22 replies to this topic

[Anthony]

Hey all got a problem,

Have just rebuilt the carb and all sorts of rubbish came out, however we cannot get it to fire now. How do I initially set up the carb for it to fire?

Any help would be appreciated.

Thanks,
Ant.

[Retro_10s]

Firstly check everyting else before playing with the fuelling, check the electrics, check you have spark etc.

[Anthony]

Ill just go check its sparking.

[nathansminis]

this happened on mine.

rebuilt the carb, fitted, and everything was working. it was running before i stripped it all apart. and for the life of me i couldnt get it started. neither could my dad, neither could or motor mad family friend.

it would idle, but any sort of load put on it and it would die.

in the end, i spent the sunday evening outside in the dark at about 9 trying desperatly to get another carb off one of my project minis, as i needed the car for college in the morning.

this was quite a while ago and im stil running on my borrowed carb! it runs worse than the one i had before, using lots of fuel and running rich, but i darent touch it again!!!!

all i can say is if its not even starting then something is possibly blocked in the carb. have you let if fill the float chamber? takes a few cranks to fill up again. then its a case of getting the jet in the right height. ive heard of them going out if the jet isnt centred when you were rebulding it.

other than that im not sure. check you havent knocked anything and its all back as it was.

good luck!

[Anthony]

I am getting a spark and we fully stripped and cleaned the carb so there was definitely no blockages. When you say the jet isn't central do you mean the needle? As the jet can only go in one way. Im running a HS4 waxstat and it has a self centering needle so I can't see a problem there.

Any more suggestions?

Ant.

[Anthony]

[Anthony]

Now we have lost the spark! Running out of ideas now. Just not starting.

Are there any checks I can carry out on the ignition system?

[dklawson]

Please do not take the following question/comment in any way as derogatory.

Did you go through adjusting the carb to the default, post-rebuild settings? Very frequently on this board I see people posting who say they rebuilt a carb but they can't get the car started because they failed to center the jet, failed to set the jet tube height, and didn't make any attempt to set the choke and fast idle.

Before you despair, what settings have you attempted?

[Anthony]

This is the thing, what are the default post-rebuild settings? When you say centre the jet I don't understand. From what I can see the jet just slides in and the needle centres itself. What about the jet tube height?

Thanks for the help dkl I don't take anything as derogatory (unless it clearly is!)

Ant.

[dklawson]

Different carbs use different techniques and different settings. I can only provide info on the HS series of carbs.

Centering the jet is necessary on all fixed needle carbs (not spring loaded needles... however I know people who use a technique to center them also). The jet tube is held to the bottom of the carb in a spring loaded bushing. You adjust the height of the jet tube such that it is flush with the bridge inside the carb throat. Once it's flush you loosen the jamb nut holding the jet bushing to the carb body. This will allow left-right motion of the jet. The fixed needle is set in the vacuum piston such that its shoulder is flush with the lower surface of the piston. The piston is lifted (by finger) and allowed to drop such that the needle forces the jet to "center". The jam nut is then tightened a little. The piston is lifted again and allowed to fall. With the dashpot removed it should fall quickly on the bridge with a "click" and NOT stick or scrape on the way down. Once this is achieved, the jam nut is snugged up to keep the jet centered.

With the jet centered, the adjusting nut (NOT the jam nut) for the jet is backed out two (2) full complete turns. This will lower the jet below the bridge to the initial starting position.

Don't forget you have to set the float level in the float bowl also as part of a rebuild. This needs to be set such that an inverted float bowl lid has the float arm positioned about 1/8" above the surface of the lid.

All of the above apply only to the HS series of carbs. Others will have to spell out the procedures for HIF and such carbs. I don't know them.

Please don't take this wrong but this is not a task you should have started without having a manual at hand that fully describes your carburetor.

[Anthony]

The carb I have is a waxstat HS4. It has a self centering needle and as such I haven't carried out any centering of the needle as there seems to be no possibility of adjusting the jet position. My main concern is the position of the jet when I first try to start the car. You say that the jet should initially be flush with the bridge inside the carb float. I don't fully understand what you are saying. It seems that my jet may be too low. To get it up so that it is flush with the brass jet bearing I would have to screw the adjusting nut almost all the way up. At one stage I tried this and it just didn't feel right. It was almost to the stage where I would need a spanner and I have always only used finger pressure in the past when adjusting the mixture. Interested to know what you think.
With regard to the float chamber my float is fully plastic and as such there doesn't seem to be any adjustment. As part of the SU rebuild kit there was a new spring loaded needle and brass fitting into which the needle seats. I used both of these to effect a recondition of the float chamber. I am happy that the float chamber is correct.

