***FIXED!!**** engine problem, need ideas!

[351ciofgrunt]

Hey guys,
I have a problem with my GQ patrol TB42 carbie. I'm out of ideas.

Symptoms
- car idles okay with a slight miss
- soon as you start driving it there's shuddering, surging and also some backfiring through carb, kind of feels like when a fuel pump is gone and the cars starving for fuel. Problem just started one day.

What I've done so far:

Fuel
First replaced fuel pump, then replaced carbie which made no difference, then eliminated fuel system entirely by ripping off fuel system and replacing with straight LPG gas (impco model E and 425)
- made no difference to problem

Compression
-compression tested all cylinders and they are within 5 psi of 165psi

Spark
Replaced points, ignition coil, checked and gapped spark plugs, checked ignition timing

Engine oil looks good and clean
Coolant looks good and clean

I'm out of ideas

I suspect a cracked cylinder head, perhaps a crack between two combustion chambers however it didnt show up on the compression test, but maybe its small enough to only cause a problem under combustion pressures and not cranking pressure?

[shortyq]

did you check the ignition timing?

[STIKA]

Do they have a vacume advance set up on the on the dizzy

[RAY185]

What did you gap your points to?

[eugene]

my mate had the same problem, he changed spark plug gaps to fix it, i can ask him what he gapped them to.

[351ciofgrunt]

Yes i checked the ignition timing

no its not spark plug gaps, i've played around with everything from 25thou to 40thou

Its not the points or the points gaps because besides replacing the points i also ended up replacing the points entirely with the electronic ignition that replaces the points and it made no difference.

[351ciofgrunt]

Do they have a vacume advance set up on the on the dizzy

It wont be the vacuum advance because this problem only happens when i'm accelerating, when the vacuum advance wouldnt be operating

[STIKA]

Do they have a vacume advance set up on the on the dizzy

It wont be the vacuum advance because this problem only happens when i'm accelerating, when the vacuum advance wouldnt be operating

I thought that was when you got more vacuum

[351ciofgrunt]

Do they have a vacume advance set up on the on the dizzy

It wont be the vacuum advance because this problem only happens when i'm accelerating, when the vacuum advance wouldnt be operating

I thought that was when you got more vacuum

No the vacuum advance is for when you are cruising at light throttle, theres not much vacuum when accelerating
but thanks for the ideas, keep them coming!

[simkell]

have you changed the ignition coil and lead, may be breaking down under load.

do you have an exhaust restriction or inlet restriction or manifold leaks?

[DamTriton]

Change the condenser (capacitor) on the dizzy. $5 should fix your probs....

[jessie928]

Change the condenser (capacitor) on the dizzy. $5 should fix your probs....

no condensor with pertronics/electronics

check out your coil first and the wiring to the resistor. make sure you have 12v on one side and 9 v on the other, and make sure that you run the pertronics to the 12v side at the LEAST, better stil run it to a relay and juicy 12v. and run a new separate wire to the - post of the coil, donot use existing wiring.

also, check for slop in the dizzy shaft.

did you replace the ignition leads?

also, check the muffler.

and another note< NEVER assume something works just because its
a. brand new
b. spare sitting around. reason i say this is in regards to your coil.

Jes

[mkpatrol]

Broken wire somwhere.

[Rangie Thing]

How about dizzy cap, might have a hairline crack.

[351ciofgrunt]

Hey guys Problem fixed!!

Thanks for the good ideas.

It turned out to be a combination of:

* dodgy spark plug lead (timing light showed it was only firing 70% of the time at idle and not at all when revving)

* vacuum leaks (old hoses gone rock hard and cracked)

The lesson i've learned is dont overlook the basics!!

I'm so happy... :-)