19 replies to this topic

[nichmoss]

Recheck the carb - float level, nominal idle setting and nominal mixture strength. Does the piston drop to the bridge easily, freely and with a click as it contacts - do this with the damper out.

I'd you're sure of the carb, when you push the choke in can you hold 1000 rpm with the throttle? If so, your idle setting is probably too slow and needs increasing. If you can't, then the mixture is probably too weak and needs to be made richer. These are the two things that the choke gives you.

On the overheating, if you're sure that the piston rings are correctly sized and all bearings are good, then you think it overheats because of the gauge and not because of excess friction. Does the top hose get very hot? If not, then perhaps the thermostat is stuck closed. These are loads of things to check but if it's not blowing off water then it's hard to believe it's overheating. For me, 5 minutes at 1400 rpm sitting still may very well cause the temperature to come up. I would drain all antifreeze and refill with the correct amount to be sure. Make sure the heater is on.

Be very careful with everything you do and if you're concerned about the temperature then turn the engine off.

Good luck, Chris

[Ricester]

Recheck the carb - float level, nominal idle setting and nominal mixture strength. Does the piston drop to the bridge easily, freely and with a click as it contacts - do this with the damper out.

I'd you're sure of the carb, when you push the choke in can you hold 1000 rpm with the throttle? If so, your idle setting is probably too slow and needs increasing. If you can't, then the mixture is probably too weak and needs to be made richer. These are the two things that the choke gives you.

On the overheating, if you're sure that the piston rings are correctly sized and all bearings are good, then you think it overheats because of the gauge and not because of excess friction. Does the top hose get very hot? If not, then perhaps the thermostat is stuck closed. These are loads of things to check but if it's not blowing off water then it's hard to believe it's overheating. For me, 5 minutes at 1400 rpm sitting still may very well cause the temperature to come up. I would drain all antifreeze and refill with the correct amount to be sure. Make sure the heater is on.

Be very careful with everything you do and if you're concerned about the temperature then turn the engine off.

Good luck, Chris

Great advice thanks for that.

I’m sure of the carb. The dash pot moves lovely, without the damper it’s a nice slide and click down. With the damper it’s markedly slower, but a consistent slide down with no friction/bindy feel.

I suspect the mixture is too weak and this can in turn be adding to the overheating.

Piston rings are correct size - pistons are +20 and rings are +20, I triple checked when I bought and fitted. I gapped them properly too.

The top hose gets very hot, as does the top of the rad, after about 4 minutes.

My plan is to drain the coolant and flush the radiator. I’ll check for any issues there. If none, I’ll ensure this time when refilling I’ll be extra careful around air lock issues.
Then I’ll richen the mixture with the carb. I’ve been running it with no air filter which I assume is likely to have weakened the mix further.

I also have 2 fan pulleys - a large one and a smaller one. I fitted the larger one after reading about minis struggling to build up heat because of the constant pump/pulley and if you can use a larger pulley, do so. I’m now going to switch to the smaller one given the issues.

I’m hoping as a result of the combination of things mentioned this will resolve both the overheat and the cut out at under 1400 rpm. I’ll keep posting. Thanks for the help.

[sonscar]

Is the exhaust manifold starting to glow?Retarded timing can cause overheating quite rapidly.I find the book timing figures to be low with modern fuels.More expert people may dispute this and care is needed.My 998 runs about twenty degrees at idle with vacuum connected.Check carefully for air leaks from carb to the cylinder head as this can cause erratic running and overheating.
Start afresh and forget all you have done so far.Assume that I brought this car to you as a non runner and check everything.Good hunting,Steve..

[Ricester]

Thanks, no the exhaust manifold isn’t glowing, I’m not letting it get to that stage. The temp gauge is going to “hot” and when it’s there I’m turning the car off.

[Ricester]

Hey, just an update on all of this in case anyone reads it back in years to come (as I have on many other posts here) 

 

The idling issue was down to my stupidity in not blocking off the breather pipe in the carb. There are still air leaks in the carb around the spindle but it runs much much better now and can happily sit at 1,000rpm no problem. In addition to blocking off the breather pipe I stripped down the carb again, changed the damper and the spring for new ones and the piston now moves down much quicker than the video posted, this seems to have made a great difference. I have also used valve stem seals around the spindle (both sides) to mitigate the air leaks. This is a temp fix until winter time ish when I intend on stripping the carb back off and sending it away to AC Dodd for a full service and fix up. 

 

The temp issue - well after much messing around - the culprit was the voltage stabiliser. Simple answer is it was never hot, the gauge was just telling me that. Changed out the voltage stabiliser and it sits happily at "N". 

 

Im so glad to have fixed these issues. I got the colourtune kit and sorted the mix (was running lean also,) and timed it back in again. Fingers crossed all goes well for a while. Thanks again for everyones input.