Rough running

[nigel jarrett]

Please could anyone help with the running problem that is bugging me on my D9 PA javelin 1949 .The car will start easily and idle reasonably ,if you Rev it ,it will have a flat spot and constantly spit back through both carbs.also if you turn the mixture screws out more than a 1/4 turn it will not idle.when you drive it feels flat.
I have striped and cleaned the carbs more than once ,set plugs points and timing by the mark on the flywheel (cyl 1&2)
The distributor is off of a later javelin as the original was seized so I don't know if the problem was there with that distributor .I have had the hydraulic tappets out cleaned and checked them.checked the crankcase breather in the filler kneck.if I put my finger over it it will stall.I have checked thourily for air leaks ,I am now running out of ideas any help would be appreciated .one point there is short reach plugs fitted is this correct ?

[Forumadmin]

This would be my check list, but my suspicion is the distributor is too far advanced (worn max advance stop, weak springs, wrong distributor) .
1. Fresh petrol.
2. Static ignition timing, TDC.
3. Idle ignition timing, TDC
4. Vacuum pipe off, 1200 rpm, ignition timing, about 15 deg beforeTDC
5. Vacuum pipe off, 2400 rpm, ignition timing, about 22 deg beforeTDC
6.Vacuum pipe on, 600 rpm, ignition timing, about 0 beforeTDC, but then blip throttle and should go to 10 deg BTDC momentarily.
7. The above checks centrifugal and vacuum advance. What is the colour of the plugs?
8. What has been done since engine ran properly? Timing chain moved? Different camshaft? Check spark polarity and colour? Could be ignition coil.
9. Fit set of new NGK plugs BP6HS or Bosch WR7B+ (not Champion)
10 Check jet sizes and washers under inlet valve in carbs. Did you disturb gasket under emulsion block?
11 Check Filter bowl gasket.
12. Possibly fuel pump not delivering enough juice. No easy way to check unless you can put a T piece into the delivery line and check pressure. But usually if priming by hand delivers pressure then it should be OK. Check pertol filter and gauzes in carb banjos.

[nigel jarrett]

Thank you I will work through the list ,I am going to have a look at the original distributor today .the one that is on the car has been made up from 3 others using the best bits ,
The car has always run like this since I have owned it .Prior to purchase it had sat in a barn for 30 years unused and in a part restored state,with no indication of the engine being touched

[richard turner]

Compression test.
Sticking valves.
Burnt out valves dependent on compression test results.
Plus all Keith's stuff!

[Forumadmin]

Since so long storage then I would take the heads off and grind in the valves! A compression test should be over 140psi (at starter cranking speed after 4 revolutions) on all cylinders and have a max range of 10 psi from lowest to highest. It might be a lower (120 psi) for a low compression engine or higher (160 psi) for a good engine..
I would also flush out the engine with flushing oil and clear 30 years of muck out of it.
Likewise with the water system and I would fit a recon radiator as that is with certainty clogged.

The bores might also be rusted, so be careful reving the engine and breaking a ring. An endoscope could tell you this and the condition of the valves, but I would take the heads off to know everything is OK. You can also check liner pinch by looking at the head gasket, thus saving a likely leaking one at the worst possible time. I would also check for cracks between the valve seats. There is a reason the car was taken off the road.....

It is false economy not doing these things, as the time spent sorting or recovering from problems will be saved. It also means the car does not let you down at the worst possible time.

[BobCulver]

On a car with unknown background anything is possible. I dont suppose plug leads are reversed!
Symptoms are weakness. Flat fuel a real possibility. Is the breather suddenly allowing too much flow when it fully opens? The air cleaner has a richening effect; is it better with bonnet closed? There is the elusive pilot jet. Does the engine stall without the breather because it becomes hopelessly rich?
Could be wrong carbs or float bowls. Are venturis book size? numbers on carb body? Carbs bowls supposed to have paper gaskets with holes in the right places..
A cobbled dsitributor could be very wrong; even advancing in reverse, wrong rotor, firing beyond the rotor etc
Frail ignition may miss under load. Without stressing with long sparks, does it produce a stream of say 3/16 inch on one lead or do these stop when the missing occurs.?
if compressions feel reasonable on the handle OK. A burned valve is obvious and if extreme causes constant missing of one cyl. Worn but not broken rings have negligible effect.
A quick check of cam timing can be made from rocker movement; the inlet and exh valve pairs "rock"" a shade after tdc with normal clearances.

it is rare for hydraulic tappets to be retained, altho very desirable if working properly.

Is there a carbon in middle of distributor cap?

keep On

Bob Culver

[Forumadmin]

A possible hint from here in bulletins 16 and 19.

[nigel jarrett]

Up date on problem,the original Dnky distributor has been checked over ,vac advance freed up and diaphragm tested ok ,points gap checked on all 4 lobes then refited ,leads and caps checked,basic timing set ,the motor fired up and ticked over ,the timing was tweaked by ear until the engine would Rev up crisply with no spitting I am now waiting to get my hands on a timing light ,probably Monday .
The radiator was recored last year as it was 80% blocked ,the sump was removed and checked for sludge etc but was all clear
Thank you for all your ideas they have all been very helpful

[Forumadmin]

It is important to understand the vacuum advance mechanism fitted to Javelin and Jupiter engines. The vacuum is taken from just upstream of the throttle butterfly, rather than the intake manifold. This means that the vacuum unit is not operational when the butterfly is closed, but might be operational if it is slightly open, say with the choke on or on light throttle.

