Possible Jupiter induction noise?

[Bev]

Hi everyone, I am looking for some help/advice regarding the noise that's happening when I rev the engine on my Jupiter 1a, or accelerate through the gears. It drops and goes away on the overrun from any speed and is fine when ticking over. It doesn't seem to be mechanical as I have listened all over the engine with the tried and tested hose and listened with a mechanics stethoscope . The only way I can describe it is being like the induction roar you can get coming from some carbs. It's so loud it turns heads but sadly, all for the wrong reasons. Due to numerous problems, this is the first time it's been on the road since I bought the car just before the covid outbreak . I am new to Jowett and live way out in West Wales without another Jowett/Javelin anywhere near me, so for this reason I can't compare like with like (engine).

Hoping someone can help
Many Thanks, Bev Spiers

[Keith Clements]

i would check the ignition advance through the rev range. it is likely a worn distributor giving too much advance or weak springs giving wrong advance curve.
Distributor doctor can fix . Ask for the Clements curve that is suitable for modern petrol.
Since you have had camshaft issues, it could also be valve timing. This must be set using a dial micrometer as per the book but a rough check can be done by reducing tappet clearance to zero on no 1 inlet and seeing when(crankshaft degrees) valve starts to open. This should be just before the 12 deg btdc on flywheel. Note this is NOT the 1/2 mark which is tdc on 1 and 2 cylinder.

[Bev]

Thanks for your reply Keith, I am confident about the valve timing as the engineer had all the dial guages etc. and followed lots of tech info for the engine. I will look at the ignition advance/retard as a few years ago I fitted an electronic distributor. I know it's not everyone's cup of tea but it performs very well. Having said that, no one has ever found any timing marks on the flywheel so setting the timing at times has been an issue. Walter has had the most success finding TDC when he had the push rod covers off. As I've said, everything except the roar is working fine. Many thanks. Bev

[Keith Clements]

Look at the Jowett patient topic. Worth checking TDC by looking down spark plug hole and seeing when it occurs, perhaps using some soft wire. Electronic distributors with weights will still suffer from wear, only those using a computer map will be able to produce the correct map but will need the correct map installed. MG type dizzies will NOT have the correct map and max advance. The vacuum advance may also be wròng.

[Chris Spencer]

Just as an aside to the issue what air filters do you have fitted to the car - are they the originals or something that is after market - Have you tried running the car without them to gauge any noise difference / have you checked the filters / filter housings for any cracks / holes etc

[Keith Clements]

Not sure how Walter found TDC with push rod covers off! The only accurate way would be with dial gauge extension through spark plug hole. If flywheel has been lightened then there should still be a line or two or three on it, even if small.

Valve timing is critical with the opening of the inlet timed to start just before TDC with 13 thou lift at 12 deg. Note you must adjust tappet to zero gap before doing this and the lift is on push rod NOT the valve. The rocker is a lever and increases lift at valve.

The push rod is accelerating fast so the dial gauge will move quickly. If the camshaft is non standard , which might be case if car was used for racing, then this setting may not apply.

[Bev]

Hi Keith, I'm afraid things are getting a bit to technical now. As I've said previously, after the camshaft repair/modifications were recently completed, the car has for the first time since I bought it, well over two years ago, been running well and at last long last it's usable. The roar on acceleration as I describe it is annoying more than anything so I was keen to see if it was normal, or if not, could someone suggest a fix. I am going to try your suggestion about ignition advance/retard and see if it quietens down a bit.

By the way, I've posted my camshaft story on " My Jowett Experiences " .

Once again, thanks for replying to the post, Regards Bev

As an aside and to set the record straight, Walter is an extremely respected vehicle engineer within the Vintage/Veteran car world in the UK and beyond and carries out work on every kind of car/vehicle imaginable.

[Tony Fearn]

I'm afraid things are getting a bit too technical now.

Hi Bev.
Could it be a gremlin in the exhaust silencer and/or system?
You should hear Barry Widmer's 2 cylinder Jowett!!
Tony.

[Bev]

Thanks Tony, exhaust joints were one of the first things I checked but I will look at them again.

Hi Chris, air filters are the original (cleaned) ones on the usual tubes/pipes, although the pipes are silicone rubber. The noise appears to be the same when I replace them temporarily with some short after market ones that I have. I must say , I haven't spent a lot of time listening at the carb tops with the filters off as revving the engine in my garage with door open may wind my neighbour up to much. To be fair, I should wait for them to go out first before I have another listen.

Thanks all, Bev

[Bev]

[BarryCambs]

I paid Ian Preistly at JCS £10 for that 'silencer' in good faith, so I'm not changing it until I've have my money's worth Tony! Problem is, it's stainless steel, and incredibly well built, so it could be with us for a long time.