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Mike6

Help with problem

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My car is an early carb turbo so thinking it is a carb problem have posted here. The background is car was running fine about 6 weeks ago. When I put her back in the garage noticed a weep coming from one of the front rad hoses. Decided to replace all front end hoses and clean everything up. Ran car in garage a few times to get fans operating and bleed system. All fine, infact car started first time after 6 weeks.

Took car out for a run yesterday and got just down road when it started juddering as I changed through gears. It then let out a real crack - like a motorbike backfiring and not the normal popping and banging you get with these cars. Thinking it might need fuel managed to get car to garage and filled up. Car then ran fine but only kept her out for another 20 minutes.

 

This morning exactly the same thing at same spot a hundred yards or so down the road. Revs probably about 3000 it juddered a number of times then let out this really loud crack. Engine carried on running so at lower revs got car home where it ticked away nicely on the drive with rock steady revs under 1000.

 

The only thing I can think of is carb jets as nothing else on car was touched and it has been in the garage and  was running fine when last used. Does this seem a sensible place to start. Thanks 

 


Sorry should have mentioned Stevens carb turbo

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My feeling, for what it's worth, comes down to the old adage that the more you think it's carburettion, the more it turns out to be ignition. The sparks cutting out and coming in again could give exactly the sort of CRACK! you describe. I'd be looking at the sparks, first.....things like cracked distributor cap, dodgy leads, connectors etc.

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John

 

Thats what I was worried about - not sure how the loud crack could have anything to do with the carbs. However, just about everything electrical was replaced around a year ago. All purchased from SJs so should be good stock. At about the same time I also replaced fuel filter, pump, regulator and all fuel lines. The only thing not done say in last 5 years is to clean out carbs and I understand the main jets kick in at around 3000rpm but could a blocked main jet lead to that sort of condition.. 

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I have a similar ish problem.  Yesterday I took one out for the first time for a while.  Ran OK  when driven sedately.  Accelerate up to 70 mph gently and was still OK but think I could feel a very slight judder but very minor.  Accelerate fairly hard and the think jumps around like a kangaroo.

 

I am assuming it is probably plugs/leads/maybe coil.  Not being able to cope under a heavy load.  Leads are two years old so should be OK.

 

Any suggestions would be most welcome

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Hi Make Sorry to here your problem.

It Can be elctronic isse like otter said, but you May check The fuel line/ fuel pump too..

As you mention running 20 minuts ok, so it sound like fuel feeding not enough ?

Yasuo

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Thanks Yasuo. Waiting for new gaskets for the carbs. In the meantime I have taken the float chamber lids off. Petrol in there and didnt look too dirty. Cannot say the same for the one jet I have removed. Whilst the hole doesnt seem blocked the base of the jet was filthy and covered with a varnish film. Presumably non of that should be there.

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No....varnish is getting to be more and more of a problem with modern petrols. I fought varnish problems all last summer on my boat! With the Lotus, it takes very little to obstruct the jets enough to cause problems....if anyone finds a solvent that dissolves the stuff, please write about it, as I have tried everything in my workshop apart from acid!!

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Agree with John, sounds very much an ignition problem.

 

Can it be reproduced by revving the engine stationary? If so, you could fit spark indicators to all leads to check for loss of spark.

 

When the regulator was replaced did you check the fuel pressure? This is essential, I bought one from SJ and the adjustment was miles out, so far in fact that the carbs overflowed, in a very dangerous way. I checked with them and they confirmed they are not supplied pre-adjusted, they are just random.

 

Soaking the jets in acetone seems to work for the varnish.

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Yes checked the pressure at the regulator and adjusted at the time. Still cannot understand how it can be ignition when everything was fine before changing the front hoses. Anyway now removed jets and noted their position. One main jet was really clogged up and very varnishy around the brass exterior and one smaller jet was dirty. Also the jet that sits away from the main cluster was completely blocked on both carbs. Havent a clue what they do but obviously worth spending some time on.

Waiting for the carb kit from SJs but very hesitant to try and remove the float pins to get the gasket on as they look like they could easily break. Think I will try reusing the gasket first.

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The pins come out easily if you push them the right way!! Des Hammill's book is the authoritative source...they go in the opposite direction to that which seems obvious...get it wrong and one half of the split support breaks off!!

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Add a bit of redex additive in with the fuel - certainly helps with the buildup of varnish and gum

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molemot - thanks, does that mean I push the pin towards the split end or the other way.

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I have the Des Hamill book and the advice to tap the shaft through from the solid mounting side seems ridiculous and I ignore it when I do it.

If you do this, it means the entire shaft has to pass through the split mounting and any deviation from being driven straight is going to risk breaking the split.

 

I would tap out from the split side but be 100% sure to use a punch which only contacts the shaft itself not the mounting.

