disgusting overrun and constant speed, opinions please

beelzebubs · Post by **beelzebubs** » Mon Jul 06, 2009 9:52 pm

Hi guys, aint been one here in a long long while

But I'd like to pick your brains, might be real obvious, but please help.

My Mk1 Granny Coupe is running a 10a lump out of and SD1, it was on twin su's running through a GM auto box, but I dont like petrol, so I binned the fuel tank in favour of a beautiful back box.

Now, I didnt notice it so much on the auto, but now I'm running a type 9, I'm almost scared to drive it due to rough running.

one the over run, I.e Tick over in gear coming to lights etc, the einging is kangaroo'ing, and slaming the gearbox back and fore, and also if you try to keep a constant speed, like cruising at 30 or even 70, again the running is not at all smooth.

Reving it up is fine, I can get it up through the full rev range, and the engine is fine under load while accelerating, and is also sweet on tick over.

Right, I'm running an efi manifold, of unknown origin, and I dont think the top is mated to the base, so I had to remove the trumpets to get the lid on, I also plugged all the injector holes but tapping them out and fitting bolts to plug the holes, and I'm running a single point 60mm lpg mixer, right on the throttle mount.

I'm thinking that maybe the lack of trumpets would be causing this over run problem? or does any one knoe if perhaps RV8's just dont like running on lpg with the efi manifolds on single point?

Answers greatly apreciated please

thanks guys

Pawl

ppyvabw · Post by **ppyvabw** » Mon Jul 06, 2009 11:57 pm

I have to say I'm a little drunk but you have just said a whole load of stuff I don't know!

I'm taking from your post this is an engine running solely on LPG which I don't know anything about.

Im sure the lack of trumpets is not exactly helping but probably not the cause of the problems. Why did you remove them? I have just sold an lpg mixer that attached to the throttle mouth. I had never used it but I assume as these thing exist they might work???? I sold it because I didn't want it.

As I say I don't know anything about LPG but i'd say it was an air/LPG mixture issue of some kind.

beelzebubs · Post by **beelzebubs** » Wed Jul 08, 2009 7:47 pm

yup Gas only, with a mixer ring at the mouth of the throttle mouth.

Took the trumpets out as the top of the manifold just wouldnt fit over them....mix and match of egay parts.

If I got a twin su manifold, and put a blanking plate over one of the carb mounts, and mounted my mixer on the remaining open port, would that feed all 8? or does each carb fuel 4 cylinders?

btw, this is the engine running on gas

http://www.granadaclassics.com/vroom.htm

ppyvabw · Post by **ppyvabw** » Wed Jul 08, 2009 10:44 pm

beelzebubs wrote: If I got a twin su manifold, and put a blanking plate over one of the carb mounts, and mounted my mixer on the remaining open port, would that feed all 8? or does each carb fuel 4 cylinders?

No that wouldn't work, each side serves four cylinders. I don't know about the specifics of LPG but I think the trumpets need to go back in, if they don't fit your plenum then shorten them all by an equal amount or at least get a die grinder and smooth the hols in the trumpet base.

I don't think that's your main problem though, I reckon it's a fuel issue. Someone more knowledgeable could advise.

beelzebubs · Post by **beelzebubs** » Thu Jul 09, 2009 12:13 am

I've LPG'D many a vahicle with no problems, and this particular kit came off an SD1, so I suspect its tuned, and throttle and idling are fine...So I'm suspecting the lack of trumpets.

I suppsode the easiest bet would be to get another manifold and rape it off its trumpets and top cover.

I'll hit up ebay and let you know.

I'm sure its a fuel thing though, as it was fine as an auto on Su's

ChrisJC · Post by **ChrisJC** » Thu Jul 09, 2009 7:40 am

Single point LPG on an EFi manifold is not a problem. I do just that absolutely fine.

The mixer might be getting the arse without trumpets though as the airflow will be non-uniform.

Chris.

beelzebubs · Post by **beelzebubs** » Thu Jul 09, 2009 8:34 am

well i just bought a matched based trumpets and lid of egay, so I'll let you know if that cures it.

beelzebubs · Post by **beelzebubs** » Mon Nov 02, 2009 8:40 pm

okily, worked out i had a crack in one of the header pipes, also under the throttle body there should have been something bolted to the bottom, throttle position sensor maybe? Well there were two 6 mm holes open to the atmoshphere, so I put some bolts in there, together with a matched trumpet base to plenum chamber, I also stuck a back fire valve at the end of the intake and this has reduced the intake and it now runs like a dream.

A bit of tuning required still though, as it still smells like a calor gas fire from behind