Poor running on LPG

kstrutt1 · Post by **kstrutt1** » Mon Mar 17, 2008 3:59 pm

I have just installed a RV8 in my TR7, it previously ran fine on LPG with standard 2.0 I4 engine (twin 1.75 SU) so for the RV8 I fitted the same 30mm mixers and K&N filters assuming if anything the higher displacment should make things better on light load but may be a problem at higher loads, I seem to have the opposite, it runs fine under load but will not start on LPG or run smoothly at idle(in fact it won't idle much below 1000rpm).
The mixers are a pretty crude design with a pipe projecting into the airflow, but seemed to work Ok on the 2.0 engine.

On petrol it runs very smoothly even at a 500rpm idle.

The key difference from the TR7 is that I had to install the mixers up the other way with the feed from the bottom to clear the bonnet, has anyone any experince of this and weather this can cause issues?

For a simple test I can put them up the other way, if this works I will have to put a elbow on the gas pipe very close to the mixer and then install the meetering screws in the feed pipe to enable me to close the bonnet, any idea if this is likely to be a problem?

Kevin

leepop633 · Post by **leepop633** » Mon Mar 17, 2008 6:15 pm

Is the RV8 twin carbs? Wheres it putting the gas in? On my RV8i ive got a 40mm mixer. I think 30mm is a little small but i could be wrong. What kind of flow regulator have you got? Is there a vaccum leak so it isnt pulling the gas through? What system have you got? Just straight from the tanks, to vapouriser, then to the carb with no lambda loop? I would bin the K&N as it will cause probs and will increase the chance of backfire as i found out and cost me a little fortune to find out why my mpg's halved. Use a standard airfilter on a single point system. Its up to you im just passing on my experience.

ChrisJC · Post by **ChrisJC** » Mon Mar 17, 2008 9:56 pm

You need an exhaust gas analyser to see if the mixture is anywhere near where it should be.

You might also need to close up the plug gaps a tad.

Chris.

kstrutt1 · Post by **kstrutt1** » Tue Mar 18, 2008 9:38 am

Thanks fo the feedback other experince is so usefull,

The system is a conventional evaporator system with 2 30mm mixers on SU carbs, and no closed loop hego control.
Looking at it last night I believe I may have found a leak path from the carb dash pot vent holes to the engine side of the miixer so this so obviously my first item to fix.

The problem I have with aircleaners is than the standard RV8 systems will not fit under the bonnet, I could use standard the standard trumpts and fit a foam type filter but this probably would be no better than the K&N.

As I use the car every day I do want the best possible fuel consumption so If you had good results with standard type filters it will have to look at weather I can fit fit 2 of the type intended for a single SU (ie Montego etc) remotely mouinted on the suspension turrets with lengths of flexible pipe connecting thenm to the carbs or does anyone have any better ideas?

leepop633 · Post by **leepop633** » Tue Mar 18, 2008 4:39 pm

The leak wouldnt help. I used a 38 dgas carb on my RV8 but you will struggle for room with an airfilter aswell. Is the carbs up against the bulkhead? If theres room behind will the rangie filter not fit? Sits below dash pot level i think. Try the K&N's mate, it might be fine. Mine was till a nasty backfire. If your really struggling use the K&N but buy magnecor leads. I bought some for mine and its never hiccup'd since.