Crap to Cream Pt 52 Engine diagnostics, bit of a backfire, got any ideas? In the comments please.

[@123rtheo]

Air leak in the manifold perhaps

[@CrapToCream]

I have used new gaskets every time I have taken either the exhaust or intake manifold off which in total would be about 8 for the rebuild so far. Anything is possible however I would like to think probability would be low.. Both halves of the engine are similar when checking the balance and the mixture so I would say the indicators say the gasket is good. Thanks anyway, always something to keep in mind when I "go in again".

[@MGB-learning]

Did someone install a mild street cam in the motor? Look for air leaks, you may have a bad gasket on the intake side.

[@CrapToCream]

I rebuilt the engine myself, installed a standard cam, unless I was supplied with the wrong part, air leak is still an option, haven’t got into checking for air leaks just yet.

[@MGB-learning]

I have seen that quality of parts are very poor now a days. There is a possibility that the cam was not built to speck and was machined wrong. A simple and less expensive check would be verifying that all your gaskets on your intake side are good. What condition and type exhaust system is installed on the car? Some of the free flow exhaust or oversized mufflers have the tendency to allow the powerplant to have mild backfire like what I am seeing on the video. Second question.. Does the brake booster hose connection to the intake manifold have a check valve or just a simple connector? @@CrapToCream

[@StevenPope-qn3qb]

Hi, I think it’s running a bit rough at idle, my A series engined Sprite sounds smoother at idle. Use a strobe light (if you have one) to check the ignition timing.

[@CrapToCream]

Hi Steve, thanks for the comments and feedback, I do have a strobe light and dwell meter, checked with both without much success. It is to do with the timing pretty sure you’re on the money here. More investigation is still required.

[@ooipoppy]

I can't offer any advice, Marty, but Rose says 'Hi'👋🏻

[@CrapToCream]

Thank you Peter, you can say hi to Rose from me. 👌

[@danielwoodard680]

It sounds great at idle. Timing may go back a degree or two. I wish we could see an O2 sensor reading. In California, we used the in side exhaust pipe smog testers for years. Hard to find now.. short point : read exhaust gases for mixture.

[@CrapToCream]

Back in my youth we also used to use the O2 sensor, I found it a bit more difficult with twin carbs though, easier with a single.

[@carstenmoore5760]

Hi Marty, Engine sounds good. A couple of points spring to mind 1) You could try tweaking the ignition timing slightly. That engine was designed in the days of leaded fuel. Modern petrol with all the additives they include now if a different product. The factory timing spec is probably out of date to modern fuels. I seem to remember the advice was to retard the ignition a couple of degrees when unleaded was introduced in the UK. 2) Have you got the correct amount and grade of oil in the dash pots? It can make a huge difference on how the engine performs. 3) Are the carburettors in balance? Hope this helps.

[@CrapToCream]

Hi Carsten, 1) good one this, I have a 123 distributor in the engine with several settings, I’m working on this one, presently set on what is recommended in the manual. 2)The oil in the dash pots is a light machine oil , don’t know what grade, if you know the right grade please let me know. 3) In a word yes, checked this before I put the Colourtune plug in. I’ve always been advised that the mixture is the last thing to adjust when tuning the engine.

[@carstenmoore5760]

@@CrapToCream Hi Marty, With ignition timing, I would have play about with the settings to see which suits best. The manual was probably written around 50 years ago. Fuel technology has moved on in the meantime. I believe SU recommend SAE 20 in their carburetors but of course as the damper piston wears, the thin oil can make the mixture artificially rich leading to hesitation and flat spots. I fill mine with standard 20/50 motor oil which seems to work well. I've heard of some people using gearbox oil to slow the piston down even further! Another point worth mentioning, is the fuel fresh? Modern petrol seems to have a limited lifespan before going 'stale' creating all manner of running issues. Hope you get it sorted. It could just need a good blast down the road to settle things in.

[@CrapToCream]

This seems to be quite a contentious issue, i'll give the 20-50 a shot nothing to lose, I found in the manual a 15-50 recommended, "back in the day" I used to use the old 3 in 1 oil this seemed to work quite well. I have also found that Penrite make a "dashpot oil" however there is no grade mentioned so I don't know what this is. Might give that a shot again you never know. Carsten, re the fuel I only put fuel in a couple of weeks ago 98 octane to take the MG to the testing station prior to that everything has been dry for the last three ish years.

[@carstenmoore5760]

@@CrapToCream Hi Marty. You're right the dash pot oil is a contentious issue. There is no right or wrong answer. It depends on a number of factors and which is right for your car. Are the carburettors new or worn? How has the engine been set up for performance? (ported? sports cam?), Driving style: spirited or sedate? Burlen Ltd which still manufacture SU carburettors in the UK only list the SAE 20 as a dash pot oil. If you obtain a service pack from the MG owners club they will supply the same spec oil. Personally I find it a bit too thin which is why I use 20/50. I note a previous reply that the manual actually specifies 20/50. As you say, nothing to be lost in experimenting. Why not try some gearbox oil to get a feeling of performance at the other end of the viscosity spectrum? There will be a happy medium somewhere. Would be a good idea to read the bottle on the Penrite dash pot oil as I think they provide one for carburettors WITHOUT dampers. Maybe the car just needs an 'Italian tune-up' to let things settle in, as you can't have covered my miles yet.

