v8 running poor

[bobtail 26]

hi to all my v8 3.5 on carbs runs fine till it gets hot then starts to miss and i dont no were to start to find out whats making it do this

[cooper]

First thing i'd do is check the HT and dizzy, see whats happening there, then check the rest of the ignition system.

Cheers

Shaun

[FridgeFreezer]

Is it points or does it have an amp module under the coil? Those like to go faulty when warm. See here for how to replace/upgrade for cheap.

[bobtail 26]

Is it points or does it have an amp module under the coil? Those like to go faulty when warm. See here for how to replace/upgrade for cheap.

thanks for the help ill try that this weekend and let you no how i get on

[Snoopy]

thanks for the help ill try that this weekend and let you no how i get on

You have a PM

[ramon alban]

hi to all my v8 3.5 on carbs runs fine till it gets hot then starts to miss and i dont no were to start to find out whats making it do this

Hello Bob, i'm not a carb person but if your engine starts ok and only misses when it warms up it could be the mixture is staying too rich due to mixture control or choke problems.

Check the spark plugs for signs of over fuelling

If they are normal then go to the ignition system and clean all the parts inside and out with WD40 and dry everything off with a dry cloth.

This will eliminate condensation and grime and hopefully any HT tracking.

If that does not work check the rotor arm and dizzy cap for tracking and substitute for known good'ns if poss.

After that its the leads and plugs and after that the dizzy innards and coil + amplifier if there is one.

Come back with results thus far.

[bobtail 26]

You have a PM

cleaned every think new plugs a bit better but still not right will not pull very well when under load

[orangemach5]

cleaned every think new plugs a bit better but still not right will not pull very well when under load

Could be the coil itself breaking down, i had this whe i had the carbtooted 3.5 in my rr. As soon as it warms up the spark gets weak, changed the coil and problem solved.

If you can get hold of some spark testers, little orange carrot shaped sticks that go ontop of your spark plug and the your ht lead goes on top of the tester. They flash everytime a spark is present, this way you will be able to rule out whether its ignition or fuel related.

Testers arent expensive, about £8 for 4.

[ramon alban]

cleaned every thing, new plugs a bit better but still not right will not pull very well when under load

Bob, I asked you the following:

if your engine starts ok and only misses when it warms up it could be the mixture is staying too rich due to mixture control or choke problems. Check the spark plugs for signs of over fuelling.

I see you changed plugs, but what was their condition regarding overfueling, wettish, sooty or normal? An answer would be helpful before moving to the next stage.

You have clearly got sparks otherwise iit could not run at all and the sparks can get affected by heat in the coil/amplifier, but its less likely for their performance to simply deteriorate in the repetitive pattern you describe, and more likely an ignition problem stops the engine dead, even when the fault is intermittent.

However, if changing ign components does not solve it, going back to your original post.

----- V8 3.5 on carbs runs fine till it gets hot then starts to miss -----

and add to that

will not pull very well when under load

changes the complexion of the problem.

When cold with a rich mixture or bad timing the engine may start and run OK without load but as it warms up the correct timing is also required for it to perform under load.

Suggest you also check the ignition timing at idle, somewhere in the region of 2 - 4 deg BTDC if you are using low/med octane unleaded fuel, would be a good place to be.

When you have eliminated the possibility of overfuelling and ignition, attention may have to go towards the camshaft being worn. I've heard that some lobe wear can often emulate other more common problems.

Keep the symptoms coming!