Put it on and timed to about 14deg BTDC. It revs nicely etc on petrol, but hunts a little at idle.
Flip it to gas, and all hell breaks lose! Random back-fires, flames from the exhaust, hunting at idle. Am I right in thinking this is over-fuelling?
Sorry, I didn't really know the best place to post this, as it incorporates timing, petrol and gas!
Cheers
Tom.
Rover 3.5 V8 landy - Completely rebuilt and purring... Now awaiting a good tune!!
As cool as it is (I can take it down da strip wif ma homies an rev it wif ma m8s an their corsas' init!) it runs rough as hell.
After tweaking the LPG we can't really seem to srt it and I've just made it not run on gas at all now
I'm sure it's not running on both, as I switch to the middle position on the changeover switch (no fance sequential here!) and run the carbs out of petrol before I change to gas, to the carbs and lines are empty of petrol.
Rover 3.5 V8 landy - Completely rebuilt and purring... Now awaiting a good tune!!
My old Rangie's timing was critical on LPG, a couple of degrees out and it would pop, bang and, for a final flourish, a backfire a few seconds after switching off. Sometimes as I was walking away, even! I think it was happiest around 18 degrees BTDC but don't hold me to that, it was a few years ago now. Maybe fiddle with your timing some more?
OK. I can't decide whether it's timing or fuelling.
It seems to run OK when you've got your foot down. Of course both fuelling and timing change when you go back to closed throttle.
I think I'd try fiddling with both idle timing and idle mixture.
1st guess is that it sounds to me like it's too lean on idle, which there's a screw on the vapouriser for that.
Ok I'll poke about some more today.
I'll try 18degs BTDC as a start point (cheers Nick) and play with the fuel from there.
I'm tempted just to lock off the timing at a god value for petrol, and take it to the local LPG fitters for tuning. They do everything IIRC, including timing.
Cheers all
Tom.
Rover 3.5 V8 landy - Completely rebuilt and purring... Now awaiting a good tune!!
Really f****d off now. Unplug the vac hose and it runs beauuuuuutiful, except for the dead-spot at top or bottom. I can get it to idle nicely and run on petrol ok with the vac, but switch to gas and BANG! From both exhaust and inlet manifold.
Had a good go at setting up the static timing and idle etc as well.
It's impossible to get an idle below 1400rpm without the engine stalling, on gas, or 1500 on petrol, with or without the vac.
If I measure the revs usin a 'Gunson Testune' borrowed from a neighbour, it shows 1400rpm idle, fine.
The rpm range can be switched between 4, 6, and 8 cyls, so I got that right. It increases the revs shown proportionally when I move the switch, so this works fine. To be honest it sounds like a fast idle, but then it always has. But now the really odd bit - When I rev the engine to 5k, it sounds not that fast. When I revved the engine to what I frequently rev to (on sound) it was way over the max on the scale, which is 6k. It's probably doing 7k and doesn't sound like its struggling at all, and it revs there easily. I'm using a torquey grind cam (similar specs to the 'max-torque' one RPI sell), but other than that the engine's standard (but totally rebuilt).
I'm not running solid lifters or anything and it's not been ported in any way, and still has standard Rangey headers.
Now I'm no expert, but 7k shouldn't be possible on a standard engine should it, let alone easy?!
And another thing to add: When I was doing the timing, I held the strobe up to my eye at idle. It was slow enough that I coul see the individual flashes at idle. Occasionally it misses a flash (engien misses a spark) and sometimes it doulbe-flashes. This is about every 10 seconds.
I'm sure this is to do with my cap and rotor-arm so they're getting replaced tomorrow.
Could the double-sparking, if it increases proportionally to engine rpm, account for the extra rpm I seem to be reading, and could the double spark also account for the back and front-firing with the vac unit? It just seems strange that it doesn't still do it without the vac.
Sorry for the long post, but there's a lot to consider!!
Tom.
Rover 3.5 V8 landy - Completely rebuilt and purring... Now awaiting a good tune!!
some advance units have 2 connections on them, if your has do you have it connected to the correct side. Something else to check is that your timing marks are right. There are different pulleys and different pointers so do a TDC and check your marks. Alternatively stop using the strobe and just use your ears. Turn the dizzy till you think it sounds its best.
I noticed some have 2 connections, but the new one just has one, and it's just on the advance side (so I'm not vacuum retarding!)
My dad and I checked the TDC a while ago with a screw-driver in the #1 plug hole. TDC on the pulley is correct - how novel!
I did it by ear to start with, using the whole 'put it in 4th going quite slowly on a hill and advance till it pinks, then retard 2 degrees' method.
Now the vac works it's so undriveable that I can't do that, so I used the strobe to try and get it near right, then do it by ear, but still all I can hear is BANG!
I think it't time to give up and part with my wallet and give it to someone who knows that the fudge they're doing!
Rover 3.5 V8 landy - Completely rebuilt and purring... Now awaiting a good tune!!
The Original Tom wrote:
It's impossible to get an idle below 1400rpm without the engine stalling, on gas, or 1500 on petrol, with or without the vac.
If I measure the revs usin a 'Gunson Testune' borrowed from a neighbour, it shows 1400rpm idle, fine.
That's a fast idle. Have you also checked and re-checked for possible air leaks? Too lean a mixture would also explain some of the symptoms you describe here and earlier.
[Disclaimer] Not that I know anything about these bi-fuel systems. We don't have them here in Finland.[/Disclaimer]
-TimoV
Diesel is for poor people.
Range Rover 3.9EFI, 1990
ChrisJC wrote:Is the pipe for the vac unit coming from the right place on the carb?
Chris.
I thought there was only one place? It comes from the side of the carb nearest the manifold, and lies just beyond the butterfly. e.g on the vaccumed side of the butterfly. There's only a pipe on 1 carb and it's a small brass fitting proruding from the top of the near-side carb. (SU HIF6's)
I had thought of an air leak, but don't know how to test for them?
I had the coolant system presure tested recently as I thought the manifold was poorly seated but it held pressure fantastically. I would have thought if the water channels were sealed it meant the entire manifold would be sealed?
What's the protocal for testing for air leaks? A can of quick-start pointed at each inlet area in turn and spray the line between head and manifold?
This still doesn't account for the irrationally easy 7k top-end though!
I wouldn't use easy start as its too explosive and you know you have ignition problems. Use a can of WD40 instead and spray round all the mating surfaces including the carb to manifold. I would even test the carb spindles as it wouldn't be the first time these have been worn and cause problems. Also check you don't have any cracked vac pipes or open connections.
