Misfire

[flying pasty]

Hi Digger

The only thing i changed was the points & condenser to electronic ignition, the plugs the leads & rotar arm, the carb has had a rebuild kit as the main jet was leaking petrol not from the float bowl but from the bottom of the carb itself, the fuel supply was changed from gravity to a fuel pump(mechanical).
When i first brought it a year ago she was running on all four & to be honest it wasn`t until i took it in to the local garage to have the timing done & the carb properly rebuilt by them that it came to light about the misfire, They reported to me that No1 cylinder has a misfire on it, they found this by removing the lead on No1 plug & found no difference in the idle speed yet on removing the leads on 2,3 & 4 individually the engine virtually nearly died.
Nothing major has been done to the engine apart from the tappets have been re gapped to the correct setting of .006.

Robbie

[morrag]

So, keeping it simple, check and publish your pumping pressures for each cylinder. Put a timing disc on, and chech the valve timing, this will reveal any tappet etc. probs, forget about carburation, you only have one and its obviously supplying the other 3 cyliders ok. Those two checks will reveal if the head needs lifting, so, go on, what are you waiiting for.... ..Morrag

[ROD]

Im with Digger re the firing order, as this is something i thought of that is so easy to get wrong.perhaps the garage got the firing order wrong? Dont rely onwhat they did, check the firing order yourself, not against any old cap or leads you may have spare.check the static timing vs the firing order.

[morrag]

Rod, there is no way to have 1 out of 4 wrong as regards firing order!! and with 3 cylinders behaving, then your probs are obviously with No.1. Sherlock Holmes got it about right when he stated, "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth!"...   Morrag

[kapri]

Rod, there is no way to have 1 out of 4 wrong as regards firing order!! and with 3 cylinders behaving, then your probs are obviously with No.1. Sherlock Holmes got it about right when he stated, "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth!"...   Morrag

My method of troubleshooting as well !

I recently had a new Reliant cap with a duff contact for one terminal.

[digger06]

Rod, there is no way to have 1 out of 4 wrong as regards firing order!! and with 3 cylinders behaving, then your probs are obviously with No.1. Sherlock Holmes got it about right when he stated, "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth!"...  Morrag

I agree , you cant, but when you have 2 swapped , sometimes it seems like only one cyl is firing, it was just worth a double check on that and the rotation the firing order is on the dizzy, its free, head off will start costing money,

1 3 4 2 , ANTI clockwise? I think

[ROD]

The engine was firing on all four prior to visiting the garage to do the carb and timing, what have they done to create the misfire?

[terry t]

The engine was firing on all four prior to visiting the garage to do the carb and timing, what have they done to create the misfire?

Rod. I don't think they created the misfire  they found it when doing other checks and setting it up?

[terry t]

Robbie. are you sure its a 850 engine check stamp on the side of the block just below the head.

have you checked the valve timing

850cc inlet opens 15 degrees. exhaust closes  25 degrees BTC. 

750cc inlet opens 20 degrees. exhaust closes  20 degrees BTC

[ROD]

Terry..he said that it was running fine , then the misfire came to light when he took it into the garage to have work done?

[terry t]

Terry..he said that it was running fine , then the misfire came to light when he took it into the garage to have work done?

Yes Rod it was always there. I came to light when he took it to the garage.
this is what Robbie has already said

the misfire is the same, no it doesn`t get worse its like the whole cylinder doesn`t exist, she ticks over beautifully no flat spots & revs are smooth.
yet when the plug lead is disconnected from No1 cylinder there is no change in tone.
Doesn`t make any sense at all, she drives really smooth .

[kapri]

The fact that the tappets were miles out ,to me ,suggests worn / broken cam lobes. I'd measure the lift on all valves .

Using a Colortune set up will confirm what is actually happening in the cylinder as the glass tube allows you to see the actual spark / combustion as it happens.

[flying pasty]

Hi Terry
The engine number is OB/85/58673.

[terry t]

Hi Terry
The engine number is OB/85/58673.

Yes that's a 1973/850cc
not sure on the other letters and numbers but there's some info on here fifer will know

[Olds]

OB =February 1980
85 = 850