The vacuum unit fitted to the Jowett should give a maximum of 10 deg additional advance.

The centrifugal advance settings should be checked with the vacuum advance disconnected as it is assumed that the setting is for when the throttle is open when the engine needs to give its power. This is not the case when you are checking the timing with the engine under no load with the vaccum pipe disconnected, so you might find the engine note is retarded. The engine note should change when the vacuum is reconnected.

The vacuum should advance the ignition by up to 10 deg if the throttle is closed whilst running at 2000rpm. The amount of vacuum created is very dynamic so is not very easy to check. Connnecting a vacuum gauge to the same port as the advance mechanism is not advised but on a a Jav/Jup you can connect one to the other carb. (You may have to drill a small hole as usually there is not one in the other carb. Note position just upsteam of the butterfly is critical. This position is different from where vacuum gauges are normally attached downstream in the manifold. ) I can check vacuum units on the bench with the distributor tester which has a vacuum pump and gauge .

To check approximate operation of the unit on the car, start by holding at a constant 1000rpm, depress the accelerator to get up to 2000rpm, and then release the accelerator to get back to 1000rpm, watching the ignition advance as you do this. You should see the advance momentarily decrease as the speed increases from 1000 to 2000, then stabilise to a higher value than when at 1000rpm (due to centrifugal advance), then increase again as you take the foot off the throttle (more vacuum), then stabilise back down to the original value at 1000rpm (a little vacuum).

I suspect my poor operation of the programmable unit at low speeds may be due to the vacuum unit interacting with it since the black box is continuously measuring the pulses to know the speed of the engine and altering the advance and dwell accordingly.

I used to have a number of different cars fitted with manifold vacuum gauges (often called 'Economy meters' ). It probably did save fuel when driving on motorways as you could relax your right foot quite a bit without losing speed. On my Subaru GTB, as well as the vacuum gauge, it had a turbo boost gauge which was much more exciting to play with. Getting the second turbo spun up to provide maximum boost was a challenge, and then releasing turbo gate to dump the boost with a great squish was a memorable noise.

[BobCulver]

The use of timing lights on old cars where static ign spec was for handcranking can cause confusion as several degrees of advance often occurs at idle speed. Also dangerous on a Javelin. The light best used to confirm the auto functioning and smoothly. Safely observable from a chalk mark on the crank pulley. If the stops in the distributor are not worn excessive advance range from handcranked static unlikely.
Consistant resetting is vital if any conclusions to be drawn. I arrange distr lead to form a 1/8 gap and crank whilst watching flywheel. The precise point of breaking is audible from the spark. (Do not allow a large gap as stresses parts)

Bob Culver

[Forumadmin]

With the completion and then test run of the rebuilt water pump on the SC, I decided to do some tuning to try to get rid of a misfire at about 3800rpm.

The timing was checked as in previous post to find out that it was too far advanced. This I was prepared for as we have been fiddling with the dizzy in an attempt to rectify this anoying misfire.
This dizzie is a standard non-electronic unit rebuilt and adjusted on the test bed. My super duper timing light with adjustable digital advance confirmed the centrifugal advance curve and the vacuum advance. But I did notice that vacuum advance came on immediately the throttle was opened giving 30 degrees total advance at 2500rpm.

In practice then, on an unloaded engine, the vacuum advance kicks in when the throttle is opened which may seem contrary to what you might expect, since it is supposed to kick in when the throttle closes and vacuum builds up.

Anyhow I set the timing up as per the book and then went to collect Amy from the station. The misfire is now at 4500rpm so getting better. I think from the sound it is fuel starvation so will check the jet sizes. These carbs are not the correct ones and somehow found their way onto the car during the rebuild.

[BobCulver]

The vacuum does kick in at small throttle opening; when fully closed the hole is on the outside of the butterfly. As load comes on manifold vacuum diminishes.
Carbs can be from a myriad vehicles, ditto bowls. Emulsion blocks differ from spec to spec.Also progression, drillings etc. if venturis are wrong stock jets ditto.

Bob Culver

[nigel jarrett]

Latest update ,carried out a run ,performance improved apart from a flat spot after throttle off on a down hill rum ,timing checked with stroke light showing 20degrees btdc ,anything less and it starts to spit back through the carbs ? Mixture screws on carbs have to be screwed right in or 1/4 out no more .I am beginning to think that the valve timing is out !this is my next check lot carry out

[nigel jarrett]

Valve timing was checked with a dial gauge on no1 inlet valve , it appear to be set at tdc and not 12 deg btdc as stated so next step timing cover off

[nigel jarrett]

Latest update,the car got so bad that it would not go uphill unless you selected a low gear and no more than half throttle.I just about got it to Powderham Classisc Show where on the Jowett stand we all got our heads together listed what was done and had more subsections to check,John Airey of the Severnside lent me an electric fuel pump .
Over the next couple of weeks all basics were checked ,an extra earth fitted to distributor ,fuel system was blown through back into tank ,carbs stripped and blown through again and finally fitted the electric fuel pump the car has now run approx 100 miles and is running quite acceptable ,thank you all for your help