Carb Issue

Post by **PSL184** » Mon Jul 14, 2008 6:49 pm

1098 running a standard carb and I can't get the mixture to run weak enough. Even with the nut right up it's still hunting a little at tick over and I've got a sooty exhaust - Do I need a new needle or seals or carb or car ?????

Post by **MoggyTech** » Mon Jul 14, 2008 7:05 pm

Checks to make

Air Cleaner Clean
Choke/linkage allowing jet to return fully home when choke off
Fuel level in float chamber not too high (Needle Valve or Float)
Main Needle shoulder FLUSH with bottom of carb piston.

Post by **PSL184** » Mon Jul 14, 2008 7:17 pm

MoggyTech, I understand 1, 2 & 3 but how do I check 4 ?
Thanks....

Post by **MoggyTech** » Mon Jul 14, 2008 7:22 pm

Remove carb dashpot oil filler, then two screws holding dashpot to carb body.
Carefully lift off dashpot, and take care not to damage the large spring that comes off with it. Lift out carb piston, taking care not to bend the needle.

Turn piston upside down and check that the shoulder of the needle is flush with the base of the piston. The needle is held in place by a small grub screw, and these sometimes work loose, allowing the needle to move in the piston.

Post by **PSL184** » Mon Jul 14, 2008 8:04 pm

OK, thanks - I'll check out and report back....

Post by **minor_hickup** » Mon Jul 14, 2008 8:35 pm

Usually if the carb cannot be adjusted lean enough at idle and hunts away then a worn jet is usually the culprit. If this is the case it needs servicing, a service kit will provide a new jet and all the gaskets you need. However if the throttle butterfly slops about and has plenty of play it will need a rebuild. The kit is fairly expensive and requires accurate drilling, not a DIY proposition. Usually a rebuilt exchange carb is an easier way to go.

Post by **PSL184** » Mon Jul 14, 2008 8:58 pm

OK, thanks. I'll check all as above and see where to go from there....

Post by **AJT** » Wed Jul 16, 2008 10:00 am

I've just re-built mine and it's now excellent: the job is not complicated and doesn't require drilling. All you need is:

Carb service kit (jet, gaskets, float valve)
Needle
Throttle Spindle

What I discovered was the a worn spindle allows air into the carb and makes adjustment impossible: the hardest part of re-building is jet centering so that the piston does not stick. I found that taking the adjustment nut and spring off, then the jet sleeve totally out to free it up then replacing was the easiest.

Quite satisfying compared with buying a new one and not difficult if you have a couple of hours to spare.

Post by **Kevin** » Wed Jul 16, 2008 11:53 am

I've just re-built mine and it's now excellent: the job is not complicated and doesn't require drilling.

It will do if the body or bushing is worn but in your case only the spindle was worn so no problem

Post by **PSL184** » Wed Jul 16, 2008 1:59 pm

Right I've checked all the items as listed above and can't see any problems so I guess its gonna have to be a new jet. I'll look around for rebuild kit prices - any one have any suggestions?
Cheers, Rich

Post by **MoggyTech** » Wed Jul 16, 2008 2:15 pm

http://morrisminorspares.co.uk/shop/pro ... d86eb2645b

Post by **PSL184** » Wed Jul 16, 2008 3:08 pm

Bargain !! - I'll get one ordered....

Post by **MoggyTech** » Wed Jul 16, 2008 6:00 pm

PSL184 wrote:Bargain !! - I'll get one ordered....

I ordered one a few months back, it's genuine SU parts and top quality kit.

Post by **Alec** » Thu Jul 17, 2008 6:54 pm

Hello PSL184,

there is no reason for jets to wear, unless the jet is not centred in which case it wouldn't run well anyway. I would make that a last item to check\replace.

Alec

Post by **bmcecosse** » Thu Jul 17, 2008 7:53 pm

Yes - the jet should last a very long time. Worry more about fuel level in the float chamber. The needle valve can leak slightly - no harm when running, the engine needs the fuel, but when idling it can rise too high and lead to 'rich' idling.

Post by **PSL184** » Thu Jul 17, 2008 8:21 pm

OK, well..... I have no real history as I've only had this one a few weeks.... The exhaust is very black and sooty to the point where the tip of the exhaust is being eaten away (you know the effect). It runs fine and idles fine except that it hunts/misses a little (its not as smooth as the other one). The needle is seated correctly, choke off fully, carb adjusted as per manual but no luck in correcting the stumble. What kind of level should I be looking for in the float chamber. I compared the level to our other one and it looked the same??

Post by **bmcecosse** » Fri Jul 18, 2008 2:06 pm

With the 'bell' removed from the carb - loking down on the jet - the fuel should be visible about 1/8" below the jet - with the pump switched on. If it's flowing over the jet - well, there's the problem.

Post by **PSL184** » Fri Jul 18, 2008 4:29 pm

....and if it is flowing over the jet, then I adjust the float level ??

Post by **MoggyTech** » Fri Jul 18, 2008 5:04 pm

PSL184 wrote:....and if it is flowing over the jet, then I adjust the float level ??

I would replace the needle valve in the top of the float chamber housing lid, if fuel level is too high

Post by **PSL184** » Fri Jul 18, 2008 5:20 pm

MoggyTech wrote:
PSL184 wrote:....and if it is flowing over the jet, then I adjust the float level ??
I would replace the needle valve in the top of the float chamber housing lid, if fuel level is too high

fair point, but isn't the float level adjustable by "bending" the arm?