[dklawson]

The carb I have is a waxstat HS4. It has a self centering needle and as such I haven't carried out any centering of the needle as there seems to be no possibility of adjusting the jet position. My main concern is the position of the jet when I first try to start the car. You say that the jet should initially be flush with the bridge inside the carb float. I don't fully understand what you are saying. It seems that my jet may be too low. To get it up so that it is flush with the brass jet bearing I would have to screw the adjusting nut almost all the way up. At one stage I tried this and it just didn't feel right. It was almost to the stage where I would need a spanner and I have always only used finger pressure in the past when adjusting the mixture. Interested to know what you think.
With regard to the float chamber my float is fully plastic and as such there doesn't seem to be any adjustment. As part of the SU rebuild kit there was a new spring loaded needle and brass fitting into which the needle seats. I used both of these to effect a recondition of the float chamber. I am happy that the float chamber is correct.

I did not say the jet tube should be flush with the "carb float", I said flush with the "carb throat".

The jet bearing is the part I was calling the jam nut. It's my understanding that there are ways to center the jet even on a carb with the Waxstat... however, this is only hearsay on my part as I'm not familiar with them. Regardless, if with the jet tube all the way up flush with the bridge the piston can be lifted and fall all the way to the bottom with a click... your centering is OK.

You might indeed have to use a wrench to run the jet tube up flush with the bridge. I've never tried to turn any of the adjusting nuts by hand, I have a small SU wrench just for this adjustment. Others will have to confirm the number of downward turns required on the HS4 with Waxstat. The HS2 uses two full turns down from flush.

Since you're comfortable that the float is set right, crank the engine for a few seconds, then remove the float bowl cover and see how high the fuel is. It is variable but should probably be within 5/8" of the top of the bowl with the lid off. Even the plastic floats with the metal arms can be adjusted. Careful tweaking of the little finger near the fulcrum can be made in some cases. Another method used on other carbs is to put fiber washers of the correct thickness between the float valve body and the lid. If the fuel is only about an inch deep at the bottom of the bowl or something... the float level is wrong.

In an earlier post you said you have now lost spark. Since you had spark earlier and the engine hasn't been running, this begs the question... what have you done in the meantime? Have you intentionally changed something or perhaps accidentally bumped something while looking at fuel issues. Download and review the troubleshooting part of my PDF on Lucas points ignitions. Even if you have electronic ignition, you can use this for look for problems everywhere except the ignition module.
http://home.mindspri...tsIgnitions.pdf

Once you get the car running and are happy with its basic state of tune, check out this link for future reference:
http://www.nireland....ph/waxstats.htm

Edited by dklawson, 06 April 2008 - 05:06 PM.

[Anthony]

Doug,

Thank you for your help so far. We have traced the lack of spark to the dizzy so will be replacing cap and whatnot.

The first link looks very helpful however second link you posted doesn't seem to work.

Thank you,

Ant.

[dklawson]

Curious about that second link. It wouldn't work for me even if I cut and pasted it into a new browser. The link/site is still up so I'm not sure what the deal is. It's easy to find. Go to Google and key in this string: +"waxstat" +"conversion". The nireland link will be the first hit and should work from Google.

After my last post I was trying to remember how you center the spring loaded needles. What I finally remembered is that there is a tool used to do this. Basically it's a stub of a fixed needle with a diameter to JUST fit inside the jet tube. You fit that temporarily in place of the spring loaded needle, lower it into the jet tube before tightening the jet bearing, then tighten the bearing and remove the piston to fit the proper needle. It's a lot of steps but I remember this method being discussed by numerous MG-Midget and AH-Sprite owners.

So what happened to the cap and rotor that they need replacing? Don't shotgun the repair and troubleshooting, that gets expensive. Use a volt meter and work backwards through the ignition system until you determine where power is being lost.

[998dave]

'default' settings are in Haynes, along with a guide to setting things up.

As for spark, do you have points? these may also require replacing / gap setting, etc.

Dave