1.8TC B Series experts needed!

[Cabrio_Simon]

Trying to tune my 1.8TC B series is driving me mad. Whatever I do I can't get it right. I hope one of you experts may be able to give me a few pointers.

The symptoms are lumpy idle and plucking below 2500rpm. This is most noticeable at 30mph in 4th. Above that it pulls sweetly and strongly and above 3500rpm it is a flier. When I bought the car I was informed by the previous owner that it had a big valve head but I don't whether it was also fitted with a high lift cam which, I suppose could cause lumpy tickover.

I am 99% sure that the ignition system is right having fitted an Aldon contactless ignition, new leads and plugs and I have set the valve clearances as per Haynes. Air cleaners are the pancake type and I have tried AAU and AAA needles.

Having read the Haynes Manual and lots of internet articles on this subject I have balanced and set the carbs as instructed, even using Gunsons Carbalancer and Colourtune. It's a bit better but you wouldn't say it was sweet. It will tick over at 900 - 1000rpm but the engine rocks about and that is translated to lumpy feel at low throttle on the road. Had a look at the plugs and they look a perfect colour.

I'm starting to think I should throw some money at the job by asking a local MG specialist to have a look, but I bought the car to learn and I don't like giving up.

Thanks and sorry for this tome!

[h_m_cumming]

Re: 1.8TC B Series experts needed!

Hi Simon. Have you checked the ign. timing using a strobe? It sounds as though it might be too far advanced.
Can you get to the front of the crankshaft pulley to fit a timing disc and check the valve timing. That might help in diagnosing the possible problem if it has had a wild cam fitted.

[Cabrio_Simon]

Re: 1.8TC B Series experts needed!

Hi Hugh

I have set the timing using a good strobe light. It is set at 15 btdc (Haynes Manual suggested). Any more retarded and it wont pick up, any more advanced it ticks over better but still plucks at low revs and tends to pink.

[dogoncrazy]

Re: 1.8TC B Series experts needed!

Hi Simon,
I would go with Hugh's advice on the timing disc and try to determine the valves opening and closing points in degree terms,from there you should be able to ascertain which cam you have.You say the plugs colour looks ok which to me suggests that all else must be pretty close to being right.My money's on you having a wilder than standard cam-engine out to change it I'm afraid!

[h_m_cumming]

Re: 1.8TC B Series experts needed!

Just a thought, are the advance/retard bob weights free and working? When you used the strobe could you see the marks advance as you increased the revs?
When I had the 1800 engine in our Roadster it had a hairy cam and the timing was 8deg. BTDC with the strobe at 1000rpm. and the vaccuum pipe disconnected. It produced 120bhp on the dyno at Osselli.

[Cabrio_Simon]

Re: 1.8TC B Series experts needed!

Thanks all.

Hi Hugh - I feel like I know your car as since you kindly sent me your CD pictures etc I have often looked at how you have done things.

I'm pretty sure that the dizzy is advancing properly (even if it wasn't how would that effect tickover setting when the advance is disconnected?) but I will check again to make sure. I timed mine to the book recommendation (after a lot of trial and error using less and more advanced settings, this seemed the best compromise) so I am surprised that Hugh ended up at only 8 btdc. I'm sure mine won't run at that, in fact it ticks over better at more advanced settings. Does this suggest anything in terms of the type of cam in mine or that I am setting something up wrongly?

I have thought that I may need to try ABA or AAS needles (standard Marina TC needles 1971 - to 1974) and new seats or maybe re-bush the carb spindles etc but surely I should be able to compensate for spindle / bush wear, even different needles, to at least get a smooth tickover, ignoring performance over the rest of the rev range. How much play at the carb spindle ends is acceptable? If they're worn would it make it impossible to adjust the mixture properly? I suppose mine have about 0.5mm play when warm. Many of the answers on this subject on MG website forums talk about manifold or carb air leaks but surely I should be able to compensate for leaks with a slightly richer mixture to get smooth low revs running even if there is a leak.

Having set the carbs using Colourtune and having tried different settings ie. more rich and more lean but still ending up with lumpy tickover I wonder if the problem is not due to the mixture and could be ignition system related, as you suggest. Could it be the coil? It's a newish Intermotor unit but I left the ignition on for 30 minutes accidentally 6 months ago and the coil got very hot before I turned it off. Or am I clutching at straws?