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Andy

Thanks for that. Does that book explain what that jet does that sits away for the cluster of 4.  They were both completely blocked at the bottom hole on mine and I am intrigued as to what effect that might have had.

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Do you mean the ones under the brass screw caps? They are the accelerator pump jets.

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Andy - Yes it seems the accelerator pump jets were blocked - must make some difference to running of car. Also managed to get the float pins out following your advice. Thanks. Just waiting for kit

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Well kit arrived so refitted with new gaskets. New float needle and thoroughly cleaned all jets andchecked jet float heights - set to 15mm as per manual. Tried to start car and think it almost catched a few times but then flooded. Removed spark plugs which were soaked with fuel. When everything dried checked whether spark at plugs - all firing nicely but noticed a fair amount of fuel blowing out the plug holes. Is this normal.

 

Took float covers off again and levels looked very high, with some fuel even looking like it had blown into plenum. Everything inside float chamber including all jets soaking wet. Again is this normal on trying to fire up car. Checked fuel pressure at regulator and spot on 4psi . So fuel pump delivering at correct pressure, strong spark at plugs but perhaps too much fuel???. Does this suggest I may have opened up jets but all I did was clear with the help of a needle from a wire brush.

 

I am tempted to lower floats and recheck again tomorrow but any suggestions would be appreciated.

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There will be fuel all over the place if its not being burned.

 

Maybe check spark using either spark indicators on all plugs or a timing light connected to each in turn.

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Thanks Andy. I have contacted an autelectrician who will look at problem for me unless I can get her started in next few days. Was worried about overfueling but if it is normal for the fuel to blow out of spark plug hole then will tinker with floats and try and get her started again. Meanwhile battery on charge to make sure full cranking is available. 

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Sounds like you got the engine completely flooded. NO...there should not be the amount of fuel sculling about as you describe. Check the carb. float valves....how did you set the float levels?...you need to hold the carb tops so that the float hangs with the float valve just in contact with the operating tang..and the gasket on as well, iirc.  With that much fuel around the place, it isn't going to start. The old trick with a flooded engine is to depress the throttle fully and then crank until it starts...can take a while, but full throttle allows the engine to pass loads of air through which dries it out. DON'T pump the throttle as every pump squirts fuel directly into the inlets...the carb accelerator pumps can squirt for several feet, like a water pistol, so you can very rapidly flood the thing.

You can turn the fuel pump off by pulling out the red button on the top of the inertia cut out...on the RH wheel arch on my 82 Turbo. That allows you to check the sparks without risking flooding the engine. Ensure you have a good spark from all the plugs.

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Thanks everyone for the advice, much appreciated. I had set the float levels as you describe John but rechecked again. I then noticed that on the lids and near to the jet housings there are a number of holes (?) which seemed to have been filled with lead in manufacture. They were a bit proud compared to the other surfaces where the gasket fits. The original gasket was a fairly thick thing whereas the new gasket in the kit is wafer thin rubber. It occurred to me that this new gasket might not seal the chambers properly hence allowing petrol to get into the air chambers. I therefore smoothed all these before refitting and she started first turn.

 

It ran a bit lumpy and revs were dropping so I upped the throttle adjuster a turn and she ticked over nicely although probably a bit on the rich side. I drove up and down the drive and engine revved responsively and gave her a good rev past 3000rpm with no ill effect. I am tempted to take her out for a drive but we go away for a week tonight on a landmark Anniversary and if I break down somewhere I would not be forgiven. At least I can also put it out of my mind and assume it will run fine.

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Did you get the gasket set for the Turbo? The pressure carbs use different gaskets to the normally aspirated...it's a blow through system, which is why there is a fuel pressure regulator...to make sure that the fuel goes into the carbs against the turbo boost pressure. Just a thought...hope you've found the problem!!

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I had a problem with the floats catching on the sides of the carbs jamming them so i could not get the correct level I took them off several times and found it was quite easy to fit them slightly off line as my jets were blocked also and i agree with the above make sure you have the correct top cover gaskets.

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Hi John

 

Got the set from SJs and told him the car so hopefully I got sent the correct set. Have checked their site just to make sure and the gasket in the overhaul kit looks exactly the same as the one in HC gasket set. Infact the stock code on my invoice states SJ910E007 so presumably thats for the 910 HC turbo engine.

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I have rebuilt a few Dellortos and all the advice given here is spot on.

 

I bought a cheap Ultra Sonic bath to rebuild my carbs this is superb for cleaning jets etc. I even cleaned my carb bodies. The ultra sonic cleans all the very fine unseen areas of the jets and carbs. The result on the road is quite marked. 

Small Ultra Sonic Baths for cleaning jewelry which will be of a size that could easily clean carb jets can be bought for as little as £15. These bring up the brass fittings to like new condition. This is the method the professionals use to clean carbs. I even used a home made bath solution of water/fairy liquid & white vinegar. :D

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