Gunson Gastester

[minor_9_er]

Just got my gastester from aep/

I am a little disturbed that the unit is so touchy. It cannot be disturbed one centimeter or else the reading will go way out of calibration.

As for using the unit, what are the co% both part load and idle to be set at and at what rpm should one be using for the reading??

[dean]

What do you expect for $135
It might also help to know what car you have

[minor_9_er]

In my budget, 135 dollars is alot of money.... I have a 1973 911 s mechanical fuel injection.....

Thanks

[dean]

I set my 930 CIS to 3% at 900 rpm. Try that and see how it runs. I don't know the specs. for your car

[DRV]

I believe the gastester will be damaged if used above idle.
Dennis

[minor_9_er]

Hope not, I told thesupplier how I intend on using it, his problem, refund!!!!

[dean]

Did you read the manual that came with the gas tester? It is not damaged by revs.

[minor_9_er]

That is good to hear.

I made my adjustment for part load at 3000 rpm, set it to 6-7 %, and idle at app. 4%.

While the car drives out well and idles great, there is still an annoyindg stumble in the 2000-2500 rpm range and a slight miss in the 3200 range.

At 80-90 mph, the car is awesome.

I have done a plug read, and the one annoying plug that was always carboned, is now reading good.

I am inclined to beleive that I may have an electrical issue in that particular cylinder, maybe a weak spark related to the beru connector or a bad plug itself.

I think I will switch the plug and go for a cruze...

[Mike M]

Let us know what you find. I have a similar annoying stumble at about 3200 rpm on my 69S. I don't know enough about MFI to start playing with it.

[pbs911]

I used the Gastester with great success. A couple weeks ago I had to smog my car. I set it for both idle and at 2500 rpms. When it was tested, the expensive smog station equiptment came back with results within .01 of the Gastester. No bad IMHO.

I thought JW recomended that the CO level on MFI systems should be set at 7% at idle? I don't know anything about MFI, but perhaps that is the cause of the stumble?

[Peterfrans]

I am also fumbling around with my gas tester adjusting the part load. I set it to 4 at 2500 rpm/7degrees throttle valve, as per the manual. I am not to happy with its performance now. What is the consensus on the right, performance wise part load setting?

[minor_9_er]

First off, any mfi adjusment for part load while the car is stationary cannot be taken as per the guidlines in the book.

All tests in the book are calculated for "load bearing" conditions.
Dyno test figures are given in a "corrective" figure in comparrison to the road test.

So in effect, a stationary test must further be corrected for a good result.

If I recal correctly the dyno rpm test for part load is 2400 rpm, hold on while I look(pause)......Yes that's it, but without any load, we must improvise, increase the rpm to simulate a higher demand.

Co% levels for 2.4 litre are as follows...

2-2.5% road
4%- dyno
?% stationary,

one must perform a study on the difference for a corrected dyno to sitting value in order to come up with a sure enough value to publish.

So we must improvise and play around, from the many accounts of the try and try again method, 6-7% seems like a common figure, as for the test rpm, I tend to think that above 3000 rpm, closer to 3500 is a more likely range for the reading.

As for the idle setting, no reason why any different than book value should be used...

Just remember to follow religiously the steps leading to this stage and all should be well.

Here is a link, if any havent found it yet...

http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

Good luckkkkkk, I am about to kick the cat again myself......

[john walker's workshop]

quit messing around with outdated book specs and set the idle to 7-8% if you ever want it to run right. same for midrange @3000 rpm. timing 35° total.

[minor_9_er]

Personally, I always like to use a standard in order to base any thing against...

This is very important when deriving correlative tables of figures.

It is no messing around in my opinion, just fact finding.

I have just reset part load @ 3800 rpm 6-7%, and at idle 6%, I can just tell by the mid range lack of stumbling while bringing the throttle up through the range , that there ought not be any stumble any more in the 2500 range, so commonly reported by the others in may posts and as I was experiencing.

It is important to use facts when tuning without a guide, you sound like so many people I do business with whom buy cars without looiking in wholesale guide... Doesn't make sense.

In addition, I dont think that it is necessary to inhale the heavy exhaust charge while running rich, it really sucks...

[Peterfrans]

Just to make sure, is the 7-8% part load setting JW is referring to under load or standing still ( I measured mine under load, with the gunson on the passengers seat).

[minor_9_er]

That would have to be a standing still reading. Anything else would be way too rich...

[minor_9_er]

Just an FYI,

I wasn't happy with my results after my test run, much stumble in the mid range.

I decided to mess around a little more, finding it somewaht difficult to lower the idle beyod 6% or so, meaning the part load reading at 3000 for 6% I was able to achieve was based upon an adjustment to the govenor pump that was way out of whack. Likely the idle adjustment was way too lean.

If I am correct in assuming, the govenor in the pump, the main centrifugal weight which is involved in the outcome of both adjustment figures, must have be over adjusted in the idle circuit, too lean, thus giving a very high number of counter clockwise clicks for the part load.

What tipped me off was the feel on the tension in the idle adjustor, seemed as if I was running out of detent to go any leaner.

I decided to go back to basics, bottomed out both the adjusters and made my way up the scale.

When the car was able to run, just run, I began to tune in the part load, dialed it in, then not to my surprise while observing the idle reading, I was forced instead of in the past to go lean, but rather to go rich.

Now I know that I am in the right "spectrum" of the pumps operation.

If you find yourself having to go lean on the idle after setting part load, likelyhood is that you need to go rich direction mucho then go back to adjusting the part load.

I would every better suggest to do as I did, bottom both out and get it to just run, then dial it in...

I only see this as sensible due to having dis assembled a ppump in the past and observed the actions of the centrifuge when I adjusted the idle adjuster.

Just because its an idle setting, doesn't mean it lessen it's effect on the rest of the cuircuit, if you asked me, it bears more influence on part load than in the reverse.

If you want to understand the physics of the centrifuge govenor and the idle settings have on it, just open the pump and take a look.....

Time for chow......

[BK911]

Go through the MFI check measure and adjust manual for the 10 commandments. MFI should be the last thing you touch. Originally my 2.4E had bad transition performance. I tried tuning the MFI without much improvement. I finally started from the basics and did a compression test and found 2 bad holes. No MFI tuning would have overcome that!

Make sure the car is completely warmed up BEFORE you start adjusting the CO settings. If not all your settings will change once the car warms up. I have a 2.4E and set CO around 7% at idle and at 3k RPM with no load. The car has awesome performance from idle to redline, no hesitation or annoying miss.

Good luck!
BK

[minor_9_er]

What do you mean by bad holes??? Low compression??? Holed pistons??? Broken compression rings????Please elaborate....

What was the corrective measure???

Please advise....

[minor_9_er]

Final update,

- after having dialed the system, gone for another run, fingers crossed.

-found nice transition, but as soon as the temps neared and broke 180c, I began to experience the stumbles. No problem, return trip home, adjust pump two clicks richer part load, another short road test, better, but not good enough.

- two more clicks richer, VOILA excellent response, transition and power, idle no differently, although I am sure I will need a click

leaner for the idle setting, but WOW, the car has come back to life.

- This couldn't have come at a better time, its 12 minutes to my 37th birthday, and I was getting ready to give up on this car.(NOT).

-So in conclusion, the Gunson is a great tool, better to be looking
at a reference instead of counting in your head all the time. It didn't give me the exact destination, but it lead me on the road to it.

- Much more cost effective than the labour rate in any shop, and can be used for any other car in the future.

Time for some cake!!!