Carb woes

[GraemeH]

My working commando was only firing on one cylinder even after cleaning the carbs from a gooey mess. I even bought the tiny .4mm and glued it to a WD40 straw as suggested here to drill to unblock the pilot jet. Nothing doing. I had purchased new AMAL premiers for my project bike and duly fitted them to the working bike which then started on both cylinders first kick.... but, 2 new problems arose:

1. once warmed up, tickover is 2000rmp and the slides are definitely at the bottom. According to the AMAL box I have #17 pilot jets. Other than removing the carbs and checking the pilot jet size, what else could cause this?

2. when I stopped I noticed petrol gurgling out of one of the tickler knobs. I guess I need to check the float level, but what else might cause this?

Thanks for any pointers and encouragement - had carbs off and on 3 times yesterday, though the main frustration is actually getting the air filter in and out.

 

[marinatlas]

Check both fuel level first .

 

[kommando]

1. once warmed up, tickover is 2000rmp and the slides are definitely at the bottom. According to the AMAL box I have #17 pilot jets. Other than removing the carbs and checking the pilot jet size, what else could cause this?


2. when I stopped I noticed petrol gurgling out of one of the tickler knobs. I guess I need to check the float level, but what else might cause this?

1. You will likely have an air leak at the manifold, test by spraying WD40 at the joints and noting any change in revs. When the revs change you have found the leak, the carb to float joint can leak too and air get sucked in.

2. Float level or the float needle is not closing properly due to dirt or damage to needle or the needle seat.

You size of pilot jet will not affect the tickover enough to raise it to 2000 rpm but on the 850 at least it will idle and pull away better with 19 jets.

 

[o0norton0o]

Also, check that your needle clip didn't get caught in the spring that holds it down in the inner body of the carb where they are supposed to seat under the spring. The needle also can miss the jet when you engage the inner body when you assemble the carb and keep that carb from idling because the needle isn't actually falling inside the needle jet. To check them, you can usually take the air filter off and put a finger into each carb to feel the needle go up and down when you lift the throttle..

 

[GraemeH]

To check them, you can usually take the air filter off and put a finger into each carb to feel the needle go up and down when you lift the throttle..

Will do - but as mentioned, this is the most tedious part of the process, as bad as wielding the sawn-off Allen key between the carbs, with the oil pipe in the way. If only the air filter and its spam tin had been 1cm thinner.

 

[SteveBorland]

Will do - but as mentioned, this is the most tedious part of the process, as bad as wielding the sawn-off Allen key between the carbs, with the oil pipe in the way. If only the air filter and its spam tin had been 1cm thinner.

Use a 5.5mm spanner on the Allen key - makes it (almost) a doddle to get the inner bolts out.
Can't help with. the ham can, I've a K&N, but it cannot possibly be as bad as my hate job from yesterday - changing a headlight bulb on my Alfa 147. I spent almost 2 hours buggering about with it, being hidden from view and almost inaccessible to normal hands. The high beab bulbs take about 20 seconds to change but the low beams (which are the only ones which blow)......

 

[gpzkat]

On the filter assembly - I used some bungee cords - I think they're called shock cords over there, hooked to the front metal filter housing to pull it tight against the carbs, compressing the (new) rubber boots. Then I lubed up the outside of the air filter rubber on both sides with silicone spray. 'Armor All' or blue window cleaner would work too. Then, from the right (throttle) side, I pushed the filter and metal mesh in almost horizontally, and wiggled it upward in a twisting motion. Worked for me. Oh, if you cut the Allen key just right you can get it to work pretty good, not hitting the valve cover cap, giving a 1/6 turn each time. Maybe I got lucky but it's not that bad. Bevel the edges of the working end.

I have non-adjustable floats, and the left side was too high, spewing through the tickler. I found an 'E' clip from a needle jet in my pile of Suzuki parts that slid onto the float needle and spaced the float just enough to lower the fuel height. It won't come off. It would be better to have 'stay-up' (i.e. adjustable and ethanol resistant) floats, but this works for now. I had a bad miss at 2500-5000 RPM on the left side, replaced the slide needle as that is what I read about that could be the problem. The issue is solved, but I think the float level and worn slide were also part of the problem. I replaced the slides and slide needles on both carbs with Wassell parts, and it is brilliant.

My '82 Suzuki GS1100E (x2) air filter housing is about the most difficult mounting job of any bike. But without it, running pods and a pipe, the bike just runs terribly. That big plenum chamber helps with the CV carbs and gives it major low/mid range grunt. Pods give great response & power - above 8K RPM.

That Norton filter is 3X oversized but sorta looks cool! I don't think it has much effect on the overall performance though.

 

[o0norton0o]

Will do - but as mentioned, this is the most tedious part of the process, as bad as wielding the sawn-off Allen key between the carbs, with the oil pipe in the way. If only the air filter and its spam tin had been 1cm thinner.

You can also remove the float bowls and main jet to check the needles are positioned properly. The needles should be evenly sticking out below the jet holder if they are engaged properly. Pretty obviously, if they are uneven that's a sign of a problem, but if they are protruding evenly and you are sure they are engaged on the correct height on the needle, then you've checked that they are correctly positioned and you should move on to something else...

 

[acotrel]

With my bike, there is nothing behind or around the carbs, so life is much easier. When I had road bikes, it was often easier to take a broader approach. If the carbs had gunk in them, I would take the tank off and clean it thoroughly before fitting clean carburetors. I would make sure the carburetors worked properly before fitting the air cleaner. When you start in the middle, you are not being systematic. You cannot tune the carburetors with the air cleaner removed, but you can check their operation for smoothness, bottoming and lack of flooding. With Japanese type carburetors, you can measure the float levels before fitting the carbs. If you have old carburetors the floats can be checked for leaks by immersing them in very hot water. Mk2 Amal carbs are almost Mikunis.

 

[kommando]

If only the air filter and its spam tin had been 1cm thinner.

RGM do exactly that, a thinner spam tin and in stainless.

COMPLETE TWIN CARB NARROW AIR FILTER ASSEMBLY, STAINLESS STEEL

COMPLETE TWIN CARB NARROW AIR FILTER ASSEMBLY STAINLESS STEEL FOR COMMANDO 050744E

www.rgmnorton.co.uk

 

[GraemeH]

Did the WD40 test on the manifolds, no signs of leaking. Did exactly the same ride as yesterday and idle stayed at around 1200rpm and there was no sign of petrol dripping...

So I have no idea what happened yesterday - a mixture of first ride with brand new carbs, hot day, constant traffic jams with idle at 2000rpm ... the motor was seriously hot when I got home. Maybe it didn't appreciate that.

Thanks for all the tips though. Bevelling the ends of the 5.5mm allen key sounds like a good idea as it's always a pain to engage for that 1/6 of a turn.

Now I will have more time for my project bike.

 

[SteveBorland]

I have non-adjustable floats, and the left side was too high,

If you don't have the Stay-up type float from the Premier carb, the float level is set by moving the float needle seat up or down in the bowl. Warm it up with a hot air gun, then with a suitable drift, gently tap the seat up to drop the fuel level.

 

[jseng1]

I know people who had the problems you experienced - so they went to a different brand of carbs.

 

[gpzkat]

If you don't have the Stay-up type float from the Premier carb, the float level is set by moving the float needle seat up or down in the bowl. Warm it up with a hot air gun, then with a suitable drift, gently tap the seat up to drop the fuel level.

Yep, I read about that, but needed to get it going without taking the carb off to see if the slide and needle fixed the main issue, so i did a quick 'hack' that works... for now.