running rough once engine is hot

Hi guys I have a tb42 carby in a 89 gq petrol/gas.. I am having problems with my truck. once it gets hot its does not run right. it will cough, splatter and some times back fire. The timing is right and I set the tappets. I have one that is a bit noisy that I have to check but when cold is fine. When I put my foot down or go up hills when the truck is hot is when it does it. When I put I foot down its wants to go but doesn't. It also does it on gas. I have also put carby cleaner through the carby and sprayed all the links on the outside,put a new air cleaner on it as well. I am thinking the carby is the problem. its a standard Nissan carby. any suggestions would be great.

Thanks

Could be a few things... have done the basics? Checked plugs leads rotor etc? Does it do it on either fuel? Could be the vacume secondarys playing up

Will need to know if same on Gas as Petrol or same with both.

Yeah it does it on gas and petrol. How do I check the vacuum

Check all the small rubber hoses, some may be brittle and perished
has your patrol PCV valve in rocker cover.?
Now if its happening on both what is a common part like your Dizzy or leads shorting

I will check rotor and distributor cap in a minute. Leads and plugs were replaced ago. Could be a fouled plug.

It has two hoses coming out the top one goes to air cleaner the other goes down between the intake and head. The one that goes between the intake has a split the were it connects to rocker cover. Not sure about PVC valve.

Vents gases out of rocker covers if you idle then remove this and stick your thumb over the end motor should stall.
That split is obviously wrong and will need attention

do you have an "immobilizer" fitted?
check the earths on this, my old GQ would sometimes play up on gas, and when I went to change a relay on it, we found a loose earth behind the Elect Ignition off the Coil.
also, check to see if your Coil is the correct one for Gas - they need the "flame thrower" type.
also, when it was last tuned, was it tuned for Gas or Petrol or trying to get a happy medium????
petrol timing about 9* BTDC
Gas timing about 14* BTDC

to get the best results, work out what you want to run in 80-90% of the time, and tune it to that.
mine was tuned to Performance on Gas (320Km out of 80L tank) but I could pull away in 5th at 100Kms per hour (up to 140Kms). Mind you, I was only getting 250Km out of 50L of Petrol, and it would run slightly hot when it was in petrol


cheers

A good indication that your engine is sucking in air at an unwanted source(ie vacuum leak) is at the exhaust end with engine running, the exhaust will make a consistent putt putt sound. If you can hold your hand about half a metre away from the exhaust, you shouldn't feel much exhaust pressure. If you do, it's a good indication you've got a vacuum leak somewhere.

Ok thanks will go out and try those things now. Thanks for your help guys.

Ok I put my thumb over the rocker cover were the hoses go and nothing happened. So I take this that there is a vacuum leak.

ok so today I replaced a couple of hoses that were split. one from bottom of carbie to rocker and another smaller one. I also changed timing to 14d before tdc. It ran worse then before. so will be putting that back in the morning. I found a vacuum hoses that is connected to a 4 way splitter on the firewall but I cannot find were it goes. tried one spot but ran terrible. rotor button is on order, should get it Wednesday. Another question I have is when should the butterfly open and how much should it open. mine barely opens at all.

What butterfly you talking about mate???
I its your choke butterfly at the top of your carby, & its not opening its jammed closed & you've just found your problem.....

yeah its the one at the top. when I pull the rod on the side of the choke which is attached to the butterfly it opens but when using throttle it doesn't. should the air cond rod that moves should that be touching the screw with the spring under it.

Ok so it's losing power on both petrol and gas but only when it gets hot.
A faulty (or on the way out) coil will break down spark when they start to get hot. Are you able to swap another coil for a test run? (making sure that it's the correct coil for the engine).
Do you have the original points setup or an electric ignition module?

Not sure about points. Or if its a electric. I think it might be an electric one as there is a red and black wire coming out of dizzy. The coil looks to be a standard item. Looking at a gt40 cool. Would they be ok for the gas. I think my carbie is stuffed. I took it off today. The secondary butterfly on the bottom was'nt open at all. The lever was on the wrong side so changed that and then the truck wouldn't start at all. Also the choke butterfly isn't opening and closing like it should either. It's either open or closed nothing in between. Have another one coming tomorrow. So hopefully can get to the bottom of this. It's starting to annoy the crap out of me.

I feel your pain mate. The carbys on the TB42 can be very temperamental when they get old. Also, lpg will slowly kill the carby. If it's in bad shape then hopefully another carby will help.
I would look into the ignition side of things too. By the sounds of it you have electriconic ignition. If you take the rotor button out and lift the plastic cover under it you will be able to see for sure.
I had a faulty ignition module and it ran fine when cold but would start missing spark worse and worse as it heated up.

so far so good on motorculture

Hi guys. I have soughted the missing and everything now. But it doesn't run on gas. I have changed the carbie. And alot of other things. Also it idles low. Can someone please tell me were the idle screw is. I think I know which one it is but I want to make sure. It ended up being faulty new plugs. Replaced coil rotor button dizzy cap coil lead,

You haven't accidently dis lodged a wire from your gas solenoid,
Now you have all new plugs,leads etc your LPG should be spot on.
Idle screw should be easy to find , with engine off look for what
looks like a stop screw usually with a spring under it