If you would like to join the DLOC, please visit the Club's website https://www.dloc.org.uk/
Please don't post someone's email address. Some people don't want to risk it being harvested by spambots and GDPR regulations discourage it.
Always look at "ACTIVE TOPICS" which gives all posts in date & time order if you can't find a post as topics are sometimes moved; or look at "Your Posts".
Reg. nrs. Please add reg. nr. when posting a photo or anything about a car as this will help searches. Don't add punctuation next to nr. as this negates search.

spitting back through Carbs

User avatar
Kbeal
Posts: 103
Joined: Mon Feb 15, 2016 9:01 pm

Re: spitting back through Carbs

Post by Kbeal »

I have pertronix Electronic ignition. I do have a spare module which I’ll try out first.
Kevin

bobtills
Posts: 36
Joined: Wed Sep 25, 2019 6:05 pm
Location: North Wales

Re: spitting back through Carbs

Post by bobtills »

When I was a lad, and did a bit of car fixing, spitting back through the carbs was almost always inlet valves or seats that were pitted.

In other words, the gasses leak through on the compression stroke.

Although it doesn't seem likely that pitting has suddenly occurred over the winter, it's a possibility, and a sticking valve is also a possibility.

Ian Slade
Posts: 546
Joined: Sat Feb 13, 2016 9:54 am
Location: Scotland

Re: spitting back through Carbs

Post by Ian Slade »

Generally spitting back through the carbs is timing, if at higher rpm then check the balance weight shaft is free to move independently of the main shaft, there are cases where it has restricted movement, this is critical on a V8, you can get the Daimler V8 to run backwards, not very well and amusing to watch.
The condenser or capacitor is a spark quencher, if open circuit you will get arcing across the points, if short circuit it will short the points to earth.
Owner since the 70's, Genghis is slightly to my left.

bobtills
Posts: 36
Joined: Wed Sep 25, 2019 6:05 pm
Location: North Wales

Re: spitting back through Carbs

Post by bobtills »

Or a broken valve spring

Big Col
Posts: 491
Joined: Tue Feb 16, 2016 12:45 pm
Location: Leeds

Re: spitting back through Carbs

Post by Big Col »

I would gamble it’s the electronic ignition, but saying that I am often wrong.
The other thing is a crack in the rotor arm causing a problem when it speeds up.
Colin,
I may be slow but I’m rough as well !

buckfield
Posts: 158
Joined: Wed Feb 10, 2016 11:38 am
Location: south wales

Re: spitting back through Carbs

Post by buckfield »

Hi, it does sound like an ignition issue, I have the pertronix system fitted, I had a similar issue with lack of performance and spitting back and no power etc, check the rotor arm for movement on the shaft, it must be a nice tight fit, this could be an issue if the arm is moving on a worn shaft or slack dizzy shaft, as had been said in the previous post the arm could be cracked, and I dispensed with the lucas arm and got a dizzy doctor (red) arm, this issue with a slack arm on the shaft maybe a pertronix only issue tho, and that could be the way the system is crammed into an 8 cylinder dizzy, ie the magnets may be so close together, others on here will know if that is the case. also check your coil connections. pertronix systems can fail so don't discount that either. I have had mine now for 14 years and so far reliable but did change the coil to an uprated type, but the system can run on a lucas type as well.hoipe this helps. tony

User avatar
Kbeal
Posts: 103
Joined: Mon Feb 15, 2016 9:01 pm

Re: spitting back through Carbs

Post by Kbeal »

Thanks for all the advice - plenty to work with.

It only spits back at high RPM so I too suspect the timing which is why I started both the advance mechanisms - but hey - who knows! My gunson strobe timing light packed up on Monday so I'm waiting for a new one to arrive (might be some time as it's not classed as essential). Possibly it was faulty so the timing might not be spot on. That will be the first job. Then I'll replace the pertronix unit - I have a spare as the thought of trying to reinstate points in the dark & wet don't appeal. I checked the distributor bob weights when I had the base plate assembly off to replace the vacuum advance unit so I know that's all free. Dizzy arm and cap came new last year from the Distributor Doctor and all seemed well but I will look again. Coil is new flamethrower and HT leads were also new last year - the sealed unit ones from Barry Thorne. I have new jet diaphragms so maybe I'll get the carbs off and have a look at the old ones if none of the above cures the problem. It will be light relief from the decorating regime introduced by The Management as we ride out the covid-19 epidemic.

Hopefully not sticky valves / broken springs.....

I'll report back as I go.

cheers
Kevin

User avatar
JohnM
Posts: 138
Joined: Thu Feb 11, 2016 1:31 pm
Location: N W London

Re: spitting back through Carbs

Post by JohnM »

Kevin,
I know that I suggested looking at fuel supply (and still do) but your mention of the Flamethrower coil triggered a memory......
I'd been helping a friend install +ve earth electronic ignition into his Swallow Doretti, and while I was setting up the engine, I was having difficulty getting it to run cleanly on the Pertronix setup, which was all new.
Rather than swap back to points, my "jotter" tells me I simply tried a Lucas sports coil instead, and the engine ran cleanly. This was repeatable between the Flamethrower and any standard coil I tried.
I contacted the supplier in the States, who was surprised but changed the coil without a quibble, and it now runs fine, but it's left a question mark in my mind about these coils. Interestingly, they only guarantee the coils for 3 months in use, I think.........

So, long story short, it might be worth just swapping out that Flamethrower for a standard coil.

Just my thoughts as always, and sympathies with the decorating - SWMBO has me working in the garden!

John
John M in Middlesex, NW London
1962 SP250 "B" Spec

buckfield
Posts: 158
Joined: Wed Feb 10, 2016 11:38 am
Location: south wales

Re: spitting back through Carbs

Post by buckfield »

Hi, just a thought about the coils, I have changed a coil on this system, and I specified a epoxy filled type not an oil filled type, you might also have an issue with HT leads going out of resistance and the pertronix system can knock them out, and I remember from years back that pertronix had issues with solid core leads (copper core) but that might be sorted by now. good luck. Tony

Big Col
Posts: 491
Joined: Tue Feb 16, 2016 12:45 pm
Location: Leeds

Re: spitting back through Carbs

Post by Big Col »

I often talk bollocks but,
My experience is that mechanical things tend to have a positive and traceable aspect when a fault occurs. The only thing that tends to happen with time standing is oxidation or seizure.
Electronic items are a different beast and can give the appearance of normality but actually be in shit state.
Your original post suggests a time standing. I would check the basic mechanical items but then move on quickly.
Never ever trust what you can’t see! Ghosts, internet scams and electronics all fall into that category.
Colin,
I may be slow but I’m rough as well !

Post Reply