Not starting after carb change

Post by **winger300** » Wed Mar 24, 2004 6:28 pm

I put on my HS4 carb today, however it will now not start...

The first problem was fuel leaking from the bottom of the float chamber. I undid this to find the rubber seal had perished. I've replaced that now, so i know fuel is getting into and out of the float chamber.

The piston isn't sticking at all either. The thing im not sure about is setting the mixture. I turned the adjustment to halfway. But differnt settings didn't help. I've not touched the dizzi, so im assuming that is still ok.

What's next to check?

Post by **Alec** » Wed Mar 24, 2004 8:25 pm

Hello Winger,
the basic jet setting for the S.U. is twelve flats or two full turns down from the jet flush with the bridge. However, I would expect to hear some reaction with virtually any setting as you would be using the choke initially.
An easy check is to dribble some fuel into the carb while you crank the engine, if it fires then you have some sort of fuel supply problem. Just check that the needle is correctly fitted to the piston, the shoulder should be flush with the bottom of the piston.

Alec

Post by **winger300** » Wed Mar 24, 2004 9:01 pm

perhaps i'd better check the ignition again, it would be an annoying coincidence!

When i first turned on, the float chamber leaked at the bottom, so i took the rubber seal out, and slipped it over the little fuel pipe, then pushed it all in and scewed it up. Is this correct? How can i be sure fuel is getting up this tube into the jet?

Post by **winger300** » Thu Mar 25, 2004 3:31 pm

got it working! Im not quite sure what was wrong, but fiddling with the jet and pipe seemed to make it work. Timing was really advanced also, which i dont understand since i've not move the distributer, and it certainly hasn't slipped.

The only problem now is that it idles a little too fast, even with the throttle closed right up to the stop. Any ideas whats causing this? I've plugged the breater outlet up, is this correct? or should i connect this to my rocker cover?

Post by **rayofleamington** » Thu Mar 25, 2004 3:41 pm

fast idling - I presume you found all adjustment screw/s?
The butterfly should come very close to completely shutting off the inlet air - worth having a look to see if it is all assembled correct.
Might be an air leak then

(carb / carb to manifold / manifold)

Post by **winger300** » Thu Mar 25, 2004 4:14 pm

I've blanked the breather hose outlet off, is this correct? when i uncover it, the revs drop, and they can be adjusted using the idle speed screw. However the revs now rise and fall, say between 500-2000 rpm, which is really strange. and the engine sounds really rough. Whats causing this?

I'm not using the correct needle either. I think i have an AAM, which is probably not helping things.

Post by **Alec** » Thu Mar 25, 2004 4:49 pm

Hello Winger,
if you are refering to the 1\2" outlet on the carburettor, this should be blocked off. It will weaken the mixture a lot at idle with it open.
One thing about S.U. carburettors is that whatever needle is fitted (keeping within the jet size group) the idle dimension is the same or near enough on all needles. Therefore the wrong needle will not affect the idle significantly. Ray mentioned the adjustment screws, make sure there is a clearance between the choke idle screw and the choke cam with the choke pushed in.
If you lift the piston, with the engine switched off, then let go, it should smoothly drop and stop with an audible click.
With the jet set two turns down, and a correct float level you should get a reasonable idle, unless as Ray says there is and air leak somwhere. If you can't find one and the carburettor is set as above, I would double check the ignition and valve clearnces etc to ensure the rest of the engine is healthy.

Alec

Post by **winger300** » Thu Mar 25, 2004 5:03 pm

thanks for the reply.

The choke is set fine. The piston isn't sticking. Air leak sounds most likely. but how can i locate it?

Post by **Matt** » Thu Mar 25, 2004 5:09 pm

i heard something about spraying oil around, when the revs changed when you sprayed a spot thas where the leaks is...... i might be wrong tho as normal

Post by **Alec** » Thu Mar 25, 2004 5:12 pm

Hello winger,
If you have some WD40, or the like spray it along the flanges, with the engine running, and when you see a cloud of smoke from the exhaust, you have found it.
good luck,

Alec

Post by **Willie** » Thu Mar 25, 2004 6:48 pm

WINGER.. what engine are you using? and do you have
a solid oil filler cap or one with a gauze filter in it?

Post by **winger300** » Thu Mar 25, 2004 8:26 pm

i have a 1098 engine, with a 12G940 head, Min-its alloy inlet, standard exhaust manifold and HS4 with K&N.

I bought a small K&N type filter for the rocker cover, so i would prefer not to connect the carb and rocker cover, but blank the connector on the carb instead.

Im thinking there must be an air leak where the manifold meets the head. The alloy manifold flanges are quite a bit thicker than the exhaust ones, and i dont think i did a good enough job with the washers to compensate for it...

are there some proper washers to buy? or should i just improvise something? any good suggestions? i used exhaust clamp washers which have a kind of bevelled edge.

