Carb+lpg significant power loss

[Rosedrift]

Hello from Greece!

I've got some problems after the installation of an lpg system in my single carbed nissan sunny 1989 model.(no cat, no lamda sensor)
The reducer is a brc at90E.
Actually i don't have a way to find out if the mixture is lean or rich, but here is what i found out.
1.The idle is very stable at 800rpm but sometimes at traffic lights the engine stops running.
2.I've got a big power loss throught all rpms. I'm facing this problem mainly during night time with colder outside temperature.
3.In low rpms if i step hard on the gas pedal, the engine stalls.

I haven't noticed misfire, my sparks are heat rate 6 (ngk) with 0.9mm gap, i've didn't change the ignition advance.
thanks

[rossko]

I'd take it back to the installer and ask them about it?

If you are trying to set it up yourself, try this
http://www.diy-lpg.co.uk/articles/files ... -loop.html

[Rosedrift]

Thanks for the quick reply. Yeah i have already read the link you sent me, but i don't have a lamda sensor to check the mixture.
the only thing I know is that CO emmision (at idle) are about the same with gasoline and lpg

[rossko]

Okay, what would you like to happen next?

[Rosedrift]

Actually i want to undersatand if it's rich or lean from the symptoms.
That's why I'm asking you as more experienced

[rossko]

I can't tell from here. If the CO is about right, the mixture is probably about right - at idle. That doesn't tell you anything about how it is away from idle.

Is this a conversion you've paid for, or a DIY job using parts you've found, or something inbetween?

[Rosedrift]

Everything installed is brand new and yes I paid for it. Can you reccomend something?
e.g adjustment on gas analyzer?

[rossko]

If you've paid somebody to do a job, and you're not happy with it, the usual thing is to go back to them.

Yes, if you have access to an analyzer, of course use it to help setting up. See what mixture is like at 3000rpm or so, and use the result in conjunction with the help guide you've already read.

Confident the correct mixer has been fitted for this car?

[Rosedrift]

Well i've noticed that the clips of the air filter box hadn't closed properly so more air was passing in the carb.
I've also changed the spark's gap to 0.70mm and took it for a ride. No more stalling! Still the difference in acceleration is about 20% less than with gasoline.
Definitely i have to drive it back to the installer to see if I can gain some more power. I don't have a clue if the mixer is the correct one.
Let me ask you 2 questions
1. If the mixture is rich on lpg how the sparks look like? (mine are white-grey after 200 miles)
2. I know that with efi engines the power loss with lpg is not noticable. Can we say the same for carbs?

[Gilbertd]

Sparkplugs do have a lighter colour running on LPG than petrol but you can't go on that alone as an indication of how well it is running. 0.7mm seems to be a very small plug gap and too small a gap can cause problems with running, although usually at lower revs. A mixer system will result in a drop in power but it will affect running on both fuels due to the mixer placing a restriction in the air intake. If the system is set up correctly, there should be little difference between the power on petrol or gas. Are you comparing the performance on gas with petrol since the conversion was done or before?

[Rosedrift]

Hi and thanks for your answer.
I am comparing since the conversion was done to my car.

[Clifford Pope]

I set up a basic open loop system by ear and on-road testing, just like tuning an old-style carburettor.

Set the throttle so that you get a constant speed of about 3000 rpm, and then turn the mixture screw up or down until you get the fastest speed.
Then let it idle and adjust the idle screw until you get a nice even idle at a reasonable speed.

The test it on the road, eg by going up a regular local hill, and judge how it pulls. Next time try a small degree of enrichment. If it's better, try a bit more. If it doesn't make any difference, back it off. keep backing it off in stages until you notice it not pulling so well, then re-enrich it one notch.

That gives a pretty good basic setting. Adjust the idle again, then re-check the power mixture, because the two do inter-relate a bit.

As long as you are confidant you have been sold the right mixer for the engine, that should work.

[Rosedrift]

Thank you very much for the information! That will be the next step if i won't be satisfied from the installer.
As I said I've changed the gap of spark plugs to 0.70mm but today I realised the engine doesn't rev more than 4500rpm on petrol (rev limit is about 6700rpm). One more thing I realized is that my exhaust after 45 minutes driving on lpg (mainly highway driving) with average of 3000rpm is extremely hot. I don't know if this happened from lean mixture or because of higher temperature that lpg causes

[Gilbertd]

The difference in combustion temperature between petrol and LPG is negligible, it's something like 20 degrees higher at 1,700 degrees. But an exhaust does get extremely hot anyway when run at sustained speeds. To give you a rough idea, the exhaust system on a Mazda RX-8 grows an inch in length due to thermal expansion after a long, fast run.

[Clifford Pope]

Or to give another example, an overloaded LandRover crawled up our hill in low gear. It was shedding a trail of dried on rings of burning cow-muck from the tail pipe.

[Rosedrift]

Ok people,today I went back to the installer to check it. I left with same car he does everything by experience.No need of electronics! At least he explained to me how that thing works and with patience I will fix it by myself.
I came back home, opened the hood and I did exactly what Clifford Pope said.I've ended with a much better car, power in low and mid range rpm is about the same as petrol still I'm loosing hp on high revs.Idle is stable at 800rpm and goes more when lights or a/c is on. I don't know what to do now but I think I must play more with the idle screw.
Oh, I found out that the reducer is quite big for my engine.It supports 100kw but my car is only 60kw

I forgot to mention that the power valve is now adjusted to 1 more turn counter clockwise from what the installer had it