• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Engines dies when hot....

Share this page

JamesWilson

JamesWilson

Yoda
Country flag
Offline
HELP!

I have a 1275, twin carb MG Midget engine in my Rochdale Olympic kit car.

It starts well when cold and runs fine, both at idle and at speed.

Dwell and timing seem spot-on. The plugs, wires, distributor cap, rotor, condensor and coil are all new or new-ish. It is not impossible that one may be faulty, but they all seem to work OK when cold....

It has a new thermostat, water pump and radiator (for a 2.6 liter London Taxi, because the original was too prone to overheating it had a small area and low capacity- this fix seems to allow it to come up to operating temp and stay there regardless)

The problem is that I can take it out for a drive and after 4-5 miles it starts to act like it's overheating, mis-firing and running increasingly poorly until it stalls and dies. It will not restart. But if left to cool almost completely down it can be restarted and runs as though nothing happened.

I'm at a complete loss to explain it.

I thought it might be vapor lock but there's fuel in the carb float chambers and in the underhood fuel filter. There is no heat shield between the exhaust and the carbs. Ive not had this problem before.

The coil seems quite hot, but swapping it for a cold spare one doesn't fix the problem.

The temp guage never goes above the normal range and the coolant doesn't seem excessively hot.

The only explanation I can now think of is some kind of internal bloackage to coolant flow in the engine block that causes localized overheating....

Any ideas/suggestions?
 
I'm thinking vacuum leak....intake manifold is common, or one of the SUs. Did you check to see if you have spark? You said you have fuel, in both carbs? I do not like that you do not have a heat shield....it was put there to prevent boiling of the fuel in the carbs.....which your car could be doing.
Good luck....keep checking stuff.
Scott in CA
 
Question- the two coils that you have- do you know is they are 1.5 ohm (external resistor required) or 3 ohm (no resistor required) units?
Since you say that they are "new ish" they could both be the wrong (1.5 ohm) ones.
BillM
 
smaceng said:
I'm thinking vacuum leak....intake manifold is common, or one of the SUs.
Scott in CA
Click to expand...

+1 those are precisely the symptoms i had with mine (1500) turned out to be the intake manifold bolts had loosened just enough. Here is a quick way to check. Next time it happens (or make it happen) take off your air filters and cover the throats of the SUs partially. See if it starts. If it starts with restricted air you have effectively adjusted the mixture and will then need to sort out where else it is getting air.
 
Why do you think it's overheating if it doesn't show on the gauge or boil over?

If you pull the choke does it help?


I, much like JP have had my intake lossen as well. It has happened several times. in each case it was long enough for me to forget and suspect carbs. After fighting carbs for weeks I'd get flustered and switch to a different system...only to find a loose intake. I already had $$$ tied up in the new system so I would go ahead and swap anyway. I'd make a mental note of it for next time but...

(and you guys wonder how/why I have every induction system avalible for a 1500 except for Minkunis and FI.
 
The lower hose is under suction. Look to see if it is "collapsing" when running. If so, cooling will be compromised.

I've seen thermostats fail (and block flow). Remove it temporarily and see if that improves things.

And I agree with Bill about double-checking to see if you have a coil that requires an external ballast.

Finally, when you converted the rad, you didn't accidentally install a Mini fan, did you? I've seen this happen when folks use some of their spare parts. Mini fans look just like a Midget fan, but the blades are "backwards" and will cause overheating.
 
I checked the coil reistance and they're all 3 ohm. I has though there might a a partial internal short.

There's fuel in both carb bowls.

The heat shiled was missing when I first got the car three+ years ago and it's only recently that these problems have developed. I SHOULD get one and will, but I'm thinking past experience shows something else might be the problem.

I'll check the lower hose. It wouldn't hurt to re-new that. I've done everything else.

There's a manually controlled electric fan that's the same as before. I switch it on once the car has come up to running temperature.
 
You really should have a heat shield. The fuel in your carbs is probably boiling without it--maybe even with it.

Also, many of the ignition condensers available today are pretty poor quality. I can imagine one being OK when cool and failing when hot. Have you checked the basics, like making sure you're getting good spark and the right fuel level in the float chambers?
 
Ashley Hinton just introduced a new SS Heat Shield.
 
Sarastro said:
You really should have a heat shield. The fuel in your carbs is probably boiling without it--maybe even with it.
Click to expand...

A heat shield is a good idea but I'll wager it's not a fuel issue.
 
I had a flaky condensor once that exhibited similar behaviour. I'd guess a fuel delivery problem based on the symptoms, but the fuel in the float bowls seem to rule that one out.

Greg
 
How about blocked vent on the cap. Whe it starts acting up loosen the gas cap and see if issue goes away. You may need a new gas cap.
 
I vote for condenser, cheep and you should have an extra or two in any case.

Available at your favorite auto store.
 
Back
Top