine wont start thread" that it is possible to run the fuel to the wrong pipe on the carb and figure it is possible to screw it further in twin carbs so I'm not at all sure he has them all plumbed together proper.

 

Any help appreciated.  I could probably take a picture and post it if that would be helpful since I'm going to stop by to check out the car tomorrow after work.

 

Thanks

[iwatkins]

Running on twin carbs on an injection car?

I would first check you have the correct fuel pump.

Carbs run on a low pressure feed, just enough to replenish the float chamber when it's needed, with no return.

An injection car, which is what you started with, runs huge fuel pressure to injectors plus a return.

If you mix both systems, you'll be in trouble.

A carb takes what it wants from a reservoir. An injector gets what it wants from the injector duty cycle.

I would seriously suggest changing your "guy'.

In fact to anyone who understands carbs.

Cheers

Ian

[Earwax]

Excellent post by Ian

 

check fuel pump - only need a pump capable of 3-4 psi unless you are running a fuel regulator. As Ian says injected run something higher like 15-30 psi at a guess. ( which is too much pressure for your float stop needle to take- thus flooding)if you have a fuel regulator (highly probable) is for injection then you could swap it for a lower spec.

 

Without needing your mechanic, if you take the airfilters off the carbs and take the damper or 'cap out of the carb top    ..then you can put your fingers at the back and through the throat - you can lift the carb pistons up and also feel the needles ( be careful not to bend) -  when released they should fall with a click or clunk at the end.

 

if no needles then something like a BF or CS2 will get you close enough to start.   But again as Ian says -if you go to someone who understands SU carbs and has a range to test you can get a more precise needle fit ( and buying two needles for each guess can get expensive)

[radgator1]

Thanks for the quick reply Ian.  Maybe I wasn't clear enough.  We are not trying to step down the high pressure from an SPI car to carb pressure.  Other than the fuel hose that goes from the rear of the car to the firewall, none of the old fuel system is being used.  New (carb type) fuel tank, and new fuel pump, no return (thats why I said he capped the return line that is still in place from the old SPI system) so it is definitely not that.  And It's not so easy to find a mechanic who has worked on a Mini here but he is very versed in american muscle cars and their carbs has 2-3 in his shop at any one time.  

 

 

 

 

 

 

Any ideas on why the excessive fuel?  My ideas (which may be stupid) that I am hoping to get addressed,

 

1.  no needles in carbs?

2.  Needed to replace all of the SPI fuel line and somehow that is causing an issue?

3.  He has the fuel line going to the wrong pipe on the carbs (seems most likely, but what do I know)?

Edited by radgator1, 30 April 2013 - 12:44 AM.

[ANON]

here you go...http://sucarb.co.uk/technical

[Dan]

  I think most likely is incorrect connection.  Can you stick up a photo of the installation?

[iwatkins]

Yep, I would do some research as Anon has posted and ensure for the carbs you have that everything is connected up properly. I would also be looking at putting in the correct needles to at least get you a baseline if they are not already fitted. You don't say what carbs you have, but do you have any idea at all? Or a photo or two would help.

 

I've never tried running a car without a needle but I doubt that is your problem. It is only a metering device rather than a pressure valve as such. Sure it would be like running the car on wide open throttle regardless of throttle position but I cannot see that flooding through the engine with fuel. It should simply allow a metered amount of to be sucked up through the jet and through the carb to the engine.

 

If you have HS type carbs, with a float reservoir on the side or HIF types where the reservoir is underneath, i would check that the valve in those is closing when the floats rise up on the fuel surface. It could well be that these valves are not closing and you are getting full fuel pressure at the jet in the carb and that is what you are seeing, literally fuel being pumped through the jet, carb and engine.

 

Think of it this way, fuel is forced from the fuel tank, through filters and hoses to this float reservoir. This float reservoir basically has a ballcock like you would find in a toilet cistern. As fuel pours in to this float reservoir the float rises upwards and eventually shuts the valve. As fuel is used, the float lowers and lets more fuel in under pressure then shuts again (etc.). The fuel in the reservoir then flows under gravity only to the bottom of the jet and is sucked up by the vacuum above it as air flows into the carb, atomising it. The needle just provides a metering device to ensure the right amount of fuel gets sucked into the engine for a given load on the engine.

 

Cheers

 

Ian

[Dan]

  It might be that your mechanic, if he is unfamiliar with SUs, is confusing the metering needle with the float chamber needle valve.  I can't imagine them being built without needle valves in the chambers but that would lead to flooding.

 

  Also, SUs don't have a throttle pump so the throttle position is not related to fuel flooding directly.

[radgator1]

Great info, thanks for the replies and links.  I'll bring this information to my guy and also take a picture of the connections and post here to see if it looks correct.

 

Kevin