running rough once engine is hot

[wakerider]

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

[davo94]

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

[threedogs]

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

[wakerider]

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

[threedogs]

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

[wakerider]

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

[wakerider]

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.

[threedogs]

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

[Bigcol]

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

[Parksy]

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.