12ht running rough/miss at certain rpm? (1 Viewer)

[paz12ht]

G'day folks, first post but have been lurking for some time.

Got a small problem with my 12ht between 1000 and 1500 rpm, she starts to run really rough (near like a miss), doesn't happen though when it is cold, runs as smooth as the proverbial!

Only happens with no load on the motor, does not affect when powering or highway driving it seems, also noticed it seems to idle rougher when warm (sounds a bit like it has a lumpy cam)!!

Have done a fair bit of research on the 'net about it and has been said it could be the spring in the governor, anyone know what spring it is and exactly what is wrong with said spring if this is it?

Also read it is normal for a 12ht to be doing it at around 1700rpm, not sure if it should be for a 500 rpm range though like mine?

What else could it be, am going to pull the tappet cover off it and check valve clearances just to eliminate the possibility it could be that, maybe timing as well?

She goes like a power house for a stock motor other than the above problem, yet to do boost etc but want to get this out of the road first.

Have changed fuel filters etc a few days ago, i bought the motor just recently and have swapped it into my '89 60 that had a 2H so have no real idea on the history of the motor either, though i am sure the sump has been off for some reason at one time.

Did try the search function, after 34 pages i thought i had better pop my post cherry.

Thanks,
Paz

 

[chet]

it could be a dirty injector. oh and welcome to the forum.

 

[Tapage]

I would try to feed the IP directly to isolate the problem maybe from taking air in the line ..

 

[paz12ht]

Thanks for the replies gents (and the welcome).

Okay, so injectors i should be able to crack each one and see if there is a difference when it has the rough run, if it does then i can investigate it further, cool.

Feeding from a bottle will be easy, will give it a go.

In my search last night i did find someone with the exact same problem as mine that had posted up, but he never did get back to post what his outcome was (single poster).

Thansk,
Paz

 

[MutleyFJ62]

Hey Paz, couple of things, if you dont know for certain the klms or history of the engine, you may be due to pull the injectors and have them rebuilt.
Secondly, worst case scenario is a cracked piston, with the heat allowing it to open up. These motors are pretty tough, my last one had a hole in piston 2 and it had a slight lump/stumble to it at idle and a bit above. When i pulled the head, found the ring land had cracked and thats what had hammered a hole in the piston.
I'd be checking injectors and pump first though.

 

[paz12ht]

Secondly, worst case scenario is a cracked piston, with the heat allowing it to open up. These motors are pretty tough, my last one had a hole in piston 2 and it had a slight lump/stumble to it at idle and a bit above. When i pulled the head, found the ring land had cracked and thats what had hammered a hole in the piston.
I'd be checking injectors and pump first though.

Hmmm, i wonder if it did have a hole in the piston if it should be getting heaps of blow-by out the breather cap when cap off and running, have checked this on mine and it doesn't seem to have any at all, did yours?

Paz

 

[MutleyFJ62]

Mine didnt have any blow by at all. Had just a slight roll/lump to it at idle, but nothing else at all.

 

[HJ61 12HT]

I have driven quite a few 12HTs, almost all have a jerky area when warm at about 1500rpm with no load.
If its just that problem then I wouldn't worry about it too much, probably governer bouce? aparantly you can do a very fine adjustment on the pump somehow to reduce this effect, it's on here somewhere...

If the idle is errratic, then i think it points to some other problem inside the injection pump, or perhaps an air leak of some sort in a fuel line, so check the fuel lines first.

Simon

G'day folks, first post but have been lurking for some time.

Got a small problem with my 12ht between 1000 and 1500 rpm, she starts to run really rough (near like a miss), doesn't happen though when it is cold, runs as smooth as the proverbial!

Only happens with no load on the motor, does not affect when powering or highway driving it seems, also noticed it seems to idle rougher when warm (sounds a bit like it has a lumpy cam)!!

Have done a fair bit of research on the 'net about it and has been said it could be the spring in the governor, anyone know what spring it is and exactly what is wrong with said spring if this is it?

Also read it is normal for a 12ht to be doing it at around 1700rpm, not sure if it should be for a 500 rpm range though like mine?

What else could it be, am going to pull the tappet cover off it and check valve clearances just to eliminate the possibility it could be that, maybe timing as well?

She goes like a power house for a stock motor other than the above problem, yet to do boost etc but want to get this out of the road first.

Have changed fuel filters etc a few days ago, i bought the motor just recently and have swapped it into my '89 60 that had a 2H so have no real idea on the history of the motor either, though i am sure the sump has been off for some reason at one time.

Did try the search function, after 34 pages i thought i had better pop my post cherry.

Thanks,
Paz

 

[paz12ht]

Bit of a show off video i put on YouTube for the new 3" mandrel system yesterday .

At around 17 or 18 seconds you can briefly pick up a hint of the rough run in the higher rev range.

Whats the verdict on idle, normal 12ht?

60 Series 12ht 3" Mandrel Exhaust - YouTube

 

[MutleyFJ62]

Even with a 3" system, thats a bit lumpy for a 12HT. You have fueling issues. Time to get friendly with yoru injectors and pump

 

[paz12ht]

Even with a 3" system, thats a bit lumpy for a 12HT. You have fueling issues. Time to get friendly with yoru injectors and pump

Yahhhhhhhh, not!!!!

Oh well, guess i will start with the path of least resistance and get the injectors done first!

Paz

 

[MutleyFJ62]

Let us know what you find...

 

[paz12ht]

Let us know what you find...

Done some digging in the last day or so, used a big screw driver like a stethoscope and had a bit of a listen to the injectors, 4 out of the 6 open with a really loud crack, very distinct, the other two are more of a thud, definitely can hear a huge difference, guess i need a new/rebuilt set.

Will pull them maybe Sunday and see what i can see, might even give them a clean up myself.

Paz