The problem that persists is that sub 2500rpm running is lumpy and, in my amateurish way, I feel that if I can get this smooth then an adverse effect on higher rev performance may point to the underlying problem. I am, however, very aware that a little knowledge is a dangerous thing!

[AndrewKB]

Re: 1.8TC B Series experts needed!

I'm sorry to disappoint, but ... Take it to a rolling road where they know about twin SU setups and save yourself the continuing grief. You know it makes sense! The problem is finding someone that does "know about twin SU setups". I've used a couple - Aldon (West Midlands) is the closer of the two to you - and the car came back transformed afterwards.

[dogoncrazy]

Re: 1.8TC B Series experts needed!

Simon
Have been thinking more about your problem and had similair many moons ago when I had a MG Midget,turned out to be a burnt out exhaust valve -have you done a compression check? On a personal level I would't touch Intermotor stuff with a bargepole,I speak as one who has had at one time in my life supplied their products to the trade,I switched to Commercial Ignition as I was getting so many duff units!

[philcoyle]

Re: 1.8TC B Series experts needed!

Simon, what you dont say is, was the car like it when you bought it or has the problem developed later.
If it has big valves different cam etc, what about the exhaust? you can't put more fuel and air into an engine if you can't get it out just as quick.
You mentioned that the mg site suggested it may be an air leak and this could well be the case, everything on an engine from the time the fuel goes through the carb until it exits out the exhaust is defined,no allowance is made for tiny leaks, bad fitting gaskets, bad fitting vacuum pipes and so on. So stand back have a think, is that manifold gasket leaking? does that advance and retard pipe fit tightly, and the most contentious one of all is your servo leaking and drawing in air,it's always worse on tick over,the depression in the manifold will always find the easiest route i.e. by-pass the carb, hope this helps,sit back ,think, and check everything, even if you don't think it important.

[dogoncrazy]

Re: 1.8TC B Series experts needed!

Simon
I think Phil raises a good point with regard to the question of is the car worse since you bought it or were you trying to cure a problem that already existed.Is it worse since you changed plugs/leads etc, are the leads in the correct firing order,have you had the dizzy out and timed it 180 degrees out.I've done all those at one time or another and failed to see the wood for the trees!

[Cabrio_Simon]

Re: 1.8TC B Series experts needed!

Hmmmm!

Andrew - I think you are probably right, but I'm not ready to give up just yet although I think I am approaching my point of incompetence.

Alan - I will do a compression test tomorrow. Hope it's not that. All the plugs are the same colour though.

Phil - The car has always tended to be lumpy at tickover since I bought it 2 years ago but it seems to be getting worse or more likely I've become more fussy as I have improved the rest of the car! Trouble is, the car was well built in 1988 but I think it's had a long lay-up and uncertain history since. I'm not moaning because I knew I was taking a chance when I bought it and this is all part of the fun. Isn't it?! Exhaust is stainless with single side mounted box so pretty sure it's ok. I disconnected the servo and plugged the manifold last night -no effect. Got half a turn out of the inlet manifold nuts - they are shared with the exhaust and look a bit strange as the inlet manifold is thinner than the exhaust manifold where it meets the head so the washer behind the nut is on an angle between the 2. Should it be like that? Plan to continue my checks tonight and will report any progress.

Was talking to a mechanic friend today. He's just rebuilt his MGB engine and used a fast road cam. Guess what? Lumpy tickover and low speed running!

[dogoncrazy]

Re: 1.8TC B Series experts needed!

Simon
Think washer should be 'stepped' to accomodate, check with the MG spares guys

[philcoyle]

Re: 1.8TC B Series experts needed!

Simon, no nut (me included)should ever put uneven pressure on a washer, it seems that your problem lies in the direction of the manifold,I dont know that engine too well but as I said before no one makes, (a that will do) piece of engineering, the washers should not be at an angle. Check the original manifold inlet/exhaust against yours,by looking at manuals ask on web sites etc,because I think you are about to crack the problem.

[Cabrio_Simon]

Re: 1.8TC B Series experts needed!

It's sorted!!!! Loose carbs was the problem. I can't believe it was such an obvious thing and how thick I am not to have checked that earlier. Got to reset the mixture tonight but it's already transformed.

Just went for a 6.30am blast round the moors above Bolton. Good fun normally but so much better in a car that feels right.

Thank you to all for your interest and help.

[dogoncrazy]

Re: 1.8TC B Series experts needed!

Simon
Glad it's sorted. As Phil said ,sometimes you have to just take a step back and reassess.