Low compression on cylinders 1 and 2

[StephenT]

I added M/M Oil to each cylinder and let it sit for 24 hours. Then recheck the compression; 1- 185psi, 2- 175psi, 3- 165psi, 4- 180psi.

After restarting the engine cylinders 2 and 4 seem to be responding normally. Cylinders 1 and 3 seem not to be firing at idle (no response when plug wire is pulled). Then raised the idle to ~3500rpm. At this speed cylinder 1 now responded to the plug wire being pulled. Cylinder 3 still has no response.

I’m wondering now if I’m looking at a carburetor issue? With cylinder 1 responding at a higher rpm maybe the idle circuit is not functioning. And perhaps the cylinder 3 issue is carb as well.

I just rebuilt the carbs, my first attempt at a dcoe so I would not be surprised if that’s the problem.

Is it possible to diagnose the carb while running? Or should I pull them off and go through them again?

Steve

[pharriso]

Yes, sounds like the idle circuit may be be blocked on number 1 -Mixture screw not screwed full in?

[RichardHawkins]

Steve,

Easy start can sometimes be a useful diagnostic tool. With a puff of easy start down the carburettor throat of the cylinder you suspect, the revs should increase if you have a carburettor problem, if the revs don’t increase you, probably have an ignition problem.

With respect to help from the group, I often talk to one of my Lotus friends, who often replies have you asked elan.net. I am frequently embarrassed about the questions I ask as I think they are a bit dumb, but have never had a bad response. This is another excellent feature of our group.

Richard Hawkins

[The Veg]

What's the marvel mystry oil is it like "Redex" an UCL (upper cylinder lub).

Among other uses, yes. Here's a little info:

https://en.wikipedia.org/wiki/Marvel_Mystery_Oil

Of course like any cocktail of petroleum distillates it has all kinds of handy uses. Back in the '90s I was into radio-control model aeroplanes, which used very small glow-plug engines that ran on a blend of methanol and nitromethane, with castor-oil added for lubrication. The engines were made of aluminium, so it was recommended that at the end of the flying day, a few drops of a light oil should be put into the carburettor and then spin the engine some to work it through, mostly to protect against corrosion since the methanol in the fuel-residue is hygroscopic. The castor-oil residues could become sticky too. Marvel Mystery Oil was excellent as an after-run oil to keep the engine nice and clean and free-spinning.

Okay, now back to the subject of this thread.
[/hijack]

[alaric]

Hi. I just bought MMO from amazon. I'm hoping it helps with my carbs

Sean.

[Billmack]

Try a leakdown test. That will tell where the compresdion is going

[StephenT]

I purchased a can of starter fluid and did the puff test. I was able to get all cylinders to respond to the fluid. I pulled the idle jets and blew out the passages. I have gone through the tuning process again and everything seems much better. It’s not perfect but this is an old engine that would definitely benefit from a total rebuild but I feel it’s good enough for now and I can proceed to my next tasks and get it on the road for further evaluation. I would still like to do a leak down test. I’ll try to borrow a tester.

I have let the engine off idle for quite a while and temp has not been an issue. I’m a little surprised since I haven’t done anything to the radiator other than flush it out with the garden hose. I did add a bottle of water pump lubricant.

Thanks to everyone for the advice, I will post again in a few days as I move on to the clutch with fingers crossed.

Steve

[2cams70]

Those compression figures are reasonable for an old engine of unknown origin. I wouldn't bother with a leak down test. You already know what you need to know at this stage. Just get the car on the road to find out the rest you need to know about the engine - that is of course provided:

1. No serious oil leaks, no coolant leaks
2. Oil pressure OK
3. No unusual noises
4. Temperature OK.
5. You've done the basic stuff - oil change, head bolt torque, valve clearance check, checked the ignition timing, points, etc.

By the way put some coolant in it as soon as you can. Don't let it sit around with just water and water pump lubricant in the mix.

[alan.barker]

Stephen,
Good luck to bleed the Clutch and get it moving under it's own steam.
Alan

[ill_will]

Hi Steve,

A couple of things that don't seem to have come up which may (or may not) be useful.

You mentioned you'd rebuilt the carbs, so I wondered how well they are balanced? If you don't have a flowmeter, and you haven't already, you can do a first approximation by removing the progression hole covers, putting a light at the intake end of the carbs, and then gradually cracking the throttle open (engine off) so you can see through the holes where the throttle positions are relative to one another. Not very precise, but better than nothing. You can get a sense of whether the butterfly shafts are twisted too.

The other thing I've used in the past to diagnose idle issues is a Gunsons Colourtune. Again, a bit crude, a bit of a faff, but quite cheap and then you can see what happens when adjusting the idle bypass screws. I had some DCOEs on a tired Alfa 1750 GTV which needed quite a different setting on one barrel to the others, and never totally got to the bottom of it.

Good luck.

Will

[StephenT]

Thanks for the suggestions. I did examine the throttles through the progression hole covers and all four butterflies are in about the same position at idle. The first progression hole is blocked at each throat.

I have never tried a Colourtune. I have often wondered if they are actually useful.


Steve

[ill_will]

Hi Steve,

In my experience they are fairly useful for looking at combustion at idle, as you can get a sense of how rich the mixture is from the flame colour, and also how stable the combustion is. You can pick them up for about 20 quid on eBay.

One other thing that I forgot to mention is you could check how much scatter there is with a timing light - I've had tired distributors with a lot of wear adding a lot of randomness to the process. Checking the five leads in the dark is also useful to check there is no arcing where it shouldn't be.

Cheers,

Will

[StephenT]

I’ll keep an eye out for a bargain colourtune. It would make a good addition to my tool box.

I have replaced the plug and coil wires but checking the timing to see how much variation there is sounds like an easy indicator of distributor health.