Slow running

[k. rogers]

I am experiencing problems with the slow running on my recently acquired Javelin. I've adjusted the tappets as there were a few which were too tight, so affecting the compression. She pulls very well on the move, but is quite uneven on tick-over. I noticed that there is a certain amount of petrol which runs down behind the bowls when the pump is used manually before starting - is this normal? All the jets appear to be seating ok and the shut-off valves seem to be doing their jobs. I have replaced the fibre washers under the latter just in case and also replaced the emulsion block gaskets which were both perished. The plugs are a good grey colour after a run so I feel the problem must just be affecting the tickover. I have also tried turning the slow-running screws in and out by the same amount to see if it improves things, but no luck!

Any comments would be very welcome as i'm not very experienced with these 'modern' Jowetts!

[Forumadmin]

When you manually pump does it stop pumping and do you get stiff resistance. If not either your floats are not floating or the needles are not closing.

Listen to any air intake around the carbs when idling. Warn throttle bearing, poor gasket seal are usual causes.

Do compression check.

Check all plugs are clean , ignition leads dizzie cap.

Disconnect throttle linkage between carbs and set up each throttle stop. Listen for even sucking or use air intake balance manometer.

Check choke and throttle closing.

[k. rogers]

Thanks for the lead, Keith. Both floats are ok and I have just replaced the shut-off valves with new ones which has solved the flooding issue but not the poor idling. My next approach will be the gaskets between carburettors and cylinders as there is definitely seepage of petrol visible around at least one of them. I will keep you posted.

[robert lintott]

Getting good steady slow running and getting smooth acceleration away from idling is often a matter of luck! In addition to what has been suggested two points ; do not try for a very slow idle , accept ca 800 rpm ---guesswork of course . Also check that when the choke control is pushed right in ,ie off, that the blades of the chokes are vertical , conversely for good starting that both are across the air intake when the control is pulled out . Bob

[k. rogers]

Thanks for that Bob, though I have already checked the choke setting and syncronisation. I have just finished fitting new gaskets under the carbs and it seems to have made all the difference! I need to run the car and do some finer tuning once she is warmed up but am pleased with how much more even the slow running is already. However, it is two steps forward and one back at the moment because I noticed a leak of petrol from the supply pipe to the nearside carb at the in line joint, presumably through being disturbed. I tried tightening but with no joy, so I stripped the joint to clean up using wire wool and tried again and still couldn't get a tight seal - in the end I split the brass nut by using too much force, so I now need to source a replacement pipe. But at least I know I have made some progress!

[Forumadmin]

Use PTFE tape as used by plumbers, this works on those brass fittings and is OK with petrol. Assemble joint with nut retracted and whilst holding together wrap 2 turns of tape clockwise around the whole joint so as to seal both halves and the thread. Then tighten (but not too much).

[David Morris]

Hi Ken,

I sympathise with getting a smooth tockover, it can be a real problem but you sound as if you are nearly there!. Are you using a synchronometer plugged into the carb inlet tubes, with the rubber cups temporilarily taken off? I have found this is the best way to balance the carbs and you would be very welcome to borrow mine if you havn't got one? The length of the carb link rod is very critical to adjust and using the synchronometer only a few thou's adjustment on the length of the rod will cause an unbalance. DCB 246 came with a home-made 'click' adjuster made of brass fitted into the link rod and just a single 'click' on the adjuster wheel will throw the balance out. Jowett's didn't do a very good job of the original adjuster on their link rods, it can drive you potty trying to get it right, as well as being far too close to the fan for safety!

Another thing to check, and most of the old hands would recommend this, is the AC induction valve, screwed into the oil filler tube. It's a weird device and you can take it apart by unscrewing the barrel. It gets gunged-up and needs regular cleaning out. Also, check that the spring holding the interior valve is ok and that the seating faces of the valve are not damaged. They get 'hammered' and you can face them up on a stone. I have seen all sorts of mods made to this valve by previous owners, varying from no springs, double or broken springs, soldered washers with a pinhole in the centre across the outlet etc. etc. You cannot tell from the outside, so I recommend you take it apart to see what's inside!

Anyway, I hope it goes ok! All the best,

David

[k. rogers]

Thanks for that info, David, it will come in useful. Is the device you are talking about the same as something called a 'carbalancer' in the Frost catalogue which measures air flow? If it is it would be worth the £20 odd splash out!

[k. rogers]

Now here's the thing - having replaced the gaskets under both carbs which has improved the slow running to a certain extent, I have had a go at setting the carbs up using the air regulating screws. On the offside carb I have found the best position of the screw to be between 1.5 and 2 turns from fully closed which is what I would expect (correct me if I'm wrong). However, on the nearside carb there isn't a 'good' setting for the screw but I would say it needs to be in almost fully or the tickover becomes even more uneven! This would indicate there is still air getting in somewhere, but I can't think what else to look at - any hints, please?

[Forumadmin]

Get some tube. Stick it in your ear and search around the base and throttle for some sucking noises.

Check your vacuum advance take off.

[David Morris]

Hi Ken,

Your setting for the mixture screw for the off-side carb is just about right. I don't know why the N/S one won't set-up correctly, perhaps you still have an air leak around the base of the carb and Keith's tube may help here?

On the question about the 'Carbalancer', I have tried this tool and it didn't work for me! The tool I am talking about is the Synchronmeter. If you Google 'Amazon' and put in 'Synchronmeter', you will see the tool I mean. It really works, and is ideal to fit into the air intake tubes of the Javelin! It's a bit more expensive, and as you will only need to use it once or twice a year, you would be more than welcome to borrow mine?

Tell you what, I'll put it in the car tomorrow, as we leave to set up the section stand at the Bristol Classic Car Show this weekend, and if Alan Jarratt comes to the stand on the Saturday, we could pass it over to him?

All the best,

David

[David Morris]

Hi Ken,

Just had a second thought! Have you got cylinder heads with the older metal cover for the original 'baynoet' plug caps? If so, air may be getting under the metal shield in the vicinity of the carb mounting and causing the leak?

All the best,

David

[TedAllen]

With the engine running, spray some WD40 around the carb gasket area. If the engine speeds up then it means there is a leak and the WD40 has been sucked in, acting as extra fuel.

Ted

[k. rogers]

Ted - thanks for that, an excellent tip which I will try tomorrow!

David - I was just about to ask about your suggestion of air getting in under the extra plate before I read your entry! How are you supposed to get a gasket between the plate and the cylinder head? I assume there must be some sort of seal there....
(Thanks for the offer of your tool - I will be very grateful)

[chapman]

It may be worth a try whilst you are spraying to try to spray round the spindle holes where the choke flap fits as this has a poor bearing and can wear allowing air in .It can be corrected with a bush.
Tom