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100 misfiring

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curtis

curtis

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I though I would ask your opinions before starting to investigate. It might save some time!!
My 100 starts and runs well. However, after it has run a while, say 15 mins and I stop and switch off there is a problem when I restart a few minutes after.
The car misfires badly, almost too much to move off. If I keep a very low throttle it is reduced and by gradually working up through the gears I can proceed. After about a mile like this I can gently accelerate and it clears.
Any thoughts?
 
Hi Curtis, sorry for a late response. You might just pull the sparking plugs right after the next run and shut off to see if they might be gas fouled for some reason with the carbies.---Regards-Keoke
 
Good point.
So far I have checked and cleaned the plugs and checked and cleaned the carbs. Nothing unusual found.
However I didn't get time for a run before a rainstorm and I was still trying to get a good seal on one of the banjo unions. Still can't stop the fuel leaking out. I had this problem before and even with new fibre washers it still leaked. Hmmmm!
 
Oh, try putting a bit of gasket sealer on the fibre washer Curtis and see if it will not strop the leak.---Keoke
 
There IS a difference in gaskets. I have found that the black fiber ones seal much easier than the red fiber.

Your first problem,
If you have the standard H4 carbs, make sure that the float bowl vents are not blocked. The "vent" consists of two slots on the carb top around the hold down bolt. There should be a metal vent cap over the slots. Then a fiber washer between the cap & center bolt. If the caps have been omitted or there is a washer between cap & float bowl top, the washer will likely seal the vent.

If the vents are not open, fuel pressure, or pressure in the bowls from heat build up, will force fuel out the main jets cause flooding, & prevent new fuel from entering the bowls.
D
 
Keoke. I thought petrol would get through gasket sealer? But I'll try it.

Dave. I'll check those vents on the carbs.

Thanks both.
 
Curtis -

Sounds to me like you have some sort of fuel delivery problem.

My guess is there is lots of crud in your fuel system and your fuel pump is having to work too hard, causing it to overheat and stop working, or work poorly.

After you've run the car for a while, put your hand on the fuel pump. If it is super hot, that's your problem.
 
Further update.
Have checked the vents on the carbs and they are OK.
Have "sealed" the banjo and no leak at present.
No chance to go for a run as busy preparing for a rally in the Twin Cam at the end of the week.
Alan I will investigate your suggestion but I don't think it fits the symptoms?
Normally all is well and I can drive as long as I want to. The problem comes when I restart and then it disappears.
 
Curtis -

Duh..... /bcforum/images/%%GRAEMLIN_URL%%/crazy.gif

I just re read your problem and I have a very good idea of what it may be.

I think you are getting vapor lock, so my fuel delivery idea wasn't too far off.

The 100 fuel pump is right over the exhaust pipe, so when it gets hot, the line from the tank to the fuel pump will turn to vapor and you will get the exact symptoms you are talking about. Driving for a while on the freeway clears the problem because the air circulation helps cool the pump and fuel lines down.

Try wrapping some header tape around the exhaust pipe on the total length that runs under the fuel pump... I did this on my 100 and it cured any vapor lock problems.
 
Hi Curtis/Dave Russell,
I have always used the red fibre washers and have soaked them in kerosene to stop them drying out and leaking, had the leak problem on the front banjo last year after a refurb, the garage had installed them dry, they ok now
 
Alan, I can't see why this overheating would suddenley happen. Even in v hot weather the problem hasn't arisen before. I am not sure if my pump is in the regular position but it seems far enough away to me not to be a problem.
Anyway, I'm off for four days to compete in a rallye so the Healey will have to take a back seat for a while. Will keep you posted. Thanks for all the ideas.
 
Curtis -

This vapor lock problem is very common on the 100. I am not surmising or guessing here, I am simply relaying the collective experience of many many 100 owners including myself.

The solution I proposed will literally take you five minutes to fix once you take the tire off. I might suggest you give it a try anyway, whether you believe me or not. It's good insurance and a better solution than the rubber sleeve that was put over the fuel pumps from the factory for this very reason.

While you're in there you can take the fuel pump out and clean it up - sanding the contacts and cleaning out any gook in the check valves.
 
Mine was built in August or September '53. It is ~ #800 off the line. It is quite early.
 
cool! I'd sure like to get one of the melamine ID tags they put on the early 100... mine is missing.
 
healynut,
I have got my hands on a card with the correct dimensions and thickness and colour that fit with my recollection of mine which I have lost /bcforum/images/%%GRAEMLIN_URL%%/frown.gif
I also have some pics of very early plates, not sure if they didnt change (stamping?) of same as time went by
Do you have the ali id plate adjacent the regulator box on the firewall in the engine compartment?
 
Mate from OZ -

Unfortunately I have no ID plates on my early BN1 except the original chassis rail plate, so I can't help you on the ali plate you speak of... apologies.

I know I can replace them all with reasonable facsimilies... except the melamine plate inside the car... been looking for a source for that for some time. Maybe if you can post your information I can check around HK and see if I can make up something that looks like the original.
 
Back to the original problem.
The car had been very much down on power along with the other difficulties.
Well today I decided to get back down to sorting it out.
VERY red faced to report that I have been driving on one carb. I can't believe how I didn't realize it. I suppose that coming out of the Twin Cam rally car and then into the Healey I was making allowances for the power difference.
Anyway I celebrated with a good fast run in the country. It's a new car.!!
 
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