Something i noticed when driving, at about half throttle opening there is a whistling sound, which goes away at lower or higher throttle. Other than this, it drives fine, plenty of torque, and a really grunty exhaust note at high revs, kinda sounds like i've got a V8 or something!

Does anyone have an explanation of why the timing was so far out, it was fine before i changed the head&carb, but afterwards i was a good 10 degrees after TDC, with it set correctly, i had to bend the vacuum advance pipe to clear the dynamo, so i know it hadn't slipped, perhaps the HS4 carb presents a different vacuum... which leads to my next question about tuning. Rolling roads; Will any garage that offers rolling road tuning know how to setup the SU carb? will they supply the needles? and will they re-configure the dizzies advance curve?

Post by **Willie** » Thu Mar 25, 2004 10:48 pm

I think you will find that the 1098 engines which were set
up to use a CARB with a breather pipe connection( as opposed
to a breather to the AIR FILTER) do not have an outlet pipe
on the rocker cover. On this type of engine the oil filler cap
is the thick one with an internal mesh filter in it, this is now the
INLET for the engine. The OUTLET is now from the tappet
cover under the manifold and the rubber pipe from there should
go to the CARB pipe.??
Your whistle is almost certainly an air leak on the manifold.

Post by **winger300** » Thu Mar 25, 2004 11:11 pm

thats interesting, originally my car had a green rocker cover, with a pipe to the air filter, and the tappet chest cover has a pipe that is about 10 inches long, and just points downwards.

When i changed the engine, the new engine had the same configuration, but with an alloy rocker cover, and the air filter had an elbow pipe connecting it to the carb, and the breather hose from the rocker attached to this.

Post by **Cam** » Thu Mar 25, 2004 11:17 pm

When I put my system together, I filed the aluminium manifold mating flange (rear) to match the thickness of the exhaust manifold flange, then just used the standard large washers and brass manifold nuts.

Can't explain why the timing was out. Maybe it always was?? The vacuum presented by the carb should be roughly the same and will not affect the timing past it's maximum advance anyway and is only really effective at tickover and deceleration. At wide open throttle there is no vacuum present and the dizzy is only relying on centrifugal advance. In any case, you are supposed to set it with the vacuum pipe disconnected (and plugged)! So it should be irrelevant anyway!

The best bet is to go to a rolling road place that specialises in Minis as they will be used to the A-series engine, SUs and Lucas dizzys.

Post by **Kevin** » Fri Mar 26, 2004 11:00 am

Will any garage that offers rolling road tuning know how to setup the SU carb? will they supply the needles? and will they re-configure the dizzies advance curve?

The should be able to do that with no problem.

Post by **Willie** » Fri Mar 26, 2004 4:20 pm

I'll ask again , what type of oil filler cap do you have? solid or
one with a mesh filter?

Post by **winger300** » Fri Mar 26, 2004 4:59 pm

Sorry Willie,

its a solid one.

I replaced the manifold gasket this morning, and tightened down the bolts properly this time. The ones on the inside of the intake manifold are really hard to get at!

I sprayed WD40 around, and there was no smoke, so i don't think there are any leaks now.

Its running a lot smoother now, however it still running a little fast, the ignition light glimmers when first started from cold, but when it heats up its running a little quicker, and the light goes out at idle.

One thing i did notice when assembling the carb is that the butterfly has a hole in it. So maybe this is the issue. I think the butterfly on my HS2 was solid, and i've seen others that have a sprung valve, but this one simply has a hole. I guess this is the cause?

It seems to drive better now too, and the whistle has stopped.

Post by **Alec** » Fri Mar 26, 2004 7:20 pm

Hello Winger,
that certainly won't help, if there's a hole it should have a spring loaded valve. Block it off with a short screw and nut.
Then see how it runs.

Alec

Post by **Willie** » Fri Mar 26, 2004 8:17 pm

A hole? that's interesting. do as Alec says. If you have the
the solid oil filler cap then you should have the carb 'breather
intake' pipe blocked off (as you have) and you should have the
rocker cover breather (OUTLET) pipe connected to the air filter.
the bent pipe on the tappet chest cover,under the manifold, is
now the INLET for engine breathing as per the majority of 1098's.
The rule of thumb is: If the breather pipe is connected to the AIR-
FILTER then the oil filler cap should be a thin solid one. If the
breather pipe FROM THE OIL TRAP WHICH IS FIXED TO THE FRONT
TAPPET CHEST COVER (under the manifold) is connected directly to the CARB then the oil filler cap
should be a thick, ventilated,one with a mesh filter on it (should
say" replace every 12000 miles" on it. Your problems seem
to have been with the leaking manifolds....good luck.

Morris Minor Owners Club

Not starting after carb change

Not starting after carb change

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