[@CrapToCream]

@@carstenmoore5760 I have another Weber 32/36 DGV downdraft carburetor, same one I installed on the 1st of July 2021 on my other MG I've now sold. Despite some of the feedback I got the MG went really well, I never did turn the carburetor around, I never saw the need because it ran so well. This is another option I have open to me.

[@george5022]

Sounds like valve timing a tooth or two out, poping at the exhaust on overrun, usually timing issue. remove the valve timing cover check those two dots, Try to richen it up half a turn on each carburettor Merry Christmas and happy new year

[@CrapToCream]

So here we go 😂, I’m contemplating a supercharger, if and when I go down that track could check the timing marks. I’m pretty confident they are right, however I was also pretty confident the dizzy drive slot was right, it was only 180 degrees out….. thank you for the suggestion.

[@Yetterben]

Weak spark at idle coupled with snap back timing when you let off up top.

[@CrapToCream]

As I found out later on there were several issues, in the end the main one was a broken servo unit, I was adjusting everything to compensate for a leaking servo unit so one half of the engine was running rich and the other half running weak. I was adjusting the SU's to compensate, I only found the real problem when I converted to the Weber. That was when the problem showed itself properly, I just was not expecting the servo unit to be the problem. Thank you very much for the constructive comments.

[@aresosweet888]

on my old mgd prod sport i re did the timing curve on dizzy and run into same prob to cure it i put on a electronic dizzy and used a cdi coil made a huge diff NOTE i ran su carbs org / 2 inch / and webbers 44 mm 140 cam from wade and head done then later retro fitted a donnington head from a mga it was a load of trial and error to get right but in end was well worth it SIDE NOTE I TOOK IT OUT TO 2 LITER AS WELL that was loads of fun to do gearbox i used was a 5 speed toyota behind it

[@CrapToCream]

Wow, this certainly sounds like an adventure, my engine is pretty stock right now apart from mods to improve the reliability, such as the electronic dizzy. Thank you for the insight into what is possible. Something to maybe consider a bit later on.

[@charlesfarran8942]

Hi Marty, I agree that the engine sounds good. I run my 1980 (original 18V engine on a 123 distributor & set it in accordance with the chart provided for the MGB engine type (that was way back in 2013 before the upgraded ones which can be set up with a lap top)). That said, i am aware that no two MGB engines are precisely the same , so there maybe some merit in tweaking the ignition timing slightly. I take it you are using standard spark plugs (Champion N9Y or NSK BP6ES) & carb springs & carb needles ? I have always used SU carb oil in the dash pots & have never found it too light even on holidays in the south of France in very hot conditions. Exhaust popping can be more pronounced where you have an exhaust that is not fitted sufficiently well round the joints - although this was presumably covered during the vehicle test. I note you have replaced the OE rocker cover with an alloy one & cap. I did this , but wasn't happy with the cap arrangement /lack of breathing so reverted to the OE with plastic breather cap. Are there any air leaks round any of the carb/manifold fittings? May just be worth putting a few road miles of spirited driving to see if things improve before going through loads of adjustments! Cheers, Charles

[@CrapToCream]

All good advice Charles, thank you, i'll check the plugs, now you mention it I'm pretty sure they are the NGK BP6ES, not the Champion ones, I'll check, thank you. They might even be the Iridium ones. "Spirited driving", I like it :). Carb needles are the ones that came in the SU overhaul kit. Same markings as the ones that came out of the original fitment.

[@charlesfarran8942]

Hi Marty, I see you are using K & N type air filters which many do as replacements for the OE "Black Pots". I believe some recommend a change in needles to obtain the optimum air /fuel mix when this is done. If you have the original air cans (& clean filters) , given that you have installed replacement standard needles & the engine otherwise is essentially stock, it would be interesting to see if your engine ran without showing the current symptoms - you might have to adjust the mixture levels when doing so , but it might narrow down what the issue(s) are & possibly indicate a change in carb needles is required! I take it you are using higher grade fuel - I run mine on Shell V Power (or Tesco Momentum which is approx 99 Ron in the Uk) & Castrol Valvemaster. Cheers, Charles @@CrapToCream

[@ChrisLondon-s1w]

Check the points/condenser 🤔

[@CrapToCream]

Hi Chris, I’ve done away with the points and condenser set up, gone with a 123 ignition dizzy, saying that I’m still experimenting with setting, so you could be in the money anyway.

[@patadamson4005]

Might need different needle profile?

[@CrapToCream]

Thank you for your suggestion, I’m doing a YT vid on my findings after much investigation, I’ve even gone to fitting the Weber 32/36 to the engine and had similar symptoms. I’ll let you watch the vid to be enlightened 😂🤣🤣

[@toyfiretrucking]

could your exhaust system just be highlighting something normal that a standard exhaust would hide.

[@CrapToCream]

Like the way you think 😅